Data Sheet No. 179 - Mass Transfer in Distillation and Drying

Abstract

Publisher Summary This chapter describes mass transfer in distillation and drying. When a concentration gradient exists within a fluid that consists of two or more components, each constituent tends to flow in a direction such as to reduce the concentration gradient. This is known as mass transfer. In a still fluid or one flowing streamline in a direction normal to the concentration gradient, transfer is affected by the random movement of molecules. In turbulent flow, this is supplemented by eddy currents. In the absorption of a soluble gas by a liquid from a mixed gas, mass transfer first takes place from the bulk of the gas to the liquid surface and then into the bulk of the liquid. Neither the insoluble gas nor the liquid move in the direction of mass transfer. In a fractionation column, the less volatile gases diffuse to the liquid surface and the more volatile gases move at an equal molar rate away from the liquid surface. In the liquid phase, the less volatile material diffuses away from the gas–liquid interface. Where there is no forced flow of fluid across a surface, heat or mass transfer occur through natural convection.