The description of turbulent flow behaviour with the standard Navier-Stokes equations requires high mesh resolution and consequently results in an unfeasible computational effort for fixed beds. Therefore, the computationally efficient Reynoldsaveraged Navier-Stokes (RANS) approach is applied to model the turbulent transport ). Thereby, the standard steady-state governing equations are formulated in terms of averaged solution variables and the stress tensor is modified by an additional tensor T RANS , which must be calculated by an appropriate turbulence model. Solving steady-state governing equations to simulate the transient characteristic of turbulence can lead to an inaccurate description of dynamic flow phenomena and convergence problems. However, this approach is commonly used in PRCFD of catalytic fixed bed reactors since transient simulations of such complex geometries still demand non-reasonable computational costs ). In the presented work, the realizable k-ϵ turbulence model according to is chosen to compute T RANS . Moreover, the averaged diffusive heat and species mass flow in the bulk phase is calculated as function of the turbulent eddy viscosity µ turb by changing the thermal conductivity to λ f + cp,f µturb P rturb and the diffusion coefficient to D m,i + µturb Scturb ρf .