Internal convective heat transfer to gases in the low-Reynolds-number 'turbulent' range

摘要

For internal vertical gas flow in tubes withstrong heating ratesat lowturbulentReynolds numbers, a typical experimental observation is that the local Nusselt number varies roughly as the square of the decreasing local Reynolds number. An aim of the present note is to examine this situation. This examination leads to the hypothesis that the behavior results from the evolution of the thermal boundary layer developing within the primarily molecular transport layer which is also growing from the wall. Comparisons to direct numerical simulations demonstrate that reasonable predictions are provided by an extension of the Leveque similarity analysis forlaminarthermal boundary layers. The present observations modify and improve our fundamental understanding of the process called “relaminarization” in these flows.