Mass transfer modelling of hollow fiber membrane contactor for apple juice concentration using osmotic membrane distillation

Abstract

The present research study is based on theoretical and experimental investigation of hydrophobic porous hollow fiber membrane contactor (HFMC) module. The mass transfer diffusional model was developed for osmotic membrane distillation (OMD) and applied in apple juice concentration. The mathematical model was developed, taking into consideration the resistance-in-series concept for the mass transfer of water vapor molecules across the hydrophobic HFMC. The model was adapted to include the pore geometry, dimensionless numbers and concentration variation due to viscosity. The water vapor transport model was then simulated in MATLAB® and successfully validated with the experimental data. The model was applied to study the effects of driving forces for mass transfer and membrane porosity. Process parameters like juice concentration, stripping solution concentration, and Reynolds number were also studied to evaluate their effect on the overall mass transfer co-efficient and water vapor flux. The OMD experiments for the concentration of clarified apple juice were carried out in a laboratory-scale HFMC mini-module composed of two independent circuits, for stripping solution (CaCl2) and apple juice, respectively, in a total recycled mode. For the concentration of clarified apple juice, the evaporation flux ranged from 0.122 to 0.472 kgm−2h−1 resulting in a juice concentration of 30°Brix. The increase in pore diameter from 0.1 to 0.6 µm resulted in an increase in the mass transfer coefficient from 1.57 × 10−10 to 7.23 × 10−10 ms−1. Similarly, water vapor flux was increased from 0.02 to 0.50 kgm−2h−1, when the activity coefficient was changed from 0.1 to 0.5. Moreover, the results indicated that if the experimental parameters are carefully controlled, the simulation results can be used to predict the OMD process efficiency.