Vapour absorption refrigeration systems
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VAPOUR ABSORPTION REFRIGERATION SYSTEMS
Submitted to :
Mr. Sumit Sharma
Presented By :
Akshay Mistri, Rahul Kumar
Tarun Sharma, Zubin Rizwan
Section : 6MAE3Y
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CONTENTS• Introduction
• Simple Vapour Absorption System
• Practical Vapour Absorption System
• C.O.P of Ideal Vapour Absorption System
• Properties of Ideal Refrigerant and Absorbent
• Properties of Ideal Refrigerant-Absorbent combination
• Advantages of Absorption system over Compression system
• Domestic Electrolux Refrigerator
• Principle & Working of Domestic Electrolux refrigerator
• Advantages & Disadvantages of Domestic Electrolux Refrigerator
• References
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INTRODUCTION
• It is a heat operated system.
• It is quite similar to Vapour Compression systems. Condensation and evaporation takes place at two different pressure levels to achieve refrigeration.
• The main motive is to raise the temperature of the refrigerant from evaporator pressure to condenser pressure.
• Here refrigerant is dissolved in inert liquid in absorber and pumped to condenser.
• After raising pressure of refrigerant it is separated from solution by heating.
• After condensation in condenser, refrigerant is throttled by expansion valve and then it evaporates in evaporator providing the refrigeration effect.
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SIMPLE VAPOUR ABSORPTION SYSTEM
• Ammonia vapour from evaporator is absorbed by water in absorber. Condensation heat released is absorbed by cooling water.
• After being pumped to generator, heat is supplied which gives ammonia vapour. Weak sol. sent back to absorber.
• High pressure vapour is condensed to high pressure liquid ammonia in condenser.
• Liquid ammonia is throttled by expansion valve, and then it evaporates absorbing heat from evaporator.
Simple Vapour Absorption System
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PRACTICAL VAPOUR ABSORPTION SYSTEM
Water vapours if reach condenser may block the expansion valve. Therefore, analyser-rectifier is used practically.
Analyser : Strong solution flows down the trays. Due to high saturation temperature water condenses down and vapours escape through.
Rectifier : A water cooled heat exchanger which further condenses water vapour. (If any left)
Heat Exchanger : Used to cool weak solution from generator. It also heats the strong solution coming from pump, thereby reducing heat to be supplied at generator, increasing economy.
Practical Vapour Absorption System
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COEFFICIENT OF PERFORMANCE OF IDEAL ABSORPTION SYSTEM
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C.O.P OF IDEAL ABSORPTION SYSTEM (CONTINUED)
Various energy transfers in VARS
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C.O.P OF IDEAL ABSORPTION SYSTEM (CONTINUED)
= C.O.P of Carnot refrigerator working b/w temperature limits & .
= C.O.P of Carnot engine working b/w temperature limits & .
Thus C.O.P of ideal absorption system,
= [ ] x [ ]
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PROPERTIES OF IDEAL REFRIGERANT & ABSORBENT
Properties of ideal refrigerant :
• It should boil b/w 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.
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PROPERTIES OF IDEAL REFRIGERANT-ABSORBENT COMBINATION
• 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
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ADVANTAGES OF ABSORPTION SYSTEM OVER COMPRESSION 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 favour absorption system.
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DOMESTIC ELECTROLUX REFRIGERATOR
• Developed from an invention by “Carl Munters” & “Baltzer Von Platen”.
• Also known as “Three-fluid absorption system” and “Munter’s Platen System”.
• Three fluids used are ammonia, hydrogen and water.
Domestic Electrolux Refrigerator
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PRINCIPLE & WORKING OF ELECTROLUX REFRIGERATOR
Principle : If a liquid is exposed to an inert atmosphere, it will evaporate until atmosphere becomes saturated with the liquid vapours. Evaporation thus produces cooling effect.
Working :
• Liquid evaporates into gas at low temperature in evaporator.
• mixture enters absorber where is absorbed in water, returns back.
• Strong sol. in goes to generator, where it is heated and vapours then go to water separator.
• Water separates in separator, weak sol. Sent back to absorber and vapour move to condenser. After condensation in condenser liq. moves to evaporator.
Working cycle of Electrolux Refrigerator
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POINTS WORTH NOTING (FOR
ELECTROLUX REF.)
• Complete cycle is carried out entirely by flow of gravity of refrigerant.
• With this type of machine, efficiency is not important since the energy input is very small.
• Due to low C.O.P, it cannot be used for industrial purposes.
ROLE OF HYDROGEN
• Helps in maintaining uniform total pressure throughout the system.
• Permits the refrigerant to evaporate at low temperature in evaporator, corresponding to its partial pressure.
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ADVANTAGES(ELECTROLUX REF.)
• No pump/compressor required.
• No mechanical troubles, low maintenance.
• No lubrication required, no wear-tear.
• Completely leak proof.
• Noiseless.
• Easy control, only by heat input.
• More complicated in construction and working.
• Low C.O.P.
• If spoiled once, cannot be repaired and has to be replaced fully.
DISADVANTAGES(ELECTROLUX REF.)
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REFERENCES
• Er. R.K. Rajput.Vapour Absorption Refrigeration Systems. Feb 03, 2014, “A textbook of Refrigeration & Air-conditioning-2013”.
• Prof. M. Ramgopal. Various energy transfers in VARS (image). Feb 02, 2014, from http://nptel.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Ref
• Prof. R. C. Arora. Domestic Electrolux Refrigerator (image). Feb 02, 2014, from http://nptel.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Ref%20and%20Air%20Cond/pdf