Experimental and numerical investigation of a new hollow fiber-based multi-effect vacuum membrane distillation design

Abstract

Distillation systems can achieve much higher energy efficiency by utilizing multiple effects to internally recycle latent heat. Flat sheet membrane distillation systems (i.e., the Memsys MDS range of products) have taken advantage of this, but hollow fiber vacuum membrane distillation systems have not yet been systematically designed to incorporate the multi-effect concept. To advance this concept, a hollow fiber-based multi-effect VMD (HF V-MEMD) was designed and manufactured to internally recover the latent heat of the permeate vapor between effects using hollow helical baffles. A mathematical model was developed to investigate the effect of the operating and design conditions on the permeate flux, the gained output ratio (GOR), and the specific total energy consumption (STEC). It was found that a GOR of 1.5–3.5 can be achieved across a range of operating conditions. Additionally, for an optimal module design (e.g., 500 m2/m3 packing density, 0.5 m module length, and a 0.2–0.3 m shell diameter), the results indicate that a 4-effect design can improve the STEC by more than 60% compared to a single-effect design. Overall, this study concludes that the proposed energy-efficient HF V-MEMD design is most suitable for compact, portable systems to alleviate water scarcity in rural arid-regions.