A comprehensive analysis and empirical correlations for Nusselt number, friction factor and exergy destruction of helical tube equipped with spring-wire

Abstract

Abstract Although different kinds of turbulators are employed through the straight tubes, spring-wire is the only applicable turbulator for helical tubes which has been recently proposed by some researchers. The geometrical characteristics of spring-wire (including wire-diameter, spring-diameter and spring-pitch) severely affect the thermal, frictional and exergetic behavior of fluid flow through the helical tubes. In this research, spring-wire (with different geometries) is employed as a turbulator for helical tube to provide empirical correlations of Nusselt number, friction factor and exergy destruction for spring wire through the helical tubes (as the functions of flow parameters and geometric characteristics) which have not been provided before. It is noted that, the correlations of the straight tubes (equipped with turbulator) cannot be employed for helical tubes. Notable thermal/exergetic behaviors were observed for spring-wire though helical tubes. Larger wire-diameter of turbulator provided higher heat transfer coefficient and higher Nusselt number. Smaller spring-pitch provided higher heat transfer coefficient but lower Nusselt number. Indeed, higher heat transfer coefficient does not necessarily mean higher Nusselt number for spring-wire turbulators which is explained in detail in this study.