Analysis of subcooled flows boiling in horizontal rectangular mini-channels under microgravity conditions

Abstract

In the aerospace field, microgravity significantly impacts flow boiling heat transfer performance and the bubble behavior. This study uses water as the working fluid and employs numerical methods to investigate flow boiling heat transfer in rectangular mini-channels under microgravity conditions. A coupled Volume-of-Fluid and Level-Set method (VOSET) is utilized for precise tracking of vapor–liquid interfaces. The study reproduces flow patterns and heat transfer characteristics under various heat fluxes and flow velocities, revealing the effects of microgravity on flow boiling heat transfer. At low mass flux densitiy of 100 kg/(m2·s) and heat fluxes of 300 kW/m2, the absence of buoyancy in microgravity causes bubbles to adhere to the heating wall, forming dry patches. Conversely, under normal gravity, buoyancy promotes bubble detachment from the wall, leading to lower pressure drop and better heat transfer. As the heat flux increases to 400 kW/m2, bubbles rapidly grow into large bubbles, eventually reaching a size comparable to the mini-channel dimensions. Under both gravitational conditions, bubbles become confined by the mini-channel walls, resulting in similar dry patches areas, thus diminishing the impact of microgravity on heat transfer performance and pressure drop. Subsequently, the study explored the impact of microgravity on heat transfer performance, with mass flux densities varying from 100 kg/(m2·s) to 1000 kg/(m2·s) and heat fluxes ranging from 300 kW/m2 to 500 kW/m2. As mass flux densitiy increases, inertial forces become more dominant. Notably, when mass flux densitiy exceeding 500 kg/(m2·s), the heat transfer performance and pressure drop under different gravitational conditions becomes consistent, diminishing the influence of microgravity on heat transfer.