What is a "flash gas" in the context of refrigeration?

In refrigeration, "flash gas" refers to the vapor that is formed from a refrigerant when it experiences a drop in pressure. When a liquid refrigerant enters a low-pressure area, some of it evaporates, turning into vapor due to the sudden decrease in pressure. This phenomenon occurs because the liquid refrigerant's saturation temperature is significantly lowered at lower pressures, causing a portion of it to boil off, creating vapor.

This concept is vital to understanding how refrigeration systems operate, particularly in components like evaporators and expansion devices, where pressure changes are common. The generation of flash gas is an important consideration for system efficiency and performance, as it impacts the heat exchange process and overall system dynamics.

The other options represent different concepts related to refrigeration. Liquid refrigerant at equilibrium does not accurately describe the dynamic nature of flash gas formation nor its connection to pressure changes. Heat absorbed by the refrigerant is a part of the refrigeration cycle but does not define flash gas. Excess refrigerant in the system could lead to operational inefficiencies but is not synonymous with flash gas.