A.increase compressor discharge pressure on demand
B.increase compressor operating speed as necessary
C.allow the motor to turn the compressor opposed only by friction
D.reduce the compressor frictional load when starting
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A.Radiation
B.Conduction
C.Convection
D.Each of the above
A.Shortage of refrigerant oil
B.Slight shortage of refrigerant
C.Excessive condenser cooling water flow
D.Faulty expansion valve
A.vary their speed according to temperature and load
B.start and come up to speed before air compression begins
C.change speed according to overload demands
D.reduce compressed air charge density
A.radiation
B.conduction
C.convection
D.condo-radiation
A.used in either the fully dosed or fully opened position
B.installed with the stem down
C.used for steam service only
D.used to throttle or regulate the flow of liquid
最新試題
An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.
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 （）.
Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.
Low compressor head pressure in a refrigeration system can be caused by（）.
The output volume of a positive fixed displacement pump can be changed only by （）.
The rate of heat transfer from a hot region to a cold region is affected most by the （）.
The control mode in which the final control element is moved from one of two flexed positions to the other is known as （）.
Thermostatic expansion valves can be adjusted for （）.
The rate of heat transfer between the hot and cold fluids passing through a shell-and-tube type heat exchanger will （）.