Heat transfer in a turbulent slot jet flow impinging on concave surfaces ☆ Ebru Öztekin a , Orhan Aydin b, ⁎, Mete Avcı b a Trabzon Vocational School, Karadeniz Technical University, 61300 Trabzon, Turkey b Department of Mechanical Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey abstract article info Available online 3 April 2013 Keywords: Heat transfer Slot jet Impingement cooling Concave surface Nusselt number An experimental and numerical study is conducted to investigate turbulent slot jet impingement cooling characteristics on concave plates with varying surface curvature. Air is used as the impingement coolant. In the experimental work, a slot nozzle specially designed with a sixth degree polynomial in order to provide a uniform exit velocity profile was used. The experiments were carried out for the jet Reynolds numbers in the range of 3423 ≤ Re ≤ 9485, the dimensionless nozzle-to-surface distance range of 1 ≤ H/W ≤ 14 for di- mensionless values of the curvature of impinging surfaces in the range of R/L = 0.5, 0.725, and 1.3 and a flat impingement surface. Constant heat flux was applied on the plates. Numerical computations were performed using the k-ε turbulence model with enhanced wall functions. For the ranges of the governing parameters studied, the stagnation, and local and average Nusselt numbers have been obtained both experimentally and numerically. The numerical results showed a reasonable agreement with the experimental data. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Because of its high local convective heat transfer rate, jet impinge- ment cooling is widely used in many applications since it is compar- atively inexpensive, effective and easily adjustable. Some typical applications of impinging air jets include cooling of electronic equip- ments, hot steel plates and turbine blades, surface coating and cleaning, fire testing of building materials, drying of textiles and paper, freezing of tissue in cryosurgery and annealing of glass. The extensive and increasing volume of applications and the inter- esting and complex flow physics of jet impingement cooling have been attracting many researchers. As a result, a huge volume of stud- ies has appeared in the existing literature. However, the vast majority of studies have been on flat surfaces (for which the topic has been documented in detail and well understood), while little data is available for non-flat surface geometries although they are mostly encountered in practice (e.g. the surface of the turbine blade). There is very limited data on curved impingement surfaces, which are the focus of the present study. Moreover, most of the data reported on curved impingement surfaces in literature have been merely on semi- circular or hemispherical concave/convex surfaces. Brahma et al. [1] studied stagnation point heat transfer for a single round jet impinging on a concave hemispherical surface. Gau and Chung [2] investigated the effects of surface curvature on heat trans- fer for a slot jet impinging on concave/convex surfaces. Lee et al. [3] experimentally studied turbulent flow and heat transfer of a jet impinging on a hemispherical concave surface. Yang et al. [4] experi- mentally studied slot jet impingement cooling on a concave surface. They investigated the effects of nozzle configuration and curvature. Cornaro et al. [5] conducted flow visualizations for a turbulent axisymmetric jet impinging on semicylindrical concave and convex surfaces. Choi et al. [6] experimentally studied fluid flow and heat transfer for jet impingement cooling on a semi-circular concave surface. Kayansayan and Küçüka [7] experimentally studied the im- pingement cooling of a semi-cylindrical concave channels by confined slot jet. Chan et al. [8] studied the surface heat transfer characteristics of a heated slot jet impinging on a semicircular convex surface and they presented correlations of local and average Nusselt numbers with Reynolds numbers and the dimensionless slot nozzle-to-impingement surface distance for the stagnation point and the circumferential distri- bution. Souris et al. [9] performed the numerical modeling of jet im- pingement cooling onto a semicircular concave surface and evaluated the performance of two-equation turbulence models (such as the k-ε model). Olsson et al. [10] investigated the heat transfer from a slot air jet impinging on a cylinder shaped food product placed on a solid surface by using computational fluid dynamics and examined the distri- bution of the local Nusselt numbers around the cylinder for various Reynolds numbers, jet-cylinder distances, and cylinder curvature. Gilard and Brizzi [11] studied the aerodynamics of a slot jet impinging on a concave wall. They investigated the influence of the radius of the wall curvature, the impingement height and the Reynolds number on the flow field by conducting flow visualizations, velocity measurements by particle image velocimetry (PIV) and mean pressure measurements. Jefferson-Loveday and Tucker [12] numerically studied turbulent heat transfer impinging on a concave surface by using large-eddy type simu- lations. Sharif and Mothe [13] conducted a parametric study of the International Communications in Heat and Mass Transfer 44 (2013) 77–82 ☆ Communicated by W.J. Minkowycz. ⁎ Corresponding author. E-mail address: oaydin@ktu.edu.tr (O. Aydin). 0735-1933/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.icheatmasstransfer.2013.03.006 Contents lists available at SciVerse ScienceDirect International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt