A New Approach to Correlate Heat Transfer Data for Turbulent Flow in Smooth Pipes Based on Generalization of Reynolds Number
This paper shows that the conventional Reynolds number has a clear physical meaning only for laminar, hydraulically developing or unsteady flow, while the generalized Reynolds number is physically meaningful for both laminar and turbulent regimes; the two Reynolds numbers coincide only in case of laminar flow. A review of widely used heat transfer correlations for turbulent liquid flow in smooth pipes (Re > 2000) is presented, and new correlations are developed using the generalized Reynolds number. The analysis is based on a database of 1025 experiments (including 110 in the transitional regime), covering Re = 2000-522000 and Pr = 0.18-414. The proposed correlations apply over the same ranges and show improved statistical performance, exceeding commonly cited correlations by 4.7-7.8 percentage points. It is also demonstrated that the range Re = 2000-4000 represents a hybrid region where both Reynolds and Graetz numbers simultaneously affect the Nusselt number.