单项选择题X 纠错
A.The two objects must be in physical contact
B.The two objects must be the same size
C.There must be an existing temperature differential
D.There must be an existing weight differential
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单项选择题
A.insufficient lubrication
B.insufficient refrigerant
C.excess refrigerant
D.excessive opening of the expansion valve
单项选择题
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
单项选择题
A.Radiation
B.Conduction
C.Convection
D.Each of the above
单项选择题
A.Shortage of refrigerant oil
B.Slight shortage of refrigerant
C.Excessive condenser cooling water flow
D.Faulty expansion valve
单项选择题
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
单项选择题
A.radiation
B.conduction
C.convection
D.condo-radiation
单项选择题
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
单项选择题
A.Radiation
B.Conduction
C.Natural convection
D.All of the above
单项选择题
A.A gate valve
B.A globe valve
C.Any check valve
D.Any needle valve
单项选择题
A.a shortage of compressor oil
B.warm food in the refrigerator
C.excessive condenser cooling water
D.a shortage of refrigerant