A Comparative Study of Thermal Design Correlations for Turbulent Flow in Helical-Enhanced Tubes

Abstract

A number of investigators have carried out studies on enhanced tubes, leading to better understanding of their thermal hydraulic characteristics. The variables considered in these investigations include the ''design'' parameters, namely, height, pitch, and helix angle of the rib, and the tube diameter, and ''flow'' variables such as the Reynolds number and the Prandtl number. The pressure drop and heat transfer correlations needed for prediction of the performance of ribbed tubes can be developed using either an analogy approach or an empirical technique. These two methods are explained, along with the many correlations that have been developed based on them. The numerous studies pose a dilemma for the designer in selecting the most appropriate correlation. This article outlines the various correlations that are available for predicting the thermal-hydraulic performance of turbulent flows in enhanced tubes. Specific correlations that are valid for particular enhancement types as well as general correlations are presented. The correlations are applied to a comprehensive database and the predictions are analyzed. A parametric analysis carried out using the different correlations indicates the relative influence of enhancement design parameters on friction factor and heat transfer. In particular, the design variables affect the heat transfer/friction factor characteristics differently for various tube types.