Experimental investigation on heat transfer in laminar, transitional and turbulent circular pipe flow with respect to flow regime boundaries

The empirical prediction methods for heat transfer coefficients in the transition regime between laminar and fully turbulent flow are still subject to changes. This situation reflects a lack of reliable experimental data, which are consistently determined over a wide range of relevant Reynolds and Prandtl numbers. This contribution presents new measurement data, in particular 164 data points for heat transfer coefficients, consistently determined over a wide range of Reynolds and Prandtl numbers, ranging from 13 < Pr < 70 and 375 < Re < 13100. In addition, the widely accepted prediction method for heat transfer in circular pipes according to Gnielinski is tested with the present data and other relevant data from literature. This method relies on a linear interpolation between the heat transfer coefficients at the onset of the transition regime and that of the fully turbulent regime. Consequently, working on a consensus about the values of these onset points is an important issue. In this contribution, the transitional flow regime has been found to start at Re-t = 2300, and the fully turbulent flow regime to start in the range of 4100 < Re-t < 5400. Those findings support the latest version of Gnielinskis method, published in 2013, as well as other recent work on the topic, particularly that of Everts and Meyer. (C) 2019 Published by Elsevier Ltd.