3.9 New-Newtonian Flows
Thomas F. Irvine Jr. and Massimo Capobianchi
Introduction
An important class of ?uids exists which differ from Newtonian ?uids in that the relationship between
the shear stress and the ?ow ?eld is more complicated. Such ?uids are called non-Newtonian or
rheological ?uids. Examples include various suspensions such as coal?water or coal?oil slurries, food
products, inks, glues, soaps, polymer solutions, etc.
An interesting characteristic of rheological ?uids is their large ?apparent viscosities?. This results in
laminar ?ow situations in many applications, and consequently the engineering literature is concentrated
on laminar rather than turbulent ?ows. It should also be mentioned that knowledge of non-Newtonian
?uid mechanics and heat transfer is still in an early stage and many aspects of the ?eld remain to be
clari?ed.
In the following sections, we will discuss the de?nition and classi?cation of non-Newtonian ?uids,
the special problems of thermophysical properties, and the prediction of pressure drops in both laminar
and turbulent ?ow in ducts of various cross-sectional shapes for different classes of non-Newtonian ?uids.
Classification of Non-Newtonian Fluids
It is useful to ?rst de?ne a Newtonian ?uid since all other ?uids are non-Newtonian. Newtonian ?uids
possess a property called viscosity and follow a law analogous to the Hookian relation between the
stress applied to a solid and its strain. For a one-dimensional Newtonian ?uid ?ow, the shear stress at
a point is proportional to the rate of strain (called in the literature the shear rate) which is the velocity
gradient at that point. The constant of proportionality is the dynamic viscosity, i.e.,
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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