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The water vapor diffusion can be enhanced by the heating from municipal solid waste, and significantly impact the evaporation process in the earthen final cover. The parameters associated with the water vapor diffusion are usually measured by using the instantaneous profile method. This method is very time-consuming because the drying process lasts a long time. In this study, a bottom heating method is proposed to accelerate the drying process in a loess soil column. A constant temperature of 70 °C is applied at the bottom of the soil column. The thermo-hydraulic response of the loess is monitored along the soil column. A numerical model is developed to simulate the coupled thermo-hydraulic process. The numerical model is used to back analyze the tortuosity τ of the loess for vapor diffusion and the parameter a of an empirical evaporation function. We found that the bottom heating accelerated the drying process of the soil column by almost 22 d compared with the conditions without heating under the same evaporation boundary. Before Day 15, the proportions of the enhanced vapor flux in the total water loss were higher than 50%, dominating the evaporation process. The experimental and numerical study demonstrated that the proposed heating method is able to obtain the parameters of vapor diffusion more efficiently than the conventional method.概要目 的土质覆盖层下的城市固体废弃物由于生化降解反应具有更高温度,该温度梯度增强了土质覆盖层内的水蒸气扩散,在覆盖层的蒸发模拟中不容忽视。与水蒸气扩散相关的参数一般通过瞬态剖面法测量,但在一定蒸发边界下的土体干燥过程会持续很长时间,因此这种传统测量方法十分耗时。本文旨在提出一个底部加热的新方法加速黄土土柱脱湿,更为高效地获取水蒸气运移相关参数。创新点1. 提出一个全新的底部加热方法用于加速土体脱湿,同时利用提出的数值模型反分析得到水蒸气运移的相关参数挠曲度τ;2. 发现底部加热加速脱湿的根本原因在于极大增强的水蒸气扩散。方 法1. 研制一套室内黄土土柱试验装置(图3);2. 在土柱底部施加恒温70 °C,监测黄土的水热响应(图4);3. 提出一个数值模型模拟这一水热耦合运移过程,利用该模型反分析影响水蒸气运移的关键参数,包括试验黄土的挠曲度τ 和经验蒸发公式的参数a。结 论1. 在相同蒸发边界下,相比不加热的情况,底部加热使土柱脱湿加速了最高22 天;2. 在第15 天前,加热增强的水蒸气流量主导黄土蒸发过程,一直占总水分损失量的50%以上;3. 试验及数值模拟结果均表明,相比传统方法,本文提出的底部加热法可更为高效地获取水蒸气运移参数。

Laboratory and numerical study on an enhanced evaporation process in a loess soil column subjected to heating