【作者】 王磊；

【导师】 马军星；

【作者基本信息】 长安大学 ， 机械工程（专业学位）， 2023， 硕士

【摘要】 宏观均匀的水泥浆体在微观层面上并不均匀,有部分粉体颗粒发生团聚,使水泥无法充分水化,导致其宏观性能降低,产生不利影响,甚至引起严重后果,因此研究提升水泥浆微观均匀程度的方法具有非常重大的实际意义。本课题组为解决上述问题提出了中高速净浆搅拌技术,采用孔板式叶片搅拌桨作为搅拌装置,旨在改善水泥浆体中的颗粒团聚现象,获得微观均匀程度较高的水泥浆,然后再与粗细骨料混合搅拌制备高强度混凝土。本文主要工作及结论如下:(1)浆体中水泥颗粒受力分析。浆体中颗粒受力源自两方面:颗粒间相互作用及流体对颗粒的作用,颗粒间相互作用是团聚结构形成的关键。在搅拌过程中,水泥粉体颗粒团聚与破碎由颗粒间作用力以及液体对团聚颗粒的作用,即液动力共同决定。(2)通孔对团聚颗粒破碎效果的影响分析。建立了团聚颗粒模型,并采用CFD-DEM方法对团聚颗粒通过通孔发生破碎的过程进行数值模拟,分别探究了通孔形状、通孔尺寸以及初始入口流速对团聚颗粒破碎的影响。结果表明:团聚颗粒在通过通孔后所受剪切力发生明显变化,而法向力变化则不明显;当通孔为圆孔、孔径越小且初始入口流速越大时,孔后流体流速与流体湍流动能最大,颗粒受到剪切力最大,有利于改善颗粒团聚现象。(3)叶片开孔率分析及流场模型验证。结合已有设备进行流场建模,并合理划分网格、划分区域、设置边界条件并选择相关参数,对不同叶片开孔率下的搅拌流场进行仿真分析,确定有利于提升固液两相搅拌均匀性的最佳开孔率,并且进行样机试验,确定最佳开孔率的同时对模型进行验证。结果表明:所建模型可靠性较高,可准确反映实际搅拌结果;最佳叶片开孔率为0.3,且随着开孔率减小,搅拌功耗加大。(4)变速搅拌效果分析。对不同变速条件下的搅拌流场进行仿真,分析其固液混合分散特性,探究变速方式、起始搅拌转速以及变速差值对固液两相搅拌混合分散均匀性的影响。结果表明:相较于恒速以及“高速-低速-高速”的搅拌方式,采用“低速-高速-低速”的变速方式更有利于提升固液两相混合均匀性;较高起始转速和较大变速差值对提升固液两相混合均匀性也有利,但超过一定限度后对均匀性的提升很有限,功耗增加则较大。更多还原

【Abstract】 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.更多还原