Boiling heat transfer in nanoscale membrane evaporators

The construction of wall microstructures to increase liquid retention for improving cooling performance has been extensively studied; however, the effect of membranes in the evaporator on boiling heat transfer remains insufficiently researched. This study employs non-equilibrium molecular dynamics (NEMD) simulations to investigate the thermodynamic behavior of boiling heat transfer in membrane-based evaporators with different nanoporous sizes, with corresponding comparisons drawn against the thermal performance of a membrane-less evaporator. The evaporation rate, heat flux, heat transfer coefficient, and Kapitza thermal resistance are evaluated to characterize the boiling heat transfer performance. The maximum heat flux before explosive boiling incipience, as well as the inception time of the wall drying-out crisis, are discussed under different heating power operations. The results demonstrate that membrane-based evaporators enable longer cooling duration. Such cooling time is attributed to the mass-transfer resistance imposed by the membrane, which regulates the liquid ejection and vapour release, thereby enhancing the liquid coverage of the wall. Within the explosive boiling regime, increasing the heating power elevates the maximum heat flux. The membrane-based evaporator exhibits a higher maximum heat flux compared to the membrane-less evaporator under the same conditions. Special attention should be given to the fact that the drying-out inception time in the membrane-based evaporator is at least 2 times that of the membrane-less evaporator under varying imposed heat powers. Moreover, a smaller membrane pore size is beneficial for delaying the inception time of the drying-out crisis.