A.Radiation
B.Conduction
C.Natural convection
D.All of the above
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A.A gate valve
B.A globe valve
C.Any check valve
D.Any needle valve
A.a shortage of compressor oil
B.warm food in the refrigerator
C.excessive condenser cooling water
D.a shortage of refrigerant
A.molecular fluid vibration
B.energy losses
C.wide pressure variations
D.mechanical damage to control valves
A.Keeps the refrigerated space cooler
B.Reduces the efficiency of the plant
C.Takes the load off the compressor
D.Has no affect on the system
A.proportional band
B.the error signal
C.the reset signal
D.feedback
最新試題
The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
Which of the following problems could cause the high pressure cutout switch to shut down the compressor in a refrigeration system?（）
An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by （）.
Which of the listed pumps is NOT a positive displacement pump?（）
An internal bypass is provided on some hydraulic system suction strainers to help reduce the possibility of （）.
The usual symptoms of cavitation in a centrifugal pump is （）.
Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）
Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by （）.
If the viscosity of the liquid being transferred remains constant as the discharge pressure increases, the rotary pump （）.
If the suction pressure at the refrigeration compressor is below normal, the cause can be（）.