313A Compressors & Condensers

Question 1

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

Accepted Answer

Reciprocating (piston) compressor

Answer

Scroll compressor

Answer

Centrifugal compressor

Answer

Screw compressor

Question 2

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

Accepted Answer

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

Answer

Lower initial purchase cost

Answer

Ability to handle liquid slugging without damage

Answer

Higher compression ratios suitable for industrial refrigeration

Question 3

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

Accepted Answer

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

Answer

Oil foaming in the crankcase that starves bearings of lubrication

Answer

A buildup of sludge on compressor valves reducing efficiency

Answer

Excessive oil circulation through the system causing liquid hammer in pipes

Question 4

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

Accepted Answer

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

Answer

To heat the discharge gas before it enters the condenser

Answer

To maintain minimum ambient temperature around the compressor

Answer

To prevent ice formation on the compressor body in low-temperature applications

Question 5

In a hermetic compressor, how is the motor cooled?

Accepted Answer

By the suction refrigerant vapour passing over the motor windings

Answer

By an external fan mounted on the compressor shell

Answer

By a separate water-cooling circuit connected to the shell

Answer

By oil circulated through an external heat exchanger

Question 6

What is compression ratio in a refrigeration compressor?

Accepted Answer

The ratio of absolute discharge pressure to absolute suction pressure

Answer

The ratio of refrigerant mass in the discharge line to suction line

Answer

The ratio of compressor displacement to cylinder volume

Answer

The ratio of compressor motor watts to cooling capacity in watts