Forces viscosity

Dynamic similarity requires that the rado of input force, viscosity, density, and surface tension be equal. For the same fluid, only two of these four forces need be equal, because the density and viscosity will be the same [34, 29]. 

Effective porosity (Ne) is of more importance and, along with permeabihty (the ability of a material to transmit fluids), determines the overall ability of the material to store and transmit fluids or vapors readily. Where porosity is a basic feature of sediments, permeability is dependent upon the effective porosity, the shape and size of the pores, pore interconnectiveness (throats), and properties of the fluid or vapor. Fluid properties include capillary force, viscosity, and pressure gradient. 

Effects of Mechanical Energy or Forces Viscosity Sound velocity Density and specific gravity... 

In a shock wave the compression is tied to a change in entropy, the only source of which are the dissipative forces—viscosity and heat conductivity. In the calculation we obtain a negligible front depth and compression time in the shock wave. We emphasize that this is a result of the calculation, not an assumption necessary to write the conservation equations. 

The thixotropic effect is shown in Fig. 9.3. The viscosity curves are for a material that is exposed to first increasing and then decreasing shear rates. Thixotropy results from the ability of the dispersed particles to come together and form network structures when at rest or under low shearing forces. Viscosity decrease occurs when this structure breaks down due to shearing stress and the resistance to flow decreases. (See Fig. 9.4.)... 

Therefore, the molar conductivity is a parameter directly linked with the mobility and not with concentration. The basic unit is [S/m] per [mol/m ], or Sm /mol. The mobility, p, is related to the random molecular collisions and corresponding frictional force (viscosity t ) experienced by the migrating ion. The frictional force, f, is ideally related to the hydrodynamic radius, a, of the ion according to Stoke s law ... 

Manifestations of Intermolecular Forces Surface tension—the tendency for liquids to minimize their surface area—is a direct result of intermolecular forces. Viscosity—the resistance of liquids to flow—is another result of intermolecular forces. Both surface tension and viscosity increase with greater intermolecular forces. 

Normally, the deformation behavior of a viscous polymer is specified in terms of viscosity, a measure of a material s resistance to flow by shear forces. Viscosity is discussed for the inorganic glasses in Section 12.10. 

Apparent viscosity (greases) NFT 60-139 ASTM D 1092 Forced passage of the grease in a capillary tube... 

When fluid flow in the reservoir is considered, it is necessary to estimate the viscosity of the fluid, since viscosity represents an internal resistance force to flow given a pressure drop across the fluid. Unlike liquids, when the temperature and pressure of a gas is increased the viscosity increases as the molecules move closer together and collide more frequently. 

Viscosity is measured in poise. If a force of one dyne, acting on one cm, maintains a velocity of 1 cm/s over a distance of 1 cm, then the fluid viscosity is one poise. For practical purposes, the centipoise (cP) is commonly used. The typical range of gas viscosity in the reservoir is 0.01 - 0.05 cP. By comparison, a typical water viscosity is 0.5 -I.OcP. Lower viscosities imply higher velocity for a given pressure drop, meaning that gas in the reservoir moves fast relative to oils and water, and is said to have a high mobility. This is further discussed in Section 7. 

The paper discusses the application of dynamic indentation method and apparatus for the evaluation of viscoelastic properties of polymeric materials. The three-element model of viscoelastic material has been used to calculate the rigidity and the viscosity. Using a measurements of the indentation as a function of a current velocity change on impact with the material under test, the contact force and the displacement diagrams as a function of time are plotted. Experimental results of the testing of polyvinyl chloride cable coating by dynamic indentation method and data of the static tensile test are presented. 

The shear viscosity is an important property of a Newtonian fluid, defined in terms of the force required to shear or produce relative motion between parallel planes [97]. An analogous two-dimensional surface shear viscosity ij is defined as follows. If two line elements in a surface (corresponding to two area elements in three dimensions) are to be moved relative to each other with a velocity gradient dvfdx, the required force is... 

The modification of the surface force apparatus (see Fig. VI-4) to measure viscosities between crossed mica cylinders has alleviated concerns about surface roughness. In dynamic mode, a slow, small-amplitude periodic oscillation was imposed on one of the cylinders such that the separation x varied by approximately 10% or less. In the limit of low shear rates, a simple equation defines the viscosity as a function of separation... 

Horn R, Smith D T and Haller W 1989 Surface forces and viscosity of water measured between silica sheets Chem. Rhys. Lett. 162 404-8... 

Polymers owe much of their attractiveness to their ease of processing. In many important teclmiques, such as injection moulding, fibre spinning and film fonnation, polymers are processed in the melt, so that their flow behaviour is of paramount importance. Because of the viscoelastic properties of polymers, their flow behaviour is much more complex than that of Newtonian liquids for which the viscosity is the only essential parameter. In polymer melts, the recoverable shear compliance, which relates to the elastic forces, is used in addition to the viscosity in the description of flow [48]. 

Flow behaviour of polymer melts is still difficult to predict in detail. Here, we only mention two aspects. The viscosity of a polymer melt decreases with increasing shear rate. This phenomenon is called shear thinning [48]. Another particularity of the flow of non-Newtonian liquids is the appearance of stress nonnal to the shear direction [48]. This type of stress is responsible for the expansion of a polymer melt at the exit of a tube that it was forced tlirough. Shear thinning and nonnal stress are both due to the change of the chain confonnation under large shear. On the one hand, the compressed coil cross section leads to a smaller viscosity. On the other hand, when the stress is released, as for example at the exit of a tube, the coils fold back to their isotropic confonnation and, thus, give rise to the lateral expansion of the melt. 

Lubricants are added to lower interfacial frictional forces between individual particles and/or between particles and fonning die surfaces to improve compaction and ejection (i.e. extraction of the pressed compact from the fonning die). Individual particle surfaces can be lubricated by an adsorbed film that produces a smoother surface and/or decreases interiDarticle attraction. Fonning (die) surfaces can be lubricated by coating with a film of low-viscosity liquid such as water or oil. 

The dotted lines represent hydrogen bonds. The high boiling point and viscosity of the pure acid indicate strong intermolecular forces of this kind. 

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