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

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

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

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

When a refrigeration compressor has developed a high head pressure as a result of a refrigerant overcharge, you should （）.

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

One cause of high head pressure occurring in a refrigeration system can be （）.

If the viscosity of the liquid being transferred remains constant as the discharge pressure increases, the rotary pump （）.

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

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