Numerical analysis of a direct contact membrane distillation system using diesel internal combustion engine waste heat

Membrane distillation (MD) is a water treatment technology which can produce high-quality distillate using low-grade heat from waste heat sources. MD is especially promising for off-grid locations, such as disaster-stricken areas and military bases where power infrastructure is damaged or non-existent and therefore portable power generators are temporarily deployed. In this study, Direct Contact Membrane Distillation (DCMD) systems running on the waste heat from a diesel generator was numerically analyzed by using a one-dimensional thermal-hydraulic network model considering the water vapor transport across the flat-sheet membrane of the DCMD systems. The DCMD systems analysis employs two designs of the DCMD system with single and multiple membrane modules connected in a parallel arrangement. A numerical analysis considering various operating variables (concentration of sodium chloride (NaCl), flow rates, and inlet temperatures of feed and permeate streams) and a design variable (membrane module length) of the DCMD systems was performed to investigate their effects on water distillation performance and thermal efficiency. It was found from the numerical analysis that shorter membranes produce larger water mass flux at higher thermal efficiency. Furthermore, higher flow rates of the feed and permeate streams and greater Inlet Temperature Differences (ITD) between the feed and permeate streams and less NaCl concentration produce more distilled water.