The prediction of coupled nonisothermal multiphase flow in porous media has been the subject of many theoretical and experimental studies in the past half a century. In particular, the evaporation phenomenon from the shallow subsurface has been extensively studied based on the notion of equilibrium phase change between liquid water and water vapor (i.e., instantaneous phase change). One of the frequent assumptions in equilibrium phase change approach is that liquid water is hydraulically connected throughout the vadose zone. Furthermore, classical soil‐water retention curves (e.g., van Genuchten model), which have been extensively used in the literature to model evaporation process, are only valid for high and intermediate saturation degrees. Although these limitations have been addressed and improved in separate studies, they have not yet been rigorously incorporated in the numerical modeling of nonisothermal multiphase flow in shallow subsurface of in‐field soils. Therefore, the aim of this study is to investigate the coupled heat, liquid, and vapor flow in soil media through the Hertz‐Knudsen‐Schrage (HKS) phase change model and by incorporating a water retention model which captures the soil‐water characteristics from full to oven‐dried saturation degrees. A numerical model is developed and validated against the in‐field experimental data. Reasonable agreements between the calculated and measured values of water contents at all depths, as well as the temperature, and cumulative evaporation are observed. Results also confirm that the contribution of the film flow in overall mass flow in the medium is required for accurate modeling and cannot be ignored.

中文翻译：

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利用非平衡相变方法分析浅埋地下土壤的非等温多相流

在过去的半个世纪中，多孔介质中非等温多相流耦合的预测一直是许多理论和实验研究的主题。特别地，已经基于液态水和水蒸气之间的平衡相变（即瞬时相变）的概念对来自浅地下的蒸发现象进行了广泛的研究。平衡相变方法中的常见假设之一是，在整个渗流区，水都是通过液压方式连接的。此外，经典的土壤水分保持曲线（例如van Genuchten模型）已在文献中广泛用于模拟蒸发过程，仅对高饱和度和中等饱和度有效。尽管这些限制已在单独的研究中得到解决和改善，尚未将它们严格地结合到田间土壤浅层地下非等温多相流的数值模拟中。因此，本研究的目的是通过Hertz-Knudsen-Schrage（HKS）相变模型并结合保水模型来研究土壤介质中的热，液体和蒸汽耦合流，该模型可以捕获土壤中水的特征。完全达到烤箱干燥的饱和度。开发了一个数值模型，并针对现场实验数据进行了验证。观察到所有深度的水含量的计算值和测量值以及温度和累积蒸发量之间的合理一致性。结果还证实，膜流对介质中总质量流的贡献是精确建模所必需的，不可忽略。