Bubble Nucleation and Growth on Microstructure Surface under Microgravity

Understanding the nucleation and growth dynamics of the surface bubbles generated on a heated surface can benefit a wide range of modern technologies, such as the cooling systems of electronics, refrigeration cycles, nuclear reactors and metal industries, etc. Usually, these studies are conducted in the terrestrial environment. As space exploration and economy expanding at an unprecedented pace, the aforementioned applications that potentially deployable in space call for the understanding of thermal bubble phenomena in a microgravity setting. In this work, we investigate the nucleation and growth of surface bubble in space, where the gravity effect is negligible compared to the earth. We observe much faster bubble nucleation, and the growth rate can be ~30 times higher than that on the earth. Our finite element thermofluidic simulations show that the thermal convective flow due to gravity around the nucleation site is the key factor that effectively dissipates the heat from heating substrate to the bulk liquid and slows down the bubble nucleation and growth processes. Due to the microgravity field in space, the thermal convective flow is negligible compared to the terrestrial environment, leading to the localization of heat around the nucleation site, and thus enables faster bubble nucleation and growth in space. We also find that bubble nucleation can be influenced by the characteristic length of the microstructures on the heating surface. The microstructures behave as fins to enhance the cooling of the surface. With finer microstructures enabling more efficient surface to liquid heat transfer, the bubble nucleation takes longer.