Experimental Investigation of the Heat Transfer under Air or Helium-Xenon Mixture Flow into the Heated 7-Rod Bundle with Spaced Grids

The experimental results on heat transfer and pressure drop during the gas coolant flow into a space formed by a dense packing of 7 heated tubes are presented. To fix the tubes rigidly, 8 spacer grids, evenly distributed along the tube lengths, are used together with longitudinal displacers, which ensure a uniform gas flow field in the internal and external channels of the tube bundle. As a working fluid, gas mixtures with a large difference in the Prandtl number were used: air (Pr = 0.7) and helium-xenon mixture (Pr = 0.23). The experiments were carried out in the range of Reynolds numbers of 1926–11200. The wall temperature distributions of the central and peripheral tubes along the length are measured in detail. Particular attention is paid to the areas of gas flow restructuring near the spacer grid. The heat transfer coefficients and friction factors are determined, and the obtained correlations are compared with the known correlations for round channels. The effect of spacer grids, fixing the heated tubes, on local and average heat transfer and friction factors has been analyzed.