在双面加热的窄缝环形流道中流动沸腾换热研究

在窄缝流道内发生沸腾换热现象时，由于沸腾产生的汽泡受窄缝流道的限制，受压变形而消除了汽泡表面张力对传热的影响。因此对此现象进行基础性理论研究具有很重要的意义。本文在常压下用蒸馏水对窄缝间隙为 0.75mm的垂直环形流道，进行了流动沸腾传热实验研究。实验段的有效加热长度为 900mm，其加热方式为内外侧双面加热，实验的流量变化范围在 1.67× 10－ 5～ 5.83× 10－ 5m3/s。通过实验得到了在不同质量流速和热流密度下双面加热的窄缝流道中内外侧沸腾换热系数随干度变化的分布和特点。研究结果表明，由于在窄缝流道中存在着大量的运动聚合受压变形汽泡，因此使内外侧沸腾换热系数都很高 (可达 105W· m－ 2· K－ 1以上 )。

Study on Flow Boiling Heat Transfer Characteristics in Narrow Double-side Heating Annulus

The effect of surface tension on boiling heat transfer has been eliminated for the boiling bubbles which are constrained, squeezed and deformed when boiling happens in the narrow channel. It is accordingly important to carry out the fundamental theoretic research on this phenomenon. This paper covers a flow boiling heat transfer experiment in vertical narrow annulus with double-side heating. Experiments are performed with stilled water in the annular test section with effective heating section of 900mm and gap width of 0. 75mm under the pressure condition of 1atm or so. The flow rates range from 1.67×10-5 to 5.83× 10-5m3/s. By the experiment, the profiles of the boiling heat transfer coefficient versus mass quality and characteristics at different mass flux and different heat flux have been obtained. It has been concluded in this paper that both inner and outer boiling heat transfer coefficient in narrow double-side heating annular channel are very high (up to over 105 W · m-2 · K-1), which is contributed to by existence of a large amount of moving, coalesced and deformed bubbles in the narrow channel.