posted on 2024-11-25, 18:46authored byQuoc Linh VE
Direct contact membrane distillation (DCMD) is one of the desalination technologies used to produce freshwater from saline water. Using spacers is an appropriate solution for enhancing the DCMD mass flux. This research aimed to examine the effect of spacers on DCMD performance under different operating conditions.
In the first stage of the study, only the heat transfer property was investigated in a DCMD module with an impermeable copper plate in two cases: empty channels and spacer-filled channels. Based on the theoretical model and experimental validation, the heat transfer correlations for the DCMD module with and without spacer were proposed.
In the second stage, both heat and mass transfer characteristics were studied in spacer-filled DCMD channels with a hydrophobic polytetrafluoroethylene (PTFE) membrane under the influence of experimental conditions: feed inlet temperature, feed concentration, feed and permeate volume flow rate, and spacers with different configurations and materials. Initially, a more accurate methodology for selecting the appropriate theoretical model for membrane thermal conductivity was proposed for further studies based on experimental data analysing permeate flux and heat balance in spacer-filled channels. Further, the primary findings were employed to investigate the mass transfer property that occurred in a boundary layer by analysing the mass transfer coefficient (MTC), boundary layer thickness (BLT), shear stress and pressure drop. A new model based on film theory and boundary layer theory was applied to point out the mass transfer correlation for each spacer. Finally, the DCMD performance with regard to mass flux, temperature polarisation coefficient (TPC), concentration polarisation coefficient (CPC), heat transfer coefficient, thermal efficiency (TE), gain output ratio (GOR), and specific thermal and electrical energy consumption (SECt, SECe) was analysed. Consequently, the most effective spacer was determined based on the ability of mass flux enhancement and energy consumption issues. The study also found that between spacer configuration and material, configuration has the most impact on DCMD outputs.