TRANSIENT AND STATIONARY AXIAL DISPERSION IN VORTEX ARRAY FLOWS .1. AXIAL SCAN MEASUREMENTS AND MODELING OF TRANSIENT DISPERSION EFFECTS

摘要

Whereas conventional RTD experiments yield incomplete and potentially misleading information, the axial scan method is shown to be a powerful technique to analyze the transient dispersion effects in vortex array flows (VAFs). Applying different initial tracer distributions to a given vortex, and making axial scans of the spreading tracer distribution, allowed, for the first time, to quantify and classify the complete set of strongly different transient dispersion modes. As a model system, the laminar Couette-Taylor flow has been selected. By working under high viscosity conditions, the time scale of the different acting phenomena has been enlarged to such an extent that even the fastest dispersion events could be extensively studied and quantified. It is shown that in laminar VAFs effective axial dispersion coefficients can be obtained which vary over orders of magnitude, just by applying different initial tracer distributions to a given vortex. A first principles two-dimensional model (valid when the mixing along the streamlines occurs fast) with which all observed transient dispersion effects can be accurately represented is proposed. The insights obtained in the present study are especially useful for the development of VAF reactors for the treatment of strongly viscous fluids. (C) 1997 Elsevier Science Ltd. All rights reserved. [References: 24]