Particle-fluid heat transfer close to the bed wall: CFD simulation and experimental study of particle shape influence on the formation of hot zones

Abstract

This paper investigated the heat transfer from a wall-affected non-spherical particle to the turbulence gas flow both numerically and experimentally. In the numerical section, a three-dimensional finite element method was used to solve the partial equations using FEMLAB version 2.3. In the experimental section, the axial flow over a single naphthalene particle with the tube to particle diameter ratio (N) ranging within 4.5–6.7 was examined and the Nusselt number was calculated by heat and mass transfer analogy. The effects of the tube wall, particle shape, and particle rotation angle were tested on the formation of hot zones in detail. The results indicated that the wall effect can be ignored when particle-tube wall distance per particle diameter was greater than 0.143 (yc/Dp ≥ 0.143). Internal holes did not play an important role in reducing the hot zones though they increased the heat transfer rate per unit volume of the particle and reduced the pressure drop due to the higher porosity of packed bed. The minimum hot zones were observed for the tri-lobe particle at the axial rotation angle of zero when the particle leaned against the wall tangentially. The predicted results were well congruent with the experimental results. The results obtained by this study can be applied to discovering more about the hot spots and obtain a better catalyst particle for packed bed reactors.