Liquid-metal-based heat recovery

Improving energy conservation and efficiency is important in achieving carbon neutrality and limiting global warming. Liquid metals with low melting points are rapidly emerging as advanced materials for efficient heat recovery. Owing to the advantages of liquid metals, such as their low melting point, high boiling point, high thermal/electrical conductivity, nonflammability, and nontoxicity, liquid-metal convection can be applied to develop high-temperature waste heat recovery systems that can accommodate heat flux at temperatures above 600 °C, with a convective heat transfer coefficient exceeding 10,000 W/(m² K). Moreover, liquid-metal thermoelectric and magnetohydrodynamic generators can recover low-grade and low-temperature heat to produce electricity. Liquid-metal-based heat recovery technologies have progressed significantly in academia, and typical applications based on these technologies have been implemented in the steel and chemical industries. However, to the best of our knowledge, a systematic review describing low-melting-point liquid metals and their applications in heat recovery is unavailable. Therefore, in this chapter, we review low-melting-point liquid-metal heat recovery technologies from the perspectives of material, mechanism, and application. First, liquid-metal materials are introduced; subsequently, heat recovery mechanisms based on liquid-metal convection and thermoelectric and magnetohydrodynamic generation are presented. Additionally, typical liquid-metal heat recovery applications in industrial heat transfer and energy fields are interpreted. In conclusion, scientific and technical challenges, in addition to future developments in these areas, are highlighted in this chapter.