Experimental and numerical study of air-gap membrane distillation (AGMD): Novel AGMD module for Oxygen-18 stable isotope enrichment

In this article, a novel module is presented to enhance the performance of air gap membrane distillation (AGMD) process. Experimental examinations were performed to modify a conventional AGMD module by presenting a new geometry and analyze the influence of this modification on the performance of the process. Also, three-dimensional (3D) numerical simulation was performed to reveal all aspects of this modification. In numerical study, the momentum, heat and mass transfer equations are solved with turbulent model (k-e realizable) to observe the flow feature inside the new AGMD geometries. Furthermore, the effect of radial baffles as well as feed flow rate (0.25, 0.50 and 0.75 kg/min) are investigated. In order to verify the numerical results, the simulated permeate flux was compared to the experimental data and low discrepancy (less than 6%) was observed. The results also indicate that the mass flux was improved (about 6%) as the rectangular-type module was replaced by the disk-type one. Moreover, our findings show that applying four, six and eight radial baffles to disk type modules significantly enhanced the permeate flux by 10, 13 and 14.7%, respectively. Most importantly, the applicability of the membrane distillation (MD) process for enrichment of 18 O water isotope of distilled water was studied using a laboratory operating disk-type AGMD module. This module was employed based on the best-performed geometry obtained from the numerical results. The achieved separation factor was 0.9823 which shows that this approach is a reliable method for isotope separation.