Taking the induced magnetic field, the electrode current, the load position and the conductive area of the load into consideration, the performance of an LMMHD generator under load condition is investigated with COMSOL and 3D numerical simulations. Results show that the load position and the conductive area of the load might affect the output power and the generation efficiency. When the load is placed in the middle of electrodes and the ratio of the conductive area of the load to electrodes is about 0.8, the output power and the generation efficiency are maximum.
The power generation experiment of an 11.5 kW MHD generator was done successfully in 1959 and this confirmed the feasibility of MHD power generation technology (Brogan et al., 1962). And performances of LMMHD generators were studied in Argonne National Laboratory in 1963 (Petrick et al., 1964). Since then, the LMMHD generator has been studied around the world and remarkable results have been achieved. Nowadays LMMHD generators have been widely used in variable displacement vehicles, wave energy power generation systems and thermoacoustic power generation systems (Haaland, 1995; Liu et al., 2018; Brekis et al., 2020).
The basic working principle of an LMMHD generator is Faraday's law of electromagnetic induction. The liquid metal is driven to cut the magnetic line of flux in the generation channel by an internal combustion engine or a wave energy converter or a thermoacoustic engine, realizing the direct conversion of mechanical energy into electrical energy. In recent years, with the steady increase of computational capabilities, the performance of LMMHD generators has been studied numerically. The effect of the induced magnetic field on the performance of an LMMHD generator was investigated by numerical simulations (Shingo et al., 2007). The results showed that as the inlet velocity of the liquid metal increased, the generation efficiency of the single channel LMMHD generator decreased. Furthermore, the induced magnetic field could be almost negated by using double generation channels. As a result, the LMMHD generator could obtain almost constant generation efficiency at any inlet velocity of the liquid metal. The large-eddy simulation of the turbulent duct flow in an LMMHD generator was examined to reveal the behavior of the MHD flow and the turbulent structure (Hiroki et al., 2011). It was found that the non-uniform magnetic flux density in the streamwise direction produced two eddy currents, and they caused the wall-jet flows with M-shaped mean streamwise velocity profiles in the plane perpendicular to the applied magnetic field. An equivalent circuit model of the LMMHD generator was built based on the basic steady-state electromagnetic characteristics and 3D simulations of the generation channel (Zhao et al., 2011). The calculative and experimental results were compared, which showed that the proposed equivalent circuit model and calculation methods were valid with a higher computational accuracy. The 3D numerical simulation analysis of the generation channel of an LMMHD generator was carried out based on the computational fluid dynamics method (Yi et al., 2021). Results showed that the input energy decreased with the increase of load factors, but there was an optimal load factor to maximize the output power and the generation efficiency.
