As suggested by , a partitioned approach is applied to solve the governing equations of the coupled domains. Therefore, the solution of the fluid and solid phase is computed iteratively in parallel but separated from each other by the segregated solver employing the SIMPLE algorithm within the commercial software Siemens Simcenter STAR-CCM+ 2021.1. The domains are coupled via calculation and updating of the boundary conditions at the shared fluid-solid interface during the iteration procedure. In general, it makes no difference what type of boundary condition is used at the fluid-solid interface. However, in STAR-CCM+ only the Dirichlet boundary in species mass transport and the Neumann boundary in heat transport considers the secondary gradient. Hence, for heat transport the heat flux and for species mass transport the mass fraction is applied as boundary at the interface. Moreover, STAR-CCM+ provides the option to neglect secondary gradients in the definition of boundary conditions. Doing so, the value of Ṡκ,f and Ṡκ,s must be set to zero for the calculation of the flux and scalar at the interface. Due to the rapid change in the calculated boundary condition at the interface, updating the boundary scalar or flux with every iteration results in divergence of the simulation. This is illustrated exemplary in Figure (top) for a flow past a sphere, as described in section 4.2, with a constant heat source inside the sphere (orange line).