Forced Convection From a Nonisothermal Cylinder in Crossflow

Abstract

When nonuniform thermal boundary conditions are imposed on the surface of a circular cylinder in crossflow, the heat transfer characteristics can be quite different compared to what is found for isothermal or constant heat flux boundary conditions. In the present analysis, two kinds of nonuniform boundary condition along the circumference of the cylinder are considered in a uniform stream of air: step changes and linear profiles. To cite only one motivating application, step changes in temperature can arise on the surface of an external, cylindrical, solar central receiver. As the working fluid (water) flows through the vertical tubes that ring the circumference of Solar One (a solar central receiver in Barstow, CA), the solar flux on the receiver heats the water from a liquid to a superheated state. In this process, portions of the receiver panels, and thus portions of the circumference of the cylinder, function as a preheater, boiler, or superheater. Hence the surface temperature can vary significantly around the cylinder. Common engineering practice has been to use an average wall temperature with an isothermal cylinder heat transfer coefficient when estimating the convective loss in these kinds of situation.