單項選擇題Which of the listed conditions can lead to cavitation氣穴in a centrifugal pump?（）

A.Vapor pockets formed in the suction flow stream
B.Rough easing volute surfaces
C.Worn wearing rings
D.Heavy fluid in the flow stream


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1.單項選擇題A centrifugal bilge pump requires priming （）.

A.primarily to lubricate the shaft seals
B.due to the inability of this type of pump to lift water to cover the suction (eye) of the impeller
C.to initially unload the pump by having its head pressure equal to discharge pressure
D.in order to overcome the potential energy of water in the discharge line

2.單項選擇題The process of removing moisture from air is known as（）.

A.humidification
B.dehumidification
C.vaporization
D.evaporation

3.單項選擇題The heat gained per pound of refrigerant in the evaporator is known as the（）.

A.latent heat of vaporization
B.sensible heat
C.refrigerating effect
D.specific heat of vaporization

5.單項選擇題On all vessels equipped with refrigeration units of over 20 cubic foot capacity, （）.

A.a gas mask suitable for protection against each refrigerant used, or a self contained breathing apparatus must be provided
B.it is the sole responsibility of the chief engineer to ascertain that all members of the engineering department are familiar with the use of gas masks or breathing apparatus
C.spare charges shall be carried for at least 50% of each size and variety of gas masks and/or self contained breathing apparatus
D.all of the above