卧螺离心机转鼓内基于稠密颗粒流气-液-固三相耦合运动过程机理的研究

发布时间：2018-05-19 18:34

本文选题：稠密颗粒流 + 气-液-固三相曳力方程　；参考：《天津大学》2015年博士论文

【摘要】：卧式螺旋离心机是工业上常用的固液分离设备,其基本原理是利用离心力和螺杆轴向推动力实现密度不同的液固两相的分离。该设备具有自动化程度高,能够无人值守连续性生产的特点,应用前景十分广阔。在卧螺离心机正常工作过程时转鼓内存在气-液-固三相流中各相之间耦合运动,而现有的两相流理论无法准确描述气-液-固多相颗粒流在离心机转鼓内流动状态,使离心机的固液分离理论不能满足实际的工业生产需求。因此,本文基于欧拉模型理论体系,建立能够用于多相流的曳力模型,在螺旋线坐标下构建卧螺离心机数学模型,分析固液两相在离心机内的运动机理,研究在不同操作条件下颗粒流在离心机内部的运动规律,提出离心机出口物料含水率的预测方程,为离心机的结构设计和操作工艺优化提供理论基础和科学依据。基于颗粒流运动理论,本文完善了稠密颗粒运动本构方程以描述在离心机工作过程中固相颗粒在其内部的运动行为。通过在传统稠密颗粒流固相摩擦压力方程中提出了新的压力常数,在固相摩擦黏度方程中添加颗粒碰撞摩擦黏度方程和滞后运动方程,并提出了新的流体湍流与颗粒碰撞对拟热动能源项模型以封闭颗粒拟热动能平衡方程,完善了稠密颗粒运动本构方程。并通过颗粒拟静态堆积实验和稠密颗粒流剪切力运动实验,验证了该本构方程对模拟稠密颗粒流运动行为的可靠性。应用建立的稠密颗粒流运动模型方程,研究了颗粒群拟静态堆积和剪切力运动过程中的力学性质的变化。针对现有连续相-分散相的两相流曳力理论模型,无法模拟卧螺离心机运行过程中气-液-固三相并行存在的运动状态,本文建立了新的多相流流体力学耦合计算模型(TCP理论模型)用以模拟气-液-固三相间的耦合运动行为关系。根据卧螺离心机内气相和液相的运动特点,在该模型中,气相和液相按照体积分数加权的形式组合为一个新的虚拟连续相,进而将气-液-固多相流体系简化为虚拟连续相-分散相的多相流体系。将原有的气-液-固三相间复杂的曳力作用行为简化为两部分:一是虚拟连续相与分散相之间的曳力作用;二是虚拟连续相内部的动量分配过程。通过气-液-固三相鼓泡床实验对该模型进行了验证,结果表明TCP理论模型有效的简化了数值模型中的各个相间复杂的曳力耦合计算过程,在非均匀性相分布体系中实现了有效平滑的从多相流流动到单相流运动过程中的过渡,提高了计算精度。采用TCP理论模型,对三相鼓泡床中的气相、固相和液相的运动状态进行了模拟研究,讨论这三相流体之间的运动耦合性质及其相互作用关系。采用本文完善的稠密颗粒流运动本构方程和提出的TCP理论模型,在螺旋运动参考系下建立了卧螺离心机数值模型,用以描述离心机转鼓和螺杆的相对运动过程对转鼓内混合物料运动的作用规律,并通过卧螺离心机污泥脱水实验的研究验证了数学模型对于卧螺离心机内部流场运动模拟的可靠性。在此基础上,本文分析了固相和液相在离心机内部运动机理,当固液两相在离心力作用下按照密度差在离心机内部分层后,这两相在离心机轴向推动作用下的运动发生变化:由于固相颗粒群与离心机内壁面具有较大的摩擦作用,其所受到离心机的剪切作用较强,因此固相运动速度随离心机内壁面的推动作用逐渐增加,固相的运动方向亦随之在离心机筒段内发生折返;与之相对,由于液相的黏度较小,其所受到的离心机的剪切作用较弱,因此液相的运动方向较难发生变化。固相颗粒在进入离心机后会向离心机的小端方向运动,而液相则从离心机的大端处溢流而出。所以固液两相在离心机轴向方向按照彼此所受到的剪切作用的强弱,这两相之间的相对运动方向发生改变。通过研究不同操作条件下离心机内部流场流动行为,得到了离心力和轴向推力对固相和液相在离心机内部运动的影响规律。针对在离心机不同操作条件下固相和液相在离心机出口处的运动过程研究,提出了卧螺离心机出口物料含水率预测方程。
[Abstract]:The horizontal spiral centrifuge is a commonly used solid-liquid separation equipment in industry. Its basic principle is to separate the liquid and solid two phases with different density by using the centrifugal force and the axial thrust of the screw. The equipment has the characteristics of high automation and unmanned continuous production. The application of the equipment is very wide. The normal working process of the decubitus centrifuge is done. When the current theory of two phase flow can not accurately describe the flow state of gas liquid solid particle flow in the centrifuge drum, the theory of separation of solid and liquid of the centrifuge can not meet the actual demand of industrial production. Therefore, this paper is based on the Euler model theory system. The model of the drag force for the multiphase flow is enough, and the mathematical model of the horizontal screw centrifuge is constructed under the spiral coordinate. The movement mechanism of the solid and liquid two phases in the centrifuge is analyzed. The motion law of the particle flow in the centrifuge is studied under different operating conditions. The prediction equation of the water content of the centrifuge outlet is put forward, which is the structure design and operation of the centrifuge. The process optimization provides theoretical basis and scientific basis. Based on the theory of particle flow motion, this paper perfects the motion constitutive equation of dense particles to describe the motion behavior of solid particles in the centrifuge working process. A new pressure constant is put forward in the traditional dense particle flow solid friction pressure equation, and the solid friction viscosity in solid phase is obtained. In the degree equation, a particle collision friction viscosity equation and a lagging motion equation are added. A new fluid turbulence and particle collision model is proposed for the quasi thermal energy term model with closed particle quasi thermal equilibrium equation, and the motion constitutive equation of dense particles is perfected. The reliability of the constitutive equation is verified to simulate the motion behavior of dense granular flow. The change of mechanical properties in the process of quasi static accumulation and shear force movement is studied by using the motion model equation of dense particle flow. The theory model of the current drag force of the current continuous phase and dispersion phase can not simulate the movement of the horizontal screw centrifuge. In the course of the moving state of gas liquid solid three-phase, a new multi phase flow hydrodynamic coupling calculation model (TCP theoretical model) is established to simulate the coupling motion behavior relationship between gas liquid solid three phase. According to the motion characteristics of the gas phase and liquid phase in the decanter centrifuge, the gas phase and liquid phase are in accordance with the volume fraction in this model. The weighted form is combined into a new virtual continuous phase, and then the gas liquid solid multiphase flow system is simplified as a virtual continuous phase dispersed phase multiphase flow system. The original complex drag action of the gas liquid solid three phase is simplified into two parts: one is the drag force between the virtual continuous phase and the dispersed phase, and the two is in the virtual continuous phase. The momentum distribution process of the part is verified by a gas-liquid solid three-phase bubbling bed experiment. The results show that the TCP theoretical model effectively simplifies the complex drag coupling calculation process of each phase in the numerical model, and realizes the effective smooth sliding from multiphase flow to single phase flow in the non-uniform phase distribution system. The moving state of gas phase and solid phase and liquid phase in a three-phase bubbling bed is simulated by using the TCP theory model. The motion coupling properties and the interaction relationship between the three-phase fluid are discussed. The dynamic constitutive equation of dense particle flow and the proposed TCP theory model are adopted in this paper. The numerical model of the decanter centrifuge is set up under the reference frame of the spiral motion to describe the action of the relative motion of the centrifuge drum and the screw on the movement of the mixed material in the drum, and the reliability of the mathematical model is verified by the study of the sludge dewatering experiment of the decanter centrifuge. On this basis, the motion mechanism of the solid and liquid phase in the centrifuge is analyzed. When the solid-liquid two phases are stratified in the centrifuge under the action of the density difference under the action of the centrifugal force, the motion of the two phase under the centrifugal force of the centrifuge is changed. As the solid particle group has greater friction with the inner wall of the centrifuge, it is subjected to a large friction effect. The shear action of the centrifuge is stronger, so the solid motion velocity increases with the inner wall of the centrifuge, and the motion direction of the solid phase is also reentrant in the centrifuge tube section. After entering the centrifuge, the solid particles move to the small end of the centrifuge, and the liquid phase spillage from the large end of the centrifuge. So the solid and liquid two phases are in the axial direction of the centrifuge in accordance with the shear strength of each other, and the relative motion direction between the two phases is changed. The centrifuge under different operating conditions is studied. The effect of centrifugal force and axial thrust on the motion of the solid and liquid phase in the centrifuge is obtained by the centrifugal force and the axial thrust. The prediction equation for the water content of the outlet material of the centrifuge is put forward in view of the movement process of the solid and liquid phase at the centrifuge outlet under the different operating conditions of the centrifuge.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ051.84

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