狭窄空间内沸腾传热机理

通过实验观察,分析了狭窄空间内沸腾传热特征,得到表征通道宽度的Ｂｏｎｄ数存在临界值（０．６）。通道超临界和亚临界情况沸腾传热机理完全不同。对于超临界通道（Ｂｏｎｄ数≥０．６）沸腾传热是池沸腾传热和液相对流传热的叠加。亚临界通道（Ｂｏｎｄ数＜０．６）情况,加热表面被聚合汽泡和液柱周期性交替冲刷。汽泡通过加热面时,汽泡与加热面间存在一层薄液膜,这时主要通过液膜蒸发传热。液柱通过时为液相对流传热。上述模型均考虑了介质沿加热面的流动。模型预测的结果与实验值吻合良好,同时也证实了狭窄通道强化传热时存在最佳宽度与高度。

MECHANISM OF BOILING HEAT TRANSFER IN NARROWSPACE

On the basis of our experimental observation an analysis of boiling heat transfer mechanism in narrow space is developed and a model of boiling heat transfer is provided as fol-lows:There exists a eritical gap size(Bond=0.6) which identifies two boiling regimes.For the su-per-critical channels with Bond ≥0,6,two-phase heat transfer is assumed to be a superposition of pool boiling and liquid convective components.For subcritical channels(Bond <0.6), since each elementary portion of the wall surface is periodically washed either by a thin liquid film or by a liquid plug,the heated surface is first cooled by evaporation for the time duration during which it is covered by the coalcsced bubble; liquid flows into the space immediately after the bubble passes. Flow along the heated surface is taken into account.The results predicted from the model are consistent with the experimental heat transfer data The influence of gap sizes,plate heights,and heat fluxes on heat transfer is given and discussed. There exists an optimum channel size of heat transfer enhancement.