Parametrization of secondary flow intensity for laminar forced convection in twisted elliptical tube and derivation of loss coefficient and Nusselt number correlations by numerical analysis

Abstract

The parameters used to specify the intensity of secondary flow in helical coiled tube and tubes with twisted tape insert can be obtained easily without knowing whole detail velocity field. It is found these parameters determine the characteristics of heat transfer and fluid flow. There are no parameters to specify the intensity of secondary flow in a twisted elliptical tube. Thus, this paper tried to find out a parameter that can be obtained easily and can specify the intensity of secondary flow in twisted elliptical tube. The effort was made to establish the correlations between the intensity of secondary flow and the flow friction factor or average Nusselt number. The results show that three types of parameters can be used to describe the intensity of secondary flow in twisted elliptical tube; there exists close relationships between these parameters. Among them a swirl parameter can be obtained without knowing whole detail velocity field. The average Nusselt number of twisted elliptical tube is the summation of Nusselt number of straight elliptical tube and Nusselt number term induced by secondary flow. And friction factor of twist elliptical tube can be divided into the friction factor of straight elliptical tube and a friction factor term caused by secondary flow.