Numerical Simulation of Migration of Leaked Pollutants in Underground Buried Tube Under Periodic Temperature Boundaries

Abstract

The risk of underground environmental pollution caused by the surface contaminants of buried tubes and the leakage of its internal working fluid is increasing with the large-scale application of borehole heat exchangers. Previous studies have shown that periodic freezing and melting processes can cause redistribution of contaminants concentration. Similarly, the periodic heat injection and heat extraction of buried pipes can also cause redistribution of contaminants concentration. However, fewer related studies can be found presently. In this paper, the Multiple-relaxation–time lattice Boltzmann model (MRT-LBM) is used to simulate the contaminants migration in porous media under periodic temperature boundaries. By regarding the contaminants leakage point as the continuous injection point source and the accumulative flow rate of contaminants as an additional item of source term, the mathematical model of solute migration and the Darcy velocity model are established; the unsteady heat conduction and convection equations were established by regarding the heat injection and heat extraction in summer and winter time as a various cylindrical heat source. Coupling the above equations and combined with the D3Q7 model of lattice Boltzmann methods (LBM), the relationship between the contaminants concentration front and the periodic temperature period is obtained, thus the accumulation position of the contaminants can be determined.