The Effect of Support Grid Features on Local, Single-Phase Heat Transfer Measurements in Rod Bundles

Local, average heat transfer measurements in a rod bundle downstream of support grids with and without flow-enhancing features are investigated for Reynolds numbers of 28,000 and 42,000. Support grids with disc blockage flow-enhancing features and support grids with split-vane pair flow enhancing features are examined. Grid pressure loss coefficients and feature loss coefficients are determined based on pressure drop measurements for each support grid design. Results indicate the highest heat transfer enhancement downstream of the support grid designs with disc blockages. In addition, the local heat transfer downstream of the split-vane pair grid designs indicates a region of decreased heat transfer below that of the hydrodynamically fully-developed value. This decreased region of heat transfer is more pronounced for the lower Reynolds number case. A correlation for the local Nusselt numbers downstream of the standard support grid designs is developed based on the blockage of the support grid. In addition, a correlation for the local Nusselt numbers downstream of support grids with flow-enhancing features is developed based on the blockage ratio of the grid straps and the normalized feature loss coefficients of the support grid designs. The correlations demonstrate the tradeoff between initial heat transfer enhancement downstream of the support grid and the pressure drop created by the support grid.