Flash evaporation

Flash evaporation (or partial evaporation) is the partial vapor that occurs when a <a href="/facts/Boiling_point/E2BK9QoS">saturated liquid</a> stream undergoes a reduction in pressure by passing through a <a href="/facts/Thermal_expansion_valve/TTvjb0tf">throttling valve</a> or other throttling device. This process is one of the simplest <a href="/facts/Unit_operation/7TAe9XH0">unit operations</a>. If the throttling valve or device is located at the entry into a <a href="/facts/Pressure_vessel/5mGeFbpQ">pressure vessel</a> so that the flash evaporation occurs within the vessel, then the vessel is often referred to as a <a href="/facts/Vapor%E2%80%93liquid_separator/txvzAUvS">flash drum</a>.
If the saturated liquid is a single-component liquid (for example, <a href="/facts/Propane/E0b23KGh">propane</a> or liquid <a href="/facts/Ammonia/MtLtJFtz">ammonia</a>), a part of the liquid immediately "flashes" into vapor. Both the vapor and the residual liquid are cooled to the <a href="/facts/Saturation_temperature/E2BK9QoS">saturation temperature</a> of the liquid at the reduced pressure. This is often referred to as "auto-refrigeration" and is the basis of most conventional <a href="/facts/Vapor_compression_refrigeration/oT3EM4nS">vapor compression refrigeration</a> systems.
If the saturated liquid is a multi-component liquid (for example, a mixture of <a href="/facts/Propane/E0b23KGh">propane</a>, <a href="/facts/Isobutane/Bd8H7rsH">isobutane</a> and normal <a href="/facts/Butane/InIHpYlY">butane</a>), the flashed vapor is richer in the more <a href="/facts/Relative_volatility/TY9ynnC6">volatile</a> components than is the remaining liquid.
Uncontrolled flash evaporation can result in a boiling liquid expanding vapor explosion (<a href="/facts/Boiling_liquid_expanding_vapor_explosion/kEJbkcs9">BLEVE</a>).

Flash evaporation open-in-new

Flash evaporation