Support grids are an integral part of nuclear reactor fuel bundle design. Features, such as vane pairs, are placed on the downstream edge of support grids to enhance heat transfer and delay departure from nucleate boiling. The complex flow fields created by these features cause spatially varying heat transfer conditions on the surfaces of the rods. Azimuthal variations in heat transfer for a standard grid, split-vane pair grid, and disc grid are measured in the present study using a heated, thin film sensor. Normalized values of the variations in Nusselt number are presented for the support grid designs at axial locations ranging from 2.2 to 36.7 Dh. Two Reynolds numbers, Re = 28,000 and Re = 42,000 are tested. Results identify distinctive azimuthal variations in Nusselt number for all three of the support grid designs tested. The split-vane pair grid exhibits the largest variations in azimuthal heat transfer while the disc grid has the most uniform heat transfer.

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