A Study Of The Trailng Effect And Simulation For The Indoor Dispersion Experiments:Based On High Permeability Porous Media

This paper carried out the experiment of solute transport for high permeability porous medium,and conducted the trailing analysis and numerical simulation for the breakthrough curve based on experimental data.River sand with three different sizes(0.125mm~0.3mm?0.3mm~0.5mm and 0.5mm~0.7mm)were chosen in this study,and five dispersion experiments with different flow rates were introduced to test those media.Therefore,15 experiments were conducted in this paper,and the experiment results were displayed in c-t figure.Moreover,each of those breakthrough curves were fitted by using traditional advection-dispersion equation and advection-dispersion equation with time-fractional order,which is based on Riemann-Liouville fractional derivative form.According to the fitting results,this paper analyzed the reason of trailing,and conducted simulation for trailing phenomenon.The main conclusions are:1)The effective porosity of each experimental sand-pile were measured,the results are: for a sand-pile with media size between 0.125 mm and 0.3mm,the mean permeability coefficient and effective porosity are 48.73m/d and 0.284,respectively;for a sand-pile with media size between 0.3mm and 0.5mm,the mean permeability coefficient and effective porosity are 37.73m/d and 0.258,respectively;for a sand-pile with media size between 0.5mm and 0.7mm,the mean permeability coefficient and effective porosity are 54.33m/d and 0.298,respectively.According to the testing results,the minimum value of mean permeability coefficient is 37.73m/d,so the medium can be classified as porous medium with high permeability.Moreover,the permeability coefficients are similar among those sand-piles,so the medium is relatively homogeneous.2)First,this paper used traditional advection-dispersion equation to fit the breakthrough curve obtained from experiment,and obtained corresponding dispersity and effective porosity under different experiment conditions.For the same sand-pile and sample,results show that the dispersity and effective porosity can lie between a certain range.3)Based on the fitting results of breakthrough curve obtained from traditional advection-dispersion equation,the trailing phenomenon can be observed from most of the breakthrough curves.According to the experiment condition,this paper proposed that the trailing phenomenon is influenced by the homogeneity of porous medium,and non-homogeneity can easily lead to trailing phenomenon.Moreover,experiment results show that there is no obvious correlation between flow rate and trailing phenomenon.4)The trailing phenomenon can be observed when using traditional advection-dispersion equation to fit the breakthrough curve.In order to handle this problem,this paper introduced a advection-dispersion equation with time-fractional order,which is based on Riemann-Liouville fractional derivative form,to fit the measured C-t curve.Fitting results show that this equation is favorable to solve the problem of trailing phenomenon.