The impact between multiple droplets onto hot surface is an important process in a spray cooling. The present study was conducted to investigate the dynamics of multiple droplet impact under various surface tensions. Here, the ethylene glycol with compositions of 0%, 5%, and 15% was injected through a nozzle onto stainless steel surface as the multiple droplet. The solid surface was heated at the temperatures of 100 °C, 150 °C, and 200 °C. To observe the dynamics of multiple droplets, a high speed camera with the frame rate of 2000 fps was used. A technique of image processing was developed to determine the maximum droplet spreading ratio. As the result, the surface tension contributes significantly to maximum spreading ratio. As the droplet surface tension decreases, the maximum spreading ratio increases. The maximum spreading ratio appears when the percentage of the ethylene glycol is 15% at the temperature of 150°C. From the visual observation, it is shown that a slower emergence of secondary droplets (droplet splashing) is carried out under a lower surface tension. Hence, surface tension plays an important role on the behavior of emerging secondary droplets. Furthermore, results of the experiments are useful for the validation of available previous CFD models.

The present study was conducted to investigate the dynamics of multiple droplets impact under various surface tensions. Here, the ethylene glycol with compositions of 0%, 5%, and 15% were injected through a nozzle into the stainless steel surface as the multiple droplets. The solid surface was heated at the temperatures of 150ºC. The dynamic of multiple droplets have been observed with frame rate of 2000 fps by a high speed camera. A technique of image processing was developed to determine the maximum droplets are spreading ratio. As the result, the surface tension contribute to the maximum spreading ratio significantly. When the droplet surface tension decreases, the maximum spreading ratio increases. The maximum spreading ratio appears when the percentage of the ethylene glycol is 15% at the temperature of 150ºC. From the visual observation, it was shown that a slower emergence of secondary droplets (droplet splashing) was carried out under low surface tension.