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    Effects of Extended Jet Holes to Heat Transfer and Flow Characteristics of the Jet Impingement Cooling
    (Asme, 2019) Tepe, Ahmet Umit; Arslan, Kamil; Yetisken, Yasar; Uysal, Unal
    In this study, effects of extended jet holes to heat transfer and flow characteristics of jet impingement cooling were numerically investigated. Cross-flow in the impinging jet cooling adversely affects the heat transfer on the target surface. The main purpose of this study is to reduce the negative effect of cross-flow on heat transfer by extending jet holes toward the target surface with nozzles. This study has been conducted under turbulent flow condition (15,000 <= Re <= 45,000). The surface of the turbine blade, which is the target surface, has been modeled as a flat plate. The effect of the ribs, placed on the target surface, on the heat transfer has been also investigated, and the results were compared with the flat surface. The parameters such as average and local Nusselt numbers on the target surface, flow characteristics, and compressor power have been examined in detail. It was obtained from the numerical results that the average Nusselt number increases with decreasing the gap between the target surface and the nozzle. In addition, the higher average Nusselt number was obtained on the flat surface than the ribbed surface. The lowest compressor power was achieved in the 5Dj nozzle gap for the flat surface and in the 4Dj nozzle gap for the ribbed surface.
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    Experimental and numerical investigation of jet impingement cooling using extended jet holes
    (Pergamon-Elsevier Science Ltd, 2020) Tepe, Ahmet Umit; Yetisken, Yasar; Uysal, Unal; Arslan, Kamil
    In this study, jet impingement cooling on flat surface was investigated experimentally. The aim of this study is to elucidate the effect of extended jet holes on the heat transfer performance of the in-line array jet impingement configuration. The studies were performed under fully turbulent flow condition (16250 <= Re <= 32500). Local Nusselt number (Nu) distribution on the surface of interest was obtained experimentally by using Transient Liquid Crystals (TLC) method. Numerical investigations were conducted as the same configuration with the experimental method to explore the flow and heat transfer characteristics. SST k-omega with low-Re correction turbulence model was used for solving turbulence equations. Experimental and numerical studies were conducted on 1 x 6 (in-line array) jet impingement cooling configuration. Dimensionless jet to jet spacing (X-n/D-j), dimensionless jet plate to target plate spacing (Z/D-j) and dimensionless target plate width (Y/D-j) were taken as 5.0, 6.0 and 6.0, respectively. Five different G(j)/D-j= (1.0, 2.0, 3.0, 4.0 and 5.0) were investigated and the results were compared with orifice plate jet impingement configuration (Z/D-j=G(j)/D-j=6.0). Average and local Nu number distributions, pressure drop of the system, flow characteristics and Performance Evaluation Criterion (PEC) were examined in detail. Numerical results were compared with the experimental data and it was obtained that SST k-omega turbulence model was able to accurately predict the average and local Nu number distributions on the surface of interest. The maximum average and local Nu numbers were obtained on the condition of G(j)/D-j=2.0. Furthermore, PEC shows that the most feasible dimensionless nozzle to target plate gap was G(j)/D-j=2.0 at all Re numbers. (C) 2020 Elsevier Ltd. All rights reserved.
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    Jet impingement cooling on a rib-roughened surface using extended jet holes
    (Pergamon-Elsevier Science Ltd, 2020) Tepe, Ahmet Umit; Uysal, Unal; Yetisken, Yasar; Arslan, Kamil
    In this study, jet impingement cooling on a rib-roughened surface has been investigated experimentally. The aim of this study is to investigate the effect of extended jet holes on the heat transfer performance and flow characteristics of the jet impingement cooling on a rib-roughened surface. The studies have been conducted under turbulent flow condition (16,250 <= Re-j <= 32,500). Transient Liquid Crystals (TLC) method has been employed to investigate the average and local Nusselt number (Nu) distributions on the surface of interest. Six inline arrays of jet impingement configuration have been examined as the jet impingement cooling system. Jet holes were extended towards the target surface with the nozzles. Various dimensionless nozzles to the target surface gaps (G(j)/D-j = 1.0, 2.0, 3.0, 4.0 and 5.0) have been investigated. Rectangular cross-sectional ribs were located on the surface of interest for the augmentation of heat transfer. Experimental studies were conducted on the dimensionless rib height as H-r/D-j = 0.42. In addition, numerical studies were carried out to investigate the flow and heat transfer characteristics. The effect of various dimensionless rib heights (H-r/D-j) on convective heat transfer performance has also been investigated numerically. SST k-omega with low-Re correction turbulence model was used for solving turbulence equations. Average and local Nu number distributions, flow characteristics and Performance Evaluation Criterion (PEC) were examined in detail. Results were compared with the orifice plate (G(j)/D-j = 6.0) jet impingement configuration. Results showed that SST k-omega turbulence model accurately reveals the experimental data. Application of extended jet holes is a feasible method for practical application of the jet impingement cooling, especially at relatively low dimensionless nozzle gap (G(j)/D-j <= 4.0). Furthermore, improperly designed rib height has been found to diminish heat transfer performance.