1. 1
CHAPTER 1
INTRODUCTION OF THE ADSORPTION TECHNIQUE
1.1 INTRODUCTION
Looking at the present scenario, we can easily conclude that we are in the state where
we cannot imagine our life without the involvement of technology. In every sector of
our life we can find a deep impact of products given by the development of technology.
One of those sectors is the area of refrigeration and cooling. This has become a very
important part in our daily life whether it is for air conditioning, for refrigerators, food
storage, etc.
In southern developing countries, up to 30% of food is spoilt due to lack of refrigeration
during transport and storage because conventional refrigeration systems are not
affordable. Furthermore, electric power often is not available in the villages. And that
brings the necessity of the development of solar powered refrigerators.
We, in our project, have taken a step in the process of developing a non-conventional
refrigeration technique bringing adsorption process in action and using sun as power
source. In areas with abundant sunshine, solar radiation is the most easily accessible
energy source. Solar refrigerators can work independently of the electrical network. In
Africa about 1800 solar refrigerators are used to store vaccines (WHO). Usually, cold is
produced by a vapor compression cycle, which is driven by electric power gained by
solar cells. However, the investment of about US$ 2000 is high and the population
cannot afford such systems. In addition, the high-tech production of solar cells and the
service of these refrigerators seem to be difficult in developing countries. Therefore the
solar refrigerator must be extremely simple and reliable; the local industries should be
able to produce and repair it. In this respect adsorption refrigerators look promising.
In the simplest case they consist of two vessels connected by a tube. They need no
mechanical or electrical power, and are driven by low temperature thermal energy,
which is easily gained by solar collectors. The technology of solar collectors is simpler
than that of solar cells and collectors can be built "in a garage”.
In addition to environmental benefits and energy saving, adsorption cooling systems
have many other advantages: simplicity of construction, lack of moving parts, simple
control, quiet operation and low operating costs. Furthermore, compared with
absorption cooling devices, the adsorption system do not require pumps or rectification
columns, they show no problems with corrosion and crystallization, and are less
sensitive to shocks.
Solar adsorption refrigeration is an option to overtake the drawbacks of the conventional
cooling system. The adsorption refrigeration is based on the evaporation and
condensation of a refrigerant combined with adsorption. This project will describes the
design and fabrication of the experimental chamber, the experimental procedure and its
feasibility towards development of an alternative eco-friendly refrigeration cycle for

2. 2
replacement of chlorofluorocarbons. The objective of this project is to establish an
alternative eco-friendly refrigeration cycle for producing a temperature usually
encountered in a conventional refrigerator.
1.2 AIM AND OBJECTIVES OF THE PROJECT
The main aim of this project is to work on the idea of harnessing the solar heat for the
purpose of adsorption phenomena and develop a model of an eco-friendly refrigerator
system.
To achieve the above mentioned research aim, the project objectives are set out below:
1. Review of theoretical and experimental research work on adsorption
refrigeration cycles.
2. Review of various adsorbents to understand their advantages and disadvantages
and the parameters that are used in evaluating of new materials.
3. Review the characteristics of the adsorbent-adsorbate pair i.e. Silica Gel and
Water.
4. To find out the areas of improvement in the Adsorption Refrigeration System.
1.3 HISTORY
Industrial design and development of adsorption cooling systems started in the 1920s by
using silica gel and sulfur dioxide, Miller. However, because of the new development of
CFC refrigerants and the development of mechanical vapor-compression the adsorption
cooling technology was abandoned until the 1970s when IGT conducted a technical
feasibility study of water vapor adsorption cooling system. However, this technology
was not as popular as the mechanical vapor compression driven cooling system in the
1970s. Two design and development companies, Tchernev and Meunier started work on
adsorption working pairs to be used in adsorption cooling systems. This was used for
the cooling of vaccines in developing countries. However, because of this development
the interest in this type of technology started to grew rapidly in the 1980s with many
cooling system researchers worldwide working on a variety of adsorption cooling
system. A company called Nishiyodo Kuchou Manufacturing Company (Japan) in 1986,
designed and manufactured the first industrial adsorption cooling system. Since then,
the adsorption chiller has been used and closely evaluated in a wide area of applications
in Japan, Europe and USA with high initial acceptance.
The adsorption phenomenon was applied at ancient times, where charcoal was the
dominant adsorbent. It was used to reduce copper, zinc and tin ores for bronze
manufacturing by Egyptians and Sumerians 3750BC. The first quantitative observations
were carried out by Scheele 1773 and Fontana 1777, where they experimentally
reported some gases adsorption by charcoal and clays. Saussure 1814 reported that all
gases can be taken up by porous materials (sea foam, cork, charcoal and asbestos)
exothermally.
The first invention of an adsorption cooling system happened in 1848, when Faraday
demonstrated an adsorption refrigeration system utilizing ammonia and silver chloride
as working pair. In 1929, Hulse and Miller described an adsorption system for the air
conditioning of railway carriages using silica gel and sulphur dioxide as the working

3. 3
pair. Due to the low performance of adsorption cooling systems compared to the vapor
compression systems, research and development of adsorption cooling systems was
slowed down. In the last three decades, the adsorption cooling systems are laboratory
and commercially developed to be applied in different applications. The adsorption
cooling development is due to the need of replacing the conventional vapor compression
systems to meet the new environmental regulations.
Fig1.1: Mechanical Adsorption Chiller
Places with high insulation usually have a large demand for cooling to preserve food,
drugs and vaccines, and much research has been devoted to develop machines that could
employ solar energy efficiently for such purpose. The development of adsorption
refrigeration powered by solar energy emerged in the late 1970s following the pioneer
work of Tchernev, who studied a basic solid adsorption cycle with the working pair
zeolite-water. Since then a number of studies have been carried out, both numerically
and experimentally, but the costs of these system still make them non-competitive for
commercialization.
Based on the results of a previous study, Pons and Guilleminot concluded that the solid
adsorption system could be the basis for efficient solar powered refrigerators, and they
developed a prototype with the pair activated carbon-methanol. The machine produced
almost 6kg of ice per m2 of solar panel when the solar heat was about 20 MJ day-1 , with
a solar COP of 0.12. This rate of ice production remains one of the highest obtained by
a solar powered ice maker.
Critoph mentioned a solar vaccine refrigerator studied in his laboratory in the early
1990s. Such machines could keep the cold box at 0˚C during the daytime after one
adsorption cycle performed during the previous night.

4. 4
Fig 1.2- Solar Adsorption Chiller
1.4 ENVIRONMENTALREGULATIONS
The environmental regulations were adopted to solve the problems of ozone depletion
and global warming, which are the major problems nowadays. The thinning of ozone
layer that absorbs 98% of the sun’s high frequency ultraviolet lights has been confirmed
in 1980s. In 1985, Vienna convention provided a framework for Montreal protocol that
ratified ozone depleting substances in 1987. The original protocol has been amended
several times for developed and developing countries, between 1990 (London) – 2007
(Montreal). Conventional vapor compression refrigeration cycles are utilized ozone
depleting refrigerants such as CFCs and HCFCs. The Montreal protocol ratified to stop
the production of CFCs in developed countries in 1995 and planned to phase-out
HCFCs completely by 2030.
Fig 1.3: Montreal protocol HCFCs phase-out plan
The global warming is the phenomenon of increasing the Earth’s average temperature
due to the trapping of energy emitted from the Earth. This amount of energy is about 1/3

5. 5
of the incoming solar radiation and is trapped by means of greenhouse gases (GHG).
Some trapping of heat is desired, but excess trapping will affect the natural environment
balance by melting polar ice caps and more evaporation of ocean water. Polar ice caps
melting causes unusual floods and ocean water evaporation causes more clouds cover
and hence reduces the incoming solar radiation to offset the greenhouse effect.
In 1997, the Kyoto protocol was initially adopted in Japan to stabilize greenhouse gas
concentrations in the atmosphere at a level that would prevent dangerous anthropogenic
interface with climate system. The protocol cue into force in 2005, and 191 states have
ratified the protocol in September 2011. The protocol addressed six greenhouse gases
namely; carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O),
Hydrofluorocarbon (HFC), Perfluorocarbons (CxFy) and Sulphur hexafluoride (SF8). It
is statistically predicted that the equivalent CO2 level will be doubled by 2050, tripled
by 2100 and quadruple by 2150, even if Kyoto protocol is adopted. Many vapor
compression refrigeration systems utilize HFCs, but the direct effect of the released
HFCs to the atmosphere is negligible. HFCs contributed about 3% during time period
2000-2100 of the total contributed by all the greenhouse gases. However, electrically
driven vapor compression refrigeration systems contribute about 15% of the world man
made CO2 output, and hence contribute more significantly to carbon footprint and
global warming compared with refrigerant contribution. Industrial countries that ratified
Kyoto protocol have legally bound targets and timetables for mandatory cutting
greenhouse gas emissions.
1.5 ADVANTAGES OF ADSORPTION OVER ABSORPTION
REFRIGERATION
Attribute Adsorption Absorption
Heat source • It is powered by sources of wide • Very sensitive against source
temperature range. temperature and the variation
• Temperature as low as 50˚C can Must Be tightly Controlled
be used as heat source, while between 82˚C and 100˚C.
Heat sources With temperature • Heat source must be higher than
close to 500˚C can be used 70˚C to avoid the crystallization
directly without producing any problem, even in two-stage
kind of corrosion problem. cycle.
• There is no limitation for the low • Severe corrosion would start to
temperature reservoir. occur For temperatures Above
200˚.

6. 6
• Low temperature reservoir must
be 18-29˚C
Operating • It Is utilized by solid sorbents • It is utilized by liquid sorbent
Consideration And hence it is suitable for and hence it is suitable for
conditions With serious Stationary Units only, Where
vibration, such as in fishing unfavourable absorbent Flow
boats and locomotives. from the generator / absorber to
• It Is almost noiseless system, the evaporator / condenser.
where there are not many • Daily shutdown due to the
moving parts. dilution of sorbent solution
• Operation possibility over
8000hr per year.
Maintenance • There are No special • It needs regular monitoring and
requirements For maintenance, maintenance for:
where few used moving parts − Liquid analysis – pumps
(vacuum pump). − Control system
• Annual cleaning of condenser − Back up boiler
tubes is required. − Air leakage
• Simple Control system is − Sorbent exchange
required − Heat exchanger replacement due
to salt corrosion.
Lifetime • It has Relatively very long • The maximum life time is 7-9
lifetime and there are no special years,due to the problem of salt
disposal requirements. corrosion.
Table 1.1: Advantages of Adsorption over Absorption Refrigeration

7. 7
1.6 TERMS RELATED TO THE SYSTEM
a. ADSORPTION
Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or
dissolved solid to a surface. This process creates a film of the adsorbate on the
surface of adsorbent. According to IUPAC, adsorption is the increase in the
concentration of the substance at the interface of the condensed and a liquid or
gaseous layer owing to operation of surface forces.
This process differs from absorption, in which a fluid is dissolved by or
permeates a liquid or solid respectively. Adsorption is a surface-based process
while absorption involves the whole volume of the material. Similar to the
surface tension, adsorption is a consequence of surface energy.
Types of Adsorption:
Types of adsorption will depend upon the vacuum pressure present between
vapour or gas molecules and porous adsorbent, adsorption are classified into two
types:
1. Physical adsorption (Physisorption):
If a force of attraction existing between adsorbate and porous material surface
this is the Vander Waal’s forces, the adsorption is physical adsorption. In
physical adsorption the attraction between the vapour or gas and porous material
surface are weak, hence this type of adsorption can be easily reversed by
heating.
2. Chemical adsorption (Chemisorption):
If the force of attraction existing between vapour or gas and porous material
surface are the same strength as chemical bonds, this type of adsorption is
named chemical adsorption. In chemisorption the force of attraction is strong
therefore chemisorption adsorption cannot be easily reversed.
Factors Affecting Adsorption
The rate of adsorption is governed by the following factors:
 Type of adsorbate and adsorbent.
 The surface area of adsorbent.
 Experimental conditions.
Adsorption isotherms measured on a range of gas - solid systems have a variety
of forms, and can be grouped into one of six types according to the International
Union of Pure Applied Chemistry (IUPAC) Classification 1994 with the
majority resulting from physisorption, figure shows the six types of isotherms,
which only hold for the adsorption of a single component gas within its
condensable range, and are very useful for the study of porous materials.

8. 8
b. ADSORBENT
These are the substances used for adsorbing the adsorbate. Eg- zeolite, silica gel,
activated carbon, etc. Adsorbents are used usually in the form of spherical
pallets, rods, moldings,, or monoliths with a hydrodynamic radius between 0.25
and 5 mm. They must have high abrasion resistance, high thermal stability and
small pore diameters, which results in higher exposed surface area and hence
high capacity of adsorption. The adsorbents must also have a distinct pore
structure that enables fast transport of the gaseous vapors.
The adsorbents are classified based on the adsorption process as: physical
adsorbents, chemical adsorbents and composite adsorbents. This section presents
in details the characteristics of each type of these adsorbent:
 Physical Adsorbents
Physical adsorbents are usually porous materials with different pore sizes. It
adsorbs the adsorbate (refrigerant) by an intermolecular force called (Van der
Waals force). The physical adsorbent can retain its original properties after
removing the refrigerant by adding heat during the desorption process as
explained previously. This advantage lets the physical adsorbent be commonly
used in practical application. The performance of adsorption refrigeration cycle
increases when the amount of cycled refrigerant increases. Most of the physical
adsorbents suffer from low adsorption kinetics and hence low cyclic refrigerant
flow rate. The main physical adsorbent classes are mesoporous silicates,
zeolites, metalaluminophosphates, porous carbons and metal organic
frameworks.
 Chemical Adsorbents
Chemical adsorbent sorbs the adsorbate (refrigerant) chemically by Valence
force, where one layer of refrigerant reacts with the surface molecules of the
adsorbent. Chemical adsorbent sorbs more adsorbate at higher rate compared to
physical adsorbent. Its stability is lower than a physical adsorbent, where

9. 9
chemical pair molecules never keep their original state which limits its practical
applications. Chemical adsorbents suffer from swelling and agglomeration
which negatively affect the heat and mass transfer performance, especially in
cycles that operate under low pressure. Chemical adsorbents mainly include
metal chlorides, metal hydrides and metal oxides.
 Chemical/ Physical Adsorbents Composite
Adsorption and desorption are respectively exothermic and endothermic
processes and the chemi-sorption heat is higher than the physi-sorption heat.
Higher adsorption rate (kinetics) means more refrigerant flow rate and hence
better cooling capacity. A chemical adsorbent using salt of poor heat and mass
transfer due to low thermal conductivity and with agglomeration phenomenon is
not practical especially in low pressure systems. The aim of using composite
adsorbents is to enhance the performance of physical adsorbents (increase the
adsorption capacity) and avoid the aforementioned drawbacks of the chemical
adsorbents (swelling, agglomeration and poor conductivity). Examples of
composite adsorbents, the combination between metal chloride and activated
carbon fibres, expanded graphite, silica gel or zeolite.
Fig 1.4: Silica Gel Fig1.5- Activated Carbon
Porous Adsorbent Materials:
Almost all porous adsorbents materials have the capacity to adsorb water vapour
and gases by physical and or chemical forces. The porous media materials used
on adsorb purpose are called the adsorbents. The moisture or gases adsorbed can
be driven out from the adsorbent by heating, and the cooled 'dry' adsorbents can
adsorb moisture or gases again. The popular adsorbents are silica-gel, zeolite,
and activated carbon.
These porous media materials can be subdivided into 3 categories, set out
by IUPAC :
 Microporous materials: 0.2–2 nm
 Mesoporous materials: 2–50 nm
 Macroporous materials: 50–1000 nm
The common porous adsorbents used as packing in a adsorption bed
cooling system are silica gel, zeolite and activated carbon

10. 10
c. ADSORBATE
An adsorbate is any substance that has undergone adsorption on the surface of
adsorbent. These substances get stickled on the surface of the solid substance
(adsorbent) and get released upon getting heat from an external source. Eg- water,
ammonia,etc.
There are many refrigerants utilized in adsorption refrigeration systems, but the
appropriate refrigerant need to be selected based on a number of considerations
such as:
• Latent heat of vaporization: where the higher the refrigerant latent heats of
vaporization, the better the performance of the cycle.
• Thermal stability: stable refrigerant thermophysical properties mean stable
cycle over the operating temperature range.
• Environmental friendly: most of adsorption refrigeration cycles utilize
environmentally friendly refrigerants with no ozone depletion and low global
warming potential. Natural refrigerants such as water, ammonia are most
commonly used ones.
• Flammability: some of the refrigerants utilized in adsorption refrigeration
systems are flammable within certain concentration. The flammability issue
should be taken into account especially when high generation temperature is
used in the cycle.
• Toxicity: some of the refrigerants applied in adsorption refrigeration cycle are
toxic and hence stringent safety measures should be implemented which may
limit their application.
• Explosion: hydrogen refrigerant utilized with salts hydrides, it is an explosive
one. This means more consideration and initial cost during manufacturing of
such type of cycle.
• Compatibility: some refrigerants are corrosive and need special material of
relatively high cost. Thus the machines cost increases limiting its market
potential. The optimum refrigerant is the one that satisfies the maximum number
of consideration with high grade. The commonly applied refrigerants in
adsorption cycles are water, ammonia, methanol and ethanol. Some other
refrigerants are used in the adsorption technology, but not commercially applied
such as hydrogen, oxygen, methyl alcohol, R134a, R22, R732 and R407.
d. COEFFICIENT OF PERFORMANCE (COP)
COP is the ratio of heat taken from the space to be cooled during evaporation of
the refrigerant to the amount of heat delivered to the system for heating and
desorption.
𝐶𝑂𝑃 =
𝑄 𝑢𝑠𝑒𝑓𝑢𝑙
𝑄 𝑑𝑎𝑖𝑙𝑦
(1.1)

11. 11
Where,
Qdaily is the solar radiation falling on the collector surface daily;
Quseful is the effective heat has to be removed from the water
COP is highly dependent on the temperature of the heat source: the
higher the temperature, the greater the COP value. However, above a certain
temperature, changes are small.
e. SPECIFIC COOLING CAPACITY (SCP)
The specific cooling capacity SCP is defined as cooling capacity per kg of the
adsorbent.
𝑆𝐶𝑃 =
𝑄 𝑢𝑠𝑒𝑓𝑢𝑙
𝑚 𝑎
(1.2)
Where,
ma is the mass of the adsorbent used.
1.7 COMPONENTS OF THE SYSTEM
a. ADSORBER TANK
It is the vessel which contains the mixture of adsorbent and adsorbate in a proper ratio.
Inside it there contains a copper tube in which hot water from collector flows through.
There is a pressure gauge at the top which shows the pressure inside the vessel. An
outlet is provided for the vapor to flow into the condenser and an inlet is also present for
the vapor to come in from the evaporator and get adsorbed. At one time, only one of
them is opened with the help of manual valves.
Fig 1.6
b. CONDENSER
A condenser is a device or unit used to condense a substance from it gaseous to its
liquid state, by cooling it. In so doing, the latent heat is given up by the substance, and
will transfer to the condenser coolant.
There are basically two types of condensers: Air Cooled & Water Cooled.

12. 12
Fig 1.7
c. SOLAR COLLECTOR
A solar collector collects heat by absorbing sunlight. A collector is a device for
capturing radiation. It transforms solar radiation into heat and transfers that heat to a
medium (water, solar fluid or air).
Solar collectors are either non-concentrating or concentrating. In the non-concentrating
type, the collector area is the same as the absorber area. In these types the whole solar
panel absorbs light. Concentrating collectors have bigger interceptor than absorber.
Flat-plate and evacuated-tube solar collectors are used to collect heat for space heating,
domestic hot water or cooling with an adsorption chiller.
Fig 1.8
d. EVAPORATOR
An evaporator is a device used to turn the liquid form of the chemical into its gaseous
form. The liquid is evaporated or vaporized into a gas.
An evaporator is used in air-conditioning system to allow a compressed cooling
chemical, such as Freon, to evaporate from liquid to gas while absorbing heat in the

13. 13
process. It can also be used to remove water or other liquids from mixtures. The process
of evaporation is widely used to concentrate foods and chemicals as well as salvage
solvents.
Fig 1.9

14. 14
CHAPTER 2
LAYOUT AND PRINCIPLE OF ADSORPTION REFRIGERATOR
2.1 BASIC LAYOUT OF THE SYSTEM
Fig 2.1- Layout of Adsorption Refrigeration
Description: Basically the system is a Single Bed Intermittent Cooling System. It
consists of the adsorber which is filled with the mixture of adsorbent and the adsorbate.
This mixture is being heated with the hot water provided by the solar flat plate collector.
There is a pressure gauge which shows the pressure inside the adsorber and a manual
valve which is opened after reaching the required pressure. A condenser is present for
condensing the vapor from adsorber and then the evaporator for cooling purpose. The
arrangement of the components is shown in fig.
The whole arrangement is air tight and the circulation is via insulated pipes which
reduces the loss of heat to the environment. There is regular monitoring of the system so
as to check out the proper functioning of the system. The components are kept at
different levels so as to maintain the head for proper flow of the fluid in the system.

15. 15
2.2 OPERATING PRINCIPLE
Fig 2.2
Principle: The system basically works on two steps which are described below-
Step 1: Desorption
Drying of the adsorbent (zeolite or silica gel) is dried by heat input. Water vapor flows
into the condenser and is liquefied under heat emission by a water-cooled or air-cooled
condenser. When the adsorbent is dry, the heated water input is stopped and the
condenser valve closes.
Step 2: Adsorption
The condensate is allowed to circulate in evaporator where it absorbs heat from the
stuffs to be cooled. This water vapor is then made to flow to the adsorber where water
vapor is adsorbed on the surface of the adsorbent. After a cool down phase the reverse
reaction and the evaporation of the liquid condensate starts. The valve to the evaporator
opens and the dry adsorbent aspirates water vapor. In the evaporator, water evaporates
and generates cold, which can be used for air-conditioning. During the adsorption
process heat is rejected which has to be dissipated. In a final phase, the condensate is
returned to the evaporator and the circuit closed.

16. 16
The advantages of this working principle are no moving parts, no electricity involved at
all and its structural simplicity. The operation of the valve is not essential; a system
without the valve can still work.
Fig 2.3- Adsorption Step Fig 2.4- Desorption Step
2.3 PROCESSESINVOLVED
The system comprises of four steps. They are described below:
Phase 1: ISOSTERIC HEATING PROCESS 1-2
Fig 2.5

17. 17
The adsorbent temperature increases, which induces a pressure increase, from the
evaporation pressure up to the condensation pressure. The adsorbent releases the
adsorbate in this phase and the pressure inside the adsorber increases due to the closing
of the valve at the outlet of the adsorber. The heat at this stage is equal to the latent heat
of the adsorbate. This period is equivalent to the “compression” phase in compression
cycles.
Phase 2: ISOBARIC HEATING PROCESS 2-3
Fig 2.6
During this period, the adsorber continues receiving heat while being connected to the
condenser, which now superimposes its pressure. The adsorbent temperature continues
increasing, which induces desorption of vapor. This desorbed vapor is liquefied in the
condenser. The condensation heat is released to the second heat sink at intermediate
temperature.
This period is equivalent to the "condensation" in compression cycles.

18. 18
Phase 3: ISOSTERIC COOLING PROCESS 3-4
Fig 2.7
During this period, the adsorber releases heat while being closed. The adsorbent
temperature decreases, which induces the pressure decrease from the condensation
pressure down to the evaporation pressure.
This period is equivalent to the “expansion” in compression cycles.
Phase 4: ISOBARIC COOLING PROCESS 4-1
Fig 2.8

19. 19
During this period, the adsorber continues releasing heat while being connected to the
evaporator, which now superimposes its pressure. The adsorbent temperature continues
decreasing, which induces adsorption of vapor. This adsorbed vapor is evaporated in the
evaporator. The evaporation heat is supplied by the heat source at low temperature.
This period is equivalent to the "evaporation" in compression cycles.
2.4 MATHEMATICAL MODEL
The present simulation study reports a numerical transient model for the adsorption
system based on energy and mass balance. The system design parameters and operating
conditions are input to the model and system performance indicators viz. coefficient of
performance (COP), specific cooling capacity (SCC) and specific daily water
production (SDWP) are computed by the model. The numerical values of various
system parameters and operating conditions used in the simulation are as tabulated in
table 1. The intermediate pressure assumed during two stage operation is given by
which is a close approximation of the optimal value [18]. The pressure drops in steam
flow circuit are neglected. Further, it is assumed that hot water and cold water tanks are
sufficiently large and provide constant temperature water output. The adsorption
dynamics is modeled using the linear driving force(LDF) relation in this study:
where the expression for effective diffusivity Deff used is as reported by Sakoda and
Suzuki .The Tόth isotherm relation is used to estimate the equilibrium uptake for the
RD type silica gel +water pair. Recently there have been studies reporting improved
models for adsorption kinetics. However, these models are highly non-linear and
computationally intensive and hence are not used in this study. Lumped model approach
is utilized to describe the energy balance in adsorber beds i.e. the silica gel, adsorbed
steam and the body of heat exchangers are assumed to be at same temperature. Further,
the adsorbed phase is modelled as saturated liquid water. Using the aforementioned
assumptions, the energy balance for the stage-1 adsorber bed during adsorption and pre
cooling process can be written in an integrated form:
q=1 for adsorption phase and 0 for pre-cooling phase. A similar equation is used for
modelling desorption and preheating processes. The evaporator energy balance is

20. 20
divided into three parts. During the initial period of tsw only one bed from stage-1
adsorber beds interacts directly with the evaporator. Hence, the energy balance of the
evaporator during this period leads to the following equation:
However, after this period two beds get connected to the evaporator and adsorb steam
from it with a phase difference, during which the energy balance may be written as:
Furthermore, for t > tads bed-1 proceeds to preheating process and the evaporator
interacts only with the bed-2. Hence during this period the energy balance is given by:
For a single-stage system, the beds from stage-1 directly interact with the condenser
wherein the temporal scheme of modelling the condenser is similar to the evaporator.
The condenser energy balance can also be written in three parts as follows:
In a two-stage system the steam desorbed by stage-1 beds, instead of reaching the
condenser, is adsorbed by the stage-2 beds which desorbs it into the condenser at a
higher pressure. Thus, the rate of desorption from stage-1 needs to be coupled to the rate
of adsorption of stage-2 adsorber beds. For the stage-1 desorption process and stage-2
adsorption process the following equations can be written:

21. 21
From mass balance between the two stages one can conclude that the amount of
desorbed steam from stage-1 given by
and amount of adsorbed steam in stage-2 given by
have to be equal. Thus, the mass transfer between the beds at any given time step will
be governed by the slower of the two beds. To numerically model this inter-stage mass
balance in each time step, following criterion is enforced:
The energy balance for stage-2 desorption and pre-heating processes is similar to
equation 3, and is given by:
LMTD method is used to model heat transfer to heating/cooling media. Cooling/heating
media outlet temperatures are given by the following relations:

22. 22
During the switching process i.e. precooling and preheating processes, the pressure
changes in the bed are affected by mass balance across adsorbed and vapour phase
within the bed, the vapour phase pressure, the void volume of the bed (Vbed ) and
adsorption kinetics which in turn is influenced by Tόth isotherm relation.
The mass balance of water in vapour and adsorbed phases can be written as:
Assuming ideal gas behavior of the steam, the bed pressure at any time can then be
estimated by using the ideal gas relation:
The numerical modelling for adsorber bed starts from adsorption process and hence the
initial condition chosen corresponds to the end of pre-cooling process. The initial
temperature is chosen as ambient temperature, the initial pressure as evaporator pressure
and the initial uptake corresponds to heat source temperature and evaporator pressure.
The results reported are after cyclical steady state is achieved.
Various input parameters for the present model include the cycle time and ambient
temperature. The cycle time comprises of sorption time and switching time. The
sorption time determines the degree of saturation of the adsorber beds at the end of
adsorption/desorption processes whereas the switching time determines the pressure at

23. 23
the end of pre-heating and pre-cooling process. The switching time chosen in this study
is such that the adsorber bed pressure at the end of preheating phase is enough to
overcome the plenum/condenser pressure. The numerical values for switching time
assumed are listed in tables2 and 3 for single and two stage systems respectively. The
output parameters from the model are the performance indicators of the adsorption
system viz. the specific cooling capacity (SCC), coefficient of performance (COP) and
specific daily water production (SDWP) defined below:

24. 24
CHAPTER 3
DESIGN AND SETUP OF THE SYSTEM
3.1 INITIAL PROPOSEDDESIGN
Fig 3.1
Description:
Initially we were trying to make an adsorber bed containing the mixture of adsorbent
and adsorbate in it. The adsorbent used by us is Silica Gel and the adsorbate is Water.
The mixture was fed inside the solar collector box and the direct heating of the mixture
had to be carried out. There were valves at different points which were to be opened and
closed at the regular interval so as to make the fluid flow at different components of the
system.
It can be seen in the above layout that the adsorption and desorption process, both are
carried out at the collector. There was no any requirement of heating agent as sunlight
itself is carrying out the heating process. The condenser was air-cooled type and there
was a requirement of vacuum pump so as to remove air from the system and also to
assist the proper flow of the refrigerant.

25. 25
Specifications to be rendered
Table 3.1

26. 26
Experiment to be carried out
Time Valve 1 Valve 2 Valve 4 Process
08.00 Close Close Close Heat
adsorbent
11.00 Close Open Close Heat
adsorbent
Condensation
19.00-07.00 Open Close Open Evaporation:
Cooling cycle
Table 3.2
Proposed view of the System
Fig 3.2

27. 27
3.2 FAILURE OF THE DESIGN
While performing works at the initial stage, we came across some design problems and
the proposed design failed. There were some limitations and challenges which were
difficult to be sorted out.
Causes of Failure:
 The proposed idea of filling up the solar collector box with the mixture of
adsorbent and adsorbate didn’t work. It was difficult for us to maintain pressure
inside the collector since air leakage was a big issue.
 The vacuum to be maintained was also creating problem.
 The feasibility of the refrigerant flow was a big question since the pressure
inside the adsorber bed cannot be maintained at the constant level.
 The wooden box was not efficient enough to hold the mixture and to do proper
heating inside.
 The water-cooled condenser was not applicable since it required an extra water
pump to make the flow of water.
3.3 MODIFICATION OF THE DESIGN
Fig 3.3

28. 28
Modification No. 1
Since it was difficult for us to make a solar collector that will hold the mixture of
adsorbent and adsorbate, we made a separate adsorber tank which contains a coil of
copper tube in which the hot water from solar collector flows and heats the mixture.
That means we are using water as a heating agent and keeping the adsorber pair in a
separate adsorber tank. This helped us in creating a high pressure vapor inside the
adsorber tank. Also the requirement of creating vacuum inside the solar collector was
eliminated.
For the efficient heating of the water inside the solar collector we made the use of
series of convex lenses whose focuses were on the tube in which water was flowing.
This helped us in getting very hot water in a very low period of time. It was a kind of
concentrating type solar collector which concentrated the heat of sun on the tube for a
quick and efficient heating of the water inside the tube.
Fig 3.4
Fig 3.5
COPPERTUBE INSIDETHE
ADSORBERTANK
USE OFSERIES OF LENS INSTEAD
OF FLAT PLATE FOREFFICIENT
HEATING

29. 29
FAILURE OF THE USE OF LENS CONCEPT
As expected lens was very much efficient in heating the water and we were getting hot
water in no time. But the problem was the heating was not consistent as the focus of the
lens changes when the position of sun changes and the plywood we used blocked the
rays of sun. Every time we need to rearrange the collector box and bring the focus of
lenses on the tube.
Modification No. 2
Since the concept of lens failed and we were not getting the hot water consistently, we
again switch to the flat plate concept and replace the lens panel with the glass plate. The
heating was slow and the temperature rise was not as much as concentrating lens panel
but the heating was consistent and it was not required to rearrange the solar collector.
Fig 3.6
REPLACEMENT OF LENS PANEL
WITH THE FLAT PLATE FOR THE
PURPOSEOF CONSISTENT
HEATING

30. 30
CHAPTER 4
PERFORMANCE CHARACTERISTICS AND EVALUATION OF
THE SYSTEM
4.1 ADSORBENT-ADSORBATEPAIRS
The selection of any pair of adsorbent/adsorbate depends on certain desirable
characteristics
these are listed below:
(i) Evaporation temperature below 0˚C.
(ii) Small size of molecules such that it can easily be adsorbed into the adsorbent.
(iii) Microspores of diameter less than 20 A.
(iv) High latent heat of vaporization and low specific volume.
(v) Thermally stable with the adsorbent at the cycle operating temperature ranges.
(vi) Non-toxic, non-corrosive and non-flammable.
(vii) Low saturation pressures (above atmospheric) at normal operating temperature.
Evaluating adsorbent or adsorbate (refrigerant) independently is not sufficient, where
adsorption characteristics vary based on adsorption pairs. Table presents the
characteristics of the most commonly used adsorption pairs based on the practical cyclic
operating conditions.
The best adsorption pair is the one that satisfies the important requirements which
differs depending on the application. Herein, a comparison has been made for the
commonly used and applied adsorption pairs based on 16 criteria. For each criterion the
best adsorption pair is marked by 5 and the worst is marked by 1. The same weight is
used for each criterion due to their equal importance. For example, complex
manufacturing techniques influence the capital cost and hence the commercialization of
the system. On the other hand, the temperature and quantity of energy required for
adsorption influences the energy savings and the range of industries that can benefit
from such systems. Therefore they should be equally weighted.
At present, three types of working adsorbate and adsorbent, respectively, are favored for
pairing for use in adsorption refrigeration technology: ammonia, methanol and water for
adsorbate and activated carbon, silica-gel and zeolite for adsorbent.

31. 31
Table 4.1: Characteristics of commonly used adsorption pairs
Criteria
AC, ACF/ AC, ACF/ AC, ACF/ AC, ACF/ Silica-gel/ Zeolites/
Ammonia Methanol Ethanol R134a Water Water
Adsorption rate 2.7 5 3.3 3.7 2.9 1
Adsorption heat 4 4 5 3.8 2.8 1
Desorption temperature 2.4 4 4 4.4 5 1
Maximum recovered
5 1 2.4 4.7 3.2 3.2
Temp
Vaporization Latent heat 3.3 2.7 2.2 1 5 5
Manufacturing complexes 5 2.9 1.6 4.8 1 1

32. 32
Thermal stability 5 1 5 5 5 5
ODP 5 5 5 5 5 5
GWP 5 5 5 1 5 5
Non-toxicity 1 4 4 5 5 5
Non-flammability 1 1 1 5 5 5
Non-explosive 2.2 1 1 1.9 5 5
Refrigerant compatibility 1 4 4 5 4 4
Refrigerant solidification 4.1 5 2.6 4.8 1 1
Average COP and SCE 1 3.9 4.4 1.2 5 5
Cost 3 3 3 3 5 4
Sum 50.7 52.5 53.5 59.3 62.7 56.2
Table 4.2: Evaluation of commonly used Adsorption Pairs
We, in our project, have selected Silica Gel and Water as the adsorption pair and
studied the characteristics and properties of the pair using as the adsorbent and
adsorbate respectively in our system.
4.2 SILICA GEL
Silica gels have been the object of many studies in adsorption cooling in recent years.
This is due to the adsorption capability of water vapor because of the physical porous
structure of silica gel and large surface area. It has the adsorption capability to adsorb
50% of its mass of vapor without changing its mass. The adsorption ability of silica gel
increases when the polarity increases. One hydroxyl can adsorb one molecule of water.

33. 33
Each kind of silica gel has only one type of pore, which usually is confined in narrow
channels. The pore diameters of common silica gel are 2, 3 nm (A type) and 0.7 nm (B
type), and the specific surface area is about 100–1000 m2/g. Type A- silica gel is a fine
pore silica gel it has a large internal surface area. Having a high moisture-adsorbing
capacity at low humidity and is used as an adsorbent in adsorption cooling system. Type
B contains large pores so type B adsorbs water vapor at low heat and releases it at high
heat so this type of silica gel would be more practical for system design to desorbs water
vapor at high humidity and adsorbs at low humidity. Type C silica gel is also fine pore
silica gel. It is known as macro-pored silica gel available in spherical this type will also
work as a good adsorbent in adsorption cooling system. It is important to compare the
adsorption capacity of different types of silica gels as this will help to determine which
silica gel has the best performance for the different design configurations.
Silica gel–water belongs to low temperature working pairs, which can be driven by heat
sources of between 60°C and 85°C under low pressure. In silica gel, silica attached with
the grains of hydrated SiO4. In silica gel, adsorption occurs with the presence of a
hydroxyl group in its structure. The COP depends on the polarization of the hydroxyl
ions which are present in silica gel structure which form hydrogen bonds with oxides.
The average pore size of silica gel is approximately 650m2/g.
Silica gel is produced by the partial dehydration of silicic acid polymer (SiO2).nH2O.
In silica gel and water combination water is used as a refrigerant with the silica-gel
adsorbent.
The adsorption–desorption process is
SiO2.(n−1)H2O (s)+H2O (v)↔SiO2.nH2O (s)+ΔH
Where,
ΔH denotes the amount of heat produced during the adsorption process.

34. 34
Fig 4.1
4.3 BET THEORY
The BET equation is an accepted equation applied to the explanation of the physical
adsorption process. The adsorption method which the BET equation is based describes
the multilayer physical adsorption on the basis of the kinetic method proposed by
Brunauer, Emmett, and Teller in (1938).
The BET adsorption theory is an addition of the Langmuir theory, which is the theory
for monolayer to multilayer adsorption with the following:
(a) Vapour or gas molecules physically adsorb on to a porous adsorbent in layers.
(b) The BET equation is applied to each layer of vapour or gas molecules.
The resulting BET equation is expressed by:

35. 35
P and P0 are the balance and the saturation pressure of adsorbents at the temperature of
adsorption, v is the adsorbed gas or vapour and vm is the adsorbed vapour amount. c is
the BET constant which is:
E1 is the of adsorption for the vapour layer one and EL is for the vapour layer two and
upper layers (see figure.15) for a 3D representation of a multilayer of water vapour
sites.
Fig 4.2
4.4EXPERIMENTSCARRIED OUT
Experiment No 1:
We filled up the adsorber tank with silica gel and water in the ratio 1:3 and set the
apparatus in the required form. After that we left it in the open space of terrace
where there was abundance of sunlight. We already knew that it was a long process
and will take a long period of time to generate pressure inside the adsorber tank. We
did our best to make it airtight and leak proof. For that we used tools like m-seal,
liquid plastic sealing and so on.
The system was arranged according to the flow to be generated and the calculated
heights and angles of the components were set. The joints were properly checked
and the system was left on the terrace for about 4 hours.

36. 36
Fig 4.3
Result: After the duration of 4 hours we found out that there was no rise of pressure
inside the adsorber tank which depicted that there was no generation of vapor inside. On
checking the pipes for the flow of hot water inside the tank we found out that there was
no circulation of water.
Interpretation of Result: After studying carefully the system we came with the
conclusion that the circulation was not happening due to the drawback of
Thermosyphon.
Limitation of Tubes used in Adsober Tank: We kept the water tank above the solar
collector and made the water flow via pipe to the collector tubes. The water inside the
collector tube is heated by solar energy and is supposed to flow back to the water tank
according to the principle of thermosyphon.
Principle of Thermosyphon: Thermosyphon is a method of passive heat exchange,
based on natural convection, which circulates a fluid without the necessity of a
mechanical pump. Its purpose is to simplify the transfer of liquid or gas while avoiding
the cost and complexity of a conventional pump.
Convective moment of the liquid starts when liquid in the loop is heated, causing nit to
expand and become less dense, and thus more buoyant than the cooler liquid in the
bottom of the loop. Convection moves the heated liquid upward in the system as it is
simultaneously replaced by cooler liquid returning by gravity.
In case of solar collector, when the water inside the collector gets heated, its density
decrease and is replaced by the denser cold water and hence the hot water rises up to the
water tank which is above the collector. Due to this phenomenon there is no need of
extra water pump to take the liquid up to tank.

37. 37
Fig 4.4
Drawbacks of Thermosyphon: Thermosyphon must be mounted such that liquid rises
up and flows down to the collector with no bends in the tubing for liquid to pool. The
system has to be completely airtight, if not; the process of thermosyphon will not take
effect and cause the water to only evaporate only a small period of time.
Circulation Problem: In our system the hot water inside the tube of solar collector had
to flow through the tubes of adsorber tank for the heating purpose of adsorption pair and
had to rise up to the water tank again for competing the water flow cycle. Since we were
not using any mechanical pump flow making this flow, we were relying on the concept
of thermosyphon. But due to the drawbacks of thermosyphon which is stated above, it
was not possible for us to circulate the water inside the system as there so many bends
in the tube inside the adsorber tank via which the water had to be flown. This prevented
the water to rise up to the tank.
Fig 4.5
NO OFBENDINGSIN THE TUBE
THAT PREVENTTHE CIRCULATION
OF WATER

38. 38
Experiment No: 2
Since there was no circulation due to bends in the tube, we made the use of an electrical
water pump for circulating the water along the system. Due to the use of water pump
there was a proper circulation of the water along the tube of adsorber tank and we were
getting the water back into the water tank.
Result: The temperature of the hot water out of the collector was about 48-50 ˚C which
was not sufficient to make the desorption of water from the silica gel as the temperature
required was 70-80 ˚C
Interpretation of Result: Due to the continuous running of water pump, water was not
getting sufficient heat from the sun to attain the required temperature of 70-80 ˚C.
Experiment No: 3
As we were unable to obtain the required hot water we used an immersion rod to pre
heat the water in the water tank. This results in the increase of temperature of water up
to 70 ˚C and there was proper heating inside the adsorber tank.
Result: The water pump on getting high temperature inside stopped working. We then
kept the system on its own circulation. After certain time we opened the valve through
which the vapor flows in to the condenser. There was a flow of a little water vapor in
the condenser.
Interpretation of Result: After the third trial we finally were able to generate the water
vapor but due to lack of air tightness and finishing on making of the components we
were not able to achieve the desired result.
4.5 OBSERVATIONSAND READINGS
Temperature of water in water tank, t1 = 35˚C
Temperature of water at the outlet of solar collector, t2 = 75˚C
Pressure inside adsorber tank, p = 10 lb/inch2
= 0.689 bar
Temperature inside evaporator, t3 = 20˚C
Enthalpy of condensed liquid entering evaporator at 20˚C, h1 = 83.9 kJ/kg
Enthalpy of vapor leaving evaporator at 20˚C, h2 = 1643.5 kJ/kg
Mass of adsorbent used, ma = 2 kg

39. 39
4.6 CALCULATIONS
COP of the system =
𝑄 𝑢𝑠𝑒𝑓𝑢𝑙
𝑄 𝑑𝑎𝑖𝑙𝑦
=
𝑡 𝑒
𝑡 𝑔
=
20
75
= 0.266
SCP of the system =
𝑄 𝑢𝑠𝑒𝑓𝑢𝑙
𝑚 𝑎
=
ℎ2−ℎ1
𝑚 𝑎
=
1643.5−83.9
2
= 779.8 kJ/kg
4.7 COSTING
Components Cost(Rs.)
Condenser 1000
Solar Collector 2500
Water Tank 500
Stand 1000
Evaporator 2000
Valves 400
Adsorber Tank 600
Piping 800
Pressure Gauge 200
Copper Tube 800
Digital Thermometer-2 500
Table 4.3
Other Costs:
Welding Cost = Rs.400
Silica Gel = Rs.2200

40. 40
Adhesives and Sealing = Rs.200
Machining Operations and Finishing Cost = Rs.300
Total System Cost = Rs.13,400
Extra Experimental Components Costs:
Lens Panel = Rs.1500
Water Pump = Rs.250
Immersion Rod = Rs.300
Net Project Cost = Rs.15,450

41. 41
CHAPTER 5
AREAS OF IMPROVEMENT AND FUTURE SCOPE
5.1 AREAS OF IMPROVEMENTS
Improvement No. 1: Use of Double or Multi-bed System-
The model we made was a single bed intermittent cooling system. It means it cannot
perform the cooling action continuously. At one part of time only the desorption action
takes place while the other part of time comprises with the adsorption phenomenon. The
cooling action takes place during the time of adsorption. Hence the time taken by the
system is longer as compared to conventional cooling system.
The problem of intermittent cooling can be removed by the use of Double Bedded or
Multi-Bedded System. Due to the use of these types of systems the process can be
continuous.
 Double Bed System
In order to achieve a continuous cold production two adsorption beds work in
combination, i.e. one adsorption bed desorbs while the other adsorber generates cold by
adsorbing in the meantime. A simple two-bed adsorption refrigeration cycle of
separated heat exchangers consists of four main parts namely: reactors (adsorber or
desorber based on operating mode), evaporator, and condenser. The reactors are packed
with adsorbent material which has the capability of adsorbing or desorbing the
adsorbate / refrigerant during the adsorption or desorption process. Interconnecting
valves are used to control the refrigerant flow as shown in the flow diagram. Adsorption
is an exothermic process, so the heat of adsorption needs to be removed by means of
continuous cooling. On the other hand, during the desorption process heating is required
to release the refrigerant from the adsorbent pores.
The aforementioned components are controlled to work sequentially through four
modes namely; isosteric heating (preheating switching) (1-2), isobaric desorption /
condensation (2-3 / 2-3`), isosteric cooling (precooling switching) (3-4) and isobaric
adsorption / evaporation (4-1 / 4'-1). In the isosteric heating/cooling also named
switching periods, the refrigerant amount in the reactor chambers remains constant.
During the switching modes all interconnected valves are closed to keep the amount of
refrigerant in the reactors constant during preheating / precooling. As a result, during
the preheating mode the reactor pressure increases from the evaporation pressure to the
condensation pressure and vice versa during the precooling. During the isobaric cooling,
one of the reactors is connected to the evaporator to suck the refrigerant vapor from the
evaporator producing the cooling effect. During the isobaric heating the other reactor is
connected to the condenser to deliver the refrigerant to be condensed and then flow to
the evaporator through the liquid line.
Using two adsorption reactors is necessary to obtain continuous cooling by making both
of them work in parallel, while one reactor is in adsorption phase, the other one will be
in desorption mode.

42. 42
Table 5.1: Two bed Cyclic Operation and Valving
Fig 5.1
During the switching mode heat and/or mass recovery can be used. During mass
recovery, the adsorber and desorber are connected to speed up the pressure reduction of
the hot bed and pressure increase of the cold bed and hence the mechanical equilibrium
by means of pressure swing. During the heat recovery period, the cooling water flows
through the hot bed and then to the cold bed, which reduces the heat required for
regenerating the refrigerant and hence improve the cycle performance. Based on the
review of literature the COP of two-bed adsorption refrigeration cycle of different
operating schemes is usually between 0.60-0.70.

43. 43
Fig 5.2
Improvement No. 2: Removal of Valves
In our system, we have made the use of manual valves which are needed to be opened
or closed at regular intervals for the operations to be carried out. We can develop a
system containing no valves which will reduce the cost of the system and also the
effectiveness since the actions will take place on their own. There will be less chances
of leakage as the number of joints will reduce. This will certainly increase the COP of
the system.

44. 44
Fig 5.3
Fig 5.4
Improvement No. 3: Avoiding Bends in the tube
Due to many bending in the tube in which the hot water has to be flown, it was not
possible for us to make the circulation complete as the principle of thermosyphon only
works in smoother tubes. This has to be eliminated by the use of some other method
such as open loop height difference flow.

45. 45
5.2 APPLICATIONS
Depending on the desired temperature, the use of adsorption cooling system can be
divided into three categories, air conditioning(8-15˚c),refrigeration for food, vaccine
and medicines storage(0-8˚c),freezing and ice making(<0˚c).
There is a heavy demand for air conditioning in industrialized countries particularly in
big cities in summer. Solar collector connected with an adsorption cooling device may
be used for air conditioning purpose prototypes of such system already exist .They are
designed for use in trade, servicing and industrial buildings and also in vegetables, fruits
and grain depots. Beside these prototypes described in the literature, there are also
adsorption cooler driven by solar energy which are used in commercial buildings. Japan
and USA are the leaders in this area, however, in Europe the market of these devices is
also developing and they can be found in real buildings like hospitals or factories. To a
large extent it is a result of such programmes as climasol or solar. The adsorption air
conditioning systems driven by waste heat which comes from e.g. automobiles exhaust
gases or industrial processes are also under development. Because adsorption cooling
device have large volume and mass nowadays they can be used only in locomotives,
boats, buses and trucks or in industrial buildings in which a lot of waste heat is
produced.e.g. in chemical, steel or power plant.
The need for preservation of food products such as vegetables, fruit, milk, and meat in
order to extend their availability on the periods in which they are not produced, opens
another field for the application of adsorption cooling system, especially those which
are driven by solar energy. Such systems can also be used for medicines and vaccines
storage. Their work can be based on blowing the cold dry air produced by the device
into space to be cooled when the temp rises inside. The product which is cooled plays
the role of a cold storage material.
Another promising way of application of adsorption chillers is freezing and ice making
.In this case the temperature must be below 0˚C, so heat source must have higher
temperatures than in the case of cooling or air conditioning. Many prototypes of ice
making adsorption devices driven by solar energy exist in the world. Its work
corresponds to the natural diurnal and nocturnal solar periods. Desorption occurs during
the day, adsorption and ice- making during night. These systems are usually built as
well insulated containers which are cooled by the produced ice .Medicines, vaccines and
food can be kept in them in those region of the globe, in which there is no access to
electricity and thus the application of conventional refrigerators is not possible. Another
possibility is to use waste heat as an energy source .prototypes of such devices are also
known. The product ice can be used .e.g. for fish preservation on fishing boats.
Adsorption heat pumps are device based on similar principle as adsorption cooling but
they can be used for both heating and cooling .in this case solar energy geothermal
energy or waste heat can be used as source of driving energy.
5.3 FUTURE SCOPES
We are in the verse of energy crisis. Soon there will be no extinction of conventional
energy resources. In that respect we will have to rely on the non-conventional energy
resources. Solar is one of the most widely used and effective means of non-conventional

46. 46
energy resource. At such scarce condition when there will be no electricity left for
running the conventional refrigerators, these types of solar refrigerators will play an
important role. Some of the major future scopes of solar powered adsorption
refrigeration are as follows:
 These refrigerators can be used when there will be no electric power left for
running compressor based refrigerators. These refrigerators, since make the use
of sun’s energy, will be used in areas where there is no electricity production or
the production is low.
 They can be used in the areas of Africa and Tropical Region where the climate is
very hot and most of the food and other important stuffs become unusable due to
lack of storage.
 These refrigerators are eco-friendly and emit no any harmful gases such as CFCs
which will deplete the Ozone layer and contribute to enhance Global Warming.
Hence these can be used in order to prevent ozone layer depletion and upgrade a
healthy and pure environment.
 Because of the less moving parts, these refrigerators will be long lasting as
compared to other refrigerators containing compressors.
 This technique of cooling can even be used for cooling public places such as
cinema halls, malls, departmental stores, etc. by using the ducts flow technique
as in air conditioning.
 In the spacecrafts and rockets for cooling the engine and as well as when
reentering into earth's atmosphere.
The main barriers to uptake of adsorption refrigeration technology:
 in their current state of development systems are bulky and of higher cost
compared to competing vapour absorption systems
 only two manufacturers of commercial products and distribution channels are
not well established
 application range of commercial products is currently limited to temperatures
above 0˚C. unavailability of packaged equipment off the shelf for application in
the food sector
 insufficient experience and performance data from commercial applications to
provide confidence in the application of the technology.
Although in the principle, solar thermal powered adsorption refrigeration systems work
fine technically and have huge potential markets, there are a lot of challenges/works
exist (Hu, 1998) before such a market is established. The solar adsorption cooling
technology is not mature yet.
In recent years, the author has been concentrated on the studies which will make the
solar cooling technology more commercially ready to air- conditioning industry.
It is realised that the vacuum working condition required by the current system is a
potential drawback for the technology. Although the complete vacuum tightness may be
achieved for small unit by the modern manufacture (welding) technology, it is still no
guarantee for the big system which may have hundreds of joints. A new concept/idea
which can adjust the working pressure of the system to near atmospheric pressure is

47. 47
being studied. The new idea is to use a selective adsorbent and an inert gas as a pressure
adjusting agent to increasing the total system pressure to near atmospheric. The concept
is so far proved workable partially (Hu and You, 1998; You et al, 2000a, 2000b, 2000c,
and 2000d). This investigation may be of benefit to the effects to remove the leaking
problem may be faced by the large system (eg. air conditioning systems) in which the
complete physical tightness is impossible to achieve. Another challenge ahead is to
make public and air-conditioning industry aware, support and acceptance of this
idea/technology/concept.
5.4 CONCLUSION
This report is the review on the fundamental understanding of adsorption refrigeration
cycle and its application on refrigeration. As solar energy is used as an energy source,
cooling systems are environment friendly and it compete the absorption and
compression devices.
Solar thermal cooling technologies are being used for industrial and household cooling
purposes. These cooling systems are more applicable in remote areas where
conventional cooling is difficult and solar energy is readily available. These systems are
also more suitable than conventional vapor compression refrigeration systems as
working fluid used does not create pollution. Using stronger adsorbents and doing
improvement in the heat transfer process, the adsorption system can be a great
alternative to the future refrigeration need. To increase the attractiveness and application
of adsorption systems, research and development is required to increase efficiency and
reduce size and cost of systems through heat and mass transfer enhancement as well as
develop systems for low temperature applications below 0˚C. This will require further
development of working pairs (fluid and bed).
Although there are challenges ahead, R&D works done shows that the solar powered
solid adsorption refrigeration technology is very promising and has the great potential to
beneficial to the environment through its application in ice storage air conditioning
systems. Integrating the solar ice making capacity into the system to share some (if not
all) ice making load would have significant environment benefit and save customers
further dollars. We believe that the refrigeration and air-conditioning engineers should
have a concern for the environment and therefore should take an active interest in the
work we are undertaking.
5.5 REFERENCES
[1] M. Li, R.Z. Wang, Y.X. Xu, J.Y. Wu, A.O. Dieng; Experimental study on dynamic
performance analysis of a flat plate solar solid-adsorption. refrigeration for ice maker;
Renewable Energy 27, 211–221 (2002).
[2] Louajari, M.; Mimet, A.; Ouammi, A. Study of the effect of finned tube adsorber on
the performance of solar driven adsorption cooling machine using activated carbon-
ammonia pair.Appl. Energy 2011, 88, 690–698.
[3] Mannuel I,González, M.I.; Rodríguez, L.R. Solar powered adsorption refrigerator
with CPC collection system: Collector design and experimental test. Energy Convers.
Manag. 2007, 48, 2587–2594.

48. 48
[4] Fadar, A.E.; Mimet, A.; Pérez-García, M. Modelling and performance study of a
continuous adsorption refrigeration system driven by parabolic trough solar collector.
Sol. Energy 2009, 83,850–861.
[5] X. Q. Zhai and R. Z. Wang, “Experimental investigation and performance analysis
on a solar adsorption cooling system with/without heat storage,” Applied Energy, vol.
87, pp. 824-835, 2010.
[6] Grenier Ph., Guilleminot J.J., Meunier F. and Pons M. (1988). Solar powered solid
adsorption cold store, A.S.M.E. Trans.-J. Solar Energy Eng.110, 192-197
[7] L.W. Wang, R.Z. Wang, J.Y. Wu and K. Wang; Compound adsorbent for adsorption
ice maker on fishing boats; International journal of refrigeration 27, 401-408 (2004).
[8] Chang.M. Li, R.Z. Wang; Heat and mass transfer in a flat plate solar solid
adsorption; Renewable Energy 28, 613–622 (2003).
[9] Fadar, A.E.; Mimet, A.; Pérez-García, M. Modelling and performance study of a
continuous adsorption refrigeration system driven by parabolic trough solar collector.
Sol. Energy 2009, 83, 850–861.
[10] BOUBAKRI, A., GUILLEMIONT, J. J., & MEUNIER, F. 2000. Adsorptive solar
powered ice-maker: experiments and model. Solar Energy, 69(3), 249-263
[11] Wang L W ,Wang R Z,Oliveira R G.A review on adsorption working pairs for
refrigeration .Renewable and Sustainable EnergyReviews2009;13:518–34.
[12] Hassan HZ, Mohamad A A, Al-Ansary H A. Development of a continuously
operating solar driven adsorption cooling system:thermodynamic analysis and
parametric study. Applied Thermal Engineering 2012 ;48:332–41.
[13] Mr. Anieban Sur,Dr. Randip K.Das Review on solar adsorption cycle IJMET July
–Aug 2010 pp 190226.