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 the energy efficiency keeps varying with the attack angle, the thrust of this investigation is to identify the best attack angle(s) for the stipulated task. For that purpose, four distinct attack angles (i.e., 15 deg, 30 deg, 45 deg and 60 deg), representing the entire effective range, are considered. Since spatial positioning of the generators too has a strong bearing on 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-offs. 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 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 the specified Reynolds number.