Consider the following statements regarding vapour absorption systems in the field of refrigeration: 1. In ammonia-water absorption system, ammonia is the refrigerant. 2. In water-lithium bromide system, water is the refrigerant. 3. Ammonia-water absorption reaction is endothermic. 4. The amount of ammonia absorbed by water is inversely proportional to the temperature of ammonia. Which of the above statements are correct?
Consider the following statements regarding vapour absorption systems in the field of refrigeration: 1. In ammonia-water absorption system, ammonia is the refrigerant. 2. In water-lithium bromide system, water is the refrigerant. 3. Ammonia-water absorption reaction is endothermic. 4. The amount of ammonia absorbed by water is inversely proportional to the temperature of ammonia. Which of the above statements are correct? Correct Answer 1, 2 and 4
Concept:
Ammonia water absorption reaction is exothermic.
Le-Chatelier’s principle: It states that if a constraint (such as a change in pressure, temperature, or concentration of a reactant) is applied to a system in equilibrium, the equilibrium will shift so as to tend to counteract the effect of the constraint.
Absorption of ammonia is exothermic, so heat can be assumed as product. Now if product (heat or temperature) is increased, equilibrium will shift towards left side (reverse absorption). Hence, increase in temperature decreases the amount of ammonia absorbed.
In vapour absorption refrigeration systems most commonly these two pairs are used.
1. Water-Lithium Bromide (H2O – LiBr) system for above 0ºC applications such as air conditioning. Here water is the refrigerant and lithium bromide is the absorbent.
2. Ammonia-Water (NH3 – H2O) system for refrigeration applications with ammonia as refrigerant and water as absorbent.
About VARS:
In vapour absorption refrigeration system (VARS), the components used are Evaporator, Absorber, Pump, Generator, Condenser, Expander.
In vapour compression refrigeration system (VCRS), the components used are Evaporator, Compressor, Condenser and Expander.
Thus generator, absorber and pump are absent in VCRS.
In VARS less mechanical work is used compared to VCRS.
In the vapour absorption system, the compressor is replaced with the absorber, pump and generator.
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