Study On Magnetohydrodynamic （MHD） Instabilities And Suppression Method In Cylindrical Liquid Metal Battery

With the rapid development of social economy,renewable energy,such as solar energy and wind energy,has attracted increasing attention because of its pollution-free and abundant reserves.However,due to the influence of geographical location,seasonal climate and other factors,renewable energy is generally unstable and intermittent.Therefore,large-scale energy storage equipment is needed to connect the unstable upstream supply end with the downstream power grid users who need stable supply,so as to improve the energy conversion and utilization rate.In recent years,with the development of energy storage technique,Liquid Metal Battery（LMB）,as a potential cheap large-scale energy storage technology for power grid,has become a research hotspot.However,due to the all-liquid structure of LMB,many instabilities appear in LMB,such as the Taylor instability caused by the induced magnetic field generated by battery charging and discharging;the Sloshing instability caused by external disturbance;the internal temperature difference caused by the battery Rayleigh-Bénard instability;and the Electro-Vortex Flow caused by changes in current density.The flow of the magnetic fluid（or magnetohydrodynamics,MHD）inside the LMB is based on the above-mentioned instability coupling and the more complex flow phenomenon,and this flow is easily affected to result in short-circuit,and further the occurrence of safety accidents,which severely limits the wide application and commercialization of the LMB.To solve the above problems,according to the working principle of LMB,this work establishes the physical model and mathematical model for simulation research,and develops a solver for simulating the instability of magnetohydrodynamics in LMB by improving the solver of multiphase Inter Foam in Open Foam-4.x.Through the conventional LMB simulation study without grids,the internal flow field,the distribution of induced magnetic field and the characteristics of Lorentz force are obtained,in which the distribution of induced magnetic field inside the battery is concentric circles around the axis,and the distribution of Lorentz force is pointing to the axis along the radius.In addition,when the battery works stably,there is a stable flow inside the battery,and the flow first appears at the interface between the cathode and the electrolyte material.With the increase of the voltage,the flow velocity at the interface between the cathode and the electrolyte becomes larger,and the electrolyte layer begins to deform.The continuous working of the battery may lead to the short connection between the anode and the cathode.Meanwhile,the larger the electric potential,the shorter the normal working time of the battery will be.Through further simulation,it is found that the critical voltage of LMB internal instability is 95 V in our specified LMB,and the instability occurs when the threshold is exceeded.According to the LMB internal instability mechanism,this research proposes a new instability suppression technology segmentation based on grid structure on multiphase liquid interface so as to achieve the inhibition effect of coupling instability of LMB,the grid structure is composed of electric insulation,magnetic insulation baffle,baffle and the cathode contact and completely extends to the anode.When 3 baffles are placed in the LMB,the threshold of LMB is 117 V,which is 22 V higher than the threshold of LMB without baffles.The existence of baffles weakens the flow of the cathode and electrolyte layer,enhances the flow of the positive electrode,and inhibits the precipitation of solid metal compounds in the positive electrode.If 4 baffles are used in the LMB,the instability in LMB threshold is 163 V,a 46 V increment compared with the threshold of 3 baffles.Therefore,with the addition of grid,the battery can be charged and discharged with a larger voltage,thus improving the charge and discharge efficiency.The calculation results show that the more the number of baffles used,the better the inhibition effect on the MHD instabilities in LMB,but the number of baffles should be determined according to the actual situation.In addition,the grid structure inserted into the LMB can change the distribution of the circular induced magnetic field inside the battery,effectively reducing the induced magnetic field and Lorentz force,thus improve the stability of the LMB.