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

In this study, process enhancements achieved by the use of 3D printed feed spacers based on triply periodic minimal surfaces (TPMS) were comparatively assessed using the two most common membrane distillation (MD) configurations: air gap (AGMD) and direct contact (DCMD). The MD performance was assessed based on the impact of spacer design (TPMS vs. commercial spacer) on flux and feed channel pressure drop, and their consequent impact on the levelized cost of water (COW). The studied spacer architectures led to a minimal improvement (≤17%) in AGMD flux, much lower than that achieved in DCMD (≤57%). Consequently, for a waste heat-operated MD process, the spacer-induced channel pressure drop became the most influential cost bottleneck on COW. Generally, the contribution of the pumping cost to the total operating cost was found to be greater for DCMD than AGMD. Thus, the COW of a waste heat operated DCMD is more sensitive to a decrease in spacer-induced channel pressure drop than in an AGMD. For an MD process operated with additional heat cost, the flux improvement achieved using TPMS spacers reduces the thermal energy component of the operating cost. Ultimately, this predominantly contributes to a lower COW.