BT-22 Non-Equilibrium Model for Mist Flow in Tubes

J. W. Palen

Xist currently uses an equilibrium model that overestimates the amount of droplet evaporation in mist flow and superheat produced inside a heated tube. For example, when a light hydrocarbon is vaporized and superheated in a single tube pass, the equilibrium model currently used is too optimistic. Droplets actually evaporate very slowly and are difficult to remove from the vapor stream unless some type of insert is used in the tube. The software indicates that the results are optimistic and warns that twisted tape inserts are required. If inserts are not incorporated in the tube design, the user may expect much more superheating than actually is obtainable. To rate the performance of such exchangers more realistically, HTRI has developed a new theoretical non-equilibrium model for mist flow and vapor superheating heat transfer in a tube; this model depends on an assumed droplet vaporization heat transfer coefficient.