The Effects of the Material Conductivity on the Dynamics Behavior of the Multiple Droplets Impacting onto Hot Surface.

The effect of material conductivity on the dynamics behavior and the heat transfer phenomena of multiple water droplets impacting onto heated solid surfaces has been studied experimentally. The droplet diameter and Weber number were 2.8 mm 46.2 respectively. The test materials were Stainless Steel, Aluminum, and Cooper. The test temperatures ranged from 110°C - 140°C. The droplet dynamics during the impacting on the hot surfaces were investigated by using a high-speed video camera. To gather the quantitative information, a new developed image processing technique was developed. It is able to track the bubble movement, the contact time and spreading ratio can be determined. As a result, it is noticed that at 110°C, droplet impacting on aluminum showed the highest spreading ratio among the materials. The spreading ratio of droplet impacting on copper is the lowest. At 140°C, it is found that for all materials, the small bubble has started to appear around the first droplet and the contacting solid surface. Meanwhile on stainless steel, although the spreading ratio is low, the solid-liquid contact time is the highest among the test materials. Finally, it is generally concluded that the presence of second droplet improves the wettability, so the effectiveness of cooling process is significantly better. [ABSTRACT FROM AUTHOR]