The properties of liquid metals with low melting point were compared and their influence on the performance of a demonstration LMMHD wave energy conversion device was calculated and analyzed. The results show that with the same external force and input work, when NaK78 is the working liquid, the system has the largest output power and highest efficiency. The maximum output power of NaK78 is about three times of U-alloy47 and eight times of mercury. The average efficiency of NaK78 is two times of U-alloy47 and four times of mercury.
A reciprocating liquid metal MHD generator was first proposed by Haaland (1995) and pure liquid metal was forced to flow back and forth in the MHD channel by an external force. Compared with the conventional LMMHD power generation, such as the two-phase generator cycle (Petrick and Lee, 1964), it adopts a linear drive and thus eliminating the energy losses associated with the thermodynamic cycle. The working liquid is pure liquid metal which has high conductivity and is in one-phase flow, so there are no slip losses between two phases and nor separation losses and the power density is very high. Moreover, it can provide variable power corresponding to the demand with high efficiency throughout the range of power usage. So, it has potential applications in vehicle engines (Haaland, 1995), distributed energy systems (Shimizu, Maeda and Hasegawa, 2004) and wave energy direct conversions (Koslover and Law, 2005, Peng, Zhao, Sha, Li, Xu and Lin, 2006). Converting ocean wave motion into electricity is a specific method to harness the immense power of ocean waves. In a conventional wave energy conversion system, a high-speed rotary generator with a low-magnitude force is usually adopted. However, an ocean wave moves slowly and has a high-magnitude force. So there must be an intermediate step, such as gears, hydraulic systems, to couple ocean waves with rotary generators. As a result, the conversion devices are bulky, expensive, unreliable, and meager in their output.
