Data processing is carried out in an international collaborative context, based on theoretical models and numerical simulations. The RUBI project began in 2005 as part of the ESA Map Boiling project bringing together several European teams. The experiment [1] was launched to the International Space Station in July 2019 and operated until February 2021. The fluid used was the refrigerant N-perfluorohexane. Bubbles were nucleated on an artificial cavity located on a surface heated with heat flux ranging from 0.5 to 1.5W/cm². The bubble nucleation was triggered by a laser pulse. Experiments were performed in pool boiling as well as in the presence of external forces such as an electric field, shear flow, or a combination of both. Different liquid subcooling up to 10°C, pressures from 0.5 to 1 bar, flow rates up to 700ml/min were tested. High-speed Black and White camera recorded the images of the bubble growth and departure. The temperature field at the surface of the heated wall was measured by an infrared camera.

In pool boiling, the bubbles grow and do not detach during the 10 s of the experiments (figure 1). Bubbles have a spherical shape. Pool boiling experiments are unique test cases for the validation of theoretical model and numerical simulation [2, 3]. In flow boiling, the bubbles grow on the nucleation site and detach by sliding along the heated surface. After detachment a new bubble spontaneously nucleates on the site and detaches and the cycle continue (Figure 2). Occasionally, bubbles detachment normal to the heater surface was also observed. The detachment of the bubbles from the surface was due to a coalescence mechanism [4].