Predictions of turbulent flow and convection in round tubes, channels and concentric circular annuli based on a correlating equation for the fraction of the shear stress due to turbulence have previously been shown to be within the scatter of the best experimental data. However, the sufficiency of this agreement has been questioned because of the scatter and limitations in scope of that data. As a supplementary test, the sensitivity of the predictions to each of the numerical empiricisms and arbitrary functions of the model has been investigated. On the whole, the uncertainties in these values and functions are not found to influence the predictions significantly. (c) 2005 Elsevier Ltd. All rights reserved.