Etude de la croissance d'une bulle de vapeur en microgravité

Boiling liquid–vapor flows are encountered in a wide range of industrial applications, including steam generation in nuclear power plants, cooling of electronic components, and thermal management systems such as heat pumps and air-conditioning systems. Boiling liquid–vapor flows are also present in space applications, for example in two-phase flow loops used to cool electronic equipment in telecommunications and Earth observation satellites. In space launch vehicles, cryogenic tanks are exposed to solar radiation, which can induce boiling inside the tanks and lead to overpressure, requiring venting to maintain safe operating conditions. The limited understanding of boiling physics under microgravity conditions remains a major obstacle to the development of space technologies, particularly in the context of space exploration. Understanding boiling under microgravity conditions is the primary objective of the Multiscale Boiling Experiment (RUBI), which was conducted aboard the International Space Station between 2019 and 2021. A large experimental database was collected and can be used to validate theoretical models and numerical simulations. Improving modelling and numerical simulation tools is a key challenge for the development of future space technologies. To investigate boiling on isolated bubbles using advanced diagnostic techniques, the Multiscale Boiling (RUBI) experiment was developed over more than a decade by several European research teams within the framework of the ESA BOILING project. The experiment was operated aboard the International Space Station (ISS) between 2019 and 2021. Experiments were conducted on an isolated nucleation site under pool boiling conditions, as well as in the presence of external forces induced by an electric field and/or a shear flow. Side-view visualization was performed using a high-speed black-and-white (BW) camera operating at 500 fps (frames per second) to capture bubble growth and departure. A high-speed, high-resolution infrared (IR) camera was also used to record the temporal and spatial evolution of the wall temperature and compute the heat flux at the bubble foot on the heater surface. The PhD project will be carried out under the joint supervision of Univ. Toulouse IMFT and TU Darmstadt. Both institutions have extensive expertise in experiments, modelling and direct numerical simulation of boiling. Both teams have actively contributed in the development of the RUBI experiment, participated in monitoring the experiments in orbit and post-process the data. The PHD thesis will be devoted to the analysis and modelling of the bubble dynamics and heat transfer in a shear flow. Unlike in pool boiling (in stagnant liquid), in flow boiling the bubble will grow on its nucleation site and depart under the effect of the flow and slide along the heated wall. BW images have been processed at IMFT to determine the bubble growth rate and radius of detachment. The time evolution of the bubble radius evolves as R(t)=kt^n, with k and n dependent on the experimental parameters such as heat flux, flow rate, and subcooling. A careful modeling of the bubble growth rate requires estimating the heat flux from the wall, especially close to the contact line and the heat flux around the bubble. The methodology will be based on complementary approaches: data processing of infrared temperature (IRT) measurements to obtain the local heat flux, modeling of the evaporation heat flux in the contact line vicinity and numerical simulations of flow and temperature field around the growing bubble to estimate the interfacial mass flux. The expected outcomes of the project include a detailed comparison between the numerical simulation results and the experimental data obtained from the RUBI experiment. The results will be published in peer-reviewed journals and presented in international conferences. École doctorale : MEGEP - Mécanique, Energétique, Génie civil, Procédés Direction : Catherine COLIN Financement : MSCA COFUND BEST