This study compares and analyses the heat transfer between a novel jet array impingement configuration (designated as NPR) and a baseline jet orifice plate (flat) in a maximum crossflow scheme. Both jet plates feature inline arrays of 20 x 26 circular air jets that orthogonally impinge on a flat target surface consisting of 20 segments, parallel to the jet plates. The NPR plate consists of staggered semi-spherical pimples (protrusions) and dimples (imprints) with a jet-to-pimple diameter ratio (Dj,p/Dp) of 0.07 and jet length-to-pimple diameter ratio (L/Dj,p) of ~ 1 with a protrusion ratio (tp/Dj,p) of 2.78. The dimples (imprints) have a jet-to-dimple diameter ratio (Dj,d/Dd) of 0.14 with an (L/Dj,d) of 0.5 and an imprint ratio (td/Dj,d) of 1.28. The averaged jet diameter for the NPR plate is calculated based on the definition of the total effective open area of the jets, which is equal to 3.49 mm. The flat plate is designed to be compared to the NPR plate and consists of jet orifice diameters (Dj) of 3.49 mm, with a length-to-diameter ratio (L/Dj) of ~ 1. In both plate configurations, the streamwise and spanwise directions jet-to-jet spacings (X/Dj), (Y/Dj), respectively, are maintained constant at 7.16. The physical mechanisms that cause the change in heat transfer, normalized by Nusselt number, when comparing both configurations are discussed in two regions: impingement and crossflow. Turbulent flow structures and experimental heat transfer are explored over three jet-averaged Reynolds numbers (Reav,j) of 5,000, 7,000, and 9,000, and are compared to available numerical results. Jet-to-target wall ratio (Z/Dj) is varied between (2.4, 2.87, 3.25, 4, and 6) jet diameters. Subsequently, multiple regression of the logarithms is used on the results obtained from the heat transfer experiments and are correlated into a dimensionless approach. Appropriate statistical methods are also reported along with the correlations for both flat and pimple-dimple plates. Enhancement of up to 23% in the heat transfer coefficient in the NPR plate is seen in the crossflow region, where the crossflow effects are maximized. However, this convex-concaved plate yields lower globally-averaged heat transfer coefficients.
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Doctor of Philosophy (Ph.D.)
College of Engineering and Computer Science
Mechanical and Aerospace Engineering
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Zawati, Husam Nizar Ahmad, "Heat Transfer and Correlations of Jet Array Impingement with Flat and Pimple-Dimpled Plate" (2020). Electronic Theses and Dissertations, 2020-. 157.