Thermal performance assessment of spacer-filled air-gap membrane distillation systems with varying saline feeds

Air gap membrane distillation (AGMD) represents a promising technology for seawater desalination, yet performance limitations associated with temperature polarization and inadequate flow dynamics present significant obstacles. Feed channel spacers constitute a proven strategy for mitigating polarization and fouling through enhanced fluid mixing and turbulence generation, thereby improving transport phenomena and permeate productivity. This work presents three novel spacer designs (Mix-1, Mix-2, and Spiral), developed based on industrial mixing principles to promote enhanced flow mixing and consequently improve mass and heat transfer mechanisms within the feed channel. Comprehensive experimental evaluation was conducted using a laboratory-scale module across a broad range of operating conditions, including feed temperatures of 45–75 °C, flow rates of 11–33 kg/h, and salinity concentrations reaching 70 ppt. Results demonstrate that the Spiral spacer configuration achieved the greatest improvements, delivering up to 95 % higher permeate flux, more than 35 % lower in specific energy consumption, and up to 85 % higher in thermal efficiency relative to baseline spacer-free operation.