Sensitivity of the turbulent Schmidt number and the turbulence models to simulate catalytic and photocatalytic processes with surface reaction limited by mass transfer

Abstract

Based on CFD’s simulations using RANS and SGDH (Standard Gradient Diffusion Hypothesis), this study presents an alternative to better predict turbulent catalytic systems with surface reaction limited by mass transfer selecting an optimal turbulent Schmidt number (Sct). Simulations of H2O2 degradation were performed in an annular reactor with Mn/Al oxide immobilized into the wall using the AKN, RSM and standard k-ε turbulence models with the Sct varying from 0.2 to 1.1. The numerical apparent reaction constant (kapp) was compared with literature data to verify the prediction errors. The ideal Sct was applied to simulate the benzoic acid photocatalytic degradation in photocatalytic reactor coated with TiO2 for different flow rates. The results showed that the Sct of 0.8 for AKN, 0.7 for RSM, and 0.2 for standard k-ε are the best for systems with high mass transfer limitations and the Sct of 1.1 for AKN, 1.0 for RSM, and 0.4 for standard k-ε are the best for systems with low mass transfer limitations. It was concluded that all turbulence models predicted well the mass transfer when the ideal Sct was used and the standard-k-ε model could be an alternative since the prediction error was less than 6.5% with low computational cost.