Thermal efficiency enhancement of the direct contact membrane distillation: Conductive layer integration and geometrical undulation

The roles of high conductive layer integration and geometry undulation are investigated in order to improve the performance of the direct contact membrane distillation processes. In particular, the temperature polarization coefficient, mass flux and thermal efficiency are evaluated for the baseline and undulated flow under integrated superconductive layer membrane. This work caters for experimental and numerical model development. Experimentally, a countercurrent flow module for the desalination of sea water was developed using a flat-sheet electro-spun Polyvinylidene fluoride membrane generated and characterized by the author's group for model validation. A steady state, conjugated heat, Navier-Stokes flow model computational fluid dynamics model was developed and subjected to the exact thermal and velocity flow conditions. The setup comprises two adjacent channel flows representing the hot saline feed and the cold fresh permeate channels. The two channels are thermally coupled through the hydrophobic membrane that is equipped with superconductive feathering layers. The results show agreement between the numerical model and experimental model measurements for the surface temperature distribution and the inferred temperature polarization co-efficient. In view of these plausible results and in line with numerous works on direct contact membrane distillation, a combined Knudsen and Poiseuille flow model is integrated to estimate the permeated mass and heat flux and explore improving the Membrane Distillation system in terms of thermal efficiency. While the role of superconductive feathering showed insignificant improvement in the temperature polarization coefficient, mass flux and thermal efficiency, the effect of combined undulated channels geometry was more pronounced. The gain obtained in the mass flux reaches 5.8% at lower feed temperature (50 °C), which is associated with a 5.8% gain in thermal efficiency and a 9.5% gain in temperature polarization co-efficient. It reaches a 6.1% gain in mass flux and thermal efficiency and a 9.5% gain for temperature polarization co-efficient at a higher feed inlet temperature.