Laminar- and Slug-Flow Heat Transfer Characteristics of Fuel Rods Adjacent to Fuel Subassembly Walls

Multiregion heat transfer analyses, based on both laminar and slug flows, have been performed to explore the heat transfer characteristics of the rods located in the corner and edge regions of LMFBR nuclear fuel subassemblies. By adopting physical parameters of practical interest, the rod-average Nusselt numbers of these rods were calculated for equilateral triangular arrays of rods having pitch-to-diameter ratios in the range 1.05 ≤ P/D ≤ 2.00. A mathematical scheme is presented for determining the laminar velocity field which, in this case, constitutes a mixed boundary-value problem specified in a domain of irregular shapes. For the special cases of peripherally uniform temperature or uniform heat flux at the outer wall of the cladding, rod-average Nusselt numbers were also calculated and compared with those for central rods.