The study of heat transfer in gas-liquid two-phase flows is a highly active research field that is of great interest for both numerical modelling and experimental investigation of physical phenomena. Due to the high heat transfer efficiency during flow boiling, such research has significant practical applications in cooling the most thermally loaded components of current fission nuclear reactors as well as future fusion reactors.
Past studies have developed numerous numerical methods and models for accurately simulating turbulent single-phase flows. With advancements in fluid dynamics and the increasing computational power of supercomputers, research is now shifting towards more complex multiphase phenomena, including boiling in various flow regimes, critical heat flux, and boiling crisis. In the latter case, a thorough understanding of bubble dynamics is essential due to the high bubble density and intense interactions, including bubble coalescence and breakup caused by turbulent flow. The modelling of such flows has been a major challenge for decades and remains a key focus in fluid mechanics research today.
The young researcher will study the dynamics of two-phase flows, interactions between bubbles, and the influence of heat transfer on their behaviour. This research will be conducted with advanced Computational Fluid Dynamics (CFD) tools using high-performance computing clusters (HPCs), as well as state-of-the-art experimental measurement techniques. These include high-speed cameras operating in the visible and infrared (IR) light spectrum and non-intrusive velocity measurements using the Particle Image Velocimetry (PIV) method. Our research group has recently developed an innovative method for non-intrusive velocity measurements in the gas phase of two-phase flows. This breakthrough provides access to previously unobservable bubble dynamics and will serve the researcher both for visualization and validation of numerical simulations. The method’s applicability will be tested across various flow regimes, from slug to bubbly isothermal flow.
Simulating two-phase flows under isothermal conditions using only fundamental continuum fluid mechanics equations is insufficient. Additional modelling is required to accurately describe bubble coalescence and breakup. The young researcher will initially simulate isothermal two-phase flow, however, in the next step will also attempt to replicate boiling conditions, where strong interactions between bubbles occur. The long-term goal of this research is to enhance the understanding of complex two-phase flow dynamics across different boiling regimes and contribute to the development of more accurate models for simulating multiphase flows.
Figure 1: THELMA lab at the Reactor Engineering division (R4) of JSI.