The Souders–Brown equation (named after Mott Souders and George Granger Brown) has been the tool for obtaining the maximum allowable vapor velocity in vapor–liquid separation vessels (variously called flash drums, knockout drums, knockout pots, compressor suction drums and compressor inlet drums). It has also been used for the same purpose in designing trayed fractionating columns, trayed absorption columns and other vapor–liquid-contacting columns.

A vapor–liquid separator drum is a vertical vessel into which a liquid and vapor mixture (or a flashing liquid) is fed and wherein the liquid is separated by gravity, falls to the bottom of the vessel, and is withdrawn. The vapor travels upward at a design velocity which minimizes the entrainment of any liquid droplets in the vapor as it exits the top of the vessel.

Souders Brown Equation:


V = ( K * sqrt((PL - PV) / PV) )
Where,
V = Maximum Allowable Vapor Velocity
K =Vapor Velocity Factor
PL =Liquid Density
PV = Vapor Density