Direct contact membrane distillation: modelling and concentration experiments

Direct contact membrane distillation (DCMD) process was chosen to produce a highly concentrated apple juice using hollow fiber modules. A high 64 degr ees Brix concentration was achieved. The trans-membrane driving force decre ased with increasing extra-fiber temperature but increased with higher feed and distillate flow rates in the intra- and extra-fiber volumes, respectiv ely. Flux inversion was sensitive to small differences in temperature betwe en the intra- and extra-fiber volumes and could be prevented by increasing the intra-fiber feed temperature by 2-4 degrees C. Flux rates were dependen t upon the temperature polarisation coefficient (TPC) and the effect of the concentration polarisation coefficient (CPC) was negligible. Trans-membran e flux was also significantly increased by thermal-osmotic distillation (TO D) using a high concentration of CaCl2 as the permeate solution. A new model describing the fluid dynamics and membrane behaviour within the DCMD system is presented. In particular, the influence of various properti es of membrane morphology, such as the distribution of pores of different d iameters and elastic and other mechanical properties upon flux were taken i nto account in this model. (C)2000 Elsevier Science B.V. All rights reserve d.