Variation Of Rheological Parameters Research Articles

A rheological study on nano-bubble assisted flotation of phosphate fine particles

ABSTRACT The application of ultrafine bubbles a.k.a. nano-bubbles (NBs) in upgrading the flotation recovery of fine particles has been extensively investigated from various perspectives over the last two decades. However, their rheological aspect has not been studied yet, which is presented for the first time in this paper. To this end, the current study addresses the effect of six crucial variables including solid content (5%, 15%, and 25% (w/w)), presence and absence of NBs, inner diameter of a Venturi tube (1.5 and 2.2 mm), pH of pulp (4.5–11) and frother dosage (3, 13, and 33 mg/L) on the variation of rheological parameters i.e. shear stress, shear tension, and viscosity. Ultrafine bubbles were generated in a conditioning tank through the hydrodynamic cavitation mechanism using a fatty-acid-based frother (Flo-Y-S), while the rheological responses were continuously monitored and measured by a rheometer and parallel plate spindle (for pulp) and a double gap spindle (for NBs). Flotation tests were conducted on a high-grade phosphate ore (d80 = 37 µm) using a mechanically agitated Denver®-type (D12) flotation cell. The experimental results revealed that fluid behavior without NBs using 13 mg/L frother was in the range of shear rates less than 1 s−1 non-Newtonian and close to the shear thinning state, while it became completely Newtonian in the range of 1 to 1500 s−1. However, the presence of NBs at the same frother content changed this tendency to non-Newtonian and Newtonian fluids at shear rates of <30 s−1 and >30 s−1, respectively. It was also found that either in acidic (5.5) or strong alkaline (11) domains, the pulp viscosity trends were almost close to each other and varied from 0.002−10 to 0.002−4 Pa.s, respectively. On the other hand, on the same trend, the amount was lowered to three times in the neutral range (7.5) and weak alkalinities (9). Diminishing the inner diameter of the Venturi tube from 2.2 mm to 1.5 mm led to an increment of shear stress and viscosity about twice at the shear rates <100 s−1. The results of evaluating frother dosage showed that an increase in the amount of frother dosage, which reduced bubble dimensions, exceeded the viscosity and the amount of shear stress. Finally, we concluded that the rheological properties significantly impacted the selective separation of NB-assisted flotation processes and need further investigations in the future.

Rheological concerns arising from the use of anti-freezing additives in cement mortar with/without SP and AEA for low-temperature construction

This paper aims to provide insights into the coupled influence of typical anti-freezing agents (AFAs) and cold environment on rheological performance of cement mortar with/without different superplasticizer (SP) and air-entraining agent (AEA) components. Fresh mixtures were prepared with chemical admixtures singly or in groups (AFA; AFA/SP; AFA/SP/AEA) for the continuous measurement of their time-dependent rheological behavior at variable temperatures (24 °C; 0 °C; −5 °C; −10 °C). Hydration kinetics, pore solution and air-void system were systematically evaluated to provide evidences supporting for the variations in rheological parameters. It was found that the yield stress of mixture decreased and the plastic viscosity increased with the temperature falling from 24 °C to 0 °C, while both the yield stress and the plastic viscosity increased rapidly with the temperature falling from 0 °C to −10 °C. Temperature could affect the rheological parameters development by changing the interaction of SP with ions. For the SP-plasticized mixtures under low temperature, the dosage of calcium nitrite (CN) as AFA should be carefully restricted. For the air-entrained mixtures, the incorporation of CN enhanced the shear stress in the high shear rate region, while the incorporation of ethylene glycol (EG) showed a converse behavior. The results will provide theoretical supports for the manufacture and the early-age properties control of flowable concrete during winter construction.

Experimental and Numerical Study on the Permeation Grouting Diffusion Mechanism considering Filtration Effects

Permeation grouting estimation is important for the design of grouting engineering. Filtration effects and rheological behavior play a key role in permeation grouting diffusion of cement-based grouts. To better understand the effect of filtration and grout rheological behavior on the grouting diffusion mechanism, one-dimensional permeation grout injections in sand columns under constant flow rate were performed by a self-developed experimental procedure. Experimental results showed that there were dramatic variations in rheological parameters and porosity along the diffusion distance. However, the rheological parameters changed slightly with time for each position. Based on the experimental results, a numerical model considering the filtration effect and grout rheological behavior was established to describe the mechanism of grout flow in porous media. In addition, numerical solutions from the proposed model are compared with the experimental results. The comparative results showed that the proposed numerical method can match the laboratory tests well. Finally, the effects of the grout flow velocity and the water/cement ratio of the grout on the diffusion mechanism are also discussed.

Influence of Free and Encapsulated Olive Leaf Phenolic Extract on the Storage Stability of Single and Double Emulsion Salad Dressings

Valorization of wastes has become an unavoidable goal in the olive oil industry. A possible approach is the recovery of leaf phenolic compounds, which have a great interest for food industries, due to their antioxidant and antimicrobial activities. Thus, this study aims at comparing the effects of encapsulated (e-OLE) and free olive leaf extract (f-OLE) on storage stability of salad dressings prepared as single and double emulsion systems. Creaming, rheological properties, double emulsion yield, pH, total phenol content (TPC), antioxidant activity, and peroxide value (PV) of the dressings were monitored over 90 days at 4 °C. Microstructure examination showed a more homogeneous distribution of the droplet size with the inclusion of OLE. No creaming and very little variations in rheological parameters (< 10%) were observed. OLE enrichment and double emulsion systems significantly (P < 0.05) improved the rheological behavior, with a higher effect of e-OLE due to the alginate-pectin beads. OLE enrichment extended the oxidation induction period from 15–20 days to 50 days. In conclusion, the work demonstrated that OLE encapsulation by emulsification-internal gelation technique was effective in gradually releasing polyphenols during salad dressing storage, thus increasing product protection toward oxidation phenomena.

Impact of Crustal Rheology on Temperature‐Dependent Viscoelastic Models of Volcano Deformation: Application to Taal Volcano, Philippines

AbstractWe use ALOS‐1 interferometric synthetic aperture radar data spanning the period of 2007–2011 to obtain time‐dependent ground deformation data over Taal caldera related to the 2010–2011 volcanic unrest, which did not lead to an eruption. We employ finite element models that account for subsurface thermomechanical properties to test for viscoelastic deformation. We also examine the variability of crustal rheological parameters of the temperature‐dependent Arrhenius formulation for viscosity, to investigate the effects on surface deformation. Deformation at Taal is observed to be time dependent and explained by a linear rate of pressure increase in a shallow magma reservoir at 5‐km depth within a hot and viscoelastic upper crust. The best‐fitting rheological properties of the local setting are consistent with either a felsic or hydrothermally altered uppermost crust. We show the significantly different effects that the variation of rheological parameters has on surface deformation, highlighting the importance of incorporation into future studies of deformation at different volcanic settings.

Effects of Inclination of Micro-capillary on Blood-Viscosity of Diseased Blood in Presence of Metallic Ball

Dynamic changes in rheology of blood within microvasculature structures can be used for diagnosing chronic non-communicable disease at earlier stages. Behavior of blood in microvascular structures (capillaries) is mysterious. In case of capillaries present in brain, such dynamic continuum induces hindrance to oxygen diffusion through circumvented nerve fibers at the junction of blood-brain barriers. It causes temporary regional hypoxia. Therefore, understanding the rheology of blood in micro-confined capillaries may evolve as a tool for early prediction of hypoxia. Viscosity of blood in micro-capillaries can be measured by principle of falling ball viscometer. But this technique produces inconsistent result for non-Newtonian fluid. In this paper, we have presented an investigation on dynamic behavior of blood rheology within micro-capillaries inclined at different degrees of inclinations. Experimental results are complemented with detailed numerical simulations. Experimental observations reveal significant variation of rheological parameters of blood in micro-capillaries. Inter-gender variations confirm the contribution of hematocrit in blood for this variation. The rheological parameters of blood with diseased condition are found to vary with the different degrees of inclination of the micro-capillary. Effect of rolling ball on the red blood cells (RBCs) during interaction in the capillary of the viscometer is found to induce deformative stress on membrane of RBC. It is also confirmed by the continuous sustainability of the higher magnitude strain rate near the wall (between boundaries of ball and wall). Inclined angle of capillary tube was also found as a parameter for defining rheology of blood in micro-capillary.

Evaluating the applicability of rheometry in steel fiber reinforced self-compacting concretes

ABSTRACT The use of self-compacting concrete in civil construction industry presents various advantages, since the material shows adequate workability during fresh state. When fiber reinforcement is used, there are changes in its behavior that require attention. This study aimed to evaluate the applicability of rheological tests and the correlation between its results and those obtained with regular tests used to control SCCs. In that sense, different mixtures of SCC with different steel fiber contents were produced in order to be analyzed in the experimental program described. Rotational rheology tests and slump flow and L-box tests were performed. The results showed that slump flow test did not present good correlations with rheological parameters. On the other hand, this test was able to point out the risk of segregation of the mixtures with higher fiber contents. A good correlation was obtained between the L-box test results and rheological parameters. The L-box was also able to show loss in the passing ability of SCC related to the rise of plastic viscosity and yield stress. These tests also presented a good correlation with the rheological parameters when lower fiber contents were used. Although the rheometry test was unable to evaluate these problems, this kind of test gave more objective and reliable data on variations in rheological parameters related to the increase of fiber content, and proved to be a more reliable test to this kind of application, especially when applied together with the conventional tests.

Influence of formulation on the structural networks in ice cream

Six different formulations, corresponding to three types of fat (hydrogenated or refined coconut oils or refined palm oil) and two mixtures of mono- and di-glycerides, namely saturated and partially unsaturated were chosen to investigate the influence of the oil phase nature and the low molecular weight emulsifier type on the networks present in ice cream. Ice creams were characterized for particle size distribution of fat globules, melting resistance and amount of proteins in the aqueous phase. Variation of rheological parameters as a function of temperature allowed following the ice network melting, the fat globule aggregation state and destabilization, and the structural arrangement of proteins. Presence of unsaturated fatty acids in the emulsifier promoted an increased percentage of agglomerated fat globules, increased melting time and higher storage modulus values at 5 °C. The influence of the fat type on ice cream characteristics was mainly illustrated by different rheological parameters and, to a lesser extent, by melting time, whereas the amount of proteins in the aqueous phase did not allow discriminating among the formulations.