Abstract

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.

Notes

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Graduation Date

2020

Semester

Spring

Advisor

Kapat, Jayanta

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering

Format

application/pdf

Identifier

CFE0008063

URL

http://purl.fcla.edu/fcla/etd/CFE0008063

Language

English

Release Date

May 2020

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

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