Problem Based Solving Design Of Evaporator Cooler

A

Problem Based Learning Report On

Design of Evaporator Cooler For the subject of REFRIGERATION AND AIR CONDITIONING Under the guidance of PROF. N. S. AHER By SR NO. 1 2 3 4

BATCH T-10 T-10 T-10 T-10

PROF. N. S. AHER (Name & Sign of Guide)

CLASS TE-C TE-C TE-C TE-C

ROLL NO 212 214 215 216

NAME Jathar Kunal Kamlakar Hajare Mayuresh Mehetre Vaibhav Balasaheb More Ajay Nimba

SIGN

Dr. A.G. THAKUR Vice Principal & Head Mechanical Engineering Department

A) :-PEOs:1.To prepare students for successful and efficient careers in industry that meet the needs of Indian and Multinational companies. 2.To develop the ability among students to synthesize and analyse the data and technical Concept for application to product design and development. 3.To provide opportunity for students to work as part of teams on multi-disciplinary Projects. 4.To provide students with a sound foundation in the mathematical, scientific and engineering fundamentals. 5.To promote awareness among students about life-long learning and to introduce them to professional ethic and code of professional practice. 6.To inculcate in student’s ethical values and belongingness towards society. 7.To provide opportunity to undertake innovative projects and research. 8.To make students aware of the latest developments in engineering and technology.

POs : 1.Demonstrate ability to apply basic knowledge in mathematics, science and engineering. 2.Demonstrate the ability to conduct experiments, interpret and analyse data, and report results. 3.Demonstrate the ability to design mechanical systems, in general and a thermal system or a process that meets desired Specifications and requirements. 4.Demonstrate the ability to function in a team as a member or a leader. 5.Demonstrate the ability to identify, formulate and solve Mechanical Engineering problems. 6.Demonstrate and understanding of their professional and ethical responsibilities. 7.Communicate effectively in both verbal and written forms. 8.Have the confidence to apply engineering solutions in global and societal contexts. 9.Capable of self-learning. 10.Familiar with modern engineering software tools and equipment to analyse mechanical engineering problems. 11.Capable to demonstrate creativity. 12.An ability to prepare design documentations and to make effective presentations.

Mapping :

SR.

SUBJECT

PO

PEO

1.

Introduction to Evaporator Cooler

12

8

2.

Understanding the Concept of Evaporator Cooler

5

2,4

3.

Design parameter Consideration In Evaporator Cooler

2,3

5

4.

Design of the Evaporator Cooler

11

3,2

5.

Finding Iteration value using Software

10,12

6

Introduction

The global population in the year 2008 has hit an unprecedented level of 6.5 billion. It continues to rise drastically, and is predicted to hit 8 billion by the year 2025 (United Nations, 2008). In addition, with the economic rise of highly populous countries such as China and India, there is also an unprecedented rise in the overall global standard of living. From an agriculture perspective, these facts translate into an immense increase in the demand for food. Naturally, this entails a subsequent increase in the price of food and agricultural products worldwide. It should also be noted that industries such as the biofuel industry constitute market forces that contribute to the rise in the demand and price of agricultural products. Agricultural engineers are faced with the task of not only meeting the food requirements of the ever increasing global population, but to also maintain relatively low costs for food products. From basic economics principles, stabilizing the cost of a product undergoing an increase in its demand requires either an increase in its supply or a decrease in its cost of production. However, with agricultural products, such a task is not so simple: the amount of land that can be cultivated has reached its practical limit. Furthermore, soaring energy prices continue to push the costs of production from the growing stage to the transportation stage of production higher and higher. The only possible way left to stabilize the cost of food is to establish and implement new and efficient methods for crop production, postharvest drying and storage, as well as distribution and transportation. It should be noted, that such Although all of these aspects are important when trying to tackle the challenge of meeting stabilizing the cost of food, this design project only explores the post harvest storage aspect of food production. In southeast Asia, postharvest losses range from 10%- 37% for rice (International Rice Commission, 2002). Furthermore, in India, post harvest losses are in the range of 25-50%. These losses translate into a significant loss in the overall supply of agricultural products.

(Indirect type Evaporator cooler) (1)

EVAPORATIVE COOLING SYSTEM DESIGN: The evaporative cooling system was designed to deliver a quasiuniform mass of air in terms of temperature and relative humidity. The theoretical expectation for the design was that a control volume (in the present case, a cold storage room) would eventually be in equilibrium with the incoming air. Once the point of equilibrium was reached, it was postulated that the humidifying system would maintain the temperature and relative humidity at a relatively constant level. Simply providing moisture to a control volume will provide a certain amount of cooling but only in a batch process: after saturation conditions are reached, no further cooling can be provided and the temperature will increase due to heat influx from the higher temperature ambient surroundings. For this reason, it was decided to provide an air flow Evaporative Cooling Design Set-Up: The set-up consisted of the following components: - Humidifying unit (MDFD-1) - Mixing chamber - Blower - Delivery pipe - Insulating foam to insulate door opening - Cold storage room at Bioresource Engineering Machine Shop

(Domestic Evaporator Cooler Process)

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Design of Indirect Evaporator Cooler For Domestic Purpose: In principle and based on the energy and mass conservation law, a set of differential equations are to be considered along with the length of Indirect Evaporative cooler as follows, according to the schematic diagram of heat and mass transfer as shown in Above Fig. The heat

transfer from the water film into the secondary air flow: 𝑑𝑄𝑆 = ℎ𝑠 (𝑇𝑊 − 𝑇𝑆 )𝑑𝐴……………………..(1)

The mass

flow of water that is evaporated into the secondary air: 𝑑𝑊 = ℎ𝑚(𝜔(𝑇𝑤) − 𝜔)𝑑𝐴…………………… (2)

The heat

transfer from the primary air into the water film: 𝑑𝑄𝑃= 𝑈𝑍 (𝑇𝑃 − 𝑇𝑊)dA…………………. (3.a) 𝑑𝑄𝑝 = −𝑚𝑠𝑑𝐸𝑝…………………………………. (3.b)

The overall

heat transfer coefficient is: 𝑈𝑍 =1/(1/ℎ𝑝+𝛿𝑤𝑎𝑙𝑙/𝑘𝑤𝑎𝑙𝑙+1ℎ𝑊)………………(4)  The water

mass balance (refer to Fig.2) yields: 𝑑𝑚𝑤 = 𝑑𝑊……………….(5) The water and air mass balance (refer to Fig.2) yields: 𝑚𝑆𝑑𝜔 = 𝑑𝑚𝑤…………….(6) The overall

energy balance on the process for the A and B control surface can be expressed as: 𝑚𝑠𝑑𝐻𝑆 = −𝐻𝑝𝑤𝑑𝑊 − 𝑑𝑄𝑠 (7.a) 𝑚𝑠𝑑𝐻𝑠 + 𝑑𝑄𝑝 = 𝑚𝑊𝑑𝐻𝑊 + 𝐻𝑤𝑑𝑚𝑊…… (7.b)

The enthalpy of humid air equals the sum of the enthalpies of the dry air and water vapor. The specific enthalpy of humid air is also defined per unit mass of dry air. For lower pressure, the specific enthalpy of water vapor is almost a linear function of temperature. Therefore, the enthalpy of humid air can be expressed as: H(T) = 𝐶𝑝𝑇 + 𝜔(2.501 + 1.805 × 10−3𝑇 ……………….(8) By using equations (1) -(3) and rearrangement of equations (5) -(8), a set of ordinary differential equations are described below: 𝑑𝜔/𝑑𝑥=( −ℎ𝑚𝑓𝑚𝑎(𝜔(𝑇𝑤)−𝜔)/𝑚𝑠………………………(9) 𝑑𝑇𝑆/𝑑𝑥= −𝑎𝑚𝑠𝐶𝑝 (ℎ𝑚𝑓𝑚𝐶𝑝𝑤 [𝜔(𝑇𝑤) − 𝜔] + ℎ𝑠)…………….(10) 𝑑𝑇𝑊/𝑑𝑥=𝑚𝑠𝐶𝑤(ℎ𝑚𝑓𝑚[𝑇𝑤(𝐶𝑊−𝐶𝑝𝑤)−ℎ𝑓𝑔] ∙ [𝜔𝑇𝑤 − 𝜔]− ℎ𝑠 (𝑇𝑤 − 𝑇𝑠 ) + 𝑈𝑧 (𝑇𝑝 − 𝑇𝑤))……………………………………………………(10) 𝑑𝑇𝑝/𝑑𝑥= −𝑈𝑍𝑎(𝑇𝑝−𝑇𝑊)/𝑚𝑃𝐶𝑃………………………….(12)

ANALYTICAL SOLUTION : On solving the above differential equation, we obtain the following relation: 𝑇𝑝𝑜 = (𝑇𝑝𝑖 − 𝑇𝑊)𝑒𝐴𝑥 + 𝑇𝑤……....(13) Where, 𝐴 =−𝑈𝑍×𝑎×𝑛/𝑚𝑝×𝐶𝑝……(14)

A large no. of materials are present, like metals and its alloys, fibres, polycarbonate, ceramics, zeolites etc, which can be used for Indirect Evaporative Cooling systems. In this paper Aluminium has been selected because of it’s following advantages : High thermal conductivity (229 W/m k) Low cost Low density which helps in reducing the overall weight of the IEC system. Easy availability MATLAB PROGRAM FOR FOR DIFFERENT ITERATION TO OPTIMISE THE DESIGN PARAMETERS OF IEC : clc clear all Tpi = input (' Temperature of Primary air at inlet (°C) = '); V = input (' Velocity of primary air at inlet (m/s) = '); Tw = input (' Temperature of Water (°C) = '); n = input ('No. of plates = '); t = input (Thickness of plates (mm) = '); a = input (Width of plates (m) = '); L = input (Length of plates (m) = '); 𝛿 = input (Channel width (m) = '); Cp = 1005; Pr = 0.711; k = 0.027; 𝜈 = 16.97×10^-6; 𝜌 = 1.127; Re = (V×L)/ 𝜈; hp = (0.664*(Re^0.5)) × (Pr^(1/3) ×k)/L; CA = ( 𝛿 /2) × a× n; mp = ( 𝜌 ×CA×V) ×3600; Vp = mp/ 𝜌; At = n×a×L; Uz = hp; A = (-Uz × a × n × 3600) / ( mp × Cp) ; x=0 ; for i = 1:60; x = x + 0.01; T = ( Tpi – Tw ) × exp( A × x ) + Tw ;

if i==1 fprintf(' T(0.000000)=%f\n ', Tpi); end fprintf(' T(%f)=%f\n ',x,T); end fprintf(' T(0.000000) = %f °C\n ', Tp i); fprintf(' T(%f) = %f °C\n ', x , T ); fprintf(' Volume flow rate = %f m3/hr\n ', Vp ) ; fprintf(' Mass flow rate = %f kg/hr\n ', mp ) ; fprintf(' Total heat exchange Area = %f\n ', At ) ; x = [ 0.0:0.01:0.6 ] ; y = ( Tpi- Tw ) × exp(A × x) + Tw ; plot (x,y) ;

The Theoretical results are summarized below: Thickness of plates, t = 0.4 mm Length of plates, L = 0.6 m Width of plates, a = 0.4 m Channel width, 𝛿 = 4 mm No of plates, n = 70 Total heat exchange area, At = 16.8 𝑚2 Velocity of primary air, V = 1 m/s Velocity of secondary air, Vs = 0.5 m/s Size of plates = L × a = 0.6 ×0.4 𝑚2 Volume flow rate of primary air = 175 𝑚3/ℎ𝑟 Mass flow rate of primary air = 200 kg/hr Mass flow rate of secondary primary air/ primary air = 0.5

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CONCLUSION : The proposed model of Indirect Evaporative Cooler (IEC) is Flat Plate – Concurrent type. A total of 70 flat plates are used.Size of the plate used is 0.6m*0.4m with thickness of 0.4mm. The material used for the plates is Aluminum due to its higher thermal conductivity, easy availability, low density and low cost. The plates used are wick attained on one side to increase the water retaining capacity of the Aluminum plates.These plates are arranged parallel with spacing of 4mm. The primary air and secondary air is flowing alternatively through the flow passages. The proposed design is giving temperature reduction of the supply air to upto 18-22 °C with volume and mass flow rate of 175 m3/hr and 200 kg/hr.

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REFERANCE : -ASHRAE. Handbook of Standards.American Society of Heating and Refrigeration and Air Conditioning. -Thakur , Dhingra DP , Parameters influencing the Saturation Efficiency of an Evaporators. -www.ijert.com -www.arpnjournals.com

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