Establishment of Colburn ‘j’ factor and Fanning friction factor ‘f’ correlations for a compact heat exchanger having perforated wavy fins using Computational Fluid Dynamics

Abstract

Wavy fins find widespread application in compact heat exchangers, due to their ability to achieve high heat transfer coefficients and lower friction factors, resulting in reduced pumping power requirements and improved overall efficiency. Despite the extensive literature available on these fins, no previous study has explored the influence of perforations on wavy fins. This study aims to establish accurate correlations for evaluating the Colburn ‘j’ factor and Fanning friction factor ‘f’ in wavy fins incorporating perforations, specifically tailored for compact heat exchangers. The Colburn ‘j’ factor guides the determination of the heat transfer coefficient, while the Fanning friction factor ‘f’ is instrumental in assessing pressure drop across the fin, both essential considerations in the rating and sizing of compact heat exchangers. The numerical model involves a perforated wavy fin constructed from ‘aluminum’ with ‘air’ as the fluid medium. To derive correlations, 1458 cases were simulated using ANSYS Fluent, systematically varying geometric parameters such as fin height (h), fin spacing (s), fin thickness (t), hole diameter (d), and fin pitch (p). The study spans Reynolds numbers from laminar () to turbulent (

). ‘j’ & ‘f’ factor values were validated using experimental data for wavy fins without perforations, followed by additional analysis incorporating perforations. The analysis showed a 19%–35% increase in the ‘j’ factor and a 21%–33% increase in the ‘f’ factor for perforated wavy fins compared to plain wavy fins. New ‘j’ and ‘f’ factor correlations were established, with over 96.3% and 95.0% of the points within ±16% and ±18% bounds, respectively. These innovative correlations applicable across the entire spectrum of operating and design conditions are expected to facilitate a more streamlined design process for compact heat exchangers featuring this unique fin geometry, enabling designers to reduce iterations during the design phase.