Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.

Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.

The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its （）.

The rate of heat transfer from a hot region to a cold region is affected most by the （）.

A pressure drop through the refrigerant liquid line may cause （）.

The temperature differential occurring between the inlet temperature of the fluid to be cooled and the outlet temperature of the cooling medium in a shell-and-tube heat exchanger is greatest in which of the flow designs listed?（）

Thermostatic expansion valves can be adjusted for （）.

Low compressor head pressure in a refrigeration system can be caused by（）.

An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.

Which of the following problems could cause the high pressure cutout switch to shut down the compressor in a refrigeration system?（）