Shear Viscosity Of Fluid Research Articles

Friction Theory Modeling of the Non-Newtonian Viscosity of Crude Oils

Rheological behavior is key for the evaluation, simulation, and development of petroleum reservoirs. In previous papers, friction theory models have been used to develop accurate, even reference quality, descriptions of the Newtonian shear viscosity of fluids. The friction theory has also been successfully used to accurately model an ample range of reservoir fluids ranging from natural gas to heavy oils (with viscosities up to thousands of mPa s). In this work, the basic friction theory approach has been further extended to the description of the non-Newtonian shear viscosity of crude oils. The extension is carried out by modifying the basic approach by further introducing a shear rate dissipation parameter for the scaling of the non-Newtonian behavior and a wax-appearance-related temperature. The resulting approach is straightforward and can reproduce the non-Newtonian behavior of crude oils with an accuracy close to the experimental uncertainty. The extended model is consistent with the overall friction theory approach and can be applied to the full range of oil reservoir production conditions, which is demonstrated by the ability of the model to calculate the expected rheological properties of a reconstituted reservoir fluid. In its current form, the proposed model has three adjustable parameters for a full characterization of the investigated oils, and no further parameters are needed in case the fluid is reconstituted. The model is able to reproduce the experimental Newtonian and non-Newtonian rheology over the wide temperature ranges of the studied waxy oils to within an overall average absolute percentage deviation under 15%. Consistent with previous investigations, the addition of a natural gas should yield lower deviations for the reconstituted fluid.

Reversing the perturbation in nonequilibrium molecular dynamics: an easy way to calculate the shear viscosity of fluids.

A nonequilibrium method for calculating the shear viscosity is presented. It reverses the cause-and-effect picture customarily used in nonequilibrium molecular dynamics: the effect, the momentum flux or stress, is imposed, whereas the cause, the velocity gradient or shear rate, is obtained from the simulation. It differs from other Norton-ensemble methods by the way in which the steady-state momentum flux is maintained. This method involves a simple exchange of particle momenta, which is easy to implement. Moreover, it can be made to conserve the total energy as well as the total linear momentum, so no coupling to an external temperature bath is needed. The resulting raw data, the velocity profile, is a robust and rapidly converging property. The method is tested on the Lennard-Jones fluid near its triple point. It yields a viscosity of 3.2-3.3, in Lennard-Jones reduced units, in agreement with literature results.

Shear Viscosity of a Fluid Composed of Infinitely-Thin Hard Needles

The shear viscosity of an ideal gas composed of infinitely-thin hard needles was studied by the molecular dynamics simulation. The shear viscosity of the hard-needle fluid increases linearly with increasing density at high densities, though it is almost constant at low densities. No anomaly of the shear viscosity is detected around the density at which the self diffusion coefficient has the minimum. The Stokes–Einstein relation does not hold in the hard-needle fluid.

Approach to the non-equilibrium time-periodic state in a ‘steady’ shear flow model

The standard non-equilibrium molecular dynamics algorithm for steady shear flow (SLLOD) employs Lees—Edwards periodic boundary conditions. It is not widely known that these boundary conditions make the system non-autonomous. The ‘steady state’ shear stress is in fact time periodic. The standard response theory derivations for steady shear do not take proper account of these non-autonomous terms. In this paper we correct this deficiency. We show that these non-autonomous terms invalidate the Green-Kubo relation for the finite frequency shear viscosity of fluids under Lees-Edwards periodic boundary conditions.

Viscosity prediction for perfluoropolyalkylether fluids

The temperature dependence of a fluid's shear viscosity is critical in determining its suitability as a liquid lubricant over an extended temperature range. We have applied van Krevelen's equations to a series of ten linear and branched perfluropolyalkylethers (PFPAEs) to predict viscosity-temperature. Calculated viscosities were a factor of ten or more greater than experiment at all temperatures, indicating that these “universal” equations are inadequate for these atypical fluids. Therefore, new semi-empirical viscosity equations have been derived and parameterized specifically for PFPAEs utilizing recent data. The new equations predict values within a factor of two of experimental viscosities in almost all systems, and hence should be useful in the molecular design of new PFPAE fluids for high temperature lubricants.

Measurement of pressure loss in the flow of polymer solutions through packed beds of particles

Flow behavior of polymer solutions through packed beds of particles, which are used as a model of porous media, is experimentally examined. Two packing patterns are prepared and the test fluids used here are aqueous solutions of polyacrylamide (PAA) at three different concentrations. In the measurement of pressure loss, it is observed that the curve of pressure loss makes a sudden change at the critical flow rate. Below the critical flow rate, the pressure loss depends on the shear property of the fluids and can be expressed by the modified Darcy’s law applying the power law model to the shear viscosity of fluids. Beyond the critical flow rate, however, the transient elongational property of the fluids dominates the flow behavior in packed beds of particles and yields the excess pressure loss for the PAA solutions.

Measurement of Pressure Loss in the Flow of Polymer Solutions through Packed Beds of Particles

Flow behaviour of polymer solutions through packed beds of particles, which are used as a model of porous media, is experimentally examined. Two packing patterns are prepared and the test fluids used here are aqueous solutions of polyacrylamide(PAA) at three different concentrations. In the measurement of pressure loss, it is observed that the curve of pressure loss makes a sudden change at the critical flow rate. Below the critical flow rate, the pressure loss depends on the shear property of the fluids and can be expressed by the modified Darcy's law applying the power law model to the shear viscosity of fluids. Beyond the critical flow rate, however, the transient elongational property of the fluids dominates the flow behaviour in packed beds of particles and yields the excess pressure loss for the PAA solutions.

The effect of finite phonon and roton mean free paths on the attenuation of fourth sound in HeII filled porous solid

Measurements of the attenuation of fourth sound in a HeII filled porous solid always show anomalously high values at low temperatures [M. A. Kriss, UCLA thesis (1969); H. J. Lauter and H. Wiechert, J. Low Temp. Phys. 36, 139 (1979); S. R. Baker, UCLA thesis (1985)]. It is shown that this anomaly can be attributed to a reduction in the apparent normal fluid shear viscosity due to the finite mean free paths of phonons and rotons. Results of a model calculation of the mean free path correction to the attenuation of fourth sound in a HeII filled porous solid, which separately treats the average drift of phonons and rotons as the flow of an ideal gas through a porous solid [A. E. Scheidegger, The Physics of Flow Through Porous Media, Third Edition, 1974, p. 173], compare very well with measurements made in 1‐μ packed powder down to 1.1 K at SVP, where the observed anomaly amounts to more than an order of magnitude. [Work supported by ONR.]

On the Deformation of an Elastic Particle Falling in a Viscous Fluid

The steady motion of a flexible solid particle in a quienscent unbounded viscous fluid is investigated theoretically. It is assumed that the particle is a homogeneous, isotropic elastic body obeying Hooke's law and that the undeformed particle is spherical in shape. It is further assumed that the motion of fluid obeys the Stokes equation. It is shown that for small values of the parameter α=η U 0 / G R 0 , where η is the shear viscosity of fluid, G the shear modulus of the particle and U 0 the terminal settling velocity of a rigid particle whose radius is R 0 , the particle deforms into a prolate spheroid and the deviation from a sphere is in proportion to α 2 . The effect of the deformation on the terminal settling velocity of the particle is also included in the analysis.

Viscosity of steam in the critical region

The shear viscosity of fluids exhibits an anomalous enhancement in the close vicinity of the critical point. A detailed experimental study of the viscosity of steam in the critical region has been reported by Rivkin and collaborators. A reanalysis of the experimental data indicates that the behavior of the viscosity of steam near the critical point is similar to that observed for other fluids near the critical point. An interpolating equation for the viscosity of water and steam is presented that incorporates the critical viscosity enhancement.

Improved acoustic viscosimeter technique

An improved technique has been developed for studies of the shear viscosity of fluids. It utilizes an acoustic resonator as a four-terminal electrical device; the resonator’s amplitude response may be determined directly and simply related to the fluid’s viscosity. The use of this technique is discussed briefly and data obtained in several fluids is presented. Subject Classification: [43]35.10, [43]35.68; [43]85.52.

Dense fluid shear viscosity and thermal conductivity—the excess

\Ve have developed a nonequilibrium molecular dynamic method to directl), simulate dense fluid transport (Ashurst and Hoover, 1975). The trajectories of N interacting atoms in a £i.,ed volume V are numerically computed. External forces, which are restricted to special boundary regions, do work and extract heat in order to maintain the hydro­ dynamic boundary conditions which produce a steady shear-momentum or heat flux. The transport coefficient is deternlined from the time average of the flux and corre­ sponding gradient in the volume V . . Experimental observation of dense fluid shear viscosity and thermal conductivity data reveals that the excess co­ efficient, that part above the temperature-dependent dilute gas value, is almost temperature independent (Diller et aI., 1970; Hanley et al., 1972). In order to calculate repre­ sentative dense fluid transport coefficients, we have se­ lected the Lennard-Jones potential (twelfth-power repul­ sion with sixth-power attraction) as a simple, yet realistic, atomic potential. Mos.t atomic interactions occur with en­ .ergy of order kT; thus, for high temperatures, the Lennard' Jones potential is effectively a single inverse power poten­ tiaL The single inverse nth power potentials have special scaling features since the potential and its derivatives de­ pend only upon the combination of energy and particle size feTn. Thus, if the density and temperature are com­ bined into one variable x [== (density) (temperature) -Un], then all svstems with identical scaled initial conditions and the same' x value will have identical dynamic evolution (Hoover et aI., 1971). The reduced excess transport coeffi­ cients times (dkT) 1/2+2/11 are functions of x only, not density and temperature separately, throughout the £uid phase. Since, at high teD,lperature, the repulsive core potential dominates momentum transport, the high-temperature Lennard-Jones shear viscosity must approach the scaling behavior of the inverse-12th-power viscosity. I\'onequilib­ rium molecular dynamic calculations for the Lennard-Jones shear viscosity have shown this to be true and we have found that the scaling is sllccessful even at the triple point (Nc?/V :::: 0.8.5, kTh = 0,70). The LenHard-Jolles shear viscosity has been calculated (with 108 and 216 atoms) along two isotherms co~respondillg to room temperature forhvdrogen and helium (kT/ f :::: 3.5 and 28) for densi­ , ~ [ , ( ,,' , / 1 I 1 Th tieS up to reezmg \1, rr , = ,0 i, see ·lgllre. 8 cnlcubted redl;cPci excess shear viscosity A'l) for x > ....0.5 is well descrikJ by the simple expression

Nonlinear effects in the shear viscosity of fluids near the critical point

We present a microscopic theory for the nonlinear shear viscosity of fluids near the critical point, and find that dependence on shear gradients should be observable in capillary viscometer experiments. We suggest that the leveling off (cusplike behavior) of viscosities that has been observed experimentally may be a result of shear gradient effects. Further experiments to test our theory are suggested.

Shear gradient dependence of the viscosity of critical mixtures

We present a theory of the nonlinear shear viscosity of fluids near the critical point, and suggest that the experimentally observed leveling off (cusplike behavior) of the excess viscosity may be due to shear gradient effects.