微细化沸腾传热实验研究

Experimental Investigation on Microbubble Emission Boiling Heat Transfer

气泡微细化沸腾是沸腾到达某个临界热负荷后,加热面温度升高不大,与该临界热负荷相比,热流密度大幅提高的沸腾现象。本文在设计完成一可视化实验装置的基础上,通过高速摄影仪观察并结合采集的壁温数据,对常压下直径为10mm铜加热面上的池式气泡微细化沸腾现象进行了研究,并讨论了液体过冷度对其的影响。实验发现,气泡微细化沸腾状态下,加热面上生成1层极其不稳定的气膜,气液交界面上不停地有大量微小气泡生成并以极高速度射入过冷液体中。随加热面热流密度的增大,气膜厚度波动周期缩短,气膜最大厚度减小,所生成微小气泡的直径也明显减小。实验中获得的最高热流密度达9MW/m2。

Microbubble emission boiling （MEB） is a phenomenon that the heat flux increases more rapidly compared to the critical heat flux （CHF） with a little increase of the heating surface superheat. A subcooled pool boiling experimental setup was built up to investigate the bubble behaviors of MEB under the atmospheric condition at different liquid subcoolings with the help of high-speed video camera. The heating element of the experimental setup is a copper block with its upper part of a 10 mm diameter cylinder. The experimental results show that, in MEB regime, an unsteady vapor film spreads on the heating surface. Numerous microbubbles are emitted into subcooled liquid continuously with an extremely high speed from the interface. Along with the rise of heat flux, the oscillation period of vapor film along its thickness gets shorter and the maximum thickness also becomes smaller. The microbubble diameter under higherpower heating is much smaller than that under low heating flux. The maximum heat flux in the experiment is about 9 MW/mz at 60 K subcooling.