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
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A.Radiation
B.Conduction
C.Natural convection
D.All of the above
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
A.Dehydrators must be used continuously in a refrigeration system
B.A 25 ton refrigeration system has the same cooling effect as melting 25 tons of ice in 24 hours
C.A thermostatic expansion valve is used to control refrigerated space temperature
D.The liquid receiver functions to collect and remove non- condensable gases
A.Hydraulic
B.Mechanical
C.Pneumatic
D.Electrical
A.Energy can be created or destroyed
B.Energy may not be transformed
C.The total quantity of energy in the universe is always the same
D.None of the above
A.evaporator
B.compressor
C.expansion valve
D.condenser
最新试题
If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will （）.
When the steering gear is in operation, you should （）.
An excessive charge of refrigerant in an air-cooled refrigeration system can cause （）.
Low compressor head pressure in a refrigeration system can be caused by（）.
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?（）
An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by （）.
When a refrigeration compressor has developed a high head pressure as a result of a refrigerant overcharge, you should （）.
One cause of high head pressure occurring in a refrigeration system can be （）.
A pressure drop through the refrigerant liquid line may cause （）.
The amount of fluid friction or internal friction inherent in a mineral lubricating oil is reflected as a measure of its （）.