Mixing-cell boundary conditions and apparent mass balance errors for advective–dispersive solute transport

摘要: In many field or laboratory situations, well-mixed reservoirs like, for instance, injection detection wells and gas distribution sampling chambers define boundaries of transport domains. Exchange solutes gases across such can occur through advective diffusive processes. First we analyzed where the inlet region consists a reservoir, in systematic way by interpreting them terms type. Second, discussed mass balance errors that seem to appear case resident injections. Mixing cells (MC) be coupled mathematically different ways domain advective-dispersive occurs: assuming continuous solute flux at interface (flux injection, MC-FI), concentration (resident injection). latter case, leaving mixing cell defined two ways: either as value when is approached from mixing-cell side (MC-RT -), it column +). Solutions these types with constant or-in one case-distance-dependent parameters were compared each other well solution two-layer system, first layer was characterized large dispersion coefficient. These solutions differ mainly small Peclet numbers. For most real model MC-RI + considered relevant. This type modeled an exponentially varying coefficient within porous medium. A will appropriate because Eulerian nature usually dominating gaseous diffusion coefficient, whereas asymptotically growing more due Lagrangian mechanical dispersion, which evolves only fluid flow. Assuming between column, model, entails discontinuity. discontinuity arises inherently definition cell: process included equation, but does not description cell. There, convection appears homogeneous Thus, close contact generally underestimated. leads (apparent) errors, are often reported similar situations erroneously used judge validity models. Finally, defines universal basis regarding boundary. Depending on parameters, represents, its limits, (C) 1998 Elsevier Science B.V. All rights reserved.