Pseudo-plastic flow

The pump ratio should increase when the power law index decreases. The practical lower limit is 1.5 and should be used for polymers with almost Newtonian flow characteristics. The upper limit of the pump ratio is 2.0 and should be used for polymers with very strong pseudo-plastic flow behavior. 

For the above pseudo-plastic flow, one may apply a power law fluid model, a Bingham model [9] or a Casson model [10]. These models are represented by the following equations respectively. 

In order to understand the nature and mechanisms of foam flow in the reservoir, some investigators have examined the generation of foam in glass bead packs (12). Porous micromodels have also been used to represent actual porous rock in which the flow behavior of bubble-films or lamellae have been observed (13,14). Furthermore, since foaming agents often exhibit pseudo-plastic behavior in a flow situation, the flow of non-Newtonian fluid in porous media has been examined from a mathematical standpoint. However, representation of such flow in mathematical models has been reported to be still inadequate (15). Theoretical approaches, with the goal of computing the mobility of foam in a porous medium modelled by a bead or sand pack, have been attempted as well (16,17). 

Venneker, B. C. H., Turbulent flow and gas dispersion in stirred vessels with pseudo plastic fluids , Ph.D. Thesis, Delft University of Technology, Delft, Netherlands (1999). 

The melt flow under isothermal conditions, when it is described by the rheological equation for the Newtonian or power law liquid, has been studied in detail63 66). The flow of the non-Newtonian liquid in the channels of non-round cross section for the liquid obeying the Sutterby equation have also been studied 67). In particular, the flow in the channels of rectangular and trigonal cross section was studied. In the analysis of the non-isothermal flow, attention should be paid to the analysis 68) of pseudo-plastic Bingham media. 

Cross, M.M. Rheology of non-Newtonian fluids a new flow equation for pseudo-plastic systems. J. Colloid Sci. 1965, 20, 417 37. 

Cream-colored, odorless, free-flowing powder. Dissolves readily in water with stirring to give highly viscous solus at Low concns. Forms strong films on evaporation of aq solns. Resistant to heat degradation. Aq solus are highly pseudo -plastic. 

Increases in both particle concentration and magnitude of intcrparticle forces may lead to an increase in the size of floes to such an extent that they form a particle network gel, see Chapter 13) which resists flow until the yield stress is reached. The system becomes first pseudo-plastic and then plastic. 

An alternative classification for shear thinning and thickening is pseudo-plasticity and diiatancy however, these flow categories are rather limited to the so-called power law fluids. The flow behavior of a power law fluid may be described by the e. pression... 

If flocculation occurs slowly, the viscosity, measured at low rates of shear, increases with time during the rest period after an efficient shearing. When this happens the paint is said to be thixotropic. If there is no dependence on time or on the previous treatment of the paint and if the viscosity decreases as the rate of shear increases, then the paint is said to be pseudo-plastic. If there is a minimum stress required before any flow can occur at all, the viscosity behaviour is said to be plastic. All these types of behaviour are, of course, contrary to Newton s equation and are grouped together under the heading of non-Newtonian viscosity. 

Deviations from Newtonian flow can occur when shear stress does not increase in direct proportion to shear rate. Such deviation may be in the direction of thickening (called dilatent flow) and in the direction of thinning (called pseudo plastic). Related to non-Newtonian flow is the behavior of thixotropic liquids when subjected to shear, as explained above. Flow behavior can be represented by the following equation ... 

The given presentation of the mechanism of the interaction of polymer molecules with turbulent flow admits a peculiar theoretical examination. The presence of polymer addition besides the increase of longitudinal viscosity is resulted in the appearance of such rheological solution properties as elastic plasticity, pseudo-plasticity, anisotropy. In [3] the influence of different rheological fluid characteristics on the wall turbulence is theoretically analyzed within the limits of monoharmonic approximation, which affords to take into account turbulent blows-out. Different variants of rheological behaviour were considered. For all that we succeded to show, that the decrease of turbulent friction arose only in mediums, possessing... 

Flow behavior index for pseudo-plastic non-Newtonian liquid (—) Number of orifices in a given multiorifice nozzle (—)... 

Let us now turn to VED. Its magnitude is the local scalar product (r y), which depends on the local melt viscosity and shear rate. As noted above, it is an appreciable heat source in flowing polymer melt streams. Since the melt viscosity is shear rate and temperature dependent, decreasing significantly with an increase in both, the dependence (sensitivity) parameters - the pseudo-plasticity index and the activation energy for flow - are important to the resulting local heatir. Local overheating, because of VED, may be created for melt elements that are exposed continuously to... 

Flow properties See melt-flow index, viscosity, pseudo-plastic fluid, and rheology. 

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