Dynamics of sub-atmospheric zones and their impact on the fluid flow and heat transfer characteristics of impinging air jet on circular standalone ribbed targets

Abstract

Impinging jets are widely recognized for their exceptional heat transfer performance across various applications. Understanding the underlying principles of impinging jets is crucial for improving their effectiveness. In this study, an experimental investigation was conducted to evaluate the static pressure and heat transfer performance of a highly turbulent air jet on a standalone rib target surface. For this study, various parameters were considered, including rib diameters (8 mm to 28 mm), nozzle-to-plate spacing (H/D) (0.5-6.0), and Reynolds numbers (Re) ranging from 20,000 to 40,000. The results indicated that pressure and heat transfer distributions in the impinging jet strongly depended on H/D, Re, and rib diameter. The flow structure of the jet under detached ribs changed compared to the smooth surface, revealing complex flow behavior due to the formation of strong recirculation zones, which resulted in significant sub-atmospheric pressure regions. Consequently, heat transfer performance increased dramatically by 112% at the junction of this interplay, while an average heat transfer performance enhancement of 52% and a thermal performance factor of 1.63 was achieved using the standalone ribs compared to the smooth target surface. The heat transfer coefficients increased upon using the rib up to a diameter of 15 mm, after which a decreasing trend was observed. The optimum results were obtained with a rib diameter of 15 mm. This approach not only enhanced performance, but also opened new avenues for designing more effective cooling systems and improving the overall thermal management of engineering systems.