A diffusion-based approximate model for radiation heat transfer in a solar thermochemical reactor

An approximate method for fast calculations of the radiation heat transfer in a solar thermochemical reactor cavity is proposed. The two-step method with separate calculations for solar and thermal radiation is based on the diffusion approach. The usual P1 approximation is generalized by use of an equivalent radiation diffusion coefficient for the optically thin central part of the cavity. The resulting boundary-value problems are solved using the finite element algorithm. The accuracy of the model is assessed by comparing the results to those obtained by a pathlength-based Monte Carlo simulation. The applicability of the proposed model is demonstrated by performing calculations for an example problem which incorporates a range of parameters typical for a solar chemical reactor and spectral radiative properties of polydisperse zinc oxide particles.