TURBULENT HEAT TRANSFER IN DUCT FLOW
The problem of calculating the convective heat transfer in turbulent flows is practicable with satisfactory accuracy only on the basis of empirical relationships. This is due to the essential difficulties envolved with the treatment of momentum and heat flux dominantly caused by turbulent fluctuations. For theoretical considerations the Reynolds shear stress is taken into account by using either mixing-length concepts or modeled transport equations. Usually the Reynolds heat flux is considered by assuming a constant turbulent Prandtl number. This is a rough assumption, because the ratio of the turbulent diffusivities for momentum and heat is not constant as experiments have shown. The aim of the present work is to improve such theoretical considerations. This is in a first step tried for the simple case of a fully developed channel flow. The turbulent shear stress as well as the turbulent heat flux are taken into account by using carefully modeled transport equations. The calculated profiles of the Reynolds fluxes, the turbulent diffusivities for momentum and heat as well as the turbulent Prandtl number are shown. The results seem to be reasonable compared with experimental investigations.