A Study On Response Characteristics And Tomographic Monitoring Of Electrical Capacitance For Water Content And Nacl Solution Flow Processes In Porous Media

Water content and the migration of water is an important work in the study of groundwater. And the present study method mainly include TDR、 MRK ERT and so on. But reports of water content and flow in porous media with electrical capacitance tomography method have been rare. Electrical capacitance tomography method is a new method in the study of water content and flow. The method is based on the theory that each phase of the tested material has different permittivity which will change when the component distribution or concentration of each phase varies, and thus they make the measuring electrode capacitance change. Considering the capacitance values measured as the projection data, the permittivity distribution can be got by a certain set of image reconstruction algorithms and then the material distribution of images will be obtained. The research of electrical capacitance on water movement in porous media through monitoring and analyzing is the supplementary and improvement to the research method of water flow in porous media can help us to understand the water flow theory in porous media and check the other method.Firstly, the effectiveness of electrical capacitance tomography method in the measurement of water content of porous media was discussed, and then the water content of the porous media is discussed through electrical capacitance tomography method. The water content from the electrical capacitance tomography method and oven drying method were compare.Then, the temporal and spatial variation of electrical capacitance in the NaCl solution infiltration and flow of the porous media in the laboratory was investigated. The accuracy and repeatability of electrical capacitance tomography method was discussed.The results of the effectiveness of electrical capacitance in the measurement of water content of porous media clearly indicate that, with the use of rod-like sensors, the measured electrical capacitance with1kHz frequency can be used to construct a good relationship between capacitance and water content.Electrical capacitance tomography method is found to be very good through comparison the water content from the electrical capacitance method and oven drying method, so this method is feasible and accurate.,The experiment of the infiltration and flow process of the NaCl solution in porous media in the laboratory shows that Capacitance in the response of the NaCl solution was very sensitive, Capacitance is very small before the NaCl solution is added into the sand, but Capacitance will be very larger after sand contains NaCl solution. The response of the capacitance can be know from the time variation relationship curve between the capacitance and the flow process of NaCl solution, the image map was get through electrical capacitance tomography method, and the infiltration and flow process of the NaCl solution in porous media are clearly in the image map. According to the image map the scope of influence of NaCl solution can be out.