單項(xiàng)選擇題The principal purpose of sub-cooling liquid refrigerant prior to its entering the expansion valve is to （）.

A.increase the refrigerating effect, by decreasing the amount of flash gas
B.allow the refrigerant to enter the throttling device in a saturated condition
C.increase the refrigerating effect by increasing the amount of flash gas
D.minimize the temperature drop of the liquid as it passes through the solenoid valve to the outlet side


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1.單項(xiàng)選擇題Refrigerant is normally sub-cooled in a refrigeration or air conditioning system condenser to （）.

A.maintain adequate coil back pressure
B.prohibit flashing in the liquid line
C.reduce refrigerant volume in the system
D.reduce compressor discharge line loading

2.單項(xiàng)選擇題An advantage of a helical gear pump over a simple gear pump is that the helical gear pump is capable of （）.

A.maintaining a steadier speed
B.delivering liquids over greater distances
C.operating for longer periods of time
D.producing a smoother discharge flow

3.單項(xiàng)選擇題The size of ball and roller bearings can be identified by the （）.

A.rolling member size
B.inner race cone width
C.manufacturers numerical code
D.outer ring width

4.單項(xiàng)選擇題A centrifugal pump produces flow with a resulting discharge head by energy conversionIt is typical for the energy conversion to follow the order of （）.

A.mechanical energy to kinetic energy to potential energy
B.mechanical energy to potential energy to kinetic energy
C.potential energy to mechanical energy to kinetic energy
D.kinetic energy to mechanical energy to potential energy

5.單項(xiàng)選擇題If an operating bilge pump is developing good vacuum, but is unable to discharge any water, which of the following problems is the most probable cause?（）

A.The wearing rings are excessively worn
B.The suction strainer is clogged
C.The discharge valve is clogged
D.The shaft is worn