In absorption cycle cooling systems, which substance serves as the refrigerant?

• A. Water
• B. Lithium bromide
• C. Ammonia
• D. Freon

Answer: (A)

Absorption cooling relies on a refrigerant that can be absorbed and released by an absorbent in a cycle driven by heat. In the common LiBr–water absorption chillers, water serves as the refrigerant while lithium bromide acts as the absorbent. The LiBr solution absorbs water vapor from the evaporator; when heat is applied, the water desorbs, moves to the condenser, returns to the evaporator as a liquid, and vaporizes to provide cooling. Water works well here because LiBr has a strong affinity for it, enabling an efficient, pumpless cycle. Ammonia would be the refrigerant in a different ammonia–water absorption system, and Freon is used in vapor-compression systems, not absorption, so they don’t fit this setup.