Influence of conjugate heat transfer in compact heat exchangers with vortex generators

An experimental study was carried out to highlight conjugate heat transfer effect in compact heat exchangers (400 < Re-2H < 2600). In order to enhance local heat transfer coefficient, Vortex Generators (VG) are punched out of the fin. In a first time, the heat transfer augmentation due to the addition of VG was measured on a constant temperature fin. An unsteady method with infrared thermography measure the local heat transfer coefficient. In addition, to show the influence of the heat diffusion in the fin, a steady method was developed to determine the local heat flux density. This work showed that the fin efficiency has a strong influence on the Vortex Generator performance. VG can increase the heat transfer by up to 35% on a fin with an efficiency equal to I (constant temperature), whereas this enhancement is about 23% for a brass fin and 7% for a steel fin. Finally, we show that the theory of the fin efficiency (with separate effect of convective and conductive transfer) is valid in the majority of industrial applications (<eta> > 0.75).