Teaching technique for internal forced convection flows through tubes cooled or heated by external natural convection. I. Horizontal orientation

Abstract

AbstractThis report is concerned with a distinct instructional technique that facilitates the teaching of laminar forced convection flow through a horizontal tube exposed to external natural convection. A simple one‐dimensional lumped‐based formulation enabled the determination of the mean bulk and wall temperature distributions of the internal fluid flow as well as the total rate of heat transfer between two axial stations in the region of thermal development. Streamwise‐mean values for the internal and circumferential‐mean values for the external Nusselt numbers have been taken from standard correlations reported in undergraduate textbooks on heat transfer, leading to the immediate calculation of a mean, equivalent Nusselt number, which serves to regulate the thermal interaction between the two fluid streams. Representative results for a complete combination of internal and external fluids, expressed in terms of their respective thermal conductivity ratios, are discussed at length. The thermal quantities were computed with a pocket‐size calculator and compared favorably with those based on a more general and rigorous two‐dimensional differential formulation. The latter was utilized as a baseline solution, and inevitably required a finite‐difference procedure on a personal computer.