The Influence of The Hybrid Technique Utilizing Trapezoidal Longitudinal Ribs and Hemispherical Dimples Within an Elliptical Tube on Thermal-Hydraulic Performance

Abstract

This paper introduces a novel hybrid heat transfer enhancement technique combining Longitudinal Trapezoidal Ribs (LTRs) and Inline Hemispherical Dimples (IHDs) on the surface of an elliptical tube. A three-dimensional numerical investigation was conducted using Software STAR-CCM+ to evaluate thermal-hydraulic performance under constant heat flux boundary conditions, with air as the working fluid across a Reynolds number (Re) range of 2,900 to 10,300. The hybrid geometry expands the heat transfer surface area while generating secondary flows and longitudinal vortices that disrupt the hydrodynamic and thermal boundary layers. Quantitative results indicate that the proposed configuration increases the Nusselt number by up to 1,200% compared to a smooth elliptical tube, accompanied by a 410% increase in pumping power. Consequently, a maximum thermal performance factor of approximately 5.8 was achieved, demonstrating that this hybrid geometry is a highly effective passive technique for thermal performance enhancement.