單項(xiàng)選擇題When the propeller blades are integral with the hub, the propeller is called a （）.

A.built up propeller
B.solid propeller
C.controllable pitch propeller
D.suction back propeller


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1.單項(xiàng)選擇題The tendency of a flammable liquid to vaporize is indicated by its （）.

A.ignition temperature
B.flash point
C.flammable range
D.convection index

2.單項(xiàng)選擇題Moisture in the refrigerant may （）.

A.freeze on the expansion valve seat and reduce the flow of liquid refrigerant
B.emulsify the oil in the condenser
C.freeze in the king valve
D.clog the oil trap

3.單項(xiàng)選擇題Why will a two stage flash type distilling plant tend to operate more efficiently when operating in cold seawater?（）

A.The colder seawater passing through the condenser tube bundles of the various stages increases evaporator vacuum
B.The amount of heated feed water discharged from the feed water heater after cndenser is increased
C.Fewer non-condensable gases are created by the flow of colder seawater
D.More seawater is allowed to pass through the flint stage overflow weir

4.單項(xiàng)選擇題Moisture is removed from a refrigeration system by（）.

A.bleeding refrigerant from the condenser
B.opening a drain petcock on the oil separator
C.condensing the water in the heat exchanger
D.using a dehydrator cartridge

5.單項(xiàng)選擇題A centrifugal pump vibrates excessively during operationUpon disassembling the pump it is found that the impeller is out of balanceWithout an available spare, you should （）.

A.drill holes through the heavy side of the impeller until it balances
B.weld counterweights to the light side of the impeller
C.remove metal from the heavy side by machining in a lathe
D.acid wash and serape the heavy side until it balances