Report - Experimental Performance Evaluation of Vortex Tube Refrigerator

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Report - Experimental Performance Evaluation of Vortex Tube Refrigerator...

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Project Report on

EXPERIMENTAL PERFORMANCE EVALUATION OF VORTEX TUBE REFRIGERATOR

For the award of the degree of Bachelor of Engineering by Mr. Swagat D Karekar B80800822 Mr. Akshay C Mirasdar B80800841 Mr. Jay O Bamb B80800845

Guided by Prof. Vinay V. Ankolekar Assistant Professor, BSCOER Narhe, Pune Maharashtra

DEPARTMENT OF MECHANICAL ENGINEERING BHIVARABAI SAWANT COLLEGE OF ENGINEERING AND RESEARCH, NARHE, PUNE 411041 (MS) 2013 - 2014

EXPERIMENTAL PERFORMANCE EVALUATION OF VORTEX TUBE REFRIGERATOR

______________________________________ A project report submitted to the Bhivarabai Sawant College of Engineering and Research, Narhe, University of Pune, Pune

in partial fulfillment of the requirements for the degree of

Bachelor of Engineering by

Mr. Swagat D Karekar Mr. Akshay C Mirasdar Mr. Jay O Bamb

B80800822 B80800841 B80800845

Under the guidance of

Prof. Vinay V Ankolekar Assistant Professor, BSCOER Narhe, Pune Maharashtra

Department of Mechanical Engineering, Pune, 411041 (MS) 2013 – 2014

CONTENTS ACKNOWLEDGEMENT

i

ABSTRACT

ii

ABBREVIATIONS

iii

LIST OF FIGURES

v

LIST OF TABLES

vi

CHAPTER

PAGE

TITLE

NO.

NO. 1

1-23

INTRODUCTION 1.1

Principle and theory

2

1.2

Working

6

1.3

Types of Vortex Tube

7

1.3.1 Counter-flow Vortex tube

8

1.3.2 Uni-flow Vortex tube

8

1.3.3 Dividing vortex tube

9

1.3.4 Uncooled vortex tube

10

1.3.5 Cooled Vortex tube

10

1.3.6 Dividing vortex tube additional stream

11

1.3.7 Triple-stream vortex tube

11

1.3.8 Self-evacuating vortex tube

12

1.3.9 Vortex ejectors

13

1.4

Types and number of inlet nozzles

13

1.5

Advantages

15

1.6

Limitations

16

1.7

Applications

18

2

24-31

LITERATURE REVIEW 2.1

2.2

Experimental research on vortex tube

24

2.1.1 Thermo-physical parameters

27

2.1.2 Geometrical parameters

28

Theoretical research on vortex tube 2.2.1 Adiabatic

compression

and

adiabatic

29 29

expansion model

3

2.2.2 Effect of friction and turbulence

29

2.2.3 Acoustic streaming model

30

2.2.4 Secondary circulation model

31

DESIGN OF VORTEX TUBE 3.1

3.2

4

Important equations

32

3.1.1 Cold mass fraction

32

3.1.2 Cold and hot temperature difference

33

3.1.3 Normalised temperature drop/rise

33

3.1.4 Cold orifice diameter

34

3.1.5 Isentropic efficiency

34

3.1.6 Coefficient of performance

35

Design of vortex tube

38

3.2.1 Maximum temperature drop tube design

38

3.2.2 Maximum temperature drop tube design

41

COST ESTIMATION 4.1

32-44

Details of Material Purchased and their

45-47 46

Cost

5

RESULTS AND DISCUSSION

6

CONCLUSION

7

FUTURE SCOPE

48-51 52 53-55

7.1

Further research

53

7.2

Future developments

54

REFERENCES

56-57

ACKNOWLEDGEMENT

It is my privilege to express deep gratitude to everyone who has rendered valuable help in presenting this dissertation work. First and foremost, I would like to express my sincere gratitude to my guide Prof V V Ankolekar, for whom I have greatest amount of respect and admiration. He has not only afforded me the opportunity to work on this topic but also provided valuable guidance and support throughout my time as a student in Mechanical Engineering Department, Bhivarabai Swant College of Engineering and Research, Narhe, Pune (MS). His enthusiasm, interest and inspiration, was a constant source of motivation for my encouragement. I am greatly thanking him for sparing his precious time, help and patience in the betterment of my dissertation work. I am sincerely thankful to Dr (Prof) D V Jadhav, Principal, and Prof. P. R. Kale, Head of Mechanical Engineering department, for their kind guidance and support throughout this project work. I express my deep gratitude to all staff members of Mechanical Engineering Department for providing me valuable suggestions and help during my project work. I would like to thanks to all my friends, especially who have helped me extensively right from the beginning of the project. And last but not least the backbone of my success & confidence lies solely on the blessing of my parents. I owe my loving thanks to them. They have lost a lot due to my work. Without their encouragement and understanding, it would have been impossible for me to finish this work.

Mr. Swagat D Karekar Mr. Akshay C Mirasdar Mr. Jay O Bamb

i

ABSTRACT A vortex tube is a structurally simple device with no moving parts that is capable of separating a high pressure flow into two low pressure flows with different energies, usually manifested as a difference in temperatures. The vortex tube is relatively inefficient as a standalone device because its COP is very low as compared to a VapourCompression refrigeration cycle. The effects of cold fraction, number of nozzles, orifice diameter, inlet pressure, hot end diameter and angle are experimentally investigated. The use of vortex tube for small capacity applications is always justified if the compressed air is readily available, because of lack of moving parts, non-requirement of external power like electricity. Main application is spot cooling. In this way it is ideal for use in situations where safety is critical or maintenance is difficult.

Keywords: No moving parts, Energy Separation, Critical conditions

ii

ABBREVIATIONS Symbol

Description

α

Outlet Valve Angle

AC

c/s area of cold orifice

AN

c/s area of nozzle

AT

c/s area of vortex tube

β

Cold orifice Diameter Ratio

CFD

Computational Fluid Dynamics

COP

Coefficient of Performance

D

Vortex tube diameter

DC

Cold orifice diameter

DN

Diameter of nozzle

Ɛ

Cold mass fraction

h

enthalpy

K

Thermal conductivity

L

Length of vortex tube

MC

Mass flow rate of cold stream

Mi

Total / inlet mass flow rate

θ

Direction of rotation

p

pressure

Q

Heat energy

RHVT

Ranque-Hilsch Vortex tube

iii

S

Entropy

TC

Cold temperature

Tin

Inlet temperature

Th

Hot air temperature

U

Internal energy

W

Work done on system

w

Mechanical energy used in cooling Specific heat ratio

iv

LIST OF FIGURES Chapter No.

Figure

Title of Figure

No.

01

Page No.

INTRODUCTION 1.1

Flow Pattern Inside The Vortex Tube

3

1.2

Energy Separation in a Counter-Flow Vortex

4

Tube 1.3

Interior of Vortex Tube

7

1.4

Counterflow Vortex Tube

8

1.5

Uniflow Vortex Tube

9

1.6

Dividing Vortex Tube

9

1.7

Cooled Vortex Tube

10

1.8

Dividing vortex Tube with Additional Stream

11

1.9

Triple-stream Vortex tube

12

1.10

Self-evacuating Vortex tube

12

1.11

Vortex Ejector

13

1.12

Conventional Nozzle

15

1.13

Nozzle of Archimedes’

15

1.14

Recompression Chamber

18

1.15

Cooling Blow Molded fuel tanks

20

1.16

Cooling an Ultrasonic Weld

20

1.17

Joule-Thomson Refrigeration Cycle

21

1.18

Vortex Tube Refrigeration Cycle

22

03

DESIGN OF VOTEX TUBE 3.1

Different Orifice Diameters

35

3.2

Different Number of Nozzles

37

3.3

Vortex Tube Test Rig

44

05

RESULTS AND DISCUSSIONS 5.1

Graph of Pressure vs. Temperature

v

49

LIST OF TABLES Chapter Table No.

Title of Table

Page

No.

02

No. LITERATURE OVERVIEW

2.1

Summary of Experimental Studies on Vortex Tube

24

2.2

Summary of Numerical Studies on Vortex Tube

26

2.3

Lengths and Diameters of Vortex Tube Used By Other

31

Researchers 03

DESIGN OF VORTEX TUBE 3.1

Geometrical Parameters of Vortex Tube

43

3.2

Thermo-Physical Properties of Working Medium

43

04

COST ESTIMATION 4.1

05

Expenditure for the Project

45

RESULTS AND DISCUSSIONS 5.1

Observations of Vortex Tube Test Rig

vi

48

CHAPTER 1 INTRODUCTION The vortex tube (also called Ranque Hilsch vortex tube) is a simple mechanical device which splits a compressed gas stream into cold and hot streams without any chemical reactions or external energy supply. This device separates an isothermal compressed gas flow into two different flows with different temperatures. It has advantages compared to other refrigerating or heating devices in point of being simple, small and light, having low cost, using no electricity or chemicals and having long operation time. Cold gas stream leaves the tube through a central orifice near the entrance nozzle, while hot gas stream flows toward regulating valve and leaves the tube. The vortex tube was invented in 1933 by French physicist Georges J. Ranque. and German physicist Rudolf Hilsch improved the design and published a widely read paper in 1947 on the device, which he called a Wirbelrohr (literally, whirl pipe). The vortex tube was used to separate gas mixtures, oxygen and nitrogen, carbon dioxide and helium, carbon dioxide and air in 1967 by Linderstrom-Lang. Vortex tubes also seem to work with liquids to some extent, as demonstrated by Hsueh and Swenson in a laboratory experiment where free body rotation occurs from the core and a thick boundary layer at the wall. Air is separated causing a cooler air stream coming out the exhaust hoping to chill as a refrigerator. In 1988 R.T.Balmer applied liquid water as the working medium. It was found that when the inlet pressure is high, for instance 20-50 bar, the heat energy separation process exists in incompressible (liquids) vortex flow as well. When high-pressure gas (6 bar) is tangentially injected into the vortex chamber via the inlet nozzles, a swirling flow is created inside the vortex chamber. When the gas swirls to the center of the chamber, it is expanded and cooled. In the vortex chamber, part of the gas swirls to the hot end, and another part exist via the cold exhaust directly. Part of the gas in the vortex tube reverses for axial component of the velocity and move from the hot end to the cold end. At the hot exhaust, the gas escapes with a

1

higher temperature, while at the cold exhaust, the gas has a lower temperature compared to the inlet temperature. [11] A Vortex tube has the following advantages compared to the normal commercial refrigeration device: simple, no moving parts, no electricity or chemicals, small and lightweight, low cost, maintenance free, instant cold air, durable (because of the stainless steel and clean working media), adjustable temperature. But, its low thermal efficiency is a main limiting factor for its application. Also the noise and availability of compressed gas may limit its application. Therefore, when compactness, reliability and lower equipment cost are the main factors and the operating efficiency becomes less important, the RHVT becomes a nice device for heating gas, cooling gas, cleaning gas, drying gas, and separating gas mixtures, DNA application, liquefying natural gas and other purposes [11 1.1 Principle and Theory The theory of the Hilsch vortex tube, which is also known by the name RanqueHilsch vortex tube dates back to the 1930s where French physicist George Ranque invented an early prototype. Around 1945 when the German army occupied most of France, Rudolf Hilsch, a German physicist improved Ranque’s design to create a better version of the tube. The tube was named after the inventors, but most often it is attributed to Hilsch, who paid a notable contribution to the improvement of vortex tube. In the middle section of the tube is the inlet for the compressed air. Note that the inlet is much closer to the cold outlet than the hot outlet. There is a very important aspect of the tube related to this feature which will be discussed shortly. The middle part which says spiral chamber in this part. This spiral chamber is the essential component of the tube because it is the source of the hot and cold separation of the gas. How it works is based primarily on the physics of rotational motion and on Maxwell’s law of random distribution as shown in Fig 1.1 Following the introduction of the compressed working fluid into the vortex tube tangentially, in the linear momentum of the working fluid is converted to the angular momentum. Because of the centrifugal characteristics of the forced vortex flow, the

2

Fig 1.1 Flow Pattern Inside the Vortex Tube peripheral fluid led to the annular space has a higher angular momentum, therefore kinetic energy, than that of the fluid in the central region. Naturally, this fact results in the temperature near the tube wall to be higher than that in the central part. Maxwell‘s law states is the basis of the kinetic theory of gases, which in turn helps explain fundamental properties of gases such as diffusion and pressure. Usually the law refers to velocity, but can also be applied to molecular momentum. In this particular case, we are focusing on velocities of all the molecules in the spiral chamber. From the law scientists can create what are known as Maxwell-Boltzmann distribution functions, which have importance in physics and chemistry. Since the velocity of these molecules near the tube wall is higher than the initial velocity as the gas entered the tube, these molecules have higher kinetic energy. Note that the change in kinetic energy must have come from somewhere; the only logical possibility is that internal molecular energy was converted to kinetic energy because there are no power sources or other work being done on the compressed air. Also note that somewhere upstream, work had to be done on the air to compress it, which

3

critical in showing that the tube does not violate any thermodynamic laws.

Fig. 1.2 Energy Separation in a Counter Flow Vortex Tube The first law of thermodynamics states that the increase of internal energy of a thermodynamic system is equal to the amount of heat energy added to the system minus the work done on the system by its surroundings Mathematically, this law is U=Q–W

.................. Eqn (1)

Or, written in differential form, dU = dQ – dW

................... Eqn (2)

In the equations, U refers to internal energy of the system, Q refers to heat of the system, and W refers to the work done on the system by its surroundings. Applying equation [1] to the vortex tube, the thermodynamic law reduces to equation [3] below: dU = dQ

.................. Eqn (3)

Since no work is done on the system. This means that any change in internal energy is related to a change in heat of the system. The first law applies as the gas enters the tube because as it begins to spin and create the vortex, since no work is done on the system, internal energy must be converted to kinetic energy and hence a temperature drop occurs in all molecules as internal energy also drops. Fig 1.2 shows an estimated schematic of how the air moves within the tube.

4

Once the initial internal energy drop occurs and the gas begins diffusing in the forced vortex pattern, kinetic energies of the molecules begin to change. As the molecules diffuse towards the tube wall, their kinetic energy must be high because they require more energy to rotate around in the Θ–direction where the radius of rotation is maximum than molecules close to the center, where the radius is zero There is also a pressure gradient from diffusion in the radial direction that helps propel kinetic energy to the molecules at the tube walls. As a result of this pressure gradient, the overall energy (kinetic and potential) of molecules at the tube walls will be higher than the molecules at the tube axis as shown in Fig1.2 Looking back for a moment, one can now understand why the cold outlet valve is much closer to the inlet than the hot outlet valve. As the molecules travel down the tube, the molecules begin slowly in both the z- and Θ directions. This slowing is a reduction in the axial convection of the vortex as it moves down the tube. In other words, the molecules diffusion rate slows down as the gas fills more space and relieves pressure, causing a slower propagation of the molecules down the line. As this happens, less kinetic energy is used and converted back to internal energy, which in turn increases the temperature of the gas. Since the original radial pressure gradient caused a flow of kinetic energy towards the outer molecules, they have more kinetic energy to convert back to internal energy and hence have higher temperature. This conversion of the kinetic energy separation into a thermal energy separation is known as viscous dissipation of kinetic energy. The reason the cold outlet is close to the inlet as a result of the desire to reduce the effects of viscous dissipation of kinetic energy. The outlet must be close to the inlet because the further away it gets, the more viscous dissipation will occur and hence the higher the gas temperature will be. The reason the cold outlet is not directly next to the inlet is to give the system space to utilize the radial pressure gradient and to transfer kinetic energy to the molecules at the tube wall. The outlet then is logically positioned to remove gas from the center of the tube. The hot outlet is positioned further from the inlet than the cold outlet is for similar reasons. Instead of getting the air out quickly to keep it cold, the scientist lets it travel farther down the tube, warming up by prolonged viscous dissipation of kinetic energy. As the gas travels

5

down the tube, axial convection also decreases, reducing the gradient of temperature and pressure down the tube to make a more unified stream. By the time the stream reaches the outlet, nearly all of it is the same temperature and has a higher temperature than the inlet due to the increase kinetic energy it had initially. The outlet is drawn from the tube walls though to obtain the molecules with maximum high temperature. Other than the theory behind how the vortex tube works, there are two other major theories that drive this experiment. The first and second laws of thermodynamics will hopefully hold the key to explaining why the tube is not miraculously producing something from nothing. The first and second laws give rise to the Enthalpy and Entropy balances respectively. These balances are two equations that show how the thermodynamic variables of enthalpy (H) and entropy (S) are maintained and conserved in the system. Enthalpy can be considered to be the amount of heat energy, in whatever form, a substance or system contains. This includes internal energy, work done on the system, etc. Entropy is a measure of randomness in a system, or in other words the amount of energy that is not free to do work. The two balances will hopefully prove that the system is not getting a Temperature change for free. At a pressure drop ratio of 5 and ambient temperature, temperature differences of 30 K (or 10 % of ambient) are easily obtained, sufficient for simple refrigeration. In a conventional refrigeration system, there is a compressor, so the work power is the input power of the compressor. But in the RHVT system, usually a compressed gas source is used, so it is not easy to define the work power.

1.2 Working How can cold air and hot air be obtained from one compressed-air stream. Lots of people have tried to explain it, including the French physicist who invented the Vortex Tube in the 1930's, Georges Ranque. Many different theories have been put forward.

6

Vortex Tubes behave in a very predictable and controllable way. When compressed air is released into the tube through the vortex generator, you get hot air out of one end of the tube

Fig.1.3 Interior of Vortex Tube and cold air out the other. In Fig1.3 a small valve in the hot end, adjustable with the handy control knob, lets you adjust the volume and temperature of air released from the cold end. The vortex generator—an interchangeable, stationary part—regulates the volume of compressed air, allowing you to alter the air flows and temperature ranges you can produce with the tube.

1.3 Types of Vortex tube [9] Vortex tubes are classified by their main technological and design features: flow configuration, the method of heat supply (removal), and how removal of low-pressure gas streams is organized. For the positioning of the cold exhaust, there are two different types: counter flow vortex tubes and parallel flow (uniflow) vortex tubes. Vortex tubes are classified as uncooled (adiabatic) and cooled (non-adiabatic) according to the method of heat supply (removal). On the other hand according to the how removal of low-pressure gas streams is organized vortex tubes are called as dividing vortex tubes, self-evacuating vortex tubes, and vortex ejectors.

7

1.3.1 Counter-Flow Vortex Tubes In counter flow vortex tubes the cold exhaust is placed on the other side from the hot exhaust, as shown in Fig. 1.4. The working gas is tangentially injected into vortex tube via inlet nozzles positioned next to the cold exhaust. A strongly swirling flow is created and the gas proceeds along the tube. The outer region of the flow is found to be warmer than the inlet gas, while gas towards the centre of the tube experiences cooling. Part of the gas in the vortex tube reverses for axial component of the velocity, and it moves from the hot end to the cold end. An orifice positioned just behind the flow inlets separates the cool central gas, which then exits the tube at the left hand side. The warm peripheral flow leaves at the right hand side of the tube, where a valve is positioned to allow regulation of the relative quantities of hot and cold gas.

Fig. 1.4 Counterflow Vortex Tube

1.3.2 Uniflow Vortex tube When the cold exhaust is placed at the same side of the hot exhaust, it is named ‘‘uniflow (or parallel flow) vortex tubes’’. The fundamental aspects of this configuration are the same as for the counter flow tube. Its distinguishing features are that the orifice and valve are combined at one end of the tube, while other end of the tube, adjacent to the inlet nozzles is sealed (Fig.1.5). Many investigators have

8

suggested that uniflow tubes perform less well than equivalently proportional counter flow designs. So, most of the time, the counter flow geometry has been chosen.

Fig. 1.5 Uniflow Vortex Tube

1.3.3 Dividing Vortex Tubes Figure shows a dividing vortex tube schematically. The dividing vortex tube is the best-known and most widespread type of RHVTs. It has both cold and hot flow. It has up to ten designs, as shown in Fig. 1.6, and is used on various industries.

Fig. 1.6 Dividing Vortex Tube

9

1.3.4 Uncooled (Adiabatic) Vortex Tubes Adiabatic vortex tubes are the ones where heat transfers to environment are neglected. It is distinguished from other vortex tubes; however, by maximum cooling power, which allows it to be used most efficiently at the higher temperature level in a combined regenerative throttling cycle

1.3.5 Cooled (Nonadiabatic) Vortex Tubes Nonadiabatic vortex tubes are ones heat transfer from the hot fluid to a cooling fluid occurs. These tubes are also called ‘‘cooled vortex tube’’. Figure 1.7 shows such a cooled vortex tube schematically. The cooled vortex tube differs from the dividing vortex tubes in that its hot end is closed, it is fitted with an outer jacket which is fed a cooling fluid, and all the gas entering the nozzle inlet emerges cooled (20–30 K) through the diaphragm aperture, i.e. in the given case Ɛ = 1. The cooling vortex tube does not produce strong cooling effects. It is distinguished from other vortex tubes; however, by maximum cooling power, which allows it to be used most efficiently at the higher temperature level in a combined regenerative throttling cycle.

Fig 1.7 Cooled Vortex Tube

10

1.3.6 Dividing Vortex Tube with an Additional Stream Another configuration of the dividing vortex tube is one with an additional stream, as presented in Fig. 1.8. At the hot end, in the center of the control valve, there is an orifice which allows feedback gas to be injected into the vortex tube. These tubes are also called as double circuit vortex tubes. First circuit consists of a peripheral vortex circuit with the working fluid entering the tube through the nozzles. Second circuit is an axial vortex circuit composed of additional gas entering vortex tube through the orifice at the hot end. The dividing vortex tube with an additional stream ensures that Ɛ
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