Hydrodynamics and heat transfer in packed beds with liquid upflow

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The authors investigate the radial heat transfer in packed columns with liquid flow and compare their results with those of studies carried out with gas flow. The heat transfer experiments are performed in a packed bed heated electrically through the wall with upward flow of water and aqueous solutions of ethylene glycol. The particle diameter has been varied from 1 to 6 mm, and the reactor inner diameter is either 50 or 100 mm. Radial and axial temperature profiles are measured inside the packed bed. The heat transfer parameters of the packed bed are obtained by fitting the parameters of two-dimensional, homogeneous model to the measured profiles: the radial effective thermal conductivity of the packed bed (Λ r), and the wall heat transfer coefficient. The conductivity of the packed bed incresaes linearly with the fluid velocity but when the ratio of Λ r to the thermal conductivity of the fluid is plotted against the fluid Peclet number (Pe d = Re d Pr), the slope is found to be lower for liquid than predicted for gas. This different behaviour is explained by differences in the flow regimes. The experiments in gas flow are usually carried out in turbulent flow, whereas the experiments in liquid flow are in an intermediate regime (between laminar and turbulent). A new correlation is proposed for this regime, depending on both Prandtl and Reynolds number of the fluid. Results on heat transfer coefficient at the wall and on wall channelling are also presented.