Abstract:

For a liquid droplet in high temperature surroundings of airflow convection and thermal radiation, the heat and mass transfer model of heating and evaporation has been established. The homogeneous boiling criterion was combined with the evaporation model to predict the inside boiling effect of droplet. A computer code was developed to solve the combined governing equations numerically. After verifying, the temperature rising and evaporating process of an n-dodecane droplet were simulated, in which the thermal expansion and property dependence on temperature were considered. The occurrence of boiling inside droplet is investigated for various high temperature conditions of convection and thermal radiation. The results show that the heating of high temperature convection and thermal radiation can both rapidly rise the temperature of droplet and the evaporation is accompanied by an obvious size expansion. Different from the convection heating, however, the thermal radiation can result in more rapidly rising of temperature inside the droplet. When the radiative temperature is high enough and the temperature of convective airflow is lower, the boiling will take place inside the droplet whose radius is not very small. It is also found that the droplet superheat need for boiling increases with the evaporating process.

Key words: liquid droplet, evaporation, high temperature, thermal radiation, boiling

摘要：

建立了液滴在高温对流和辐射环境中的受热和蒸发模型，结合液滴均质沸腾模型，编制了计算程序。以正十二烷液滴为例，考虑液滴的膨胀效应以及液滴与周围气流的热物性变化，数值模拟了高温辐射与对流加热下的液滴升温和蒸发过程。分析了不同对流和高温辐射条件下，液滴内部是否能够发生沸腾。研究表明，液滴在高温辐射和对流加热下，蒸发伴随热膨胀；高温热辐射加热可导致液滴内部温度高于表面温度，升温到一定程度后可达到液滴内部沸腾状态；影响液滴沸腾的因素有液滴半径、辐射温度、环境气流温度等；同时，随着液滴蒸发，高温环境中液滴的沸腾过热度逐渐增大。

关键词: 液滴, 蒸发, 高温, 热辐射, 沸腾