Experimental Investigation of Heat Transfer and Flow Mixing in Pebble Beds

The purpose of this paper is to investigate the thermal hydraulic characteristics of two types of test sections: pebble beds placed between cylinders and thin annular pebble beds (i.e., spheres dumped in thin annular slots). The investigations were performed for axial air flow. The experimental results of heat transfer from the spheres, as well as the results of heat transfer from a cylinder for both types of test sections, are presented. In addition, the results of flow-mixing investigations in pebble beds between axially streamlined cylinders are described. From these results, correlations were developed that can be used to predict the heat transfer characteristics.

The results of the experimental investigation of pebble beds between cylinders demonstrated that the randomly arranged pebble bed is preferable to the regular rhombic structure from the points of view of design simplicity, heat transfer from the cylinder, drag coefficient, and flow mixing. The results of the experiments in the case of thin annular pebble beds demonstrated that the maximum heat transfer from the spheres is at the relative width of the annular slot K, equal to 1.07 and 1.75 of the sphere's diameter