Solar Dryer Final Thesis.docx

“Design and Fabrication of Solar Dryer”

Submitted By Name

: Adeela

Roll No.

: BN664651 Submitted To

Name

: Hina Yaqoob

Submitted in partial fulfillment of the requirement for B.ed (1.5 year) program

FACULTY OF EDUCATION ALLAMA IQBAL OPEN UNIVERSITY, FAISALABAD. March, 2019  Adeela, 2019

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Faculty of Education Allama Iqbal Open University, Islamabad

APPROVAL FORM The research project attached hereto, titled*______________________________ __________________________________________________________________ Proposed and submitted by ____________________Roll No._______________ in partial fulfillment of the requirements for the degree of B.Ed. (1.5 year) (mention area of specialization) is hereby accepted.

Supervisor: ________________________ (Signature) (Supervisor Name Here)

Evaluator: ________________________ (Signature) (Evaluator Name Here)

Dated: _________________ (Day-Month-Year)

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DECLARATION

I____________________________ Daughter/Son of ____________________________ Roll No. __________________________ Registration # _________________________ A student of B.Ed. (1.5/2.5 year) programme (mention here area of specialization) at Allama Iqbal Open University do hereby solemnly declare that the research project entitled _______________________________________________________________________ submitted by me in partial fulfillment of B.Ed. (1.5/2.5 year) programme, is my original work, and has not been submitted or published earlier. I also solemnly declare that it shall not, in future, be submitted by me for obtaining any other degree from this or any other university or institution. I also understand that if evidence of plagiarism is found in my thesis/dissertation at any stage, even after the award of a degree, the work may be cancelled and the degree revoked.

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ABSTRACT The application of solar drying technology in agricultural area to preserve vegetables, fruits, and other crops has proved to be practical, economical, and eco-friendly. Solar drying system is used to dry crops extensively in many countries. Solar drying may be used for the complete drying process or as a supplement to the artificial drying process. Solar dryer technology may be used in small-scale food processing industries to produce sanitary and high-quality food products. Solar dryers can be broadly classified into direct, indirect, and specialized solar dryers (Foster and Mackenzie 1980). Indirect Solar Dryer – As the name suggests, this method does not expose the crop directly to the sunlight. The solar radiation is absorbed and converted into heat by another surface (like a black top) usually called the collector. Air that will be used for drying is passed over this surface and gets heated, which is then used to dry the food item inside the dryer. The main advantage of indirect mode of drying is that the temperatures can be controlled. The sizes can vary from kilograms to metric tons, but it is expensive and more complex to construct when compared to direct solar dryers.

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TABLE OF CONTENT CHAPTER NO 1

1.0

Introduction

1

1.1

Drying

1

1.2

Some Background to the Drying Concept

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1.3

Capturing Solar Energy

19

1.4

Importance of Solar Dried Food

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1.5

Objectives

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CHAPTER NO 2 2.0

Literature Review

23

2.1

Solar Dryer

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CHAPTER NO 3 3.0

Materials and method

31

3.1

Materials

31

3.2

Method

31

3.2.1 Construction of the mixed-mode solar dryer

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3.2.1.1 Solar Dryer Components 3.2.2 The orientation of the solar collector

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3.2.3 Operation of the dryer

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3.2.4 Design calculations

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3.2.5 General description of the domestic passive solar food dryer

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3.2.6 Testing of the solar dryer

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CHAPTER NO 4 4.0 Results and conclusion

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4.1 Results

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4.1.1 Hourly variation of temperature and relative humidity in the solar dryer

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4.1.2 Drying behavior of cassava and plantain in the dryer

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4.1.3 Hourly moisture loss and moisture content of cassava and plantain

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4.1.4 Evaluated parameters of the dryer and Comparison of

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solar drying and sun drying CHAPTER NO 5 5.0 Conclusion and Recommendation

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5.1 Conclusion

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5.2 Recommendation

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REFERENCES

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CHAPTER NO 1 INTRODUCTION 1.1 Drying

Drying is an excellent way to preserve food and solar dryers are appropriate food preservation technology for sustainable development. Drying was probably the first ever food preserving method used by man, even before cooking (Alamu et al., 2010). It involves the removal of moisture from agricultural produce so as to provide a product that can be safely stored for longer period of time. “Sun drying” is the earliest method of drying farm produce ever known to man and it involves simply laying the agricultural products in the sun on mats, roofs or drying floors. This has several disadvantages since the farm produce are laid in the open sky and there is greater risk of spoilage due to adverse climatic conditions like rain, wind, moist and dust, loss of produce to birds, insects and rodents (pests); totally dependent on good weather and very slow drying rate with danger of mound growth thereby causing deterioration and decomposition of the produce. The process also requires large area of land, takes time and highly labour intensive. In order to protect the products from above mentioned disadvantages and also to accelerate the time for drying the products, control the final moisture and reduce wastage through bacterial action, different types of solar dryer can be used (Exell 1980; Fohr and Figueredo 1987; Ghazanfari and Sokhansanj 2002; Janjaia et al., 2008; Khalil et al., 2007, Roa and Macedo 1976; Ting and Shore 1983; Yaldyz and Ertekyn, 2001). With cultural and industrial development, artificial mechanical drying came into practice, but this process is highly energy intensive and expensive which ultimately increases product cost. Recently, efforts to improve “sun drying” have led to “solar drying”. Solar dryers are specialized devices that control the drying process and protect agricultural produce from damage by insect pests, dust and rain. In comparison to natural “sun drying”, solar dryers generate higher temperatures, lower relative humidity, and lower product moisture content and reduced spoilage during the drying process. In addition, it takes up less space, takes less time and relatively inexpensive compared to artificial mechanical drying

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method. Thus, solar drying is a better alternative solution to all the drawbacks of natural drying and artificial mechanical drying. The solar dryer can be seen as one of the solutions to the world’s food and energy crises. With drying, most agricultural produce can be preserved and this can be achieved more efficiently through the use of solar dryers. Solar dryers are a very useful device for: 1. Agricultural crop drying. 2. Food processing industries for dehydration of fruits and vegetables. 3. Fish and meat drying. 4. Dairy industries for production of milk powder. 5. Seasoning of wood and timber. 6. Textile industries for drying of textile materials, etc. Thus, the solar dryer is one of the many ways of making use of solar energy efficiently in meeting man’s demand for energy and food supply, total system cost is a most important consideration in designing a solar dryer for agricultural uses. No matter how well a solar system operates, it will not gain widespread use unless it presents an economically feasible alternative to other available energy sources. Food scientists have found that by reducing the moisture content of food to between 10 and 20%, bacteria, yeast, mold and enzymes are prevented from spoiling it. The flavor and most of the nutritional value is preserved and concentrated. Drying and preservation of agricultural products have been one of the oldest uses of solar energy. The traditional method, still widely used throughout the world, is open sun drying where diverse crops, such as fruits, vegetables, cereals, grains, tobacco, etc. are spread on the ground and turned regularly until sufficiently dried so that they can be stored safely. However, there exist many problems associated with open sun drying. It has been seen that open sun drying has the following disadvantages. It requires both large amount of space and long drying time. The disadvantages of open sun drying need an appropriate technology that can help in improving the quality of the dried products and in reducing the wastage. This led to the 2

application of various types of drying devices like solar dryer, electric dryers, wood fuel driers and oil-burned driers. However, the high cost of oil and electricity and their scarcity in the rural areas of most third world countries have made some of these driers very unattractive. Therefore interest has been focused mainly on the development of solar driers. Solar dryers are usually classified according to the mode of air flow into natural convection and forced convection dryers. Natural convection dryers do not require a fan to pump the air through the dryer. The low air flow rate and the long drying time, however, result in low drying capacity. One basic disadvantage of forced convection dryers lies in their requirement of electrical power to run the fan. Since the rural or remote areas of many developing countries are not connected, the use of these dryers is limited to electrified urban areas. Drying is one of the methods used to preserve food products for longer periods. It has been established as the most efficient preservation technique for most tropical crops. This project presents the design, construction and performance of a solar dryer for food preservation. In the dryer, the heated air from a separate solar collector is passed through a glass, and at the same time, the drying cabinet absorbs solar energy directly through glass arrangement. The results obtained during the test period revealed that the temperatures inside the dryer and solar collector were much higher than the ambient temperature during most hours of the daylight. The temperature rise inside the drying cabinet was up to 74% for about three hours immediately after 12.00h (noon). The dryer exhibited sufficient ability to dry food items reasonably rapidly to a safe moisture level and simultaneously it ensures a superior quality of the dried product. Dehydration is drying by synthetic heating under controlled temperature, clamminess, and air flow. The fundamental drying processes are classified as sun drying, atmospheric dehydration, and vacuum dehydration. Solar dehydration is the process of elimination of water molecules or compounds. When we pragmatic the world dehydration, the first thing that may come to mind is straggling water or lacking water. This is a perfect procedure to remember what occurred during a dehydration response. Fundamentally, the water is underprovided, because the water was lost. Classification of drying systems All drying systems can be classified primarily according to their operating temperature ranges into two main groups of high temperature dryers and low temperature dryers. However; dryers are more commonly classified broadly according to their heating sources into fossil fuel 3

dryers (more commonly known as conventional dryers) and solar-energy dryers. Strictly, all practically realized designs of high temperature dryers are fossil fuel powered, while the low temperature dryers are either fossil fuel or solar-energy based systems. Solar energy has the greatest potential of all the sources of renewable energy and if only a small amount of this form of energy is used, it will be one of most important supplies of energy especially when other sources in the country have depleted. Energy comes to the earth from the sun. This energy keeps the temperature of the earth above that in colder space, causes current in the atmosphere and in the ocean, causes the watercycle and generate photosynthesis in plants. The solar power where sun hits atmosphere is 1017 watts, whereas the solar power on earth‘s surface is 1016 watts. The total world-wide power demand of all needs of civilization is 1013 watts. Therefore, the sun gives us 1000 times more power than we need. If we can use 5% of this energy, it will be 50 times what the world will require. The energy radiated by the sun on a bright sunny day is approximately 1 kW/m2 , attempts have been made to make use of this energy in raising steam which may be used in driving the prime movers for the purpose of generation of electrical energy. However on account of large space required, uncertainty of availability of energy at constant rate, due to clouds, winds, haze etc., there is limited application of this source in the generation of electric power. Now-a-days the drawbacks as pointed out that energy cannot be stored and it is a dilute form of energy, are out dated arguments, since the energy can be stored by producing hydrogen, or by storing in other mechanical or electrical devices, or it can be stored in containers of chemicals called eutectic or phase changing salts. These salts which store large quantities of heat in a relatively small volume, melt when they are heated and release heat later as they cool and crystallize. The energy can be concreted in solar furnaces of 5000o C. The facts speak in favor of solar energy, as we have seen in analysis of commercial energy sources, that world‘s reserves of coal, oil and gas will be exhausted within a few decades. Nuclear energy involve considerable hazards and nuclear fusion has not yet overcome all the problems of even fundamental research, compared with these technologies, the feasibility of which is still 3 uncertain and contested, the technical utilization of solar energy can prove useful. Utilization of solar energy is of great importance to India since it lies in a temperature climate of the region of the world where sun light is abundant for a major part of the year.

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Applications of solar technology Solar energy refers primarily to the use of solar radiation for practical ends. All other renewable energies other than geothermal and tidal derive their energy from the sun. Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies. The applications of solar energy which are enjoying most success to-day are: (1) Heating and cooling of residential building. (2) Solar water heating. (3) Solar drying of agricultural and animal products. (4) Solar distillation on a small community scale. (5) Salt production by evaporation of seawater or inland brines. (6) Solar cookers. (7) Solar engines for water pumping. (8) Food refrigeration. (9) Bio conversion and wind energy, which are indirect source of solar energy. (10) Solar furnaces. (11) Solar electric power generation by (i) Solar ponds. (ii) Steam generators heated by rotating reflectors (heliostat mirrors), or by tower concept. (iii) Reflectors with lenses and pipes for fluid circulation (cylindrical parabolic reflectors).

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(12) Solar photovoltaic cells, which can be used for conversion of solar energy directly into electricity or for water pumping in rural agricultural purposes. The heat from solar collectors is directly used for warming the living spaces of a building in conventional ways e.g., through radiators and hot air registers. When the building does not require heat, the warmed air or liquid from the collector can be moved to a heat storage container. In the case of air, the storage is often a pile of rocks or some other heat-holding material, in the case of liquid, it is usually a large, well-insulated tank of water, which has considerable heat capacity. Heat is also stored in containers of chemicals called eutectic or phase changing salts. These salts, which store large quantities of heat in a relatively small volume, melt when they are heated and release heat later as they cool and crystallize. When the building needs heat, the air or water from its heating system passes through the storage is warmed, and is then fed through the conventional heaters to warm the space. For sunless days or cloudy days, an auxiliary system as a back-up, is always required. The same is true for solar cooling systems. In the United States, heating, ventilation and air conditioning (HVAC) systems account for 30% (4.65 EJ) of the energy used in commercial buildings and nearly 50% (10.1 EJ) of the energy used in residential buildings. Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy. Thermal mass is any material that can be used to store heat—heat from the Sun in the case of solar energy. Common thermal mass materials include stone, cement and water. Historically they have been used in arid climates or warm temperate regions to keep buildings cool by absorbing solar energy during the day and radiating stored heat to the cooler atmosphere at night. However they can be used in cold temperate areas to maintain warmth as well. The size and placement of thermal mass depend on several factors such as climate, day lighting and shading conditions. When properly incorporated, thermal mass maintains space temperatures in a comfortable range and reduces the need for auxiliary heating and cooling equipment. A solar chimney A solar chimney (or thermal chimney, in this context) is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated causing an updraft that pulls air through the building.

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Performance can be improved by using glazing and thermal mass materials in a way that mimics greenhouses. Deciduous trees and plants have been promoted as a means of controlling solar heating and cooling. When planted on the southern side of a building, their leaves provide shade during the summer, while the bare limbs allow light to pass during the winter. Since bare, leafless trees shade 1/3 to 1/2 of incident solar radiation, there is a balance between the benefits of summer shading and the corresponding loss of winter heating. In climates with significant heating loads, deciduous trees should not be planted on the southern side of a building because they will interfere with winter solar availability. They can, however, be used on the east and west sides to provide a degree of summer shading without appreciably affecting winter solar gain. Solar energy units for heating domestic water are commercially available and are used by millions of people in various parts of the world, for example in Australia, Israel, and Japan etc. A solar water heater commonly comprises a blackened flat plate metal collector with an associated metal tubing, facing the general direction of the sun. The collector is provided with a transparent glass cover and a layer of thermal insulation beneath the plate. The collector tubing is connected by a pipe to an insulated tank that stores hot water during non-sunny periods. The collector absorbs solar radiation and by transfer of resulting heat to the water circulating through the tubing by gravity or by a pump, hot water is supplied to the storage tank. Solar hot water systems use sunlight to heat water. In low geographical latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar heating systems. The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools. As of 2007, the total installed capacity of solar hot water systems is approximately 154 GW. China is the world leader in their deployment with 70 GW installed as of 2006 and a long term goal of 210 GW by 2020. Israel and Cyprus are the per capita leaders in the use of solar hot water systems with over 90% of homes using them. In the United States, Canada and Australia heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GW as of 2005. 7

Solar water heating system For domestic, industrial and commercial applications are at present available. In commercial establishments, there is great potential especially in hotels, hospitals, guest houses, tourist bungalows, canteen etc. For industrial applications solar water heating system can meet the low and medium temperature process heat requirements hot water up to 90oC, hot air up to 110oC and low pressure steam up to 140oC. These are especially useful in engineering, textile, chemicals, pharmaceutical, food processing, and sugar, dairy and other industries. Hot water systems have relevance for many agricultural and village industries, such as for handloom fabrics, Seri-culture, leather tanning and handmade paper. Solar distillation Admits solar radiation through a transparent cover to a shallow, covered brine basin; water evaporates from the brine and the vapor condenses on the covers which are so arranged that the condensate flows there-from into collection troughs and hence into a product-water storage. In arid, semi-arid, or coastal areas, there is abundant sun light that can be used for converting brackish or saline water into potable distilled water. A traditional and wide-spread use of solar energy is for drying particularly of agricultural products. This is a process of substantial economic significance in many areas. The process is of special interest in the case of soft fruits; these are particularly vulnerable to attack by insects, as the sugar concentration increases during drying. Fruit dryer in which fruit is placed, in carefully designed racks to provide controlled exposure to solar radiation often improves quality and saves considerable time. A simple cabinet dryer consists of a box, insulated at the base, painted black on the inside and covered with an inclined transparent sheet of glass. Ventilation holes are provided at the base and at the top of the sides of the box to facilitate a flow of air over the drying material, which is placed on perforated trays in the interior of the cabinet base. Large drying systems like grain, paddy, maize, cash crops like ginger, cashew, pepper etc., spray drying of milk; timber and veneer drying; tobacco curing; fish and fruit drying, etc. have also been developed. Solar refrigeration Solar refrigeration is intended for food preservation (or storage of biological and medical materials) and deserves top-priority in country like India. Solar air conditioning can 8

be utilized for space cooling. Solar assisted heat pumps would provide both cooling and heating. Active solar cooling wherein solar thermal collectors provide thermal energy to drive thermally driven chillers (usually Adsorption or Absorption chillers).The solar thermal energy system can be also used to produce hot water. There are multiple alternatives to compressor-based chillers that can reduce energy consumption by 80%, with less noise and vibration. Solar thermal energy can be used to efficiently cool in the summer, and also heat domestic hot water, and the building in the winter. The Audubon Environmental Center in Los Angeles is one example among many). Single, double or triple iterative absorption cooling cycles are used in different solar-thermalcooling system designs. The more cycles, the more efficient they are. In the late 1800s, the most common phase change refrigerant material for absorption cooling was a solution of ammonia and water. Today, the combination of lithium and bromide is also in common use. One end of the system of expansion / condensation pipes is heated, and the other end gets cold enough to make ice. Originally, natural gas was used as a heat source in the late 1800s. today, propane is used in recreational vehicle absorption chiller refrigerators. Innovative hot water solar thermal energy collectors can also be used as the modern "free energy" heat source. Efficient absorption chillers require water of at least 190 °F (88 °C). Common, inexpensive flat-plate solar thermal collectors only produce about 160 °F (71 °C) water, but several successful commercial projects in the US, Asia and Europe have shown that flat plate solar collectors specially developed for temperatures over 200 °F (featuring double glazing, increased backside insulation, etc.) can be effective and cost efficient. Evacuated-tube solar panels can be used as well. Concentrating solar collectors required for absorption chillers are less effective in hot humid, cloudy environments, especially where the overnight low temperature and relative humidity are uncomfortably high. Where water can be heated well above 190 °F (88+ °C), it can be stored and used when the sun is not shining. For 150 years, absorption chillers have been used to make ice (before the electric light bulb was invented). This ice can be stored and used as an "ice battery" for cooling when the sun is not shining, as it was in the 1995 Hotel New Otani in Tokyo Japan. Mathematical models

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are available in the public domain for ice-based thermal energy storage performance calculations. The ISAAC Solar Icemaker is an intermittent solar ammonia-water absorption cycle. The ISAAC uses a parabolic trough solar collector and a compact and efficient design to produce ice with no fuel or electric input, and with no moving parts. Cold storages are very important for preservation and conservation of food articles. There are two methods of solar refrigeration. (a) Vapour absorption refrigeration system that utilizes low grade thermal energy obtained from flat plate collectors with a little modification. (b) Concentrating (focusing) collectors to supply heat at a higher temperature to a heat engine which then drives the compressor of a conventional refrigerator. Solar refrigeration with an absorption system is a better way of direct utilization of energy. The vapour absorpton system replacing the compressor by a generator absorber assembly can work with wide range of absorbents and refrigerants. In absorption system motive power required is very small C.O.P. of the system is low. Electricity from Solar EnergyElectricity can be produced from the solar energy by photovoltaic solar cells, which convert the solar energy to electricity. The most significant applications of photo voltaic cell in India, are the energisation of pump sets for irrigation, drinking water supply and rural electrification covering street lights, community TV sets, medical refrigerators and other small power loads. Electricity is directly generated by utilizing solar energy by the photo voltaic process. When photons from the sun are absorbed in a semi-conductor, they create free electrons with higher energies than the electrons are created, there must be an electric field to induce these higher energy electrons to flow out of the semiconductor to do useful work. The electric field in most solar cells is provided by a junction of materials which have different electrical electrical properties. The photovoltaic effect can be described easily which for p-n junction in semi-conductor materials of solar cells which are silicon, cadmium, sulphide/copper sulphide, Gallium Arsenite etc. Solar thermal power production system In a solar thermal power production system the energy is first collected by using a solar pond, a flat plate collector, focusing collector or heliostats (turnable mirrors). This energy is 10

used to increase the internal energy or temperature of a fluid. This fluid may be directly used in any of the common or known cycles such as Rankine, or through a heat exchanger to heat a secondary fluid (working fluid) which is being used in the cycle to produce mechanical power from which electrical power can be produced easily. Solar thermal power cycles can be broadly classified as low medium and high temperature cycles. Low temperature cycles generally use flat plate collectors or solar pond, maximum temperatures are limited to above 90 to 100oC. Medium temperature cycles work at maximum temperatures ranging from 150 to 300oC, using concentration or focusing collectors. High temperature cycles work at maximum temperatures above 300 oC. In solar tower concentration system (Tower power concept), the incoming solar radiation is focused to a central receiver or a boiler mounted on a tall tower using thousands of plane reflectors which are steerable about two axes and are called heliostats. Sunlight can be converted into electricity using photovoltaics (PV), concentrating solar power (CSP), and various experimental technologies. PV has mainly been used to power small and mediumsized applications, from the calculator powered by a single solar cell to off-grid homes powered by a photovoltaic array. For large-scale generation, CSP plants like SEGS have been the norm but recently multimegawatt PV plants are becoming common. Completed in 2007, the 14 MW power station in Clark County, Nevada and the 20 MW site in Beneixama, Spain are characteristic of the trend toward larger photovoltaic power stations in the US and Europe. As an intermittent power source, solar power requires a backup supply, which can partially be complemented with wind power. Local backup usually is done with batteries, while utilities normally use pumped-hydro storage. The Institute for Solar Energy Supply Technology of the University of Kassel pilot-tested a combined power plant linking solar, wind, biogas and hydro storage to provide load-following power around the clock, entirely from renewable sources. Result to-date show solar energy to be quite competitive with other sources of energy, if the solar power plant size is about 100-200 Mwe, with 3-6 hours thermal storage.Over the last few years, few experiment power plants have been built or under construction in U.S.A, France, Italy and Japan. Solar Vehicles: Development of a solar powered car has been an engineering goal since the1980s. The World Solar Challenge is a biannual solar-powered car race, where teams from universities and 11

enterprises compete over 3,021 kilometers (1,877 mi) across central Australia from Darwin to Adelaide. In 1987, when it was founded, the winner's average speed was 67 kilometers per hour (42 mph) and by 2007 the winner's average speed had improved to 90.87 kilometers per hour (56.46 mph). The North American Solar Challenge and the planned South African Solar Challenge are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles. Some vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption. In 1975, the first practical solar boat was constructed in England. By 1995, passenger boats incorporating PV panels began appearing and are now used extensively. In 1996, Kenichi Horie made the first solar powered crossing of the Pacific Ocean, and the sun21 catamaran made the first solar powered crossing of the Atlantic Ocean in the winter of 2006– 2007. There are plans to circumnavigate the globe in 2010. In 1974, the unmanned Sunrise II plane made the first solar flight. On 29 April 1979, the Solar Riser made the first flight in a solar powered, fully controlled, man carrying flying machine, reaching an altitude of 40 feet (12 m). In 1980, the Gossamer Penguin made the first piloted flights powered solely by photovoltaic. This was quickly followed by the Solar Challenger which crossed the English Channel in July 1981. In 1990 Eric Raymond in 21 hops flew from California to North Carolina using solar power. Developments then turned back to unmanned aerial vehicles (UAV) with the Pathfinder (1997) and subsequent designs, culminating in the Helios which set the altitude record for a non-rocket-propelled aircraft at 29,524 metres (96,860 ft) in 2001. The Zephyr, developed by BAE Systems, is the latest in a line of record-breaking solar aircraft, making a 54-hour flight in 2007, and month-long flights are envisioned by 2010. A solar balloon is a black balloon that is filled with ordinary air. As sunlight shines on the balloon, the air inside is heated and expands causing an upward buoyancy force, much like an artificially heated hot air balloon. Some solar balloons are large enough for human flight, but usage is generally limited to the toy market as the surface-area to payload-weight ratio is relatively high. Solar sails are a proposed form of spacecraft propulsion using large membrane mirrors to exploit radiation pressure from the Sun. Unlike rockets, solar sails require no fuel. Although the thrust is small compared to rockets, it continues as long as the Sun shines onto the deployed sail and in the vacuum of space significant speeds can eventually be achieved. 12

The High-altitude airship (HAA) is an unmanned, long-duration, lighter-than-air vehicle using helium gas for lift, and thin-film solar cells for power. The United States Department of Defense Missile Defense Agency has contracted Lockheed Martin to construct it to enhance the Ballistic Missile Defense System (BMDS). Airships have some advantages for solar-powered flight: they do not require power to remain aloft, and an airship's envelope presents a large area to the Sun. Solar Pond: A solar pond is large-scale solar thermal energy collector with integral heat storage for supplying thermal energy. A solar pond can be used for various applications, such as process heating, desalination, refrigeration, drying and solar power generation. A solar pond is simply a pool of saltwater which collects and stores solar thermal energy. The saltwater naturally forms a vertical salinity gradient also known as a "halocline", in which low-salinity water floats on top of high-salinity water. The layers of salt solutions increase in concentration (and therefore density) with depth. Below a certain depth, the solution has a uniformly high salt concentration. There are 3 distinct layers of water in the pond: 1. The top layer, which has a low salt content. 2. An intermediate insulating layer with a salt gradient, which establishes a density gradient that prevents heat exchange by natural convection. 3. The bottom layer, which has a high salt content. If the water is relatively translucent, and the pond's bottom has high optical absorption, then nearly all of the incident solar radiation (sunlight) will go into heating the bottom layer. When solar energy is absorbed in the water, its temperature increases, causing thermal expansion and reduced density. If the water were fresh, the low-density warm water would float to the surface, causing a convection current. The temperature gradient alone causes a density gradient that decreases with depth. However the salinity gradient forms a density gradient that increases with depth, and this counteracts the temperature gradient, thus preventing heat in the lower layers from moving upwards by convection and leaving the pond. This means that the temperature at the bottom of the pond will rise to over 90 °C while the temperature at the top layer will not vary as such. The power can be generated using the Sterling Cycle.

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1.

High temperature dryers High temperature dryers are necessary when very fast drying is desired. They are

usually employed when the products require a short exposure to the drying air. Their operating temperatures are such that, if the drying air remains in contact with the product until equilibrium moisture content is reached, serious over drying will occur. Thus, the products are only dried to the required moisture contents and later cooled. High temperature dryers are usually classified into batch dryers and continuous-flow dryers. In batch dryers, the products are dried in a bin and subsequently moved to storage. Thus, they are usually known as batchin-bin dryers. Continuous-flow dryers are heated columns through which the product flows under gravity and is exposed to heated air while descending. Because of the temperature ranges prevalent in high temperature dryers, most known designs are electricity or fossil-fuel powered. Only a very few practically-realized designs of high temperature drying systems are solar energy heated. 2.

Low temperature dryers In low temperature drying systems, the moisture content of the product is usually

brought in equilibrium with the drying air by constant ventilation. Thus, they do tolerate intermittent or variable heat input. Low temperature drying enables products to be dried in bulk and is most suited also for long term storage systems. Thus, they are usually known as bulk or storage dryers. Thus, some conventional dryers and most practically-realized designs of solarenergy dryers are of the low temperature type. Solar dryer: Drying by the sun under an open sky for preserving food and agricultural produce has been practiced since earliest times. Conversely, this method has many disadvantages, i.e., products get spoiled due to rain, wind, wet, and dust; loss of productivity due to birds and animals; deterioration in the harvested crops due to putrefaction, insect attacks, and fungi. Apart from this, this process is labor-intensive and time-consuming and preferred a large area for scattering the produce out to dry. Recently developed artificial mechanical drying is energy intensive. But eventually, it increases the product price. The modern tend of solar drying apparatus offers an exceptional method that can process the vegetables and fruits in clean, disinfected and hygienic conditions to national and international standards with zero energy

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costs. It utilized most appropriate energy and time and taken less area. It improves product quality. It makes the process more efficient and defend from the environment. Types of solar driers Solar-energy drying systems are classified primarily according to their heating modes and the manner in which the solar heat is utilized. In broad terms; they can be classified into two major groups, namely •

Direct (integral) type solar dryers.

•

Indirect (distributed) type solar dryers.

•

Direct solar dryers have the material to be dried placed in an enclosure, with a

transparent cover on it. Heat is generated by absorption of solar radiation on the product itself as well as on the internal surfaces of the drying chamber. In indirect solar dryers, solar radiation is not directly incident on the material to be dried. Air is heated in a solar collector and then ducted to the drying chamber to dry the product. Specialized dryers are normally designed with a specific product in mind and may include hybrid systems where other forms of energy are also used. Although indirect dryers are less compact when compared to direct solar dryers, they are generally more efficient. Hybrid solar systems allow for faster rate of drying by using other sources of heat energy to supplement solar heat. The three modes of drying are: (i) open sun, (ii) direct and (iii) indirect in the presence of solar energy. The working principle of these modes mainly depends upon the method of solar-energy collection and its conversion to useful thermal energy. (i)Open sun drying (OSD) Open Sun Drying solar energy falls on the uneven product surface. A part of this energy is reflected back and the remaining part is absorbed by the surface. The absorbed radiation is converted into thermal energy and the temperature of product stars increasing. This results in long wavelength radiation loss from the surface of product to ambient air through moist air. In addition to long wave length radiation loss there is convective heat loss too due to the blowing wind through moist air over the material surface. Evaporation of moisture takes place in the form of evaporative losses and so the material is dried. Further apart of absorbed thermal energy is conducted into the interior of the product. This causes a rise in temperature and formation of water vapor inside the material and then diffuses towards the surface of the and finally losses thermal energy in the end then diffuses towards the surface of the and finally losses the thermal 15

energy in the form of evaporation. In the initial stages, the moisture removal is rapid since the excess moisture on the surface of the product presents a wet surface to the drying air. Subsequently, drying depends upon the rate at which the moisture within the product moves to the surface by a diffusion process depending upon the type of the product. (ii)Direct type solar drying (DSD) Direct solar drying is also called natural convection cabinet dryer. Direct solar dryers use only the natural movement of heated air. A part of incidence solar radiation on the glass cover is reflected back to atmosphere and remaining is transmitted inside cabin dryer. . A direct solar dryer is one in which the material is directly exposed to the sun‘s rays. This dryer comprises of a drying chamber that is covered by a transparent cover made of glass or plastic. The drying chamber is usually a shallow, insulated box with air-holes in it to allow air to enter and exit the box. The product samples are placed on a perforated tray that allows the air to flow through it and the material. Solar radiation passes through the transparent cover and is converted to low-grade heat when it strikes an opaque wall. This low-grade heat is then trapped inside the box by what is known as the ‗greenhouse effect.‘‘ Simply stated, the short wavelength solar radiation can penetrate the transparent cover. Once converted to low-grade heat, the energy radiates. (iii)Indirect type solar drying (ISD) This type is not directly exposed to solar radiation to minimize discolorations and cracking. The drying chamber is used for keeping the in wire mesh tray. A downward facing absorber is fixed below the drying chamber at a sufficient distance from the bottom of the drying chamber. A cylindrical reflector is placed under the absorber fitted with the glass cover on its aperture to minimize convective heat losses from the absorber. The absorber can be selectively coated. The inclination of the glass cover is taken as 45o from horizontal to receive maximum radiation. The area of absorber and glass cover are taken equal to the area of bottom of drying chamber. Solar radiation after passing through the glass cover is reflected by cylindrical reflector toward an absorber. After absorber, a part of this is lost to ambient through a glass cover and remaining is transferred to the flowing air above it by convection. The flowing air is thus heated and passes through the placed in the drying chamber. The exhaust air and moisture is removed through a vent provided at the top of drying chamber.

16

Applications of solar driers The change of main variables such as moisture content along the drying tunnel is considered unlike in previous works where uniform distribution is assumed .This is a study of tunnel green house drier which is continuous type. The conditions for improvement of efficiency are evaluated. A linear relationship between the tunnel output temperature and incident solar radiation is obtained. The drier production is presented by a performance parameter which is defined as the ratio between the energy actually used in the evaporation and the total available energy for the drying process. A non-dimensional variable is also defined which has all the meteorological information. It is found that, the average moisture content value of the tunnel can be considered to be constant. The construction and working of solar tunnel drier is explained in detail. Three fans run by a solar module are used to create forced convection. The drying procedure and the instrumentation are also described. The major advantage of solar tunnel drier is that the regulation of the drying temperature is possible. During high insulation periods, more energy is received by the collector, which tends to increase the drying temperature and is compensated by the increase of the air flow rate. The variation of voltage with respect to radiation in a given day and variation of radiation with respect to time of the day are presented. The comparative curves using the tunnel dryer and natural sun drying are presented to show that, the tunnel drying time is less . A substantial increase in the average sugar content is observed. The economics of the drier is worked out to show that, the payback period is 3 years. 1.2 Some Background to the Drying Concept The idea of using solar energy to produce high temperature dates back to ancient times. The solar radiation has been used by man since the beginning of time for heating his domicile, for agricultural purposes and for personal comfort. Reports abound in literature on the 18th century works of Archimedes on concentrating the sun’s rays with flat mirrors; Modern research on the use of solar energy started during the 20th century. Developments include the invention of a solar boiler, small powered steam engines and solar battery, but it is difficult to market them in competition with engines running on inexpensive gasoline. During the mid-1970’s shortages of oil and natural gas, increase in the cost of fossil fuels and the depletion of other resources stimulated efforts in the United States to develop solar energy into a practical power source. Thus, interest was rekindled in the harnessing of

17

solar energy for heating and cooling, the generation of electricity and other purposes (Leon, et al., 2002). 1.3 Capturing Solar Energy Solar radiation can be converted either into thermal energy (heat) or into electrical energy. This can be done by making use of thermal collectors for conversion into heat energy or photovoltaic collectors for conversion into electrical energy. Two main collectors are used to capture solar energy and convert it to thermal energy, these are flat plate collectors and concentrating collectors. In the course of this project, emphasis is laid much on the flat plate collectors which are also known as non-focusing collectors. 1.4 Importance of Solar Dried Food For centuries, people of various nations have been preserving fruits, other crops, meat and fish by drying. Drying is also beneficial for hay, copra, tea and other income producing non-food crops. With solar energy being available everywhere, the availability of all these farm produce can be greatly increased. It is worth noting that until around the end of the 18th century when canning was developed, drying was virtually the only method of food preservation. (Bena et a.l, 2002) Ikejiofor (1985) stated that the energy input for drying is less than what is needed to freeze or can, and the storage space is minimal compared with that needed for canning jars and freezer containers. It was further stated that the nutritional value of food is only minimally affected by drying. Also, food scientists have found that by reducing the moisture content of food to 10 to 20%, bacteria, yeast, mold and enzymes are all prevented from spoiling it (Gallali, et al., 2000). Microorganisms are effectively killed when the internal temperature of food reaches 145°F. The flavour and most of the nutritional value of dried food is preserved and concentrated. Dried foods do not require any special storage equipment and are easy to transport (Waewsak, et al., 2006). Dehydration of vegetables and other food crop by traditional methods of open-air sun drying is not satisfactory, because the products deteriorate rapidly, studies showed that food items dried in a solar dryer were superior to those which are sun dried when evaluated in terms of taste, colour and mould counts (Gallali, et al., 2000).

18

Solar dried food are quality products that can be stored for extended periods, easily transported at less cost while still providing excellent nutritive value (Alamu, et al., 2010). This project work therefore presents the design and construction of a domestic solar dryer. HYPOTHESIS: The sun is the most important source of heat and light in the universe. During primitive times, the sun was solely used for its heat and light for all day to day activities, when there was no electricity. With increased usage of fossil fuel and thermal electricity, there is now a risk of global warming. It is being feared that if Earth progresses at the rate at which it is currently moving on, there will not be much of resources left for our future generations. All this has led the world incline towards alternative sources of power. While wind and hydro energy are also making progress, it is solar energy that has become the favored one amongst masses, mainly due to its increased affordability. At the same time the quality control and quality preservation becomes also more and more importance items for processing of agricultural products than before. In the systems which used solar energy to dry different agricultural products, the moisture content is removed by air which heated by sun arrays energy with temperature range of 50 o C to 60 o C. The percentage of moisture content is varies from product to product. A solar dryer is another application of solar energy, used immensely in the food and agriculture industry. Though sun is still used as the direct source for drying food items and clothes in certain parts of the world. An indirect source of solar power can also be used for the same purpose in the form of a solar dryer. The main disadvantage of drying directly under the sun is contamination – dirt, animals, insects etc. Also there is a fear of sudden change in weather conditions like wind or rain. 1.5 Objectives The objectives of this project are 

To design and construct a solar dryer



To evaluate the solar dryer’s performance

The device must be easy to assembly, disassemble, and use. The device must be low cost so that it can be purchased by farmers in developing countries, or a government organization to distribute to its citizens. 19

Physical Principles of the Conversion of Solar Radiation into Heat: The fundamental process now in general use for heat conversion is the greenhouse effect. The name come from its first use in green houses, in which it is possible to grow exotic plants in cold climates through better utilization of the available sunlight. Most of the energy we receive from the sun comes in the form of light, a shortwave radiation, not all of which is visible to the human eye. When this radiation strikes a solid or liquid, it is absorbed and transformed into heat energy; the material becomes warm and stores the heat, conducts it to surrounding materials (air water, other solids or liquids) or reradiates it to other materials of lower temperature. This reradiation is a long wave radiation. Visible sunlight is absorbed on the ground, at a temperature of 20oC, for example emits infrared light at a wavelength of about 10m, but (CO2 does not absorbs the incoming sunlight which has a shorter wavelength).

20

CHAPTER NO 2 LITERATURE REVIEW 2.1 Solar Dryer

In many parts of the world there is a growing awareness that renewable energy has an important role to play in extending technology to the farmer in developing countries to increase their productivity (Waewsak, et al., 2006). Solar thermal technology is a technology that is rapidly gaining acceptance as an energy saving measure in agriculture application. It is preferred to other alternative sources of energy such as wind and shale, because it is abundant, inexhaustible, and non-polluting (Akinola 1999; Akinola and Fapetu 2006; Akinola et al., 2006). Solar air heaters are simple devices that heat air by utilizing solar energy and are employed in many applications requiring low to moderate temperature below 80 C, such as crop drying and space heating (Kurtbas and Turgut, 2006). Drying processes play an important role in the preservation of agricultural products, they are defined as a process of moisture removal due to simultaneous heat and mass transfer (Ertekin and Yaldiz, 2004). According to Ikejiofor (1985) two types of water are present in food items; the chemically bound water and the physically held water. In drying, it is only the physically held water that is removed. The most important reasons for the popularity of dried products are longer shelf-life, product diversity as well as substantial volume reduction. This could be expanded further with improvements in product quality and process applications. The application of dryers in developing countries can reduce post-harvest losses and significantly contribute to the availability of food in these countries. Estimations of these losses are generally cited to be of the order of 40% but they can, under very adverse conditions, be nearly as high as 80%. A significant percentage of these losses are related to improper and/or untimely drying of foodstuffs such as cereal grains, pulses, tubers, meat, fish, etc. (Bassey, 1989; Togrul and Pehlivan, 2004) Traditional drying, which is frequently done on the ground in the open air, is the most widespread method used in developing countries because it is the simplest and cheapest method of conserving foodstuffs. Some disadvantages of open air drying are: exposure of the foodstuff

21

to rain and dust; uncontrolled drying; exposure to direct sunlight which is undesirable for some foodstuffs; infestation by insects; attack by animals; etc. (Madhlopa, et al., 2002). In order to improve traditional drying, solar dryers which have the potential of substantially reducing the above-mentioned disadvantages of open air drying, have received considerable attention over the past 20 years (Bassey, 1989). Solar dryers of the forced convection type can be effectively used. They however need electricity, which unfortunately is non-existent in many rural areas, to operate the fans. Even when electricity exists, the potential users of the dryers are unable to pay for it due to their very low income. Forced convection dryers are for this reason not going to be readily applicable on a wide scale in many developing countries. Natural convection dryers circulate the drying air without the aid of a fan. They are therefore, the most applicable to the rural areas in developing countries. Solar drying may be classified into direct, indirect and mixed-modes. In direct solar dryers the air heater contains the grains and solar energy passes through a transparent cover and is absorbed by the grains. Essentially, the heat required for drying is provided by radiation to the upper layers and subsequent conduction into the grain bed. In indirect dryers, solar energy is collected in a separate solar collector (air heater) and the heated air then passes through the grain bed, while in the mixed-mode type of dryer, the heated air from a separate solar collector is passed through a grain bed, and at the same time, the drying cabinet absorbs solar energy directly through the transparent walls or roof. Therefore, the objective of this study is to develop a mixed-mode solar dryer in which the grains are dried simultaneously by both direct radiation through the transparent walls and roof of the cabinet and by the heated air from the solar collector. The performance of the dryer was also evaluated. Soponronnarit (1995) reviewed the research and development work in solar drying conducted in Thailand during the past 15 years (since 1980s). He found that, in terms of techniques and economy, solar drying for some crops such as paddy, multiple crops and fruit is feasible. However, the method has not been widely accepted by farmers. Most of the solar air heaters developed in Thailand has used modifications to the building roofs. Both bare and glass-covered solar air heaters were reported to be technically and economically feasible when compared to electricity but have not been able to compete with fuel oil.

22

Bahnasawy and Shenana (2004) developed a mathematical model of direct sun and solar drying of some fermented dairy products (kishk). The main components of the equations describing the drying system were solar radiation, heat convection, heat gained or lost from the dryer bin wall and the latent heat of moisture evaporation. The model was able to predict the drying temperatures at a wide range of relative humidity values. It also has the capability to predict the moisture loss from the product at wide ranges of relative humidity values, temperatures and air velocities. Enein (2000) reported a parametric study of a solar air heater with and without thermal storage for solar drying applications. An optimization process for a flat-plate solar air heater with and without thermal storage was carried out. Three kinds of material for thermal storage were used, i.e. water, stones and sand. The average temperature of flowing air increases with the increase of the collector length and width up to typical values for these parameters. The outlet temperature of flowing air was found to decrease with an increase of the airflow channel spacing and mass flow rate. The thermal performance of the air heater with sensible storage materials is considerably higher than that without the storage. An optimal thickness of the storage material of about 0.12 m was found to be convenient for drying various agriculture products. In addition, the proposed mathematical model may be used for estimating of the thermal performance of flat platesolar air heater with and without thermal storage. Pangavhen, et al. (2002) proposed a design, development and performance testing of a new convection solar dryer, the solar dryer is capable of producing average temperature between 50 and 55°C, which was optimal for dehydration of grapes as well as for most of the fruits and vegetables. This system was capable of generating an adequate natural flow of hot air to enhance the drying rate. The drying airflow rate increases with ambient temperature by the thermal buoyancy in the collector. The collector efficiencies ranged between 26% for mass flow rate of 0.0126 kg/s of air and 65% for mass flow rate of 0.0246 kg/s. This was sufficient for heating the drying air. The drying time of grapes was reduced by 43% compared to the open sun drying. Bena and Fuller (2002) developed a direct-type natural convection solar dryer with simple biomass burner. It was expected to be suitable for small-scale processors of dried fruits and vegetables in non-electrified areas of developing countries. The capacity of the dryer was found to be 20–22 kg of fresh pineapple arranged in a single layer of 1-cm-thick slices. The key features of the biomass burner were found to be the addition of thermal mass on the upper 23

surface, an internal baffle plate to lengthen the exhaust gas exit path and a variable air inlet valve. The author also suggested some modifications to further improve the performance of both the solar and biomass components of the dryer. Ekechukwu and Norton (1999) presented a comprehensive review of the various designs, details of construction and operational principles for a variety of practical solar-energy drying systems. The appropriateness of each design type for applications used by rural farmers in developing countries was discussed. Bennamoun and Azeddine (2003) studied a simple, efficient and inexpensive solar batch dryer for agricultural products through simulations. They used onion as the dried product, and the shrinking effect was taken into account. In addition, it was suggested that the study could be developed for other agricultural products and for the behavior of solar dryer in different seasons. Sebaii, et al. (2002) reported a study of an indirect type natural convection solar which investigated experimentally and theoretically for drying grapes, figs, onions, apples, tomatoes and green peas. The drying constants for the selected crops were obtained from the experimental results and were then correlated with the drying product temperature. Linear correlation between drying constant and product temperature were proposed for the selected crops. The empirical constants of Henderson’s equation were obtained for all the materials from investigation, which are not available in the literature. The proposed empirical correlation suggested that it could well describe the drying kinetics of the selected crops. Gallali, et al. (2000) reported the result of an investigation of some dried fruit and vegetables (grapes, figs, tomatoes and onions) based on chemical analysis (vitamin C, total reducing sugars, acidity, moisture, and ash content) and sensory evaluation data (color, flavor, and texture). They compared products dried by solar dryers and natural sun drying. The study indicated that using solar dryers gives more advantages than natural sun drying, especially in terms of drying time. Karathanos and Belessiotis (1997) reported the sun and solar air drying kinetics of some agricultural products, i.e. sultana grapes, currants, figs, plums and apricots. The drying rates were found for both solar and industrial drying operations. Air and product temperatures were measured for the entire industrial drying process. It was shown that most materials were dried in the falling rate period. Currants, plums, apricots and jigs exhibited two drying rate periods, a first slowly decreasing (almost constant) and a second fast decreasing (falling) drying rate 24

period. In addition, they indicated that the industrial drying operation resulted in a product of superior quality compared to products dried by solar dehydration. Leon, et al. (2002) presented a review of existing evaluation methods and the parameters generally considered for evaluation of solar food dryers. These parameters can be classified as: (i) Physical features of the dryers; (ii) Thermal performance; (iii) Quality of dried product; (iv)Cost of dryer and payback period. a. Physical features of dryer -

type, size, and shape

-

collector area and solar aperture

-

drying capacity/loading density (kg/unit aperture area)

-

tray area and number of layers

-

loading/unloading convenience

-

loading/unloading time

-

handling, cleaning, maintenance convenience, and ease of construction b. Thermal performance -

drying time/drying rate up to 10% product moisture content (d.b.), (this may,

however, vary from product to product) -

dryer/ drying efficiency until product moisture content reaches 10% (d.b.)

-

first day drying efficiency

-

drying air temperature and relative humidity

-

maximum drying temperature at no-load and with load

-

duration of drying air temperature10°C above ambient

-

airflow rate

c. Quality of dried products 25

-

sensory quality (color, flavor, taste, texture, aroma)

-

nutritional attributes - quantified for easy comparison

-

rehydration capacity - consistency in presentation

-

uniformity of drying

Crop drying is the most energy consuming process in all processes on the farm. The purpose of drying is to remove moisture from the agricultural produce so that it can be processed safely and stored for increased periods of time. Crops are also dried before storage or, during storage, by forced circulation of air, to prevent spontaneous combustion by inhibiting fermentation. It is estimated that 20% of the world‘s grain production is lost after harvest because of inefficient handling and poor implementation of postharvest technology, says Hartman‘s (1991). Grains and seeds are normally harvested at a moisture level between 18% and 40% depending on the nature of crop. These must be dried to a level of 7% to 11% depending on application and market need. Once a cereal crop is harvested, it may have to be stored for a period of time before it can be marketed or used as feed. The length of time a cereal can be safely stored will depend on the condition it was harvested and the type of storage facility being utilized. Grains stored at low temperature and moisture contents can be kept in storage for longer period of time before its quality will deteriorate. Some of the cereals which are normally stored include maize, rice, beans. Solar drying may be classified into direct and indirect solar dryer. In direct solar dryers the air heater contains the grains and solar energy which passes through a transparent cover and is absorbed by the grains. Essentially, the heat required for drying is provided by radiation to the upper layers and subsequent conduction into the grain bed. However, in indirect dryers, solar energy is collected in a separate solar collector (air heater) and the heated air then passes through the grain bed, while in the mixedmode type of dryer, the heated air from a separate solar collector is passed through a grain bed, and at the same time, the drying cabinet absorbs solar energy directly through the transparent walls or the roof. Energy is important for the existence and development of human kind and is a key issue in international politics, the economy, military preparedness, and diplomacy. To reduce the impact of conventional energy sources on the environment, much attention should be paid to the development of new energy and renewable energy resources. Solar energy, which is environment friendly, is renewable and can serve as a sustainable energy source. 26

Hence, it will certainly become an important part of the future energy structure with the increasingly drying up of the terrestrial fossil fuel. However, the lower energy density and seasonal doing with geographical dependence are the major challenges in identifying suitable applications using solar energy as the heat source. Consequently, exploring high efficiency solar energy concentration technology is necessary and realistic. Solar energy is free, environmentally clean, and therefore is recognized as one of the most promising alternative energy recourses options. In near future, the large-scale introduction of solar energy systems, directly converting solar radiation into heat, can be looked forward. However, solar energy is intermittent by its nature; there is no sun at night. Its total available value is seasonal and is dependent on the meteorological conditions of the location. Unreliability is the biggest retarding factor for extensive solar energy utilization. Of course, reliability of solar energy can be increased by storing its portion when it is in excess of the load and using the stored energy whenever needed. Solar drying is a potential decentralized thermal application of solar energy particularly in developing countries. However, so far, there has been very little field penetration of solar drying technology. In the initial phase of dissemination, identification of suitable areas for using solar dryers would be extremely helpful towards their market penetration. Solar drying is often differentiated from ―sun drying‖ by the use of equipment to collect the sun‘s radiation in order to harness the radiative energy for drying applications. Sun drying is a common farming and agricultural process in many countries, particularly where the outdoor temperature reaches 30 oC or higher. In many parts of South East Asia, spice s and herbs are routinely dried. However, weather conditions often preclude the use of sun drying because of spoilage due to rehydration during unexpected rainy days. Furthermore, any direct exposure to the sun during high temperature days might cause case hardening, where a hard shell develops on the outside of the agricultural products, trapping moisture inside. Therefore, the employment of solar dryer taps on the freely available sun energy while ensuring good product quality via judicious control of the radiative heat. Solar energy has been used throughout the world to dry products. Such is the diversity of solar dryers that commonly solar-dried products include grains, fruits, meat, vegetables and fish. A typical solar dryer improves upon the traditional open-air sun system in five important ways.

27

It is more efficient. Since materials can be dried more quickly, less will be lost to spoilage immediately after harvest. This is especially true of products that require immediate drying such as freshly harvested grain with high moisture content. In this way, a larger percentage of products will be available for human consumption. Also, less of the harvest will be lost to marauding animals and insects since the products are in safely enclosed compartments. It is hygienic. Since materials are dried in a controlled environment, they are less likely to be contaminated by pests, and can be stored with less likelihood of the growth of toxic fungi. It is healthier. Drying materials at optimum temperatures and in a shorter amount of time enables them to retain more of their nutritional value such as vitamin C. An added bonus is that products will look better, which enhances their marketability and hence provides better financial returns for the farmers. It is cheap. Using freely available solar energy instead of conventional fuels to dry products, or using a cheap supplementary supply of solar heat, so reducing conventional fuel demand can result in significant cost savings.

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CHAPTER NO 3 MATERIALS AND METHOD

3.1 Materials The following materials were used for the construction of the domestic passive solar dryer:  Wood (gmelina) - as the casing (housing) of the entire system; wood was selected being a good insulator and relatively cheaper than metals.  Glass - as the solar collector cover and the cover for the drying chamber. It permits the solar radiation into the system but resists the flow of heat energy out of the systems.  Mild steel sheet of 1mm thickness and aluminum painted black – for absorption of solar radiation.  Wooden frames for constructing the trays.  Nails and glue as fasteners and adhesives.  Insect net at air inlet and outlet - to prevent insects from entering into the dryer.  Hinges and handle for the dryer’s door.  Paint (black).

3.2 Method 3.2.1 Construction of the solar dryer The materials used for the construction of the mixed-mode solar dryer are cheap and easily obtainable in the local market. The solar dryer consist of the solar collector (air heater), the drying cabinet and drying trays. 3.2.1.1 Solar Dryer Components Drying chamber: The drying chamber was made up highly polished wood wish consist of three drying trays also made of wood, the material has been chosen since wood is a poor conductor of heat and its smooth surface finish and also heat loss by radiation is minimized. Cover plate: This is a transparent sheet used to cover the absorber, thereby preventing dust and rain from coming in contact with the absorber, it also retard the heat from escaping, common materials used for cover plates are glass, fibre glass, flexi glass,but the materaial used for this project is glass

29

Absorber plate: This is a metal painted black and placed below the cover to absorb, the incident solar radiation transmitted by cover thereby heating the air between it and the cover, here aluminum is chosen because it’s quick response in absorption of solar radiation and also copper because of its good ability to keep the absorbed solar radiation. Insulation: This is used to minimize heat loss from the system, it is under the absorber plate, the insulator can withstand stagnation temperature, it is fire resistant and not subject to outgoing gassing and it is damageable by moisture or insect, insulating materials are usually fibre glass, mineral wool, Styrofoam and urethanes, but here styrofoam was chosen.

3.2.2 The orientation of the solar collector: The flat-plate solar collector was always tilted and oriented in such a way that it receives maximum solar radiation during the desired season of used. The best stationary orientation is due south in the northern hemisphere and due north in southern hemisphere. Therefore, solar collector in this work is oriented facing south and tilted at 17.11o to the horizontal. This is approximately 10 o more than the local geographical latitude (Abeokuta a location in Nigeria, 7.11o N), which according to (Adegoke and Bolaji 2000), is the best recommended orientation for stationary absorber. This inclination is also to allow easy run off of water and enhance air circulation.

3.2.3 Operation of the dryer The dryer is a passive system in the sense that it has no moving parts. It is energized by the sun’s rays entering through the collector glazing. The trapping of the rays is enhanced by the inside surfaces of the collector that were painted black and the trapped energy heats the air inside the collector. The greenhouse effect achieved within the collector drives the air current through the drying chamber. If the vents are open, the hot air rises and escapes through the upper vent in the drying chamber while cooler air at ambient temperature enters through the lower vent in the collector. Therefore, an air current is maintained, as cooler air at a temperature T enters through the lower vents and hot air at a temperature Te leaves through the upper vent. When the dryer contains no items to be dried, the incoming air at a temperature ‘T a’ has relative humidity ‘Ha’ and the out-going air at a 30

temperature ‘Ta’, has a relative humidity ‘He’. Because Te>Ta and the dryer contains no item, Ha > He. Thus there is tendency for the out-going hot air to pick more moisture within the dryer as a result of the difference between Ha and He .Therefore, insulation received is principally used in increasing the affinity of the air in the dryer to pick moisture.

3.2.4 Design calculations 1.) The energy balance on the absorber The energy balance on the absorber is obtained by equating the total heat gained to the total heat lost by the heat absorber of the solar collector. Therefore, IA c = Qu + Qcond + Qconv + QR + Qρ

(Bolaji, 2008)

Where: I = rate of total radiation incident on the absorber’s surface (Wm –2); Ac = collector area (m 2); Qu = rate of useful energy collected by the air (W); Qcond = rate of conduction losses from the absorber (W); Qconv = rate of convective losses from the absorber (W); QR = rate of long wave re-radiation from the absorber (W); Qρ = rate of reflection losses from the absorber (W). The three heat loss terms Qcond, Qconv and QR are usually combined into one-term (QL), i.e., QL= Qcond + Qconv + QR . (2) If τ is the transmittance of the top glazing and I T is the total solar radiation incident on the top surface, therefore, IA c = τ ITAc . (3) The reflected energy from the absorber is given by the expression: Qρ = ρτ ITAc

(Bolaji, 2008)

31

Where ρ is the reflection coefficient of the absorber. Substitution of Eqs. (2), (3) and (4) in Eq. (1) yields: τITA c = Qu + QL + ρτ ITAc , or Qu = τ ITAc (1 – ρ) – QL. For an absorber (1 – ρ) = α and hence, Qu = (ατ)ITAc – QL, (5) Where α is solar absorptance. QL composed of different convection and radiation parts. It is presented in the following form (Bansal, 1990): QL = ULAc(T c – T a), (6) Where: UL = overall heat transfer coefficient of the absorber (Wm –2K –1); T c = temperature of the collector’s absorber (K) 2. Angle of Tilt (β) of Solar Collector/Air Heater. The angle of tilt (β) of the solar collector is given by the formula below: β = 100 + lat ф

(Alamu, 2010)

Where lat ф is the latitude of the collector location, the latitude of Abeokuta where the dryer was designed is latitude 7.11°N. Hence, the suitable value of β use for the collector: β = 10° + 7.11° = l7.11° 3. Isolation on the Collector Surface Area. The value of isolation for Abeokuta i.e. average daily radiation H on horizontal surface and average effective ratio of solar energy on tilted surface to that on the horizontal surface R are 978.69W/m2 and 1.0035 respectively

(Olaleye, 2008)

Thus, isolation on the collector surface was obtained as Ic = HT = HR = 978.69 × 1.0035 = 982.11W/m2 32

(GEDA-Gujarat Energy Development

Agency, 2003) 4. Determination of Collector Area and Dimension. The air gap height was taken as 5.6cm = 0.056m and the width of the collection assumed to be 45cm = 0.45m. Thus, volumetric flow rate of air V'a = Va × 0.056 × 0.38 A V' a= 0.15 × 0.056 × 0.38= 3.19 × 10-3m3/s Thus mass flow rate of air: Ma = vaρa

(Dorf, 1989)

Density of air ρa is taken as 1.2252kg/m3 at S.T.P Ma = 3.19 × 10-3 × 1.2252 = 3.91 × 10-3kg/s Therefore, area of the collector AC AC = (3.91 × 10-3 × 1000 × 30)/(0.5 × 982.11) = 0.239m2 The length of the solar collector (L) was taken as; L = Ac/B = 0.3537/0.45 = 0.53m Thus, the length of the solar collector was taken approximately as 0.6m. Therefore, collector area was taken as (0.45* 0.53) 2 = 0.239m2. 5. Determination of the Base Insulator Thickness for the Collector. For the design, the thickness of the insulator was taken as 7cm. The side of the collector was made of wood, the loss through the side of the collector will be considered negligible. 6) Collector efficiency: This is computed from: η= ρCpVΔΤ/Aιc.

(Ezekoye, 2006)

where (ρ) is the density of air (kg/m 3), (Ic) is the insolation on the collector, (Δ ) is the temperature elevation, (cp) is the specific heat capacity of air at constant pressure (J/kg K), (V) is the volumetric flow rate (m 3/s), and (A) is the effective area of the collector facing the sun (m 3). 7) Dryer efficiency: This is given as:

33

ηd=ML/IcAt.

(Ezekoye, 2006))

Where (L) is the latent heat of vaporization of water, (M) is the mass of the crop, and (t) is the time of drying. 8) Moisture Content (M.C.): The moisture content is given as: M.C=(Mi – Mf)/ Mi

( Ezekoye,2006))

where Mi = mass of sample before drying and Mf = mass of sample after drying. 9) Moisture loss ML: The Moisture Loss is given as: ML= (Mi – Mf) (g)).

(Ezekoye, 2006)

where Mi is the mass of the sample before drying and Mf is the mass of the sample after. 3.2.5 General description of the solar dryer The designed and constructed solar dryer consists of two major compartments or chambers being integrated together, the solar collector compartment, which can also be referred to as the air heater, and the drying chamber, designed to accommodate three layers of drying trays on which the produces (or food) are placed for drying. In this solar dryer constructed, the greenhouse effect and thermo siphon principles are the theoretical basis. There is an air vent (or inlet) to the solar collector where air enters and is heated up by the greenhouse effect, the hot air rises through the drying chamber passing through the trays and around the food, removing the moisture content and exits through the air vent (or outlet) near the top of the shadowed side. The hot air acts as the drying medium, it extracts and conveys the moisture from the produce (or food) to the atmosphere under free (natural) convection, thus the system is a passive solar system and no mechanical device is required to control the intake of air into the dryer. 3.2.6 Testing of the solar dryer The testing of the solar dryer was done in the month of April- May, the dryer was placed outside with the collector facing the sun. The collector has been rigidly fixed to the dryer at an angle of 17.11° to the horizontal to obtain approximately perpendicular beam of sun 34

rays. The drying chamber was loaded with cassava and plantain chips estimated to weigh averagely 46g and 38g of 6mm and 5mm thickness respectively. Under no load condition, the temperature of the heated air inside the dryer, the collector chamber and the ambient air was taken every one hour interval, starting from 9am to 6pm, and also in the absence of an hygrometer two thermometers were used to measure the relative humidity, where one thermometer has its sensor whirled with a weak, with the weak touching water in a beaker to get the wet bulb temperature , and the other thermometer provided the normal temperature which gives the dry bulb temperature. The wet bulb and dry bulb temperature were used to obtain the relative humidity on the psychometric chart, this was done every one hour interval, starting from 9am to 6pm. A dry bulb thermometer was used for the temperature measurement in the solar dryer, the initial moisture content was measured using a DHG-9030 Drying oven and the variation in weight loss was measured using an electronic scale

35

CHAPTER NO 4 RESULTS AND DISCUSION 4.1 Results 4.1.1 Hourly variation of temperature and relative humidity in the solar dryer Fig. 4.1 shows a typical day’s results of the hourly variation of the temperatures in the solar collector and the drying cabinet compared to the ambient temperature. The dryer is hottest about mid-day when the sun is usually overhead. The temperatures inside the dryer and the solar collector were much higher than the ambient temperature during most hours of the daylight. The temperature rises inside drying cabinet for about three hours immediately after 12.00h (noon). This indicates prospect for better performance than open-air sun drying. Fig. 4.2 shows the diurnal variation of the relative humidity of the ambient air and drying chamber. Comparison of this figure with Fig.4.1 shows that the drying processes were enhanced by the heated air at very low humidity.

4.1.2 Drying behavior of cassava and plantain in the dryer Fig 4.3 shows the drying curve for Cassava slices and Plantain slices in the solar dryer. It was observed that the drying rate increased due to increase in temperatures between 10.00h and 14.00h but decreased thereafter, which shows the earlier and faster removal of moisture from the dried item. The mass of water removal of 199.9g and 153.6g in cassava and plantain respectively using the solar dryer was achieved as against 156.8g and 125.3g in cassava and plantain using the sun drying method. The collector efficiency of the mixed-mode solar dryer during the test period was found to be 37.9%.

36

Fig. 4.1: A typical day results of the diurnal variation of temperatures in the solar dryer.

37

90 80 70 60 50 Ambient

40

Drying chamber 30 20 10 0 9

11

13

15

17

19

Local time (Hour )

Fig4.2: A typical day results of the diurnal variation of relative humidity in the dryer.

38

80

70

60

50

40 Cassava Plantain 30

20

10

0 9

11

13

15

Local time (Hour )

Fig. 4.3 drying curve for Cassava slices and plantain slices

39

17

19

4.1.3 Hourly moisture loss and moisture content of cassava and plantain Table 4.1 shows the masses of three samples of cassava slices considered and their average masses when calculated, which was used to determine the average moisture loss in grams of the samples from 9.00am when they were placed in the dryer to 6.00pm, and the hourly average percentage moisture content (dry basis) of the cassava. Table 4.2 shows the masses of three samples of plantain sliced considered and their average masses when calculated, which was used to determine the average moisture loss in grams of the samples from 9.00am when they were placed in the dryer to 6.00pm, and the hourly average percentage moisture content (dry basis) of the plantain. Comparison of the percentage moisture content ( dry basis) of the cassava and plantain slices shown in Table 4.1 and Table 4.2 gives the drying curve for cassava and plantain slices.

40

TABLE 4.1: Hourly Moisture Loss and Moisture Content for Cassava

Time

M1 (g)

M2

M3

(g)

(g)

Av mass

M loss

M Content (%)

(g)

(g)

d.b

9.00

48.0

46.2

44.9

46.4

---

67.5

10.00

44.5

42.8

41.5

42.9s

3.5

54.9

11.00

38.9

37.3

36.0

37.4

9

35.0

12.00

36.8

35.2

34.1

35.4

11

27.9

13.00

35.1

34.1

32.9

34.0

12.4

22.7

14.00

33.9

33.1

30.3

32.4

14

17.0

15.00

31.8

30.0

29.6

30.5

15.9

10.1

16.00

30.4

28.2

27.5

28.7

17.7

3.6

17.00

29.8

27.7

27.0

28.2

18.2

1.8

18.00

29.4

27.2

26.5

27.7

18.7

41

TABLE 4.2: Hourly Moisture Loss and Moisture Content for Plantain

Time

M1

M2

M3

(g)

(g)

(g)

Av mass

M loss (g)

(g)

M Content (%) d.b

9.00

46.8

42.0

27.6

38.8

---

71.6

10.00

43.2

38.9

25.1

35.7

3.1

58.0

11.00

37.5

33.0

20.7

30.4

8.4

34.5

12.00

35.5

32.5

19.4

29.1

9.7

28.8

13.00

33.5

31.1

18.1

27.6

11.2

22.1

14.00

31.9

29.3

17.0

26.1

12.7

15.5

15.00

29.5

27.5

15.9

24.3

14.5

7.5

16.00

28.3

26.4

15.3

23.3

15.5

3.1

18.00

27.9

25.9

15.0

22.9

15.9

1.3

18.00

27.6

25.5

14.6

22.6

16.2

M1...............mass of specimen 1 M2...............mass of specimen 2 M3...............mass of specimen 3 M loss..........moisture loss Av mass.........average mass M content........Moisture content

42

4.1.4 Evaluated parameters of the dryer and Comparison of solar drying and sun drying Table 4.3 and Table 4.4 shows the variations in the mass of water removed in the case of both solar drying and sun drying and Table 4.5 shows evaluated parameter of the solar dryer such as Isolation on the collector surface area, dryer and collector efficiency, volume and area of the dryer, collector slope and declination which were calculated in chapter three, and also moisture loss and moisture content determined when the oven drying method was used.

43

TABLE 4.3: Solar drying

Cassava

Plantain

Initial mass (g)

Final mass

Initial mass

(g)

Final mass (g)

(g)

45

26.1

46.8

28.3

39

20

38.3

20.1

44.5

24.9

42

25.1

46.1

27.1

33.6

21.1

48

27.9

27.6

15.3

46.2

25.8

27

16.6

45.1

24.7

39

24.6

44

23.2

41

24.8

47.1

26.5

38.2

20.8

46.2

25.1

36.3

19.5

451.2

251.3

369.8

216.2

TOTAL Cassava Mass of water removed = (451.2-251.3) g =199.9g

Plantain Mass of water removed = (369.8-216. =153.6g

44

TABLE 4.4: Sun-drying

CASSAVA Initial mass (g)

PLANTAIN Final

Initial

mass (g)

mass

Final mass (g)

(g) 48

30.4

36

20.4

43

28.5

27.1

17

46.2

28.8

42

26.1

44.9

31.4

27.8

17.9

36.4

24.1

38.9

22.5

41.8

25.7

47.2

37.1

36.4

22.7

27.6

17.5

44.5

29.1

33.9

31

48.2

30.6

36.5

28.2

47.8

29.1

44.5

18.5

428.2

280.4

361.5

236.2

Cassava Mass of water removed = (437.2-280.4) g =156.8g Plantain Mass of water removed =125.3g

45

Table 4.5: Evaluated Parameters of the Dryer Parameter

Values obtained 2

Isolation on the Collector Surface Area. 982.11 W/m Moisture content (M.C)

62.4%w.b (cassava) Oven method 61.0%w.b (plantain)

Moisture loss (ML)

29.84g (cassava) average 20.56g (plantain)

Dryer efficiency ηd

34.5% (per day) 3

Volume of Dryer chamber(V) 0.0506m

2

Collector Area (A) 0.2385m Collector Efficiency ηc

37.9% (average) O

Declination (8) 10 Collector slope (β)

O

17.11

46

Plate 4.1 Before drying the cassava and plantain chips

Plate 4.2 Solar dried cassava

47

Plate 4.3 Solar dried plantain

CHAPTER NO 5

CONCLUSION AND RECOMMENDATION

5.1 Conclusion From the test carried out, the following conclusions are made: 1.) The solar dryer can raise the ambient air temperature to a considerable high value for increasing the drying rate of agricultural crop. 2.) The product inside the dryer requires lesser frequent attention compare with those in the open sun drying in order to prevent attack of the product by rain or pest (both human and animals). 3.) The dryer was used to dry cassava and can be used to dry other tuber crops too e.g yam 4.) There is ease in monitoring when compared to the natural sun drying technique. 5.) The capital cost involved in the construction of a solar dryer is much lower to that of a mechanical dryer. The mass of water removal of 199.9g and 153.6g in cassava and plantain respectively using the solar dryer was achieved as against 156.8g and 125.3g in cassava and plantain using the sun drying method. The appearance of the Cassava and plantain as captured in Plate 4.1 to Plate 4.5 reveals uniform and better drying in solar drying as compared with open sun drying. FEASIBIILITY STUDIES AND MARKET NEEDS Cost Economics, of Food Solar dryer System enterprises are worked out for fruits and vegetables. 1 Million For one unit of 10 dryers. It can transact 10 tons of fruits or fruit bars in dehydrated form. This is an excellent income and profitable venture in rural Saudi Arabia. The cost benefit analysis of our dryers indicates that a commercial venture of a project with 10 solar dryers will give the payback period of 2 - 2½ years.

48

The profitability of the technology in terms of employment potential and income generation is established and acceptability of the product in the market is evaluated from the proven market demand. Our expectation about the feasibility of the technology for rural employment has been realized. The reasons for the success are: 1. The grass root level Non-Government and voluntary organizations have devotion for service to rural people and have the ability to capacity building and skill development among rural women. 2. Food Solar drying process is the integration of food science and technology and solar drying technology disciplines. So the practice followed in solar food processing is based on these two techniques. To make the solar food processing products, one needs rigorous training in this technology by well qualified persons, close monitoring and supervision of the operations and following the food safety, clean & hygienic practices, quality consciousness and assurance in day to day production. The social entrepreneurs have proved very successful in this respect. 5.2 Recommendation The performance of existing solar food dryers can still be improved upon especially in the aspect of reducing the drying time and probably storage of heat energy within the system. Also, meteorological data should be readily available to users of solar products to ensure maximum efficiency and effectiveness of the system. Such information will probably guide a local farmer on when to dry his agricultural produce and when not to dry them. Also, i will implore Agricultural engineering department to allow its students in partaking in the course titled WRM 202 from the Water resources and agrometeorology department,this will give them an insight about climatology and meteorology which will enhance them in their final year project if it is related to such. And lastly, the department should povide adequate equipments e.g Moisture meter,this will assist project students in their evaluation processes.

REFERENCES 1. Adegoke, C.O and Bolaji, B.O. 2000. Performance evaluation of solar-operated thermo syphon hot water system in Akure, International Journal of Technology. 2(1): 35-40. 49

2. Akinola, A.O. 1999. Effects of drying and rewetting on some physical properties of cocoa beans. Journal of Agriculture, Science and Technology. 3(2): 125-131. 3. Akinola, A.O; and Fapetu, O.P. 2006. Exergetic analysis of a mixed-mode solar dryer. Journal of Solar Energy and Applied. Science. 1 : 205-10. 4. Akinola, O.A; Akinyemi, A.A; and Bolaji, B.O. 2006. Evaluation of traditional and solar fish drying systems towards enhancing fish storage and preservation in Nigeria. Journal of Fishery International, Pakistan 1(3-4): 44-9. 5. Alamu, O.J; Nwaokocha, C.N and Adunola, O. 2010. Design and construction of a domestic passive solar food dryer, Leonardo Journal of Sciences, p. 71-82. 6. Bahnasawy, A.J and Shenana, J.R. 2004. Evaluation of a solar crop dryer for rural applications in Botswana. Botswana Journal Technology 11(2): 58-62. 7. Bena, B and Fuller, R.J. 2002. Determination of the average coefficient of internal moisture transfer during the drying of a thin bed of potato slices. Journal of Food Engineering. 48(2): 95-101. 8. Bennamoun, N.P and Azeddine, H. 2003. Technical feasibility assessment of a solar chimney for food drying, Solar Energy, vol. 82, pp. 198-205, 2008. 9. th 10. Bolaji, B.O. 2005. Performance evaluation of a simple solar dryer for food preservation. Proc. 6 Ann. Engineering. Conf. of School of Engineering and Engineering Technology, Minna, Nigeria, pp. 8-13. 11. Ekechukwu, L and Norton, S.D. 1999. Development and use of solar drying technologies, Nigerian Journal of Solar Energy 89: 133-64. 12. Enein, N.E. 2000. Experimental investigation of solar air heater with free and fixed efficiency and energy loss, Intenational Journal of Science 1(1): 75-82. 13. Ericson, J. 1980. Global solar radiation measurements in England. Renewable Energy, 30(3): 1203－1220. 14. Ertekin, C and Yaldiz, O. 2004. Drying of egg plant and selection of a suitable thin layer drying model, Journal of Food Engineering 63: 349-59. 50

15. Exell R. H. B. 1980. A simple solar rice dryer, basic design theory. Sunworld, 4, 186 - 191. 16. Ezekoye, B. A and Enebe, O.M. 2006. Development and performance evaluation of modified integrated passive solar grain dryer. The Pacific Journal of Science and Technology, (2): 185－190. 17. Fohr, J.P and Figueredo, A.R. 1987. Agricultural solar air collectors: design and performances. Journal of Solar Energy 38(5): 311-321 18. Gallali, G; Garg, H.P; and Prakash, J. 2000. Solar drying versus open sun drying, A framework for financial evaluation, Solar Energy, vol. 80, pp. 1568-1579 19. Ghazanfari, A and Sokhansanj, S. 2002. Experiments on solar drying of Pistachio nuts. Energy 20. Conversion Management 27: 343-349. 21. Ikejiofor, I.D. 1985. Passive solar cabinet dryer for drying agricultural products. In: O. Awe 22. (Editor), African Union of Physics. Solar Energy Conversion, University of Ibadan, Nigeria, pp. 157-65. 23. Janjaia, S; Srisittipokakuna, N; and Balab, B.K. 2008. Experimental and modelling performances of a roof-integrated solar drying system for drying herbs and spices. Journal of Energy 33: 91–103 24. Karathanos, K and Belessiotis, L. 2002. Natural convection solar dryer with biomass backup heater, Solar Energy, vol. 72, pp. 75-83. 25. Khalil, E.J; Al-Juamily, Khalifa, N; and Yassen, T.A. 2007. Testing of the performance of a fruit and vegetable solar drying system in Iraq. Journal of Desalination. 209: 163–170 26. Kurtbas, I and Turgut, E. 2006. Experimental investigation of an indirect type natural convection solar dryer. Energy Conversion and Management, 43(16): 2251-2266. 27. Leon, T.K; Mechlouch, R. F; and Brahim, A. B. 2002. A study of the drying effect on lemon slices using a closed-type solar dryer, Solar Energy. vol. 78, pp. 97-103, 2005 28. Madhlopa, A; Jones, S.A; and Kalenga-Saka, J.D. (2002). A solar air heater with composite absorber systems for food dehydration. Renewable Energy 27: 27–37. 51

29. Olaleye, D.O. 2008. The design and construction of a solar incubator, Project Report,submitted

to

Department

of

Mechanical

Engineering,

University

of

Agriculture,Abeokuta.pp 11-19 30. Pangavhen, P.H, Malick, M.A.S. and Buelow, F.H. 2002. Modeling and experimental studies on a natural convection solar crop dryer, Solar Energy, vol. 81, pp. 346-357, 2007. 31. Roa, G and Macedo, I.C. 1976. Grain drying in stationary bins with solar heated air. Journal of Solar Energy 18: 445-449 32. Sebaii, S; Balladin, D.A and Headley, O. 2002. Solar dryer with thermal storage and biomass backup heater, Solar Energy, vol. 81, pp. 449-462, 2007. 33. Soponronnarit, O.1995. A solar air heater with composite absorber systems for food dehydration, Renewable Energy 27: 27–37. 34. Ting, K.C and Shore, G.C. 1983. Daily efficiency of flat plate solar air collectors for grain drying. Journal of Solar Energy, 31(6): 605-607 35. Togrul, I.T and Pehlivan D. 2004. Modelling of thin layer drying kinetics of some fruits under open-air sun drying process. Journal of Food Engineering 65: 413-425. 36. Waewsak, J; Chindaruksa, S; and Punlek, C. 2006. A mathematical modeling study of hot air drying for some agricultural products. Thammasat Intenational Journal of Science 11(1): 14-20. 37. Yaldyz, O and Ertekyn, C. 2001. Thin layer solar drying of some vegetables. Journal of Drying 38. Technology, 19(3&4), 583–597 39. Ajayi, C., Sunil, K.S., and Deepak, D. 2009. “Design of Solar Dryer with Turbo ventilator and Fireplace”. International Solar Food Processing Conference 2009.

40. Brenidorfer B, Kennedy L, Bateman C O (1995). Solar dryer; their role in post harvest processing, Commonwealth Secretariat Marlborough house, London,Swly 5hx. 52

41. A.A. El-Sebaii; S.M. Shalaby (2012): Solar drying of agricultural products: A review, Renewable and Sustainable Energy Reviews 16, 37– 43.

42. Fadhel; S. Kooli; A. Farhat; A. Bellghith (2005): Study of the solar drying of grapes by three different processes, Desalination 185, 535–541.

43. GuttiBabagana; Kiman Silas and Mustafa B. G. (2012): Design and Construction of Forced/Natural Convection Solar Vegetable Dryer with Heat Storage, ARPN Journal of Engineering and Applied Sciences, VOL. 7, NO. 10.

44. B.K. Bala; M.R.A. Mondol; B.K. Biswas; B.L. Das Chowdury; S. Janjai (2003): Solar drying of pineapple using solar tunnel drier, Renewable Energy 28, 183–190.

45. Wang, Y., Zhang, M., Mujumdar, A.S., Mothibe, K.J., RoknulAzam, S.M. Effect of blanching on microwave freeze drying of stem lettuce cubes in a circular conduit drying chamber, (2012) Journal of Food Engineering, 113 (2), pp. 177-185.

46. Zhonghua Dr., W., Long, W., Zhanyong, L., Mujumdar, A.S. Atomization and Drying Characteristics of Sewage Sludge inside a Helmholtz Pulse Combustor (2012) Drying Technology, 30 (10), pp. 1105-1112.

47. Jiang, Y., Xu, P., Mujumdar, A.S., Qiu, S., Jiang, Z. A Numerical Study on the Convective Heat Transfer Characteristics of Pulsed Impingement Drying (2012) Drying Technology, 30 48. (10), pp. 1056-1061. 53

49. J. Kaewkiew; S. Nabnean; S. Janjai (2012): Experimental investigation of the performance of a large-scale greenhouse type solar dryer for drying chilli in Thailand. Procedia Engineering 32, 433 – 439.

50. J.K. Afriyie; M.A.A. Nazha; H. Rajakaruna; F.K. Forson (2009): Experimental investigations of a chimney dependent solar crop dryer, Renewable Energy 34, 217– 222 51. Sharma, A., Chen, C. R., Vu Lan, N., 2009. Solar- energy drying systems: A review. 52. Renewable and Sustainable Energy Reviews, Vol.13, pp. 1185-1210. 53. Sodha, M.S., Dang, A., Bansal, P.K., Sharma, S.B., 1985. An analytical and experimental study of open sun drying and a cabinet type drier. Energy Conversion &Management,, Vol.25(3), pp. 263–271. 54. Thoruwa, T.F.N., Johnstone, M.C., Grant, A.D., Smith, J.E., 2000. Novel, low cost CaCl2based desiccants for solar crop drying applications. Renewable Energy, Vol.19, pp.513-520. 55. Xie, W.T., Dai Y.J., Wang, R.Z., Sumathy, K., 2011. Concentrated solar energy applications using Fresnel lenses: A review Renewable & Sustainable Energy Revıews, Vol. 15(6),pp. 2588 – 2606. 56. Torres-Reyes, E., Gonzalez, N.J.J., Ibarra-Salazar, B.A., 2002. Thermodynamic method for designing dryers operated by flat plate solar collectors. Renewable Energy, Vol.26.pp. 649– 660. 57. Youcef-Ali, S., Desmons, J.Y., 2004. The turbulence effect of the airflow on the calorific losses in foodstuff dryers. Renewable Energy, Vol.29, pp.661-674. 58. Adegoke, C.O.; and Bolaji, B.O. 2000. Performance evaluation of solar-operated thermosyphon hot water system in Akure. Int. J. Engin. Engin. Technol. 2(1): 35-40. 59. .Akinola, O.A.; Akinyemi, A.A.; and Bolaji, B.O. 2006. Evaluation of traditional and solar fish drying systems towards enhancing fish storage and preservation in Nigeria. J. Fish. Int., Pakistan 1(3-4): 44-9.

54

60. Bassey, M.W. 1989, Development and use of solar drying technologies, Nigerian Journal of Solar Energy 89: 133-64. 61. Bolaji, B.O. 2005. Performance evaluation of a simple solar dryer for food preservation. Proc. 6 Ann. Engin. Conf. of School of Engineering and Engineering Technology, Minna, Nigeria, pp. 8-13. 62. Ertekin, C.; and Yaldiz, O. 2004. Drying of eggplant and selection of a suitable thin layer drying model, J. Food Engin. 63: 349-59. 63. Ikejiofor, I.D. 1985. Passive solar cabinet dryer for drying agricultural products. In: O. Awe (Editor), African Union of Physics. Proc. Workshop Phys. Tech. Solar Energy Convers, Univ. of Ibadan, Nigeria, pp. 157-65. 64. Itodo, I.N.; Obetta, S.E.; and Satimehin, A.A. 2002. Evaluation of a solar crop dryer for rural applications in Nigeria. Botswana J. Technol. 11(2): 58-62. 65. Kurtbas, I.; and Turgut, E. 2006. Experimental investigation of solar air heater with free and fixed fins: efficiency and energy loss. Int. J. Sci. Technol. 1(1): 75-82. 66. Madhlopa, A.; Jones, S.A.; and Kalenga-Saka, J.D. 2002. A solar air heater with composite absorber systems for food dehydration. Renewable Energy 27: 27–37. 67. .Togrul, I.T.; and Pehlivan, D. 2004. Modelling of thin layer drying kinetics of some fruits under open-air sun drying process. J. Food Engin. 65: 413-25.

55