Ostwald-de Waele Equation Research Articles

Methodology for calculating the pasta dough flow parameters in stepped cylindrical channels

The introduction provides information about the state of the problem and substantiates the relevance of the research. The purpose of the work is to develop a methodology for calculating the relationship between pressure losses during the flow of pasta dough in channels with a stepped-variable cross section with the dimensions of the channel structural, as well as with the pasta dough rheological properties and the performance of device. In the methodological part of the work, the applied rheological model is described and a technique for mathematical modeling of power and kinematic parameters of pasta dough flow in stepped cylindrical channels is given. Due to the small contribution of the pasta dough shear strength to the total pressure loss, a rheological model of a non-linear-viscous medium is used, which is described by the power – law rheological Ostwald–de Waele equation. Neglecting the elastic deformations of the dough and the elastic change in volume, we assumed the condition of constancy of the volume and mass flow (productivity) for any cross section of the channel in each of its sections. In the main part of the work, analytical dependencies are presented that relate the magnitude of the pressure drop to overcome viscous resistance during the flow of pasta dough in channels with a stepped-variable cross section with the dimensions of the structural elements of the channel, as well as with the rheological properties of the pasta dough and the performance of the device. These dependences formed the theoretical basis for calculating method of the pasta dough flow parameters in stepped cylindrical channels. The technique was tested on the example of an industrial macaroni press matrix equipped with a system of stepped-variable channels in the pre-forming zone. The results of the research can be used in the design of new sizes of matrices for pasta dough molding as well as in the educational process in the training of food production process engineers.

Modelling the Relations of Rheological Characteristics with Composition of Plaster Mortar.

The rheological properties of fresh plaster mortars, with varied contents of porous fillers and polymer admixtures, have been studied. The quantities of fine limestone and expanded perlite, and dosages of methyl hydroxy ethyl cellulose and ethylene vinyl acetate were varied in the experiment. Effective viscosity (at a shear rate from 0.045 to 5.705 s−1) and the thixotropy of the mixes were determined with rotational viscometer for 18 compositions (according to the design of the experiment). Each of the 18 viscosity curves were described with the Ostwald–de-Waele equation. The Experimental–Statistical models describing the dependencies of the parameters of the rheological model and of mix thixotropy on the composition factors were built on the obtained data. ES-models have allowed the individual and synergetic effects of mix components on the rheological characteristics to be evaluated. The expanded perlite powder can increase the viscosity by two times, probably due to its pozzolanic effect increasing the content of the CSH phase during cement hydration. The thixotropy can be increased by the quantity of limestone. The computational experiments with ES-models have made it possible for the information set, without a noticeable interrelation between rheological characteristics, to be stratified into subsets, in which such interrelations differ significantly.

Characterisation of Hyaluronic Acid Blends Modified by Poly(N-Vinylpyrrolidone).

The viscosity behaviour and physical properties of blends containing hyaluronic acid (HA) and poly(N-vinylpyrrolidone) (PVP) were studied by the viscometric technique, steady shear tests, tensile tests and infrared spectroscopy. Viscometric and rheological measurements were carried out using blends of HA/PVP with different HA weight fractions (0, 0.2, 0.5, 0.8 and 1). The polymer films and HA/PVP blend films were prepared using the solution casting method. The study of HA blends by viscometry showed that HA/PVP was miscible with the exception of the blend with high HA content. HA and its blends showed a shear-thinning flow behaviour. The non-Newtonian indices (n) of HA/PVP blends were calculated by the Ostwald–de Waele equation, indicating a shear-thinning effect in which pseudoplasticity increased with increasing HA contents. Mechanical properties, such as tensile strength and elongation at the break, were higher for HA/PVP films with wHA = 0.5 compared to those with higher HA contents. The elongation at the break of HA/PVP blend films displayed a pronounced increase compared to HA films. Moreover, infrared analysis confirmed the existence of interactions between HA and PVP. The blending of HA with PVP generated films with elasticity and better properties than homopolymer films.

Numerical investigation of unsteady pulsatile Newtonian/non-Newtonian blood flow through curved stenosed arteries.

A numerical investigation of Newtonian/non-Newtonian unsteady pulsatile entry blood flow inside a 3D curved stenosed artery is presented. For considering the non-Newtonian effect (shear thinning or shear thickening behavior), the blood viscosity is characterized by the power-law model (Ostwald de Waele Equation). At the inlet of the artery, a realistic pulsatile waveform is utilized according to the experimental data reported by other researchers. This study belongs to the analysis of the curvature ratios, percentage and length ratio of stenosis, and blood thickening on hemodynamic characteristics of the flow. The results emphasize that the maximum wall shear stress happens near the stenosis neck and as expected, by decreasing the stenosis length, the maximum value of wall shear stress increases. In addition, the results indicate that the shear thickening fluid shows a more stable velocity profile rather than the shear thinning fluid flow.

Rheological, dynamic mechanical and transport properties of compatibilized starch/synthetic copolymer blends

The method of mechanical activation due to shear stress in the rotor-stator device (RSD) was used to combine the gelatinized starch and the latex of the styrene-acrylic copolymer (SAC). The influence of composition and method of mechanical activation on the rheological behavior of the aqueous starch/SAC blends, as well as on the dynamic mechanical properties, water sorption and salt transfer of the films was studied. A decrease in the starch content in water mixtures and joint activation were shown to promote a decrease in their viscosity and consistency index in the Ostwald-deWaele equation. The temperature dependences of the storage modulus (E′) and the mechanical loss tangent (tanδ) were obtained at tension of the starch/SAC films. An increase in E′ and a decrease in tanδ with increasing starch content have been established. Anomalous rise in rigidity was noted as the result of introduction of 20% SAC in starch. The increase in starch content is accompanied by a marked decrease in the rate and a rise in the equilibrium degree of swelling. An increase in the starch content from 20 to 80% results in a ninefold increase in the NaCl permeability coefficient.

The impact of addition of xanthan gum and guar gum on rheological properties of foams produced by continuous method

The paper presents the effect of the addition of hydrocolloids – xanthan gum and guar gum – on the rheological properties of ovoalbumin-based food foams, produced by continuous method. The foaming was carried out in a column apparatus with additional aeration equipped with a paddle stirrer. In order to determine the rheological parameters, a hysteresis loop test was carried out. The results of the study were described using the Ostwald-de Waele equation. The effect of the addition of hydrocolloid on the rheological properties of the obtained foams was characterized, and the synergistic effects between the hydrocolloids used were described.

Influence of added gelatin on the rheological properties of a Fucus vesiculosus extract

The influence of gelatin from bovine skin on the rheological properties of hydrogels in an extract from the alginate-containing algae Fucus vesiculosus was studied. The shear rate and dynamic mechanical analyses were used to determine the rheological properties. FT-IR spectroscopy showed that the main structural component of the Fucus extract was sodium alginate. The changes of the rheological properties of the extract with the introduction of gelatin are explained using the framework of the alginate–gelatin complexation model. The Fucus extract showed a weakly expressed non-Newtonian behaviour since the flow index in the Ostwald–De Waele equation is 0.91–0.94. The introduction of gelatin (1.0 wt.%) into the extract at 24 °C led to the formation of a hydrogel, whereas the extract itself cannot form a gel with these conditions. Further increasing the concentration of gelatin led to an exponential increase in the yield stress, plastic viscosity and apparent viscosity of the hydrogels. The introduction of gelatin into the Fucus extract at 4 °C led to a non-additive increase in the elastic modulus (G′), and a decrease in the tan δ of the hydrogels, i.e., strengthening of the elastic properties and weakening of viscous properties in these systems. The changes in the rheological parameters of a Fucus extract after the introduction of gelatin can be explained by an increase in the concentration of triple helices in the macromolecular chains of the gelatin, which are the elastic elements in the 3D mixed gel network.

Structural Version of Ostwald—de Waele Equation: Fractal Treatment

Structural treatment of Ostwald—de Waele equation is proposed. It involves the representations of fractal analysis for describing the rheological properties of the rubber/disperse filler system. It is shown that the magnitude of viscosity and the type of system flow are determined by the filler particle structure (aggregates) characterized by their fractal dimension. In turn, this dimension is determined by the mechanism of aggregate formation. The model proposed makes it possible to predict the viscosity of the rubber/disperse filler systems for different filler contents and shear rates.

Rheological study of the behavior of water-in-oil emulsions of heavy oils

Unconventional oils (heavy and extra-heavy oils) represent approximately 55% of the oil reserves of the world. These oils are characterized for their high viscosity and gravity due to the high amount of resins and asphaltenes, natural emulsifiers, which combined with the presence of water and shear, in the production and transport of the oil in pipelines, may form the emulsions, usually water-in-oil (W/O). This study evaluated the rheological behavior of W/O emulsions of five heavy oils from the sedimentary basin of the Brazilian coast, with API gravity between 10.8 and 19.0. Factors related to the stability (temperature, amount of emulsified water, salt concentration) and rheological behavior of the W/O emulsions (dynamic viscosity, stress and shear rate) were evaluated and related to the oil chemical composition in terms of saturates, aromatics, resins and asphaltenes (SARA). The emulsions were prepared with deionized water, formation water (55 g L−1 of NaCl) and water saturated with sodium chloride (270 g L−1 of NaCl) under mechanical stirring at 5000 rpm. Rheological assays of the emulsions were performed at 30–80 °C, and the obtained data were treated using the Ostwald-de Waele equation. The results of the rheological evaluation showed that in stable emulsions there was a 1212% increase in the dynamic viscosity as a consequence of the amount of aqueous phase, while temperature minimized this effect, at 60 °C it was observed a reduction of more than 80% in the viscosity. In these emulsions the flow rate was positive, increasing as a function of temperature, and the inverse effect was observed when correlated to the amount of water. The unstable emulsions presented lower results for the dynamic viscosity if compared with the results of the dehydrated oils, caused by the presence of non-emulsified water. In general, the elevation of salt concentration and temperature aided in the stabilization of unstable emulsions. Oils with a total acid number minor 1.3 mgKOH·g−1 and asphaltene/resin, aromatic/saturated and asphaltene/aromatic ratios higher 0.2 formed unstable emulsions, resulting in the appearance of non-emulsified water during the rheological tests.

Wplyw organicznych rozcienczalnikow i rozpuszczalnika na wlasciwosci reologiczne plastizoli PVC

The results of rheological investigations of poly(vinyl chloride) plastisols with dibutyl phthalate, di(2-ethylhexyl) phthalate or dibutyl sebacate as plasticizers, with addition of diluent (xylene, n-butyl acetate or butanol) and a solvent (cyclohexanone) are presented. Dependence of viscosity of a composition (measured using Hoppler viscometer) on shearing stress was described by Ostwald-de Waele equation. Maximal viscosity (h O ) and pseudoplasticity factor (n) were determined using this equation (Table 2 and 3). Activation energy of viscous flow (Table 5 and 6) has been calculated from Arrhenius-Guzman equation. It was found that introduction of diluent into the plastisol decreases both (η O ) and (n). However increasing amount of cyclohexanone causes at first increase in viscosity and pseudoplasticity and then they decrease (Fig. 3). It was also found that rheological properties of plastisols are highly influenced by the processes of plastisol particles' association and interactions between the components of a composition leading to formation of spatial structures. The phenomena proceeding on the surface of particles, in the solvation layer, play significant role. Their mechanisms were interpreted on the basis of the values of miscibility coefficients for the pairs of particular components of the composition (Table 7).

Rheological Properties of Pastes Obtained from Starches Derived from Immature Cereal Kernels

AbstractThe results presented in this work concern the starches of three basic varieties of cereal cultivated in Poland – wheat, rye and barley – harvested at different stages of maturity in 1997 and 1998. Starches from these kernels were isolated by a laboratory method. The flow curves and thixotropic properties of 5% starch pastes at 50°C and controlled shear rates between 0 and 600 s−1 were obtained. All the investigated starch pastes were non‐Newtonian, plastic and thixotropic fluids, that differed in their values of yield stress. The pastes from immature cereal starches were characterised by a higher plasticity because they needed a higher shear stress (τ) to achieve the yield stress (τ01) in comparison with the pastes from the mature cereal starches. At applied shear stress the pastes from the “immature” starches had a higher thixotropy in comparison with the “mature” ones. Pastes from immature starch were more susceptible towards shearing forces but at the same time they exhibited a better ability to rebuild their structure. The description of the flow curves by the Ostwald‐de Waele equation allows the conclusion that pastes from the immature starches have a higher structural viscosity. In addition, the application of the Casson model allows to describe the flow curves and determine the yield stress and the plasticity properties of the investigated pastes. However, the viscosity values calculated from the Casson model do not reflect differences in viscosity among the samples.