The Principle of Refrigeration System

Update:20 Dec 2017
Summary:

For refrigeration system that use expansion valves, bac […]

For refrigeration system that use expansion valves, backwashing and expansion valve selection and improper use are closely related. Expansion valve selection is too large, the superheat setting is too small, the temperature package installation method is not correct or insulation bandage damage, expansion valve failure may result in back to liquid.

For small refrigeration systems that use capillaries, overfilling may cause backflushing. Evaporator frosting serious or fan failure heat transfer worse, non-evaporated liquid can cause back to liquid.

Frequent fluctuations in temperature can also cause expansion valve malfunction caused by back to liquid. For refrigeration system where backwash is more difficult to avoid, installing a gas-liquid separator and using pump-down shutdowns, which allow the compressor to drain the liquid refrigerant in the evaporator before shutting down, can effectively prevent or reduce the risk of backwashing.

Back to the air-cooled compressor at start-up, the crankcase of the phenomenon of intense foaming of the lubricant is called liquid start. Blistering at start-up with liquid can be clearly observed on the oil sight glass. The basic reason for starting with liquid is that a large amount of refrigerant dissolves in the lubricant and sinks below the lubricant, suddenly boiling when the pressure suddenly drops, and causes the foaming of the lubricant. The duration of blistering depends on the amount of refrigerant, usually a few minutes or ten minutes. A lot of bubbles floating on the oil surface, and even full of crankcase. Once it is drawn into the cylinder through the intake port, the foam is reduced to a liquid (a mixture of lubricant and refrigerant) that can easily cause liquid strikes. Obviously, the liquid attack caused by the start of the liquid only occurs during the start-up process.

Unlike backwash, the refrigerant that causes the fluid to start is fed to the crankcase in a "refrigerant shift" fashion. Refrigerant migration refers to the process or phenomenon of the compressor being stopped, the refrigerant in the evaporator being in the form of gas, entering the compressor through the return air line and being absorbed by the lubricating oil, or mixed with the lubricating oil after being condensed in the compressor.