A Critical Study on Air Gap Membrane Distillation System

Membrane Distillation is an environmentally friendly, low-temperature, thermal-based membrane desalination process that is considered one of the most potential water separation methods. However, it remains unattractive for largescale industrial applications due to the reduced performance ratio caused by temperature polarization on the feed side of the polymeric membrane. This study introduces a novel bi-conductive concept in a designed lab-scale Air Gap Membrane Distillation (AGMD) system approaching a continuous evaporation process through a composite membrane. The design demonstrates a hydrophilic high-conductivity characteristic on the feed side and a hydrophobic low-conductivity characteristic on the permeate side. We studied the effect of the metallic layer on permeate flux under different operating parameters. Results show that heat is efficiently transferred to the liquid-vapor interface by reducing thermal resistance between the feed channel and polymeric membrane, thus improving the energy efficiency and distillate flux. The influence of operating parameters (i.e., brine mass flow rate, heating temperature, and brine concentration) are evaluated in a bi-conductive system, and results are compared to a conventional AGMD system without metallic layer and designed feed channel. Here, we reported a maximum water permeate flux of by taking advantage of bi-conductive AGMD system at a low brine mass flow rate range, and an average of improvement in gained output ratio without applying heat recovery methods. The study presented an effective application of the bi-conductive concept using metallic layers with inherent high thermal conductivity to reduce thermal resistance. This provides new design concepts for the commercially available membrane-based thermal water filtration and purification processes.