Surface radiation effects on mixed convection heat transfer in a horizontal duct

Abstract

A numerical analysis of heat transfer in a heated horizontal duct is carried out to study the effect of surface radiation from duct inner walls on mixed convection heat transfer. The duct is differentially heated, wherein the opposing vertical walls are maintained at two specified isothermal temperatures, while the horizontal walls are perfectly insulated. Air enters the heated duct in a hydrodynamically fully developed condition, and steadily flows under laminar conditions while undergoing thermal development within the heated duct. For a set of specified temperature differences across the isothermal vertical walls, the heat transfer rate to the airflow is evaluated, and the fluid flow patterns are obtained for a range of flow rates, duct aspect ratios, and wall emissivities. Critically examining the fluid flow patterns and the characteristics of the hot wall Nusselt number, the significance of wall radiation effects on mixed convection heat transfer is identified and analysed in this study. It is found that the interaction of surface radiation and mixed convection influences the transport phenomena within heated ducts.