1. use of renewable energy source for

1.    
Introduction

 

The aim of our project is use of renewable energy source for
refrigeration using vapor absorption cycle. The vapor absorption system
consists of evaporator, absorber, pump, generator condenser, and expansion
valve. In the vapor absorption system, the refrigerant mainly used are ammonia
water solution or lithium bromide solution.

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Refrigerant in evaporator gets energy from surrounding and
converts into vapor form. Then this vapor refrigerant get mix with absorber and
forms a solution, this solution is transfer to the generator by a pump where
heat is supplied by solar or exhaust gases to separate refrigerant from
absorber. The refrigerant in vapor form goes to condenser and condenses into
liquid form. The expansion valve is used between condenser and evaporator for
pressure drop.

2.      Scope

The scope of our project is use of renewable source for operating
vapor absorption cycle. Design and calculations of different components of the
cycle. Fabrication and prototyping.

 

3.    
Basic diagram of vapor absorption cycle:

 

4.    
Working

The vapor refrigeration system consists of processes like
evaporation, compression, condensation and evaporation. The refrigerants mainly
used are lithium bromide water solution and ammonia water solution. In lithium
bromide water solution water act as refrigerant and lithium bromide act as
absorber whereas in ammonia water solution ammonia act as refrigerant and water
act as absorber. Processes like evaporation absorption condensation and
expansion are shown above in the figure.

5.    
Literature review

Refrigeration
has become an essential part of the way we live our life. Almost everyone has a
household refrigerator, but not many know of the process required to produce
the drop in temperature that we know as refrigeration. 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 to its environment. Refrigeration is a
process to keep a cool element or to reduce the temperature of one element below
that of the other. The refrigeration process is, in essence then, 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 was done by the system; so in order to do the
reverse; work must be done to 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 vapor-compression
system, and the absorption refrigeration system. In recent developments of
thermal engineering, the
Refrigeration technologies play an important role in today’s industrial
applications. 1

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 vapor absorption systems.
These systems are popular because they are reliable, relatively inexpensive and
their technology is well
established. However, these systems require high-grade energy (mechanical or
electrical) for their operation. Apart from this, the recent discovery that the conventional
working fluids of vapor absorption 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
absorption system, which mainly uses heat energy for its operation. Moreover, the working
fluids of these systems are environment-friendly 2.

5.1. Desirable
Properties of Refrigerant Absorbent Mixtures
Refrigerant-absorbent mixtures for VARS (vapor absorption refrigeration system)
should possess some desirable properties of the refrigerant should be more volatile
than the absorbent, in other words the boiling point of refrigerant should be
much lower than the absorbent. So, that the solution in the Generator need only
to be heated to the temperature required boiling off only the refrigerant. This
ensures that only refrigerant (pure) circulates through refrigerant circuit
(evaporator-condenser-expansion valve).The refrigerant should exhibit high
solubility with solution in the absorber. The absorbent should have a strong
affinity for the refrigerant. This will minimize the amount of refrigerant to
be circulated. Operating pressures should be preferably low so that the walls
of the shells and connecting pipes need not to be thick. It should not undergo crystallization
or solidification of the system. Because crystallization will block the free flow
of solution in the line. The mixture should be safe, chemically stable,
noncorrosive, and inexpensive and should be available easily. The refrigerant should
have high heat of vaporization 3, 4.Mostly two refrigerants absorbent
mixture are used in absorption cycle (VARS).

5.1.1. Ammonia-Water
Systems
Since the
invention of absorption refrigeration system, NH3- H2O has been widely used.
Both ammonia (refrigerant) and water(absorbent) are highly stable for a wide
range of operating temperature and pressure.NH3 has a high latent heat of
vaporization and the freezing point is -77°C, which is necessary for efficient
performance of the system, for that it may be used for low- temperature
applications. But both ammonia and water are volatile, the cycle needs a rectifier
to strip away water that normally evaporates with ammonia. Without a rectifier,
the water would accumulate in the evaporator and offset the system performance.
Other disadvantages of its high pressure, toxicity, and corrosive action of
copper and its alloy. Ammonia/Air mixtures are barely inflammable but may be
explosive in the case of high percentages of ammonia between 15.5 and 27 % by
volume 5.

5.1.2 Lithium
Bromide-Water Systems
The use of
LiBr-Water for VARS began around 1930. Two outstanding features of LiBr-Water
are non-volatility absorbent of LiBr (no need of a rectifier) and extremely
high heat of vaporization of refrigerant (water). However, using H2O as a
refrigerant limits the low-temperature application to that above0°C. As H2O is
the refrigerant, the system must
be worked under vacuum conditions. At high concentrations, the solution is
prone to crystallization. One way to prevent this to happen
to add one or more extra salts e.g., ZnBr2, ZnCl2.The addition of the third
component of the
basic water-lithium bromide solution
pushes the crystallization limit away from the normal operating zone. Hence the strong
solution can be cooled in the heat exchanger to near absorber temperature
without salt crystallization, thus improving the
performance of the system. COP is high (0.7 to 0.9) as compared to (0.5 to 0.6)
for Ammonia-Water
systems 6

5.2 Heat Exchanger

Transfer of heat from one fluid to another is an important
operation for most of the chemical industries. The most common application of
heat transfer is in designing of heat transfer equipment for exchanging heat
from one fluid to another fluid. Such devices for efficient transfer of heat
are generally called Heat Exchanger. Heat exchangers are normally classified
depending on the transfer process occurring in them. General classification of
heat exchangers is shown in the figure.

 

 

 

5.2.1 Classification of Heat Exchangers

 

The tubular exchangers are widely used in industry for the
following reasons. They are custom
designed for virtually any capacity and operating conditions, such as from high
vacuums to ultra-high pressures (over 100 MPa or 15,000 psig), from cryogenics
to high temperatures (about ll00°C, 2000°F), and any temperature and pressure
differences between the fluids, limited only by the materials of construction.
They can be designed for special operating conditions: vibration, heavy
fouling, highly viscous fluids, erosion, corrosion, toxicity, radioactivity, multicomponent
mixtures, and so on. They are the most versatile exchangers made from a variety
of metal and nonmetal materials (graphite, glass, and Teflon) and in sizes from
small (0.1 m^ 2, 1 ft. ^ 2) to super-giant (over 100,000 m ^2, 10 6 ft^2). They
are extensively used as process heat exchangers in the petroleum-refining and
chemical industries; as steam generators, condensers, boiler feed water
heaters, and oil coolers in power plants; as condensers and evaporators in some
air-conditioning and refrigeration applications; in waste heat recovery applications
with heat recovery from liquids and condensing fluids; and in environmental
control.7

Shell and tube heat exchanger

Shell-and-tube exchangers are basically noncompact
exchangers. Heat transfer surface
area per unit volume ranges from about 50 to 100 m2/m3(15 to 30 ft2/ft3). Thus,
they require a
considerable amount of space, support structure, and capital and installation
costs. As a
result, overall they may be quite expensive compared to compact heat
exchangers. The latter
exchangers have replaced shell-and-tube exchangers in those applications today
where the
operating conditions permit such use. For the equivalent cost of the exchanger,
compact heat
exchangers will result in high effectiveness and be more efficient in energy
(heat) transfer.
Shell-and-tube heat exchangers are classified and constructed in accordance
with the
widely used Tubular Exchanger Manufacturers Association (TEMA) standards , DIN
and
other standards in Europe and elsewhere, and ASME Boiler and Pressure Vessel
Codes.
TEMA has developed a notation system to designate the main types of
shell-and-tube
exchangers. In this system, each exchanger is designated by a three-letter
combination, the first
letter indicating the front-end head type, the second the shell type, and the
third the rear-end
head type. Some of the common shell-and-tube exchangers are BEM, BEU, BES, AES,
AEP, CFU, AKT, and AJW. The three most common types of shell-and-tube exchangers
are fixed tubesheet design, U-tube design, and the floating head type. In all
types, the front-end head is stationary, while the rear-end head could be
either stationary or floating depending upon the thermal stresses in the shell,
tube, or tubesheet due to temperature differences as a result of heat transfer.
8

Finned tube heat exchanger

Finned-tube heat exchangers are predominantly used in space
conditioning systems, as well as other applications requiring heat exchange
between two fluids. One important widespread use is in residential air
conditioning systems.

Finned-tube heat exchangers, or coils, consist of
mechanically or hydraulically expanded round tubes in a block of parallel
continuous fins. Fin-tube heat exchangers are designed for maximum heat
transfer between two fluids with a minimum pressure drop associated with each
fluid. The design of finned-tube heat exchangers requires specification of more
than a dozen parameters, including but not limited to the following: transverse
tube spacing, longitudinal tube spacing, tube diameter, number of tube rows,
fin spacing, fin thickness, and fin type (plain or enhanced).9

5.3 Solar Collector

Solar energy is a very large,
inexhaustible source of energy. Solar energy could supply all the present and
future energy needs of the world on the continuing basis. This makes it one of
the most promising of the unconventional energy sources. In addition to its
size, solar energy has two other factors in its favor. First unlike fossil
fuels and nuclear power, it is an environmental clean source of energy. Second,
it is free and available in adequate quantities in almost all parts of the world
where people live.

Solar
thermal collectors are used to heat up a fluid, generally water or a mixture of
glycol and water depending of the configuration of the solar thermal system.
They are adopted for many applications in both industrial and residential
sectors. All have a common operating
principle: to capture solar radiation, converting it to useful heat and transferring
it to a working fluid.10

5.3.1Types of solar collector

 

 Unglazed Collectors
Unglazed solar collectors are the simplest solar thermal collectors. It
consists of an absorber with embedded channels where the fluid circulates.
Insulation is not used. Generally, the absorber and the pipes are made in
plastic materials. The working principle is very simple. Basically, solar
radiation impacts on the absorber heating it up. Since the absorber is treated
with special paints only a very small solar radiation portion is reflected back
to the environment. The produced heat is then transferred to the fluid which
circulates in the pipes. The efficiency is strongly affected by the external
conditions, particularly by external air temperature and wind. Indeed, at low
air temperatures, although the solar irradiance is strong, unglazed collectors
are not available to heat up the fluid. Despite they are not able to increase
the temperature of the fluid up to 50 °C, unglazed collectors are widely used
for pool heating applications.11

Flat Plate Glazed Collectors
Different from the unglazed collectors, flat plate Glazed collectors
have a glass cover above the absorber, creating a cavity filled with gas
(usually air), which generates the greenhouse effect. The cover acts also as a
barrier against the wind. Advanced glasses, specifically treated, are used as
covering material in order to reduce optical losses. It has to be mentioned
that increasing the number of glass coverings is not productive due to optical
losses increment. Both absorber and pipes are made of metals with enhanced
absorbing properties. All these components are encapsulated in a frame as shown
in Fig. Insulation is used on the back and sides surfaces of flat plate glazed
collectors to reduce heat losses. Thus, solar radiation is absorbed through the
glass by the metal absorber, heating up the fluid which circulates within the
pipes.12

Evacuated Tubes Collectors
This solar collector consists of two main parts: vacuum pipes and the
manifold as shown in figure. Along the manifold a set of vacuum pipes are
installed. Particularly, each vacuum pipe consists of an inner tube and an
outer tube; between them the vacuum is created to enhance the thermal features
of the collector, decreasing thermal losses.13

 

Parabolic Solar Collectors

A parabolic trough concentrator consists of a reflecting surface
mounted on a reflector support structure having the profile of a parabola. A
receiver assembly comprising a circular absorber tube with suitable selective coating
and enclosed in a concentric glass envelope is centered along the reflector
focal line. Maintain focusing of solar radiation on the receiver assembly. The incident
energy is absorbed by a working fluid circulating through the absorber tube.14

 

6.    
Conclusion

After reading all this we come to the conclusion that we
will be using lithium bromide, water solution as a refrigerant in our project.
We also go for fin type and shell in tube heat exchanger designing. Evacuated
tubes collector are the most effective one from other types. We may be go for
this type of collector or for parabolic collector. “Changing may be done in
these selective elements if required”.

7.    
Work Done

 

ü 
Literature Review

ü 
Calculation in progress 

 

8.    
Work to be done

 

·        
Calculation

·        
Analysis

·        
Fabrication

·        
Testing

 

 

 

 

Refrences

 

1 Poberžnik S.; Goricanec D.; Krope J.,Traditional vs.
alternative energy house heating source, Proceedings of the 2ndIASME / WSEAS International Conference on Energy &
Environment (EE’07), Portoroz,n Slovenia, May 15-17, 2007

2 Feng X.; Goswami D. Y., Thermodynamic Properties of
ammonia-water mixtures for Power-cycle application, Energy, 24, 1999, pp. 525-536

3 G. Ali Mansoori and Vinod Patel, “Thermodynamic
Basis for the Choice of Working Fluids for Solar Absorption Cooling Systems “Solar Energy, Volume 22, Issue 6, 1979, Pp
483 491.

4José
A. Manrique, “A Solar Air-Cooled Water-Ammonia Absorption Chiller”
61st Ati National Congress –International Session “Solar Heating andCooling”Pp
1-5

5 SoterisKalogirou, George Florides, Savvas Tassou, Louis
Wrobel” Design and Construction of A Lithium Bromide Water Absorption Refrigerator” Clima 2000/Napoli 2001
World Congress – Napoli (I), 15-18 September 2001

6 Manu.S, T.K., T.B.Prasad,Nagendra Dept.of Mech.Engg., Sri
Siddhartha Institute of Technology, Tumkur
“Theoretical
Model of Absorber for Miniature LiBr-H2o Vapor Absorption Refrigeration System
“International Journal
of Modern Engineering Research (IJMER) www.ijmer.com Vol.2, Issue.2, Mar-Apr 2012 pp-

 7 Incropera, F.P.
and DeWitt, D.P., 1996. Fundamentals of Heat and Mass Transfer, 4th
Edition, John Wiley & Sons, New York, N.Y..

8 Indian
Standard (IS: 4503-1967): Specification for Shell and Tube Type Heat
Exchangers, BIS 2007, New Delhi

9 Garimella,
S., Coleman, J.W., Wicht, A., 1997. Tube and Fin Geometry Alternatives for
the Design of Absorption-Heat-Pump Heat Exchangers. Enhanced Heat Transfer,Vol.
4, pp. 217-235

10 Kalogirou SA
(2004) Solar thermal collectors and applications. Prog Energy Combust Sci 30:231–295.
doi:10.1016/j.pecs.2004.02.001.

11 12 13
Kalogirou SA (2014) Solar energy collectors. Sol Energy Eng 125–220.
doi:10.1016/B978-0-12-397270-5.00003-0

14 Powell Kody M and Thomas F Edgar (2011), “Modeling and Control
of a Solar Thermal Power Plant with Thermal Energy Storage”, Chemical
Engineering Science, Vol. 71, pp. 138-45

 

 

 

 

 

 

 

 

 

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