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Advantages and Disadvantages of VARS
1.
2. Properties of Ideal Refrigerant & Absorbent
Properties of ideal refrigerant :
• It should boil between
2˚-10 ˚C and condense at
40 ˚C or above. (pressure
around atmospheric)
• Large latent heat of vaporization.
• High critical temperature.
• Low specific heat.
• Stability in complete cycle.
Properties of ideal absorbent :
Greater affinity for
refrigerant.
Heat released during
absorption of refrigerant
should be minimum.
High boiling point.
Low specific heat.
Chemical stability.
3. Properties of Ideal Refrigerant and Absorbent
Refrigerant should have high affinity for absorber at low
temperatures & less affinity at high temperatures.
Mixture should have low specific heat and viscosity.
It should be non-corrosive.
Large difference in normal boiling points of refrigerant and
absorbent.
Commonly used combinations in air-conditioning
applications :
• Ammonia-water
• Lithium-bromide water
4. LiBr-Water vs Ammonia-Water
For LiBr-water solution
• It uses water as refrigerant(boiling point 100ºC) and Lithium-
Bromide(boiling point 1265ºC) as its absorbent
• Is used in a number of air conditioning applications. This system is useful
for applications where the temperature required is more than 32 ºF(0º).
• Water used as the refrigerant in the absorption refrigeration system
means the operating pressures in the condenser and the evaporator must
be very low
• The system can be achieved even without installing the expansion valve
in the system, since the drop in pressure occurs due to friction in the
refrigeration piping and in the spray nozzles.
• It has lesser components than ammonia-water absorption.
5. For Ammonia-Water solution(Aqua Ammonia System)
• Uses Ammonia(NH3, Boiling point -33.34ºC) as refrigerant and
Water(Boiling point ºC) as absorber
• Most commercial and industrial refrigeration applications occur at
temperatures below 32(0º) F and many are 0 F(-17.78º). As a
result, a fluid which is not subject to freezing at these
temperatures is required. So the lithium bromide/water cycle is
no longer able to achieve this conditions, because water is used
for the refrigerant.
• Have a disadvantage in acquiring extra parts compare to LiBr-
water system but does have an advantage in operating pressure
above atmospheric that avoid air leakage.
6. Comparison of Vapor Compression Refrigeration System versus
Vapor Absorption Refrigeration System
7. Vapor Compression Refrigeration System versus Vapor Absorption
Refrigeration System
Vapor
Compression
Refrigeration
Vapor
Absorption
Refrigeration
System
8. Comparison of Vapor Compression Refrigeration
System versus
Vapor Absorption Refrigeration System
9. Advantages of using Vapor – Absorption Refrigeration
System
• As there is no moving part in the entire system, the operation is essentially quite and
subjected to a very little wear.
• The load variations does not effect the performance of a vapour absorption system.
• Absorption system may be designed to use any readily available source of thermal
energy such as process steam ,hot exhaust from furnaces and solar energy, therefore
they can be used in places where electric power is hard to obtain or is very
expensive.
• In here pump is used for pumping refrigerant absorbant solution, which consumes less
power.
• Maintenance cost is low as because of absence of moving part.
• In the absorption refrigeration system no refrigerant produces the greenhouse
effect, so their use won’t be stopped in future.
10. Advantages of using Vapor – Absorption Refrigeration
System
No moving part except pump-motor, which is comparatively smaller than compressor
system.
Quiet in operation, low maintenance cost.
Can work only with thermal energy as an input.
Can be built for huge working capacities. (even for above 1000 TR)
Can be operated at designed C.O.P’s or even at part loads by varying generator
temperature.
Space and Auto. control requirements favor absorption system.
In ammonia-water absorption refrigeration system, ammonia is used as the
refrigerant, which is easily and cheaply available. In lithium bromide system, water is
used as the refrigerant, which is also available cheap.
11. Disadvantages of using Vapor - Absorption Refrigeration
System
• Set up is too large as it consists of three more equipment those are
absorber, generator ,and pump.
• Initial cost is high.
• Corrosive in nature.
• Low working pressure.
• Due to low working pressure the cop of vapour refrigeration is low, it
is about 1.1
• High heat rejection system is required, as heat is being rejected
from condenser, analyzer, rectifier and absorber.
13. References
• Vapour Absorption Refrigeration Systems Version 1 ME, IIT Kharagpur
• Refrigeration Cycles, Prof. U.S.P. Shet , Prof. T. Sundararajan and Prof. J.M .
Mallikarjuna
• Principles of Refrigeration by Roy J. Dossat, fourth edition, Prentice Hall
• Refrigeration and Air Conditioning Systems by CP Arora
• A Review of Absorption Refrigeration Technologies; Pongsid Srikhirin , Satha
Aphornratana, Supachart Chungpaibulpatana
• Vapour Absorption Refrigeration Systems – Vikan Vijayant Rana
• Vapour Absorption Refrigeration Systems - Akshay Mistri, Rahul Kumar, Tarun Sharma,
Zubin Rizwan
