The longitudinal vortices can potentially enhance heat transfer with small pressure loss penalty. Vortex generators (VGs) which can generate longitudinal vortices are widely used in fin-and-tube heat exchangers for heat transfer enhancement. But for a long time

researches are carried out focusing on the effect of the shape and parameters of VGs on heat transfer and the relationship between the longitudinal vortices intensity and heat transfer intensity is analyzed qualitatively. The quantitative relationship between the longitudinal vortices intensity and heat transfer intensity is seldom reported. Longitudinal vortex is a typical secondary flow

and thus the longitudinal vortex intensity can be defined using the secondary flow intensity parameter. In this paper

the numerical models of flat tube bank fin heat exchanger with VGs mounted on the fin surfaces are studied for different fin and VGs parameters. The longitudinal vortices intensity is quantitatively defined using the nondimensional secondary flow intensity parameter Se. The relationship between the longitudinal vortices intensity and the heat transfer intensity and that between the increment values of Se and Nu caused by the longitudinal vortices are quantitatively studied. The results show that there is no corresponding relationships neither between Nu and Re

nor between Se and Re. Similarly

no linear relationship exists between the friction factor f and the values of Re and Se. But the corresponding relationship exists not only between Se and Nu but also ΔSe and ΔNu. The longitudinal vortices intensity determines the heat transfer intensity in the flat tube fin heat exchanger.