微粒子の振動輸送の解析

Abstract

振動コンベヤは，粒子を跳躍移動させる傾斜振動トラフを備えた装置であり，固体材料の輸送用に産業で広く用いられている．しかし，粒子にはたらく付着力や流体抵抗の基礎的検討は行われておらず，微粒子を対象とした振動輸送を詳細に説明する報告は見当たらない．本報では，二次元振動する平板上の微粒子の挙動に関する最新の実験的および理論的研究の成果をまとめて記す．平板に付着した粒子に十分な強度の二次元振動を加えると，粒子は平板から分離して跳躍を繰り返すが，平板に対して接線方向に外力を加えると粒子は回転し始め，これにともなって，粒子・平板間相互作用力が著しく低下するので，比較的小さい外力でも粒子は平板から分離する．また，粗粒子は一次粒子として前後に大きく跳躍しながら移動するのに対し，微粒子は反発係数の小さい凝集粒子を容易に形成し，微小な跳躍を一定方向に繰り返すので，凝集粒子の平均移動速度は粗粒子に比べて大きくなる．これらの現象は，理論的確率モデルおよび粒子軌跡の数値シミュレーションによって説明できる．

The vibrating conveyor is a machine with an obliquely oscillating trough that induces the saltation of particles. It is widely used for the transport of solid materials in industry. However, basic studies on the adhesive forces and fluid resistance that act on the particles have been neglected, and there have been few reports detailing the vibratory conveying of fine particles. This review summarizes the latest experimental and theoretical results on the behavior of fine particles on a two-dimensional oscillating plate. When a sufficiently high intensity of two-dimensional vibrations is applied to particles adhering to a plate, the particles become detached and bounce repeatedly. The external force in the tangential direction of the plate induces particle rolling, which decreases the particle-plate interaction force; as a result, even a relatively small external force will allow the particle to become detached from the plate. Furthermore, coarse single particles are transported by the repeated larger bounces with both forward and backward motions. On the other hand, fine particles can easily form agglomerated particles with low restitution and bounce slightly but only forward. Consequently, the transport velocity of agglomerated particles is greater than that of coarse single particles. These phenomena can be explained with a theoretical probability model and numerical simulation of the particle trajectory.