Geometry contributions to natural convection heat transfer enhancement by the chimney effect

Abstract

Natural convection heat transfer enhancement continues to be an evolving problem in the design of passive safety systems in nuclear engineering. Increasing heat rejection rates guarantees safety and higher heat duty. This study numerically investigated the influence of the geometry of an adiabatic extension appended downstream of a vertical heated cylinder. Four geometries comprising straight, diffuse, hyperboloid, and compound adiabatic extensions were studied. Nusselt number ratios, temperature distribution ratios, and mass flow rates were presented. Results showed that the compound extension geometry exuded high heat transfer enhancement capabilities by the chimney effect, and reduced wall temperature by up to 16% for the range of parameters studied. These findings are presented as a contribution to the design improvements of air-cooled passive systems, especially in advanced nuclear reactors.