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多孔介质的水热运移参数是影响介质中水热运动过程的主要因素。本文基于热示踪方法,开展了稳定流场条件下饱和层状石英砂的热示踪实验,分别采用热电偶与热成像两种方法测定了砂箱内部和表面的温度,同时结合HYDRUS模型的反问题算法对层状石英砂的水热运移参数进行了反演。研究结果表明:当介质中存在细粒夹层时,热成像图像能反映非均匀流场中热流峰面在分层界面处出现的“收束”现象;层状介质中的细颗粒夹层可导致热流锋面沿水流方向迁移速率下降、热量沿垂直于水流方向运移范围加大、温度分布更均匀。同时对于热源持续输入的系统,热成像温度在前期能较好的反映层状介质对水流运动的影响。将热示踪与HYDRUS模型相结合可较好地用于反演介质水热运移参数,反演所得的饱和导水率估值随粒径的减小显著降低,纵向热弥散度随粒径的减小而增大,而横向热弥散度变化趋势与之相反;纵横弥散比变化范围在10~120之间,且纵横弥散比随粒径减小而逐渐增大。对细砂饱和导水率的估计不足及热量损失是造成水流通量估计误差的主要原因,在模拟模型中增加细砂层测点数量可显著降低水流通量的估计误差。本研究可为非均质介质中水热迁移过程模拟与参数反演提供相应的方法。
The hydrothermal migration parameters of porous media are the main factors affecting the hydrothermal movement in the medium. In this paper, based on the thermal trace method, the thermal tracing experiments of saturated layered quartz sand under steady flow conditions were carried out. The temperature inside and the surface of the flask were measured by thermocouple and thermal imaging respectively. Combined with HYDRUS model The inverse problem algorithm inverts the hydrothermal transport parameters of layered quartz sand. The results show that the thermal image can reflect the phenomenon of “bundling” of heat flux peak surface at the interface of stratified flow in the presence of fine-grain interlayers in the medium; the fine-particle interlayers in the stratified medium can lead to heat flow The migration rate of the fronts along the water flow decreases, and the heat transfer increases along the direction perpendicular to the water flow and the temperature distribution is more uniform. At the same time, for the system of continuous input of heat source, the thermal imaging temperature can better reflect the influence of layered media on water flow in the early stage. The combination of thermal trace and HYDRUS model can be used to inverse the hydrothermal migration parameters of media. The estimation of saturated hydraulic conductivity obtained by inversion is obviously decreased with the decrease of particle size. The longitudinal thermal dispersion varies with the particle size While the transverse thermal diffusivity changed in the opposite direction. The vertical and horizontal diffusivity varied from 10 to 120, and the vertical and horizontal diffusivity increased with the decrease of particle size. The lack of estimation of the saturated hydraulic conductivity of fine sand and the heat loss are the main reasons for the estimation error of water flux. Adding the number of measuring points in the fine sand layer in the simulation model can significantly reduce the estimation error of water flux. This study can provide a corresponding method for the simulation of water-heat transfer process and inversion of parameters in heterogeneous media.