Pressure drop for parallel flow through a roughened rod cluster

A method is described of calculating the pressure drop for parallel flow through rod clusters with artificial surface roughnesses in order to improve the heat removal. The method allows the extensive experimental data on artificial roughness to be applied to rod clusters. The method is based on universal flow parameters for roughness and on general laws describing the pressure drop in non-circular channels with rough walls. The method is tested on the basis of measured results obtained from a rod cluster with 19 rough rods. The parameters determined are in excellent agreement with data measured in rough tubes and annular gaps. In this way it is possible, given the geometrical shape of the roughness elements, to calculate pressure drops and flow distributions in artificially roughened rod clusters contained in a smooth channel. The simplistic approach using an average friction factor and an overall hydraulic diameter results in rather unrealistic flow distributions and hence temperature distributions across the cluster.