(95e) Bubble Nucleation after Drop Impact on Micro-Nano Textured Surfaces

Boiling behavior is marked by formation of bubbles at a liquid-solid interface. Topography of the solid surface plays a vital role in controlling the pattern of bubble formation, due to the change in available surface area for nucleation. A good indicator of the performance of the surface texturing is the intensity with which the bubbling takes place and the region it pervades. In this work, we fabricate surfaces with nano/micro meters of spacing between pillar structures and examine boiling behavior of a liquid drop on these samples using high speed X-Ray phase contrast imaging. Three parameters, the number of bubbles, average size and their rate of growth are specifically investigated in detail. We observe that the number of bubbles produced increases with time, reaching a maximum, after which there is a decrease ultimately leading to the merging of adjoining bubbles and possibly formation of a vapor film. This can potentially establish a reference bubble size distribution to distinguish between varying boiling regimes observed at different microstructure spacings. A change in temperature of the substrate for the duration that the drop is in contact with it, leads to a variation in the rate at which the bubbles grow. The exact mechanism responsible for the observed growth rate may be diffusion or inertia controlled. We also examine the effects of microstructure spacings on the mechanisms of bubble growth rate, which has not been thoroughly studied before. Additionally, we observe that the mobility of the bubbles on the solid surface is greatly influenced by its texture and temperature. In conclusion, we expect our findings to immensely impact applications involving heat transfer such as industrial boiler design and electronics cooling.