Final answer:
Flash gas is the vapor that is produced by the pressure drop in a capillary tube. It occurs when the pressure of a liquid drops below its vapor pressure, resulting in a phase change from liquid to vapor. This phenomenon is commonly observed in refrigeration systems.
Step-by-step explanation:
The vapor that is produced by the pressure drop by a capillary tube is known as flash gas. Flash gas is the result of a phase change from liquid to vapor that occurs when the pressure of a liquid drops below its vapor pressure. This phenomenon is often observed in refrigeration systems and is an important factor in the cooling process. For example, when a refrigerant undergoes expansion through a capillary tube, it experiences a drop in pressure, causing some of the liquid to rapidly vaporize into flash gas.