Investigation of heat transfer in the test sections of pebble beds placed between axially streamlined cylinders

The purpose of this paper is to investigate the heat transfer characteristics in the test sections of pebble beds placed between cylinders and to evaluate the effect of pebble bed structure and of adjoining surfaces to the heat transfer from the spheres and from a cylinder. The local and perimeter average heat transfer coefficients from the cylinder were investigated. The results of experiments demonstrated that the heat transfer from the cylinder stratifies streamwise. The results of the investigations showed, that the heat transfer from the cylinder with a random packing of spheres is at ∼20% higher than that with a regular packing. Heat transfer from the spheres was investigated by means of the local modeling method, which reveals the heat transfer characteristics in different places of the pebble bed. The experimental results showed that in the case of rhombic pebble bed the differences in the heat transfer from the spheres can reach up to 25% depending on the position of sphere in respect to the cylinders. In the case of random pebble bed the differences in the heat transfer from the spheres in the different places were not considerable. (author)