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过热度和液膜厚度对微米级液膜闪蒸影响的数值模拟探究
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Abstract:
建立空间内微米级液膜的二维数值分析模型，采用patch形式对网格进行划分来定义不同的液膜厚度。基于Mixture模型来描述液膜与其上方的水蒸气之间的传质传热过程，研究了液膜厚度和液膜过热度对液膜闪蒸造成的影响。根据模拟得到液膜的温度数据，在数学模型的基础上，计算液膜闪蒸的蒸发质量以及蒸发质量的变化率，并引入反映闪蒸过程中温度变化的非平衡分数NEF来表示闪蒸过程的完整性。对液膜各个瞬态时间点的闪蒸状态及影响其传质传热特性的因素进行分析。结果表明：微米级液膜的闪蒸分为快速和稳定两个阶段，初始液膜厚度的增大会抑制闪蒸，由于初始厚度的不同会影响液膜底部的静压，致使达到平衡时的温度略微不同。液膜过热度会通过对表面张力产生影响，进而产生Marangoni对流，促进闪蒸的进行。
The two-dimensional numerical analysis model of micron liquid film in space was established, and the mesh was divided in patch form to define different liquid film thickness. The mass and heat transfer process between liquid film and water vapor was described based on Mixture model, and the effects of liquid film thickness and superheat on liquid film flash were studied. According to the temperature data of liquid film obtained by simulation, the evaporation mass of liquid film flash and the change rate of evaporation mass are calculated on the basis of mathematical model. The non-equilibrium fraction NEF, which reflects the temperature change in the flash process, is introduced to represent the integrity of the flash process. The flash state of liquid film at each transient time point and the factors affecting its mass and heat transfer characteristics were analyzed. The results show that the flash of micron liquid film can be divided into two stages: fast and stable. The increase of initial liquid film thickness will inhibit the flash, and the difference of initial liquid film thickness will affect the static pressure at the bottom of liquid film, resulting in a slightly different temperature at equilibrium. The superheat of liquid film can influence the surface tension, and then produce Marangoni convection, which promotes flash
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