| Developing clean and renewable energy is the only way to meet the energy demand of economic development and improve the energy consumption structure.China is rich in tidal energy resources.It's important to exploit the tidal energy.Liquid metal magnetohydrodynamic(LMMHD)power generation technology is applied to the tidal energy extraction device.The liquid metal MHD generator can replace the traditional rotary generator,reduce the energy conversion process,and greatly simplify the device structure.In this paper,the mechanism of liquid metal MHD generators is detailed studied.A method of numerical simulation based on the Fluent software is explored and characteristics of power generation channels are analyzed.Meanwhile,the dual-channel linkage liquid metal MHD generator is researched.Firstly,the governing equations of liquid metal MHD are established by coupling the equations of fluid mechanics and electromagnetism based on the basic assumptions.Two methods of induced magnetic method and potential method are given for solving current density vectors.The continuous electrode Faraday type liquid metal MHD generator is chosen by estimating the Hall parameter.Then,a three-dimensional rectangular generator channel model is established.Based on MHD module of the Fluent software,the open circuit and load characteristics are studied with the induced magnetic method and the potential method respectively.The modified k-? turbulence model and SIMPLE algorithm are used to solve the equations.The correctness of the numerical simulation method is verified by two cases in the literature.Then output power and efficiency of the generator are calculated from the energy structure.Secondly,the velocity fluctuation and the influence factor of end effect are defined.The influence rule of magnetic flux intensity,inlet velocity,channel width and interaction parameter on the kinetics and electromagnetic characteristics of a liquid metal MHD generator channel are analyzed.The results show that the velocity fluctuation,end effect and electromagnetic efficiency change significantly with the channel parameters.When the channel width is constant,with the same interaction parameters,the velocity fluctuation,end effect and electromagnetic efficiency basically stay.It is suggested to select the channel width d=0.1 m,magnetic flux intensity B0=0.5 T,and inlet velocity V0=5 m/s for an experimental prototype.On these conditions,the generator has appropriate induced electromotive force(EMF),relatively stable channel flow,weaker end effect,and higher electromagnetic efficiency.The output power and efficiency increase first and then decrease with the increase of load coefficient.The maximum output power is 1.2 kW around the load coefficient K=0.6.Finally,a dual-channel computational model with the structure of parallel channels and series electrodes is established.The characteristics of DC and AC dual-channel power generators are analyzed and the performance of dual-channel linkage liquid metal MHD generators is studied.The research shows that the induced EMF of a DC dual-channel can be increased by 52.5%and the load characteristic is better than that of a single channel generator with the same parameter.The peak value of AC induced EMF generated by reciprocating motion is higher than that of DC.In the dual-channel linkage generator,the performance is affected by the superposition of the two inlet velocities and decreases with the increase of the absolute value of phase difference.Therefore,setting a reasonable liquid metal loop and keeping similar speed of the two channels can improve the performance of a dual-channel linkage oscillating wing liquid metal MHD generator device. |
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