高热流密度下高度对微小间隙通道内流动沸腾特性的影响

Effect of Channel Height on Flow Boiling Characteristics in Minigap Channels at High Heat Fluxes

实验研究了常压去离子水在不同高度的微小间隙通道内的流动沸腾特性.实验热流密度为0~206 W/cm^(2),质流密度为200~400 kg/(m^(2)·s),间隙为1 mm和2 mm.结果显示,随着实验条件的变化,通道内出现了泡状流、清扫流、搅拌流,且在清扫流早期观察到不稳定流动现象.此外,间隙高度降低促进了流型的过渡,加快了不稳定流动的进程.1 mm通道内核态沸腾起始点的热流密度低于2 mm通道,表明间隙高度的降低更有利于气泡在低热流密度下成核;1 mm通道的过冷沸腾传热系数最高为2 mm通道的1.7倍,2 mm通道内饱和沸腾传热系数略高于1 mm通道.表明低热流密度下过冷沸腾时小通道具有更好的传热性能,高热流密度下饱和沸腾时大通道的传热稍具优势,同时表明间隙高度造成的传热差异随热流密度增大先增大后变小;1 mm通道内临界热流密度为2 mm通道的83%,表明间隙高度的降低会使得临界热流密度降低.

Atmospheric deionized water flow boiling characteristics in minigap channels with different heights were experimentally studied.The experimental heat flux range,mass flux range,and channel heights were 0—206W/cm^(2),200—400 kg/(m^(2)·s),and 1 mm and 2mm,respectively.The results show that with the change in experimental conditions,bubbly,sweeping,and churn flows appeared in the channel,and an unstable flow was observed in the early stage of the sweeping flow.The gap height reduction promoted the development of the two-phase flow pattern and advanced the process of the unstable flow.The heat flux at the onset of the nucleated boiling of the 1 mm channel was lower than that of the 2mm channel,indicating that reducing the gap height is more favorable for bubble nucleation at low heat fluxes.The subcooled boiling heat transfer coefficient of the 1mm channel was almost 1.7 times that of the 2 mm channel.The saturated boiling heat transfer coefficient in the 2 mm channel was slightly higher than that of the 1 mm channel.Thereby indicating that the subcooled boiling heat transfer in the small channel under low heat flux is more advantageous than that in the large channel,while the situation reverses in the saturation boiling heat transfer.Additionally,the difference in heat transfer caused by the gap height first increases and subsequently decreases with the increasing heat flux.The critical heat flux in the 1 mm channel was 83%of that in the 2 mm channel,indicating that reducing the gap height will reduce the critical heat flux.