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。为了定量预测这一现象，需要对液膜流速进行分析。我们开发了一种粒子网格混合方法，能够分析气/液流动及其相互作用。为了验证该方法的有效性，分析了气液逆流中的泛洪现象。通过计算得出的洪水发生时间与已有的经验相关性吻合较好。通过重新附着液滴从干后燃料棒中去除热量也很重要。我们分析了液滴对受热表面的冲击，并用粒子法计算了热量的排出。首先，在没有蒸发模型的情况下，利用不同的韦伯数和接触角对液滴的撞击进行了分析。然后用蒸发模型对其进行分析。计算得到的液滴形状和在加热表面停留的时间与已有的经验相符。采用颗粒-网格混合方法分析了液膜中的液滴夹带现象。我们可以第一次重现这种现象。用不同的密度、粘度、表面张力系数、气相速度等来计算夹带的起始时间。它与几个现有的相关性很好地吻合。然而，计算出的夹带比在数量上与现有的相关性不一致。增加计算区域和粒子数是今后的课题。

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.