Solar thermal energy systems require storage to overcome the intermittency of the source. Rock bed thermal energy storage is the ideal solution for solarized Brayton cycles. When the flow direction through a rock bed can vary, as in the case of free-standing rock piles or baffled prismatic beds, plug flow correlations no longer apply. Correlations for the change in pressure drop with flow direction are available in the literature, but correlations for the heat transfer coefficient as a function of flow direction are scarce. In this study, the heat transfer coefficients derived from computational fluid dynamics (CFD) of the flow through the interstitial volumes between particles, for a packed bed of ellipsoidal particles, heated by a constant heat flux, are described. We validated our CFD result against some experiments. The heat transfer coefficient for vertical flow is about 20 % higher than that for horizontal flow. Our CFD results compare favourably with our experimental results, and are also in agreement with Martin's correlation for heat transfer in porous media. We estimate that the uncertainty in our CFD results is about 6 %. Notwithstanding, these are some of the first results that capture the effect of flow direction relative to the ellipsoidal particles' orientation in the bed.