On the effect of turbulent fluctuations on precipitation: A direct numerical simulation – population balance study

Abstract

The objective of the present paper is to investigate the effect of turbulent fluctuations on precipitation and the implications for modelling. To this end, a coupled direct numerical simulation (DNS) - population balance study is conducted on the experiments of Schwarzer et al. (2006) on BaSO4 precipitation in a T-mixer. The unclosed terms in the averaged population balance equation are identified and evaluated via DNS. A comparison of the average nucleation and growth rates with those computed with the average values shows significant deviations indicative of the importance of fluctuations in precipitation modelling. Furthermore, the correlation between growth and number density is analysed, as well as its contribution to the reactant consumption. The study is performed at Sc=1 as it is, at present, not possible to resolve the sub-Kolmogorov scales at high Reynolds and Schmidt numbers. However, an attempt to investigate the effect of sub-Kolmogorov scales is made by performing a simulation of precipitation in a similar T-mixer at a lower (but still turbulent) Reynolds number and at Sc=1 and Sc=10. The findings indicate the presence of thinner reaction zones at higher Sc, but the effect on the product particle size distribution is marginal. An analysis of the results indicates that this is due to a compensation of the effect of thinner reaction zones by higher reaction rates occurring therein.