Numerical investigation on mass and heat transfer performance for novel vacuum membrane distillation modules enhanced by semicircular spacers

Semicircular spacers are creatively introduced into the micro vacuum membrane distillation (VMD) modules for the purpose of modifying flowing field, decreasing mass transfer resistance and enhancing water production. A two-dimensional computational fluid dynamics model is developed to conduct the performance evaluation of rectangular micro-VMD modules. Calculated results indicate that novel VMD modules obtain remarkable improvement in terms of transmembrane mass flow rate. Local velocity and vorticity magnitude around the semicircular spacers increase with augment of the dimension of semicircular spacers as revealed in flow performance evaluation. Thermal performance displays that temperature distribution evolves into uniform when the semicircular spacers are introduced and noticeable improvement can be observed in transmembrane heat flux rate, local temperature and temperature polarization coefficient (TPC) performance. Whereas, Nu number varies in a certain range depending on the configuration of semicircular spacers. This paper further discloses the effect of operating parameters on the mass transfer, heat transfer and TPC performance. It is theoretically found that performance of proposed VMD modules is more sensitive to feed inlet temperature rather than feed inlet velocity. In conclusion, semicircular spacers are believed to be effective strategies to enhance performance of micro-VMD modules, with remarkable improvement to flow field, heat and mass transfer.