Numerical study on subcooled flow boiling in narrow rectangular channel based on OpenFOAM

摘要

A wall nucleation model for sub-cooled boiling flow in narrow rectangular channels has been developed utilizing newly-reported experimental data. The model was then implemented into a two-phase Eulerian-Eulerian CFD model through use of the OpenFOAM platform, and then verified successfully by its application to five different channel cases, which differ mainly in the mass flow rate varying from 388 to 608 kg/(m~2·s) with a heat loading of 56 kW/m~2 and the inlet temperature ranging from 364.75 to 369.95 K. Meanwhile, on this basis, we studied the impact of inlet subcooling, inlet mass flow rate and wall heating power on the heat transfer mechanism of wall boiling, and found that with the increase of inlet subcooling and inlet mass flow rate, the ratio of single-phase convective heat flux gradually rose, in contrast to that of evaporative heat flux and quenching heat flux. The reason behind this was the increase of the above two factors reduced wall superheat, as well as bubble diameter and bubble influence area. However, the impact of heat flux for wall heating was more complicated. With the increase of wall heat flux, the convective heat flux increased first and then decreased, while the evaporative heat flux and quenching heat flux gradually rose, as do the wall-fluid heat-transfer temperature difference and the bubble influence area, which respectively facilitated single-phase convective heat transfer and restricted the proportion of single-phase heat transfer. The competition of these two led to the increase and the resulting decrease of convective heat flux.