Effect of mixed gas ratio on cooling performance of impinging jets

Gas jet cooling is widely used because the device is simple, oxidation can be prevented, and a uniform cooling capacity can be obtained with thin steel sheets. Because the gas jet cooling ability is affected by the physical properties of the gas such as the mixed gas ratio, a quantitative evaluation of the influence of these factors is very important. However, few studies concerning prediction of the cooling capacity of mixed gas jets in atmospheres with different concentrations have been published.

In this research, the results of experiments and a fluid analysis with an air-helium gas jet in an air atmosphere were compared with the results obtained with Martin's non-dimensional empirical equations. As the nozzle condition, a single round nozzle with a tapered shape was examined. The helium concentrations with respect to air were 0, 20, 50, and 100 vol%, and the pressure conditions were 3 and 5 kPa.

Compared with the experimental results, Martin's equations overestimated the improvement of cooling performance with increasing helium concentrations. In the analysis in the present study, it was found that mixing with ambient air increased as the helium concentration decreased.

The trend of divergence between the experimental and predicted cooling capacity was clearly presented in this research. The results of this study will make it possible to improve the accuracy of predictions of the cooling capacity of impinging gas jets with different concentrations of the atmosphere and the gas jet.