Analysis of Turbulent Heat Transfer Downstream of Mixing Vanes with Tip in Subchannel of Nuclear Reactor

Mixing vanes attached to spacer grid in rod bundle subchannel produce highly three-dimensional and strongly turbulent flow, which is effective to enhance convective heat transfer. Development of computational fluid dynamics (CFD) makes it possible to analyze the complex three-dimensional flow structure precisely, which is very instructive in understanding thermal hydraulics of the phenomena. There have been a lot of researches to investigate the flow field downstream of mixing vane experimentally and numerically. Among numerical works, Karoutas et al. (1995), In et al. (1998), and Cui and Kim (2002) performed numerical analysis using commercial CFD code to find the turbulence structure induced by mixing vane. Imaisumi et al. (1995) presented a method for three-dimensional analysis of the flow in a PWR fuel assembly. The most important factors in enhancing heat transfer in subchannels, are production of turbulent kinetic energy, cross-flow mixing in subchannel, and development of secondary flow. These factors can be analyzed precisely by solving three-dimensional Reynolds-averaged Navier-Stokes equations (RANS). The present work aims at evaluation of the effects of tip attached to the end of the mixing vane on turbulent convective heat transfer downstream of mixing vane in subchannel of nuclear reactor with three-dimensional RANS analysis. SST model is selected as a turbulence closure. 'PLUS7' Mixing vane with tip is tested in comparison with the mixing vane without tip. In addition, the effects of tip angle are also tested