vapour compression refrigeration system with liquid suction heat exchanger is benificial for engineering students .it is a final year project of mechanical engineering.
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Project report on vcr system with liquid suction heat exchanger
1. 1
A
Project Report on
“VCR System with Liquid Suction Heat Exchanger”
Submitted in partial fulfillment of the requirements
for the degree of
BACHELOR OF TECHNOLOGY
in
MECHANICAL ENGINEERING
Submitted by
Mr.Alok Singh (1313340015)
Mr. Sant Lal Patel (1313340151)
Mr. Surjeet Pandey (1413340919)
Mr. Vishal Singh (1313340183)
Under the supervision of
Mr.Tarun Goel
(Asst.Professor)
DEPARTMENT OF MECHANICAL ENGINEERING
NOIDA INSTITUTE OF ENGINEERING AND TECHNOLOGY
Greater Noida, Uttar Pradesh
Affiliated to
Dr.A.P.J Abdul Kalam Technical University
May, 2017
2. 2
DECLARATION
We hereby declare that this submission is our own work and that, to the best of our
knowledge and belief, it contains no material previously published or written by another
person nor material which to a substantial extent has been accepted for the award of any
other degree or diploma of the university or other institute of higher learning, except
where due acknowledgement has been made in the text.
The Project Report entitled “VCR System with Liquid Suction Heat Exchanger”, for
the award of the Bachelor of Technology in Mechanical Engineering and submitted to
the Department of Mechanical Engineering is an authentic record of my own work
carried out under supervision of Mr. Tarun Goel, Assistant Professor, Department of
Mechanical Engineering.
Date: May, 2017 Signature
Alok Kumar Singh (1313340015)
Sant Lal Patel (1313340151)
Vishal Singh (1313340183)
Surjeet Pandey (1413340919)
3. 3
CERTIFICATE
This is to Certify that Alok Kumar Singh (1313340015), Sant Lal Patel (1313340151),
Vishal Singh (1313340183), Surjeet Pandey (1413340919) carried out the project work
presented in this thesis entitled “Vapor Compression Refrigeration System with Liquid
Suction Heat Exchanger” for the award of Bachelor of Technology from Dr. A. P. J.
Abdul Kalam Technical University, Lucknow. The project embodies result of original
work and studies carried out by student themselves and the contents of this project have
not been submitted for the award of any other degree/diploma or any other University/
Institution.
Signature
Mr. Tarun Goel
(Asst. Professor)
Date: -
Signature
Dr. Chandan Kumar
(HOD, ME)
Date:-
4. 4
ABSTRACT
Because of simplicity and low cost, capillary tubes are used as the expansion device in
most small refrigeration and air conditioning systems. Another advantage is that capillary
tubes allow high and low side pressures to equalize during the off-cycle, thereby reducing
the starting torque required by the compressor. In this application the liquid line is
usually placed in contact with the suction line, forming a counter flow heat exchanger.
The liquid line is welded to the suction line in the lateral configuration. The temperature
of the vapour refrigerant coming out from the evaporator is less than the temperature of
the liquid coming out from the condenser. Before the expansion process, heat is
transferred from the liquid line to the suction line. As a consequence this in turn reduces
the refrigerant quality at the inlet of the evaporator and therefore increases the
refrigerating capacity. The suction line exit temperature also increases, eliminating
suction line sweating and preventing slugging of the compressor. The main objective of
this project is to evaluate the performance of refrigerator with liquid suction heat
exchanger by using R134a.
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ACKNOWLEDGEMENT
We feel our privilege in expressing our sincere thanks and words of gratitude to our
project guide, Mr. Tarun Goel, Asst. Professor, Department of Mechanical Engineering,
Noida Institute of Engineering and Technology Gr. Noida.
We are very much thankful to Dr. Chandan Kumar, HOD, Department of Mechanical
Engineering and Mr. Prateek Gupta, Project Co-ordinator, Department of Mechanical
Engineering, and Mr. Arvind Kumar, Lab Assistant, Refrigeration and Air Conditioning
lab , Department of Mechanical Engineering ,Noida Institute of Engineering and
Technology Gr. Noida, for their continuous support and sound guidance and co-operation
which enable us to complete our work in scheduled time. They motivated us to think
beyond boundaries and experiment with the things as more as possible.
We would also like to express heartful gratitude towards our honorable Director of the
institution, Dr. Ajay Kumar, for his consistence support and cooperation.
In the last, we would like to thanks our friends and those who were directly or indirectly
related to our project work.
6. 6
TABLE OF CONTENTS
Page No.
Declaration i
Certificate ii
Abstract iii
Acknowledgement iv
Table of Contents v-vi
List of Tables vii
List of Figures viii-ix
List of Symbols and Abbreviations x
CHAPTER 1: INTRODUCTION 1-27
1.1 Vapor Compression Refrigeration System 1
1.2 Operational Stages 2
1.3 List of Components 3
1.3.1 Compressor 3
1.3.2 Type of Compressor 4-5
1.4 CONDENSER 6
1.4.1 Types of Condenser 7
1.5 Expansion Valve 10
1.6 EVAPORATOR 14
10. 10
Figure 3.6 Condenser 40
Figure 3.7 Final setup of VCR System with Liquid Suction H.E. 41
Figure 4.1 P-h Graph without Heat Exchanger 42
Figure 4.2 P-h Graph with Heat Exchanger 44
11. 11
LIST OF TABLES
Page No.
Table 1.1 Properties of R-134a 25
Table 4.1.1 Observation Table 42
Table 4.1.2 Observation Table 43
12. 12
LIST OF ABBREVIATION
VCR System Vapor compression refrigeration system
TR Ton of Refrigeration
V Volt
KW Kilo watt
MPa Mega Pascal
Hp Horse Power
Psi Pound per square inch
LLSL-H.E. Liquid line/Suction line Heat Exchangers
COP Coefficient of Performance
H.E. Heat Exchanger
13. 13
CHAPTER 1: INTRODUCTION
1.1 VAPOUR COMPRESSION REFRIGERATIONSYSTEM
The vapor compression uses a circulating liquid refrigerant as the medium which absorbs
and removes heat from the space to be cooled and subsequently rejects that heat
elsewhere. A typical single stage vapor compression system has four components:-
1. Compressor
2. Condenser
3. Thermal expansion valve
4. Evaporator
Circulating refrigerant enters the compressor in the thermodynamic state known as
saturated vapor and in compressed to a higher pressure, resulting in a higher temperature
as well. The hot compressed vapor is then in thermodynamic state known as superheated
vapor and it is a temperature and pressure at which it can be condensed with either
cooling water or cooling air.
Figure 1.1 Simple VCRS
14. 14
The hot vapor is routed through a condenser where it is cooled and condensed into a
liquid by flowing through a coil or tubes with cool water or coil air flowing across the
coil or tubes. This is where the circulating refrigerant rejects heat from the system and the
rejected heat is carried away by either the water or the air (whenever may be in case).
The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid
is next routed through an expansion valve where it undergoes an abrupt reduction in
pressure. The pressure reduction results in the adiabatic flash evaporation of a part of the
liquid refrigerant. The auto refrigeration effect of the adiabatic flash evaporation lowers
the temperature of the liquid and vapor refrigerant mixture to where it is colder than the
temperature of the enclosed space to be refrigerant.
The cold mixture is then routed through the coil or tubes in the evaporator. A fan
circulates the warm air in the enclosed space across the coil and tubes carrying the cold
refrigerant liquid and vapor mixture. The warm air evaporates the liquid part of the cold
refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the
temperature of the enclosed space the desired temperature. The evaporator is where the
circulating refrigerant absorbs and removes the heat which is subsequently rejected in the
condenser and transferred elsewhere by the water on air used in the condenser.
To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again a
saturated vapor and is routed back into the compressor.
1.2 OPERATIONAL STAGES
1. Two phase liquid vapor mixture of refrigerant is evaporated through heat
transfer from the refrigeration space.
2. Vapor refrigerant is compressed to a relatively high temperature and pressure
requiring work input.
3. Vapor refrigerant condenses to liquid through heat transfer to the
surroundings.
4. Liquid refrigerant expands to the evaporative pressure.
15. 15
1.3 List of Components
There are the four principal control volumes involving these components:-
Evaporator
Compressor
Condenser
Expansion valve
Heat exchanger
1.3.1 COMPRESSOR
The gas compressor is a mechanical device that increases the pressure of a gas by
reducing its volume. An air compressor is a specific type of gas compressor.
Compressors are similar to pumps both increase the pressure of a fluid and both can
transport the fluid through a pipe as gases are compressible the compressor also reduces
the volume of the gas. Liquids are relatively incompressible while some can be
compressed the main action is to pressurize and transport liquids.
In the experiment reciprocating compressor is used. Reciprocating compressors use
piston driven by a crankshaft. They can be either stationary or portable can be single or
multi-staged, and can be driven by electric motors or internal combustion engines. Small
reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in
automotive applications and are typically for intermittent duty. Larger reciprocating
compressors well over 1000 hp (750 kW) are commonly found in large industrial and
petroleum applications. Discharge pressures can range from low pressure to very high
pressure (>18000psi or 180 MPa).
In certain applications, such as air compression, multi-stage double-acting compressors
are said to be the most efficient compressors available, and are typically larger, and more
costly than comparable rotary units. Another type of reciprocating compressor is the
swash plate compressor, which uses pistons moved by a swash plate mounted on a shaft.
16. 16
1.3.2 Types of compressor:-
1. Positive displacement compressor
2. Non positive displacement compressor
Positive displacement compressor: - these ensure positive admission and delivery
preventing undesired reversal of flow within the machine as achieved by the use of valves
in the case of reciprocating compressors. They have intermittent operation, subjected the
fluid to non-flow processes, and work is transferred by virtue of a hydrostatic force on the
moving boundary.
Examples: reciprocating compressors, rotary compressors, scroll compressors, screw
compressors.
Non –positive displacement compressor:- these have no means to prevent the reversal
of flow. The fluid is subjected to flow process and the work is transferred by virtue of
change of momentum of a stream of fluid flowing at a higher speed over blades or vanes
attached to a rotor.
Examples: centrifugal compressors.
In the vapor compression refrigeration system the reciprocating compressor are used
mainly.
Refrigerating capacity control with reciprocating compressors running at constant speed
consists in controlling the quantity of the gas delivered to match the fluctuating load. In
an efficient control system, the power consumption the compressor should be
proportional to the amount of gas delivered.
Simple on-off or start-stop control in conjunction with the thermostat is used to
advantage in small unitary equipment, such as refrigerators, air conditioners, water
coolers etc. it is particularly suited where there is a sudden large demand followed by
periods of small or no demand on capacity.
17. 17
Scroll compressors are currently preferred in residential and commercial refrigeration air-
conditioning, heat pump, automotive air-conditioning applications etc.
In the VCRS mostly reciprocating compressors are used. These are classified as follows:
a) Hermetically sealed compressors: Both compressor and motor are located
inside a sealed casing which is initially subjected to high vacuum condition.
This confines the any leakage across the piston to casing only, which is
sucked in by the compressor. Suction vapors cool the electrical motor
windings.
Figure 1.2 Reciprocating Compressor
b.) Semi hermetically sealed compressor: the only difference between this
and previous compressor is that in this compressor the head of the compressor is
located in such a way that it is accessible to repair in case of necessity. But, 100%
leak proof cannot be guaranteed.
18. 18
Figure 1.3 Semi Hermetically Sealed Compressor
c.) Open type compressor: the motor and compressor are connected by means of
coupling drive. Both are kept separately exposed to the surroundings. Here frequent
leakage of refrigerant occurs; hence the system has to be charged at regular interval to
make up the loss. It is used in those systems which have 3.5TR capacity.
1.4 CONDENSER
A condenser is a device or unit used to condensate a substance from the gaseous to liquid
state, typically by cooling it. In so doing the latent heat is given up by the substance, and
will transfer to the condenser coolant. Condenser are generally heat exchangers which
have various designs and come in many sizes ranging from rather small to large industrial
scale units used in plant processes. For example, a refrigerator uses a condenser to get rid
of heat extracted from the interior of the unit to condensate the outside air. Condensers
are used in air conditioning, industrial chemical processes such as distillation, steam
power plant and heat exchanger system. Use of cooling water or surrounding air as the
coolant is common in many condensers. A condenser unit is used in central air
conditioning systems typically has a heat exchanger section to cool down and condense
incoming refrigerant vapor into liquid, a compressor to raise the pressure of the
refrigerant and move it along and a fan for blowing outside air through the heat
exchanger suction to cool the refrigerant inside. A typical configuration of such a
19. 19
condenser unit it as follows: the heat exchanger section wraps around the sides of the unit
with the compressor inside. In this heat exchanger section, the refrigerant goes through
multiple tube passes which are surrounded by heat transfer fins through which cooling
air can move from outside to inside the unit. There is a motorized fan inside the
condenser unit near the top, which is covered by some grating to keep any objects from
accidently falling inside the fan. The fan is used to blow the outside cooling air on
through the heat exchange section at the sides and the top through grating. These
condenser units are located on the outside of the building they are trying to cool, with
tubing between the unit and building, one for vapor refrigerant entering and is need for
the compressor and fan inside the unit.
Figure 1.4 Condenser
1.4.1 Types of condenser
There are three types of condenser air cooled condenser, water cooled condenser,
evaporative.
1. Air cooled condensers: Air cooled condensers are used in small units like household
refrigerators, deep freezers, water coolers, window air conditioners, split air conditioners,
small packaged air conditioners etc. These are used in plants where the cooling load is
20. 20
small and the total quantity of the refrigerant in the refrigeration cycle is small. Air
cooled condensers are also called coil condensers as they are usually made of copper or
aluminum coil. Air cooled condensers occupy a comparatively larger space than water
cooled condensers. Because the thermal conductivity of water is more than the air.
Air cooled condensers are two types: natural convection and forced convection. In the
natural convection type, the air flows over it in natural a way depending upon the
temperature of the condenser coil. In the forced air type, a fan operated by a motor blows
air over the condenser coil.
Figure 1.5 Air cooled condenser
2. Water cooledcondenser: water cooled condensers are used for large refrigerating
plants, big packaged air-conditioners, central air-conditioning plants, etc. these are used
21. 21
in plants where cooling loads are excessively high and a large quantity of refrigerant
flows through the condenser.
There are three type of water cooled condensers, tube-in tube or double pipe type
condenser, shell and coil type condenser and shell and tube type condenser. In all these
three condensers the refrigerant flows through one side of the piping while the water
flows through the other piping, cooling the refrigerant and condensing it.
A shell and tube condenser serves the purpose of receiver, specially for pumping down
the refrigerant because there is sufficient space in the shell. The bottom portion of the
condenser also serves the purpose of sub-cooler as the condensed liquid comes in contact
with the entering water at a lower temperature. The shell is made of steel and copper
tubes are used for fluorocarbons and steel tubes for ammonia.
The shell and coil condenser consists of an electrically welded closed shell containing a
water coil sometimes of finned tubing.
The double tube arrangement, the refrigerant condenses in the outer tube and water flows
through the inner tube in the opposition direction.
Water cooled condensers are invariably used in conjunction with cooling towers, spray
ponds etc. heated water from the condenser is led to the cooling tower where it is cooled
by self-evaporation into steam air.
Figure 1.6 Water Cooled Condenser
22. 22
3. Evaporative type condenser: Evaporative type condensers are usually used in ice
plants. They are a combination of water cooled and air cooled condensers. In these
condensers the hot refrigerant flows through the coils. Water is sprayed over these coils.
At the same time the fan draws air from the bottom side of the condenser and discharges
it from the top side of the condenser. The spray water that comes in contact with the
condenser coil gets evaporated in the air and it absorbs the heat from the condenser cools
the refrigerant and condenses it.
Figure 1.7 Evaporative Type Condenser
1.5 EXPANSION VALVE
In the throttling valve the pressure of the refrigerant reduces suddenly and excessively.
With this the temperature of the refrigerant also reduces drastically. This low pressure
23. 23
and low temperature liquid refrigerant then enters the evaporator and absorbs heat from
the substance or the space to be cooled. The throttling valve is fitted between the
condenser and the evaporator. The throttling or expansion device is in the form of a small
orifice. When refrigerant passes through this small orifice its pressure reduces suddenly
due to the friction. The rate of the flow of refrigeration through the throttling device
depends upon the size and opening of the orifice. It also depends upon the difference in
pressure on the evaporator and the condenser sides. There are different types of throttling
devices, but in refrigerating and air-conditioning-system the two most commonly used
types are capillary tubes and thermostatic expansion valves.
There are two main purpose of the expansion valve:-
1. Thermodynamic function of expanding the liquid refrigerant from the condenser
pressure to evaporator pressure.
2. Control function which may involve the supply of the liquid to the evaporator at the
rate at which it is evaporated.(meet the refrigerant load i.e. regulate the amount of
refrigerant flowing in the evaporator as per load requirement means more refrigerant at
more load and less refrigerant at less refrigerant).
An expansion device is essentially a restriction offering resistance to flow so that the
pressure drops, resulting in a throttling process.
There are two types of expansion devices:-
1. Variable restriction type
2. Constant restriction type
In the variable-restriction type, the extent of opening or area flow keeps on changing
depending on the type of control. There are two common types of such control devices:
the automatic expansion valve and the thermostatic expansion valve.
There are float valves which are also variable restriction type devices. The float type
again is two types: high side float and low side float.
24. 24
High side float maintains the liquid at a constant level in the condenser and the low side
float maintains the liquid at a constant level in the evaporator.
The constant restriction type device is the capillary tube which is merely a long tube with
a narrow diameter bore.
1. Capillary tube: The capillary tube is a fixed type device. It is a long and narrow
tube connecting the condenser directly to the evaporator. Instead of the orifice, the
capillary is small diameter tubing that offers the restricted flow of the refrigerant. Its
internal diameter ranges from 0.070 to 0.090 inches depending upon the capacity of the
refrigerating or air conditioning system. The pressure drop attained through the capillary
depends upon its diameter and length. Capillary tubing made of copper is most
commonly used.
Capillary tubing is used for small refrigerating and air-conditioning systems like
household refrigerators, water-coolers, deep freezers, window air-conditioners, split-air
conditioners, small packaged air conditioners etc. for systems in which capillary tubing is
fitted, technicians have to be very careful of refrigerant charging as the overcharging can
lead excessive high discharge pressures from the compressors which leads to over
loading of the compressor and changes of refrigerant leakages from the system.
It is a self controlling device i.e. controls mass flow rate of refrigerant according to load
requirement of the system. It is used for those system which having capacity of 2-3TR.
The pressure drop through the capillary tube is due to the following two factors:
1. Friction due to fluid viscosity, resulting in frictional pressure drop.
2. Acceleration, due to flashing of the liquid refrigerant into vapor, resulting in
momentum pressure drop.
25. 25
Figure 1.8 Capillary Tube
2. Thermostatic expansion valves:- The thermostatic expansion valve is not
controlled by the temperature. It works automatically maintaining proper flow of the
refrigerant depending upon the heat load in the evaporator. Apart from reducing the
pressure of the refrigerant, the thermostatic expansion valve also keeps the evaporator
active. These days the thermostatic expansion valves used with solenoid valves are more
common.
A thermostatic expansion valve maintains a constant degree of superheat in the
evaporator.
Thermostatic expansion valves are used extensively in medium and large sized
refrigerating and air-conditioning systems. They can be used for large water chilling
plants, brine chilling plants, air-conditioners, central air-conditioning plants etc. These
are used in those plants whose having capacity up to 4-5TR.
26. 26
Figure 1.9 Thermostatic Expansion Valve
1.6 EVAPORATOR
The evaporator is usually a closed insulated space where the refrigerant absorbs heat
from the substance or food to be cooled. The space comprising the evaporator is an
enclosed space. For instance, in the case of a household refrigerator, the small enclosed
freezer section has an evaporator embedded into it. In the case of the freezer the
evaporator is enclosed in the space where ice or ice cream is to be made. The evaporator
section of refrigerators is usually insulated by using insulating materials. The
polyurethane foam (PUF), the low temperature refrigerant flowing through the evaporator
absorbs heat from the food, substance or any other enclosed space and gets converted into
27. 27
a gaseous state as its temperature rises. This is then sucked by the compressor, which
compress it, keeping the cycle of refrigerant continuous. In the case of air-conditioners
the evaporator is also called as cooling coil Usually the fan should pass the hot room air
over the evaporator coil, which is chilled, hence the air gets cooled. The air is then
supplied into the room, where it creates the cooling effect by absorbing.
Evaporators are various types. Evaporators used for industrial refrigeration and air-
conditioning purposes are very large and also called chillers. They are usually made in
the form of shell and tube types with two possible arrangements: namely dry expansion
evaporators and flooded evaporators. In dry expansion evaporators the refrigerant usually
flows through the tube side while the liquid to be chilled flows through the shell side. The
flooded system is used where large quantities of fluids have to be cooled to extremely
low temperature. Since the load in such cases is very high a large amount of refrigerant
flows through these evaporators. In flooded evaporators the refrigerant will usually pass
through the shell side while the liquid to be chilled will pass through the tube side.
1.6.1 Types of Evaporator
For smaller and home purposes there are three types of evaporators:
1. Bare-tube type
2. Plate-surface type
3. Finned evaporators.
In bare-tube evaporators the refrigerant flows through the bare-tube and the fluid to be
chilled flows directly over it.
Figure 1.10 Bare Tube Evaporator
28. 28
Plate-surface evaporators are used in household refrigerators. These evaporators are
formed by welding together two plates that have grooves on their surface. When they are
welded, the closed grooves form a sort of tubing through which refrigerant flows.
Figure 1.11 Plate Surface Evaporator
Finned evaporators are commonly used in windows. They are in the form of copper coil
over which several fins are welded to increase the cooling area of the evaporator. Hot air
passes over this evaporator and gets chilled as it enters the room.
Figure 1.12 Finned Tube Evaporator
29. 29
1.7 HEAT EXCHANGER
A heat exchanger is a piece of equipment built for efficient heat transfer from one
medium to another medium. The media may be separated by a solid wall to prevent
mixing or they may be in direct contact. They are widely used in space heating,
refrigeration, air conditioning, power plants, chemical plants, petrochemical plants,
petroleum refineries, natural gas processing, and sewage treatment. The classic example
of a heat exchanger is found in an internal combustion engine in which a circulating fluid
known as engine coolant flow through radiator coils and air flows past the coils, which
cools the coolant and heats the incoming air.
1.7.1 TYPES OF HEAT EXCHANGERS
Heat exchangers can be grouped in three broad classes:
I. Transfer type heat exchangers or recuperates
II. Storage type heat exchangers or regenerators
III. Direct contact type heat exchangers or mixers
1.7.2 DOUBLE PIPE HEAT EXCHNGER:
It is a transfer type heat exchanger or a recuperate, the two fluids are kept separate and
they do not mix as they flow through it. Heat is transferring through separating walls.
Double pipe heat exchangers are the simplest heat exchangers and used in industries. On
one hand these heat exchangers are cheap for both design and maintenance, making them
a good choice for small industries. But on the other hand, low efficiency of them beside
high space occupied for such exchangers in large scales, has led modern industries to use
more efficient heat exchanger like shell and tube heat exchanger or other ones. But yet,
since double pipe heat exchangers are simple, they are used to teach heat exchanger
design basic to students and as the basic rules for modern and normal heat exchangers are
the same, students can understand the design techniques much easier. To design of a
double pipe heat exchanger, the first step is to calculate the heat duty of the heat
exchanger. It must be noted that for easier design, it’s better to ignore heat loss in heat
exchanger for primary design. The heat duty can be defined as the heat gained by cold
30. 30
Figure 1.13 Double Pipe Type Heat Exchanger
Heat exchangers are off-the-shelf equipment targeted to the efficient transfer of heat from
a hot fluid flow.
To a cold fluid flow, in most cases through an intermediate metallic wall and without
moving parts. We here focus on the thermal analysis of heat exchangers, but proper
design and use requires additional fluid dynamic
Analysis (for each fluid flow), mechanical analysis (for closure and resistance), materials
Compatibility and so on/
Heat losses or gains of a whole heat exchanger with the environment can be neglected in
comparison with the heat flow between both fluid flows; i.e. a heat exchanger can be
assumed globally adiabatic.
Thermal Inertia of a heat exchanger is often negligible too (except in special cases when
a massive porous solid is used as intermediate medium), and steady state can be assumed,
reducing the generic energy balance to:
ΔΕ =W +Q + Σ ∫ h dm → 0 = m Δh + m Δh (1)
Where the total enthalpy ht has been approximated by enthalpy (i.e. negligible
mechanical energy against thermal energy), and Δ means output minus input.
Although heat flows from hot fluid to cold fluid by thermal conduction through the
separating wall (except in direct-contact types), heat exchangers are basically heat
convection equipment, since it is the convective transfer what governs its performance.
31. 31
Convection within a heat exchanger is always forced, and may be with or without phase
change of one or both fluids.
When one just relies in natural convection to the environment, like in the space-heating
hot-water home radiator, or the domestic fridge back-radiator, they are termed 'radiators'
(in spite of convection being dominant), and not heat exchangers. When a fan is used to
force the flow of ambient air (or when natural).
There are three type of heat exchanger on the basis of flow of fluids:
If both the fluids move in the same direction, it is a parallel flow heat exchanger. If the
fluids move in opposite direction, it is a counter flow heat exchanger. If they flow normal
to each other, it is a cross flow heat exchanger.
A heat exchanger having a large area per unit volume is called a compact heat exchanger.
The ratio of the heat transfer surface area to the volume is called the area density β. The
large surface area is obtained by attaching closely spaced thin plates or corrugated fins to
the walls separating the two fluids. Compact heat exchangers are mainly used in gas-to-
gas or gas-to-liquid heat transfer, with limitations of their volume, weight, with fins.
In compact heat exchangers, the two fluids usually move perpendicular to each other and
such flow configuration is called cross flow. When plate fins force the fluid to flow
through a particular inter fin spacing and it prevent from moving in the transverse
direction.
Figure 1.14 Parallel Flow Heat Exchanger
32. 32
Figure 1.15 Counter Flow Heat Exchanger
Figure 1.16 Cross Flow Heat Exchanger
1.7.3 SHELL AND TUBE HEAT EXCHANGER:
Shell and tube heat exchangers consist of a series of tubes. These tubes are packed inside
a shell with their axes parallel to that of the shell. Heat takes place as one fluid flows
inside the tubes while the other fluids flow outside the tubes through the shell. Baffles are
33. 33
commonly placed in the shell to force the shell-side fluid to flow across the shell to
enhance the heat transfer( by increasing the residence time) and to maintain uniform
spacing between the tubes. Because of their relatively large size and weight, shell and
tube heat exchangers are not suitable for use in automotive, aircraft and marine
applications. At both ends of the shell there are headers where the fluid accumulates
before entering the tubes and leaving them.
Figure 1.17 One Pass Shell and Tube Heat Exchanger
Figure 1.18 Two Pass Shell and Tube Heat Exchanger
34. 34
In storage type heat exchanger the hot and cold flow alternatively through a solid matrix
of the high heat capacity. When the hot fluid flows through the matrix in an interval of
time heat is transferred from the hot fluid to the matrix which store in the form of an
increase in its internal energy. This stored energy is then transferred to the cold fluid as it
flows through the matrix in the next interval of time.
Figure 1.19 Single Matrix Storage Type Heat Exchanger
Heat losses or gains of a whole heat exchanger with the environment can be neglected in
comparison with the heat flow between both fluid flows; i.e. a heat exchanger can be
assumed globally adiabatic.
35. 35
Figure 1.20 Rotary Storage Type Heat Exchanger
Figure 1.21 Direct Contact Type Heat Exchanger
36. 36
1.8 REFRIGERANT
Refrigerants are fluids that are used in refrigeration cycles and heat pumps. Most of the
time, a refrigerant will undergo a transition from liquid form to gas back and forth. The
main criteria that a refrigerant has to meet are safe usage, flammable-free and toxic-free
properties. Most refrigerants nowadays are especially designed to avoid causing climate
changes or ozone depletion, created to have the best thermodynamic abilities possible.
1,1,1,2-Tetrafluoroethane(R-134a)
1, 1, 1, 2-Tetrafluoroethane, R-134a, Forane-134a, Genetron 134-a, Florasol 134a,
Suva 134a or HFC-134a, is a halo alkane refrigerant with thermodynamic properties
similar to R-12(dichlorofluoromethane) but with very less ozone layer depletion
potential. It has the formula CH2FCF3 and a boiling point of -26.3˚c(-15.34˚f) at
atmospheric pressure. R-134a cylinders are colored light blue. The critical temperature is
122˚c or 212˚F.
Figure 1.22 Cylinder Contains R-134a Refrigerant
37. 37
1.8.1 PROPERTIESOF R-134a
Table 1.1 Properties of R-134a
Figure 1.23 Molecular Structure of R-134a
Chemical Name CH2FCF3
Molar mass 102.03gm/mole
Appearance Colorless gas
Density 0.00425 gm/c.m3,gas
Melting Point -103.3˚c(169.85k)
Boiling point -26.3˚c(246.85k)
Solubility in water 0.15% wt%
38. 38
1.8.2 Detection of Leaks
When you suspect a leak of R-134a in your air conditioning system, detection can be
done by using one of the following 5 methods. The simplest method and cost effective is
by the use of soap solution. Workshops may use more sophisticated equipments to do
this.
Fluorescent Dyes
Soap Solution
Electronic Leak Detectors
Halogen selective detectors
Ultrasonic leak detectors
1.8.3 USES
Tetrafluoroethane (CF3CH2F), R134a is part of a family of refrigerants that don’t
damage the ozone layer, like the previous CFC products did. Non-corrosive, non-
flammable and non-toxic, R134a is now being used in reciprocating compressors and
centrifuges. Widely used within the air conditioning systems of new cars, it is also
employed by pharmaceutical companies as a propellant and by manufacturers in
producing plastic foam.
There are plenty of choices for automotive refrigerants on the market, ranging from drop-
in replacements, to expensive alternatives or very cheap products. Most of the times, a
cheap price tag is a clear indicator of the automotive refrigerant’s performance. You
might be thinking you’re stretching a buck acquiring a cheap refrigerant, but you might
find out you need special equipment for evacuating the gas and disposing of it properly.
Commercial refrigeration – in charge of covering various equipment, from food coolers,
vending machines, large refrigerators for supermarkets or display cabinets. The R134a
refrigerant is safely used in all these appliances since it is effective and reliable, while
also meeting all the environmentally-friendly criteria.
39. 39
Industrial refrigeration – caters for a vast range of applications, with R134a being used in
high temperature and medium temperature chilling processes for medical freezers.
Domestic refrigeration – R134a is extensively used in the domestic sector since it meets
the consumer demands and it is highly efficient.
Transport refrigeration – covering trucks and vans that carry refrigerated containers,
R134a Freon gas is suitable for usage on trucks, trains and ships whenever food that is
particularly sensitive to temperature is transported from one location to another.
40. 40
CHAPTER 2: LITRETURE REVIEW
[1] P.A Domanski, D.A. Didion and J.P. Doyle (1992) focused on the evaluation of the
suction line liquid line heat exchanger in the refrigeration cycle. The study showed that
the benefit of application of the liquid suction heat exchanger depends on a combination
of operating conditions and fluid properties. Fluids that perform well in the basic cycle
are marginally affected by the llsl-hx, and the impact on the Coefficient of Performance
and volumetric capacity may be either positive or negative. Fluids performing poorly in
the basic cycle benefit from the llsl·hx installation through increase of the Coefficient of
Performance and volumetric capacity.
[2] S. A. Klein, D. T. Reindl, and K. Brownell (2000) extended the analysis by evaluating
the influence of liquid-suction heat exchangers installed in vapor compression
refrigeration systems. They conclude that liquid-suction heat exchangers lead to
performance improvements for any refrigerant. Under closer evaluation, liquid-suction
heat exchangers increase the temperature and reduce the pressure of the refrigerant
entering the compressor causing a decrease in the refrigerant density and compressor
volumetric efficiency. Although the compressor power is only slightly affected by the
change in state of the refrigerant entering the compressor, the refrigerant mass flow rate
is reduced.
[3] R. Mastrullo, A.W. Mauro, S. Tino , G.P. Vanoli (2007) presents the effects
produced by a suction/liquid heat exchanger installed in a refrigerating cycle, evidencing
that, its use can improve or decrease the system performance depending on the operating
conditions.They conclude that the adoption of the suction/liquid heat exchanger is a
profitable choice to prevent flash gas formation at the inlet of the expansion device and to
assure the absence of residual liquid at the compressor suction. The benefit produced by
application of the SLHX on system performances depends on the combination of
operating conditions and fluid properties
[4] G. Maruthi Prasad Yadav, P. Rajendra Prasad, G. Veeresh (2011) studied about the
application of capillary tube VCR System with liquid suction heat exchanger.
41. 41
Because of simplicity and low cost, capillary tubes are used as the expansion device in
most small refrigeration and air conditioning systems. Another advantage is that
capillary tubes allow high and low side pressures to equalize during the off-cycle, thereby
reducing the starting torque required by the compressor.
[5] G.Edision,A. Suresh & K. Narayan Rao (2012) studied about the uses of the
refrigerant R-12 in this system and they concluded that Volumetric efficiency increases
due to density of liquid increases so mass flow increase by which cooling effect
increases.
[6] Jyoti Soni and RC Gupta (2013) studied about the exergy detection ratio. They uses
diferent types of refrigerant such as R-407a, R-404a .and R-410a and they concluded that
The COP and exegetic efficiency of R407C are better than that of R404A and R410A.
The EDR of R410A is higher than that of R407C and R404A. This analysis performed at
condenser temperatures 40 °C and 50 °C and evaporator temperature ranging from 50 °C
to 0 °C.
[7] Chetan P. Waykole and H.M. Dange (2014) studied about the Evaluation of Water
Cooler with Modification of Liquid Suction Heat Exchanger The coefficient of
performance of the system can be increased either by decreasing the work of compression
or increasing the refrigerating effect or by the combination of both. The refrigerating
effect can be increased by maintaining the condition of refrigerant in lower temperature
liquid stage, at the entrance of evaporator. This can be achieved by expanding the
refrigerant very close to the liquid line i.e. by sub-cooling the refrigerant and by
removing the flashed vapour.
[8] M. Krishna Prasanna (2014) concluded that the refrigeration effect of the system is
increased up to 16% using the heat exchanger with vapour compression refrigeration
system. The COP (coefficient of performance) of the system is increased up to 16% using
the heat exchanger with vapour compression refrigeration system. Mass flow of
refrigerant (mR) is reduced up to 14% using the heat exchanger with vapour compression
refrigeration system. Heat available for desuperheating (Q) increases as the evaporation
42. 42
temperature decreases. So by attaching heat exchanger to the vapour compression
refrigeration system and regulating water into heat exchanger, outlet temperature of the
water (t2) in heat exchanger increases. That hot water can be used for useful purpose.
Power required to run the compressor is reduced up to 14% by using the heat exchanger
with vapour compression refrigeration system.
[9] Rohit Kumar Sathawane1, Prof. S. A. Patil (2016) studied about the comparision of
the performance of VCRS with and without the use of evaporative cooling on the suction
and discharge line. As a result of the current experimental study many conclusions can be
drawn regarding the use of evaporative cooling on the performance of VCRS using
porous materials. The performance of the VCRS was analyzed for a load of pull down,
150, 300 and 450 Watt with and without evaporative cooling of the suction and discharge
line. It is found that the theoretical COP of VCRS increased by 7.22% with the use of
wood fiber as the evaporative cooling pad on both the suction and discharge line. The
increase in theoretical COP of VCRS by using wood fiber on the suction line and
coconut coir on the discharge line is 6.52%.
2.1 Gaps and Opportunity
Heat transfer devices are provided in many refrigeration systems to exchange energy
between the cool gaseous refrigerant leaving the evaporator and warm liquid refrigerant
exiting the condenser. These liquid-suction or suction-line heat exchangers can, in some
cases, yield improved system performance while in other cases they degrade system
performance. Although previous researchers have investigated performance of liquid-
suction heat exchangers, this study can be distinguished from the previous studies in three
ways.
First, this paper edentates a new dimensionless group to correlate performance impacts
attributable to liquid-suction heat exchangers. Second, the paper extends previous
analyses to include new refrigerants. Third, the analysis includes the impact of pressure
drops through the liquid-suction heat exchanger on system performance. It is shown that
43. 43
reliance on simplified analysis techniques can lead to inaccurate conclusions regarding
the impact of liquid-suction heat exchangers on refrigeration system performance.
From detailed analyses, it can be concluded that liquid-suction heat exchangers that have
a minimal pressure loss on the low pressure side is useful for systems using R507A,
R134a, R12, R404A, R290, R407C, R600, and R410A. The liquid-suction heat
exchanger is detrimental to system performance in systems using R22, R32, and R717.
Because of simplicity and low cost, capillary tubes are used as the expansion device in
most small refrigeration and air conditioning systems. Another advantage is that capillary
tubes allow high and low side pressures to equalize during the off-cycle, thereby reducing
the starting torque required by the compressor.
In this application the liquid line is usually placed in contact with the suction line,
forming a counter flow heat exchanger.
The liquid line is welded to the suction line in the lateral configuration. The temperature
of the vapour refrigerant coming out from the evaporator is less than the temperature of
the liquid coming out from the condenser. Before the expansion process, heat is
transferred from the liquid line to the suction line. As a consequence this in turn reduces
the refrigerant quality at the inlet of the evaporator and therefore increases the
refrigerating capacity.
The suction line exit temperature also increases, eliminating suction line sweating and
preventing slugging of the compressor. The main objective of this project is to evaluate
the performance of refrigerator with liquid line suction line heat exchanger for different
lengths of heat exchanger by using R134a and R404a as refrigerants and compare with
different lengths of liquid line- suction line heat exchanger.
2.2 Objective
Fabrication of Vapour Compression Refrigeration System with liquid suction heat
exchanger
To increase the Coefficient of Performance of the refrigeration system.
44. 44
CHAPTER 3: EXPERIMENTAL SETUP
In vapor compression refrigerating system basically there are two heat exchangers. One is
to absorb the heat which is done by evaporator and another is to remove heat absorbed by
refrigerant in the evaporator and the heat of compression added in the compressor and
condenses it back to liquid which is done by condenser. This work focuses on heat
rejection in the condenser this is only possible either by providing a fan or by extending
the surfaces. The extended surfaces are called fins. The rate of heat rejection in the
condenser depends upon the number of fins attached to the condenser. This work
investigated the performance of condenser using condenser in the present domestic
refrigerator galvanized iron steel material fins are used. In this project mild steel material
fins are replaced and galvanized iron steel is used for the condensers. The performance of
the condenser will also help to increase COP of the system as the sub cooling region
.incurred at the exit of the condenser. The performance of the condenser is also
investigated by existing and modification condenser.
In general domestic refrigerators have no fans at the condenser and hence extended
surfaces like fins play a very vital role in the rejection of heat.
In order to know the performance characteristics of the vapor compression refrigerating
system the temperature and pressure gauges are installed at each entry and exit of the
component. Experiments are conducted on condenser having fins. Different types of tools
are also used like snips to cut the plated fins to required sizes, tube cutter to cut the tubes
and tube bender to bend the copper tube to the required angle. Finally the domestic
refrigerator is fabricated as for the requirement of the project.
All the values of pressures and temperatures are tabulated.
The figure 4 shows the experimental setup of the refrigerator. In order to know the
performance characteristics of the vapor compression refrigeration system the
temperature and pressure gauges are installed at each entry and exit of the components.
Experiments are conducted on condenser with coil spacing of the condenser on a
45. 45
refrigerator of capacity 215liters.All the values of pressures and temperatures are
tabulated.
3.1 VCRS selected for the project has the following specifications:-
1. Compressor
Type:-Rotatory
Capacity:-165 liter
2. Condenser
Type:-Bare tube pipe type
Size: - ¼″
3. Expansion Valve
Type:-Capillary Tube
Length: 5 feet
4. Evaporator
Type:-165 liter chiller box
Insulated in thermacol
5. Heat Exchanger
Flow: - Counter Flow
Size: - approx 1.2 feet
2″ diameter of PVC pipe
Approx 3 feet copper coil inserted in PVC pipe
6. Pump
Type:-Submersible
Specification:-180-220V
Head: - 2 meter
46. 46
Among many possible variations of the basic refrigeration cycle, the cycle with the
liquid-line/suction-line heat exchanger (LLSL-HX) is probably used most often. As a
result of employing this intra cycle heat exchange, the high pressure refrigerant is sub
cooled at the expense of superheating the vapor entering the compressor. Schematics of
hardware arrangement for the basic cycle and cycle with LLSL-HX are the realized
cycles are outlined on the pressure-enthalpy diagram.
The use of liquid line/suction line heat exchangers is widespread in commercial
refrigeration. The heat exchangers are often employed as a means for protecting system
components, by helping to ensure single-phase liquid to the expansion device and single
phase vapor to the compressor. in residential refrigerators, Capillary tube /suction-line
heat exchanger is used to heat the suction line above the dew-point temperature of
ambient air, thus preventing condensation of the water vapor on the outside of the water
vapor on the outside of the suction line.
Employing an intra-cycle heat exchanger alters refrigerant thermodynamic states in the
cycle, which may have significant (positive or negative) performance implications. For
any fluid and system, an LLSL-HX increases refrigerant temperature at the compressor
inlet and outlet, this is shortcoming. The coefficient of performance (COP) and
volumetric capacity may increase for some fluid-application combinations, while for
others they may decrease.
3.2 EXPERIMENT PROCEEDURE:-
The following procedure is adopted for experimental setup of the vapor compression
refrigeration system:-
1. The domestic refrigerator is selected, working on vapor compression refrigeration
system.
2. Pressure and temperature gauges are installed at each entry and exit of the components.
3. Flushing of the system is done by pressurized nitrogen gas.
4. Leakage tests are done by using soap solution, In order to further test the condenser
and evaporator pressure and check purging daily for 12 hours and found that there is no
47. 47
leakages which required the absolutely the present investigation to carry out further
experiment.
5. Switch on the refrigerator and observation is required for 1 hour and take the pressure
and temperature readings at each section.
6. The performance of the existing system is investigated, with the help of temperature
and pressure gauge readings.
7. The refrigerant is discharged out and condenser is located at the inlet of the capillary
tube.
8. Temperature and pressure gauge readings are taken and the performance is
investigated.
The following tests are conducted and calculations are shown below.
3.3 Figure of Experiment Setup:-
Figure 3.1 Inlet Pressure Gauge
48. 48
Figure 3.2 Outlet Pressure Gauge
There are two pressure gauge used in this system
1- Inlet pressure gauge
2- 2-Outlet pressure gauge
Inlet pressure gauge is attached at the inlet of the compressor which is use to calculate the
inlet pressor of the compressor.
Outlet Pressure gauge is attached between the compressor outlet and condenser inlet
which is used to calculate the the pressure of the compressed gas.
49. 49
Figure 3.3 Rotatory Compressor
In the experiment reciprocating compressor is used. Reciprocating compressors use
piston driven by a crankshaft. The reciprocating compressor generally seen where there is
requirement of high pressure and low flow(or discontinuous flow up to 30 bars).Mostly
where the air is used for hand-tools, cleaning dust, small paint jobs, commercial uses,etc.
Compressors are similar to pumps both increase the pressure of a fluid and both can
transport the fluid through a pipe as gases are compressible the compressor also reduces
the volume of the gas. Liquids are relatively incompressible while some can be
compressed the main action is to pressurize and transport liquids.
50. 50
Figure 3.4 Evaporator
The evaporator section of refrigerators is usually insulated by using insulating materials.
The polyurethane foam (PUF), the low temperature refrigerant flowing through the
evaporator absorbs heat from the food, substance or any other enclosed space and gets
converted into a gaseous state as its temperature rises. This is then sucked by the
compressor, which compress it, keeping the cycle of refrigerant continuous. In the case of
air-conditioners the evaporator is also called as cooling coil Usually the fan should pass
the hot room air over the evaporator coil, which is chilled, hence the air gets cooled. The
air is then supplied into the room, where it creates the cooling effect by absorbing.
51. 51
Figure 3.5 Liquid Suction Heat Exchanger
In the liquid suction interchanger, cool suction steam is passed through a heat exchanger
in counter flow on the hot fluid condenser. That is, two liquid flows in opposite
directions, as shown. In the heat exchanger, the heat produced by suction gas as much
that has lost liquid refrigerant. However, temperature changes are not equal.
Specific heat capacity of the refrigerant vapor less than the liquid. Thus, the increase in
the temperature of the steam is always greater than the drop in the temperature of the
liquid.
52. 52
Figure 3.6:- Condenser
In systems involving heat transfer, a condenser is a device or unit used to condense a
substance from its gaseous to its liquid state, by cooling it. In so doing, the latent heat is
given up by the substance, and will transfer to the condenser coolant. Condensers can be
made according to numerous designs, and come in many sizes ranging from rather small
(hand-held) to very large (industrial-scale units used in plant processes)
54. 54
CHAPTER 4: RESULT AND DISCUSSION
4.1 ANALYSIS
4.1.1 OBSERVATION TABLE
1. System without Heat Exchanger
Table 4.1.1 Observation Table
S.NO. Pressure
(Inlet)
Bar
Pressure
(Outlet)
Bar
Time
(Minute)
Evaporator Temp.
(0C)
Inlet Outlet
Condenser
Temp.( 0C)
Inlet Outlet
COP
1 0.7 11.03 20 26.8 -24 50.4 29.9 2.38
Figure 4.1 P-h Graph without Heat Exchanger
Where
T1=-24 0C
T2=50.4 0C
T3=29.8 0C
T4=26.8 0C
Here,
55. 55
So, from the Pressure-enthalpy diagram of HCF-134a
We get
h1=375 kJ/Kg
h2=440 kJ/Kg
h3=248 kJ/Kg
h4=220 kJ/Kg
Now,
(C.O.P) = Refrigeration effect
Compressor Work
= h1 - h4
h2 - h1
= 375-220
440-375
= 2.38
3. System with Heat Exchanger
Table 4.1.2 Observation Table
S.N
O
Pressure
(Inlet)
Bar
Pressure
(Outlet)
Bar
Time
(In
Minute
)
Evaporator
Temp. (0C)
Condenser
Temp. ( 0C)
Heat Ex.
Temp. ( 0C)
COP
Inlet Outlet Inlet Outlet Inlet Outlet
1. 0.34 10.03 20 25.4 -25 50.4 27 27 25.8 2.43
56. 56
Figure 4.2 P-h Graph with Heat Exchanger
Where
T1=-25 0C
T2=50.4 0C
T3=26.5 0C
T4=25.8 0C
So, from the Pressure-enthalpy diagram of HCF-134a
We get
h1=373 kJ/Kg
h2=440 kJ/Kg
h3=240 kJ/Kg
h4=210 kJ/Kg
57. 57
Now,
(C.O.P)= Refrigeration effect
Compressor Work
= h1- h4’
h2- h1
= 373-210
440-373
= 2.43
4.2 RESULT
Percentage increase in COP= System with H.E.-System without H.E. X 10
System without H.E.
= 2.43 -2.38 X 100
2.38
= 2.10%
So, Percentage increase in COP=2.10%
58. 58
CHAPTER 5: CONCLUSION
1 .By neglecting the reduction in refrigerant mass flow rate, one would conclude that
liquid-suction heat exchangers lead to performance improvements for any refrigerant.
Under closer evaluation, liquid-suction heat exchangers increase the temperature and
reduce the pressure of the refrigerant entering the compressor causing a decrease in the
refrigerant density and compressor volumetric efficiency.
2. Although the compressor power is only slightly affected by the change in state of the
refrigerant entering the compressor, the refrigerant mass flow rate is reduced.
Consequently, the advantage of liquid-suction heat exchangers depends on competing
effects. Figures illustrate the influence of liquid-suction heat exchangers (with no
pressure losses) on the performance of a refrigeration system for a number of refrigerants
accounting for changes in compressor volumetric efficiency.
3. The effect of a liquid-suction heat exchanger (with no pressure losses) on the
refrigeration capacity can be correlated in terms of the temperature lift and a
dimensionless grouping equal to the enthalpy of vaporization at the evaporator
temperature divided by the product of the liquid specific heat (evaluated at the evaporator
temperature) and the critical temperature. From this analysis, it can be concluded that
liquid-suction heat exchanger are most useful at high temperature lifts.
4. The liquid-suction heat exchanger results obtained for R134a follow the same trends as
the results of Domanski and Didion, (1994).The system designer must thus be very
careful in choosing when to install a liquid-suction heat exchanger in a refrigeration
system.
