Experimental investigation of an air gap membrane distillation unit with double-sided cooling channel

Membrane distillation (MD) is a non-isothermal membrane separation process capable of operating at low temperature and low transmembrane hydrostatic pressure. Air gap membrane distillation (AGMD) is one of the MD configurations. In this study, the performance of double-stage AGMD unit at different AGMD-operating parameters such as feed temperature, feed flow rate, coolant temperature, coolant flow rate and air gap width is presented. Experimental results revealed that the built double-stage AGMD unit is capable of achieving a maximum cumulative distillate production of 128.46 kg/m²h, a total (average) flux of 64.23 kg/m²h and a single-stage flux of 65.81 kg/m²h. One key feature of the proposed design is the ability of the unit to use a common cooling chamber to provide the necessary cooling required by the two feed chambers. This reduces the total capital, maintenance and total energy consumption costs. Other benefits include simple module design, easy modules installation and improved system productivity. Furthermore, the system can be operated either as a single-stage or double-stage unit. A simple theoretical model for predicting flux in single-stage AGMD unit was equally presented. The model predicted fluxes with less than 13% discrepancy.