Rheometry for non-Newtonian fluids*
2.1 Introduction
The rheological characterisation of non-Newtonian fluids is widely acknowledged
to be far from straightforward. In some non-Newtonian systems, such
as concentrated suspensions, rheological measurements may be complicated
by non-linear, dispersive, dissipative and thixotropic mechanical properties;
and the rheometrical challenges posed by these features may be compounded
by an apparent yield stress.
For non-Newtonian fluids, even the apparently simple determination of a
shear rate versus shear stress relationship is problematical as the shear rate
can only be determined directly if it is constant (or nearly so) throughout the
measuring system employed. While very narrow shearing gap coaxial cylinder
and cone-and-plate measuring geometries provide good approximations to this
requirement, such systems are often of limited utility in the characterisation
of non-Newtonian products such as suspensions, whose particulate/aggregate
constitutents preclude the use of narrow gaps. As most measuring geometries
do not approximate to constant shear rate, various measurement strategies have
been devised to overcome this limitation. The basic features of these rheometrical
approaches, and of the main instrument types for their implementation,
are considered below
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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