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|Title:||Experimental study of highly concentrated two-phase flows|
|Author(s):||Cui, Michael Minqin|
|Doctoral Committee Chair(s):||Adrian, Ronald J.|
|Department / Program:||Applied Mechanics
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The new techniques and instrumentation have been developed and successfully applied to granular shear flows in a Couette apparatus. This apparatus has been designed and constructed to obtain both global quantities and optical measurement of detailed particle movements. Over 48,000 pictures have been taken and analyzed. Concentration, velocity, and granular-temperature profiles have been obtained for the first time. The new physical phenomena observed give many physical insights.
The concentration profiles obtained in this present research suggest that the concentration of the particles is not constant across the shear layer. The particle concentration is lower near the both stationary and moving walls and higher near the center. This nonuniformity is the most distinguishable characteristic of granular flows which is different from single-phase fluid flows. The velocity profiles are also not linear across the shear layer. The velocity gradients change from the moving wall to the stationary wall. Both of them differ from the assumptions on which all current constitutive equations are based. Further study is needed to assess the effectiveness of these models.
The velocity of the particle at the wall is not the same as the wall velocity, i.e. the non-slip condition does not hold. Hence, traditional non-slip boundary condition cannot be applied to these granular flows. The slip velocity is different for different shear rates and particles under the same physical boundary conditions. This variation provides evidence that the boundary conditions are dependent not only on the walls but also on the interior flow field.
Different zones of particle concentration and velocity appear within the same shear layer. The near-wall region has lower concentration of particles and the central part is more densely packed by particles. For non-spherical particles, the velocity profiles are smoother than the corresponding profiles for spherical particles from the moving wall to the stationary wall. For spherical particles the velocity gradient is not even continuous across the shear layer. A negative velocity gradient is observed for both spherical and non-spherical particles. This phenomenon has never been seen in single-phase fluids.
Granular temperature, which is a measure of velocity fluctuation of the solid particles, has been obtained for these particles. The profile across the shear layer shows that the granular temperature is larger near both walls and smaller at the center of the shear layer. Thus it is the velocity gradient near the wall that generates the granular temperature.
|Rights Information:||Copyright 1995 Cui, Michael Minqin|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9522098|
This item appears in the following Collection(s)
Graduate Dissertations and Theses at Illinois
Graduate Theses and Dissertations at Illinois