A Review on Performance Comparison of VCRs &VARs

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International e-Journal For Technology And Research-2017
IDL - International Digital Library 1 | P a g e Copyright@IDL-2017
A Review on Performance Comparison of
VCRs &VARs
1
Madhvendra Kumar Dwivedi, 2
Mr. Dheerandra Singh
Mechanical Engineering Department
1, 2
Madan Mohan Malaviya University of technology
Gorakhpur, India
ABSTRACT: Vapour Absorption
Refrigeration Systems (VARS) and vapour
compression refrigeration system (VCRS) both are
widely used for refrigeration purpose. The major
differences in both the system are in vapour
compression refrigeration systems the input supply
is compressor work which is high grade of energy
whereas in vapour absorption systems main input is
heat supply in the generator which is low grade
energy. Energy is an essential requirement for the
economic development of any country, so our main
aim is to save energy, unless VCRS have high
performance future scope is VARS are primarily
used in large commercial and industrial
installations .In this paper discusses the various
methods for increasing the performance of both
systems so this paper focuses on the suitability of
both systems.
Keywords: Refrigeration, Coefficient of
Performance, Vapour Absorption Refrigeration
System, Vapour Compression Refrigeration
System.
1. INTRODUCTION
1.1. Vapour compression refrigeration system
(VCRS).
When the term “refrigeration” comes we make up
the mind about refrigerator that works on the
electrical supply and provides us cooling, ice and
preserves our beverages and food items from
getting exhausted. In these types of refrigerators the
components that are used are compressor,
condenser, and evaporator and expansion valves.
Basic principle taken from first and second law of
thermodynamics .This system would have wide
range of temperature for high coefficient of
performance. In this system the low pressure
temperature of the vapour refrigerant is enters into
the compressor through the inlet valve where it’s
compressed to a high temperature and pressure and
this refrigerant is discharge into the condenser
where heat is removed. An automatic expansion
valve is used for reducing the pressure and this low
pressure refrigerant enters into the evaporator [4].
Fig 1- A simple VCRS [4]
1.2. Vapour Absorption refrigeration system (VARS).
The vapour absorption refrigeration system
(VARS) comprises all processes in the vapour
compression refrigeration system like
Condensation, Expansion and Evaporation are
same only change is replacing the Compressor with

Generator Absorber and Pump. In the vapour
absorption system the refrigerant used is ammonia-
water, lithium bromide etc. The refrigerant gets
condensed in the condenser and it gets evaporated
when enter in the evaporator. Low pressure
ammonia vapour increases its pressure and enters
into the generator by Pump. Weak solution reverses
back the absorber whereas strong solution enters
the condenser through the liquid separator. The
refrigerant produces cooling effect in the
evaporator and releases heat to the atmosphere via
the condenser [3].VARS are primarily used in large
commercial and industrial installations. Compared
with vapour-compression systems, ARS have one
major advantage. The mixture should be safe,
chemically stable, noncorrosive, and inexpensive
and should be available easily. The refrigerant
should have high heat of vaporization [17].A liquid
is compressed instead of a vapour and as a result
the work input is very small (on the order of one
percent of the heat supplied to the generator) The
NH3-H2O mixture is environmental friendly which
is the only useful working pair currently used for
refrigeration purposes in absorption systems, and
despite of the new mixtures under investigation, the
ammonia- Water mixture is the only one with a
clear future [14]
Figure: 2 A simple vapour absorption refrigeration
systems [1]
2. Literature Review on VARS
&VCRS
R. A. Saidur et.al The COP of VCRS is higher than
VARS for same temperature limit There is no any
requirement of superheating and sub cooling
phenomenon in VARS but in VCRS some time
refrigerant which was in liquid form is the serious
problem for the compressor. In VARS liquid refrigerant
in the evaporator is not a serious problem. The COP of
VCRS decreases at part loads but VARS does not .Also
the VCRS has the severity of noise and vibration along
with requirement of maintenance more than that of a
VARS. The VARS are the echo friendly so there are no
any issue regarding environment for using. [10]
P. L.Vikas et.al. The result shows that the hot vapour
from the generator which enters the evaporator coil
without disturbing its phase and thus reduced the cooling
effect .Concentration of Ammonia was design for 50%
but commercially 25% concentration is available in the
market [14].
V. K Gupta et.al .The system therefore has less power
consumption and higher capacity due to the compression
of flash gas only from the intermediate pressure which is
higher than evaporating pressure and a low quality of
refrigerant which enters into evaporator. Its exergetic
efficiencies were 26% and 24% higher than these of the
conventional single-stage cycle for R12 and R134a,
respectively although the addition of extra components
such as flash tank, expansion valves etc causes extra
irreversibility. Total overall irreversible losses are lower
to the single stage cycle. [15] When the temperature
increases, heat pumps with a single-stage cycle become
increasingly inefficient. This is especially true for
conventional air-source heat pumps operating in colder
climates. The disadvantages may be overcome by
operating the two-stage heat pump of
compression/expansion. Figure 3 shows a two-stage
cycle utilizing for flash tank economizer. The flash tank
has three functions: separated the liquid and vapour
phases, desuperheat the discharge gas from low pressure
compressor and to cool the liquid with the condenser to
the saturated temperature for the intermediate
pressure.[15]

Figure: 3 Two-stage heat Pump
Siddhesh S. Arote et.al .Electric based VARS and
Evaluate the COP for mixture of lithium bromide water
and ammonia-water. When exhaust gas as a source of
energy the same COP obtained and observed that it
depends on the working conditions of the condenser,
absorber, evaporating temperature, and generator. The
water-ammonia vapour concept for utilizing exhaust
waste heat, because it is the important source of energy,
only to operate the pump very small electric power used.
The input heat energy potential power is the source for
VARS [16].
Khaled S.et.al. Worked on the topic for liquid absorption
and solid absorption system for household, industrial and
automobile applications .They show that liquid
absorption is more common in industry applications,
where as solid absorption systems were suitable for
running automobiles, owing for their limitations of liquid
handling, with the recycle of waste heat and also the
utilization of clean solar energy [18].
3. Performance of V- C System.
3.1 Effect of sub cooling:
When sub cooling perform in the condenser
refrigerating Effect (RE) increases there are no
change work input so by the sub cooling COP
increases.
3.2 Effect of superheating (in evaporator):
If superheating is done there is increase in
refrigerating Effect (RE) for the same pressure ratio
refrigerants work input increases so COP may
increase, decrease and remain same depends upon
the refrigerants.
3.3 Effect of increase in condenser pressure:
When increasing the condenser pressure this
causes Reduction in refrigerating effect (RE),
increase in compressor Work because it is the
function of initial temperature and pressure ratio.
Hence Reduction in COP, by increasing the
pressure ratio volumetric efficiency decreases. In
simple languages volumetric efficiency is the
breathing capacity of the compressor [8].
Figure:4 Increase in condenser pressure:
3.4 Effect of decrease in evaporator pressure:
When decrease the evaporator pressure or low
pressure no change in refrigerating effect (RE), by
increasing the pressure ratio increase in work input
so COP decreases and due to increase in pressure
ratio volumetric efficiency decreases.

Figure: 5 decrease in evaporator pressure
3.5 Effect of flash chamber use in V-C system:
Thermodynamically there is no change in
refrigerating effect & cop of the system when using
flash chamber only liquid refrigerant was absorbing
heat from storage space and after using flash
chamber it is the same liquid refrigerant which
absorb heat from storage space. At the inlet of
evaporator only liquid refrigerant absorbs heat from
the storage so no need of vapour refrigerants in
evaporator therefore by using flash chamber liquid
refrigerants separate from vapour at the inlet of
evaporator so this decreases the size of evaporator
[6].
3.6 Decreasing the throttling losses
In VCRS throttling is one of the irreversible
processes so this device is one of the main causes
of irreversible loss in cycle efficiency. A portion of
the refrigerant flashing to vapour during the
expansion process is reduces this losses. Other way
To eliminate these throttling losses is to change the
single-stage expansion to a multistage expansion
where flash gas is removed after each throttling
stage. For smaller expansions and compressions
reduce the refrigerant pressure to the required
pressure of evaporator. [7]
3.7 Cascading of vapour compression system
In the cascade system consists there are two or
three separate simple cycles operating in adding
with each other at different temperature levels. The
connecting point is a heat exchanger between the
different stages. This interstate heat exchanger is
the condenser for the first stage and the second
stage is the evaporator .Starting with the low
pressure cycle, the vapour from the evaporator was
compressed into the different stage compressor and
send to the interstate heat exchanger where it
rejects up its heat to the second evaporator coil.
The condensed liquid was flows to the first stage
expansion valve and the evaporator, complete the
low pressure cycle. The vapour generated in the
coil of heat exchanger by the heat it was absorbed
and compressed in the second and pass through the
cooling chamber [5]
4. Types of vapour absorption
refrigeration system
4.1: Water-Lithium Bromide (LiBr-H2O) System-
for moderate temperatures (0ºC and above)
applications especially in large capacity air
conditioning system. Here H2O is the refrigerant
and Li Br is the absorbent. The Lithium Bromide-
Water pair since water is use as refrigerant for
these reasons Li-Br - H2O systems are becoming
more popular. [4].
4.2 Ammonia-Water (NH3- H2O) System-for low
temperature less than 0℃refrigeration applications
with NH3 as refrigerant and as H2O as a absorbent
[2].There is another substance used in combination
with refrigerant and that is known as absorbent.
These pairs are frequently used in industrial
purpose as cold storage; ice plant etc where
minimum temp. is requirement.
5 Modification of Vapour
Absorption Refrigeration System
[5]
There are some drawbacks which induced in VARS
are as below:
 The rich solution entering the generator
are low temperature and the poor solution
which was entering the absorber are at
high temperature.
 .Present of absorbent in the vapors
leaving the generator and going to
refrigerant circuit.
These two are discussed along with proposed
modification.
5.1. Used liquid-liquid Heat exchanger in the
solution channel.

The saturated rich solution must be heated from the
absorber temp. (ta) to the bubble temp t1 where the
saturated poor solution must be cooled to t3 in the
absorber. This was insufficient since useful heat
must be added in generator and rejected in
absorber. System can be improved by inducing
regenerative heat exchanger .Thus reduction in the
amount of heat added in generator and increase
COP. Size would also reduce in this system .[7]
Fig 6- Diagram shows cooling and heating of poor
and rich solution.
Fig 7- Diagram shows the effect of absorbent in
the evaporator.
5.2. Using analyzers - the exhausting column
and Dephlegmator
In NH3-H2O system the vapour coming out from
the generator containing considerable amount of
absorbent vapour which reaches evaporator after
condensation this cause evaporation would not be
isothermal and required low temp. Would not be
reach in the evaporator.fig 7
6. Components of VARS
6.1 Generator:
Generator denotes as the power house of absorption
refrigeration system. . Heat is then supplied to the
mixture, due to refrigerants vaporizes and leaves a
weak solution of ammonia where the weak solution
would drain out through the pressure reducing
valve from other side of absorber. Heat supply to
Generator uses waste energy sources so it is useful
in future or its higher scope.
6.2 Condenser:
The condenser is a finned tube heat exchanger
where coolant separated in both the low‐ generator
and the single‐ effect generator is directly
condensed by the outdoor air or water. Refrigerant
flows inside a cooper tube while air or water
circulates through the aluminum fins in a cross
flow configuration. As well know, the heat transfer
coefficients of the air are quite low but both have
the purpose of cooling.
6.3 Evaporator absorber assembly:
The evaporator and the absorber are assembled
together in the same chamber for the purpose of
water vapor generated in the evaporator is directly
absorbed by the solution in the absorber. This
minimizes the piping between both components it’s
also reduces the pressure drop and consequently
improves the absorption process when the chilled
water circulates inside a cooper coil and the
refrigerant drops on its outer surface. With the
purpose of improving the heat transfer from the
chilled water to the refrigerant, both inner and outer

surfaces of the tube coil tube are enhanced surfaces
fins.
6.4 Expansion devices:
Two expansion valves where installed in the first at
the outlet of the condenser and the second at the
exit of the sub-cooler. They consist of two flow
restrictor devices generating a pressure drop in the
refrigerant entering the evaporator chamber. These
are hand controlled valves [2].
6.5 Pump:
Pump helps to pumping of the rich solution from
evaporator pressure to condenser pressure. Specific
volume of liquid is small which was present at the
entry of pump (W=− 𝑉𝑑𝑝 ) so pump work is
negligible in VARS. [8]
7 Coefficient of performance of
systems:
COPVCRS =
𝐑𝐞𝐟𝐫𝐢𝐠𝐞𝐫𝐚𝐭𝐢𝐧𝐠 𝐄𝐟𝐟𝐞𝐜𝐭
𝐖𝐨𝐫𝐤 𝐝𝐨𝐧𝐞
In case of VCRS performance should be increased
either by increasing refrigerating effect or decrease
work input to the system. COP of VACRS is
usually greater than 1. [12]
COPVARS=
𝐇𝐞𝐚𝐭 𝐚𝐛𝐬𝐨𝐫𝐛𝐞𝐝 𝐢𝐧 𝐞𝐯𝐚𝐩𝐨𝐫𝐚𝐭𝐨𝐫
𝐇𝐞𝐚𝐭 𝐬𝐮𝐩𝐩𝐥𝐲 𝐭𝐨 𝐠𝐞𝐧𝐞𝐫𝐚𝐭𝐨𝐫
In vase of VARS performance should be increased
by decreasing the heat supply to the generator.COP
of VARS is usually less than 1.
8 CONCLUSIONS:
In VARS liquid refrigerant are not a serious
problem while is in VCRS it have very large
demerits. Unless VARS have low COP, this system
is more preferable because of scarcity of electricity
and also waste heat is available and waste heat
which was the heat input of this system.
When increasing the concentration of ammonia at
the absorber exit COP continuously increases
because energy supplied to the generator decreases
which is the only input for the system. Also, the
absorber heat rejection decreases, so the
requirement of cooling media (water) decreases.
Apart from lower COP of vapour absorption
refrigeration system it is better to use because of its
eco-friendly in nature or behaviour.
9 REFERENCES:
[1] S.C. Kaushik, Akhilesh Arora, (2009), Energy
and exergy analysis of single effect and series flow
double effect water–lithium bromide absorption
refrigeration systems. 1247 – 1258
[2]Demirocak, Dervis (2008), Emerging
thermodynamic and economic analysis of a solar
thermal powered adsorption cooling system, Oct-
2008.
[3] Gomri, R (2009)., Second law comparison of
single effect and double effect vapour absorption
refrigeration systems, Energy Conversion and
Management, Vol. 50, pp. (1279-1287 ).
[4] Nwanya Stephen Chijioke, (2010), use of
energy method to simulate the performance of
LiBr-H2O absorption system, Nigerian journal of
technology, vol. 29 no.1.
[5] Uppal AH, Norton B, Probert SD (1986), A
low-cost solar-energy stimulated absorption
refrigerator for vaccine storage Applied Energy
1986; 25: 167–74.
[6] Nguyen Q. Minh, Neil James Hewitt, Philip
Charles Eames (2006) Improved Vapour
Compression Refrigeration Cycles” International
Refrigeration and Air Conditioning Conference.
[7] Sohail Bux, A.C.Tiwari (2014), Natural
Refrigerants Based Automobile Air Conditioning
System, International Journal of Emerging Science
and Engineering (IJESE) ISSN: 2319–6378,
Volume-2.

[8] V.D.Patela, A.J.Chaudhari, R.D.Jilte (2012),
Theoretical and Experimental Evaluation of
Vapour Absorption Refrigeration System,
International Journal of Engineering Research and
Applications (IJERA) ISSN: 2248-9622 National
Conference on Emerging Trends in Engineering &
Technology
[9] Arora .P.C., Domkundwar.S. S.(2000), A
Course in Refrigeration and Air-conditioning.
[10] Kyoto Protocol to the United Nations
Framework Convention on Climate Change,
1997
[11] Arora. C.P. edition (2002),A Course in
Refrigeration and Air-Conditioning,Tata McGraw
Hill, New Delhi.
[12] Kumar, .D. S. (2017), Refrigeration
& Air-Conditioning First edition, S.K. Kataria &
Sons New Delhi.
[13] R. A. Saidur, M.Rezaei A, W.K.Muzammil A,
M.H.Hassan A, S.Paria A, M. Hasan uzzaman
(2007),Technologies to recover exhaust heat from
internal combustion engines Elsevier .
[14] Sreeshankar K. K, Vikas P L, Sooraj (2013),
Vapour Absorption Refrigeration System For Cold
Storage & Power Generation in Automobiles Using
Exhaust Gas circulation
[15] Gupta, V. K., Prasad, M.(1984), Graphic
Estimation of Design Parameters for Two-Stage
Ammonia Refrigerating Systems Parametrically
Optimized, Mech. Engg. Bull., vol.15,ppno-100-
104
[16] Prof. Nilesh B. Totla, Siddhesh S. Arote,
Sujaya V. Gaikwad, Shubham Kattimani (2016) ,
Comparison of the Performances of NH3-H20 and
Libr-H2O Vapour Absorption Refrigeration Cycles.
Prof. Nilesh B. Totla.et al. Int. Journal of
Engineering Research and Application
www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 4,
(Part - 7), pp.08-13
[17] Subhash Kumar, Dr.R.RArakerimath, (2015)
Comparative Study On Performance Analysis Of
Vapour Absorption Refrigeration System Using
Various Refrigerants IPASJ International Journal
Of Mechanical Engineering (IIJME) Volume 3,
Issue 1, Pg-07-11
[18] Khaled S.(2011), Evaluation And Performance
of water- Ammonia Auto Air Conditioner System
Using Exhaust Waste, Science-Direct Energy
Procedia6,pp-467-476

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