Shear diagram fluids

The major types of fluid flow behavior can be described by means of basic shear diagram of shear rate versus shear stress, such as Figures 1-2 and 1-3. In Figure 1-2, the shear stresses are plotted against the shear rates (independent variable) which is the conventional method. However, some authors plot shear rates against the shear stresses (independent variable) as shown in Figure 1-3. With the introduction of controlled-stress rheometers, the use of shear stress as the independent variable is often desirable. 

Time-Independent Non-Newtonian Fluids. Time-independent non-Newtonian fluids are characterized by having the fluid viscosity as a function of the shear rate (or shear stress). However, the fluid viscosity is independent of the shear history of the fluid. Such fluids are also referred to as non-Newtonian viscous fluids". Figure 1 shows a typical shear diagram for the various time-independent non-Newtonian fluids. 

Figure 1. Shear diagram for the various type of fluids.

Olmsted PD (1999b) Two-state shear diagrams for complex fluids in shear flow. Europhys Lett 48(3) 339-345... 

Figure 4-185. Shear stress-shear rate diagram, (a) Newtonian fluid, (b) Bingham plastic fluid, (c) Power iaw fiuid. (d) Herschei-Buckiey fiuid.

Fig. 10.7 Schematic diagram of sphere rotating in a fluid in simple shear,...

Since fluid shear rates vary enormously across the radius of a capillary tube, this type of instrument is perhaps not well suited to the quantitative study of thixotropy. For this purpose, rotational instruments with a very small clearance between the cup and bob are usually excellent. They enable the determination of hysteresis loops on a shear-stress-shear-rate diagram, the shapes of which may be taken as quantitative measures of the degree of thixotropy (G3). Since the applicability of such loops to equipment design has not yet been shown, and since even their theoretical value is disputed by other rheologists (L4), they are not discussed here. These factors tend to indicate that the experimental study of flow of thixotropic materials in pipes might constitute the most direct approach to this problem, since theoretical work on thixotropy appears to be reasonably far from application. Preliminary estimates of the experimental approach may be taken from the one paper available on flow of thixotropic fluids in pipes (A4). In addition, a recent contribution by Schultz-Grunow (S6) has presented an empirical procedure for correlation of unsteady state flow phenomena in rotational viscometers which can perhaps be extended to this problem in pipe lines. 

Fig. 1 a, b. Schematic diagram of a flow of fluid under combined shear conditions a — between flatly parallel plates under the action of pressure difference AP = P -P2 (the upper plane moves in the direction transverse to the main flow) b — between two coaxial cylinders rotating towards one another at angular velocities flj and fi2... 

U.S. laundry detergents are typically Newtonian fluids and the viscosity of six commercial products is summarized in Figure 4.23. Several lots of each product, labeled A to F, were obtained and measurements completed at room temperature, 20 to 25°C, as a function of shear rate from 0 to 500 sec-1. Atypical shear stress-shear rate diagram is shown in Figure 4.24 for a product sampled from a 50 11 oz container. All six products tested are Newtonian with a viscosity less than 0.5 Pa s at room temperature, 21 to 23°C, with the shear rate ramped from 0 to 500 sec-1 at an acceleration rate of 0.83 sec-2. Newtonian behavior was confirmed through additional step shear rate measurements within the selected shear rate range. 

Fig. 15. Diagram showing the coherence between viscosity and shear rate The viscosity of viscoelastic substances declines with increasing velocity gradient (shear rate). This behaviour characterises pseudoelastic fluids...

Figure 14.17 Schematic diagram and TEM image (scale bar=50 nm) of a partial PANI/ MCM-41 nanocomposite (a) and flow curve of shear stress-shear rate of PANI/MCM-41 nanocomposite ER fluid (b). Reprinted with the permission from Ref [99]. Copyright 2004 American Chemical Society.

Fig. 3 Schematic diagram of the propagation of an acoustic shear wave launched by a TSM resonator loaded with a viscoelastic overlayer and exposed to a fluid. Note the progressive zero, significant, and dramatic attenuations of the wave on moving from the rigid layer (electrode plus surface feature-entrapped material) to the viscoelastic solid to the fluid. The acoustic decay lengths in these three regions are, respectively, infinity, [2C/ 1 — C7C ] / /(ft)ypf), and t A[G"//(o in the latter two instances, typical values are 2 and 0.2 pm.

Non-Newtonian Fluids in Mkrofluidics, Fig. 2 Schematic diagram of two simple flow types, (a) Simple shear flow between parallel rigid surfaces with gap... 

Fig. 82 will illustrate the conditions in this the coefficient of viscosity indicated by Poiseuille s law is plotted against shearing stress. A normal liquid is characterized by a constant rj and appears in the diagram as a horizontal line. Elastic fluids, or solutions, have a larger 77 at small t values, which decreases slowly to the Newtonian value. Super-fluid solutions, on the other hand, show normal behavior under the smallest shearing forces and progressively lower values for 77 with increasing r. 

Virtually all devices that use controllable MR fluids operate in a valvemode, direct-shear mode, or a combination of these two modes. Diagrams of the basic valve and direct-shear modes are shown in Fig. 6.76. Examples of valve-mode devices include dampers, and shock absorbers. Examples of direct shear-mode devices include clutches, brakes, chucking and locking devices, and some dampers. 

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