What is the primary function of the evaporator in a vapor-compression refrigeration cycle?

• A. Absorb heat from the conditioned space by condensing the refrigerant at high pressure.
• B. Absorb heat from the conditioned space by evaporating the refrigerant at low pressure.
• C. Reject heat to the outdoors by condensing the refrigerant.
• D. Increase refrigerant pressure to drive the cycle.

Answer: (B)

In a vapor-compression refrigeration cycle, the evaporator is where the refrigerant absorbs heat from the space by evaporating at low pressure. The refrigerant enters the evaporator as a cold, low-pressure liquid (or a very cold mixture) and leaves as a low-pressure vapor. Heat from the conditioned air transfers to the refrigerant, causing it to change phase from liquid to vapor and thereby cooling the space. The low-pressure, evaporative process is what drives the cooling effect in the evaporator.

The other descriptions correspond to different components: heat rejected to the outdoors by condensing the refrigerant happens in the condenser, and increasing the refrigerant’s pressure to drive the cycle is the job of the compressor.