EXPERIMENTAL STUDY ON THE DYNAMIC CHARACTERISTICS OF GALINSTAN DROPLET IMPACTING ON THE METAL FOAM SURFACE

The eutectic alloy GaInSn which is liquid at room temperature has a great importance in application where the special heat transfer requirements because of its excellent heat conductivity. However, the corresponding flow characteristics in GaInSn will naturally be different from conventional fluid due to the high surface tension. In present paper, we carry out studies on the spreading, recoiling and rebounding phenomenon after the impacting of GaInSn droplets on metal foam surface. The high-speed camera is used to capture the droplet contours projected by the backlight during the moving of droplets. Through the image process method, the spreading factor, height of droplet contour in the center line and the oscillation characteristic of droplet after rebounding are obtained. Results show that at the early stage of the droplet impact, the spreading characteristic of GaInSn droplet with high surface tension is proportional to the square root of the normalized time, which is consistent with that from conventional liquid, while relates with the non-dimensional pole size of foam surface during the following spreading process. The maximum spreading factor of GaInSn droplets spreading on small non-dimensional pole size of foam surface is larger than that on smooth nickel surface, and decreases with the increase of the non-dimensional pole size of foam surface. During the rebounding process, the shape oscillation can be divided into three modes due to the difference in pore structure of surface: the regular oscillation in horizontal direction and vertical direction, the oscillation in horizontal direction and vertical direction with rotation and the rotation oscillation. Finally, the traditional theoretical formula used to predict the oscillation frequency of droplets or bubbles has been extended to cases with irregular oscillation in droplet shape through the fitting of present experimental data and analysis.