Development and validation of a theoretical model for osmotic evaporation

Abstract

In this work, a mathematical model developed to describe the heat and mass transfer over time during the osmotic evaporation process is reported. The model predicted the vapor permeation flux and sugar concentration kinetics with error values of ≤36% and ≤16% respectively, during the evaporation of glucose–water solutions up to 50°Brix. Predictions of the model were experimentally validated in the range of vapor permeate flux values between 0.4 and 2kgm−2h−1. According to the model the variables having the most important effect on flux were temperature and the brine concentration. It also indicates anisotropy in the polarization of both temperature and concentration between the feed and brine sides of the membrane and points out that the heat and mass transfer phenomena occurring in the feed side of the membrane are the mechanisms controlling the process. The model was also used to describe the experimental flux and concentration kinetics of cassava starch hydrolysates. Deviations between predictions and data obtained with cassava starch hydrolysates are attributed to the high viscosity of this feed and to the increased mass transfer resistance among fibers inside the module.