Which of the listed pumps is NOT a positive displacement pump?（）

If the relief valve on the discharge side of a hydraulic pump lifts, the cause could be （）.

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

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

On tank vessels equipped with power operated cargo tank valves, the type of power operator most commonly used is （）.

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

If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.

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

The usual symptoms of cavitation in a centrifugal pump is （）.

The rate of heat transfer between the hot and cold fluids passing through a shell-and-tube type heat exchanger will （）.