Chemical Engineers' Portable Handbook
Emphasizing practice-oriented design and approaches, this guide offers a presentation of the salient and important aspects of chemical engineering for practicing professionals.
TABLE OF CONTENTS Chemical Engineers' Portable Handbook
Chapter 3: Fluid Flow
Introduction
All matter is subject to deformation and flow. In the case of liquids and gases in the simplest general manner a shearing stress ? yx can be related to a velocity gradient by means of a property of the system (viscosity ?).
| (3-1) |  |
The ? yx (shear stress) is a momentum flux and ? a momentum conductivity similar to thermal conductivity in heat transfer.
When the viscosity of the fluid is independent of shear stress, or velocity gradient (rate of shear), or time the fluid is Newtonian. In such fluids viscosity can be changed only by temperature or pressure or some combination.
There are a number of categories of fluid behavior which are summarized in Table 3-1.
| Category | Description | Examples |
|---|---|---|
| 1. Newtonian | Obeys Newton's law of viscosity ? yx = - ?( dv xdy) ? (viscosity) not affected by shear rate or time | Water, organic liquids, air, other gases |
| 2. Simple non-Newtonian | Affected by rate of shear ? yx = - ? app( dV x/ dy) ? app = ?( dV x/ dy) | Polymer solutions, polymer melts, foods, cement, certain slurries |
| 3. Complex non-Newtonian | Viscoelastic behavior ? app = ?( dV x/ dy), time) | Thixotropic, rheopectic, viscoelastic |
| 4. Fluids affected by external force field | ? = ?( dV x/ dy), external force) | Magneto-hydrodynamic fluids, electro-viscous fluids |
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