单项选择题
A.used in either the fully dosed or fully opened position B.installed with the stem down C.used for steam service only D.used to throttle or regulate the flow of liquid
Which of the following modes of heat transfer does NOT ...
单项选择题Which of the following modes of heat transfer does NOT require any physical contact between a warmer and a cooler substance?（）
A.Radiation B.Conduction C.Natural convection D.All of the above
Which of the valves listed should be used either in the...
单项选择题Which of the valves listed should be used either in the fully opened or the fully closed position?（）
A.A gate valve B.A globe valve C.Any check valve D.Any needle valve
If a refrigeration compressor is running continuously w...
单项选择题If a refrigeration compressor is running continuously without lowering the temperature in the refrigerated space, the trouble may be （）.
A.a shortage of compressor oil B.warm food in the refrigerator C.excessive condenser cooling water D.a shortage of refrigerant
