Flow with axial dispersion through a one-region pipe of uniform cross-section.
Model number: 0079
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The partial differential equation models flow into, through and out of a pipe with plug flow and axial dispersion (diffusion) along the x-axis and instantaneous radial dispersion so that concentration is uniform across the cross-section at each x-position. Consumption,Gp, equivalent to loss by a first order reaction or loss by permeation is a uniform fraction per unit time along the pipe. (This can be modified by making G a function of concentration, Gp(Cp) or of position, Gp(x).) Flow is constant, as are all the other parameters.The boundary conditions are (1) At the inflow, the diffusion coefficient, Dp, cm^2/s, times the spatial gradient in concentration, dC/dx, balances the difference between the inflow concentration and the concentration Cp just inside; (2) At the outflow, the gradient dC/dx is set to zero, as if reflecting from an impermeable surface, so that mass is lost into the outflow only by flow, Cout = Cp(x=L,t). LIMITATIONS: This model cannot approximate Newtonian parabolic flow, where the response to a flow-proportiaonal cross-sectional pulse labeling at the inflow would give a sharp upstroke and peak at 1/2 the mean transit time and then, in the absence of axial dispersion, diminish in proportion to 1/t^2. See Gonzalez-Fernandez (1962) on this point.