Development of direct simulation models of gas-liquid two-phase flow in nuclear reactors using particle-mesh hybrid method

液膜干燥是沸水堆设计和安全的重要问题。为了定量预测这种现象，需要分析液膜流量。我们开发了一种粒子-网格混合方法，能够分析气体/液体流动及其相互作用。为了验证该方法的有效性，对气液逆流中的液泛现象进行了分析。通过计算确定的溢流起始点与现有的经验关联式吻合得很好。通过重新附着液滴从干燥后的燃料棒中去除热量也很重要。分析了液滴对受热面的冲击，并采用粒子法计算了散热量。首先，在没有蒸发模型的情况下，使用不同的韦伯数和接触角分析液滴的碰撞。然后用蒸发模型进行了分析。计算得到的液滴形状和停留时间与已有的实验结果吻合较好，采用颗粒-网格混合法分析了液滴从液膜中的卷吸现象。我们可以第一次重现这种现象。使用不同的密度，粘度，表面张力系数，气相速度等计算夹带的开始，它同意与现有的几个关联。然而，计算的卷吸比并没有定量地同意与现有的相关性。计算区域和粒子数的增加是未来的研究方向。

Dryout of liquid film is an important issue for design and safety of boiling water reactors. Liquid film flow rate needs to be analyzed for quantitative prediction of this phenomenon. We developed a particle-mesh hybrid method that is capable of analyzing gas/liquid flow and their interaction. Flooding phenomenon in gas-liquid countercurrent flow was analyzed in order to validate this method. Onset of flooding by calculation agreed well with an existing empirical correlation.Heat removal from post-dryout fuel rods by reattaching droplets is also important. We analyzed droplet impact on heated surface and calculated heat removal using a particle method. Firstly, droplet impact was analyzed without evaporation model using various Weber numbers and contact angles. Then, it was analyzed with evaporation model. Calculated droplet shape and its staying time on the heated surface agreed with existing experiences.Droplet entrainment phenomenon from liquid film was analyzed using the particle-mesh hybrid method. We can reproduce this phenomenon for the first time. Onset of entrainment was calculated using various densities, viscosities, surface tension coefficients, gas phase velocities, etc. It agreed well with several existing correlations. However, calculated entrainment ratio did not quantitatively agree with existing correlations. Calculation region and particle number should be increased, which is the future subject.