Comparing and optimizing hollow fibre and flat sheet vacuum membrane distillation

Membrane Distillation (MD) systems have the potential to tackle the growing global water demand. Within various MD systems, Vacuum Membrane Distillation (VMD) systems are particularly important in addressing this issue. Hollow Fibre VMD (HF-VMD) and Flat Sheet VMD (FS-VMD) are the two main configurations of VMD systems, where limited studies are available on their comparison and optimisation under identical operational conditions. This study firstly charts the mathematical modelling of HF-VMD and FS-VMD systems that have been developed, accounting for the amount of flux, Gain Output Ratio (GOR), Temperature Polarisation Coefficient (TPC), and Specific Thermal Energy Consumption (STEC) of both configurations under same conditions (i.e., porosity, pore radius, membrane area, membrane type) have been compared. Secondly, optimisation of both systems was performed via the Particle Swarm Optimisation (PSO) algorithm to identify optimal values of operational parameters. The results show that the HF-VMD configuration exhibits higher flux, GOR, and TPC, along with lower STEC, compared to the FS-VMD system for all examined ranges of feed temperature, feed flow rate, pressure in the vacuum channel, porosity, membrane thickness and salt concentration. Additionally, TPC was sensitive to feed temperature, feed flow rate, Reynolds number, and pressure, but was found to be largely unaffected by membrane porosity, thickness, and salt concentration. Furthermore, optimisation results show that the optimal values of GOR for the examined HF-VMD and FS-VMD systems are 0.83 and 0.53, respectively. With corresponding optimal pressures of 5.07 kPa and 5.01 kPa.