Computational fluid dynamic investigation on performance of air gap membrane distillation with a rotating fan

Abstract

The objective of this research is to investigate the impact of adding an air-circulation fan with variable rotation speed on the performance of an Air-Gap Membrane Distillation (AGMD) system. An innovative model was developed, incorporating a turbulent diffusion model within the air gap to accurately account for heat and mass transfer processes involving eddy diffusivities. Computational Fluid Dynamics (CFD) model results are validated with experimental data for AGMD systems with and without a rotating fan. The findings demonstrate that the permeate flux increased three times for the Fan-assisted AGMD module compared to the conventional AGMD module at a feed temperature of 80 °C. The research revealed a 100 % increase in permeate flux at 50 °C and 60 °C feed temperatures and a remarkable 128 % increase at 70 °C feed temperature when the fan rotation speed was increased from 1000 to 4000 rpm. This increase in fan speed also led to a 56 % and 30 % boost in Evaporation Efficiency (EE) at 50 °C and 70 °C, respectively. Moreover, the study found that elevating the fan speed reduced the Specific Thermal Energy Consumption (STEC), with 42 %, 45 %, and 47 % at 50 °C, 60 °C, and 70 °C, respectively. Additionally, changing the feed velocity positively impacted permeate flux (an 80 % increase) and had a small increment in evaporation efficiency (about 3 %) in the fan-assisted AGMD module.

Keywords

• CFD model
• Turbulent diffusion
• Fan-assisted AGMD
• Permeate flux
• Energy consumption