What is a flash drum?

Vessels into which flow a mixture of liquid and vapor. The goal is to separate the vapor and liquid. For design calculations it is normally assumed that the vapor and liquid are in equilibrium with one another and that the vessel is adiabatic (no heat lost or gained). One must simultaneously satisfy a material balance, a heat balance, and equilibrium. In HYSYS/UniSim, this can be done using either a Separator or a Tank.