Effect Of Pseudoplasticity Research Articles

Effect of a homogeneous magnetic field on the viscoelastic behavior of magnetic elastomers

Viscoelastic behavior of highly elastic magnetic elastomers has been studied by three different experimental techniques: elongation, static and dynamic shears. It has been shown that the elastic modulus of the materials increases considerably in an external homogeneous magnetic field of up to 0.3 T (100-fold increase of the tangential modulus has been observed at small 1–4% deformations). The appearance of the new effect of pseudo-plasticity induced by the magnetic field has been observed leading to a considerable (up to 100-fold) increase in the shear loss modulus of the composites.

Static and Dynamic Performance Characteristics of Orifice Compensated Hydrostatic Flexible Journal Bearings with Non-Newtonian Lubricants

The combined effect of non-Newtonian lubricant behavior and bearing shell flexibility on the performance of an orifice compensated multirecess hydrostatic/hybrid journal bearing system is studied. The analysis considers the constitutive equations for the flow of a non-Newtonian lubricant through an orifice restrictor, the generalized Reynold's equation governing the flow of lubricant having variable viscosity and 3-D elasticity equations. The computed results demonstrate that loss in bearing performance due to the pseudo-plastic effect of the non-Newtonian lubricant can be mitigated by a proper selection of parameters such as the deformation coefficient (Ȼ4) and non-linearity factor ([Kbar]) or power law index (n).

Countercurrent Gas−Pseudoplastic Liquid Two-Phase Flow

Countercurrent flow limitation (flooding), two-phase flow patterns, and void fraction in countercurrent flow of gas−pseudoplastic liquids in a vertical and an inclined channel (with a 68° inclination angle with respect to the horizontal plane) were experimentally studied. The test section was a transparent tube, 2.36 m long with a 1.9 cm inner diameter. Aqueous 500 and 1000 ppm solutions of PERCOL 727 (a copolymer of sodium acrylate and acrylamide) with flow behavior indices of 0.58 and 0.35, respectively, were used as the liquid phase, and air constituted the gas phase. The gas and liquid superficial velocity ranges in the experiments were 0.5−198 and 0.8−34 cm/s, respectively. The flooding curves of both polymer solutions were similar for both angles of inclination and were similar to the flooding curves of low-viscosity Newtonian liquids. They thus indicate little effect of pseudoplasticity on flooding. The visually observed two-phase flow regimes were bubbly/slug, slug, slug/churn, and churn. Annular flow occurred only at near-flooding conditions. The flow regime transition lines showed significant differences with data representing a Newtonian liquid with a viscosity of the same order of magnitude as the polymer solution apparent viscosities. The slug flow pattern, characterized by Taylor bubbles, was the most dominant flow pattern. The measured void fractions were correlated based on the drift flux model, using different correlation parameters for bubbly/slug, and slug or slug/churn flow regimes.

Green part characterization and in situ monitoring of injection moulding : R.M. German et al (Pennsylvania State University, Pennsylvania, USA)

The rheological behavior of wax-based feedstocks has a direct impact on successful mold filling for parts produced by low-pressure powder injection molding. During a rheological test, segregation may occur within low-viscosity feedstocks, leading to errors in results, and to an improper evaluation of the flowability of powder-binder mixtures. The segregation occurring during rheological tests is not generally considered when measuring the viscosity profiles of such mixtures. In this study, the impact of testing time, testing protocol (increasing or decreasing shear rate), polymer degradation, powder deagglomeration, and temperature on the rheological properties of feedstocks was investigated. The segregation occurring during rheological testing produces a meaningful effect in low-viscosity feedstocks. Because the segregation is driven by the time spent in the molten state, the effects of segregation on viscosity were visible, particularly at the end of a long rheological test. During a short rheological test, the pseudoplastic effect occurring in wax-based feedstocks was only attributable to the binder molecules' orientation with respect to the flow. In this respect, and contrary to the information reported in literature, it was demonstrated that the dilatant effect observed was in fact more likely due to segregation occurring during the rheological test, rather than as a result of the elimination of the preferential layer formed during the pseudoplastic regime. Because the rheological properties of low-viscosity feedstocks were significantly influenced by the test duration, a rheological test duration of a few minutes must be used to precisely quantify the flowability of such feedstocks.

Non‐darcy forced convective heat transfer in a channel embedded in a non‐newtonian inelastic fluid‐saturated porous medium

AbstractThe present analysis investigates non‐Darcy forced convective heat transfer in a channel confined by two parallel walls subjected to uniform heat flux in a highly porous medium saturated with a non‐Newtonian power‐law fluid. Extensive numerical integrations have been carried out utilizing the Brinkman‐Forchheimer extension of the Darcy model in order to study the effects of pseudoplasticity, and Brinkman and Forchheimer terms on the heat transfer characteristics.

Approximate solutions for power-law fluid flow past a particle at low Reynolds numbers

A simple perturbation approximation is proposed for describing flow behaviour of particles immersed in a uniform flow and an extensional flow of power-law fluids. The present solution for particles in a uniform flow field is in good agreement with the numerical solution in the literature. Theoretical predictions indicate that the effect of pseudoplasticity on flow around particles in an extensional flow field is small compared with that for particles in a uniform flow field. From the viewpoint of perturbation techniques, existing analytical solutions based on linearization of the equations of motion for particle in a power-law fluid are re-examined. Mass transfer to a power-law fluid from a particle is also discussed.

On thermo-elastic-plastic analysis of heat-treatment processes including creep and phase changes

A method is described for calculating the stresses in a body during heat-treatment and for calculating the remaining residual stress distribution. Special attention is given to the thermo-elastic-plastic material behaviour which is highly temperature-dependent. A pseudo-plasticity effect due to microstresses appearing during phase transformations is taken into account. The stress analysis of a cylinder is performed using ADINA. Calculated results are compared with results obtained experimentally.

THE RESIDENCE TIME DISTRIBUTION FOR LAMINAR FLOW OF NON-NEWTONIAN LIQUIDS THROUGH HELICAL TUBES

Abstract The residence time distribution in a helically coiled tubular reactor is computed for laminar flow of inelastic non-Newtonian liquid at small Dean number. Effect of pseudoplasticity on the residence time distribution is explored. It was found that pseudoplaslicity of the liquid makes the residence time distribution narrower. The effect of dialalant fluid behavior is opposite but very small in magnitude. The results of numerical integrations are correlated with power law index, allowing predictions over a wide range of the index. The results could be used to predict conversion of reactions in a coiled reactor, such as continuous polymerization or fermentation reactors, where the reaction mixtures are likely to be non-Newtonian in nature. Results will be also useful in characterization of coiled chromatographic columns.

Some effects of pseudoplasticity on hold-up in aerated, agitated vessels

The flow curves of four pseudoplastic sodium carboxy methyl cellulose (CMC) solutions are reported. Each solution was air sparged at rates up to 1 vvm (vvm is the volumetric flow rate of air per minute per volume of liquid in the vessel) in a 0.56 m diameter agitated vessel of Rushton dimensions and power inputs (up to 2.0 W/kg) and hold-ups have been measured. The ratio of gassed to ungassed power versus aeration number is compared with similar data from the agitation of Newtonian fluids and is correlated by an empirical equation proposed by Kudrna. The reported hold-ups are in the range 1.5 – 8% and, for equivalent sparging and agitation conditions, increasing pseudoplasticity leads to decreasing hold-up. This decrease is due to an increasing proportion of large bubbles which have a short residence time. For each CMC solution, hold-up, aeration rate and power input can be related by ϵ H ∝ ϵ 0.3 V s 0.7 The technique for measuring hold-up allows surface topographies to be determined. These topographies suggest that when the level of agitation is well matched to the sparge rate, the upper surface of the dispersion is relatively level.

Features of the rheological behaviour of solutions of AB-type block copolymers of styrene and butadiene

Relations between viscosity and the rate of shear and elastic modulus G′ and between the dynamic viscosity ν′ and frequency have been investigated for solutions of diblock copolymers of styrene and butadiene in decalin and tetralin at 25° in the concentration interval from 0·05 to 50 g/dl. The observed effects of pseudoplasticity and anomalous frequency dependences of G′ are explained from the standpoint of formation of a macronetwork consisting of segregated domains of PS, the latter network being unstable with respect to the action of the velocity gradient field. In tetralin (a “good” solvent for both copolymer blocks) the effect is associated with thermodynamic incompatibility of the blocks. In decalin (φ-solvent for PS) at room temperature the effect is intensified on account of selective action of the solvent.

The effect of a non-Newtonian lubricant on piston ring lubrication

The effect of a non-Newtonian oil (shear thinning) on the lubrication of a piston ring is theoretically investigated. A variation of shear strain rate with shear stress that is cubic in form is used to obtain a modified form of the Reynolds equation (dynamic) applicable to a run-in ring profile which is considered to be a double parabola with a central straight portion. Numerical solutions are obtained for the film thickness, pressure and frictional force over a complete stroke for the case of a constant load. Results presented in non-dimensional form show that the effect of pseudo plasticity is to reduce slightly the minimum film thickness, peak pressure ratio and friction coefficient.