Attack angle parametrization for capacity augmentation and wake management by vortex generators in finned compact heat exchangers

Abstract

Enhancing gas-side thermal conductance is essential for the compact sizing of finned-tube heat exchangers, and this study attempts it by integrating vortex generators. The orientation of the vortex generators, which is defined by its attack angle, has a strong bearing on the degree of augmentation. As energy-efficiency keeps varying with the attack angle, the thrust of this investigation is to identify best attack angle(s) for the stipulated task. Since spatial positioning of the generators too has a strong bearing on the energy-efficiency, therefore, its effect is duly accounted for a comprehensive investigation. For the selection of optimal designs, regression-based phenomenological models are used as they apply thermo-hydraulic trade-off. After determining the best angle(s), a study is carried out to evaluate their robustness under varying operating conditions. Although phenomenological models are adequate for design optimization, they do not describe the physics of thermo-hydraulic enhancement. Therefore, a study explaining the bearing of design modifications on the local characteristics too is carried out. Additionally, a study discussing the effect of generators' attack angle on heat transfer over the wake affected surfaces, which has a predominant existence in baseline flows, is reported. It has been found that the thermal augmentation over the said surfaces is the key to compact sizing of the system. For a selected wake-region deployment, the highest relative Colburn j-factor corresponding to wake-affected fin equals 3.07 at a specified Reynolds number..