Heat Transfer to Small Cylinders Within a Packed Bed

Heat transfer to small cylinders within a porous media has been experimentally and analytically studied extensively over a varying degree of sample and particle sizes and fluid flow regimes. In general, the observations, trends and empirical correlations developed for these systems do not accurately extrapolate down to small cylinders operating under the packed bed condition. The objective of this research is to develop an empirical correlation that expresses the Nusselt number of small cylinders immersed horizontally within a packed bed subject to forced convection heat transfer, in terms of the pertinent test parameters and material properties. Heat transfer to small cylinders within a porous media has been experimentally and analytically studied extensively over a varying degree of sample and particle sizes and fluid flow regimes. In general, the observations, trends and empirical correlations developed for these systems do not accurately extrapolate down to small cylinders operating under the packed bed condition. The objective of this research is to develop an empirical correlation that expresses the Nusselt number of small cylinders immersed horizontally within a packed bed subject to forced convection heat transfer, in terms of the pertinent test parameters and material properties.A set of seven small cylinders ranging in size from 1.27 to 9.53mm were resistively heated within a 311mm diameter lab-scale packed bed. The porous medium in which the samples were immersed was fine alumina oxide sand, with mean particle sizes ranging from 145 to 33μm. Four separate Type K thermocouples were used to measure temperatures at pertinent locations within the apparatus: bed temperature, inner sample temperature, left and right sample temperatures. The apparatus was operated under flow rates up until incipient fluidization. The trends observed in this research compared well with published data, though the correlations developed from other research consistently under-predicted the heat transfer capacity within the packed bed. The correlation that was developed for calculating the mean Nusselt number was accurate to within ±15% for the entire range of tested and published data.