Confinement size dependency of flow structures and thermal characteristics in turbulent impinging air jet on a flat target surface

Abstract

Impinging jets are of significant interest because of their facile design and high heat transfer rates and enabling effective cooling. Impinging jets are specifically designed to be suitable for various industrial processes that require high heat transfer rates. In this study, an experimental study was carried out to evaluate the impact of confinement size on the wall static pressure coefficient (Cp) distribution and Nusselt number (Nu) of a turbulent air jet impinging on a flat surface. Various confinement sizes (C L /d = 0.0 to 15.0) and nozzle to target distance (z/d) ratios (0.5 to 6.0) were tested. For both unconfined and confined jets, Cp was highest at stagnation and decreased as the jet flows laterally. Sub-atmospheric pressure zones were observed for confined jet and became stronger with increasing C L /d ratio. Nu values at stagnation decreased with increasing confinements, while a secondary peak in Nu was influenced by confinement size and z/d spacing. The secondary peak intensified with confinement up to C L /d = 12.0, thereafter it weakened, and shifted towards the stagnation point with larger confinements. At z/d = 6.0, heat transfer at stagnation increased with confinement. Overall, the maximum in crease in Nu value was 5.68 % with a thermal performance factor of 1.42 achieved upon confinement (C /d = 9.0) compared to unconfined jet. Moreover, the results indicate that maintaining the confinement size smaller than the target surface is vital for achieving better heat transfer performance. This study provides critical insights for optimizing impinging jet systems, revealing the nuanced interplay between fluid dynamics and heat transfer coefficients.