Interfacial phenomena of droplets and bubbles on functionalized surfaces investigated by advanced diagnostics for future environmental and enhanced heat transfer applications (DroBFuSE)

Interaction of bubbles and droplets with solids surfaces is part of our everyday life and has been a source of intrigue for millennia. The formation of vapor bubbles (boiling) is considered as the most effective heat transfer mechanism and is fundamental in steam production (power plants) and thermal separation processes as well as indispensable for cooling of high-powered electronics. Meanwhile, behavior of droplets on solids is important in condensation heat transfer, microfluidics, biomedical engineering, and environmental sciences, to name a few. Bubble/droplet interactions with solids can be controlled through surface functionalization, which can enhance many important processes. However, the future progress is constrained by the surface robustness and the lack of fundamental understanding of bubble/droplet interaction with functionalized surfaces, which is related to the lack of appropriate diagnostic techniques and physical or semi-empirical models. DroBFuSE project addresses some of the most important knowledge gaps today, simultaneously for bubbles and droplets, through development of robust surface functionalization approaches, advanced diagnostic tools, data processing algorithms, and mechanistic modelling through the force balance approach and heat flux partitioning schemes. Among others, project deliverables include development of: Novel advanced experimental approaches for in-liquid temperature measurements during boiling (through temperature dependent absorption of near infrared light) and droplet wettability transition investigations on thick/thin substrates (including utilization of thin-film piezoelectric devices and laser interferometry). Robust hydrophobic and superhydrophobic surfaces for long-term enhanced boiling heat transfer and condensation applications. Surfaces will be created through combination of scalable surface functionalization techniques, including direct laser texturing, oxidation, hydrothermal treatment, and pos-processing via hydrophobic monolayers. Novel environmentally friendly and robust superhydrophobic surfaces based on organic hydrophobic coatings with optimized micro/nanostructure for environmental applications (i.e., water harvesting). Proof-of-concept water harvesting device aimed at capturing water from fog and process streams that include droplets in micrometer size range. Mechanistic models and sub-models able to predict the relevant bubble parameters during boiling, such as bubble departure frequency and departure diameter. These advanced models will include contributions from the thermal boundary layer and heat transfer through the liquid/vapor interface in combination with substrate properties (thermophysical properties and wettability). Model of droplet behaviour on superhydrophobic surfaces under the influence of elevated pressure induced by external forces. Project results will provide completely new insights about the effects of surface structure/wettability and substrates’ thermophysical properties on bubble dynamics, allowing a breakthrough progress on boiling surface optimization to reach heat fluxes beyond our current capabilities, and inclusion of developed modelling framework to future numerical codes. Investigations of droplets on functionalized surfaces will allow future development of environmental technologies like water harvesters, enhanced condensers, self-cleaning and anti/bacterial interfaces, unlimitedly applicable in future scientific research and our everyday life. Highly ambitious objectives will be achieved through the (i) well-defined work programme, (ii) interdisciplinary collaboration between excellent Slovenian researchers and top-tier foreign institutions (including MIT, KU Leuven, Silicon Austria Labs, Univ. of Pisa and Univ. of Toulouse), and (iii) by integrating knowledge from previous and current projects of the DroBFuSE research group members, including the ones funded by ESA (RUBI experiment) and ARRS (J2-2486, N2-0251, J2-3052, J2-1741, L2-1833).