Characteristics of Single Droplet Impact on Cold Plate Surfaces

Abstract

Droplet collision with cold solid surfaces is a fundamental phenomenon observed in low-temperature processes. In this work, a single droplet impacting on a cold surface was investigated by analyzing changes in droplet shape and dimensions recorded with a high-speed camera. At low surface temperatures (−5°C and −10°C), the droplet spreads in a very short period upon impact and then retracts, but to a diameter larger than that at room temperature, dependent on surface material property and texture. Higher impact velocity expands the spreading diameter and promotes the retraction to an extent, but at lower surface temperature (i.e., −20°C) the droplet is quickly frozen with smaller change in diameter on the stainless-steel surface rather than on the Teflon plate. The change of droplet shape upon impacting on a 30° inclined surface was also studied. The surface texture of the stainless-steel plate produced by the polishing process has an obvious effect on the droplet dimension retraction. A proper selection of wall material and process conditions can alleviate or prevent wall deposition.

Keywords:

• Cold surface
• Retraction ratio
• Single droplet
• Spreading factor
• Surface texture

ACKNOWLEDGMENTS

We are grateful to Prof. Arun S. Mujumdar, NUS, for his constructive suggestions.