CFD Based Comparison of Slit Fin and Louver Fin Performance for Small Diameter (3mm to 5 mm) Heat Exchangers

Tube and fin heat exchangers using small diameter (≤5mm outer diameter (OD)) copper tubes are emerging as desirable alternatives to heat exchangers using conventional (≥7mm OD) tubes. Enhanced fins, having slits or louvers, have high heat transfer performance and are often used in tube and fin heat exchangers. Present literature lacks air side pressure drop and heat transfer coefficient correlations for these fin designs for tube diameters smaller than 5 mm. In this paper, the development of correlations for slits fins for tube diameters ranging from 3 mm to 5 mm. These correlations are developed following the Computational Fluid Dynamics (CFD) based methodology as outlined in the companion paper “CFD-Based Airside Heat Transfer and Pressure Drop Correlation Development for Small Diameter (3 mm to 5 mm) Copper Tube Louver Fin Heat Exchangersâ€. The correlation for the Colburn j factor developed in this paper reproduces 93% of heat transfer data, obtained through CFD simulations, within 85% accuracy. The Darcy f factor correlation reproduces 98% of pressure drop data, obtained through CFD simulations, within 90% accuracy. Using these correlations, a comparative analysis for slit fin and louver fin performance is undertaken. Performance trends with respect to different fin design parameters such as the  number of slits/ louvers, slit height, etc. are addressed. The work also includes an investigation of optimal fin design for each of the fin types. These correlations, and the optimal fin designs, can be used to design air-to-refrigerant heat exchangers with tube outer diameters between 3 and 5 mm