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Benchmark Coolit predictions for impinging jets.

Courtesy of NTS Corp.

Impingement cooling in which a surface is cooled by an impinging jet (air or liquid) is an important method for cooling electronics because of its high efficiency. The high efficiency is the result of thin boundary layers formed at the point of impact and which produces very high heat transfer coefficients. The jet's boundary layer does not follow the log-law of the wall and cannot be computed using conventional CFD turbulence models with wall functions.

In this project a prediction by Coolit for a jet impinging on a flat surface was compared with experimental results from the paper by Tsubokura et al published in the Monthly Journal of Institute of Industrial Sciences at the University of Tokyo, 1997, vol 49, No. 1. The Coolit domain size was 20 jet widths by 10 jet heights. A symmetry plane was utilized to reduce the computational domain size and the grid was clustered in the vicinity of the symmetry plane and the wall.

We used Coolit's eddy viscosity model without wall functions. The jet was modeled using a Coolit Fan with the uniform velocity. At the jet inlet (i.e. at the Fan), the default value of the eddy viscosity was used. The Reynolds number based on the inlet velocity and the jet width was 6100.

Figure 1 shows a schematic of the experiment. Figures 2 and 3 show the x-velocity profile two and four jet-widths away from the jet axis, respectively. Figure 4 shows the y-velocity distribution for several locations.

Figure 1. Schematic of the experiment.
Figure 2. x-velocity profile two jet-widths away from the jet axis.
Figure 3. x-velocity profile four jet-widths away from the jet axis.
Figure 4. y-velocity distribution for several locations.

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