Effective thermal conductivity of packed beds of spheres in transient heat transfer

Temperature distributions in heated packed beds of spheres of different materials found experimentally and theoretically/numerically are presented in the paper. The modelling of transient heat transfer draws on two models - parabolic and hyperbolic, although the non-Fourier effects were not observed in the experiment. The results of modelling lead to the estimation of the effective thermal conductivity of investigated types of beds. These values are determined from the solution of the inverse problem of heat conduction. The obtained results show that both presented models can be applied to model the transient heat transfer in packed beds for the considered range of heating time, giving the same value of the effective thermal conductivity, within the discussed accuracy margin. However, it has been revealed that the effective thermal conductivity in transient heat transfer with the step change in the boundary heat flux may reach the value several times higher than in steady state conditions.