Forced Convection Boiling Heat Transfer and Dryout Characteristics in Helical Coiled Tubes with Various Axial Angles

对水和水蒸汽汽液两相流体在螺旋轴呈各种倾角放置的螺旋管内强制对流沸腾传热与烧毁特性进行了系统地试验研究，试验中系统及结构参数范围如下：压力：Ｐ＝０．４～３．０ＭＰａ质量流速：Ｇ＝１００～２４００ｋｇ／ｍ２·ｓ进口水温：Ｔ＝３０～８０℃出口干度：ｘ＝－０．０５～１．２管内壁面热负荷：ｑ＝０～５４０ｋＥ／ｍ２试验段结构参数：总长Ｌ＝６４４８ｍｍ，管内径ｄ＝１１ｍｍ，螺旋直径Ｄ＝２５６ｍｍ，螺旋升角β＝４．２７°螺旋管轴向放置倾角：水平位置（０°）、向上倾斜４５°（＋４５°）、垂直向上（＋９０°）、向下倾斜４５°（－４５°）．共进行了１０５０个工况的试验．试验结果表明，螺旋管内汽液两相流强制对流沸腾传热可以划分为核态沸腾区、两相流强制对流区、烧毁及烧毁后传热区等３种区域．通过数据处理和分析总结，给出了３区域间转变的边界方程，和３个区域内两相流传热系数的计算公式．根据试验观察和数据结果，对烧毁现象及烧毁点或区域发生的条件及机理进行了深入的分析研究，发现一系列有关现象的规律和特点，指出了其主要影响因素，并给出了烧毁点临界质量干度的预报公式．

In this paper, the forced convection boiling heat transfer and dryout characteristics of water flowing in a helical coiled tube at 0.4￣3.0 MPa pressure are experimentally studied, the axis of the helical coiled tube was arranged in four different inclination angles, that is, horizontal, 45deg upwardly inclined, upwardly vertical, and 45deg downwardly inclined. Experimental results demonstrate that the convection boiling heat transfer of water can be divided into three regions, including nucleate boiling region, forced convection region and post dryout region, some equations for the calculations of heat transfer coefficients in the three regions and for the transition boundaries between two regions were proposed respectively. Based on experimental data and observations, we found that dryout points usually occur at the front and back sides of the cross section of outlet of test section, a correlation for predicting the critical quality of dryout condition was proposed. The secondary flow induced by centrifugal force and the wall conduction around the dryout points were considered as the dominant factors affecting the critical conditions of dryout.