5.2.2 Drag on a sphere in viscoplastic fluids
By virtue of its yield stress, a viscoplastic material in an unsheared state
will support an immersed particle for an indefinite period of time. In recent
years, this property has been successfully exploited in the design of slurry
pipelines, as briefly discussed in section 4.3. Before undertaking an examination
of the drag force on a spherical particle in a viscoplastic medium, the
question of static equilibrium will be discussed and a criterion will be developed
to delineate the conditions under which a sphere will either settle or be
held stationary in a liquid exhibiting a yield stress
(i) Static equilibrium
The question of whether or not a sphere will settle in an unsheared viscoplastic
material has received considerable attention in the literature [Chhabra and
Uhlherr, 1988; Chhabra, 1993a]. For the usual case where the sphere is acted
upon by gravity, it is convenient to introduce a dimensionless group, Y, which
denotes the ratio of the forces due to the yield stress and due to gravity.
Neglecting numerical constants, the simplest definition of Y is
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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