Investigation And Optimization Of The Flow Transient Characteristics And Stability In ALIP Pump

The research and development on the fourth Generation of Nuclear Energy System have provoked different types of conceptual systems,e.g.gas-cooled fast reactors,molten salt reactors,and sodium-cooled fast reactors(SFR).The sodium-cooled fast reactor has been receiving much attention by many countries,because it has some advantages,good thermal conductivity,excellent cooling performance and high security.The annular linear induction pump(ALIP)is an ideal candidate for the coolant pump of SFR and it is an electro-magnetic pump in which liquid metal can be driven by induced Lorentz force.Compared with traditional mechanical pumps,ALIP possesses of several advantages,1)it has excellent sealing due to free of rotary parts;2)It does not require the installation of auxiliary parts such as bearings and lubrication;3)it bears low mechanical vibration and noise.The structure of ALIP is relatively simple and have easy maintenance.However,the overall efficiency is relatively low.When deviating the normal operating conditions,the instable flow could occur in the flow channel of the pump,which greatly affects the efficiency of the pump.Therefore,effort should be made in the optimization of ALIP structure to create better induced electromagnetic field and to maintain flow stability in the pump under different flow conditions.In this work,the referred ALIP prototype is the ALIP-2 with the normal flow rate of 7 m3/min in D.V.Efremov Institue in Russia.The main contents and results are summarized as follows:(1)Based on the finite element method,the Maxwell questions and Navier-Stokes equations are coupled to solve 2D and 3D models of the ALIP.The 2D model in a cylindrical coordinate system is created in which only the magnetic vector in the azimuthal direction and the velocity vector in the radial and longitudinal directions are considered.The Ampere's law is also considered in cylindrical coordinates of a two-dimensional model.In the 3D model,a scalar potential is added and edge element method is used to calculate the electromagnetic field with transient velocity.The weak forms of the equations of current continuity and Ampere's law are created by reducing the order of variables based on the Galerkin method,which provides the basic theroy of building 3D ALIP model.(2)A 2D symmetric single-side winding model(SS pump)is created in COMSOL and the double-side winding model with inner and outer coils with a ratio of 1(DS1 pump)and 0.5(DS2 pump)are created for the comparison.The results show that the differential pressure of the DS2 pump at normal operating conditions is 30% higher than that of the SS pump.The efficiency of the DS2 pump is approximately twice of the SS pump,and the efficiency of the DS1 pump is increased by 26%.It can be shown that the distribution of the double-side winding has a significant effect on the improvement of the efficiency.The improvement of the efficiency of the double-sided winding DS2 pump with an internal and external coil ratio of 0.5 is the most obvious.At high flow condition,the velocity of DS2 pump in the section along the middle of the first pole pitch(S4)to the middle of the pump(S6)is the most uniform in three models.The larger deviation of RMSD of DS2 pump at the outlet indicates that the end effect of the force affects the flow effectively.The distribution of velocity of DS2 pump is more stable than SS pump at low flow condition.This results show that the double-side configuration of winding in the DS2 pump can effectively improve the flow uniformity.Further analyse of the distribution of Lorentz force,the Lorentz force of the double-side winding pumps appears a hump flow through the middle and lower sections of pump.At high flow conditions,the hump in the DS2 pump is more obvious than the DS1 pump.The results show that the slope of magnetic flux density produces a peak in the Lorentz force.The change of the slope of the magnetic flux density determines the degree of the hump of the Lorentz force.(3)Without considering the influence of air and stainless steels,a simplied 3D model is created.A Lagrange multiplier is added to the Ampere Law as the potential to modify the mf module in COMSOL.A weak form of the current conservation equation and Coulomb gauge are added in the modified mf module.Interpolated from the 2D model,the magnetic vector potential A? is given as the boundary condition in the 3D model.Then the transient numerical simulation of magnetic-fluid coupling is performed.The results show that the pump performance characteristics of the 3D model are consistent with the 2D model which indicating the reliability of the created 3D ALIP numerical model.The time averaged radial distribution of velocity,Lorentz force and magnetic flux density are analyzed.The results show that at the rated operating condition,the time averaged radial velocity of the sodium through the middle and downstream sections of the pump is relatively stable.The trend of distribution of velocity is opposite to that of Lorentz force.The maximum velocity occurs in the tube middle while the Lorentz force is the smallest there.The trend of distribution of magnetic flux density is similar with the 2D model through the middle and downstream sections of the pump.Overall,the ALIP does not show any instability in the modeled situation,since the nominal flow rate of the pump is simulated.The study of flow instability at lower flow rate will be done in the future work.