In arid regions, water vapor diffusion predominates the total water migration in unsaturated soil, which significantly influences agriculture and engineering applications. With the aim of revealing the diffusion mechanism of water vapor in unsaturated soil, a water vapor migration test device was developed to conduct the water vapor migration indoor test. The test results demonstrate that the characteristics of water vapor diffusion in unsaturated soil conformed to Fick’s second law. A mathematical model for water vapor diffusion under isothermal conditions in unsaturated soil was established based on Fick’s law. Factors including the initial moisture content gradient, initial moisture content distribution, soil type and temperature that affect the water vapor diffusion coefficient were analyzed. The results show that there was good agreement between the moisture content calculated by the mathematical model and obtained by the indoor experiment. The vapor diffusion coefficient increased with increasing initial moisture content gradient and temperature. When the initial moisture content gradient is constant, the vapor diffusion coefficient increases with the increase of matrix suction ratio in dry and wet soil section. The effect of soil type on the water vapor diffusion coefficient was complex, as both the moisture content and soil particle sizes affected the water vapor diffusion.

在干旱地区，水蒸气扩散占非饱和土壤中总水分迁移的主要部分，这极大地影响了农业和工程应用。为了揭示水蒸气在非饱和土壤中的扩散机理，研制了一种水蒸气迁移试验装置进行室内水蒸气迁移试验。试验结果表明，水蒸气在非饱和土壤中的扩散特性符合菲克第二定律。根据菲克定律建立了等温条件下水蒸气在非饱和土壤中扩散的数学模型。分析了初始水分含量梯度，初始水分含量分布，土壤类型和温度等影响水蒸气扩散系数的因素。结果表明，通过数学模型计算出的水分含量与通过室内实验获得的水分含量具有良好的一致性。蒸气扩散系数随初始水分含量梯度和温度的升高而增加。当初始含水量梯度恒定时，在干，湿土壤段中，蒸汽扩散系数随基质吸入比的增加而增加。土壤类型对水蒸气扩散系数的影响是复杂的，因为水分含量和土壤粒径都会影响水蒸气扩散。当初始含水量梯度恒定时，在干，湿土壤段中，蒸汽扩散系数随基质吸入比的增加而增加。土壤类型对水蒸气扩散系数的影响是复杂的，因为水分含量和土壤粒径都会影响水蒸气扩散。当初始含水量梯度恒定时，在干，湿土壤段中，蒸汽扩散系数随基质吸入比的增加而增加。土壤类型对水蒸气扩散系数的影响是复杂的，因为水分含量和土壤粒径都会影响水蒸气扩散。