A theoretical analysis of a spacer filled flat plate membrane distillation modules using CFD: Part II: Temperature polarisation analysis

This work is concerned with the theoretical analysis of the heat transfer and temperature polarisation phenomenon of Flat Plate Direct Contact Membrane Distillation. To study how different inlet velocities and temperatures affect mass flux and temperature polarisation, a 3-D CFD model using ANSYS CFX was developed and tested. The membrane was assumed fully permeable and heat and mass transfer through the membrane were modelled by implementing FORTRAN user-subroutines. This approach allowed studying how heat transfer by convection through the membrane affects the temperature profiles. Three hydrodynamic angles were tested: αf = 45°, αf = 90° and αf = 0°. From the simulations, it was found that the optimal configuration producing the highest mid-membrane temperature Tm and temperature polarisation coefficient Θ, was when the hydrodynamic angle αf = 45°. This was further corroborated by experimental results carried out on a flat plate membrane distillation module, that produced the highest flux (100.33 kg/m2·h) when the system was operating with a hydrodynamic angle αf = 45°. The least desirable configuration was found to be when the hydrodynamic angle αf = 0°, as this produced the lowest mid-membrane temperature and lowest temperature polarisation coefficient.