Numerical study on heat and mass transfer in falling film crystallization by an integrated model

Abstract

A numerical study of the falling film crystallization process for purifying material uses an integrated model to solve unsteady coupled heat and mass transfer problems with phase change. The model divides the melt continuously coming down from the top of the tube into numbers of flow bundles according to their entering time sequences (steps). The heat and mass transfer equations in the coordinate system are integrated from the top of the tube to the bottom for each fluid bundle, so that the transient crystallizing amount and crystal concentration can be calculated along the tube, using conventional formulas for fully developed heat and mass transfer of falling film liquid between the liquid and tube wall. The concentrations on both liquid-solid sides of the interface are kept in equilibrium according to their temperature-concentration phase diagram so that the solving procedure must be iterated at each time step. The calculated results of some important parameters, such as crystallization rate and naphthalene concentration, coincide qualitatively with the experiments. Finally, several factors that influence the process are studied as a good reference for designing and operating the separator.