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International audience; This publication lays the foundation for the description of the Multiscale Boiling Experiment, which was conducted within two measurement campaigns on the International Space Station between 2019 and 2021. The experiment addresses fundamental questions about two-phase heat transfer during boiling processes. For this purpose, single or few subsequential bubbles are selectively ignited on a heated substrate using a short laser pulse. A detailed investigation of the phenomena is possible, as the boiling process is temporally slowed down and spatially enlarged in microgravity. Within the Multiscale Boiling Project, the undisturbed growth of the bubbles, the influence of a shear flow, and the influence of an electric field are investigated within the same test facility using FC-72 as working fluid. Within the project, thirteen research groups from eight countries are collaborating. Over 3000 data sets have been generated over an 11-month measurement period. In the context of this publication, besides the motivation and necessity of such investigations, the basic structure of the experiment, the objectives of the investigations, and the organization are described. Finally, first results of the investigations are presented. Therefore, this publication has the primary aim to serve as a basis for many further planned publications and present the project as a whole.

Industrial applications use surfactants to control surface tension and wettability of surfaces. Instead of studying prepared solutions, we focus on the movement of the contact line after adding the surfactant. We placed the pedant drop with surfactant to a sessile drop of pure water and filmed the spreading process to obtain friction coefficient of the contact line. Our results confirmed that adding surfactants to sessile droplets drives the contact line movement. Small concentrations of LHS and SDBS as well as high concentrations of SDBS pin droplet and increase the hysteresis. Friction coefficient for cationic CTAB and zwitterionic LHS drops with the concentration increase. Anionic SDBS decreases contact angle, making the surface more hydrophilic and intensifying hysteresis.

We study the flow of an evaporating liquid film in triangular open microchannel. Above the surface of the liquid flows a gas. The sear-stress on the gas-liquid surface drags the liquid and removes the vapor. It models either flow in a channel or a flow in a single groove. The novelty of this work is that we simulate gas-driven flow with evaporation. We use Boundary element method to solve Laplace equation with mixed boundary conditions. This method gives the normal derivative of vapor concentration at the surface of the liquid. The resulting evaporation flux is growing sharply near the contact line. Integral evaporation coefficient slightly depends on the depth of the liquid. The upper gas flow drives the liquid film, resisting a velocity drop and preventing the dry spot formation.

The fast development in semiconductor technology has led to increasingly higher chip power dissipation and greater non-uniformity of the heat dissipation with the result of localized hot spots, often exceeding 1 kW/cm 2 in heat flux. As was shown in previous works of the authors, thin and very thin liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel are promising candidate for an innovative cooling technique optimizing the tradeoffs between performance and cost. The goal of the present work is to study the effect of the channel height on the critical heat flux (CHF) in a locally heated liquid film driven by the shear stress of gas in a channel.

SELENE (SELf rewetting fluids for thermal ENErgy management) is a microgravity experiment proposed to the European Space Agency (ESA) in response to the Announcement of Opportunities for Physical Sciences. Main objectives of the microgravity research onboard ISS include the quantitative investigation of heat transfer performances of "self-rewetting fluids" and "nano self-rewetting fluids" in model heat pipes and validation of adequate theoretical and numerical modelling able to predict their behaviour in microgravity conditions. This article summarizes the results of ground-based research activities in preparation of the microgravity experiments. They include: 1) thermophysical properties measurements; 2) study of thermo-soluto-capillary effects in micro-channels; 3) numerical modelling; 4) thermal and concentration distribution measurements with optical (e.g. interferometric) and intrusive techniques; 5) surface tension-driven effects and thermal performances test on different capillary structures and heat pipes; 6) breadboards development and support to definition of scientific requirements.