Study On The Characteristics Of Stirred Flow Field Of Non-newtonian Fluid

In recent years,with the rapid development of high-end equipment manufacturing industry,the use of lubricating materials to extend the service life of equipment has become a market focus.The lubrication performance of lubricating materials is limited by the mixing uniformity of additives in the preparation process.However,the agitators currently used to prepare lubricating materials with non-Newtonian fluid characteristics have problems such as low mixing efficiency and uneven mixing,which affect the performance stability of lubricating materials.Therefore,this paper carried out a study on a combined agitator for non-Newtonian fluid mixing,and discussed the influence of its structural parameters,operating parameters,and rotation mode on the fluid mixing characteristics.The study results will provide a good technical reference for the design of non-Newtonian fluid raw material mixing equipment in the industrial field.Firstly,using lubricating grease as the stirring medium,the Laminal model was selected,and the Multiple Reference Frame(MRF)method and tracer concentration method were used for single-phase numerical simulation.The effects of structural parameters such as the number of impeller blades,height from the bottom,and blade inclination angle on the unit volume stirring power(P_V),mixing time(θ_M),and effective stirring volume fraction during the stirring process were studied.The results showed that the stirrer could be applied to the mixing and stirring of highly viscous non-Newtonian fluid;The structural parameters had an impact on the stirring power per unit volume,mixing time,and effective stirring volume fraction,with the mixing time being the most significantly affected.The order of influence of each structural parameter on the mixing time was the number of blades,blade inclination angle,and height from the bottom.Compared with the initial setting,the optimal parameters,namely the number of internal propeller blades of 9,the height from the bottom of 50 mm,and the blade inclination angle of 45°,reduced the corresponding mixing time by 61.6%.Secondly,based on the optimized internal impeller structure parameters,a single-phase numerical simulation was conducted on the flow field characteristics and mixing process in the agitator under different operating conditions using the multiple reference frame method and tracer concentration method,using lubricating grease as the liquid phase.The results showed that as the feeding point position moved radially away from the center,the mixing time and unit volume mixing energy showed a decrease first and then an increase;Along the axial direction,as the height of the feeding point decreases,the mixing time showed a trend of first increasing and then decreasing;The selection of feeding point position had no effect on the stirring power per unit volume.The stirring power per unit volume was positively correlated with the internal and external impeller speeds;There was a negative correlation between mixing time,mixing energy per unit volume(W_V),and inner and outer impeller speeds;The mixing time and unit volume mixing energy were most significantly affected by the internal and external impeller speeds,and the trend of change was similar.Through single factor and orthogonal experimental analysis,the optimal operating parameters were obtained,that was,when feeding at point 3,the outer propeller speed was 80 rpm,and the inner propeller speed was 100 rpm,the corresponding mixing time was 128 seconds,which was 45.1%shorter than the initial setting.Finally,in order to deduce the transition from concentric stirring of the combined agitator to planetary stirring of the inner impeller,lubricating grease was used as the liquid phase,and calcium silicate particles were used as the solid phase.The Mixture model was used to conduct numerical simulation of the solid-liquid two-phase flow using the Sliding Grid(SG)method.The differences in flow field characteristics and solid holdup distribution uniformity under the three rotation modes of the inner impeller were explored,and experimental research on fluid stirring under three rotation modes was conducted.The results showed that the mixing efficiency and uniformity of the planetary stirring with the internal impeller of the combined stirrer were superior to other rotational methods;Compared to concentric stirring with inner and outer paddles,the mixing time is reduced by 38.46%and the uniformity of solid content is improved by 14.89%.In addition,the gear ratio of the internal propeller planetary stirring will change the motion trajectory of the internal propeller blades,thereby affecting the mixing efficiency and uniformity of the combined mixer.When the transmission gear ratio is an irrational number,the motion trajectory of the blades is relatively dense and evenly distributed,resulting in better mixing uniformity.The above results will provide a good reference for the design of new non-Newtonian fluid agitators.