Effects of heat-transfer coefficients on thermal dynamics in a near-adiabatic fixed bed

Experimental and theoretical studies were performed to investigate thermal dynamics in a fixed bed. The near-adiabatic beds packed with virgin zeolite 13X and water-saturated zeolite 13X were heated with hot nitrogen. The effect of the heat-transfer coefficient between the gas and adsorbed phases, h(s) on thermal dynamics was elucidated by a comparison of the thermally heterogeneous and homogeneous models. If h(s) is obtained from a proper correlation, the prediction of thermal dynamics by the homogeneous model is the same as that by the heterogeneous model. The heat-transfer coefficient at the inner wall, h(i), in the packed bed showed a dependency on the flow rate and temperature of hot nitrogen. A dimensionless correlation of Nu(PM), Re(PM), and Pr was obtained from the experimental results, and the relation between Nu(PM) and Re(PM) in the correlation was similar to that derived from an internal flow in the vacant bed. Using the values of heat-transfer coefficients estimated from the thermal swing experiments, the dynamics of thermal regeneration in the zeolite 13X bed saturated with water was well predicted.