Compressors & Condensers Flashcards

What type of compressor uses pistons driven by a crankshaft to compress refrigerant?

Answer: Reciprocating (piston) compressor

A reciprocating compressor uses pistons connected to a crankshaft that move up and down in cylinders to compress refrigerant vapour, and is one of the most common types in commercial refrigeration.

What is the main advantage of a scroll compressor over a reciprocating compressor?

Answer: Fewer moving parts, quieter operation, and higher efficiency at part load

Scroll compressors have fewer moving parts than reciprocating compressors, resulting in smoother, quieter operation and generally higher energy efficiency, particularly at part-load conditions.

What is 'liquid slugging' in a compressor and why is it dangerous?

Answer: Liquid refrigerant entering the compressor cylinders, which can cause mechanical damage due to incompressibility of liquids

Liquid slugging occurs when liquid refrigerant enters the compressor, and because liquids cannot be compressed, the compressor valves and pistons can be severely damaged or destroyed.

What is the purpose of a crankcase heater on a refrigeration compressor?

Answer: To keep the oil warm for easier starting in cold weather and to prevent refrigerant migration into the crankcase oil

A crankcase heater prevents refrigerant from migrating and condensing in the compressor oil during off-cycles, which would cause foaming and oil dilution on startup, potentially leading to bearing failure.

In a hermetic compressor, how is the motor cooled?

Answer: By the suction refrigerant vapour passing over the motor windings

In a hermetic compressor, the motor and compressor are sealed in the same shell, and the cool suction vapour returning from the evaporator passes over the motor windings to carry away heat.

What is compression ratio in a refrigeration compressor?

Answer: The ratio of absolute discharge pressure to absolute suction pressure

Compression ratio is calculated by dividing the absolute discharge pressure (kPa absolute) by the absolute suction pressure (kPa absolute), and high compression ratios reduce compressor efficiency and capacity.