“SEMINAR REPORT ON SOLAR ASSISTED VAPOUR ADSORPTION REFRIGERATION SYSTEM”

A
SEMINAR-II ON
“Solar Assisted Vapour
Adsorption Refrigeration System”
by
Mr. B. A. WADEKAR
(M.E. HEAT POWER ENGINEERING)
under the guidance of
PROF. R. R. KATWATE
Department of Mechanical Engineering
D. Y. Patil School of Engg, Ambi
SAVITRIBAI PHULE PUNE
UNIVERSITY, PUNE
[2017-2018]

D. Y. PATIL SCHOOL OF ENGINEERING,
AMBI (2017-18)
C E R T I F I C A T E
This is to certify that Mr. Bhagvat Anandrao Wadekar, has successfully
completed the Seminar-II entitled “Solar Assisted Vapour Adsorption
Refrigeration System” under my supervision, in the partial fulfilment of
Master of Engineering - Mechanical Engineering (Heat Power Engineering)
of University of Pune.
Date:
Place: Ambi, Pune
Prof. R. R. Katwate Prof. Y. S. Andhale
(Seminar Guide) (Head of Department)
DYPSOE, AMBI
Dr. V. N. Nitnaware
(Principal)
(External Examiner) Seal DYPSOE, AMBI

DYPSOE AMBI, M.E. Mechanical (Heat Power Engineering)
i
ACKNOWLEDGEMENT
I wish to express my deep sense of gratitude and honor towards my respected seminar guide
Prof. R. R. Katwate for his unending, inspiring and all dimensional guidance and
encouragement to complete this seminar work. His committed devotion, dedication and
hostile & disciplined attitude for me was like enlightened lamp throughout the journey.
I again thankful to my seminar coordinator Dr. S. Kadam, Head of Mechanical Engineering
Department Prof. Y. S. Andhale and all those unknown faces who helped me in all respects
to fulfil the work with effectiveness.
I also express my sincere thanks to principal of my college Dr. V. N. Nitnaware for his
encouragement to complete this Seminar. Last but not the least I also thankful to all
Teaching and Non-Teaching staff members of DYPSOE family who helped me directly and
indirectly. I again pay my sincere thanks to all web communities and publishers of research
paper those I referred for my Seminar.
I would like to say only the thing that my positive attitude, hard work and support from all
the resource persons were most helpful factor to bring this seminar to successful end. I hope
that this seminar will be most significant stepping stone for my career and would fulfil my
aspiration in every aspect.
B. A. Wadekar

ii
LIST OF FIGURES
Figure No. Name of Figure Page No
Figure 1.1 Classification of Solar Refrigeration Cycle 02
Figure 2.1 Sorption techniques used for refrigeration 07
Figure 3.1 Principle of adsorption refrigeration 11
Figure 4.1 (a) Simple Solar Adsorption Refrigeration System-Schematic,
intermittent cycle
12
Figure 4.1 (b) Simple Solar Adsorption Refrigeration System-constructive,
continuous cycle
12
Figure 4.2 Thermodynamic cycle of adsorption refrigeration 13
Figure 4.3 Solar refrigerator with parabolic collector 14
Figure 5.1
Photographic front view of vapor adsorption refrigeration
system
21
Figure 5.2 Experimental Setup (Schematic) 22
Figure 5.3 Flow chart of performance analysis 24
Figure 5.4 Plot of COP vs Tcond, Qevap=1000 kJ/hr 26
Figure 5.5 Plot of COPCarnot vs Tcond, Qevap=1000 kJ/hr 26
Figure 5.6 Plot of COP vs Tevap, Qevap=1000 kJ/hr 27
Figure 5.7 Plot of COPCarnot vs Tevap, Qevap=1000 kJ/hr 28
Figure 5.8 Plot of COP vs Tgen, Qevap=1000 kJ/hr 29
Figure 5.9 Plot of COPCarnot vs Tgen, Qevap=1000 kJ/hr 29

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LIST OF TABLES
Table No. Name of Table Page No
Table 2.1 Summary of literature 10

iv
NOMENCLATURE
A - Area, m2
AC - Activated Carbon
AC-M - Activated Carbon-Methanol
COP - Coefficient of Performance
Cp - Specific heat capacity at constant pressure, kJ/kg K
d, D - Diameter, m
M - Mass concentration ratio
m - Mass, kg
P - Pressure, kPa
Q - Heat, kJ/kg
R152a - 1,1-Difloro ethane (CH3CHF2)
SCP - Specific cooling power, kJ/kg (adsorbent)
V - Volume, m3
VAdRS - Vapour Adsorption Refrigeration System
∆Ηa - Heat of sorption, kJ/kg
∆Ηv - Heat of vaporization, kJ/kg
∆h - Change in enthalpy, kJ/kg
∆Μ - Change in Mass Concentration Ratio
Suffixes
a, b, c, d - Specific values at point a, b, c, d
ab, bc, cd, da - Specific values in process
ad - Adsorbent
ads - Adsorption
bed - Adsorbent bed
evap - Evaporator
gen - Generation / generator
max - Maximum
min - Minimum

v
INDEX
SR. NO. NAME OF CONTENT PAGE NO.
LIST OF FIGURES
NOMENCLATURE
1 INTRODUCTION 1
1.1 Classification of Solar Refrigeration Cycle 2
1.2 Need of Solar Energy Driven Refrigeration 4
2 LITERATURE REVIEW 5
2.1 Solar Cooling Techniques 5
2.2 Sorption Techniques 6
2.3 Performance Prediction of VAdRS 8
2.4 Summary of Literature
3 METHODOLOGY 11
3.1 Principle of Adsorption Refrigeration 11
4
SOLAR VAPOUR ADSORPTION REFRIGERATION
SYSTEM
12
4.1 Basic Solar VAdRS 12
4.2 Components of VAdRS 14
4.2.1 Adsorber 14
4.2.2 Condenser 14
4.2.3 Condensate receiver tank 15
4.2.4 Expansion device 15
4.2.5 Evaporator 15
4.3 Types of Adsorption Processes and Adsorbents 15
4.3.1 Physical Adsorption 15
4.3.2 Chemical Adsorption 17
4.3.3 Composite Adsorption 18
4.4 Working Pairs 19
4.4.1 Activated Carbon(AC) Fibre and Methanol 19

vi
4.4.2 Activated Carbon(AC) Fibre and Ammonia 19
4.4.3 Silica Gel and Water 20
4.4.4 Zeolite and Water 20
4.4.5 Calcium Chloride and Ammonia 20
5 PERFORMANCE OF SOLAR VAdRS 21
5.1 System Preliminary Setup 23
5.2 Experimental Procedure 23
5.2.1 Heating and Desorption 23
5.2.2 Cooling and Adsorption 23
5.3 VAdRS Performance Analysis 24
5.4 Performance 26
5.4.1 Effect of Condenser Temperature 26
5.4.2 Effect of Evaporator Temperature 27
5.4.3 Effect of Generation Temperature 28
6 SUMMARY 30
7 FUTURE PROSPECTS 31
REFERENCES 32

vii
ABSTRACT
Vapour Compression Refrigeration System (VCRS) is the widely used refrigerating system.
The input power for the compressor of the refrigeration system is electrical power or a part
of the power produced by the engine. Vapour Absorption/Adsorption Refrigeration Systems
works on low grade form of energy i.e. heat energy, which may be a solar energy, waste
heat in any industrial process. The negative environmental impacts of burning fossil fuels
have forced the energy research community seriously to consider renewable sources, such
as naturally available solar energy. The study gives an introduction of the basic principles
of these systems, the history of development and recent advances in solar sorption
refrigeration technologies are reported. The adsorption cooling typically has a lower heat
source temperature requirement than the absorption cooling. The coefficient of performance
(COP) ranges between 0.2 to 0.7. The thermodynamic properties of most common working
fluids, as well as the use of working pairs have been reviewed in this study. The study also
gives performance analysis of solar assisted VAdRS, variation of COP with variation in
generation temperature, condenser temperature, evaporator temperature is plotted. The
study also overlooks the new approaches to increase efficiency and sustainability of the
basic adsorption cycles, such as the development of hybrid or thermal energy storage.
Keywords: COP, VAdRS, Adsorption, Solar Energy, Environment.

SOLAR ASSISTED VAPOUR ADSORPTION REFRIGERATION SYSTEM
1
1. INTRODUCTION
Nature works much like a heat engine, heat flows from high temperature elements to low-
temperature elements. As it does this, work is also done on its environment. Refrigeration
is a process to keep an element cool or to reduce the temperature of one element below
that of the other. The refrigeration process is like a reverse heat engine, where heat is
taken from a cold element to be transferred to a warmer element, generally by adding
work to the system. In a heat engine, work is done by the system so in order to do the
reverse work must be done on the system.
This work input is traditionally mechanical work, but it can also be driven by magnetism,
lasers, acoustics, and other means. Several different types of refrigeration systems which
utilize different work input were considered for this work. They are the vapour
compression system and the absorption/adsorption refrigeration system. In recent
developments of thermal engineering the refrigeration technologies play an important
role in today's industrial applications. But as far as COP of this refrigeration system is
concerned, it is always a challenge to the researchers to significantly increase the COP
for these systems. The most popular refrigeration and air conditioning systems at present
are those based on the vapour absorption/adsorption systems. These systems are popular
because they are reliable, relatively inexpensive and their technology is well established.
However, these systems do not require high-grade energy (mechanical or electrical) for
their operation.
Apart from this, the recent discovery that the conventional working fluids of vapour
compression systems are causing the ozone layer depletion and greenhouse effects has
forced the scientific researchers to look for alternative systems for cooling applications.
The natural alternative is of course the adsorption system, which mainly uses heat energy
for its operation. Heat can be a waste heat in engines, power plants, geothermal energy,
Solar energy, ..etc. Moreover, the working fluids of these systems are environment
friendly. A suitable working fluid is probably the single most important factor in any
refrigeration system. The cycle efficiency and operation characteristics of an adsorption
refrigeration system depend on the properties of refrigerant, adsorbent and their mixtures.

2
The most important thermo-physical properties are heat of vaporization of refrigerant,
vapour pressure of refrigerant and adsorbent, solubility of refrigerant in solvent, heat
capacity of solution, viscosity of solution and surface tension and thermal conductivity of
the solution. Apart from this, the other selection criteria for the working fluids are their
toxicity, chemical stability and corrosiveness. Simultaneous heating and cooling are
required in many industries such as dairy plant, pharmaceutical, chemical etc. Adsorption
systems have been extensively paid attention in recent years due to the potential for CFC
and HCFC replacements in refrigeration, heating and cooling applications. Despite a
lower coefficient of performance (COP) as compared to the vapour compression cycle,
adsorption refrigeration systems are promising for using inexpensive waste energy from
industrial processes, geothermal energy, solar energy etc.
1.1 CLASSIFICATION OF SOLAR REFRIGERATION CYCLE
Figure 1.1 Classification of Solar Refrigeration Cycle [6]
Each of the methods, except the adsorption cooling technique, maintains the advantages
of its conventional type but suffers from certain limitations. PV refrigerators, in spite of
their commercial success among solar refrigerators, have high installed cost and bleak
prospects for on the rural site manufacture. Liquid absorption units have the problem of
generating some absorbent with the refrigerant during generation, thus requiring
rectification. Solid absorbents characteristically disintegrate after repeated cycles of
operation, as in the case of the CaCl2/NH3 pair. Most often, special treatments of the

3
absorbents are needed to obtain hard porous granules, thereby increasing the system first
cost. Solar adsorption refrigerators do not possess these disadvantages. The concept of
using solar energy for powering a refrigerator arose 40 years ago. Besides conventional
refrigerators powered by photovoltaic cells, heat powered machines work with either
liquid or solid sorption cycles. Solar refrigerators with liquid sorption, Li-Br + water or
water + ammonia, have been studied by many authors.
However, the use of liquid sorption for solar cooling induces two features. First, liquid
sorption cycles operate continuously, while solar energy is inherently transient during the
day and vanishes during the night. A large heat-storage must then be installed between
the solar collectors and the generator. Second, the solution is most often circulated by a
pump working all day long. This pump consumes electricity that must be supplied by
photovoltaic cells or a reliable electricity network. It therefore results that hybrid power
(solar + fuel) suits liquid sorption well. Solid sorption works differently. First, the cycles
are by principle transient: heat is accumulated in the sorbent resulting in desorption of
refrigerant vapour and only a cold-storage is necessary for providing refrigeration over
the 24 h period. Second, the cycle itself works without any mechanical input or moving
parts. In addition to reliability, full autonomy with solar energy should be achievable,
which is very attractive for installation in remote areas. There are two solid sorption
systems likely to be solar-powered: chemical reaction and adsorption. After pioneering
works, chemical reaction solar refrigerators are evoking new interest thanks to novel
composite materials impregnated with chloride salts. Solar-powered adsorption systems
have been investigated by several groups.
In addition to models, real machines have been developed. Some of them use
sophisticated solar collectors with concentration, others use the adsorbent itself,
contained in a transparent tube, as the solar-energy-absorbing material, but the most
efficient configuration seems to consist of metallic flat-plate solar collectors, single- or
double-glazed, covered with a selective surface and filled with the adsorbent bed.

4
1.2 NEED OF SOLAR ENERGY DRIVEN REFRIGERATION
Most of the cooling systems operate on vapour compression refrigeration cycle. This
system generally consumes electrical energy that is high-graded and costlier too. Also,
large-scale consumption of electricity from conventional resources like fossil fuels poses
serious problems to be solved with utmost care and concern. The immediate solution to
mitigate from environmental issues is to emphasize all energy-consuming sectors to
utilize renewable energy sources such as solar energy, wind energy and so on in addition
to waste heat from industrial processes. Among the known alternate energy sources, solar
energy is proved to be easily accessible for electricity-starved places located in tropical
regions (on our mother planet, the Earth). Though solar energy is dilute and intermittent,
its choice for refrigeration is attributed to its availability in abundance and non-polluting
nature. In recent years, heat-driven refrigeration systems have drawn significant
consideration due to their lesser environmental impact and large energy-equivalent
potential. The common heat-operated cooling system(s) that can be operated with solar
energy are vapour absorption refrigeration system, vapour ejector refrigeration system
and vapour adsorption refrigeration system. LiBr-water and aqua–ammonia absorption
systems are commercially available. However, they generally suffer from disadvantages
like crystallization, inability to realize sub-zero evaporator temperature as in case of
LiBr-water system and while, corrosion and toxicity problems encountered in aqua–
ammonia absorption system and further, they demand specialized skill for construction
and maintenance. A vapour ejector refrigeration system requires a sophisticated and
accurately designed ejector to run the system effectively and efficiently. However, a
vapour adsorption refrigeration system is found to be more attractive for the reasons, that
it is simple in construction and involves negligible operation and maintenance costs
besides, this system requires no skilled-man power and can be installed in any hilly areas
or isolated lands. [6]

5
2. LITERATURE REVIEW
The main objective of the literature review is to provide an appraisal of the new state of
the art in the field of solar refrigeration techniques. In this context, literature on
importance of solar cooling and sorption techniques involved in the cooling systems are
emphasized. One of the most important applications of refrigeration is the preservation of
perishable food products, precious and vital medicines, by storing them at low
temperature. In earlier days, the technique of cooling was started with utilization of ice
derived through natural sources and processes, but the requirement of ice in large
quantity and a suitable method to protect the cooling ice from melting have pushed the
technocrats to develop an artificial technology for producing ice in large quantity. Thus,
the history of artificial refrigeration began with the birth of laboratory-scale refrigerating
machine invented by the Scottish Professor William Cullen from University of Edinburgh
in 1755. Various research papers have been studied to understand concept properly and to
study present work done in the field of vapour adsorption for refrigeration and air
conditioning applications. Solid vapour adsorption is similar to liquid vapour absorption
system, except that the refrigerant is adsorbed on the surface of another solid known as
adsorbent.
2.1 SOLAR COOLING TECHNIQUES
The solar cooling techniques are to diminish the environmental ramification and provide
economic solution to the energy consumption issues raised by traditional cooling
methods. The use of sorption processes to produce refrigeration has been extensively
studied from the first half of the last century. Heat operated thermally driven sorption
cooling cycles are existing from 1909. Miller and Walter (1929) listed a number of
systems that utilized silica-gel and sulphur dioxide as the solid sorbent -refrigerant pairs.
Later research in this area were sedate the concept of solar operated refrigerator was
appeared about half a century back with the first model using a liquid-based sorption
cycle as discussed by Sumathy and Zhongfu(1999a). The four-core heat operated solar
energy assisted cooling systems available are absorption, ejector, desiccant and
adsorption cooling systems.

6
2.2 SORPTION TECHNIQUES
Sorption technology is used in thermal cooling mechanisms wherein the refrigerant
outcome is achieved from the physical or chemical variations (concentration difference)
between the adsorbent and adsorbate. Thermal-operated sorption cooling has been
considered as an efficient economic energy saving technique(s). Sorption cooling
technology can generate useful cooling effect for the beneficiary, based on non-
conventional sources or waste heat recovery systems. Perhaps these cooling systems are
especially simple in operation and are dependable, flexible and they are widely applied.
Figure 2.1 shows the various types of sorption cooling techniques. Heat operated
absorption and adsorption systems with sorption cooling models wherein the work
operated mechanical compressor of the common vapour compression cycle is substituted
by a heat operated compressor and sorbent. In the adsorption cooling system, the sorbent
is in the solid phase and whereas liquid phase in case of absorption systems. On heating
the solid/liquid sorbent, desorbs the refrigerant at the pressure of condenser. The vapour
refrigerant is condensed to the liquid state in the condenser, and then passed through
throttling valve to enter the evaporator at low pressure. The cooled refrigerant in the
evaporator engrosses heat from the cooled space and evaporates. Thus, it produces the
required cooling. Refrigeration using adsorption system can be used continuously, if
multiple sorption beds are used. Refrigeration using solid sorption systems requires large
surface area to transfer heat to the adsorbent materials that cost high.

7
Figure2.1Sorptiontechniquesusedforrefrigeration

8
2.3 PERFORMANCE PREDICTION OF VAdRS
“Sarbu et al (2015) in the presented work demonstrated that Solar sorption systems are
more suitable than conventional refrigeration systems because pollution-free working
fluids (instead of chlorofluorocarbons) are used as refrigerants. The review indicates that
much research has recently been performed on continuous operation absorption systems
that use NH3/H2O and H2O/LiBr as the working fluid. For solar sorption systems,
considerable reduction in unit cost or significant improvements in its performances at
present costs are still required to increase their competitiveness and commercialization
potential.
“Fernandes et al (2014) gives that experimental solar COP is still considerably low
(typically, between10% and 20%), seeming unlikely of further increase. Despite all, the
efforts made and numerous studies conducted all over the world regarding the
improvement of solar adsorption refrigeration systems. An overview of the hybrid
adsorption systems operating with the basic cycle has also been conducted in this paper,
to understand its present status and future trends.
Performance of solar cooler was analysed by Li and Wang (2003). This paper dealt with
effects of the adsorbent finned tube heat transfer, solar energy collector, coating of the
collector tubes, number of glasses used in the collector, thermal resistance of contact
materials used, thermal conductivity of the solid-sorbent materials, and packing solidity
of the solid-sorbent on the overall performance of the system.
Solar assisted sorption refrigerator utilising an evacuated tube for thermal insulation was
numerically studied by Li et. al (2003) with zeolite–water pair. They computed
relationships between the diameter of evacuated tube collector and its performance with
respect to distance among two adjacent tube centres. The study concluded for evacuated
tube diameter of 70 mm, both the COP and cooling capacity reached their highest
possible values of 0.25 and 4377 kJ/ m2
.
Anyanwu (2004) conducted transient study and performance forecasting of single solar
sorption bed refrigerator with AC - methanol pair incorporated in a tubular solar FPC.
They observed developments on COP and condensate yield ranging from 29 to 38% and
26 to 35% respectively. This was arrived based on tubes spacing, packing density of the
adsorbent and selection of the collector plate tube material.

9
Anyanwu and Ogueke (2005) reviewed the core concepts and theories of solar
adsorption refrigerator; the thermodynamic design and process development for solar
adsorption using three different pairs such as activated carbon (AC)-ammonia, AC-
methanol and zeolite - water. It was concluded in their study AC-ammonia is preferred
for providing cooling effect below freezing point of ice (for preserving food and
medicine) and zeolite – water is preferred for air conditioning. They also concluded that
in all the above three cases, the systems were dependent heavily on adsorber and
condenser temperature and lightly on evaporator temperature. The best COP’s (Solar)
were about 0.19, 0.16 and 0.3 respectively for AC-ammonia, AC-methanol and zeolite-
water with FPC.
Hamdeh and Muhtaseb (2010) designed prototype of a solar solid-sorption refrigeration
unit suitable for air-conditioning and refrigeration unit in remote areas. This device used
the AC-methanol pair. A minimum refrigerator temperature of 90
C was obtained for an
ambient temperature of 260
C and gross cycle COP of 0.688 was obtained.
Tashtoush et. al. (2011) utilised a multi-dimensional curve-fitting formula to fit the
experimental and theoretical data by correlating the COP value to one of the three
temperatures of generator, condenser, and evaporator. Many cylindrical tubes were used
in their study on solar radiation exposed sorption bed filled with AC-ammonia pair.
Solmus et. al. (2012) investigated a numerical model for mass and heat transfer of silica
gel - water pair based on local volume averaging technique. A local thermal non-
equilibrium one-dimensional model was developed to account both external and internal
resistance of mass transfer. The model simplifies along with assumptions on solid-sorbent
particle size, permeability, ideal gas radiation behavior of vapour refrigerant and viscous
dissipation. Neglected work done due to pressure changes. The surface penetrability was
deemed to be equal to the total penetrability. Adsorption bed thermo-physical properties
like thermal conductivity, specific heat and viscosity are considered to be independent of
temperature. They established that, in order to increase the performance of the sorption
bed, it is essential to reduce the heat transfer resistance.

10
2.4 SUMMARY OF LITERATURE
Table 2.1 Summary of Literature
S. N. Author Name Year Summary of Work
1
Ioan Sarbu,
Calin Sebarchievici
2015
- Solar VAdRS more suitable than VCC
- next several years will be decisive
2 Fernandes et al 2014
- intermittent Solar VAdRS
- Working Pair: AC-Methanol
- Solar COP 10% and 20%
3 Solmus et. al. 2012 - internal mass transfer resistances are focused
4 Tashtoush et. al. 2011
- many cylindrical tubes were used
- COP=0.616
5
Hamdeh and Al-
Muhtaseb
2010
- Minimum Te= 9°C & Tamb=26°C
- COP is found to be 0.688
6
Anyanwu and
Ogueke
2005
- Performance Analysis of VAdRS
- best COP’s (Solar) 0.16-0.3.
7
Rifat Ara Rouf et.
al.
2013
- Performance of an adsorption chiller with
Heat Stored in reserve tank
- Maximum COP=0.65 for direct solar
coupling while it is 0.6 for the heat storage

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3. METHODOLOGY
3.1 PRINCIPLE OF ADSORPTION REFRIGERATION
Adsorption refers to the binding of molecules (sorbate) to the surface of a material
(sorbent) without any chemical change. Adsorption occurs because the atoms, molecules
or ions at the surface of the sorbent are extremely reactive with unfulfilled valence
requirements as compared to their counterparts in the interior, which have valence
requirements satisfied. The unused bonding capacity of surface atoms may be utilized to
bond molecules of the sorbate to the surface of sorbent. It uses clathrate material: a
clathrate is an organic compound that has 3-dimentional lattices that make up a network
of micro pores or individual sites for the sorbate to reside. The sorbate, while attached to
the sorbent surface, gets trapped in cavities of the sorbents’ cage like crystals. The
material, which adsorbs gases, is known as adsorbent and the gases which are adsorbed
are the refrigerants. The adsorption capacity is a function of physical and chemical
properties of sorbate and sorbent such as; sorbent porosity, sorbate boiling point, the
operating temperature and pressure. The adsorption capacity is enhanced when the
sorbent material is activated as it increases the available surface area necessary for
adsorption. Activated carbon is an example of sorbent material. The adsorption
refrigeration technology is based on the ability of sorbent material to adsorb a relatively
large quantity of refrigerant vapour (adsorbate) at low temperature and pressure and
desorbs the refrigerant at a higher temperature and pressure. The compressor effect is
generated by heating and cooling the sorbent material and refrigerant. This result in high
pressure outward flow as the refrigerant is released during the hot desorption phase, and
inward flow or low-pressure suction during the cold adsorption phase.
Figure 3.1 Principle of adsorption refrigeration [4]

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4. SOLAR VAPOUR ADSORPTION REFRIGERATION SYSTEM
4.1 BASIC SOLAR VAdRS
Solar energy is the energy source of most adsorption devices operating with the basic
cycle. In the remaining cases the components are kept unchanged, the main difference
being the heat collection method. A solar adsorption refrigerator based on the basic
adsorption refrigeration cycle does not require any mechanical or electrical energy, just
thermal energy, and it operates intermittently according to the daily cycle. Like a simple
vapor compression system, these adsorption systems are closed systems, comprising a
compressor, a condenser and an evaporator. However, in this case, the compressor is an
adsorber powered by the thermal energy, and the cooling effect is achieved by the
evaporation of a refrigerant while the vapor produced is adsorbed by the adsorbent layer
in the adsorber. The adsorbed content of refrigerant varies cyclically, depending on the
adsorbent temperature and system pressure, which varies between a maximum limit set
by the condensation pressure and a minimum limit imposed by the evaporation pressure.
In its simplest form, a solar refrigerator is a closed system consisting of a solar collector
containing the adsorbent bed (hermetically sealed and painted in black, to optimize the
solar radiation absorption), a condenser, a receiver equipped with a 2-way valve and a
cold box with the evaporator inside. The basic adsorption cycle consists of four stages
(two isobar and two isosteric lines.)
(a) (b)
Figure 4.1 Simple Solar Adsorption Refrigeration System
(a) Schematic, intermittent cycle [3]
; (b) constructive, continuous cycle

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Figure 4.2 describes the thermodynamic processes involved in the operation of the
adsorption refrigeration system.
Figure 4.2 Thermodynamic cycle of adsorption refrigeration [4]
1. Process (a-b) (isosteric desorption)
At state a, cool canister, or adsorber, contains adsorbent saturated with a large
fraction of refrigerant at pressure slightly below Pevap. Cool adsorber is heated and
desorbs refrigerant vapour isosterically (i.e. at constant total mass in the adsorber),
to state b slightly above Pcond. At this point, vapour starts being forced out of the
hot adsorber through a check valve to the condenser.
2. Process (b-c) (isobaric desorption)
Isobaric heating desorbs more refrigerant, forcing it into the condenser until state c
attained, where the adsorber is nearly devoid of refrigerant.
3. Process (c-d) (isosteric adsorption)
The hot adsorber is then cooled isosterically (at constant total mass), causing
adsorption and depressurization, until the pressure drops below Pevap (state d),
opening another check valve to allow vapour to enter the adsorber from the
evaporator.
4. Process (d-a) (isobaric adsorption)
Isobaric cooling to state a, the refrigerant saturates the adsorbent and thus
completing the cycle. [4]
As the adsorber releases heat, cooling takes place. Consequently, the adsorbent
temperature falls down, the vapour pressure is dropped down to the evaporation
pressure. Thus, on receipt of latent heat from the space of cooling, the refrigerant is
d
c
Isobaric adsorption
Pevap
Pcond
Isobaric desorption
Isosteric
adsorption
b
Tads Tdes
a
Isosteric
desorption

14
evaporated and subsequently adsorbed by the solid sorbent in the adsorber. Typical
Solar refrigerator with parabolic collector is shown below
Figure 4.3 Solar refrigerator with parabolic collector [3]
4.2 COMPONENTS OF VAdRS
4.2.1 Adsorber
Adsorber is the main element of the adsorption refrigeration system. The adsorber
provides the necessary compression effect required for refrigeration in an adsorption
refrigeration system by absorbing and rejecting heat of adsorption and desorption. It
works like generator as well as absorber both in an AR system. It is designed as a tube in
tube heat. Perorated tubes are placed inside the bed. Activated carbon granules are filled
in the space between the adsorber tubes and perforated tubes. Aluminium chips are
proposed to be mixed with activated carbon to enhance heat transfer in adsorber bed.
4.2.2 Condenser
The condenser is a tubular heat exchanger where vapour refrigerant is chilled and
condensed at high pressure and temperature. The refrigerant vapour while passing
through the condensing coil, dissipates the latent heat into atmospheric air. The tubes are
normally constructed with plate type fins almost in all cases to increase the heat transfer
surface area. The weight-less material of aluminium is used for the fins. The space
between the fins is wider in order strengthen and to reduce dust clogging.

15
4.2.3 Condensate receiver tank
The condensate receiver tank (CRT) is an insulated vessel that stores liquid refrigerant
received from the condenser at a lower temperature. This receiving tank is placed
between condenser and evaporator. The receiving tank and connecting copper pipes are
usually insulated to avoid heat gain to refrigerant.
4.2.4 Expansion device
Liquid refrigerant from the condensate receiver is passed through a throttling device to
bring down the pressure suitable for optimum heat recovery in the evaporator. It sustains
the required pressure difference between the maximum and minimum pressure side of
the system. Hence the liquid refrigerant is vapourised at the predetermined pressure in
the evaporator. Therefore, the flow of refrigerant was controlled based on the load on the
evaporator. The throttling device usually used is capillary tube. The selection is made on
the basis of its simplicity, adaptability and cost. The capillary tube is usually made up of
copper tube of small diameter with varying length based on the application.
4.2.5 Evaporator
The evaporator consists of copper tube coiled inside a water bath. The liquid refrigerant
is at low pressure and temperature is passed through the coil and it is converted into
vapor on receiving heat from the surroundings. The latent heat gain by refrigerant is
from the surrounding medium (water) in the evaporator.
4.3 TYPES OF ADSORPTION PROCESSES AND ADSORBENTS
In adsorption process a solid adsorbent adsorb a gaseous adsorbate, which is a refrigerant.
This adsorption process can be a physical or chemical. The adsorption based on the
adsorption process is divided into three types,
a. Physical adsorption
b. Chemical adsorption and combination of both
c. Composite adsorption.
These processes of adsorption are described below,
4.3.1 PHYSICAL ADSORPTION [8]
It is caused by Vander Walls forces between the molecules of the adsorbent and the
adsorbate. Physical adsorbents with macro-pores can adsorb consecutives layers of
adsorbate, while those with micro-pores have the volume of the pores filled with the

16
adsorbate. Physical adsorbents develop the selectivity to the adsorbate after the former
undergo specific treatments, like react under a gas stream or with certain agents. The kind
of treatment will depend on the type of sorbents. These adsorbents and their adsorption
properties are discussed below.
Physical Adsorbents
The physical adsorbents are the porous materials which can reversibly adsorb a large
amount of vapour at their surface. This process is purely physical and there is no chemical
change in the adsorbent as well as adsorbate. Some of the most commonly used physical
adsorbents used in adsorption refrigeration are activated carbon or activated carbon fiber,
silica gel and zeolite. The main features of these adsorbents and their properties are
discussed as follows,
a. Activated carbon and activated carbon fiber
Activated carbon (AC) is made from material such as wood, peat, coal, fossil oil, chark,
bone, coconut shell and nut stone. The net structure of activated carbon pores is composed
of irregular channels, which have large pore area at the surface of the grain and the narrow
pore area within the grain. The specific area of carbon is between 500 to 1500 m2
/g. The
surface of activated carbon is covered by an oxide matrix and by some inorganic materials
and therefore, it is non- polar or a weak polarity. The adsorption heat of activated carbon
pair is lower than that of other physical adsorbents. Activated carbons are used as
powdered form or in granular form. Activated carbon fiber is generally used in the
production of fabric such as cloth, tissues etc. The carbon fiber has better mass transfer
performance as compared to activated carbon. The specific surface area of carbon fiber is
larger than that of activated carbon. The pores of activated carbon are more uniform and it
shows better heat transfer performance also. The disadvantage of activated carbon fiber is
its anisotropic thermal conductivity and the higher thermal resistance at contact surfaces
as compared to granular activated carbon.
b. Silica Gel
The silica gel is a type of amorphous synthetic silica. It can be realized as a rigid
continuous net of colloidal silica, connected to very small grains of hydrated SiO4. The
hydroxyl in the structure is the adsorption centre because it is polar and can form
hydrogen bonds with polar oxides such as water and alcohol. The adsorption ability of
silica gel increases when the polarity increases. One molecule can adsorb one molecule of

17
water. Each kind of silica gel has only one type of pore, which usually is confined in
narrow channels. The pore diameter of silica gel is about 0.7 to 3 nm and the specific
surface area is about 100 – 1000 m2
/g. Silica gel is widely used for desiccation because of
its adsorption capacity.
c. Zeolite
Zeolite is a type of alumina-silicate crystal composed of alkali or alkali soil. The chemical
formula of zeolite is My/n[(AlO2)y SiO2)m]zH2O Where, y and m are integers and m/y is
equal or larger than 1, n is the chemical valence of positive ion of M, z is the number of
water molecules inside a crystal cell unit. There are 40 types of natural zeolites and the
main types for adsorption refrigeration are chabazite, sodium chabazite, cowlesite and
fauzisite. About 150 types of zeolite can be artificially synthesized and they are named by
Type A, Type X, Type Y, Type ZSM. The adsorption and desorption heat of zeolites are
high, the desorption temperature required is also high. The zeolites can be used in
adsorption refrigeration for the temperature range of 200 to 3000
C.
4.3.2 CHEMICAL ADSORPTION [8]
It is caused by the reaction between sorbate and the surface molecules of sorbent. Electron
transfer, atom rearrangement and fracture or formation of chemical bond always occurs in
the process of chemical adsorption. Only one layer of adsorbate reacts with the surface
molecules of chemical adsorbent. The sorbate and sorbent molecules after adsorption
never keep their original state. Moreover, there are the phenomena of salt swelling and
agglomeration, which are critical for heat and mass transfer performance. The commonly
used Chemical adsorption working pairs are Metal Chloride and ammonia Metal hydride
and hydrogen Metal Oxide and hydrogen. The most commonly used chemical adsorption
pair is Calcium Chloride and ammonia.
Chemical Adsorbents
Chemical adsorbents are the adsorbents where the adsorption takes place because of a
reversible chemical reaction between sorbent and sorbate. The chemical adsorbents used
in chemical adsorption refrigeration mainly include metal chlorides, metal hydrides and
metal oxides.
a. Metal chlorides
The Metal Chlorides for adsorption refrigeration are mainly calcium chlorides strontium
chloride, magnesium chloride and barium chloride. Ammonia is the usual adsorbate of

18
metal chlorides. The adsorption reaction between metal chlorides and refrigerant is a
complexion reaction and the complex compound is called coordinated compound. During
adsorption process salt swelling and agglomeration can occur and influence heat and mass
transfer performance.
b. Salt and metal hydrides
Hydrogen can react with almost all elements and forms four types of hydrides. Out of
these four types salt hydrides and metal hydrides are the hydrides which can be used in
adsorption refrigeration. The salt hydrides have hexagonal crystal lattice structure with
large density. In the adsorption process H atoms become proton when they enter the space
between hexagonal crystal lattices. The electron motion is similar to the electron motion
of metal bonds. The density of salt hydrides is larger than the density of simple metals,
but the density of metal hydrides is smaller than the density of simple metals because the
mass and volume of the former does not increase proportionally in the adsorption process.
c. Metal oxides
When the metal oxides are used in adsorption refrigeration oxygen is used as refrigerant.
On the surface of the metal oxides the elements which influence adsorption performance
are the coordination number of the metal ion, the unsaturated degree of coordination, the
direction of the chemical bond on the surface of the chemical material the symmetrical
characteristic of the transition metal field and the arrangement of the active centre. The
swelling and agglomeration occurs during adsorption in metal oxides.
4.3.3 COMPOSITE ADSORPTION [8]
Composite adsorption started to be studied about 20 years ago, and they aimed to improve
the heat and mass transfer performance of the original chemical adsorbents. This kind of
adsorbent is usually obtained by the combination of a chemical adsorbent and a porous
medium, that can be or not a physical adsorbent, such as activated carbon, graphite,
carbon fibre, etc.
Composite Adsorbents
Composite adsorbents are mainly developed for improving the heat and mass transfer of
chemical adsorbents and for increasing the adsorption quantity of physical adsorbents.
The composite adsorbent has a porous structure and high thermal conductivity to help
avoiding the problem of swelling and agglomeration. The composite adsorbent increases
the adsorption capacity of physical adsorbent. The composite adsorbents are made from a

19
combination of a porous media and chemical adsorbent. Generally used composite
adsorbents are metal chlorides plus activated carbon or activated carbon fiber or expanded
graphite or silica gel or zeolite.
4.4 WORKING PAIRS
The working pair is the crucial part of adsorption refrigeration system. The basic
properties which are required for adsorption refrigeration are large adsorption capacity,
large change in adsorption capacity with change in temperature and compatibility with
refrigerant and low adsorption heat. The basic properties a refrigerant should possess are
same as that required in a vapour compression system. The adsorbent and refrigerant pair
is selected depending on the application and the source temperature. The commonly used
refrigerant adsorbent pairs are described below,
4.4.1 Activated Carbon(AC) fibre and Methanol
The adsorption process for the above mentioned pair comprises filling and condensation
of sorbate inside adsorbent pores. The adsorption mainly occurs in micro-pores whose
specific volume is generally about 0.15-0.5 cm3
/g and the surface area is about 95% of the
whole activated carbon surface area. The function of middle pores and large pores is to
mainly transport sorbate molecules to micro-pores. Activated Carbon- methanol is one of
the most commonly used working pair due to the large adsorption quantity and lower
adsorption heat is about 1800-2000 KJ/kg. Lower adsorption heat is necessary for better
values of COP. Activated carbon- methanol is a working pair suitable with solar energy at
temperatures around 1000
C. This pair is not suitable at temperatures greater than 1200
C as
decomposition of methanol occurs at this temperature. This pair has a disadvantage of
requirement of vacuum. The requirement of vacuum inside a system increases
manufacturing complexity and reduces reliability of system as a small amount of air
infiltration seriously affects the performance. The maximum value of X = 0.45 i.e. it can
adsorb up to 45% methanol by mass.
4.4.2 Activated Carbon(AC) fibre and Ammonia
Activated carbon ammonia is another common working pair. Activated carbon-ammonia
also has the same adsorption heat. The working pressure is higher, it is around 15 bar at a
condenser temperature of 400
C. It has a better mass transfer and shorter heating time.
Activated carbon ammonia pair can be used at temperature of 2000
C or above. The

20
disadvantage of this pair is toxicity and pungent odor of ammonia, the incompatibility of
ammonia with copper and relatively smaller value of X. The highest adsorption quantity
of activated carbon with ammonia is 0.29 kg/kg. The smaller value of X is compensated
by large value of latent heat of ammonia.
4.4.3 Silica gel and Water
Silica gel and water is another working pair used in adsorption refrigeration where the
ability of water to act as a refrigerant at lower pressure is utilized. The adsorption heat of
this pair is about 2500 kJ/kg. The desorption temperature required for this pair is very low
it can be up to 500
C. Desorption temperature for this pair should not be more than 1200
C
and generally lower than 900
C is used. The disadvantage of silica gel water adsorption
pair is low adsorption quantity, it is limited to 0.2 kg/kg adsorbent. Another disadvantage
of this pair is to operate below 00
C.
4.4.4 Zeolite and water
The zeolite adsorption pair is utilized in dehumidification, cooling and adsorption
refrigeration systems. The adsorption heat of this pair is about 3300-4200 kJ/kg. The
zeolites are stable at high temperatures hence this pair can be used with heat sources more
than 2000
C. As the desorption temperature is high and the adsorption heat is also high the
performance of this pair is worse than that of activated carbon-ammonia system at
temperature lower than 1500
C. This pair can have higher values of COP and specific
cooling power at temperature above 2000
C. The limitation of this pair is to work below
00
C and as the working pressure is low the mass transfer is also low. The heating time
required for this working pair is more as compared to above mentioned other adsorbent
refrigerant pairs. The maximum amount of water that can be adsorbed in zeolite (X) =
0.261kg/kg.
4.4.5 Calcium chloride and Ammonia
This is one of the most widely used chemical adsorption working pair. The adsorption
capacity of this pair is large. One mole of calcium chloride can adsorb 8 moles of
ammonia and the combination is CaCl2 (8NH3) and four six or eight moles can be
desorbed from this depending on the desorption temperature. The advantage of calcium
chloride ammonia system is its adsorption quantity which is higher than 1 kg/kg of
adsorbent. The disadvantages of this working pair are problem of swelling and
agglomeration during adsorption.

21
5. PERFORMANCE OF SOLAR VAdRS
Experimental setup used in the present study is shown in figure 5.2. It consists of an
evaporator, sorption bed, condenser, refrigerant receiver, capillary tube and measuring
equipment along with necessary valve systems. Typical photographic view of
experimental setup is shown in figure 5.1. Solar radiation transfers the heat to the
sorption material, namely, activated charcoal, for regeneration of refrigerant vapour that
has been adsorbed during earlier cycle. The activated charcoal in powder form is packed
in annular space of co-axial tubes, 6 in number. Inside this tube placed the refrigerant
tube coaxially.
Figure 5.1 Photographic front view of vapor adsorption refrigeration system

22
Figure 5.2 Experimental Setup (Schematic)

23
5.1 SYSTEM PRELIMINARY SETUP
Initially, VAdRS used for the current study is evacuated utilizing a vacuum pump. By
adopting triple vacuum technique, it was ensured that the non-condensable gases present
in the vapor adsorption refrigeration system were removed. R152a was charged then to
break the vacuum. Once again, the system was evacuated and the vacuum was held for
about 24 hours. Finally, R152a refrigerant liquid form was charged into the system
partially filled in the condenser and CRT.
5.2 EXPERIMENTAL PROCEDURE
5.2.1 Heating and desorption
Experiments were carried out in a systematic way. To start with in the morning BV1 and
PRV is closed (figure 5.2), and the sorption bed is exposed to solar irradiation. After a
prolonged time period the system reaches the set pressure. The PRV is used to maintain
the possible pressure in the sorption bed by controlling the generation temperature. The
PRV is opened and the vapour is allowed to enter the condenser. The air-cooled
condenser condenses the desorbed vapour and the liquid adsorbate kept stored in a CRT
through BV2 kept open. The level gauge reading indicates the amount of adsorbate
desorbing from the sorption bed. This process continuous till the mass concentration ratio
of the sorption bed reaches its minimum level.
5.2.2 Cooling and adsorption
Now the sorption bed should be cooled down to make it ready to adsorb vapour from the
evaporator. BV2 is being closed FCV is opened to allow the liquid adsorbate in to
evaporator through the capillary tube. FCV helps to regulate the flow of adsorbate
through the evaporator. A flow meter is used to read out the flowrate through the
evaporator. The vapour refrigerant from the evaporator is adsorbed in the sorption bed
with BV1 remains open. This process continuous till the mass concentration ratio reaches
its maximum. The refrigeration effect of the system can be measured from the cooling
observed in the water bath (evaporator). The pressure and the temperature at different
locations can be measured with the help of suitable measuring equipment. Yet again
sorption bed is heated for complete desorption then follows the next cycle of the VAdRS.

24
5.3 VAdRS PERFORMANCE ANALYSIS
Figure 5.3 Flow chart of performance analysis [15]
Coefficient of performance of single adsorbent bed can be estimated as the ratio of total
refrigeration capacity of the system to the total heat supplied to the system. For
theoretical analysis, the system performance is compared by two parameters, namely,
Carnot COP and theoretical COP.
The Carnot COP can be expressed as,
(5.1)
The theoretical COP is expressed as,
(5.2)
The eq. (5.2) can be re-written as,

25
(5.3)
The specific cooling power is expressed as,
(5.4)
The amount of heat transported (a-b) to the sorption bed is given by,
𝑄 𝑎𝑏=[𝑚(𝐶 𝑝 𝑎𝑑+𝑀 𝑚𝑎𝑥 𝐶 𝑝 𝑟𝑒𝑓)+𝑚 𝑏𝑒𝑑 𝐶 𝑝 𝑏𝑒𝑑](𝑇 𝑏−𝑇 𝑎) (5.5)
The heating is continued during isobaric desorption process (b-c). The valve between
sorption bed and condenser is opened. Condensation process starts and refrigerant vapour
is liquefied in the condenser. In this period, the pressure almost remains constant. This
pressure is known as condenser pressure. Equation 5.6 gives the amount of heat acquired
by the system in this process.
𝑄 𝑏𝑐=[𝑚(𝐶 𝑝 𝑎𝑑+𝑀 𝑚𝑖𝑛 𝐶 𝑝 𝑟𝑒𝑓)+𝑚 𝑏𝑒𝑑 𝐶 𝑝 𝑏𝑒𝑑](𝑇𝑐−𝑇 𝑏)+𝑚Δ𝐻 𝑎(𝑀 𝑚𝑎𝑥−𝑀 𝑚𝑖𝑛) (5.6)
Once valve is closed isosteric cooling period (c-d) begins. During the process adsorbent
pressure is decreased to that of evaporator. Temperature of the bed is the maximum Tc
that is decreased to Td. Heat rejection in (c-d) is given by,
𝑄 𝑐𝑑=[𝑚(𝐶 𝑝 𝑎𝑑+𝑀 𝑚𝑎𝑥 𝐶 𝑝 𝑟𝑒𝑓)+𝑚 𝑏𝑒𝑑 𝐶 𝑝 𝑏𝑒𝑑](𝑇𝑐−𝑇 𝑑) (5.7)
Isobaric adsorption (d-a) begins when the valve is opened and vaporization of adsorbate
in the evaporator is started during adsorbing of refrigerant in the adsorbent. Further, heat
is liberated due to the heat of adsorption. This generated heat is to be removed from the
sorption bed and the temperature of the pair is reduced to Ta.
𝑄 𝑑𝑎=[𝑚(𝐶 𝑝 𝑎𝑑+𝑀 𝑚𝑎𝑥 𝐶 𝑝 𝑟𝑒𝑓)+𝑚 𝑏𝑒𝑑 𝐶 𝑝 𝑏𝑒𝑑](𝑇 𝑑−𝑇 𝑎)+𝑚Δ𝐻 𝑎(𝑀 𝑚𝑎𝑥−𝑀 𝑚𝑖𝑛) (5.8)
Measured parameters from experimentation are Time, Tamb, Gi, Tgen, Pcond, Tcond, Level,
Tw, Flow, Tevap, Tads, Pevap. After conducting the test following parameters are calculated,
a) Cooling capacity (Qevap)
b) Global incident radiation on the collector (Qgi)
c) Heat required to desorb refrigerant in the sorption bed (Qg)
d) Heat rejected at the condenser (Qcond)
e) Coefficient of performance (COPCarnot and COPSolar)

26
5.4 PERFORMANCE
5.4.1 Effect of condenser temperature
Figure 5.4 shows the effect of condenser temperature on COP. It is observed that COP
decreases as the condenser temperature decreases. This decrease in COP attributed to
reduction on refrigerating effect at the given heat input. To maintain the evaporating
capacity, it is necessary to have additional mass of adsorbent in the system. Also, it
appears that the trend of the curve shows a non-linear behaviour of condenser
temperature on COP of the system.
Figure 5.4 Plot of COP vs Tcond, Qevap=1000 kJ/hr
Figure 5.5 Plot of COPCarnot vs Tcond, Qevap=1000 kJ/hr

27
From Figure 5.5 it is understood that Carnot COP remains constant or decrease little
with increase in condenser temperature. This is attributed by lower generation or
desorption temperatures.
5.4.2 Effect of evaporator temperature
Figure 5.6 illustrates the variation of COP with evaporator temperature. It is noted that
an increase in evaporator temperature at the given condenser temperature helps to rise the
refrigeration effect. Hence at a given heat input COP increases with increase in
evaporator temperature. It is further understood that a higher condenser temperature
reduces the refrigerating effect. This is the reason for drop in COP at higher condenser
temperature.
Figure 5.7 shows the variation of Carnot COP with evaporator temperature. But similar to
the condenser temperature, the evaporator temperature also has negligible effect on
Carnot COP of the system. This behaviour is attributed to similar reasons stated for
condenser temperature in figure 5.5
Figure 5.6 Plot of COP vs Tevap, Qevap=1000 kJ/hr

28
Figure 5.7 Plot of COPCarnot vs Tevap, Qevap=1000 kJ/hr
5.4.3 Effect of generation temperature
Figure 5.8 shows the effect of generation temperature on COP at different condenser
temperature. When desorption temperature increases, mass of vapour desorbed increases
therefore the refrigerating capacity increases and hence COP of the system is increasing.
However, after certain desorption temperature, the drop-in concentration ratio plays a
major role and affects the COP. When the change in mass concentration increases, heat
of generation also will increase therefore COP tends to decrease. It is further observed
that higher is the condenser temperature, results in lowering of the COP of the system.
Figure 5.9 presents the effect of generation temperature on the Carnot COP of the system.
Carnot COP of the system increases with increase in generation temperature of the
system. A rise in generation temperature leads to increase in refrigeration capacity of the
system. This causes the Carnot COP to increase with increase in generation temperature
of the system. It is also observed that condenser temperature has no significant effect on
Carnot COP.

29
Figure 5.8 Plot of COP vs Tgen, Qevap=1000 kJ/hr
Figure 5.9 Plot of COPCarnot vs Tgen, Qevap=1000 kJ/hr

30
6. SUMMARY
The range of COP for the Solar VAdRS is 0.2 - 0.7. The development of adsorption
system for refrigeration is promising. An overall thermodynamics-based comparison of
sorption systems shows that the performance of adsorption systems depends highly on
both the adsorption pairs and processes. The technology continues to develop and the cost
of producing power with solar thermal adsorption refrigeration is falling. If the costs of
fossil fuels, transportation, energy conversion, electricity transmission and system
maintenance are taken into account, the cost of energy produced by solar thermal
adsorption systems would be much lower than that for conventional refrigeration
systems.
The intermittent system has its simplicity and cost effectiveness. However, the main
disadvantages such as long adsorption/desorption time have become obstacles for
commercial production of the system. Hence, to compete with conventional vapor
compression technologies, more efforts should be made in enhancing the COP and SCP.
The environmental benefits of this technology and its non-dependence on conventional
energy sources makes it highly attractive for further developments and a potential
alternative to conventional systems in the future. The future of solar refrigeration and air
conditioning seems to be a very good proposition and no doubt will find its place in
future industrial applications. The major limiting factor at present is the shape of energy
so as to make it available whenever it is required, for example at nights and extended
cloudy days when we cannot attain a high enough temperature.

31
7. FUTURE PROSPECTS
Vapour absorption refrigeration system is not widely used due to its limitations. There
is need for certain developments like 1) Cop of the system, we have to improve the cop
of the system. 2) Size of the Condenser, Evaporator and Generator which is reduces the
size of the system. 3) Cost of System. Adsorption technology combined with other
technologies for multi-purpose application seems to be a new trend in the research. This
will widen the area of applications of adsorption technologies and make the adsorption
refrigeration more cost effective. Any method that improves the efficiency even
marginally would improve the economic viability of operating such devices. Thus,
further studies need to be carried out to validate the potential for possible application in
household refrigerators.
Other researches such as multistage and cascade cycles augers well for future for this
technology. Another possibility is combining of the adsorption refrigeration cycle with
other refrigeration cycles to improve the overall performance. For this the use of thermal
energy storage systems due to their long retention capacity of thermal energy without
losses may prove to be beneficial. Recent application of nanotechnology in adsorbent
material development is also very promising. Fluidized bed technology if integrated
with adsorption refrigeration system can also help in addressing the characteristic
weakness of poor heat and mass transfer in fixed bed adsorption cooling systems.

32
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