A numerical study of fluid flow and heat transfer over a fin and flat tube heat exchangers with complex vortex generators

A numerical work is carried out to investigate the heat transfer and fluid flow behaviors in a fin-and-flat-tube heat exchanger provided with complex vortex generators (CVGs). A new design of CVGs is proposed in the present paper, it consists of CVGs formed by two portions: a flat portion with various attack angles (β = 0°, 20°, 40° and 60°) and a curved portion with various curvature angles (α = 30°, 45° and 60°). Changes in CVGs position ratio (R*) inside the tube are also investigated and three values of R* are considered, namely: R* = 1.375, 1.750 and 2.125. Computations based on the finite volume method with the SIMPLE algorithm are conducted for the air flow. The Reynolds number is ranging from 25 to 400. The obtained results show that the vortex formed near the tubes is intensified by the flat potion of CVGs, and the curved tube guide the fluid flow towards the region behind the tubes, resulting thus in improved heat transfer rates. In a comparison with tubes without CVG, the new design suggested and especially the case with β = 60°, α = 60° and R* = 2.125 improve significantly the heat transfer (an increase by about 76%) with a moderate pressure loss penalty.