Experimental investigations on heat transfer in a circular pipe for laminar, transitional and turbulent flow are presented. Reliable prediction of heat transfer coefficients for transitional flows is still a challenging task. While methods for predicting laminar and turbulent heat transfer coefficients are widely established in literature, the proposed methods and the validity for calculating according values for the transition region and even the definition of this region itself remains a field of ongoing development. One aspect in this picture is the scarce availability of experimental data on heat transfer coefficients in circular pipe flow for Reynolds numbers in the range of 1000 < Re < 4000, especially for higher Prandtl numbers, i.e. 10 < Pr < 90. Thus, this paper focuses on providing experimental results for heat transfer in circular pipe flow for Reynolds (Re) numbers in the range of 500 < Re < 23000 and 7 < Pr < 41. The test fluid is a water-glycol mixture with a mass fraction of water of x(m) = 0.477. The results presented in this paper show good agreement with the widely used calculation methods proposed by Gnielinski in 2013 for laminar, transitional and turbulent flow. The results also confirm the presence of the transition region to occur between 2300 < Re < 4000. 184 data points in the range of 1000 < Re < 4000 are shown, since in this range scarce data are available in literature. In summary 261 heat transfer coefficients for 500 < Re < 23000 and 7 < Pr < 41 are presented, which show good agreement (80.8% are within +/- 15%) to the cited literature. (C) 2016 Elsevier Ltd. All rights reserved.