What is the term for the instantaneous change of state from liquid to vapor when a liquid flows from high to low pressure?

The process described in the question is referred to as flashing. This term specifically denotes the phenomenon where a liquid rapidly transitions to a vapor state due to a decrease in pressure. When liquid is subjected to lower pressure conditions, its boiling point decreases, and if the pressure is reduced sufficiently, the liquid can vaporize almost instantly. This is commonly observed in various industrial applications, particularly in systems like refrigeration and gas handling, where rapid pressure drops occur.

Understanding this concept is crucial for pipefitters and those working with fluid dynamics, as it directly impacts how systems are designed and operated, especially under varying pressure conditions. Flashing can lead to changes in flow characteristics and may affect system performance, necessitating careful consideration in engineering applications. The other choices, while related to fluid behavior, do not accurately capture the specific process of liquid-vapor transformation under pressure changes as flashing does.