with the momentum boundary layer thickness δ m determined by Equation . The temperature boundary layer thickness δ T is calculated by inserting the Prandtl number P r = cp,f µf λf for X, and for the computation of the concentration boundary layer thickness δ CO 2 the Schmidt number Sc CO 2 = µf ρf Dm,CO 2 is used instead. The temperature and concentration boundary layer thickness becomes smaller with increasing Re p and grows with decreasing Prandtl or Schmidt number, as shown in Figure . The CFD simulations agree well with the predictions from the equations presented by Schlichting and Gersten. This investigation demonstrates, that coupling the fluid flow around a spherical VPO catalyst with reaction inside the porous particle via the implemented conjugated heat and mass transfer model results in an accurate description of the transport at the interface. This is supported by comparisons with correlations and models in the relevant