Aqueous Solutions Of Xanthan Gum Research Articles

Sheared settling in viscoelastic shear‐thinning fluids: Empirical studies and model development

AbstractThe hydrotransport of settling particles using laminar flow as opposed to the more energy‐ and water‐intensive turbulent flow has remained a tentative option for industries due to the complexity in characterizing particle settling dynamics in opaque non‐Newtonian fluids under sheared conditions. To provide insight into this unknown physics, this study focused on viscoelastic shear‐thinning fluids and developed a semi‐empirical model to characterize the batch‐settling dynamics of dilute suspensions (<5 vol% solids concentration) experiencing a shear field. These suspensions consisted of spherical glass microparticles in aqueous xanthan gum solutions. Settling profiles were measured with Electrical Resistance Tomography (ERT) while a motorized belt generated a cross‐shear field. The data acquired by the ERT showed that introducing cross‐shear fields into such suspensions increased settling rates when compared with static settling contexts. Then, a semi‐empirical model describing the “acceleration phase” of the settling process was developed and validated at accuracies between 81% and 97%.

Relationship between texture perception and oral function: A preliminary study in young, healthy adults.

Oral frailty, characterised by reduced oral function, is associated with systemic health issues in older adults. Although the criteria for diminished oral function often focus on motor and secretory abilities, texture perception also plays a crucial role in health due to its impact on food intake and palatability. This study aimed to explore the relationship between thickness discrimination ability (TDA) and oral motor and secretory functions in healthy young individuals. Twenty-eight adults were assessed for texture perception using eight concentrations of aqueous xanthan gum solutions to determine TDA scores. Measurements of occlusal force, masticatory performance, tongue pressure, stimulated salivary flow rate and tongue-lip motor function were conducted. Spearman's correlation analysis was used to evaluate the relationship between TDA scores and oral functions. Participants were divided into high-sensitivity and low-sensitivity groups based on their TDA scores to compare oral function test results. The TDA scores varied among the participants, with higher scores correlating with higher masticatory performance (r = 0.41, p < .05). Masticatory performance in the high-sensitivity group was significantly higher than in the low-sensitivity group (211.9 ± 59.2 mg/dL vs. 157.9 ± 43.0 mg/dL, p = .013), with no significant differences in other oral functions. Masticatory performance was correlated with TDA, suggesting a link between the selection function of mastication and thickness discrimination. These findings highlight the potential relevance of texture perception in oral function and indicate the need for further exploration, particularly in older adults with declining oral health.

Global characterization of hydrodynamics and gas-liquid mass transfer in a thin-gap bubble column in presence of Newtonian or non-Newtonian liquid phase

Bubble columns are commonly used as photobioreactors (PBRs) due to their good mixing and mass transfer capabilities. Modification in design and operating parameters are nevertheless needed to intensify volumetric productivity. Thin-gap bubble column can be used in this context to operate with high biomass concentration, up to conditions where the culture becomes non-Newtonian. In the present study, the global hydrodynamics and gas–liquid mass transfer inside a 4 mm thickness thin-gap bubble column are characterized in presence of low viscosity Newtonian fluid (water) and two aqueous solutions of Carboxymethyl Cellulose and Xanthan Gum. These shear-thinning solutions are used to mimic high concentration cultures of Chlorella Vulgaris at 42 g.L−1. A range of superficial gas velocities and different capillary diameters are explored to investigate the effect of sparging on hydrodynamics and gas–liquid mass transfer. Studied parameters are flow regimes, mixing, and gas–liquid mass transfer. Results are compared with literature results in classical bubble columns to put into evidence the original effects of both confinement and liquid rheology. Among others, these results show that compared to Newtonian media, non-Newtonian media result in higher gas holdup and mixing times and a lower gas–liquid mass transfer coefficient. The findings suggest that the presence of smaller bubbles would improve mass transfer due to the increased interfacial area, while the presence of larger bubbles would improve mixing performance due to increased vorticity in their wake and relatively greater species transport.

Xanthan gum in solution and solid-like state: Effect of temperature and polymer concentration

The development and optimization of xanthan-based systems are closely related to its structure and the properties induced in the material which contains it. Considering this, the present work aimed to investigate the effect of temperature and polymer concentration on the rheological properties of xanthan gum (XG) aqueous solutions, and on morphology of corresponding films. Viscoelastic properties of the solutions with 0.4, 1.0 and 2.0 % XG have been studied in oscillatory and continuously shear regimes. A solid-like response over the entire studied frequency range was observed for investigated solutions. The Cox-Merz superposition of complex and apparent viscosities was evidenced only for 0.4 and 1.0 % XG solutions. The effect of XG content on yield stress of solutions was also discussed. The morphology of surface and cross-section of XG films, prepared by casting solution method, were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and polarized optical microscopy (POM). The morphological aspects at nanometric scale, investigated by AFM, highlighted the influence of the XG concentration on the film characteristics, the isotropy/anisotropy balance and the surface texture. SEM and POM microphotographs of film, obtained from 2.0 % XG solution, evidenced an ordered structure of polymer chains and birefringence, respectively.

Thermal hysteresis phenomena in aqueous xanthan gum solutions

The anionic hydrocolloid polysaccharide xanthan gum is widely used in the food and petroleum industries (among others) as a viscosity enhancement polymer due to its high viscosity at low concentrations and moderate temperatures. The physical properties of microbial polysaccharide xanthan gum aqueous solutions were investigated using temperature dependent viscosity measurements. Specifically, the effect of thermal history on the solution viscosity was investigated. Heating and cooling cycles were assessed in two ways, by using a “sawtooth” and “triangle” pattern, which essentially differed in the rates of cooling. The sawtooth method used a cooling rate of 2.0 °C min−1 whereas the triangle pattern had a cooling rate of 0.20 °C min−1. The sawtooth cooling rate was controlled by the speed at which the Peltier device could cool the sample, and the triangle rate was governed by the time required to measure the viscosity at each temperature on return to the initial value. Cycles measured using the sawtooth pattern for 16 mg/kg xanthan gum in water showed an 8–10% overall decrease in the viscosity over four complete cycles. Comparatively, at 320 mg/kg the xanthan gum solution showed a 25% decrease in viscosity over four cycles. The observed temperature dependent viscosity variation suggested minor modifications in the physical network structure of xanthan gum. When using a triangle heating/cooling pattern, the overall decrease in the xanthan gum solution viscosity was 5–7% for 16 mg/kg and only 10% change for 320 mg/kg solutions. The activation energy of viscous flow for the aqueous xanthan gum solutions by either method was ∼15.0 kJ/mol under all conditions. The data showed that temperature and heating cycles influence xanthan gum viscosity and thermal history, which depends more strongly on xanthan gum concentration than solution temperature.

A phase transition approach to elucidate the propagation of shear waves in viscoelastic materials

In the field of acoustics, a medium has traditionally been considered a liquid if shear waves cannot propagate. For more complex liquids, such as those containing polymer chains or surfactant aggregates, this definition begins to be unclear. By adopting a rheological model-independent approach, this work investigated by means of dynamic elastography, the liquid–solid phase transitions in viscoelastic liquid media. When the storage shear modulus G′ dominated the loss shear modulus G″, a minimal shear wave attenuation frequency region was defined and the medium was considered solid. When G″ dominated G′, the shear waves were strongly attenuated and the medium was considered liquid. The investigated medium, an aqueous solution of xanthan gum, behaved as a bandpass filter with transition bands, showing liquid–solid–liquid behavior from low to high frequency. During these transitions bands, shear waves still propagated but highly attenuated. The limiting values where shear waves were no longer observed were identified as the low and high cutoff frequencies. Finally, the ability of various rheological models to predict the phase transition frequencies and describe the dispersion curves was tested. A three-element rheological model, the Jeffreys model, was required to accurately fit the experimental response of the medium at different concentrations over the entire frequency range. Shear wave propagation methods can overcome the technical limitations of traditional rheometry and explore higher frequencies, rarely investigated in viscoelastic liquids.

Pseudo-gel ternary systems of xanthan gum in water-ethanol solutions for industrial applications

Hydrocolloids with xanthan gum are widely applied, especially considering the food and cosmetics industries. The water solution of xanthan gum demonstrates characteristics of pseudo-gel, with the relaxation time increasing exponentially as a function of time. The solubility and intermolecular association capacity of aqueous xanthan gum solutions can be influenced by various factors, especially alcohols, which promote conformational structural changes and lead to a gelation process. The study investigated the effect of pseudo-gel ternary systems of xanthan gum in water-ethanol solutions as thickening agents. Formulations differing in the mass proportion of xanthan gum and the solvent ratio were used to get model mouldings. Additionally, the rheological properties of slurries were investigated. The mass loss during drying under different conditions was evaluated (50 °C/72 h; 115 °C/45 min). The thermal stability of mouldings and pseudo-gel systems was examined with DSC-TG. The internal structure of the mouldings was assessed based on the absorption and porosity test for solvents differing in polarity. SEM imaging was used to visualise the internal structure. A hardness test with surface analysis using a profilometer was carried out. The influence of ternary pseudo-gel systems on mouldings was investigated to complement knowledge about formulating at the early stages of process design.

Non-Newtonian droplet breakup in a T-junction microdevice containing constriction induced asymmetric parallel branches

Here, we describe the breakup and post-breakup dynamics of a non-Newtonian droplet of xanthan gum aqueous solution in asymmetric parallel branch microdevices. Our experimental results reveal that the droplet breakup regimes, namely, obstruction, tunnel, combined, non-breakup, and parallel, are the functions of xanthan gum concentration and the continuous phase flow rate. We examined the influence of fluid properties on droplet breakup stages by varying the xanthan gum concentration in an aqueous solution that exhibited increasing shear-thinning and elastic properties with its concentration. Four sequential stages (squeezing, transition, pinch-off, and filament thinning) are identified during the droplet breakup process. We found that upstream pressure controlled the squeezing stage, and fluid properties mainly steered the filament rupture stage. A complex interaction between elastic, capillary, and inertial forces further divided the final stage into the stretching and fluid-drainage stages. The Hencky strain characterized the formation of a persistent cylindrical filament in the stretching stage that decayed exponentially in the fluid-drainage stage. Eventually, this study highlights the significance of parallel branches with asymmetric geometric confinements on droplet splitting. Enhanced asymmetry is observed for the elongated filament, emphasizing the dominance of feedback from the downstream confinement.

FUZZY LOGIC-BASED MODELING OF A CENTRIFUGAL BLOOD PUMP PERFORMANCE VIA EXPERIMENTAL DATA OF NEWTONIAN AND NON-NEWTONIAN FLUIDS

Using fuzzy logic methods, some complex experiments that are not possible due to critical limitations can be simulated in a short time. In this study, experimental data of Newtonian 40% aqueous glycerin solution (GS) and non-Newtonian 600[Formula: see text]ppm aqueous xanthan gum solution (XGS) working fluids were used to model the hydraulic performance of a centrifugal blood pump. A novel fuzzy logic-based model (FLM) for modeling the hydraulic performance of the pump model is proposed. In the proposed model, there are two inputs which are flow rate and impeller rotational speed and one output which is head pressure. In FLM, the range for flow rate is 1–7.8[Formula: see text]L/min in GS and 1–8[Formula: see text]L/min in XGS, and for head pressure 50–245[Formula: see text]mmHg in GS and 50–215[Formula: see text]mmHg in XGS. In addition, impeller rotational speed range is 2700–3600[Formula: see text]rpm for both fluids. The estimated results with FLM were validated with the experimental results and it was seen that the FLM was compatible with the experimental results with an accuracy of 96.25%. These results imply that the developed FLM is acceptable and can be used to assist in determining the performance of blood pumps.

FOURIER AND WAVELET ANALYSIS OF PRESSURE FLUCTUATIONS IN GAS-NON-NEWTONIAN LIQUID TWO-PHASE FLOWS IN A MICROCHANNEL

The purpose of this study was to analyze the characteristics of gas-non-Newtonian liquid flow patterns in microchannels using signal processing techniques including power spectral density (PSD) and discrete wavelet transform (DWT) analyses. Square microchannels measuring 0.8 &amp;#215; 0.8 mm were used in this study. Water, 0.1 percent by weight (wt&amp;#37;) xanthan gum (XG) aqueous solution, and 0.2 wt&amp;#37; XG were employed as the working liquids, while nitrogen gas was used as the working gas. The superficial velocities of the liquid and gas were varied between 0.05 and 1 m/s and 0.26 and 7.8 m/s, respectively. The flow patterns were recorded using a high-speed camera, while the pressure drop was measured using a differential pressure transducer. The pressure gradient data were analyzed using signal processing techniques to characterize the flow patterns. Furthermore, PSD and DWT analyses were found to effectively describe the characteristics of the flow pattern.

Insights into the dynamics of non-Newtonian droplet formation in a T-junction microchannel

The non-Newtonian shear-thinning droplet formation mechanism in a T-junction microchannel is experimentally investigated using the aqueous solutions of xanthan gum as the dispersed phase and mineral oil as the continuous phase. Influences of both phase flow rates and polymer concentration on flow regime transition are explored. It is observed that the initial vertical expansion stage is present only for the Newtonian and lower shear-thinning systems. The droplet evolution rate shows the influence of continuous phase flow rate and shear-thinning properties on the dynamics of necking stages, viz., squeezing, transition, pinch-off, and filament thinning. Analysis of Ohnesorge number (Oh) reveals that inertial force dominates in the squeezing stage, whereas viscous and interfacial force control in the filament thinning stage. Longer and stable filament generation is detected as a discerning feature for non-Newtonian systems that appears more prominent with increasing dispersed phase shear-thinning properties. The results also indicate an inverse relation of droplet length with the continuous phase flow rate and xanthan gum concentration, while the droplet formation frequency and its polydispersity vary directly with those parameters.

An experimental performance comparison of Newtonian and non-Newtonian fluids on a centrifugal blood pump

The use of substitute fluid with similar rheological properties instead of blood is important due to ethical concerns and high blood volume consumption in pump performance test before clinical applications. The performance of a centrifugal blood pump with hydrodynamic journal bearing is experimentally tested using Newtonian 40% aqueous glycerin solution (GS) and non-Newtonian aqueous xanthan gum solution of 600 ppm (XGS) as working fluids. Experiments are performed at four different rotational speeds which are 2700, 3000, 3300, and 3600 rpm; experiments using GS reach between 8.5% and 37.2% higher head curve than experiments using the XGS for every rotational speed. It was observed that as the rotational speed and flow rate increase, the head curve difference between GS and XGS decreases. This result can be attributed to the friction reduction effect when using XGS in experiments at high rotation speed and high flow rate. Moreover, due to different fluid viscosities, differences in hydraulic efficiency were observed for both fluids. This study reveals that the use of Newtonian fluids as working fluids is not sufficient to determine the actual performance of a blood pump, and the performance effects of non-Newtonian fluids are remarkably important in pump performance optimizations.

Secondary instabilities in Taylor–Couette flow of shear-thinning fluids

The stability of the Taylor vortex flow in Newtonian and shear-thinning fluids is investigated in the case of a wide gap Taylor–Couette system. The considered radius ratio is$\eta = R_1/R_2=0.4$. The aspect ratio (length over the gap width) of experimental configuration is 32. Flow visualization and measurements of two-dimensional flow fields with particle image velocimetry are performed in a glycerol aqueous solution (Newtonian fluid) and in xanthan gum aqueous solutions (shear-thinning fluids). The experiments are accompanied by axisymmetric numerical simulations of Taylor–Couette flow in the same gap of a Newtonian and a purely viscous shear-thinning fluid described by the Carreau model. The experimentally observed critical Reynolds and wavenumbers at the onset of Taylor vortices are in very good agreement with that obtained from a linear theory assuming a purely viscous shear-thinning fluid and infinitely long cylinders. They are not affected by the viscoelasticity of the used fluids. For the Newtonian fluid, the Taylor vortex flow (TVF) regime is found to bifurcate into a wavy vortex flow with a high frequency and low amplitude of axial oscillations of the vortices at${Re} = 5.28 \, {Re}_c$. At${Re} = 6.9 \, {Re}_c$, the frequency of oscillations decreases and the amplitude increases abruptly. For the shear-thinning fluids the secondary instability conserves axisymmetry. The latter is characterized by an instability of the array of vortices leading to a continuous sequence of creation and merging of vortex pairs. Axisymmetric numerical simulations reproduce qualitatively very well the experimentally observed flow behaviour.

Correlation of human perception in swallowing with extension rheological and tribological characteristics in comparison with shear rheology.

Correlation was investigated between instrumental characteristics obtained by extension rheological or tribological measurements and human perception while swallowing using aqueous solutions of xanthan gum and locust bean gum. Extension viscosity and the friction coefficient were measured using a capillary breakup rheometer and a rotation tribometer, respectively, as in our previous study. Results were compared with shear viscosity to clarify novelty and advantage of these mechanical parameters. It was indicated that perceived cohesiveness correlated the highest with the maximum extension viscosity immediately after the onset of extensional flow, perceived spinnability correlated with extension viscosity in high Hencky strain region, and perceived sliminess correlated with the friction coefficient at the critical point between the boundary lubrication and the mixed lubrication. These correlations were discussed and tried to validate considering biomechanics of human swallowing and food-human interactions.

Rayleigh–Bénard convection in non-Newtonian fluids: Experimental and theoretical investigations

We present an experimental and theoretical study of Rayleigh–Bénard convection in shear-thinning fluids with temperature-dependent properties. Experiments were performed using a cylindrical cell with a radius R̂=60 mm and height adjustable at d̂=15 and 20 mm giving a radius-to-height ratio L = 4 and 3, respectively. The fluids used are glycerol (Newtonian fluid) and aqueous xanthan gum solutions (shear-thinning fluids) at 1000 and 1200 ppm. Convection patterns are visualized by the shadowgraph method. In the theoretical part of this study, the weakly nonlinear analysis performed by Varé et al. [J. Fluid Mech. 905, A33 (2020)] is extended to take into account the variation of the thermal expansion coefficient with temperature. For the xanthan gum solutions used, the temperature dependence of the fluid parameters is sufficiently strong to obtain hexagonal cells at the onset of convection. It has been observed that their size decreases with the increase in the temperature difference across the fluid layer above the critical value. This result provides an experimental support to our theoretical study where it is shown that for hexagons, the band of stable wavenumbers is bent toward higher wavenumbers. For the glycerol, Newtonian fluid with a large Prandtl number, a slight increase in the wavelength of rolls is observed in agreement with the literature.

Experimental study on the flow and heat transfer behavior of polymer solutions in the closed liquid ring vacuum pump system

The closed liquid ring vacuum pump system, which mainly includes the liquid ring vacuum pump and the heat exchanger, is widely used for gas pumping in various industries. In this paper, the energy saving effect in the liquid ring vacuum pump and the flow and heat transfer behavior in the shell-and-tube heat exchanger are investigated for aqueous solutions of rigid xanthan gum (XG) and flexible Polyacrylamide (PAM), and the effects of the concentration, Reynolds number, polymer conformation and flow geometry on the flow behavior of polymer solutions are studied. Results show that, despite the significant differences in molecular conformation and rheological properties between XG and PAM, the similar energy saving rate, about 1.5 ∼ 17.5%, is obtained in the liquid ring vacuum pump. However, in the shell-and-tube heat exchanger, XG solutions exhibit the more obvious pressure drop enhancement and heat transfer reduction than that of PAM solutions for the same concentration. Furthermore, due to the polymer shear degradation, the shaft power in the liquid ring vacuum pump decreases first and then stabilizes, conversely, the flow resistance decreases and the flow rate increases in the heat exchanger. The great difference in the flow condition between the intense rotating gas–liquid two-phase flow field and the gentle liquid pipe flow causes the different flow behavior for XG and PAM solutions.

Instrumental characteristics from extensional rheology and tribology of polysaccharide solutions.

Instrumental characteristics from extensional rheology and tribology for aqueous xanthan gum (XG) and locust bean gum (LBG) solutions were studied in the presence or absence of simulated saliva. Extensional viscosity was calculated from the filament shrinkage behavior using a capillary breakup extensional rheometer, whereas the friction coefficient was measured using a set-up consisting of polydimethylsiloxane substrate and a glass ball bearing on a rotational rheometer. Increase in extensional viscosity was detected immediately after initiation of extensional flow, particularly XG, and also immediately before the filament rupture, particularly LBG. Extensional viscosity tended to decrease with increased addition of simulated saliva for XG, while to increase for LBG. In both cases, effect of cations in the saliva was greater than that of mucin. From the shape of the Stribeck curve (i.e., dependence of the friction coefficient on the entrainment speed) and comparison of the friction coefficient itself, lubricity of XG was greater than that of LBG. Simulated saliva added decreased the friction coefficient for each polysaccharide through functions of cations rather than mucin. Extensional viscosity and tribological measurements revealed mechanical properties of polysaccharide solutions which cannot be determined or quantified by shear viscosity alone.

Yielding and rheopexy of aqueous xanthan gum solutions

Xanthan gum (XG) is widely used in cosmetic and pharmaceutic products (creams, pastes) and in oil industry (drilling fluids) as a stabilizing and/or thickening agent. In literature, its rheological behavior is mainly presented as that of a shear-thinning or a yield stress fluid. Here, in order to clarify this rheological behavior, we study in detail the flow characteristics during continued flow under given conditions (i.e., controlled stress) for a mass concentration ranging from 0.2 to 5%. We are thus able to identify the apparent flow curve of the material after a short flow duration and the flow curve in steady state (i.e., after a long flow duration). The validity of this flow curve, determined from standard rheometry, is confirmed by magnetic resonance velocimetry. These materials start to exhibit a yield stress behavior beyond some critical xanthan or salt concentration. In that case, a significant increase (by a factor up to 5) of the apparent viscosity is observed during flow in some range of stresses, before reaching a steady state. This original rheopectic effect might be due, after some time of flow associated with deformation and reconfiguration of the XG molecules, to the progressive formation of intermolecular links such as hydrogen bonds and/or intermolecular association due to acetate residues.

Viscoelastic Particle Train Formation in Microfluidic Flows Using a Xanthan Gum Aqueous Solution.

Viscoelastic polymer solutions have been widely employed as suspending liquids for a myriad of microfluidic applications including particle and cell focusing, sorting, and encapsulation. It has been recently shown that viscoelastic solutions can drive the formation of equally spaced particles called "particle trains" as a result of the viscoelasticity-mediated hydrodynamic interactions between adjacent particles. Despite their potential impact on applications such as droplet encapsulation and flow cytometry, only limited experimental studies on viscoelastic ordering are currently available. In this work, we demonstrate that a viscoelastic shear-thinning aqueous xanthan gum solution drives the self-assembly of particle trains on the centerline of a serpentine microfluidic device with a nearly circular cross section. After focusing, the flowing particles change their mutual distance and organize in aligned structures characterized by a preferential spacing, quantified in terms of distributions of the interparticle distance. We observe the occurrence of multi-particle strings, mainly doublets and triplets, that interrupt the continuity of the particle train. To account for the fluctuations in the number of flowing particles in the experimental window, we introduce the concept of local particle concentration, observing that an increase of the local particle concentration leads to an increase of doublets and triplets. We also demonstrate that using only a single tube to connect the sample to the microfluidic device results in a drastic reduction of doublets/triplets, thus leading to a more uniform particle train. Our findings establish the foundation for optimized applications such as deterministic droplet encapsulation in viscoelastic liquids and optimized flow cytometry.

A model to calculate the pressure loss of Newtonian and non-Newtonian fluids flow in coiled tubing operations

The coiled tubing is a system consisting of a long, continuous and flexible steel pipe used in many processes, especially in the oil industry. As the fluid flow in curved pipes generates significant energy dissipation compared to a straight pipe, it is essential to predict the pressure drop to obtain the pumping pressure to be used in the operation and optimize process control. In this work, the pressure drop in the flow of Newtonian and non-Newtonian fluids was evaluated in a pilot unit and a mathematical model was developed to simulate the pressure drop along the coiled tube. Water and an aqueous solution of xanthan gum, with rheological power-law parameters similar to those observed in cement slurries, were used in experimental tests. The experimental unit is 375 m long divided into 8 layers with pressure measurements in each layer where fluids were pumped at different volumetric flow rates and curvature ratios. A mathematical model was proposed to calculate the pressure drop assuming the existence of a sequential pumping of different fluids along the coiled tubing, with different curvature ratios and internal tube diameters. The mathematical modeling could predict the pilot experiments for Newtonian fluids and, based on the results obtained in the laboratory, the parameters of a friction factor correlation for non-Newtonian fluids present in the literature were re-estimated. A case study of a real well abandonment operation with a coiled tubing system was used to validate the proposed modeling. The developed software was used to simulate the real conditions, where a good approximation to the field data was observed, with a percentage error between the experimental and calculated values below 7%.