Turbulent natural convection of sodium in a cylindrical enclosure with multiple internal heat sources: A conjugate heat transfer study

Turbulent natural convection of liquid metal in a cylindrical enclosure with locally distributed heat source has been investigated for Boussinesq number in the range of 4.5 × 011- 6.25 × 1012. The enclosure considered is an ideal model of the lower plenum of a fast reactor with tray(s) holding damaged core debris, which continuously generate heat. The focus of the study has been to assess the heat dissipation capacity of single and multiple trays in respecting the specific temperature limits on the tray(s). Heat conduction in the metallic trays and in the impervious core debris mixture and turbulent natural convection of the liquid sodium are solved as a conjugate heat transfer problem. The equations that govern the various heat transfer processes in 2-D axi-symmetric cylindrical polar coordinate system have been solved by the finite volume method. Turbulence has been modeled by the k-ε turbulence model, without the use of wall functions. The predictions of the numerical model have been validated against benchmark data reported in open literature. Also, experiments have been conducted in an ideal water model towards validation of the computational model. For typical enclosure dimensions representing a 500 MWe fast reactor, it is seen that the critical parameters are heat dissipation area of the source (area of trays) and the thickness of the heat source (debris thickness). With increase in the number of trays, the heat transfer area increases while the debris thickness reduces. Both these effects lead to reduction in the tray as well as source temperatures. The heat dissipation capacity exhibits a non-linear relationship with the number of plates.