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?（）

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

A.remain constant along the tubes length
B.be greatest in a single pass counter flow heat exchanger
C.remain constant throughout the heat exchanger
D.vary from section to section through out the heat exchanger

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

A.a low load on the unit
B.a clogged pump suction strainer
C.a blockage in the line between the pump and hydraulic motor
D.the hydraulic motor turning too fast

单项选择题A salinity indicator is used to determine the （）.

A.cause of salt contamination
B.location of salt water contamination
C.chemical makeup of feed-water
D.level of alkalinity in condensate

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

A.refrigerant overcharge
B.overfeeding by the expansion valve
C.a restricted suction strainer
D.due to short cycling of the compressor

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

A.capacity will increase
B.capacity will decrease
C.suction pressure will increase
D.suction pressure will decrease