Direct contact membrane distillation: modelling and concentration experiments

Direct contact membrane distillation (DCMD) processwas chosen to produce a highly concentrated apple juice using hollow
fiber modules. A high 64Brix concentration was achieved. The trans-membrane driving force decreased with increasing
extra-fiber temperature but increased with higher feed and distillate flowrates in the intra- and extra-fiber volumes, respectively.
Flux inversion was sensitive to small differences in temperature between the intra- and extra-fiber volumes and could be
prevented by increasing the intra-fiber feed temperature by 2-4C. Flux rates were dependent upon the temperature polarisation
coefficient (TPC) and the effect of the concentration polarisation coefficient (CPC) was negligible. Trans-membrane flux was
also significantly increased by thermal-osmotic distillation (TOD) 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 properties of membrane morphology, such as the distribution of pores of different diameters and
elastic and other mechanical properties upon flux were taken into account in this model. ©2000 Elsevier Science B.V. All
rights reserved.