单项选择题
A.bubbling refrigerant
B.overheating and oxidation
C.lowered operating temperatures
D.reducing the cloud or flash point
单项选择题 Which of the following centrifugal pump components converts the liquid kinetic energy of velocity to the potential energy of pressure?（）
单项选择题 Excessive circulation of the lubricating oil with the refrigerant in a refrigeration system will cause （）.
单项选择题 Scale accumulation on evaporator heat exchange surfaces （）.