Toward reliable thermoacoustic power generation: an efficient elastic-membrane-free U-tube liquid metal magnetohydrodynamic generator under acoustic driving

Thermoacoustically-driven liquid metal magnetohydrodynamic generators (LMHDGs) are attractive for reliable power generation in extreme environments. However, this advantage is fundamentally undermined by the common use of elastic membranes to stabilize the gas-liquid interface. Existing attempts to eliminate the membranes have typically resulted in severe performance degradation because of gas-liquid interfacial instability and acoustic mismatch. To overcome these issues, an elastic-membrane-free U-tube LMHDG was investigated through three-dimensional transient numerical simulations and prototype experiments using an opposed linear compressor as a controllable acoustic source. The results show that gravity provides bulk liquid-column restoration in the U-tube, whereas the foam-like layer on the liquid metal surface provides the dominant interfacial stabilization under the tested oscillatory conditions. Proper acoustic matching is achieved near resonance under acoustic driving, while deviating from resonance causes acoustic mismatch. Under compressor-driven operation at 15 Hz, | u | = 1.0 m/s and R e = 1.3 × 10 −5 Ω, the prototype achieved an electrical power output of 42.6 W with an acoustic-electric conversion efficiency of 52.3%. This work demonstrates efficient elastic-membrane-free acoustic-electric conversion under controlled compressor driving and establishes a practical foundation for highly reliable thermoacoustic power generation, with the LMHDG energy-conversion path free of rotating or sliding mechanical components.