Vapour absorption refrigeration (ammonia–water system): Which working fluid acts as the refrigerant in a typical absorption refrigerator?

Introduction / Context:
In the ammonia–water absorption cycle, a refrigerant is absorbed in a liquid absorbent, pumped, desorbed in the generator, condensed, expanded, and evaporated to provide cooling. Knowing which fluid is the refrigerant clarifies the roles of each component.

Given Data / Assumptions:

• Working pair: ammonia (NH3) and water (H2O).
• Typical small to industrial absorption systems.
• Cycle uses heat (not mechanical work) to drive refrigeration.

Concept / Approach:
The refrigerant is the fluid that evaporates at low temperature in the evaporator, absorbing heat from the cooled space, and then condenses in the condenser at higher pressure. In the NH3–H2O system, ammonia plays this role; water is the absorbent that dissolves ammonia in the absorber and releases it in the generator.

Step-by-Step Solution:

Verification / Alternative check:
Component naming (absorber, generator, analyzer, rectifier) in NH3–H2O systems is consistent with ammonia being the volatile refrigerant requiring rectification to remove water carryover.

Why Other Options Are Wrong:

• Water: Acts as absorbent, not the refrigerant, in NH3–H2O systems.
• Freon: Used in vapor-compression systems, not in the classic ammonia–water absorption cycle.
• Aqua-ammonia: This is the solution (ammonia dissolved in water), not the pure refrigerant fluid.

Common Pitfalls:
Confusing the solution name (aqua-ammonia) with the refrigerant; the refrigerant must be the vapor that circulates through condenser and evaporator.

Final Answer:
Ammonia