單項選擇題When it is necessary to open a refrigeration system for repairs and the system will be open for more than a few minutes, the open ends of the system should be （）.

A.dehydrated
B.purged
C.plugged
D.evacuated


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1.單項選擇題If an air compressor is used to supply compressed air to outlets throughout the engine room and on deck of a vessel, the system is known as the （）.

A.combustion control air system
B.supply air system
C.ships service air system
D.low pressure deck air system

2.單項選擇題The sensible heat of air is dependent upon the （）.

A.dry bulb temperature
B.wet bulb temperature
C.saturation temperature
D.water vapor superheat

3.單項選擇題Which of the devices listed, when used on an electro-hydraulic steering gear, keeps the movement of the redder closely in step with the steering wheel?（）

A.The follow-up gear
B.The rudder angle indicator
C.The synchronous electric transmitter
D.A rudder angle limit switch

4.單項選擇題Propeller pitch speed minus ship speed divided by the propeller pitch speed is termed （）.

A.apparent slip
B.tree slip
C.pitch
D.propulsive efficiency

5.單項選擇題A multistage centrifugal pump can be BEST described as having （）.

A.two or more impellers housed together in one casing and mounted on a single shaft
B.a single stepped impeller mounted in a progressively staged casing
C.a large radial clearance between the impeller and casing to prevent overheating due to
D.an increase in the discharge velocity of the liquid with a corresponding decrease in pressure through the stages