單項(xiàng)選擇題Which of the following statements is correct concerning a typical shipboard multi-coil refrigeration system?()

A.The liquid receiver functions to collect and remove non-condensable gases
B.A thermostatic expansion valve is used to control refrigerated space temperature
C.Refrigerant temperature in an evaporator is directly related to refrigerant pressure
D.Dehydrators must be used continuously in a refrigeration system


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1.單項(xiàng)選擇題The basic function of the centrifugal pump impeller is to ().

A.directly increase the pressure of the liquid being pumped
B.directly increase the velocity of the liquid being pumped
C.convert the potential energy of the liquid to kinetic energy
D.separate air from the liquid being pumped

2.單項(xiàng)選擇題Excessive oil foaming in the crankcase of a refrigeration compressor can result in ().

A.overheated compressor bearings
B.excess lube oil viscosity
C.carbon deposits on the compressor piston rings
D.wax crystals forming in the lubricant

4.單項(xiàng)選擇題In a refrigeration system, foaming of the crankcase oil may cause the ().

A.expansion valve to overfeed
B.compressor to knock
C.water regulating valve to fail
D.crankcase drains to plug

5.單項(xiàng)選擇題Excessive scale formation in a distilling plant may result from ().

A.poor distillate quality
B.reduced evaporator capacity
C.low brine concentration
D.improper vacuum regulation

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If the thermal bulb of an expansion valve is incorrectly placed at the center of the coil instead of the end, it will ().

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Pitting in the suction areas of a centrifugal pump bronze impeller is usually caused by ().

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

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The output volume of a positive fixed displacement pump can be changed only by ().

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The rate of heat transfer from a hot region to a cold region is affected most by the ().

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

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An excessive charge of refrigerant in an air-cooled refrigeration system can cause ().

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Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?()

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An increasing head pressure in a refrigeration system, without any corresponding change in the cooling water inlet temperature, would probably be caused by ().

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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?()

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