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.

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

LiBr-Water vs Ammonia-WaterFor 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.

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.

Comparison of Vapor Compression Refrigeration System versus

Vapor Absorption Refrigeration System

Vapor Compression Refrigeration System versus Vapor Absorption Refrigeration System

Vapor Compression Refrigeration

Vapor Absorption Refrigeration System

Comparison of Vapor Compression Refrigeration System versus

Vapor Absorption Refrigeration System

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.

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.

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.

REFERENCES

• http://www.brighthubengineering.com/hvac/66301-water-lithium-bromide-vapor-absorption-refrigeration-system/

• http://absorptionchiller4u.blogspot.com/2013/02/ammoniawater-absorption-refrigeration.html

• http://www.brighthubengineering.com/hvac/66476-absoprtion-refrigeration-vs-vapor-compression-refrigeration-system/

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