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Dilute solution normal stresses

In packed beds of particles possessing small pores, dilute aqueous solutions of hydroly2ed polyacrylamide will sometimes exhibit dilatant behavior iastead of the usual shear thinning behavior seen ia simple shear or Couette flow. In elongational flow, such as flow through porous sandstone, flow resistance can iacrease with flow rate due to iacreases ia elongational viscosity and normal stress differences. The iacrease ia normal stress differences with shear rate is typical of isotropic polymer solutions. Normal stress differences of anisotropic polymers, such as xanthan ia water, are shear rate iadependent (25,26). [Pg.140]

Although hydrogen cyanide is a weak acid and is normally not corrosive, it has a corrosive effect under two special conditions (/) water solutions of hydrogen cyanide cause transcrystalline stress cracking of carbon steels under stress even at room temperature and in dilute solution and (2) water solutions of hydrogen cyanide containing sulfuric acid as a stabilizer severely corrode steel (qv) above 40°C and stainless steels above 80°C. [Pg.376]

Akers, L.C., Williams, M.C. Oscillatory normal stresses in dilute polymer solutions. J. Chem. Phys. 51,3834-3841 (1969). [Pg.171]

Osaki,K., Sakato.K., Fukatsu,M., Kurata,M., Matusita,K., Tamura,M. Normal stress effect in dilute polymer solutions. III. Monodisperse poly-a-methylstyrene in chlorinated biphenyl. J. Phys. Chem. 74,1752-1756 (1970). [Pg.172]

The same statement can be made about inelastic non-Newtonian fluids, such as the Power Law fluid, from a mathematical solution point of view. In reality, most non-Newtonian fluids are viscoelastic and exhibit normal stresses. For fluids such as those (i.e., fluids described by constitutive equations that predict normal stresses for viscometric flows), theoretical analyses have shown that secondary flows are created inside channels of nonuniform cross section (78,79). Specifically it can be shown that a zero second normal stress difference is a necessary (but not sufficient) condition to ensure the absence of secondary flow (79). Of course, the analyses of flows in noncircular channels in terms of constitutive equations—which, strictly speaking, hold only for viscometric flows—are expected to yield qualitative results only. Experimentally low Reynolds number flows in noncircular channels have not been investigated extensively. In particular, only a few studies have been conducted with fluids exhibiting normal stresses (80,81). Secondary flows, such as vortices in rectangular channels, have been observed using dyes in dilute aqueous solutions of polyacrylamide. Interestingly, these secondary flow vortices (if they exist) seem to have very little effect on the flow rate. [Pg.732]

Comparison of the dielectric and viscoelastic relaxation times, which, according to the above speculations, obey a simple relation rn = 3r, has attracted special attention of scholars (Watanabe et al. 1996 Ren et al. 2003). According to Watanabe et al. (1996), the ratio of the two longest relaxation times from alternative measurements is 2-3 for dilute solutions of polyisobu-tilene, while it is close to unity for undiluted (M 10Me) solutions. For undiluted polyisoprene and poly(d,/-lactic acid), it was found (Ren et al. 2003) that the relaxation time for the dielectric normal mode coincides approximately with the terminal viscoelastic relaxation time. This evidence is consistent with the above speculations and confirms that both dielectric and stress relaxation are closely related to motion of separate Kuhn s segments. However, there is a need in a more detailed theory experiment shows the existence of many relaxation times for both dielectric and viscoelastic relaxation, while the relaxation spectrum for the latter is much broader that for the former. [Pg.154]

Figure 3.37 Negative ratio of the second to the first normal stress coefficients versus stress ratio. Vi /a for various dilute solutions (concentration < 0.6 wt% closed symbols) and entangled solutions (concentration > 1 wt% open symbols). (Reprinted with permission from Magda et al.. Macro-molecules 26 1696. Copyright 1993, American Chemical Society.)... Figure 3.37 Negative ratio of the second to the first normal stress coefficients versus stress ratio. Vi /a for various dilute solutions (concentration < 0.6 wt% closed symbols) and entangled solutions (concentration > 1 wt% open symbols). (Reprinted with permission from Magda et al.. Macro-molecules 26 1696. Copyright 1993, American Chemical Society.)...
Figure 6.17 Normalized intrinsic viscosity [r ]/[)7]o for a dilute solution of poly(y-benzyl-L-glutamate) (PBLG) = 208,000) in m-cresol. The line is a calculation for the rigid-dumbbell model, with the relaxation time t = lj6Dro adjusted to the value 10- sec to obtain a fit. The stress tensor for a suspension of rigid dumbbells is given by Eq. (6-36) with Cstr replaced by k T/Dro-(From Bird et al. 1987 data from Yang 1958, Dynamics of Polymeric Liquids, VoL 2, Copyright 1987. Reprinted by permission of John Wiley Sons, Inc.)... Figure 6.17 Normalized intrinsic viscosity [r ]/[)7]o for a dilute solution of poly(y-benzyl-L-glutamate) (PBLG) = 208,000) in m-cresol. The line is a calculation for the rigid-dumbbell model, with the relaxation time t = lj6Dro adjusted to the value 10- sec to obtain a fit. The stress tensor for a suspension of rigid dumbbells is given by Eq. (6-36) with Cstr replaced by k T/Dro-(From Bird et al. 1987 data from Yang 1958, Dynamics of Polymeric Liquids, VoL 2, Copyright 1987. Reprinted by permission of John Wiley Sons, Inc.)...
Polymeric solutions are inherently viscoelastic due to their long molecular chains. Dilute polymeric solutions will be of interests for microfluidic and nanofluidic applications, due to their ease of implementation. Since the polymer coils in a dilute solution are isolated and independent in their molecular movements, their viscoelastic behavior can be explained by the deformation of the individual coil or molecule in the stream [2,3]. As a result, the viscoelasticity of polymer solutions is generally attributed to the deformation of polymer chains and the consequent generation of unequal normal stresses. [Pg.3436]

James, D.F. Method for measuring normal stresses in dilute polymer solutions. Trans. Soc. Rheol. 19 (1975) 67-72... [Pg.160]

Tomita, Y. and Mochimaru, Y. Normal stress measurement of dilute polymer solutions. J. Non-Newtonian Fluid Mech. 7, (1980) 235-255. [Pg.435]

The FENE-P model is able to prediet qualitatively many effects in dilute polymer solutions sueh as shear thinning, first normal stress difference, and a stififer response in extensional viscosity. The model is an improvement on the Maxwell model, but it does not always behave well in transient flows. [Pg.24]

Housiadas and Tanner (2009), following the approach of Greco et al. (2005), have used a perturbation analysis to obtain the analytical solution for the pressure and the velocity field up to 0 (pDe) of a dilute suspension of rigid spheres in a weakly viscoelastic fluid, where

volume fraction of the spheres and De is the Deborah number of the viscoelastic fluid. The analytical solution was used to calculate the bulk first and second normal stress in simple shear flows and the elongational viscosity. The main results are... [Pg.85]

Correlation Between Steady-Shear and Oscillatory Data. The viscosity function is by far the most widely used and the easiest viscometric function determined experimentally. For dilute polymer solutions dynamic measurements are often preferred over steady-shear normal stress measurements for the determination of fluid elasticity at low deformation rates. The relationship between viscous and elastic properties of polymer liquids is of great interest to polymer rheologists. In recent years, several models have been proposed to predict fluid elasticity from shear viscosity data. [Pg.58]

The extensional thickening of polymer solutions is one form of viscoelastic behavior. This ability to support a tensile stress can also be demonstrated in a tubeless syphon with dilute aqueous solutions of polsrmers such as polyacrylamide or polyethylene oxide. If you suck up solution with a medicine dropper attached to a water aspirator and then lift the dropper out of the solution, the solution will still be sucked up. In shear, viscoelastic fluids develop normal stresses, which causes rod climbing on a rotating shaft, as opposed to the vortex and depressed surfaces that form with Newtonian liquids. Polsrmer solutions and semiliquid poljnners exhibit other viscoelastic behaviors, where, on short time scales, they behave as elastic solids. Silly putty, a childrens toy, can be formed into a ball and will slowly turn into a puddle if left on a flat surface. But if dropped to the floor it boimces. [Pg.1405]

Second, data for the somewhat more concentrated polystyrene solutions of Ashare whose primary normal stress differences are portrayed in Fig. 2-10 are represented by curves B and C. At 1% concentration, where the molecules overlap somewhat but are probably not entangled, there is a moderate drop in r/, somewhat more than in the extremely dilute solution at 5% concentration, where entanglements probably exist, the non-Newtonian effect is much more pronounced and, over about two decades of 7, ri follows rather closely a power-law relation. It is of interest that the onset of non-Newtonian flow occurs at a much higher shear rate for 1% than for 5% concentration, just as the normal stress differences achieve significant magnitudes at a higher shear rate for 1% than for 5% concentration in Fig. 2-10. Quantitative correlations will be introduced in later chapters. [Pg.52]


See other pages where Dilute solution normal stresses is mentioned: [Pg.133]    [Pg.107]    [Pg.114]    [Pg.201]    [Pg.630]    [Pg.299]    [Pg.137]    [Pg.137]    [Pg.139]    [Pg.146]    [Pg.165]    [Pg.563]    [Pg.19]    [Pg.133]    [Pg.447]    [Pg.778]    [Pg.6750]    [Pg.7176]    [Pg.761]    [Pg.195]    [Pg.50]    [Pg.178]    [Pg.108]    [Pg.123]   
See also in sourсe #XX -- [ Pg.171 ]




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