饱和含盐土壤高温蒸发速率及影响因素分析

EVAPORATION RATES IN SATURATED SALINE SOILS AT HIGH TEMPERATURES AND ITS INFLUENCING FACTORS

通过对70℃下饱和含盐砂土的蒸发实验,获得土壤水分和盐分的分布特征,重点分析初始堆积高度、初始盐分浓度等因素对蒸发速率的影响。实验结果表明,含盐土壤高温蒸发先后经历预热阶段、表层盐分浓度升高至饱和阶段、盐盖快速生长阶段以及慢速蒸发阶段。与不含盐工况相比,高温含盐土壤蒸发过程出现明显的滞后现象。蒸发速率随初始堆积高度的增加而增大,但当超过毛细特征长度以后,蒸发速率又快速下降。初始盐分浓度对蒸发速率的影响较大,尤其是高浓度下表层盐盖的生长对水蒸气扩散的削弱作用占主导因素。Pe数越大,盐分越易在表层聚集和结晶,对蒸发速率的抑制作用越强,同时盐分在土壤内部分布的不均匀性越明显。

This paper was presented to make evaporation experiments of saturated saline sand soils at 70 ℃. The dynamic variations of moisture and salt content in soil were tested and effects of initial packed heights and salt concentrations on the evaporation rate were analyzed. Results showed that evaporation of saturated saline soils undergone preheating （stage 1）, increasing of salt concentrations on the top layer till saturation （stage 2-1） and then rapid growing of salt crust （stage 2-II）, and water vapor diffusion through the salt crust at a low speed （stage 3）. Compared with soils without salt, evaporation of saturated saline soils lagged behind. As the initial packed height of soil grains increased, the evaporation rate increased first and then decreased when the capillary characteristic length was exceeded. The initial salt concentration had a great influence on the evaporation rate, where the dominated mechanism was the salt crust on the top layer that weakened the water vapor diffusion. As the dimensionless Pe number increased, the salt in soil was easily to accumulate and precipitate on the top layer, thereby inhibiting the evaporation rate, and the water content in soil tended to be a non-uniformed distribution.