Abstract:

Medium-temperature cesium heat pipes’ expensive cost and the active chemical properties of cesium medium, lead to a big difficulty for experimental study. Thus, it is of great significance to analyze and predict the start-up characteristics and internal phase-change heat transfer of the cesium heat pipe by numerical simulation. Firstly, the frozen start-up experiment of a vertical cesium heat pipe was carried out, and based on current heat pipe simulation models, an adaptive model with consideration of the linkage of evaporator and condenser was established by UDF. As proved, the maximum temperature difference of the heat pipe wall between the experimental and the numerical simulation result was less than 20K, and the sudden temperature drop at the end of the condenser was present realistically, which proved the accuracy of the model. Secondly, based on the frozen start-up experiment of a vertical cesium heat pipe with variable heating power, the evolution of wall temperature and internal phase distribution of the heat pipe during the start-up process was simulated, and the average difference of wall temperature was used to evaluate the temperature uniformity over the effective length. At last, with various evaporator lengths (200mm and 120mm), heating powers (1028.2W and 844.4W) and filling ratios (8.8%, 12% and 15%), the phase distribution, temperature distribution and pressure distribution were compared and analyzed in simulation. The optimum matching condition of the evaporator length and the filling ratio was obtained by considering of the effective working length, temperature uniformity, condensate stacking and dry-out phenomena in the evaporator. The content had great potential significance for the optimal design of heat pipes.

Key words: heat transfer, multiphase flow, numerical simulation, heat pipe, phase distribution, temperature uniformity

摘要：

近年来，有关中温铯热管的研究较少，主要因为铯热管造价昂贵且铯金属化学性质活泼，开展实验难度较大，因此通过数值模拟方法对铯热管启动特性与内部相变等过程进行分析预测具有重要意义。首先，本文开展铯热管冷启动实验，并基于目前的热管模拟模型，利用UDF建立蒸发与冷凝的自适应模型，对比实验热管稳态壁温与数值模拟计算壁温，最大温差小于20K，且较好地呈现了热管末端的温度突降，证明了模型的准确性。其次，基于竖直铯热管变功率冷态启动实验，模拟获得铯热管启动过程中热管壁面温度及内部工质相态分布的演变过程；并利用壁面温度的平均差数值评价有效长度上的均温性。最后，通过模拟研究改变热管蒸发段长度（200mm和120mm）、加热功率（1028.2W和844.4W）及充液率（8.8%、12%和15%），对比分析其相态分布、温度分布及压力分布；综合热管有效工作长度、壁面均温性、蒸发段液相堆积与干烧现象，分析蒸发段长度与充液率的最佳配比，为热管的优化设计提供基础。

关键词: 传热, 多相流, 数值模拟, 热管, 相分布, 均温性