Effect of Nozzle Geometry and Distance on Cooling Performance of Impinging Jets

Gas jet cooling is widely used because the device is simple, it is possible to prevent oxidation and a uniform cooling ability can be obtained with thin steel sheets. Because the gas jet cooling ability is affected by the gas properties and nozzle geometry, quantitative evaluation of the influences of these factors is very important. Several non-dimensional empirical equations have been proposed for prediction of the gas jet cooling ability of geometrically arranged nozzles. In this research, the accuracy of Martin's non-dimensional empirical equations was investigated by gas jet cooling experiments and fluid analyses with different nozzle geometries and distances from the cooled surface. Two nozzle geometries were examined, namely, a slit-like (linear) arrangement of round nozzles and a staggered arrangement of round nozzles. The difference between the experimental results and the results of predictions by Martin's equations increased as the distance between the nozzle tips and the cooled surface decreased. It was suggested that the characteristic difference of the jet flow between the flow development region (potential core region) and the fully developed flow region influenced the cooling ability. The trend of divergence between the experimental and predicted cooling ability was clearly presented in this research. The results of this study make it possible to improve the accuracy of predictions when the distance between the nozzle tips and the cooled surface is set within the potential core region of the jet.