粒徑篩分現象與流體特性之關係

Relationship between Size Segregation Phenomenon and Flow Characteristics

楊凱鈞(Kai-Chun Yang) ； 黃宏斌(Hong-Pin Huang)

《農業工程學報》 55卷4期 (2009/12) Pp. 47-57

https://doi.org/10.29974/JTAE.200912.0004

摘要

地質災害有時會出現重力作用、間隙流體多寡不一之顆粒流，土石流即是臺灣常見之顆粒流。觀察土石流堆積垂直剖面，則有大顆粒在上層，小顆粒在下層之粒徑篩分現象。本研究主要目的在探討此種現象之成因，並嘗試找出可能影響粒徑篩分現象之因子。經文獻蒐集以及對於垂直震動粒徑篩分現象之瞭解，本研究發現斜坡顆粒流之流況，與垂直震動顆粒流有甚多相似之處，大顆粒在流體中會隨著剪力而上昇與下沈，亦可發現無論是斜坡顆粒流或是垂直震動顆粒流，粒徑篩分現象爲流體之垂向剪力分佈所導致，並與顆粒問之摩擦作用力、碰撞作用力、黏滯剪應力與紊流剪應力有關。而粒徑越大顆粒之所以上昇越快，是由於大顆粒在獲得動能後，較不容易因爲剪力方向之摩擦作用，改變其運動之方向所致。

關鍵字

顆粒流 ； 土石流 ； 粒徑篩分

並列摘要

Some geophysical flows involve rapid gravity-driven granular flow with different interstitial fluid concentration. Debris flow is one of very typical granular-fluid flow in Taiwan, On vertical size distribution of debris flow's deposit, it is easy to observe the ”size segregation” phenomenon. This research tried to figure out the reason and factors by literature review and understanding of similar mechanism when particles shake vertically. This study shows that shear stress distribution result in the phenomenon. The main factors arc frictional stress, collisional stress, viscous stress and turbulent stress. After larger particles (the inertia are higher) obtain kinetic energy, the motion directions are harder to be changed by stresses. Consequently, the larger particles increase comparatively the vertical velocity with diameter.

並列關鍵字

Granular flow ； Ddebris flow ； Size segregation