Heat transfer at the reactor tube wall is especially important for highly exothermic reactions, such as partial oxidations and highly endothermic reactions such as methane ateam reforming. In such cases, flow rates tend to be high and the tube-to-particle diameter ratio (N) tends to be low, and the limiting resistance to heat transfer occurs very close to the tube wall. Empirical correlations of the wall heat transfer coefficient are extremely scattered and unreliable. An approach in which the individual heat transfer mechanisms are simulated and modeled is being tried by our research group.

In this presentation we focus on the conduction mode of heat transfer. CFD simulations under stagnant conditions and/or low flow rates are shown, to identify near-wall phenomena. Standard fixed bed reactor conduction models are evaluated using empirical and measured void fraction profiles, along with models for the stagnant thermal conductivity. Comparisons between the detailed CFD simulation temperature profiles and those obtained from the modeling approaches allow evaluation of their suitability to describe near-wall conduction heat transfer.