Akash.pdf

A Project Report On

MULTI TUBE MANOMETER Submitted In partial fulfillment For the award of the Degree of Bachelor of Technology In Department of Aeronautical Engineering

Supervisor

Submitted By

Name: Mr. Ranjay Singh Designation: Asst. Professor

Name: Akash S Roll No. : 16ESXAN009

Department of Aeronautical Engineering

School of Aeronautics (Neemrana) I-04, RIICO Industrial Area, Neemrana, Distt. Alwar, Rajasthan

Affiliated to Rajasthan Technical University

March 2019

Candidate’s Declaration I hereby declare that the work, which is being presented in the Project Report, entitled “MULTI TUBE MANOMETER” in partial fulfillment for the award of Degree of “Bachelor of Technology” in Department of Aeronautical Engineering and submitted to the Department of Aeronautical Engineering, School of Aeronautics (Neemrana), Affiliated to Rajasthan Technical University is a record of my own investigations carried under the Guidance of Mr. Ranjay Singh, Department of Aeronautical Engineering, School of Aeronautics(Neemrana) . I have not submitted the matter presented in this report anywhere for the award of any other Degree.

Akash S

Roll No.:16ESXAN009

School of Aeronautics (Neemrana)

Counter Signed by Mr. Ranjay Singh

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CERTIFICATE

This is to certify that Akash S of 6th Semester, B.Tech. (Aeronautical Engineering) 2018-19, has presented project report “MULTI TUBE MANOMETER” in partial fulfillment for the award of the degree of Bachelor of Technology under Rajasthan Technical University, Kota.

Date: March 9, 2019

Mr. Ranjay Singh

Prof. C.C. Ashoka

Project Guide

Director

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ACKNOWLEDGEMENT I would like to express my sincere gratitude to my project guide Mr. Ranjay Singh for his guidance and support for this endeavor. He has been tremendous source of encouragement and immense support throughout my Course. This Project would not have been in its present form without his continuous guidance and inspiration. I want to extend my special thanks to our Director, C.C. Ashoka of School of Aeronautics (Neemrana) for his help & co-operation. Regarding omission if any, I express my sincere apology & undertake all responsibilities.

Akash S B.Tech- Semester VI (Aeronautical Engineering)

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ABSTRACT This project report is an effort to elaborate and describe the construction of multi-tube manometer. A total of 24 glass tubes of 8mm outer diameter are used in this project along with a ply board of dimensions 4ft x 4ft. The glass tubes are connected together through a Polyvinyl chloride pipe of 1inch diameter. An airfoil situated in wind-tunnel with 24 holes and pipes connected to them can be tested. The 24 tubes of the manometer will be used to show the change in height of the liquid filled in the manometer respective of every hole on the surface of the airfoil. Various parameters on the surface of airfoil such as freestream pressure, freestream velocity and Cp can be easily measured through this multi-tube manometer.

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CONTENTS 1

INTRODUCTION ............................................................................................................. 1 1.1

Introduction to Aerodynamics .....................................................................................1

1.2

Pressure measurement .................................................................................................1

1.2.1

Absolute, gauge and differential pressures — zero reference ............................. 2

1.2.2

Static and dynamic pressure................................................................................. 3

1.3 2

Instruments ..................................................................................................................4

U TUBE MANOMETER AND MULTI TUBE MANOMETER ..................................... 7 2.1

Manometers .................................................................................................................7

2.1.1

Types of Manometer ............................................................................................ 7

2.2

The U-tube manometer..............................................................................................10

2.3

Multi tube manometer ...............................................................................................11

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PROCEDURE FOR CONSTRUCTION OF 24 TUBE MANOMETER ........................ 13

4

RESULT AND CONCLUSION ...................................................................................... 15

5

REFERENCES ................................................................................................................ 16

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LIST OF FIGURES

Figure 1 Aircraft fuel-pressure gauge ........................................................................................ 2 Figure 2 The difference in fluid height in a liquid-column manometer ................................... 4 Figure 3 A McLeod gauge, drained of mercury ....................................................................... 6 Figure 4 Differential U- Tube Manometer................................................................................. 7 Figure 5 Inverted u tube manometer .......................................................................................... 8 Figure 6 Inclined Tube Manometer ........................................................................................... 9 Figure 7 Digital Manometer....................................................................................................... 9 Figure 8 U tube Manometer ..................................................................................................... 10 Figure 9 Multi Tube Manometer.............................................................................................. 11

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Chapter-1

1 INTRODUCTION 1.1 Introduction to Aerodynamics Aerodynamics is the study of motion of air, particularly as interaction with a solid object, such as an airplane wing. It is a sub-field of fluid dynamics and gas dynamics, and many aspects of aerodynamics theory are common to these fields. The term aerodynamics is often used synonymously with gas dynamics, the difference being that "gas dynamics" applies to the study of the motion of all gases, and is not limited to air. The formal study of aerodynamics began in the modern sense in the eighteenth century, although observations of fundamental concepts such as aerodynamic drag were recorded much earlier. Most of the early efforts in aerodynamics were directed toward achieving heavier-than-air flight, which was first demonstrated by Otto Lilienthal in 1891. Since then, the use of aerodynamics through mathematical analysis, empirical approximations, wind tunnel experimentation, and computer simulations has formed a rational basis for the development of heavier-than-air flight and a number of other technologies. Recent work in aerodynamics has focused on issues related to compressible flow, turbulence, and boundary layers and has become increasingly computational in nature.

1.2 Pressure measurement Pressure measurement is the analysis of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in an integral unit are called pressure gauges or vacuum gauges. A manometer is a good example, as it uses a column of liquid to both measure and indicate pressure. Likewise the widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge. A vacuum gauge is a pressure gauge used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (e.g.: −15 psig or −760 mm Hg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as "gauge pressure". However, anything greater than total vacuum is technically a form of pressure. For very accurate readings, especially at very low pressures, a gauge that uses total vacuum as the zero point may be used, giving pressure readings in an absolute scale. Other methods of pressure measurement involve sensors that can transmit the pressure reading to a remote indicator or control system.

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Figure 1 Aircraft fuel-pressure gauge

1.2.1 Absolute, gauge and differential pressures — zero reference Everyday pressure measurements, such as for vehicle tire pressure, are usually made relative to ambient air pressure. In other cases measurements are made relative to a vacuum or to some other specific reference. When distinguishing between these zero references, the following terms are used: Absolute pressure is zero-referenced against a perfect vacuum, using an absolute scale, so it is equal to gauge pressure plus atmospheric pressure. Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted. To distinguish a negative pressure, the value may be appended with the word "vacuum" or the gauge may be labeled a "vacuum gauge". These are further divided into two subcategories: high and low vacuum (and sometimes ultra-high vacuum). The applicable pressure ranges of many of the techniques used to measure vacuums have an overlap. Hence, by combining several different types of gauge, it is possible to measure system pressure continuously from 10 mbar down to 10−11 mbar. Differential pressure is the difference in pressure between two points. The zero reference in use is usually implied by context, and these words are added only when clarification is needed. Tire pressure and blood pressure are gauge pressures by convention, while atmospheric pressures, deep vacuum pressures, and altimeter pressures must be absolute. For most working fluids where a fluid exists in a closed system, gauge pressure measurement prevails. Pressure instruments connected to the system will indicate pressures relative to the current atmospheric pressure. The situation changes when extreme vacuum pressures are measured, then absolute pressures are typically used instead. Differential pressures are commonly used in industrial process systems. Differential pressure gauges have two inlet ports, each connected to one of the volumes whose pressure is to be monitored. In effect, such a gauge performs the mathematical operation of subtraction through mechanical means, obviating the need for an operator or control system to watch two separate gauges and determine the difference in readings.

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Atmospheric pressure is typically about 100 KPa at sea level, but is variable with altitude and weather. If the absolute pressure of a fluid stays constant, the gauge pressure of the same fluid will vary as atmospheric pressure changes. For example, when a car drives up a mountain, the (gauge) tire pressure goes up because atmospheric pressure goes down. The absolute pressure in the tire is essentially unchanged. Using atmospheric pressure as reference is usually signified by a "g" for gauge after the pressure unit, e.g. 70 psig, which means that the pressure measured is the total pressure minus atmospheric pressure. There are two types of gauge reference pressure: vented gauge (vg) and sealed gauge (sg). A vented-gauge pressure transmitter, for example, allows the outside air pressure to be exposed to the negative side of the pressure-sensing diaphragm, through a vented cable or a hole on the side of the device, so that it always measures the pressure referred to ambient barometric pressure. Thus a vented-gauge reference pressure sensor should always read zero pressure when the process pressure connection is held open to the air. A sealed gauge reference is very similar, except that atmospheric pressure is sealed on the negative side of the diaphragm. This is usually adopted on high pressure ranges, such as hydraulics, where atmospheric pressure changes will have a negligible effect on the accuracy of the reading, so venting is not necessary. This also allows some manufacturers to provide secondary pressure containment as an extra precaution for pressure equipment safety if the burst pressure of the primary pressure sensing diaphragm is exceeded. There is another way of creating a sealed gauge reference, and this is to seal a high vacuum on the reverse side of the sensing diaphragm. Then the output signal is offset, so the pressure sensor reads close to zero when measuring atmospheric pressure. A sealed gauge reference pressure transducer will never read exactly zero because atmospheric pressure is always changing and the reference in this case is fixed at 1 bar. To produce an absolute pressure sensor, the manufacturer seals a high vacuum behind the sensing diaphragm. If the process-pressure connection of an absolute-pressure transmitter is open to the air, it will read the actual barometric pressure.

1.2.2 Static and dynamic pressure Static pressure is uniform in all directions, so pressure measurements are independent of direction in an immovable (static) fluid. Flow, however, applies additional pressure on surfaces perpendicular to the flow direction, while having little impact on surfaces parallel to the flow direction. This directional component of pressure in a moving (dynamic) fluid is called dynamic pressure. An instrument facing the flow direction measures the sum of the static and dynamic pressures; this measurement is called the total pressure or stagnation pressure. Since dynamic pressure is referenced to static pressure, it is neither gauge nor absolute; it is a differential pressure. While static gauge pressure is of primary importance to determining net loads on pipe walls, dynamic pressure is used to measure flow rates and airspeed. Dynamic pressure can be measured by taking the differential pressure between instruments parallel and perpendicular 3

to the flow. Pitot-static tubes, for example perform this measurement on airplanes to determine airspeed. The presence of the measuring instrument inevitably acts to divert flow and create turbulence, so its shape is critical to accuracy and the calibration curves are often non-linear

1.3 Instruments Many instruments have been invented to measure pressure, with different advantages and disadvantages. Pressure range, sensitivity, dynamic response and cost all vary by several orders of magnitude from one instrument design to the next. The oldest type is the liquid column manometer invented by Evangelista Torricelli in 1643. The U-Tube was invented by Christiaan Huygens in 1661. Hydrostatic Hydrostatic gauges (such as the mercury column manometer) compare pressure to the hydrostatic force per unit area at the base of a column of fluid. Hydrostatic gauge measurements are independent of the type of gas being measured, and can be designed to have a very linear calibration. They have poor dynamic response. Piston Piston-type gauges counterbalance the pressure of a fluid with a spring (for example tirepressure gauges of comparatively low accuracy) or a solid weight, in which case it is known as a deadweight tester and may be used for calibration of other gauges. Liquid column (manometer) Liquid-column gauges consist of a column of liquid in a tube whose ends are exposed to different pressures. The column will rise or fall until its weight (a force applied due to gravity) is in equilibrium with the pressure differential between the two ends of the tube (a force applied due to fluid pressure). A very simple version is a U-shaped tube half-full of liquid, one side of which is connected to the region of interest while the reference pressure

Figure 2 The difference in fluid height in a liquid-column manometer is proportional to the pressure difference

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Is applied to the other. The difference in liquid levels represents the applied pressure. The pressure exerted by a column of fluid of height h and density ρ is given by the hydrostatic pressure equation, P = hgρ. Therefore, the pressure difference between the applied pressure Pa and the reference pressure P0 in a U-tube manometer can be found by solving Pa − P0 = hgρ. In other words, the pressure on either end of the liquid (shown in blue in the figure) must be balanced (since the liquid is static), and so Pa = P0 + hgρ. In most liquid-column measurements, the result of the measurement is the height h, expressed typically in mm, cm, or inches. The h is also known as the pressure head. When expressed as a pressure head, pressure is specified in units of length and the measurement fluid must be specified. When accuracy is critical, the temperature of the measurement fluid must likewise be specified, because liquid density is a function of temperature. So, for example, pressure head might be written "742.2 mmHg" or "4.2 inH2O at 59 °F" for measurements taken with mercury or water as the monomeric fluid respectively. The word "gauge" or "vacuum" may be added to such a measurement to distinguish between a pressure above or below the atmospheric pressure. Both mm of mercury and inches of water are common pressure heads, which can be converted to S.I. units of pressure using unit conversion and the above formulas. If the fluid being measured is significantly dense, hydrostatic corrections may have to be made for the height between the moving surface of the manometer working fluid and the location where the pressure measurement is desired, except when measuring differential pressure of a fluid (for example, across an orifice plate or venture), in which case the density ρ should be corrected by subtracting the density of the fluid being measured. Although any fluid can be used, mercury is preferred for its high density (13.534 g/cm3) and low vapor pressure. For low pressure differences, light oil or water are commonly used (the latter giving rise to units of measurement such as inches water gauge and millimeters H2O. Liquid-column pressure gauges have a highly linear calibration. They have poor dynamic response because the fluid in the column may react slowly to a pressure change. When measuring vacuum, the working liquid may evaporate and contaminate the vacuum if its vapor pressure is too high. When measuring liquid pressure, a loop filled with gas or a light fluid can isolate the liquids to prevent them from mixing, but this can be unnecessary, for example, when mercury is used as the manometer fluid to measure differential pressure of a fluid such as water. A single-limb liquid-column manometer has a larger reservoir instead of one side of the Utube and has a scale beside the narrower column. The column may be inclined to further amplify the liquid movement. Based on the use and structure, following types of manometers are used    

Simple manometer Micro manometer Differential manometer Inverted differential manometer 5

McLeod gauge A McLeod gauge isolates a sample of gas and compresses it in a modified mercury manometer until the pressure is a few millimeters of mercury. The technique is very slow and unsuited to continual monitoring, but is capable of good accuracy. Unlike other manometer gauges, the McLeod gauge reading is dependent on the composition of the gas, since the interpretation relies on the sample compressing as an ideal gas. Due to the compression process, the McLeod gauge completely ignores partial pressures from non-ideal vapors that condense, such as pump oils, mercury, and even water if compressed enough.

Figure 3 A McLeod gauge, drained of mercury

Useful range: from around 10−4 Torre (roughly 10−2 Pa) to vacuums as high as 10−6 Torre (0.1 mPa), 0.1 mPa is the lowest direct measurement of pressure that is possible with current technology. Other vacuum gauges can measure lower pressures, but only indirectly by measurement of other pressure-dependent properties. These indirect measurements must be calibrated to SI units by a direct measurement, most commonly a McLeod gauge. Aneroid Aneroid gauges are based on a metallic pressure-sensing element that flexes elastically under the effect of a pressure difference across the element. "Aneroid" means "without fluid", and the term originally distinguished these gauges from the hydrostatic gauges described above. However, aneroid gauges can be used to measure the pressure of a liquid as well as a gas, and they are not the only type of gauge that can operate without fluid. For this reason, they are often called mechanical gauges in modern language. Aneroid gauges are not dependent on the type of gas being measured, unlike thermal and ionization gauges, and are less likely to contaminate the system than hydrostatic gauges.

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Chapter-2

2 U TUBE MANOMETER AND MULTI TUBE MANOMETER 2.1 Manometers The manometer is a wet meter which means that the fluid whose pressure is being measured is brought in contact with another fluid, for example mercury, which is displaced to indicate the pressure. Mercury can be used because it has a high density and so the manometer size is minimized. From the conversion table above 1 bar corresponds to 0.75m of Hg whereas from the example above, a column of water 10m is high is equal to 1 bar. Compared to water, a much smaller column of mercury is needed to measure pressure. The common types of manometer are the U-tube, the Well and the inclined manometer. Signal conditioning on a manometer consists of marking graduations on the glass column corresponding to calibrated pressure readings. With mercury manometers a range of 1mbar to 1.5bar can be easily achieved.

2.1.1 Types of Manometer Five different types of manometers are shown below with images. 1. 2. 3. 4. 5.

Differential U-Tube Manometer Inverted U-Tube Manometer Micro Manometer Inclined Manometer Digital Manometer.

Differential U-tube Manometer Differential u tube manometer are used for finding the difference between the two pressures. Differential U-tube manometer is very handy to measure the pressure difference directly and is basically similar to the U-tube manometer discussed above.

Figure 4 Differential U7 Tube Manometer

What the open end was before is now connected to a different pressure, 𝑃𝐵 so that we measure the difference, 𝑃𝐵 -𝑃𝐴 . Now we have,

Inverted u tube manometer This type of manometer is used when the difference between the densities of the two liquids is small. Similar to the previous type, A and B are points at different levels with liquids having different specific gravity. It consists of a glass tube shaped like an inverted letter 'U' and is similar to two piezometers connected end to end. Air is present at the center of the two limbs.

Figure 5 Inverted u tube manometer

As the two points in consideration are at different pressures, the liquid rises in the two limbs. Air or mercury is used as the manometric fluid. If PA is the pressure at point A and PB is the pressure at point B; PA -PB = ρ1 × g × h1 - ρ 2 × g × h2 - ρ g × g × h Where, ρ1 = density of liquid at A ρ 2 = density of liquid at B ρ g = density of light liquid h = difference of light liquid

Inclined U-Tube Manometer A common problem when measuring the pressure difference in low velocity systems - or systems with low density fluids - like air ventilation systems - are low column heights and accuracy. Accuracy can be improved by inclining the u-tube manometer.

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The figure bellow indicates a u-tube where the left tube is connected to a higher pressure than the right tube. Note that the left and the right tube must in the same declined plane for the angle to the horizontal plane to be correct.

Figure 6 Inclined Tube Manometer

Where, h = length, difference in position of the liquid column along the tube (mm, ft) θ = angle of column relative the horizontal plane (degrees) Inclining the tube manometer increases the accuracy of the measurement. Digital Manometer A digital manometer uses a microprocessor and pressure transducer to sense slight changes in pressure. It gives the pressure readout on a digital screen. It measures differential pressure across two inputs. An analog/digital output in proportion to the instantaneous pressure can be obtained.

Figure 7 Digital Manometer

Digital manometers report positive, negative, or differential measurements between pressures. With the integration of an anemometer, flow readings can also be recorded on a digital manometer.

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Digital manometer is used for designed to measure a wide range of pressures to a high accuracy. Applications include calibration facilities and laboratories. Digital Manometer can be used to measure low pressure.

2.2 The U-tube manometer This manometer is very easily constructed. It consists of a tube of glass bent into a U shape. It is then filled with a fluid. The density of the fluid dictates the range of pressures that can be measured. Both ends of the tube are pressure ports. If one port is left open to the atmosphere and the other port is connected to the pressure to be measured, the device acts as a gauge pressure meter. If both ports are connected to two different unknown pressures, the instrument acts as a differential pressure gauge.

Figure 8 U tube Manometer

The U-tube manometer is shown opposite. The difference in the height of the two columns is due to the fact that p1 is greater than p2. For equilibrium at the datum point at the bottom of the tube the total pressure in each limb must be equal. The pressure in the left limb is due to (a) the column of measuring fluid (e.g. mercury) of height h1 (b) the column of measurand fluid (e.g. air) of height h and (c) the pressure p1. The pressure in the right limb is due to (a) the column of measuring fluid (e.g. mercury) of height h2 and (b) the pressure p2. Therefore we have as follows:

Where 1 is the density of the measured fluid and  is the density of the fluid in the manometer. (Measured fluid = fluid whose pressure you are measuring). If the measured fluid is air then the pressure due to it can be ignored as the term will be very small compared to the other terms. If the measured fluid is a liquid or some other fluid of significantly high

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density then it cannot be ignored in the equation. Assuming that we have air as the measured fluid the equation above becomes:

Since g is the acceleration due to gravity and is a constant and the fluid density is a constant, the difference in pressure is directly proportional to the difference in the heights of the columns. With some experimental work graduations could be marked on the glass to give a direct pressure reading. Rearranging the above equation gives:

If p2 is atmospheric pressure then the result for p1 is an absolute pressure measurement. If a gauge pressure measurement is sufficient then we can use the following equation:

A difference in height of 8mm of mercury indicates a difference in pressure of just over 1kPa.We cannot say what the air pressure is because neither tapping is open to the atmosphere. We can only determine the differential pressure but not the absolute or gauge pressure. If the fluid whose pressure is being measured is not air but has a significant density then the 1gh term above cannot be ignored.

2.3 Multi tube manometer A multi tube manometer is pressure measuring equipment which can be used to calculate pressure at different port at same time. A 24-tube manometer for measuring pressure on models in subsonic wind tunnels and fan test sets. A backboard with graduated scale holds each manometer tube. For safety and convenience the manometer uses water as the manometer fluid. This is via an adjustable reservoir with fine-adjust hand wheel held at the side of the equipment. Water coloring is included to aid visibility.

Figure 9 Multi Tube Manometer

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The top of each manometer tube has a connection piece for tubing to connect to pressure tapings on the equipment being monitored. The whole manometer tube assembly is mounted on a swivel. This allows it to be tilted in preset increments to increase the sensitivity of measurement. Adjustable feet enable the whole apparatus to be precisely levelled before use. The manometer is supplied with operating instructions, a filling funnel and a spirit level

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Chapter-3

3 PROCEDURE FOR CONSTRUCTION OF 24 TUBE MANOMETER Material required for construction of 24 tube manometer 1. 2. 3. 4. 5. 6.

Transparent tube of 4feet Hollow pipe Support pipe Ply wood (4 x 3) Clamp Scale

Steps of Construction Step 1: Take a plywood of (4 x 3)

Step 2: Take a hollow pipe and drill it of 8mm diameter

Step 3: Fix the hollow pipe to the ply board with the help of clamp. Step 4: Fix the support pipe to the ply board. 13

Step 5: Attach transparent tube to the hollow pipe Step 6: Fill the water at 0 level.

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Chapter-4

4 RESULT AND CONCLUSION 1. The multi tube manometer is constructed using glass tubes, ply board, PVC pipe, etc. 2. The multi-tube manometer is a pressure-velocity measuring device. 3. It is used to measure various parameters such as pressure, velocity and Cp of airfoil in a wind tunnel.

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Chapter 5

5 REFERENCES [1] A History of Aerodynamics and its Impact on Flying Machines, Anderson, John David [2] Methods for the Measurement of Fluid Flow in Pipes, British Standards Institute [3] A Textbook on Fluid Mechanics, by R K Rajput [4] Fluid Mechanics by A K Banshal

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