| The macroscopic uniform cement slurry system is not uniform at the microscopic level,and some powder particles agglomerate,so that the cement cannot be fully hydrated,resulting in its macroscopic performance reduction,adverse effects,and even serious consequences,so the study of the method of improving the microscopic uniformity of cement slurry has great practical significance.In order to solve the above problems,research team proposed mediumhigh speed cement mixing technology,using perforated blades as the mixing device,aiming to improve the particle agglomeration phenomenon in the cement slurry,obtain homogeneous cement slurry,and then mix with coarse and fine aggregate to prepare high-strength concrete.The main work and conclusions of this paper are as follows:(1)Force analysis of cement particles in slurry.The force of particles in the slurry comes from two aspects: the interaction between particles and the effect of fluid on particles,and the interaction between particles is the key to the formation of agglomerated structures.In the mixing process,the agglomeration and crushing of cement powder particles are jointly determined by the inter-particle force and the action of liquid on the agglomerated particles,that is,the hydraulic force.(2)Influence analysis of hole of different parameters on agglomerated particle crushing.The agglomerated particle model was established,and the CFD-DEM method was used to numerically simulate the process of agglomerated particles breaking through vias,and the effects of perforated shape,aperture size and initial inlet flow rate on agglomerated particles were explored.The results show that the shear force of the agglomerated particles changes significantly after passing through the via,while the change of normal force is not obvious.When the aperture is a round hole,the smaller the diameter and the larger the initial inlet flow rate,the fluid flow velocity and fluid turbulence energy behind the aperture are the largest,and the shear force of the particles is the largest,which is conducive to improving the particle agglomeration phenomenon.(3)Analysis of blade aperture ratio and validation of the flow field model.Combined with the existing equipment to model the flow field,and reasonably divide the mesh,divide the area,set the boundary conditions and select relevant parameters,the stirring flow field with different blade aperture ratios is simulated and analyzed,the optimal aperture rate is conducive to improving the uniformity of solid-liquid two-phase stirring,and the prototype test is carried out to determine the optimal aperture rate and verify the model.The results show that the established model has high reliability and can accurately reflect the actual mixing results.The optimal blade aperture ratio is 0.3,and as the porosity decreases,the stirring power consumption increases.(4)Effect analysis of variable speed stirring.The stirring flow field under different variable speed conditions was simulated,the solid-liquid mixing and dispersion characteristics were analyzed,and the effects of variable speed mode,initial stirring speed and variable speed difference on the uniformity of solid-liquid two-phase stirring and mixing and dispersion were explored.The results show that compared with the constant speed and "high speed-low speedhigh speed" mixing method,the "low speed-high speed-low speed" variable speed method is more conducive to improving the mixing uniformity of solid-liquid two-phase.Higher starting speed and large variable speed difference are also beneficial to improve the uniformity of solidliquid two-phase mixing,but after exceeding a certain limit,the uniformity improvement is very limited,and the increase in power consumption is large. |
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