A NOVEL SPACER GRID WITH RECTANGULAR WING LONGITUDINAL VORTEX GENERATORS IN A 5x5 ROD BUNDLE
In this study, a novel spacer grid with rectangular wing longitudinal vortex generators (RLVGs) is designed to improve the thermal-hydraulic characteristics of fuel assembly and simplify the spacer grid structures. The impacts of the attack angle (30°, 45° and 60°) and the distribution (two patterns) of RLVGs on the thermal- hydraulic characteristics in the sub-channels of a rod bundle are numerically investigated. Numerical results show that the second flow generated by the RLVGs can spread to the downstream region of spacer grid, disturb the boundary layer of the rods and improve the heat transfer of coolant. For the novel design of pattern 1, the spacer grid with RLVGs in attack angle of 60° results in better heat transfer performance, followed by the case of 45° and then 30°. However, the spacer grid with RLVGs in attack angle of 60° brings about more pressure drop in comparison with that of 45° case. Considering both the heat transfer capacity and flow loss, it is concluded that the spacer grid with RLVGs in attack angle of 45° has superior performance. Based on these results, a novel design of pattern 2 is introduced and investigated too. With the same attack angle of 45°, pattern 2 increases the maximum transverse velocity of the second flow and decreases the average temperature on the rods surface as much as about 4°C in comparison with those of pattern 1 at the same Re conditions. Average Nusselt number along the axial direction in the sub-channels is increased up to 30%. The present results indicate that the present novel design of pattern 2 is an efficient way on improving the heat transfer of the fuel rod bundle. Of course, the overall design and manufacturing technique of this type spacer grid should be taken into consideration for practical application.