Multiscale bubble dynamics, heat and mass transfer in high-temperature molten salts: A comprehensive review

High-temperature molten salts serve as crucial working fluids in thermal-energy storage, high-temperature metallurgy, and molten-salt reactor systems, where gas evolution and injection introduce complex gas–liquid interactions. The motion of bubbles, including formation, detachment, rising, deformation, coalescence, and breakup, governs heat and mass transfer, flow mixing, and overall operational stability. Owing to high viscosity, strong interfacial tension, and pronounced temperature dependence, molten salts exhibit a viscosity-dominated and capillary-dominated regime that fundamentally differs from conventional liquid systems. This review summarizes recent progress in understanding molten-salt bubble dynamics, covering interfacial evolution, wake behaviors, and multiscale coupling mechanisms, along with advances in high-temperature imaging, interface-resolved simulations, and reactor-scale modeling. However, significant challenges remain, particularly the lack of direct measurements of thin-film drainage, limited accessibility to submicron interfacial structures, and incomplete closure models for bubble interaction and transport. Strengthening property databases, enhancing in-situ diagnostics, and establishing coordinated multiscale validation approaches will be essential for transitioning molten-salt bubble research toward predictive design and control of high-temperature gas–liquid systems.