Turbulent convective heat transfer from rough surfaces with two-dimensional rectangular ribs

Artificial roughness is often used in nuclear reactors to improve the thermal performance of the fuel elements. Although these are made up of clusters of rods, the experiments to measure the heat-transfer and friction coefficients of roughnesses are performed with single rods contained in smooth tubes. A new transformation method to obtain data applicable to reactor fuel elements from these annulus experiments is illustrated. New experimental friction data are presented for ten rods, each with a different artificial roughness made up of two-dimensional rectangular ribs. For each rod four tests were performed, each in a different outer smooth tube. For two of these rods, each for two different outer tubes, heat-transfer data are also given. The friction and heat-transfer data, transformed with the present method, are correlated by simple equations. These equations are applied to a case typical for a Gas Cooled Fast Reactor fuel element. (author)