Natural Convection Heat Transfer Characteristics of Liquid Metal Cooled by Subcooled Water

An experimental study is performed to investigate the natural convection heat transfer characteristics with subcooled coolant to create engineering database for basic applications in a lead alloy cooled reactor. Tests are performed in the ALTOS (Applied Liquid-metal Thermal Operation Study) apparatus as part of MITHOS (Metal Integrated Thermo Hydrodynamic Operation System). The relationship between the Nusselt number (Nu) and the Rayleigh number (Ra) in the liquid metal is determined and compared with the correlations in the literature and experimental results. Given the similar Ra condition, the present test results for Nu of the liquid metal pool with subcooled coolant are found to be similar to those predicted by the existing correlations or measured from previous experiments. The current experimental results are utilized to develop new engineering solutions. The new experimental correlations for predicting the natural convection heat transfer are applicable to low Prandtl number (Pr) materials that are heated from below and cooled by the external coolant above. Results from this study are slated to be used to design BORIS (Battery Optimized Reactor Integral System), a small lead cooled modular fast reactor for deployment in remote sites. Tests are performed with air, water and Wood's metal (Pb-Bi-Sn-Cd) filling a rectangular pool while the lower surface is heated and the upper surface cooled by forced convection of water. The inner dimensions of the test section are 20 cm in length, 11.3 cm in height, and 15 cm in width. Wood's metal has a melting temperature of 78 deg. C. Constant temperature and heat flux condition is adopted for the bottom heating. The test parameters include the heated bottom surface temperature of the liquid metal pool, the input power to the bottom surface of the section, and the coolant temperature. (authors)