振动和气流协同作用下颗粒物质流变特性研究

In modern industry and agriculture, great many raw materials are produced in form of particles. It is expected that the particles can be transported and processed freely as fluid. In this proposal, the external energy (mechanical vibrating and gas blowing from bed bottom) is introduced into granular bed to improve its fluidity, and the rheological properties of the granular material are researched, which can be used to predict particle dynamic characters and provide the method of particle flux controlling and measuring. The constitutive relation, especially the yield stress in this constitutive relation, is the key for influencing the flowability of granular material (solid-like state or liquid-like state, flowing or jamming). After the constitutive relation is established, the effects of the vibration parameters and gas velocity on constitutive relation are analyzed; and then the equivalence, the difference and the cooperation between vibration and gas flow are following researched. Meanwhile, By analyzing the energy transfer and dissipation of the mechanical vibration and the gas flow, the relation function between the introduced energy flux and the granular flow patterns/the equivalent viscosity of the granular flow are also addressed. In addition, the energy and entropy equation of the granular flow are established, and the granular flow is analyzed as a thermodynamic system. Based on the thermodynamic theory, the divide of flow patterns is certified in theory and the granular flowing mechanism would be further revealed.

在现代工农业中，很多原料都以颗粒的形式参与生产，人们往往希望颗粒可以像流体一样可以自由流动方便运输和处理。本申请引入外部能量（机械振动、气流）改善颗粒物料的流动性，研究颗粒物质流变特性以定量预测其流动行为，为流量控制和计量提供方法。颗粒物质本构关系尤其本构关系中屈服应力是影响颗粒流动性（类固或类液态，是否堵塞）的关键，建立颗粒物质本构模型并分析振动参数、气流速度对屈服应力的影响，研究振动和气流对改善颗粒物质流动的等效性、差异性和协同性；同时，根据振动机械能、气流压力能在颗粒物质中的传递和耗散规律，构建向颗粒系统输入能量与颗粒自身流动形态/当量粘度的关系；将颗粒物质视为热力系统，建立系统能量方程和熵方程，并基于热力学理论对其流动形态进行判定，揭示颗粒流动的热力学机理。

固体颗粒广泛存在于工农业生产和运输中，但由于流动性差，且存在流动不均匀、堵塞等现象，在加工或运输中与气体和液体物料相比有诸多不便之处。本研究从颗粒底部通入气流并对颗粒系统施加振动，探明床层在振动/气流作用下处于亚流化状态时的流动性能，建立了气流和振动对床层流化等价关系，为工农业中散料的进出料、散料运输等提供定量计量依据，同时为探索振动流化床的流化机制的奠定基础。.对于通风床层，气流可完全流化颗粒床。随着气流风速的加大，颗粒床层等效粘度逐渐降低，气速达到临界流化速度以后，床层为类似流体的完全流化状态。而对于振动床层，振动加速度决定了振动床层的屈服应力大小，但振动不能将颗粒床完全流化，即振动仅作降低临界流化风速因素。当气流速度较小时，气流对颗粒流变特性的改善作用很小，此时振动对颗粒流变特性的影响比较大，而随着气流速度的加大，振动对颗粒流变特性的影响逐渐减弱，气流对颗粒流变特性的影响呈现主要作用。将物体浸入通气振动床，振动与气流对直棒所受的竖直作用力有着等价的影响（u/umf ~ 0.748Γ）。在两者共同作用下时，浸入直棒所受的无量纲竖直作用力可以表示为：Fb/Fb,0 = U*+Γ*–1。基于浸入直棒受力与床层流动性能的等价关系，可得到颗粒床层的临界流化速度与振动强度的关系：umv/umf = 1–0.748Γ。.由于颗粒床层力链的复杂性，对浸入物体的阻力存在方向性。浸入物体垂直向下运动时阻力最大（Fm），而其它运动方向下所受阻力随运动方向角θ的增加而减小，近似满足玻尔兹曼分布，F/Fm=A2+( A1-A2)/[1+e(θ-b)/dx]。此外，阻力方向与运动方向存在偏移角，偏移角随运动方向角的增加先增加后减小，在θ约等于π/2具有最大的偏移角。