The output volume of a positive fixed displacement pump can be changed only by （）.

If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.

If the head pressure of a reciprocating refrigeration compressor is excessive, （）.

The general purpose of a heat exchanger is to （）.

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

The major source of chemical contaminants in hydraulic fluid is （）.

A gradual decrease in the discharge pressure of an operating hydraulic pump can be caused by （）.

Thermostatic expansion valves can be adjusted for （）.

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

Which of the following statements is correct concerning heat transfer?（）