In this work, a continuum 2D model is proposed to study the interaction at the interface of reactive transport processes in porous media. The analysis of the segregation produced by poor reactant homogenization at the...In this work, a continuum 2D model is proposed to study the interaction at the interface of reactive transport processes in porous media. The analysis of the segregation produced by poor reactant homogenization at the poral scale is addressed by a parametric heuristic model that considers the relative gradient of the reacting species involved in the process. The micro inhomogeneities are incorporated by means of longitudinal and transversal mechanical dispersion coefficients. A two-dimensional continuous model for the bimolecular reactive transport is considered where modelling parameters are estimated numerically from experimental data. A competitive effect between segregation and dispersion is observed that is analyzed by means of numerical experiments. The two-dimensional model reproduces properly both the total mass of the product as well as its increase with the velocity of flow and the inhomogeneity of the advanced front. The methodology used is simple and fast, and the numerical results presented here indicate its effectiveness.展开更多
The effect of vegetation on the flow structure and the dispersion in a 180 o curved open channel is studied. The Micro ADV is used to measure the flow velocities both in the vegetation cases and the non-vegetation cas...The effect of vegetation on the flow structure and the dispersion in a 180 o curved open channel is studied. The Micro ADV is used to measure the flow velocities both in the vegetation cases and the non-vegetation case. It is shown that the velocities in the vegetation area are much smaller than those in the non-vegetation area and a large velocity gradient is generated between the vegetation area and the non-vegetation area. The transverse and longitudinal dispersion coefficients are analyzed based on the experimental data by using the modified N- zone models. It is shown that the effect of the vegetation on the transverse dispersion coefficient is small, involving only changes of a small magnitude, however, since the primary velocities become much more inhomogeneous with the presence of the vegetation, the longitudinal dispersion coefficients are much larger than those in the non-vegetation case.展开更多
To characterize the mean and variance of stochastic concentration distributions in heterogeneous porous media, we derived conservation equations using the first-order perturbation approach and assuming stationary fluc...To characterize the mean and variance of stochastic concentration distributions in heterogeneous porous media, we derived conservation equations using the first-order perturbation approach and assuming stationary fluctuation fields of velocity and concentration. The concentration variance equation, similar to the mean concentration equation, consists of convection and dispersion terms with the mean water velocity and macrodispersivity. In addition, there is a production term in the concentration variance e-quation. The concentration variance production is quadratically proportional to the mean concentration gradient with a coefficient Qij , defined as the concentration variance productivity , which is the difference between the macrodispersivity Aij and the local dispersivity aij multiplied by a four-rank tensor. The macrodispersivity and the local dispersivity, respectively, result in the creation and dissipation of the concentration variance. The concentration variance is produced if the concentration gradient exists. For t→∞, Qij→0 , which indicates that the creation and dissipation of the concentration variance are balanced at large travel time. We solve the variance equation numerically along with the mean e-quation using Aij, Qij, and the effective solute velocity v . The variance productivity increases with the decrease in transverse local dispersivity and is not sensitive to longitudinal local dispersivity. The maximum concentration variance occurs near the maximum mean concentration gradient.展开更多
文摘In this work, a continuum 2D model is proposed to study the interaction at the interface of reactive transport processes in porous media. The analysis of the segregation produced by poor reactant homogenization at the poral scale is addressed by a parametric heuristic model that considers the relative gradient of the reacting species involved in the process. The micro inhomogeneities are incorporated by means of longitudinal and transversal mechanical dispersion coefficients. A two-dimensional continuous model for the bimolecular reactive transport is considered where modelling parameters are estimated numerically from experimental data. A competitive effect between segregation and dispersion is observed that is analyzed by means of numerical experiments. The two-dimensional model reproduces properly both the total mass of the product as well as its increase with the velocity of flow and the inhomogeneity of the advanced front. The methodology used is simple and fast, and the numerical results presented here indicate its effectiveness.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51479007,11172218 and 11372232)the Specialized Research Fund for the Doctoral Program of Higher Education(Grant No.20130141110016)the Fundamental Research Fund for the Central Universities(Grant No.2012206020204)
文摘The effect of vegetation on the flow structure and the dispersion in a 180 o curved open channel is studied. The Micro ADV is used to measure the flow velocities both in the vegetation cases and the non-vegetation case. It is shown that the velocities in the vegetation area are much smaller than those in the non-vegetation area and a large velocity gradient is generated between the vegetation area and the non-vegetation area. The transverse and longitudinal dispersion coefficients are analyzed based on the experimental data by using the modified N- zone models. It is shown that the effect of the vegetation on the transverse dispersion coefficient is small, involving only changes of a small magnitude, however, since the primary velocities become much more inhomogeneous with the presence of the vegetation, the longitudinal dispersion coefficients are much larger than those in the non-vegetation case.
基金NNSF of China and NSF-EPSCoR of University of Wyoming,USA
文摘To characterize the mean and variance of stochastic concentration distributions in heterogeneous porous media, we derived conservation equations using the first-order perturbation approach and assuming stationary fluctuation fields of velocity and concentration. The concentration variance equation, similar to the mean concentration equation, consists of convection and dispersion terms with the mean water velocity and macrodispersivity. In addition, there is a production term in the concentration variance e-quation. The concentration variance production is quadratically proportional to the mean concentration gradient with a coefficient Qij , defined as the concentration variance productivity , which is the difference between the macrodispersivity Aij and the local dispersivity aij multiplied by a four-rank tensor. The macrodispersivity and the local dispersivity, respectively, result in the creation and dissipation of the concentration variance. The concentration variance is produced if the concentration gradient exists. For t→∞, Qij→0 , which indicates that the creation and dissipation of the concentration variance are balanced at large travel time. We solve the variance equation numerically along with the mean e-quation using Aij, Qij, and the effective solute velocity v . The variance productivity increases with the decrease in transverse local dispersivity and is not sensitive to longitudinal local dispersivity. The maximum concentration variance occurs near the maximum mean concentration gradient.
