Abstract
The jet impingement technique is an effective method to achieve a high heat transfer rate and is widely used in industry. Enhancing the heat transfer rate even minimally will improve the performance of many engineering systems and applications. In this numerical study, the convective heat transfer process between orthogonal air jet impingement on a smooth, horizontal surface and a roughened uniformly heated flat plate is studied. The roughness element takes the form of a circular rib of square cross-section positioned at different radii around the stagnation point. At each location, the effect of the roughness element on heat transfer rate was simulated for six different heights and the optimum rib location and rib dimension determined. The average Nusselt number has been evaluated within and beyond the stagnation region to better quantify the heat transfer advantages of ribbed surfaces over smooth surfaces. The results showed both flow and heat transfer features vary significantly with rib dimension and location on the heated surface. This variation in the streamwise direction included both augmentation and decrease in heat transfer rate when compared to the baseline no-rib case. The enhancement in normalized averaged Nusselt number obtained by placing the rib at the most optimum radial location R/D = 2 was 15.6% compared to the baseline case. It was also found that the maximum average Nusselt number for each location was achieved when the rib height was close to the corresponding boundary layer thickness of the smooth surface at the same rib position.
Highlights
In the early 1960s, the jet impingement cooling technique was first introduced for internal cooling
These investigations showed that a roughened surface could enhance the local Nu by up to 50% when compared to a smooth target surface, because of the turbulence induced by the surface roughness element
Numerical analysis of a convective heat transfer process was conducted on the orthogonal air jet impingement on a smooth, horizontal surface, and a roughened uniformly heated flat plate
Summary
In the early 1960s, the jet impingement cooling technique was first introduced for internal cooling. Basic studies using a single jet impinging on a roughened surface, with and without cross-flow, have been conducted by numerous investigators such as Beitelmal and Saad [7], Sharif and Ramirez [8], Xing and Weigand [9], Gabour and Lienhard [10], and Celik [11]. These investigations showed that a roughened surface could enhance the local Nu by up to 50% when compared to a smooth target surface, because of the turbulence induced by the surface roughness element. This research employs uniform turbulence promoters with variable locations and dimensions to study the impact on the heat transfer rate between the working fluid and the heated surface
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