Effect of non-woven net spacer on a direct contact membrane distillation performance: Experimental and theoretical studies

Abstract

This study provides a comprehensive and systematic overview of the fundamental characteristics of heat and mass transfer in the direct contact membrane distillation (DCMD) process that employs different types of spacers on (i.e., adjacent to) one or both surfaces of the membrane. Detailed theoretical investigations were carried out to demonstrate the effects of spacers adjacent to the membrane surface on heat and mass transfer enhancement in the DCMD with a PTFE/PP composite membrane, complemented with experimental data for model validation. Thus, this work aimed to propose and demonstrate the heat transfer correlation for spacerfilled channels to reliably predict the heat and mass transfer improvement by non-woven net spacers in the DCMD process. The results showed that the permeate flux enhancement by the spacers ranged between 7%-19% only for the spacer-filled permeate channels and between 21%-33% only for the spacer-filled feed channels even at higher flow rates, thus indicating lower flux enhancements in the spacer-filled permeate channels. This was because the influence of spacers on flux improvement became more evident at higher temperatures owing to higher temperature polarization. In this study, the maximum flux enhancement of approximately 43% over the empty channels, which was achieved using the thinnest and densest spacer with a hydrodynamic angle of 90°, adjacent to both membrane surfaces.

Towards the first proof of the concept of a Reverse ElectroDialysis - Membrane Distillation Heat Engine

“…As a matter of fact, the future MD results projected here are similar to current ones at low concentration, and the enhancement is mostly in the high concentration range. Another potential improvement is at the level of module design, for instance using novel spacers for improving heat and mass transfer and reducing the polarization effects between the bulk stream and the membrane surface, which are also more important for high salinity feeds [54][55][56]. Overall, one can observe that using highly-performing RED membranes the effect of the uncontrolled mixing process is reduced, while the migrative flux increases, resulting in a net increase of the power produced.…”

Hole-Type Spacers for More Stable Shale Gas-Produced Water Treatment by Forward Osmosis

“…Feed spacers aid not only to support the membrane layers inside the filtration module but also to mitigate the concentration polarization (CP), resulting in lower membrane fouling and enhanced water flux production due to the promotion of unsteadiness/turbulence in the channel [ 19 , 31 ]. Research studies have been done to investigate the effect of spacer design on enhanced filtration performances and membrane fouling mitigation [ 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ]. Zhang et al [ 35 ] have investigated the effect of spacer integration in FO system in terms of CP.…”

Comparative assessment of the effects of 3D printed feed spacers on process performance in MD systems

“…In addition to effecting inter-membrane spacing in flat-sheet membrane modules [31], including spiral wound elements, feed spacers function as turbulence promoters by inducing directional changes in the flow and generating significant secondary flow structures [32]. By inducing additional flow turbulence, feed channel spacers suppress the thermal and concentration boundary layers bordering the membrane, thus reducing the temperature and concentration polarization effects, enhancing flux, and minimizing foulant adhesion [33][34][35]. Nevertheless, the presence of spacer also increases the pressure drop over the feed channel [32].…”