The ppt contains detailed study of Vapor Absorption Refrigeration System with neat sketches and description. It is well formed as per the syllabus of GTU

1. Vapor Absorption
Refrigeration System
(VARS)
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Faculty Name: Prof. Ajaypalsinh G. Barad
Branch: Mechanical
Semester: 6th
Name of Subject: Refrigeration and Air Conditioning

2. Outline
• Introduction
• Desirable characteristics of refrigerant
• Selection of pair,
• Practical H2O -NH3 cycle,
• LiBr – H2O system and its working,
• Electrolux refrigeration system
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3. Introduction:
• The vapour absorption refrigeration system is one of
the oldest methods of producing refrigeration effect.
• An ammonia is the commonly used refrigerant in a
vapour absorption system.
• The vapour absorption system uses heat energy,
instead of mechanical energy as in vapour
compression systems, in order to change the
conditions of the refrigerant.
• This system may be used in both the domestic and
large industrial refrigerating plants.
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4. • The compressor is replaced by an absorber, a pump, a
generator and a pressure reducing valve.
• In this system, the vapour refrigerant from the
evaporator is drawn into an absorber where it is
absorbed by the weak solution of the refrigerant
forming a strong solution.
• This strong solution is pumped to the generator where
it is heated by some external sources.
• During the heating process, the vapour refrigerant is
driven off by the solution and enters into the
condenser where it is liquefied. The liquid refrigerant
then flows into the evaporator and thus the cycle is
completed.
Introduction:
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5. Introduction:
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6. Solubility requirement:
• The refrigerant should have proper solubility in the
absorbent so that a strong solution, highly rich in the
refrigerant, is formed in the absorber by the absorption
of the refrigerant vapour.
Boiling point requirement:
• There should be a large difference, about 200oC, in the
boiling points of the two substances, thus absorbent
free refrigerant is boiled off from the generator.
Thermodynamic Requirement of Refrigerant –
Absorbent Mixture:
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7. Some other Properties required:
• The refrigerant should have high affinity for the
absorber at low temp and less affinity at high temp.
• It should have low freezing point.
• It should have good thermal and chemical stability
• Irreversible chemical reactions of all kinds are to be
avoided.
Thermodynamic Requirement of Refrigerant –
Absorbent Mixture:
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8. • Ammonia – Water
• Ammonia – Sodium Thiocynate
• Ammonia – Lithium Nitrate
• Ammonia – Calcium Chloride
• Water – Lithium Bromide
• Methylene Choride – Dimethyl Ether tetra ethylene
glycol
Selection of Pairs:
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9. Simple Ammonia - Water VAR:
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10. 10

11. Practical Ammonia - Water VAR:
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13. Advantages:
• Feasible to separate refrigerant from absorbent, as water is
more volatile compared to Li-Br.
• Operating pressures are low so pumping cost is low.
• Wall thickness of the system less compared to VCR.
• Water as refrigerant is non toxic, so can be directly used
for chilled coil.
• Can be built up to 1,00,000 TR capacity plants.
• Operation and maintenance cost is very low.
Lithium Bromide Absorption System:
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14. Disadvantages:
• Evaporation temperature must be kept above the freezing
point of water and hence the temperature of chilled water
cannot be less than 5oC.
• Li-Br solution is corrosive. So inhibitors need to be added
to the system to prevent the metal parts from corrosion.
Lithium Bromide Absorption System:
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15. Introduction:
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16. Introduction:
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17. Introduction:
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18. • Silent operation
• Cost effective
• Balanced pressure
• No need of valve
• No lubrication problem
• Less maintenance
Advantage of Three-Fluid
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19. • VAR uses heat energy, VCR uses mechanical energy
• Operation is simple in VAR as less moving parts
• Less wear, tear and noise.
• No bad effect of liquid refrigerant leaving the evaporator
• Law COP
• More component, bulky system
• Charging of refrigerant is difficult
Comparison of VAR and VCR
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