Mixing of solutes in heterogeneous porous media under thermally induced buoyancy-flow conditions

缺乏横向溶质混合已被确定为限制来自永久排放污染源的含水层中污染物羽流自然衰减的关键因素。羽流中的污染物与周围地下水中溶解的氧化剂之间的垂直混合是最具决定性的，因为许多羽流相当宽而不是厚。不幸的是，在标准地下水流动条件下，描述垂直分散混合的参数相当小，即使在瞬态流动条件下的非均匀介质中也是如此。为了克服地下水垂直混合不足的问题，我们建议通过局部热注入来诱导不稳定的流动状态。浮力手指和旋转流动的产生增加了溶质羽状物的表面积，从而加强了与周围地下水的混合。我们想通过沙箱控制实验研究热对流对溶质混合的影响。我们将改变填料类型、边界条件和操作模式。我们将通过光学方法测量可见光和红外光谱中的浓度和温度分布，并将其与数值模拟进行比较。目前的应用仅限于自由热对流促进准二维设置。该项目的第二阶段还将包括环境流（混合对流）的情况。

The lack of transverse solute mixing has been identified as a key factor limiting natural attenuation of contaminant plumes in aquifers originating from permanently emitting contaminant sources. Vertical mixing between the contaminants in the plume and dissolved oxidants in the ambient groundwater is most decisive since many plumes are rather wide than thick. Under standard groundwater flow conditions, unfortunately, the parameters describing vertical dispersive mixing are fairly small, even in heterogeneous media under transient flow conditions. We propose to deliberately induce unstable flow conditions by local heat injection in order to overcome insufficient vertical mixing in groundwater. The creation of buoyant fingers and rotational flow increases the surface area of the solute plume and thus enhances mixing with the surrounding groundwater. We want to study the effects of thermal convection on solute mixing by controlled experiments in sandboxes. We will vary the type of fillings, boundary conditions and operation modes. We will measure concentration and temperature distributions by optical methods in the visual and infrared spectrum and compare them to numerical simulations. The present application is restricted to free thermal convection facilitating a quasi two-dimensional set up. The second phase of the project will also include situations with ambient flow (mixed convection).