Bubble Nucleation and Growth on Microstructured Surfaces under Microgravity

Abstract

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 a terrestrial environment. As space exploration and economy expand at an unprecedented pace, the aforementioned applications that are 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 bubbles in space, where the gravity effect is negligible compared to Earth. We observe much faster bubble nucleation, and the growth rate can be ~30 times higher than that on 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 the 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 heat localization around the nucleation site, thus enabling faster bubble nucleation and growth in space. We also find that bubble nucleation can be influenced by the characteristic length of the microstructures on 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.