A novel approach to thermal desalination: membrane-less distillation

ABSTRACT A three-panel blue graphical abstract. The left panel shows a hand catching water under a tap signaling the human need for water, titled "Mounting Freshwater Pressures," calling for sustainable technologies. The middle panel shows a declining flux graph for "Air Gap Membrane Distillation," noting limitations like membrane fouling and wetting. The right panel presents "Membrane-less Air Gap Distillation" with a +46.67% flux increase, showing dashed arrows representing water vapour moving from a heated flow to a cooled wall under partial pressure difference in an air gap, describing a novel design with improved condensation rates. Emerging as an economic substitute, membrane distillation has surfaced as a cost-effective method for fresh water production from high-salinity water, using solar thermal energy or waste-heat recovery. Air gap membrane distillation (AGMD) has been developed as an enhancement to its conventional configuration. In this paper, we explore a new approach to AGMD that removes the membrane and relies on the air gap as the sole separator between the hot and condensing water. First, the numerical model is validated against three numerical and experimental results from previously published research papers on AGMD systems by simulating the same systems and comparing the condensate flux. Following validation, the condensate flux of this system at different air gap thicknesses, temperature distributions, fluid flow patterns, and the use of multiple effects are studied. This new membrane-less air gap distillation configuration entirely removes the membrane, relying on the air gap for mass transport – a fundamental departure from conventional AGMD systems. Compared with experimental and numerical AGMD systems, this configuration significantly increased the condensation rate by up to 46.67%.