Search

AbstractJet impingement is a heat transfer technique utilized in different applications in industry. It is used for cooling the turbine blade and the combustor wall because of its high cooling rate. The heat transfer (HT) and flow structure of a circular air-impinging jet over a flat target plate with a circular row of 48 roughness elements are numerically investigated using renormalization group k–ε turbulence model. Different shapes of roughness elements, namely cylindrical roughness elements (CREs), droplet roughness elements (DREs), and hemispherical roughness elements (HREs), are examined. The effects of Reynolds number changed from 7,000 to 35,000, and the roughness elements location relative to jet diameter (s/d) of 1.5, 2, 2.5, and 3 at a constant jet-to-target plate distance (H/d) of 2 are studied. Temperature distribution, local Nusselt number (Nu), average Nusselt number (Nuavg), average Nusselt number ratio (Nuavg,r), velocity distribution, turbulence kinetic energy, streamline contours, and static pressure (p) over the roughness elements are evaluated and discussed. The results showed that the existence of roughness elements has a significant effect on the thermal and hydraulic characteristics. The Nuavg,r for the CREs, DREs, and HREs is up to 1.61, 2.02, and 1.2, respectively. All roughness element shapes increase the flow velocity in the narrow area between the elements and increase the wetted area. CREs augment the HT rates by increasing the turbulence intensity, while DREs reduce the drag force effects. [ABSTRACT FROM AUTHOR]

The efficiency, availability, and reliability of thermal management for various engineering applications present a crucial challenge facing the designers and engineers. The rapid development and sophisticated technological advancement require innovative devices possessing high operating capacities that are launched into the prodigious growing markets in all engineering sectors. As a result of pronounced advancements, the jet impingement required to transfer high heat fluxes with a target surface becomes one of the essential priorities for researchers. The intensification of jet impingement can be achieved with different techniques such as passive self-exciting jets, active exciting jets, and hybrid exciting jets. The active methods of self-exciting jets include annular, swirling, and sweeping jets, while the active ones contain pulsed and synthetic jets. In the current study, the heat transfer characteristics and the fluid flow behavior of jet impingement with recent modifications of jets are reviewed comprehensively. As well, the critical methods of passive and active exciting jets considering the jet geometrical and operating parameters are introduced. Moreover, the physical phenomena for each technique in comparison to the conventional circular straight jet as well as the published empirical correlations as available, are studied. The present work reviews the published numerical and experimental investigations considering the different modified jets and its application with various installation geometries that provide a higher efficiency with the augmentation of heat transfer rate. The jet excitation causes topological metamorphosis of flow and hence has a remarkable effect on the intensification of heat transfer. • The intensification of jet impingement can be achieved with different techniques. • Active, passive, and hybrid methods of jet excitation were reviewed. • Heat transfer and fluid flow characteristics of each exciting jet were studied. • The geometrical and operating parameters of each exciting jet were introduced. • Jet excitation increased turbulence intensity and hence intensified heat transfer. [ABSTRACT FROM AUTHOR]