Numerical investigation of an axi-symmetric laminar jet impinging on a dimpled surface under uniform heat flux using a finite element method

The purpose of this study is to numerically investigate heat transfer and flow field in a semi-confined axi-symmetric laminar air jet impinging on a concave surface, or dimple, with uniform heat flux. A commercial software package relying on the finite element method was used for the simulation, and mesh convergence was examined in order to minimize computational cost. Jet impingement on a flat plate was used as a baseline reference case, and flat plate results were validated against previously published experimental data with good agreement. The effects of various parameters involved in dimple impingement -such as Reynolds number (Re) between 100-1,400; jet-to-plate spacing (H/D-j) ranging from 2 to 6 jet diameters; dimple depths (d/Dd) of 0.1, 0.15, and 0.2; and the ratio of jet diameter and dimple projected diameter (D-j/D-d) from 0.25 to 1- were all studied. Comparisons show that heat transfer reduction occurs in the presence of dimples because of the larger impingement area, which results in less momentum flux. The dimple curvature lifts the post-impinging fluid and creates a backflow, instead of allowing it to maintain contact with the surface, as is the case with flat plate impingement.