Viscosity pressure-dependent

We use a moderately temperature- and pressure-dependent viscosity which is written in nondimensional form as... 

The HCToolkit is a set of Perl modules that implement four equations of state, two flash algorithms and a multi-component, multiphase, temperature- and pressure-dependent viscosity prediction. The modules have been successfully run on MS Windows, Mac OSX and Redhat Linux. These modules can be called from another Perl code, or (via an ActiveX interface) from a front-end written in either Visual Basic or a VBA application such as Excel. 

In injection molding the pressure level can be very high, so that the assumption of pressure-independent viscosity can lead to incorrect simulation results. Some authors (e.g., Sherbelis and Friedl 1996) have considered pressure-dependent viscosity in their simulations. However, caution should be made because the pressure-dependent viscosity might invalidate the Hele-Shaw approximation. When the viscosity varies with pressure, the pressure gradient in the flow direction (say, xi direction) and that in the thickness direction have the following relation 0F/0X3 = 7i3(0j7/0P)(0F/0xi) (Huilgol and You 2006). Only if yi3(0f//0P) 1,... 

It is of course possible to redo the simple extruder analysis with a pressure-dependent viscosity. Equation 4.7b defines the die characteristic equation. Solution of the momentum equation with a moving wall then leads directly to Equation 3.15b for the wall velocity as a function of the flow rate and system geometry, even when the viscosity is pressure dependent. 

The treatment of the pressure-dependent viscosity follows an analysis for a cyhndrical cross section in the following, where an exact solution with a parabolic velocity profile for the isothermal case can be found ... 

Thereafter, using Eqs. (6.4) and (6.5) and knowing the densitjr of the ball and of the hquid allows the determination of the viscosity of the viscous liquid. Falling sphere viscometer can be used for high-pressure measurement, as those carried out in a superpress. Pressure indeed appears to change viscosity. Free volume theory refinements (see Section 6.1.3.4) incorporate pressure dependence. Viscosities of sihcates and aluminosilicates are reported to decrease with increasing pressure. 

Pen well et al. (1971) proposed the following form of pressure-dependent viscosity r](p,T, y) in the shear-thinning region of a flow curve in a capillary die ... 

Laun, H. M. Pressure dependent viscosity and dissipative heating in capillary rheometry of polymer... 

The viscosity, themial conductivity and diffusion coefficient of a monatomic gas at low pressure depend only on the pair potential but through a more involved sequence of integrations than the second virial coefficient. The transport properties can be expressed in temis of collision integrals defined [111] by... 

There is one important caveat to consider before one starts to interpret activation volumes in temis of changes of structure and solvation during the reaction the pressure dependence of the rate coefficient may also be caused by transport or dynamic effects, as solvent viscosity, diffiision coefficients and relaxation times may also change with pressure [2]. Examples will be given in subsequent sections. 

Measuring tire pressure dependence of k at different temperatures shows that the apparent activation energy at constant viscosity decreases with increasing viscosity [46, ( figure A3,6,8). From a detailed analysis one... 

In gases at moderate pressures the viscosity is almost independent of pressure, so Che factor in brackets on the right hand side does not depend on a or p, and it follows chat... 

At high neutralization levels with alkaH metal ions, many ionomers spontaneously form coUoidal suspensions in water when stirred vigorously at 100—150°C under pressure. Depending on soHds content and acid level, the dispersions range in viscosity from water-like to paste-like. These provide convenient methods for applying thin coatings of ionomers to paper and other substrates. 

A web of molten plastic is pulled from the die into the nip between the top and middle roUs. At the nip, there is a very small rolling bank of melt. Pressure between the roUs is adjusted to produce sheet of the proper thickness and surface appearance. The necessary amount of pressure depends on the viscosity. For a given width, thickness depends on the balance between extmder output rate and the take-off rate of the pull roUs. A change in either the extmder screw speed or the puU-roU speed affects thickness. A constant thickness across the sheet requires a constant thickness of melt from the die. The die is equipped with bolts for adjusting the die-gap opening and with an adjustable choker bar or dam located inside the die a few centimeters behind the die opening. The choker bar restricts flow in the center of the die, helping to maintain a uniform flow rate across the entire die width. 

Gum-Saline. Gum is a galactoso—gluconic acid having molecular weight of approximately 1500. First used (16) in kidney perfusion experiments, gum—saline enjoyed great popularity as a plasma expander starting from the end of World War I. The aggregation state of gum depends on concentration, pH, salts, and temperature, and its coUoid oncotic pressure and viscosity are quite variable. Conditions were identified (17) under which the viscosity would be the same as that of whole blood. 

The pressure dependence of effective viscosity obviously depends upon the value of the momentum accommodation coefficient. Momentum accommodation data are relatively rare, but some representative data are given in Table 1. Note that all values are relatively close to unity. Because of this observation, momentum accommodation coefficients are normally assumed to be unity in applications... 

The density of a SCF is typically less than half that of the liquid state, but two orders of magnitude greater than that of a gas. Viscosity and diffusivity are also temperature and pressure dependent. 

Both viscosity and diffusivity change from gas-fike to fiquid-like with increasing pressure Viscosity and diffusivity (which is strongly related to viscosity) are also temperature- and pressure-dependent and, in general, an order of magnitude lower and higher at least than in the liquid phase, respectively. 

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