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單項(xiàng)選擇題

Scale accumulation on evaporator heat exchange surfaces （）.

A.increases brine density
B.increases distillate salinity
C.reduces metal corrosion
D.reduces heat transfer

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單項(xiàng)選擇題

In order to properly remove air from the casing of a centrifugal pump when starting, the pump should have a （）.

A.positive head
B.negative suction head
C.mechanical seal
D.vent valve attached to the casing at the top of the volute

單項(xiàng)選擇題

The valve best suited for throttling gas or liquid flow in a pipeline is the（）.

A.gate valve
B.globe valve
C.check valve
D.plug cock

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