Dynamic Rheological Behavior of Gallium-Based Liquid Metal
In recent years,gallium-based liquid alloys had been widely used as coolants in nuclear reactor cooling systems and in concentrating solar energy,as well as lubricants in bearing systems,due to their good fluidity and high thermal conductivity,which had greatly improved the efficiency and performance of these devices.Therefore,it was of great importance to understand the rheological characteristics of liquid gallium-based alloys.Because the rotation method could measure the viscosity at different shear rate,many researchers measured the rheological properties of gallium-based liquid metals by the rotation method and obtained many valuable results.However,due to the high surface tension,high density and low viscosity of gallium-based liquid metal,it was difficult to obtain a relatively stable viscosity value by the rotation method.Therefore this work designed a viscometer with a rotating outer cylinder and Mo central rotator to measure the viscosity of gallium-based liquid metal.The rheological properties of oxidized and unoxidized Ga66.7In20Sn13.3(mass fraction)liquid metals in a wide range of shear rates(0～120 s-1)were measured.Ga66.7In20Sn13.3 liquid metal was obtained by heating gallium,indium and tin(all 99.999％purity)in argon atmosphere(O2＜0.25 × 10 6)to 200 ℃ for 4 h.The melting points of gallium,indium and tin were 30,156.6 and 231.9 ℃,respectively.The ternary eutectic Ga66.7In20Sn13.3 alloy had a melting point of 10.6 ℃.The coaxial cylinder rotary viscometer(NDJ-5S,Lichen,Shanghai)was used,and the quartz outer cylinder(30 mm in the inner diameter)was driven by the motor and rotates at a speed of(0～306 r·min-1).A pure molybdenum inner rotator with a diameter of 20 mm and a height of 50 mm was used to overcome the buoyancy of liquid metal and enhance the stability of the rotor.The measurement was carried out based on the Couette principle.According to the different rheological laws of Newtonian fluid and non-Newtonian fluid,an approximate shear rate conversion method was used to convert the shear rate of non-Newtonian fluid into that of Newtonian fluid,and the rheological relationship between τ and y was determined in both oxidized gallium-based liquid metal cases and non-oxidized gallium-based liquid metal cases.The results indicated that at a low shear rate,the viscosity of the oxidized liquid metal reached 60 mPa·s.With the increase of shear rate,the viscosity gradually decreased.When the shear rate increased above 30 s,the viscosity gradually tended to be stable value with a minimum of 7.27 mPa·s.However,the viscosity of non-oxidized liquid metal remained at 4.51 mPa·s as the shear rate varied.The results also showed that the rheological relationship of the oxidized Ga66.7In20Sn13.3 was τ=27.37γ0.69,and the rheological relationship of unoxidized Ga66.7In20Sn13.3 was τ=4.51γ+4.08.The oxidized liquid metal exhibited the characteristics of pseudoplastic non-Newtonian fluid and the unoxidized liquid metal exhibited the characteristics of Newtonian fluid.The pseudoplasticity of the oxidized liquid metal came from the elasticity of gallium oxide,which had the elastic properties similar to that of a solid and was the source of the non-Newtonian properties of the gallium-based liquid metal.Accordingly,the appearance viscoelastic of gallium-based liquid metal were made of the viscous force of liquid metal flow and the elastic deformation force of oxide film.With the increase of shear rate,the elastic force of gallium oxide reached an maximal yield stress,and the liquid metal viscosity tended to be stable.
NETL
NSTL
万方数据
