粒子と壁の衝突挙動の微視的解析

Abstract

粒子径20-300µmの粒子を対象として，気相における粒子と壁の衝突挙動を実験的および理論的に検討した．顕微高速度カメラによって得られた画像を用いて，衝突前後の速度におよぼす粒子径の依存性を定量的に解析した．平板近傍における流体抵抗の増加（すなわち，潤滑効果）を考慮した衝突速度の数値計算を行い，実験値と比較した結果，両者は良好に一致することがわかった．微粒子では，潤滑効果を含めた流体抵抗が粒子慣性と比べて大きくなることに起因して速度低下が生じることを明らかにした．さらに，衝突速度と粒子密度を変化させた実験によって，反発係数はストークス数の減少とともに小さくなることを示した．

The collision of particles having diameter ranging from 20 to 300 μm in a gas with a wall was studied both experimentally and theoretically. The effect of the particle diameter on the incident and rebound velocities was quantitatively examined by using images captured by a high-speed microscope camera. The incident velocities calculated using a model that takes into account the increase in fluid resistance near a wall surface, i.e., the lubrication effect, were in good agreement with the results obtained experimentally. Smaller particles had lower velocities owing to the increase in the ratio of fluid resistance to particle inertia. Experiments conducted by varying the incident velocity and particle density further indicated that the coefficients of restitution decrease with the decrease in the Stokes number.