單項(xiàng)選擇題Which of the following statements is true concerning the overall efficiency of air compressors?（）

A.High pressure compressors are more efficient than low pressure compressors
B.Mechanical efficiency divided by compressor efficiency will equal the overall efficiency of the compressor unit
C.Two stage compressors are generally more efficient than single stage compressors
D.The volumetric efficiency is decreased in multistage compressors


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1.單項(xiàng)選擇題The ability of an oil to separate cleanly from an oil and water mixture is referred to as its （）.

A.precipitation number
B.neutralization number
C.pour point
D.demulsibility

2.單項(xiàng)選擇題When the relief valve opens it discharges high pressure refrigerant vapor to the （）.

A.liquid strainer
B.refrigerant inlet of the condenser
C.inlet side of the evaporator
D.suction side of the compressor

4.單項(xiàng)選擇題The clearance volume for a single stage compressor is defined as the space created between the （）.

A.top of the piston and bottom side of head, with the piston at BDC
B.piston and head, including the space around the piston to the top of the upper ring and under the valves, with the piston at TDC
C.bottom of the piston and bottom side of the head at TDC, regardless of upper ring location and valve placement
D.top of the piston and bottom side of the head at TDC as compared to that which exists between the top of the piston and bottom side of head at BDC

5.單項(xiàng)選擇題Demulsibility of a lube oil is defined as （）.

A.the ability of oil to separate from water
B.the temperature at which oil flows rapidly
C.a measure of the water in a lube oil system
D.an emulsion of different grades of oil