单项选择题The sudden reduction of pressure occurring within the crankcase of a refrigeration compressor during starting causes the ().

A.sudden evaporation of wax crystals in the lubricant
B.sudden evaporation of entrapped air in the lubricant
C.release of refrigerant from the oil/refrigerant mixture
D.release of dissolved lubricant from the refrigerant


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1.单项选择题One of the consequences in continuing to operate a centrifugal bilge pump with the discharge valve closed, is that the ().

A.motor overload will open
B.relief valve will open
C.pump will overheat
D.motor will overheat

2.单项选择题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

3.单项选择题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

4.单项选择题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

6.单项选择题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

7.单项选择题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

8.单项选择题Foaming of the oil in a refrigeration compressor crankcase is caused by ().

A.refrigerant boiling out of solution from the lube oil
B.liquid refrigerant flooding the compressor and system
C.lube oil viscosity being reduced by refrigerant dilution
D.compressor suction pressure suddenly increasing

9.单项选择题Which of the listed characteristics can be applied to R- 12 vapor?()

A.It is corrosive
B.It is odorless
C.It is visible as h blue fog
D.It has a distinctive taste

10.单项选择题The percentage of impurities in a specific fuel oil sample is determined by ().

A.settling in a fuel tank
B.testing in a laboratory centrifuge
C.burning in a calorimeter
D.testing in a closed cup