Dimensional considerations for visco-elastic fluids
It has been a common practice to describe visco-elastic fluid behaviour in
steady shear in terms of a shear stress ( yx) and the first normal stress difference
(N1); both of which are functions of shear rate. Generally, a fluid relaxation or
characteristic time, f, (or a spectrum) is defined to quantify the visco-elastic
behaviour. There are several ways of defining a characteristic time by
combining shear stress and the first normal stress difference, e.g. the so-called
Maxwellian relaxation time is given by
constant values, f also approaches a constant value. Though equation (1.31)
defines a fluid characteristic time as a function of shear rate, its practical utility
is severely limited by the fact that in most applications, the kinematics (or shear
rate) is not known a priori. Many authors [Leider and Bird, 1972; Grimm,
1978] have obviated this difficulty by introducing the following alternative
definition of f
This definition is based on the assumption that both N1 and yx can be approximated
as power-law functions of shear rate in the range of conditions of
interest, that 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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