Effect of container boundaries
The problem discussed so far relates to the motion of a single spherical particle
in an unbounded, or effectively infinite, expanse of fluid. If other particles are
present in the neighbourhood of the sphere, its settling velocity will be
influenced and the effect will become progressively more marked as the
concentration of particles increases. There are three contributory factors. First,
as the particles settle, the displaced liquid flows upwards. Secondly, the particle
experiences increased buoyancy force owing to the higher density of the
suspension. Finally, the flow pattern of the liquid relative to the particles will
be altered thereby affecting the velocity gradients. The sedimentation of
concentrated suspensions in non-Newtonian fluids is discussed in section 5.2.6
.while the effect of the vessel walls is discussed here
The walls of the vessel containing the liquid exert an extra retarding effect
on the terminal falling velocity of the particle. The upward flow of the
displaced liquid, not only influences the relative velocity, but also sets up
a velocity profile in the confined geometry of the tube. This effect may be
quantified by introducing a wall factor, f, which is defined as the ratio of the
terminal falling velocity of a sphere in a tube, Vm, to that in an unconfined
liquid, V, viz.,
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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