The ESA/JAXA JEREMI (Japanese European Research Experiments on Marangoni Instabilities) Project

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The acronym JEREMI stands for "Japanese European Research Experiments on Marangoni Instabilities". This ambitious project is part of an agreement between the European Space Agency (ESA) and the Japanese Space Agency (JAXA). Started in 2001, it is now entering its final stage of preparation and is currently endorsed to fly on the International Space Station (ISS). These experiments will be executed using the FPEF (Fluid Physics Experiment Facility) of JAXA, a multipurpose facility for the investigation of fluids in microgravity. Studies of such a kind are very relevant and useful as they make it possible to observe how some physical forces, interwoven or overshadowed in normal gravity conditions (essentially the fluid surface tension and its gradients), can have a crucial impact on the behaviour of liquids (leading to the so-called "Marangoni" or thermocapillary effect). Without the complications of gravity-driven convection flows on Earth, in particular, UK scientists want to test in space fundamental theories of three-dimensional laminar, oscillatory and turbulent flows generated by these forces, which can be applied, in principle, also in a variety of "terrestrial" circumstances. More specifically, the JEREMI series of experiments is based on the so-called "liquid bridge", a drop of liquid with cylindrical free liquid-air interface held between two disks at different temperature. In space it is possible to form relatively large liquid bridges due to the absence of gravity, which would otherwise tend to deform the liquid-air interface and break the column of floating liquid. In microgravity conditions, the difference of temperature applied to the floating liquid produces buoyancy-free (purely surface-tension driven, i.e. Marangoni) convection. This type of flow is initially very regular, but it becomes oscillatory and three-dimensional if the applied temperature difference is increased beyond a given threshold. The project targets an improved understanding of this instability and the elaboration of possible means to control it by modifying the conditions at the liquid-air interface. Another objective relates to the identification of the cause-and-effect relationships at the root of the so-called "Particle Accumulation Structures" (PAS). Very recently it has been discovered that, under the effect of Marangoni flow, solid particles initially distributed uniformly in a liquid bridge can demix spontaneously from the surrounding fluid and form three-dimensional aggregates. The resulting cluster or pattern formed by particles looks like a spatially extended "closed wire" or "circuit" (having the shape of a windmill with several blades). This fascinating structure has been observed to float inside the liquid and rotate in space with constant angular velocity, thereby giving the illusion of a freely-floating "rotating solid body". An international team of scientists (from UK, Belgium, Austria, Spain and Japan) with different complementary backgrounds, expertise and perspectives, has been collaborating for more than 15 years to define precisely the set of space experiments to be executed to address the above topics. As the project is now entering its final stage, additional effort will be devoted to the elaboration of even more advanced mathematical and numerical tools to be used for the fine tuning of the experiment "input parameters" and for the interpretation of the flight results. The objective of this project is to examine experimentally and model (theoretically and numerically) fundamental physical principles still poorly known, thereby generating "new knowledge" potentially applicable in a variety of fields, which range from mechanical, chemical and thermal engineering to materials science and from the manipulation of tiny particles in small-scale systems to problems with astrophysical scale. The project aligns with the research priorities listed in the UK National Strategy on Space Environments and Human Spaceflight.