PREDICTION OF HEAT TRANSFER RATES FOR LOW REYNOLDS NUMBER TURBULENT FLOW IN TUBES.

The problem considered is heat transfer to fully developed turbulent flow in circular tubes. The idealized flow conditions considered are a smooth circular tubes, b steady flow, c constant fluid properties, d fully developed velocity and temperature profiles, and e constant wall heat flux. A generalized velocity profile was developed from the momentum equation by using Prandtls mixing length concept to evaluate eddy shear stresses. To obtain the necessary radial distribution for the mixing length, experimental data from the literature and continuity considerations were applied. Under the assumption of equal eddy diffusivities, the energy equation was solved. The resulting analytical predictions, in the form of Nusselt numbers based on tube diameter, were compared to recent low temperature difference, downstream measurements with air. For turbulent flow below Reynolds numbers of 10,000, the agreement between semi-empirical analysis and experimental data was closer than for previous analyses. The prediction can be represented by a Dittus-Boelter form, Nu 0.021 Re0.8Pr0.4 to within five per cent for Reynolds numbers above 4000. Author