Analysis of an air-cooled air gap membrane distillation module

Abstract

An air-cooled design for an air gap membrane distillation (AGMD) process offers potential for significantly lowering energy requirements and reducing cost for desalination by eliminating or reducing the balance of plant components associated with the coolant flow system. Experiments were conducted on an air-cooled AGMD module to study the effects of air gap, support mesh conductivity and hydrophobicity, and the condensing surface hydrophobicity. A novel modular design was developed in which modules could be arranged in a series configuration to increase the distillate flux. The output from the series configuration was found to yield about three times the distillate water compared to a single pass water-cooled system with the same temperature difference (ΔT). The results also indicate that the mesh conductivity has a favorable effect on the flux value whereas the hydrophobicity of the mesh has no significant effect. The hydrophobicity of the condensing surface is favorable on two accounts: first, it increases the distillate flux at temperatures below 60 °C and secondly, the temperature difference of the saline feed when it enters and leaves the module is lower, which can lead to energy savings and higher yield when used in a series configuration.