Computational Fluid Dynamics Approach to Precipitation Reactions: The Importance of Subgridscale Fluctuations

Abstract

Computational Fluid Dynamics (CFD) modeling has become widely accepted as a tool for reactor design. Recent studies by (Wei et al. 1997) and (van Leeuwen et al. 1996a and 1996b) have shown that this technique can be successfully applied to precipitation reactions. However, it was unclear if the used modeling technique of Reynolds Averaging was adequate to describe the fast and non linear process of nucleation. By using Reynolds Averaging only the time-averaged concentrations are used to calculate the nucleation rate. Because in a turbulent field the concentrations vary significantly with time an error might be introduced by doing this. In this study an experimental approach has been followed to estimate this error. It has been found that the error, introduced by using Reynolds Averaging, depends both on the turbulent intensity of the flow and on the exponential constant B in the nucleation rate kinetics. For high values of B, which correspond to the regime of homogeneous nucleation, the error can easily amount to more than 200%. For low values of B, corresponding to the regime of heterogeneous nucleation, the error amounted to a maximum of 20% at the location in the reactor where the supersaturation reaches its maximum.