Evaporators and Condensers Flashcards

Why must an evaporator be pumped out before hot gas is introduced for defrost?

Answer: To avoid hydraulic shock from hot gas hitting liquid refrigerant

Hot gas entering a coil full of cold liquid can collapse vapor and cause dangerous liquid hammer.

If liquid backs up in a condenser because the drain to the receiver is restricted, what happens?

Answer: Head pressure rises because effective condensing surface is lost

Liquid flooding the condenser tubes reduces the surface available for condensing, raising head pressure.

What health hazard makes water treatment and cleaning of evaporative condensers especially important?

Answer: Legionella bacteria growth

Warm recirculating water can breed Legionella, which spreads through drift and causes Legionnaires' disease.

In a gravity-flooded evaporator, where is the surge drum normally located?

Answer: Above the evaporator coil

The drum sits above the coil so liquid can flow by gravity into the coil and vapor can rise back to the drum.

Why do low-temperature freezer evaporator coils typically use wider fin spacing than cooler coils?

Answer: To allow frost to build up without quickly blocking airflow

Wider fin spacing lets more frost accumulate between defrosts before airflow is choked.

What is subcooling in a condenser?

Answer: Cooling liquid refrigerant below its saturation temperature

Subcooling is the temperature of liquid below the saturation temperature at its pressure.

A room requiring a warmer evaporator temperature than the common suction main is controlled by which device at the evaporator outlet?

Answer: Back-pressure (evaporator pressure) regulator

A back-pressure regulator holds the evaporator at a higher pressure, and therefore temperature, than the suction main.