PERFORMANCE ANALYSIS OF VAPOR COMPRESSION REFRIGERATION SYSTEM USING DIFFERENT DIAMETER CAPILLARY TUBE AND R12 AS REFRIGERANT

Vapour compression refrigeration system analysis 2016-17
Department of mechanical engineering,kit,tiptur page 1
CONTENTS
Chapter 1 Introduction………………………………………………………………1
1.1 Vapour Compression Refrigeration (VCR) System……………….2
1.2 Vapour- Absorption refrigeration system……………………….....3
1.3 Comparison between VCR System and VAR System……………..5
1.4 Refrigerants…………………………………………………………..5
1.4.1 First Generation Refrigerants……………………………………..6
1.4.2 Second Generation Refrigerants…………………………………..7
1.4.3Third Generation Refrigerants…………………………………….9
1.5 Desirable Properties of New Refrigerants………………………….10
1.6 R12 Refrigerant…………………………………………………...…11
1.6.1 Advantages of R12 Refrigerant…………………………………..11
1.6.2 Disadvantages of R12 Refrigerant ……………………………….12
chapter 2 Literature Review…………………….......................................................13
chapter 3 Experimental Details…………………………………………………….16
3.1 Components of VCR Test Rig………………………………………18
3.2 p-h Diagram………………………………………………………….23
3.3 Mathematical Equations used in Performance Calculation………26
chapter 4 Results and Discussions………………………………………………….27
chapter 5 Conclusions and Scope of Future Work………………………………..31
REFERENCES………………………………….......................................32

CHAPTER I
INTRODUCTION
Refrigeration is the process of producing and maintaining a body temperature lower than that of the
surroundings, i.e. atmosphere. It is defined as the science of providing, maintaining temperatures
below that of surroundings. It can also be defined as the process of removing heat from a low
temperature level and rejecting it at a relatively higher temperature level. It is nothing but removal
of heat from the body. In order to maintain the body temperature lower than the surrounding, heat
must be transferred from cold body to the surroundings at high temperature. Since heat cannot
naturally flow from cold body to hot body, external energy will have to be supplied to perform this
operation. The device used for this purpose is called refrigerating system or mechanical
refrigerator of simply refrigerator. The system, which is kept at lower temperature, is termed
refrigerated system. Nowadays many human workplaces and factories are air conditioned by using
refrigeration system. Not only work places but also perishable goods are maintained at their
required temperature to store it for a long time by refrigeration system. This device operates on a
reversed power cycle; heat engine. Basically there are two types of refrigeration system namely
Vapour Compression Refrigeration (VCR) System and Vapour Absorption Refrigeration (VAR)
System.
1.1 Vapour Compression Refrigeration (VCR) System:
The Vapour compression Refrigeration is the process in which the refrigerant undergoes phase
changes. VCR system is an improved type of air refrigeration system. The ability of certain liquids
to absorb enormous quantities of heat as they vaporize is the basis of this system. Compared to
melting solids (say ice) to obtain refrigeration effect, vaporizing liquid refrigerant has more
advantages. To mention a few, the refrigerating effect can be started or stopped at desired, the rate
of cooling can be predetermined, the vaporizing temperatures can be governed by controlling
the pressure at which the liquid vaporizes. Moreover, the vapour can be readily collected and
condensed back into liquid state so that same liquid can be re-circulated over and over again to
obtain refrigeration effect[2]. Thus the vapour compression system employs a liquid refrigerant
which evaporates and condenses readily. The System is a closed one since the refrigerant never
leaves the system. The Vapour compression refrigeration system is now-a-days used for all purpose

refrigeration. It is generally used for all industrial purposes from a small domestic refrigerator to a
big air-conditioning plant.
The vapour compression refrigeration cycle is based on the following factor; Refrigerant flow
rate, type of refrigerant used, kind of application air-conditioning, refrigeration, dehumidification,
the operation design parameters, the system equipment’s/ components proposed to be used in the
system. The vapour compression refrigeration cycle is based on a circulating fluid media, a
refrigerant having special properties of vaporizing at temperatures lower than the ambient and
condensing back to the liquid form, at slightly higher than ambient conditions by controlling the
saturation temperature and pressure. Thus, when the refrigerant evaporates or boils at temperatures
lower than ambient, it extracts or removes heat from the load and lower the temperature
consequently providing cooling. The super-heated vapour pressure is increased to a level by the
compressor to reach a saturation pressure so that heat added to vapour is dissipated/ rejected into the
atmosphere, using operational ambient conditions, with cooling media the liquid from and recycled
again to form the refrigeration cycle[3].
1.2 Vapour- Absorption refrigeration system:
The vapour absorption refrigeration system is one of the oldest method of producing refrigerating
effect. The principle of vapour absorption was first discovered by Michael Faraday in 1824 while
performing a set of experiments to liquefy certain gases. A French scientist Ferdinand developed
the first vapour absorption refrigeration machine in 1860.This system may be used in both the
domestic and large industrial refrigerating plants. The refrigerant commonly used in a vapour
absorption system is ammonia. The vapour absorption system uses heat energy, instead of
mechanical energy as in vapour compression systems, in order to change the conditions of the
refrigerant required for the operation of the refrigeration cycle[8].
In the vapour absorption system, an absorber, a pump, a generator and a pressure-reducing
valve replace the compressor. These components in vapour absorption system perform the same
function as that of a compressor in vapour compression system. In this system, the vapour
refrigerant from the evaporator is drawn into an absorber where it is absorbed by the weak solution
of the refrigerant forming a strong solution. This strong solution is pumped to the generator where it
is heated by some external source. During the heating process, the vapour refrigerant is driven off
by the solution and enters into the condenser where it is liquefied. The liquid refrigerant then flows
into the evaporator and thus the cycle is completed.

The domestic absorption type refrigerator was invented by two Swedish engineers Carl Munters
and Baltzer Van Platan in 1925 while they were studying for their under-graduate course of royal
institute of technology in Stockholm. The idea was first developed by the ‘Electrolux Company’
of Luton, England. This type of refrigerator is also called three-fluids absorption system. The main
purpose of this system is to eliminate the pump so that in the absence of moving parts, the machine
becomes noise-less. The three fluids used in this system are ammonia, hydrogen and water. The
ammonia is used as a refrigerant because it possesses most of the desirable properties. It is toxic,
but due to absence of moving parts, there are very little changes for the leakage and the total
amount of refrigeration used is small. The hydrogen being the lightest gas is used to increase the
rate of evaporation of the liquid ammonia passing through the evaporator. The hydrogen is also
non-corrosive and insoluble in water. This is used in the low-pressure side of the system. The water
is used as a solvent because it has the ability to absorb ammonia readily.
The strong ammonia solution from the absorber through heat exchanger is heated in the generator
by applying heat from an external source usually a gas burner. During this heating process,
ammonia vapour are removed from the solution and passed to the condenser. A rectifier or a water
separator fitted before the condenser removes water vapour carried with the ammonia vapour, so
that dry ammonia vapour is supplied to the condenser. This water vapour, if not removed, they will
enter into the evaporator causing freezing and choking of the machine. The hot weak solution while
passing through the exchanger is cooled. The heat removed by the weak solution is utilized in
raising the temperature of strong solution passing through the heat exchanger. In this way, the
absorption is accelerated and the improvement in the performance of a plant is achieved.
The ammonia vapour in the condenser is condensed by using external cooling source. The liquid
refrigerant leaving the condenser flows under gravity to the evaporator where it meets the hydrogen
gas. The hydrogen gas which is being fed to the evaporator permits the liquid ammonia to evaporate
at a low pressure and temperature according to Dalton’s principle. During the process of
evaporation, the ammonia absorbs latent heat from the refrigerated space and thus produces cooling
effect. The mixture of ammonia vapour and hydrogen is passed to the absorber where ammonia is
absorbed in water while the hydrogen rises to the top and flows back to the evaporator[8].

(a) (b)
Figure 1.1 Basic Refrigeration Systems a) Vapour Compression System and b) Vapour
absorption system[8].
1.3 Comparison between Vapour Compression System and Vapour Absorption System:
Vapour Compression System Vapour Absorption System
Uses low grade energy like heat. Therefore,
may be worked on exhaust systems from I.C
engine.
Uses high-grade energy like mechanical
work.
Moving parts are only in the pump which is a
small element of the system. Hence operation
is smooth.
Moving parts are in the compressor.
Therefore more wear, tear and noise.
The system can works on low evaporator
pressure also without affecting the COP.
The cop decreases considerable with decrease
in evaporator pressure.
No effect of reducing load on performance. Performance is adversely affected at Partial
loads.
Liquid traces of refrigerant present in piping
at the exit of evaporator.
Liquid traces in suction, damage the
compressor.
1.4 REFRIGERANTS
Refrigerants are the working medium used in refrigerating systems which evaporates by taking the
heat from the space that is to be cooled, thus producing the cooling effect. Refrigerant development
throughout the history took place due to different reasons, such as safety, stability, durability,
economic or environmental issues, thus giving rise to new research and equipment improvement

in terms of safety and efficiency. The refrigerants can be classified into different generations.
Different generations of refrigerants and their behaviour have been shown in below figure[9].
Figure 1.2 Generations of refrigerant [9]
1.4.1 First Generation Refrigerants
Beginnings of mechanical refrigeration, starting from early 19th century were characterized by use
of natural refrigerants. Water and air were the first refrigerants considered for use in mechanical
refrigeration systems. Refrigerators that were built in the late 1800s to 1929 used the first
generation refrigerants like methyl chloride, ammonia and sulphur dioxide. The common
refrigerants for the first hundred years included whatever worked and whatever was available.
Nearly all the first generation refrigerants were flammable, toxic or both and some were also highly
reactive. The characteristics of some of the first generation refrigerants are discussed below.
Water; Water is one of the oldest refrigerants being used for refrigeration applications down to
about the freezing of water. When water is coupled with protective solutions to prevent freezing
(i.e. propylene or ethylene glycol), it can be used well below water’s normal freezing point in
applications such as ice slurries. Water is easily available and has excellent thermodynamic and
chemical properties. Besides these advantages, there are technical challenges that result from its
high specific volume at low temperatures. These challenges include high pressure ratio across the
compressor and high compressor outlet temperatures.
Ammonia; It is denoted as R717 and is also a very old refrigerant used in vapour compression and
absorption refrigeration systems. The advantages of R717 are that they have a lower molecular
weight, wide range of working temperature because of its high critical point, high latent heat of
vaporization and easy leak detection. However, R717 also has some disadvantages. It is highly

toxic, highly irritating and flammable. Ammonia has high affinity to water, thus it is difficult to
keep ammonia dry. When it contains water, it is corrosive to copper and most copper alloys. At high
discharge temperatures generated by ammonia, it has the tendency to dissociate giving nitrogen and
hydrogen. When these gases enter condenser, their pressures are added to the condensing pressure,
thereby, increasing total pressure head and power consumption.
Sulphur Dioxide; Sulphur dioxide is one of the most used refrigerants in 1920s and 1930s, having
been replaced first by methyl chloride and later by more desirable fluorocarbon refrigerants. It is
highly toxic but non-explosive and non-flammable. It is non-corrosive in pure state but when it
combines with moisture it forms sulphurous acids and sulphuric acids which are highly corrosive.
Methyl Chloride; Methyl chloride was first used in 1878. Methyl chloride is a colourless
extremely flammable gas with a mildly sweet odour. Methyl chloride is a halocarbon of the
methane series and it has many of the properties desirable in a refrigerant, which accounts for its
wide use in the past in both domestic and commercial applications. Methyl chloride is corrosive to
aluminium, zinc, magnesium and the compounds formed in combinations with these materials. In
the presence of moisture, methyl chloride forms a weak hydrochloric acid, which is corrosive to
both ferrous and non-ferrous metals. It is also explosive. There were numerous fatal accidents that
occurred in the 1920s when methyl chloride leaked out of refrigerators. This has led to the
discovery of the next generation refrigerants. Few first generation refrigerant and their properties
have been shown in table 1.1[9].
1.4.2 Second Generation Refrigerants
The second generation refrigerants were distinguished by a shift to chloro Fluoro chemicals for
safety and durability. Thomas Midgely and his associates studied the property tables of elements of
periodic table. They disregarded compounds that are unstable, toxic, yielding insufficient volatility
and inert gases based on their low boiling point. In 1928, Midgely and his colleagues made critical

observations regarding flammability and toxicity of compounds containing elements like carbon,
nitrogen, oxygen, sulphur, hydrogen, fluorine, chlorine and bromine. Their first publication was on
fluorochloro refrigerants and it showed how the variation of chlorination and fluorination of
hydrocarbons influences boiling point, flammability and toxicity of the refrigerants. Thus CFC
refrigerants made the second generation of refrigerants. CFC is a non-toxic, non-flammable gas
with relatively high mass. It is a good refrigerant because it can be compressed easily to liquid and
carries away lots of heat when it evaporates. It is very stable that only UV rays can break it down In
fact, it’s well suited to a variety of applications because it doesn’t react with anything; it works well
as a solvent, a blowing agent, a fire extinguishing agent and an aerosol propellant. Because it is a
single molecule, not a mixture, it doesn’t separate out at different pressures or temperatures. Some
of the refrigerants of this generation are presented here along with their thermodynamic properties
and applications.
R-11; R-11 is considered to be safe refrigerant as it is non-flammable and non-explosive. It is used
in the applications like air conditioning of small buildings, factories, departmental stores, theatres
etc. It can be used in the applications where the refrigeration load ranges from 150 to 2000 tons
along with the centrifugal compressor. R-11 refrigerant is also used as the solvent and the secondary
refrigerant. The problems that have restricted the use of this refrigerant are low operating pressures
and high potential to deplete ozone layer. Since R11 has highest potential to cause the depletion of
ozone layer, as per the Montreal Protocol, its use and production had to be stopped completely.R-11
is now being replaced by other environment friendly refrigerants, of which the most common is
R-123.
R-12; R-12 is a highly versatile refrigerant that is used for wide range of refrigeration and air
conditioning applications. Refrigerant R12 is used in domestic refrigerators and freezers, liquid
chillers, dehumidifiers, ice makers, water coolers, water fountains and transport refrigeration. R12
is non-toxic, non-flammable, and non-explosive. This makes it highly popular for the domestic as
well as the commercial applications. R12 is highly stable CFC and it does not disintegrate even
under the extreme operating conditions. It is suitable for wide range of operating conditions.
Unfortunately, it is the CFC and it has unusually high potential to cause the depletion of the ozone
layer. R12 is being replaced by other refrigerants and some of the suggested replacements for R12
are: R-134a, R-401a, R- 401b. In the 1970s, after decades of dumping about a million tons of the
stuff into the air each year, scientists learned that CFC isn’t harmless after all. In 1973 Prof James
Lovelock discovered Freon to be harmful to the ozone layer. The CFC molecules are destroyed by
the sun’s ultraviolet rays in the stratosphere. When the chemical bonds are broken, the chlorine
atoms drift free, and they become a catalyst that breaks unstable ozone molecules (O3) into oxygen

molecules (O2). The chlorine is not consumed in the reaction, so it continues ruining ozone for
years. This is a big deal, because stratospheric ozone is the shield that protects all living things on
the planet from the Sun’s ultraviolet radiation. In 1987, the Montreal Protocol limits the production
and consumption of CFCs. January 2010 marked the end of global production of CFCs under the
Protocol. In 2009 the Montreal Protocol was universally ratified by 196 nations. Few second
generation refrigerant and their properties has been shown in table 1.2[10].
1.4.3Third Generation Refrigerants
The third generation refrigerants based on hydro chlorofluorocarbon (HCFC) and hydro
fluorocarbon (HFC) have been developed to replace second generation refrigerants. These offer
most of the same advantages as CFC without damaging the Earth’s ozone shield, but they were
developed before the environmental impact of fluorine was fully understood. This impact has been
termed as Global Warming Potential (GWP). Roland and Molina predicted that emissions of HFCs
could damage Earth’s atmosphere by the catalytic destruction of ozone in the stratosphere. The
hypothesis has been proven in 1985 by measurements which have shown the destruction of the
ozone layer over Antarctica. Therefore, HCFC and HFC gasses are on a schedule to be phased out
by 2030.
Natural Refrigerants; Natural refrigerants are easily available, and long experience exists with
their application dating far into the beginning of mechanical refrigeration. Many new refrigerants
have come into picture to overcome the disadvantages of using natural refrigerants but the “circle”
is now somehow closed as we already returned to natural refrigerants, but now with new
technologies and with a lot of experience behind us. Natural refrigerants divide conveniently into
hydrocarbons, ammonia and CO2 and have been discussed here.
Hydrocarbons; The dominant characteristic of the hydrocarbon refrigerants is their high
flammability. Provided precautions are taken to mitigate the consequences of their flammability,
hydrocarbons make excellent refrigerants in practice. They are miscible with mineral oils and have

relatively high critical temperatures. Propane (R290) and propylene (R1270) have normal boiling
points below –40°C and are, therefore, suitable for general refrigeration applications. Butane
(R600) and isobutane (R600a) have much higher boiling points but they also have high critical
temperatures, which tends to make them very efficient in operation. The greatest success of
hydrocarbons has been in the application of R600a to domestic refrigerators. Propane and blends
containing propane could safely be used in window air conditioners provided appropriate
precautions were taken and provided they were used in fully sealed systems. Propane could also be
used, with an acceptable degree of risk, for car air conditioning, again provided that appropriate
precautions were taken. R1270 is a refrigerant similar in performance to propane but much more
expensive and therefore unlikely to find general favour. Hydrocarbons would not appear attractive
for large-scale air conditioning applications but they will certainly appear as a refrigerant for
window air conditioners of low charge.
Carbon Dioxide; Carbon dioxide is present in the atmosphere and it is non-flammable and non-
toxic. Despite the high pressures associated with its use, carbon dioxide has been used as a
refrigerant since 1862. It is odourless, non-toxic, non-flammable, non-explosive and non-corrosive.
Carbon dioxide continued to be in use in marine refrigeration as a non-toxic alternative to ammonia
and to methyl chloride. However, the advent of halocarbons in the 1930s led to the abandonment of
the much less efficient carbon dioxide, which finally went out of use in the 1950s. The reason for
poor efficiencies obtained when using carbon dioxide as a refrigerant is that it has a low critical
temperature. There are several ways in which this defect can be overcome. As a result of modern
methods and developments, carbon dioxide is coming back into use as a refrigerant in systems
which have efficiencies at least as great as the efficiencies of halocarbon and ammonia systems. It is
an ideal refrigerant. If properly applied it is very efficient to use. Properties of different third
generation refrigerants are listed in table 1.3[11].

Figure 1.3 GWP values of some third generation refrigerants.[11]
1.5 Desirable Properties of New Refrigerants: Careful selection of refrigerant has
significant impacts on the safety, reliability and energy consumption of the system. A refrigerant
must satisfy a number of requirements related to safety, chemical stability, environmental
properties, thermodynamic characteristics and compatibility among materials [9].
Thermodynamics Properties: The thermodynamic characteristics most importantly normal boiling
point, critical temperature and heat capacity must match the application for the system to operate
efficiently.
Chemical Stability: A refrigeration system is expected to operate many years, and all other
properties would be meaningless if the refrigerant decomposes or reacts to form something else.
Safety and Impact on Health and Environment: The ideal refrigerant should have low toxicity
and be non-flammable at the same time should have zero ODP and lowest GWP.
Thermo-physical Properties: Favourable transport properties like low viscosity and high thermal
conductivity have an impact on the size of the heat exchangers and thus cost of the overall system.
A final set of practical criteria relate to materials and impact the long-term reliability of a system.
The refrigerant must be compatible with common materials of construction, including metals and
seals.
1.6 R12 REFRIGERANT
Refrigerant R12 or Freon 12 is said to be the most widely used of all the refrigerants being used for
different application. The chemical name of refrigeration R12 is dichlorodifluoromethane and its

chemical formula is CCl2F2. The molecular weight of R12 is 120.9 and its boiling point is 21.6
degree F. Since R12 has molecules of chorine and fluorine, it is called as chlorofluorocarbon (CFC).
R12 is a highly versatile refrigerant that is used for wide range of refrigeration and air conditioning
application though in many air conditioning applications it is now replaced by R22 refrigerant.
Refrigerant R12 is used in domestic refrigerator and freezers, liquid chillers, dehumidifiers, ice
makers, water coolers, water fountains and transport refrigeration. The wide ranges of application of
the refrigerant are due to its safe properties.
1.6.1 Advantages of R12 Refrigerant [5]
 Safe properties: Refrigerant R12 is nontoxic, non-flammable, and non-explosive; This
makes it highly popular for the domestic as well as the commercial applications.
 Stability: R12 is highly stable chlorofluorocarbon and it does not disintegrate even under the
extreme operating conditions. However, if it is brought in contact with the flame of fire or
the electrical heating element, it disintegrates into the toxic products. Thus whenever there is
leakage of R12 refrigerant it is advised to put all the flames off and keep the doors open so
that it can escape to the open atmosphere.
 Suitable for wide range of operating conditions: R12 has the boiling point of 21.6 degree F
(29.8 degree C) due to which it condenses at the moderate pressures at the atmospheric
temperature. This means the discharge pressure of the compressor should be only moderate
so as to produce the condensation of the refrigerant in the condenser at the atmospheric
temperature. This helps in using the compressor of low compression ratio that has higher
efficiency. Due to this property of refrigerant R12, it is used in wide range of applications
like high temperature, medium temperature and low temperature applications. It can be used
will all types of compressors like reciprocating, centrifugal and rotary.
 Miscibility with oil: Refrigerant R12 is miscible with the compressor oil under all the
operating conditions. There are two advantages of this property of R12. Firstly, there is no
problem of the oil return back to compressor. Some particles of the oil from compressor tend
to get carried away with the discharged refrigerant, because of the property of miscibility of
R12, these particles return back to the compressor easily. The second advantage of
miscibility is that the refrigerant flowing through the condenser and the evaporator is free of
the oil particles. The oil particles within the refrigerant reduce the heat transfer from it, but
such problem does not occur with R12 refrigerant. Due to this the heat transfer capacity of
the condenser and evaporator is increased, which ultimately helps increase the efficiency of
the refrigeration plant.

1.6.2 Disadvantages of R12 Refrigerant
 Low refrigerating effect per pound: The refrigerating effect of R12 per pound of its weight
is low compared to the other refrigerants. However, this is not the major disadvantage as it
can be used constructively in some cases. In the smaller systems, the greater weight of the
R12 helps controlling the refrigeration system in a better way. In the larger systems this
disadvantage is offset by the higher vapour density of the refrigerant thus the compressor
displacement required per ton of refrigeration with the R12 refrigerant is not much higher
than compared with the other refrigerants. The high heat transfer rates in the condenser and
the evaporator due to absence of the oil also helps reduce the effects of this disadvantage.
 R12 is CFC: R12 is the most widely used refrigerant, unfortunately it is the CFC and it has
unusually high potential to cause the depletion of the ozone layer. R12 is being replaced by
other refrigerants and some of the suggested replacements for R12 are: R134a, R401a and
R401b.
1.7 Objectives of the Present Work
 Reconditioning of VCR refrigeration trainer which is not in working condition.
 To find performance parameter, Coefficient of performance of VCR System at
different loads and Capillary tube dimensions.
 To find performance parameter, heat rejection in condenser of VCR System at
 To find performance parameter, power consumption of compressor of VCR System at

CHAPTER II
LITERATURE REVIEW
Various literature sources are focused towards finding out the influence of the geometrical
configurations of a capillary tube on the performance of the refrigeration system. The accurate size
of the capillary tube and its configuration can be predicted with the help of the calculations for
the refrigeration effect, coefficient of performance (COP) of the system and mass flow rate of the
system. The effects of different geometries of capillary tubes have been studied by many
researchers. Since the capillary tube can be straight, helical coiled and also serpentine coiled
and all three configurations have their own distinct effect on the system performance, thus the
literature review here is focused to give a brief introduction of the effects of the various
configurations of the capillary tube on the system performance and thus pave the path for further
studies.
Hirendra Kumar Paliwal, Keshav Kant[1], developed a flow model for designing and
studying the performance of helical coiled capillary tubes and to mathematically simulate a
situation closer to one existing in real practice. Homogeneous flow of two phase fluid was assumed
through the adiabatic capillary tube. The model included the second law restrictions. The effect of
the variation of different parameters like condenser and evaporator pressures, refrigerant
flow rate, degree of sub cooling, tube diameter, internal roughness of the tube, pitch and the
diameter of the helix and the length of the capillary tube were included in the model.
Theoretically predicted lengths of helical coiled capillary tube for R134a are compared with the
length of the capillary tube actually required under similar experimental conditions and majority of
predictions were found to be within around 10% of the experimental value.
M.Y.Taib et. Al[2], studied the performance of a domestic refrigerator and developed a test rig
from refrigerator model NRB33TA. The main objective of the performance analysis was to obtain
the performance of the system in terms of refrigeration capacity, coefficient of performance
(COP) and compressor work by determining three important parameters which are temperature,
pressure and refrigerant flow rate. The analysis of the collected data gave the COP of the system
as 2.75 while the refrigeration capacity was ranging from 150W to 205W.
J.K.Dabas et. Al[3], studied the behaviour of performance parameters of a simple vapour
compression refrigeration system while its working under transient conditions occurred during

cooling of a fixed mass of brine from initial room temperature to sub-zero refrigeration
temperature. The effects of different lengths of capillary tube over these characteristics were also
investigated. The investigation showed that with constantly falling temperature over evaporator,
refilling of it with more and more liquid refrigerant causes increase in heat transfer coefficient
which maintains the refrigeration rate at falling temperature. The study revealed that larger capillary
tubes decreases the tendency of refilling but offers less evaporator temperature while shorter
capillary tubes ensure higher COP initially but it deteriorates at a faster rate in lower temperature
range.
Nishant P. Tekade et. Al[4], reviewed the investigation about the coiling effect of spiral
capillary tubes on the refrigerant mass flow rate for the same cooling load. The work also
reviewed the effects of changes in the parameters such as capillary tube dimension i.e. capillary
tube diameter, capillary tube length, coil pitch and inlet conditions of the refrigerant to the
capillary tube i.e. degree of sub cooling and inlet pressure of the refrigerant charge.
Ankush Sharma and Jagdev Singh[5], experimentally investigated about the effects of
simple and twisted spirally coiled adiabatic capillary tubes on the refrigerant flow rate.
Several capillary tubes with different bore diameters, lengths and pitches were taken as test
sections. LPG was used as an alternative for R134a. Mass flow rates for different capillary tubes
were measured for different degrees of sub cooling with constant inlet pressure of the capillary tube.
Experiments were conducted on straight capillary tubes as well as to facilitate proper comparison.
The test results showed that mass flow rate is greater in straight capillary tube and least in
twisted spirally coiled capillary tube.
Sudharash Bhargava and Jagdev Singh[6], experimentally investigated the pitch and
length of the serpentine coiled adiabatic capillary tube on the flow of a eco-friendly gas. The
zeotropic blend (30% propane, 55% n-butane, 15% Iso-butane) is used as refrigerant in the
experiment. Various capillary tubes with distinct lengths, pitch and bore diameter were used as
the test sections in the experiment. Inlet pressure of the capillary tubes was kept constant and then
mass flow rates for different capillary tubes with different lengths and pitches were measured.
Straight capillary tubes were also investigated. The data from the experiments showed that mass
flow rate of the refrigerant in the system was less for serpentine coiled capillary tubes and was
greater for straight capillary tubes.

Thamir K. Salim[7] experimentally investigated the performance of the capillary tube
expansion device using R134a as the refrigerant in the system. All the properties of the
refrigeration system were measured for the mass flow rate ranging from 13 kg/hour to 23 kg/hour
and capillary tube coil number ( 0-4) with fixed length (150cm) and capillary tube bore
diameter (2.5mm). The test results showed that the theoretical compression power increases by
65.8% as the condenser temperature increases by 2.71% and the theoretical compression power
decreases by 10.3% as the capillary tube coil number increases. The test results also showed that
cooling capacity increases by 65.3% as evaporator temperature increases by 8.4% and the cooling
capacity increases by 1.6% as the capillary tube coil number increases in the range (0-4). The COP
decreases by 43.4% as the mass flow rate increases by 76.9% and the COP of the system increases
by 13.51% as the capillary tube coil number increases in the range (0-4). The study showed that coil
number 4 was the best for the lowest mass flow rate (13 kg/hour) and the highest mass flow rate (23
kg/hour).
M.A. Akintunde[8], investigated the effects of various geometries of capillary tubes based
on the coil diameters and lengths alone. There was no any particular attention paid on the effect
of coil pitch. This paper examined the effects that the pitches of both helical coiled and serpentine
coiled capillary tubes have on the performance of a vapour compression refrigeration system.
Several capillary tubes of equal lengths (2.03m) and varying pitches, coil diameters and serpentine
heights were used. Both the inlet and outlet pressure and the temperature of the test section
(capillary tube) were measured and were used to estimate the COP of the system. In the case of
helical coiled capillary tubes, the pitch did not have any significant effect on the system
performance, while in the case of serpentine coiled capillary tubes, both pitch and height of the
serpentine influences the system performance. Performance improved with increase in both the
pitch and the height. Correlations were proposed to describe the relationships between straight and
coiled capillary tubes and between helical coiled capillary tubes and serpentine coiled capillary
tubes. The coefficient of correlation proposed was 0.9841 for the mass flow rates of helical and
serpentine with straight tubes and 0.9864 for the corresponding COPs and 0.9996 for the mass flow
rates of helical and serpentine coiled tubes.

CHAPTER III
EXPERIMENTAL DETAILS
The apparatus is a laboratory scale working model of a Refrigeration cycle unit, portable–trolley
mounted, housed on a MS square tube frame with powder–coated metallic platform to give elegant
finish. The compressor is fitted on the platform with fan-cooled condenser. The evaporator (chiller)
made of copper coil, placed in a insulated Stainless Steel vessel with fiber glass coated interior,
housed in a wooden chamber. The Rota meter, thermostat expansion valve, solenoid valve,
pressure/compound gauge, LP/HP cutout, and voltmeter, ammeter & temperature indicator with
selector switch (to measure temperature at different points of the refrigeration system) are mounted
on the panel. Hand shut off valves are provided at different points to control the flow of refrigerant.
The major difference in theory and treatment of vapor refrigeration system as compared to the air
refrigeration system is that, the vapor alternatively undergoes a change of phase from vapor to
liquid and liquid to vapor during the completion of a cycle. The latent heat of vaporization is
utilized for carrying heat from the refrigerator, which is quite high compared with the air-cycle,
which depends only upon the sensible heat of the air. The substances used do not leave the plant
but are circulated through the system alternately after condensing and re-evaporating.
During evaporating, it absorbs its latent heat from the brine, which is used for circulating
around the cold chamber. In condensing, it gives out its latent heat to the circulating water
or air of the cooler; the machine is, therefore, known as Latent Heat Pump. It absorbs its
latent heat from the brine and gives out in the condenser [10].
All the principal parts are shown on the diagram, and path of the refrigerant flow is also shown on
the diagram. The pressure is maintained at different levels in two parts of the system by the
expansion valve (high side float valve). The function of the expansion valve is to allow the liquid-
refrigerant under high pressure to pass at a controlled rate into the low-pressure part of the system.
Some of the liquid evaporates passing through the expansion valve, but greater portion is vaporized
in the evaporator at low pressure (low temperature). The liquid refrigerant absorbs its latent heat of
vaporization from the air, water or other material, which is being cooled. The function of the
compressor is to increase the pressure and temperature of the refrigerant above atmospheric, which
will be ready to dissipate its latent heat in the condenser. In passing through the condenser, the
refrigerant gives up the heat, which is absorbed in the evaporator plus the heat equivalent of the
work done upon it by the compressor. This heat is transferred to the air or water, which is used as
cooling medium in the condenser [11].

Figure 3.1 Vapour Compression Refrigerator test rig.
Figure 3.2 Block diagram of VCR system.
1:Compressor, 2: Condenser, 3: Rota meter, 4: Filter drier, 5: Solenoid, 6: Expansion
valve, 7: Flow control valve, 8: Capillary tube, 9: Chiller box.

3.1 Components of VCR Test Rig
(a) (b)
(c) (d)
(e) (f)
(g) (h)

Figure 3.3a –h The Components of VCR Test Rig; a) Compressor Unit , b) Sectional view of
compressor, c) Condenser, d) Evaporator, e) Capillary tube, f) Filter, g) Rotameter and h) Heating
Coil.
(a) (b)
(c) (d) (e)
(f) (g) (h)

Figure 3.4 a –h The Components of VCR Test Rig; a) Solenoid Valve , b) Regulating Valve, c)
Low Pressure gauge, d) High Pressure gauge, e) Temperature Indicator, f) Ammeter, g) Voltmeter
and h) Energy Meter.
3.1.1Compressor: A refrigerant compressor as the name indicates is a machine used to compress
the vapour refrigerant from the evaporator and to raise the pressure so that the corresponding
saturation temperature is higher than that of the cooling medium. It also continually circulates the
refrigerant through the refrigerating system. Since the compression of refrigerant requires some
work to be done on it, their fore a compressor must be driven by some prime mover.
SPECIFICATION 230 V-50HZ Reciprocating mechanism 0-5Amms current.
Hermetically sealed compressor is one in which the two halves are sealed by welding or brazing.
Electric motor and reciprocating mechanism are placed inside this housing[6]. A reciprocating
compressor consists of piston, connecting rod, crank shaft. Crank shaft is rotating by an electric
motor.
During downward motion of the piston refrigerant is sucked and in upward motion refrigerant get
compressed.
3.1.2Condenser: Condenser is an important device used in high of side of refrigeration system.
Its function is to remove heat of the hot vapour refrigerant discharge from the compressor. The heat
from the hot vapour refrigerant in a condenser is removed first by transferring it to the wall of the
condenser tubes and then from the tube to the condensing or cooling medium. The selection of a
condenser depending upon the capacity of refrigeration system, and the type of refrigerant used and
the type of the cooling medium available [6].
3.1.3Evaporator: There are numerous advantages to copper piping, and it has nothing to do
with conductivity. The difference between thin steel and thin copper conductivity is quite small and
is not going to make a big difference one way or the other[10].
1. Copper is corrosion resistant compared to steel, and cheaper than stainless steel.
2. Copper is easily and reliably soldered with low-temperature fillers and torches and doesn't
require welding or brazing, and can make tight seals.
3. (Soft) copper can be easily bent using a blow torch making it usable under many situations
without cracking.
4. Copper can be crimped without applying heat.
5. Copper can handle bigger pressure differences than plastic tubing.
6. Copper doesn't leach anything into the stream inside it.

3.1.4Capillary tube: Capillary tube is one of the most commonly used throttling devices in the
refrigeration. The capillary tube is a copper tube of very small internal diameter. It is of very long
length and it is coiled to several turns so that it would occupy less space[1]. The internal diameter of
the capillary tube used for the refrigeration applications varies from 0.5 to 2.28 mm. Capillary tube
used as the throttling device in the domestic refrigerators, deep freezers, water coolers and air
conditioners [4]. Specification Copper tube Diameter -1.2mm, 0.9mm, 1.4mm
How capillary tube works? : When the refrigerant leaves the condenser and enters the capillary
tube its pressure drops down suddenly due to very small diameter of the capillary. In capillary the
fall in pressure of the refrigerant takes place not due to the orifice but due to the small opening of
the capillary [7].
3.1.5Filter: Filter driers are used to remove contaminants and moisture from the refrigerant to
prevent damage and improper operation in a refrigeration system. Refrigerant Driers not only
remove moisture, they also are intended to filter debris from the refrigerant piping system. Filtering
the refrigerant liquid/leaving the compressor/condenser protects the thermal expansion valve or
capillary tube from clogging [11].
3.1.6Rotameter: A rotameter is a device that measures the flow rate of fluid in a closed tube. It
belongs to a class of meters called variable area meters, which measure flow rate by allowing the
cross-section area the fluid travels through, to vary, causing a measurable effect.
3.1.7Heating coil: Electric heating is a process in which electrical energy is converted to heat.
Common applications include space heating, cooking, water heating and industrial processes.
An electric heater is an electrical device that converts electric current to heat. The heating
element inside every electric heater is an electrical resistor, and works on the principle of Joule
heating: an electric current passing through a resistor will convert that electrical energy into heat
energy.
3.1.8Solenoid valve: Solenoid valves play an important role within refrigeration and air
conditioning system, controlling the flow of refrigerants. Though their base function-turning the
refrigerant flows on and off- is quite simple, this function is key to ensuring space system
performance. Understanding how solenoid valves work increases the likelihood that contractors will
install, remove and reinstall valves correctly, ensuring optimum system performance and protection
[11].
3.1.9Valves: A valve is a device that regulates, directs or controls the flow of a fluid (gases,
liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various
passageways. Valves are technically fittings, but are usually discussed as a separate category. In an

open valve, fluid flows in a direction from higher pressure to lower pressure FUNCTIONS OF
VALVES; Stopping and starting flow, Reduce or increase a flow, controlling the direction of flow,
Regulating a flow or process pressure and Relieve a pipe system of a certain pressure.
3.1.10Pressure Gauges: 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.
3.1.11Temperature indicator: A thermocouple is a device consisting of two different
conductors (usually metal alloys) that produce a voltage proportional to a temperature difference
between their ends of the pair of conductors.
3.1.12AMMETER: An ammeter is a measuring instrument used to measure the current in a
circuit. Electric currents are measured in amperes (A), hence the name. Instrument used to measure
smaller currents, in the milli ampere or microampere range is designated as millimetres or micro
ammeters.
3.1.12Volt meter: A voltmeter, also known as a voltage meter, is an instrument used for
measuring the potential difference, or voltage, between two points in an electrical or electronic
circuit. Some voltmeters are intended for use in direct current (DC) circuits; others are designed for
alternating current (AC) circuits.
3.1.13Energy meter: Energy meter is a device that measures the amount of electric energy
consumed by a system or an electrically powered device. The most common unit of measurement
on the electricity meter is the kilowatt hour [kWh], which is equal to the amount of energy used by a
load of one kilowatt over a period of one hour, or 3,600,000 joules. In our project we are using two
energy meter one for compressor and second one for heater. Specification 250 volts 5- 10 amps 50
HZ Energy constant 1200 R/kWh.
3.2 P-H DIAGRAM
A pressure enthalpy diagram or (p-h diagram) is a figure with a vertical axis of absolute pressure
and a horizontal axis of specific enthalpy. It is an important diagram used frequently for a
performance calculation of a refrigerating machine. A Pressure Enthalpy graph is individual for
each refrigerant. They allow the user to quickly identify the state, temperature, pressure, enthalpy,
specific volume and entropy of a refrigerant at a given point. Enthalpy is another word for Heat
Energy and is usually measured in kilojoules per kilogram. Enthalpy is commonly found on the

x‐axis of the P-h graph. Pressure is measured generally in MPa, kPa or Bar (Absolute); it is most
commonly found on the y‐ axis of the P-h graph[8]. Temperature is measured in °C/K. and can be
found as lines of constant temperature on the P-h graph.
Point 1 to 2: Refrigerant change in a compressor
Point 2 to 3: Refrigerant change in a condenser
Point 3 to 4: Refrigerant change through an expansion valve
Point 4 to 1: Refrigerant change in an evaporator
(a)
(b)
Figure 3.5 (a) and (b) p-h diagram used in VCR Performance Calculation.[11]

[8]

3.3 Mathematical Equations used in Performance Calculation
[8][9][10]
Process 1-2 is the compression process wherein Mechanical work is to be supplied (usually in the
form of electrical energy) to a compressor. This is the quantity to be spent. Process 4 –1 represents
the useful refrigeration effect. The index of performance is defined as coefficient of performance
(not as efficiency, as for heat engines)
C.O.P. = Useful refrigeration (output) = h1 – h4………………………. (1)
Network (compressor work, input) h2 - h1
T1 =Temperature of refrigerant @ inlet of compressor
T2 = Temperature of refrigerant @ outlet of compressor
T3 = Temperature of refrigerant @ outlet of condenser
T4 = Temperature of refrigerant @ outlet of expansion
T5 =temperature of water @ chiller
C= Condenser, E= Evaporator, Let P1, P2 be pressure,
h1, h2, h3 and h4 be the specific enthalpies of the refrigerant R12. These are to be found out from
relevant p-h chart. (h2-h1) denotes the compressor work input, (h3 = h4) (throttling process is also a
constant Enthalpy process), (h1-h4) is the enthalpy rise on the evaporator i.e. the refrigeration effect
Actual COP
COP (actual) = __Q__ = Refrigeration Effect……..………………….. (2)
W Compressor input
Q = ___mw x cpw (Tf –Ti)__ kW………………………………… (3)
Duration of test
Where mw = Mass of water , Cpw = 4.18 kJ/kg-K, Tf = Final chiller water temperature,
Ti = initial chiller water temperature
W = __n x 3600 …………………………………………………………... (4)
t x k
Where n = number of revolution of energy meter disc, t = time taken in seconds, k = energy meter
constant = 1500 rev/kWh
Relative COP: COP (relative) = COP (actual) ……………………….. (5)
COP (theoretical)

CHAPTER IV
RESULTS AND DISCUSSIONS
Table 4.1: Observation and Results Obtained with Capillary tube of diameter 0.9mm at different
loads.
loads.

loads.
Calculation for 17 litre water as Evaporator Load and with 0.9 diameter
capillary tube
From enthalpy chart R-12, corresponding to point (P1T1), (P2T2), (P2T3),& (P1T4)
h1 = 187kJ/kg, h2 = 210kJ/kg, h3 = 63 kJ/kg and h4 = 20 kJ/kg
1. Net refrigerant effect (NRE) = h1 – h4 = 187-20 = 167 kJ/kg
2. Mass flow rate to obtain one TR
3. mr = 210 / NRE = 210 /167 = 1.257 kg/min
4. Work of compression = h2 – h1 = 210-187 = 23 kJ/kg
5. Heat equivalent of work of compression per TR= mrx ( h2 – h1) = 1.257 x 23 =
28.91 kJ/min
6. Theoretical power of compression = 28.91 / 60 = 0.4818 kW
7. Heat to be rejected in condenser = h2 – h3 = 210 – 63 = 147 kJ/kg
8. Heat rejection per TR = (210 / NRE) x (h2 – h3)= 1.257 x 147 = 184.77 kJ/min
9. Heat rejection ratio = 184.77 / 210 = 0.8798
10. C.O.P of saturation cycle = h1 – h4 / h2 – h1
11. (Theoretical C.O.P), COP = 187 – 20 / 210 – 187= 7.26

12. Energy consumed by compressor, E = (No. of rev x 3600) / (Energy meter const.
x time taken) =( 5 x 3600) / (1200 x 56)= 0.256 kW
For Mass of water = 5 kg,
13. Q = mwCp x (Initial water temp – Final temp, of water ) = 5 x 4.187 x (73.4 –
32.18= 479.412 / 3600 kJ/S = 0.1333 kW
14. Actual C.O.P = Heat extracted/ work done = Q / E= 0.1333 / 0.256 = 0.521
15. Relative C.O.P =Theoretical C.O.P / Actual C.O.P= 4.23 / 0.521= 8.11
Fig.4.1: Variation of COPThe v/s Evaporator load
Fig.4.2: Variation of COPACTUAL v/s Evaporator load

Fig.4.3: Variation of COPRELATIVE v/s Evaporator load
The figures 4.1, 4.2 and 4.3 show the Theoretical COP, actual COP and Relative COP respectively.
From the figure 4.1, it can be noticed that with increasing evaporator load theoretical COP
decreases in all the cases. However there is higher COP recorded with capillary tube of diameter
0.9mm. From figure 4.2 it is observed that with increase in evaporator load there is increase in
actual COP. The higher actual COP is recorded with capillary tube of diameter 0.9mm when
compared to other diameter capillary tubes. The figure 4.3 shows the relative COP and it can be
seen that increase it the evaporator load causes decrease in relative COP.
Fig.4.4: Variation of Compressor Work v/s Evaporator load
Figure 4.4 shows the variation of compression work with respect to evaporator load. It is noticed
that as the load increases the compressor work or the electric power to be supplied to the
refrigerator increases in all the cases. However the lesser amount of compressor work required with
0.9mmdiameter capillary tube.

Fig 4.5: Variation of Heat rejected in condenser v/s Evaporator load
Figure 4.5 shows the variation of heat rejected in condenser with respect to evaporator load. It is
recorded that the condenser heat rejection is more or less constant with respect to evaporator load.
But the higher heat rejection takes place in higher diameter capillary tube when compared to 0.9mm
diameter tube.

CHAPTER V
CONCLUSIONS
 The theoretical COP and Actual COP of VCR refrigerator run with R-12 refrigerant given
optimum values for expansion device; Capillary tube with 0.9mm diameter when compared
to 1.2mm dia. and 1.4mm diameter capillary tubes.
 The compressor work required is less in case of 0.9mm diameter capillary tube incorporated
VCR. The Compressor work consumed with 0.9mm diameter capillary tube is 25kw at 17kg
evaporator load whereas with 1.2mm and 1.4mm diameter capillary tubes it is 30kW and 31
kW respectively.

CONFERENCES/PUBLICATION/EXHIBITION
 Dr. T.M.Chandrashekharaiah, Abhishek K G, Ajay B, Anil Kumar T A and Avinash C D,
“Experimental Analysis of Different Size Capillary Tubes effect on VCR Performance”,
Proceedings of National Conference ‘MechMastic 2k17’ held at Kalpataru Institute of
Technology, Tiptur on 18th
May 2017.
 Dr. T.M.Chandrashekharaiah, Abhishek K G, Ajay B, Anil Kumar T A and Avinash C
D,”Design and Development of Efficient Vapour Compression Refrigerator”, Proceedings
of South India Project Exhibition (SIPE-2017) held at Kalpataru Institute of Technology,
Tiptur on 19th
May 2017.

REFERENCES
[1] Hirendra Kumar Paliwall, Keshav Kant , " A model for helical capillary tubes for refrigeration
systems," International Refrigeration and Air Conditioning Conference Purdue University , 2006
[2] M.Y.Taib, A.A.Aziz and A.B.S.Alias, “Performance analysis of a domestic refrigerator”,
National Conference in Mechanical Engineering Research and Postgraduate Students, 2010.
[3] J.K.Dabas, A.K.Dodeja, Sudhir Kumar and K.S.Kasana, “Performance characteristics of
“vapour compression refrigeration system” under real transient conditions”, International Journal of
Advancements in Technology, 2011.
[4] Nishant P. Tekade and Dr. U.S.Wankhede, “Selection of spiral capillary tube for refrigeration
appliances”, International Journal of Modern Engineering Research, 2012.
[5] Ankush Sharma and Jagdev Singh, “Experimental investigation of refrigerant flow rate with
spirally coiled adiabatic capillary tube in vapour compression refrigeration cycle using eco friendly
refrigerant”, International Journal of Mechanical and Production Engineering Research and
Development, 2013.
[6] Sudharash Bhargava and Jagdev Singh, “Experimental study of azeotropic blend(30% propane,
55% n-butane, 15% iso-butane) refrigerant flow through the serpentine capillary tube in vapour
compression refrigeration system”, International Journal of Mechanical and Production Engineering
Research and Development, 2013
[7] Thamir K. Salim, “The effect of the capillary tube coil number on the refrigeration system
performance”, Tikrit Journal of Engineering Sciences, 2012.
[8] Validation of a vapour compression refrigeration system design model, M. A. Akintunde,
Federal University of Technology, Department of Mechanical Engineering, PMB. 704, Akure,
Ondo State, Nigeria, +2348.35011797, ajyinka@yahoo.com
[9] Akhilesh Arora and Kaushik S C (2008), “Theoretical Analysis of a Vapour Compression
Refrigeration System with R502, R404A and R507A”, International Journal of Refrigeration, Vol.
31, pp. 998-1005.
[10] Jyoti Soni1 and R C Gupta (2013), «Performance analysis of vapour Compression refrigeration
system with R404a, r407c and r410a» Int. J. Mech. Eng. & Rob. Res. Vol. 2, No. 1,pp. 25-36.
[11]Lovelin Jerald, A. and 2D. Senthil Kumaran (2014), “Investigations on the performance of
vapour Compression system retrofitted with zeotropic Refrigerant R404a”
doi:10.3844/ajessp.2014.35.43 Published Online.

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