Gum Solutions Research Articles

Effect of downstream processing on the structure and rheological properties of xanthan gum generated by fermentation of Melaleuca alternifolia residue hydrolysate

Low-cost Melaleuca alternifolia residue hydrolysate has great potential as a promising substrate for xanthan gum production but further downstream processing in addition to traditional alcohol-precipitation is necessary to obtain purified xanthan gum from this substrate. In this study, the effect of downstream processing on the structure and rheological properties of xanthan gum generated by fermentation of Melaleuca alternifolia residue hydrolysate was evaluated for the first time. Compared with acid-precipitation and alkali-precipitation, dialysis was much more suitable for xanthan gum purification as demonstrated by the energy dispersive spectrometer (EDS) and thermogravimetric analysis (TGA) results, and the xanthan gum with relatively high purity could be obtained after alcohol-precipitation and dialysis. Dialysis after alcohol-precipitation showed little influence on the functional groups of xanthan gum but the microstructure of xanthan gum changed greatly in that a filamentous structure was formed after this treatment. The fermentation performance could be evaluated accurately based on the suitable downstream processing. The purified xanthan gum had similar rheological properties (pseudoplasticity and solid-like/gel-like behavior) to the typical xanthan gum according to its flow curves and linear viscoelastic analysis. However, some rheological properties (existence of Newtonian plateau in flow curves, and crossover of storage modulus (G′) and loss modulus (G″) in frequency sweep test) of the purified xanthan gum solution were different from that of the typical xanthan gum. Overall, this study can offer some important information for efficient and effective purification of xanthan gum with a good rheological performance from low-cost Melaleuca alternifolia residue hydrolysate. • Effect of downstream processing on xanthan gum structure was evaluated. • Effect of downstream processing on xanthan gum rheological properties was learned. • Melaleuca alternifolia residue hydrolysate was suitable for xanthan gum production. • Purified xanthan gum with good rheological performance was obtained.

Quality control, preparation process optimizing and anti-inflammatory effects of Premna Puberula Pamp. Pectin

BackgroundPremna Puberula Pamp. Pectin (PP) was a Wudang functional food in China. It has the effect of dispelling fire, clearing heat and detoxification in folk medicine. However, little studies have been reported for their preparation, quality control, effects and toxicity. MethodsThe P. Puberula leaves were collected from different pharms and seasons. The compounds in PP were identified using UPLC-Q-TOF-MS/MS. UV-VIS spectrophotometry with phenol-sulfuric acid and sodium nitrite aluminum nitrate were conducted for analyzing the water-soluble sugars and total flavonoids, respectively. L9(34) orthogonal experimental method was used to optimize the preparation process of PP. For the pharmacological effects of PP, the swelling right hind paw of ICR mice was modeled using subcutaneous injection of carrageenan gum solution, and the local tissue inflammatory reactions of the model mice were investigated using vernier calipers and HE staining. The serum inflammatory factor expression was detected using ELISA. The acute toxicity experiments were carried out for safety assessment of PP in ICR mice. ResultsFifty-three compounds were initially identified in PP among which flavonoids were dominant (19 out of 53). The average values of water-soluble sugar content and total flavonoid content of PP were 13.366 and 4.970 mg/g, respectively. The best preparation process of PP was powder-liquid ratio 1: 20, temperature 90 °C, and stirring time 3 min. Data showed that PP reduced paw edema and decrease the serum level of IL-6, TNF-α and IL-1β in the model mice. There was no toxic effect of PP on mice at a total dose of 6000 mg/kg/24h. ConclusionIn summary, by optimizing the preparation process, PP with stable quality can be obtained. PP has anti-inflammatory effects without toxicity.

Catalytic Oxidation of Polymers Remained in Oilfield by Transition Metal-Ethylenediamine Complex

This work is intended to seek for an efficient Fe-based Fenton reagent for clean oxidation of waste fracturing fluid containing hydroxypropyl guar gum (HGG) and other polymers in wide pH range. A series of complex was prepared with transition metal and ethylenediamine (L) by the coordination. The catalytic performance of the complexes were evaluated in the degradation of HGG, and the reaction conditions were optimized. The kinetics of HGG degradation was evaluated by means of the chemical oxygen demand (COD) and the viscosity. The results show that Fe(II)L exhibits high catalytic performance for the degradation of hydroxypropyl guar gum in a wide pH range of 7.0–11.0, the COD removal can reach to 86.4%. Under the optimum experimental conditions, the relative viscosity of hydroxypropyl guar gum solution can be reduced effectively to 7.99 from 247 with 10.0% H2O2in presence of 5.0% Fe(II)L. Besides, under the optimized condition, three typical polymers used in oilfield can be degradated effectively.

Laboratory Evaluation and Field Application of a Gas-Soluble Plugging Agent: Development of Bottom Water Plugging Fracturing Technology

The currently reported bottom water sealing materials and fracturing technologies can hardly simultaneously achieve the high production and low water cut of gas reservoirs due to the complexity of various formation conditions. Therefore, without controlling the fracturing scale and injection volume, a kind of polylactide polymer water plugging material with a density of 1.15–2.0 g/cm3 is developed, which can be used to seal the bottom water of a gas–water differential layer by contact solidification with water and automatic degradation with natural gas. This technology can not only fully release the production capacity of the gas reservoir but also effectively control water production and realize the efficient fracturing development of the target gas reservoir. Laboratory test results show that the smart plugging agent has a bottom water plugging rate of 100%, and the low-density plugging agent has a dissolution rate of 96.7% in methane gas at 90 °C for 4 h and a dissolution rate of 97.6% in methane gas at 60 °C for 6 h, showing remarkable gas degradation performance. In addition, settlement experiments show that the presence of a proppant can increase the settlement rate of a plugging agent up to many times (up to 21 times) in both water and guanidine gum solution. According to the actual conditions of well J66-8-3, a single-well water plugging fracturing scheme was prepared by optimizing the length of fracture, plugging agent dosage, and plugging agent sinking time, and a post-evaluation method was proposed. It has guiding significance to the development of similar gas reservoirs.

Instrumental characterization of xanthan gum and scleroglucan solutions: Comparison of rotational rheometry, capillary breakup extensional rheometry and soft-contact tribology

Xanthan gum and scleroglucan, two rod-like polysaccharide hydrocolloids, are compared using a wide range of instrumental techniques and methods: steady shear flow, small amplitude oscillatory shear, first normal stress difference, capillary break-up and soft-contact tribology. The aqueous solutions of these two hydrocolloids with similar flow and viscoelastic profile show marked differences in capillary break-up time and apparent extensional viscosity. This result correlates with differences in first normal stress difference and, to a lesser extent, Stribeck curve behaviour. Formulating the hydrocolloids in concentrated sucrose solution (40 wt%) shifts relaxation profiles to longer times which greatly diminishes differences in rheological and lubrication behaviour. With exception of capillary break-up tests, no other methods showed statistically significant differences between the polysaccharides dissolved in the viscosified matrix. The toolbox of techniques is also applied to probe interactions of xanthan gum and scleroglucan with human whole saliva and bovine submaxillary mucin. We report no specific interactions between either hydrocolloid and salivary proteins and suggest that any cumulative effects must stem from specific sets of linear and non-linear rheological properties of saliva/hydrocolloid mixtures. • Rheology and tribology of xanthan gum and scleroglucan are compared. • Capillary break-up provides sensitive discrimination between hydrocolloids. • Xanthan gum and scleroglucan have similar hydrodynamic volume. • Relaxation spectrum of xanthan features faster modes compared to scleroglucan.

Lepidium perfoliatum seed gum: investigation of monosaccharide composition, antioxidant activity and rheological behavior in presence of salts

BackgroundIn the present study, the effects of NaCl and CaCl2 (0–200 mM) on the rheological properties of Lepidium perfoliatum seed gum (LPSG) as a novel potential source of hydrocolloid were investigated. Sugar composition and FTIR analysis were measured to supply more structural information.ResultsThe results illustrated that LPSG had small amounts of uronic acids (6.65%) and it is likely an arabinoxylan-type polysaccharide (it has 44.66% and 31.99% xylose and arabinose, respectively). The FTIR spectra also revealed that LPSG behaved like a typical polyelectrolyte due to the presence of carboxyl and hydroxyl groups. It was observed that the gum solutions exhibited viscoelastic properties in the presence of NaCl and CaCl2 salts. The tan δ values for all samples were less than 1 but greater than 0.1, exposing the weak gel-like behavior at different ion types and ionic strengths. With increasing salts concentrations, the limiting values of strain mostly increased due to the interchain interactions (from 1.46 to 4.61 and from 0.99 to 2.13 for NaCl and CaCl2, respectively). Therefore, the addition of salts increased the stiffness of mucilage solutions in the concentrated regime. The results of frequency sweep tests revealed that storage and loss moduli were increased with increasing ion concentration. This effect was more pronounced for LPSG solutions containing Ca2+. Among various models, the model of Higiro1 showed a higher efficiency to evaluate the intrinsic viscosity of LPSG for all co-solutes (R2 ≥ 0.98). With increasing the concentration of salts, the intrinsic viscosity of LPSG decreased. Calcium ions had a more diminution effect on intrinsic viscosity than sodium ions.ConclusionsTrying to adjust the salt concentration could modify the rheological properties of food products. Because food contains a variety of additives, further research should look into the rheological properties of LPSG at different pHs, as well as the presence of other salts and sugars often employed in the food industry. LPSG has the potential to be used in biomedical, pharmaceutical, food industries, tissue engineering, and cosmetic applications due to its biocompatibility, rheological properties, and antioxidant activities.Graphical

Power Consumption Characterization of Energy-Efficient Aerated Coaxial Mixers Containing Yield-Stress Biopolymer Solutions

The operations of mixing systems utilized in a variety of industrial applications for dispersing gas in non-Newtonian fluids are complex. The main challenge is to maintain a homogeneous medium throughout the vessel. In fact, coaxial mixers have demonstrated an energy-efficient performance for systems containing rheologically complex fluids. However, the accurate characterization of the power demand for gas dispersion in yield-stress fluids using coaxial mixers remains unclear. Hence, the objective of the present work was to investigate the power characteristics of a coaxial mixing system comprising the xanthan gum solution, which is a shear-thinning fluid possessing yield stress. The power consumption of an Anchor-PBT mixing configuration was measured experimentally at different central and anchor impeller speeds, rotation modes, and aeration rates. The main effects of the operating variables and their interactions were quantified using a central composite design of experiments. Significant effects of the central impeller speed and the interaction between the anchor speed and the aeration rate were identified. Also, a generalized power curve for this mixing system was proposed based on a predefined equivalent impeller speed and impeller diameter expressions to develop the novel power number and Reynolds number. The findings of this work provide an asset in designing and scaling up of energy-efficient aerated coaxial mixers by rapidly estimating the power demand.

Production and characterization of gum exudate from apricot tree: modeling the rheology of the obtained extract

PurposeThis paper aims to investigate the effect of shear rate, concentration (4–20 kg/m3) and temperature (20°C–60 °C) on the apparent viscosity of apricot gum solutions.Design/methodology/approachApparent viscosity has been measured using a rotational viscometer.FindingsIt has been observed that the shear stress and apparent viscosity values increase at high concentrations in the prepared apricot gum solutions. However, it is understood that the higher the temperature in the operation conditions, the lower the apparent viscosity results. Power-law is found the best-fitting model to illustrate the changes in temperature and concentration. According to the consistency coefficient and flow behavior indices, the apricot gum displayed shear-thinning behavior (pseudoplastic). The apricot gum is a polysaccharide with amino and uronic acids, according to Fouirer Transform Infrared Spektrofotometre spectra.Practical implicationsThe results suggest that power-law model can be used to estimate the viscosity of apricot gum solutions at different temperatures and concentrations for applications for which flow behavior should be taken into account.Originality/valueExudate gums have good rheological properties and, therefore, are widely used in the food industry. Apricot gum is a biodegradable and abundant polysaccharide that enhances viscosity, stabilizes suspension or emulsion and improves the flow properties of foods. Different rheological models are used to investigate rheological properties. However, those models are time-independent to fit the experimental data.

Shaly detritus embedded epoxy-resin coated proppants

Proppant plays a significant role in the hydraulic fracturing process, which can affect the production of oil and gas wells. Due to the high density and low adhesion force, the settling speed of traditional proppants is fast, which will lead to the blockage of a crack channel. In this study, a proppant with double layer structure is fabricated by coating epoxy-resin and shaly detritus on ceramic proppants for the first time, respectively. The epoxy-resin enables the shaly detritus to be coated on the proppant successfully, which can provide a new method for shaly detritus treatment. The adhesive ability of shaly detritus and epoxy-resin coated proppants (SEPs) is improved by 10.4% under the load force of 500 nN, which prolongs the time for the fracture to close. At the same time, the suspending ability of SEPs is two times higher than the uncoated proppants. Once the guar gum solution concentration is 0.3 wt%, the settling time of SEPs is 36.7% longer than that of the uncoated proppants, which can effectively reduce the settlement of proppants in the crack. In addition, the hydrophobicity of the SEPs is enhanced, which reduces the water-oil ratio of crude oil and increases the liquid conductivity tested by deionized water. In summary, this new proppant is expected to promote the development of unconventional oil and gas resources.

Effects of polysaccharides' molecular structure on membrane fouling and the related mechanisms.

Fouling behaviors of polysaccharides vary with their structure, while the mechanisms underlying this phenomenon remain unexplored. This work was carried out to explore the thermodynamic fouling mechanisms of polysaccharides with different structure. Carrageenan and xanthan gum were selected as the model polysaccharides with structure of straight and branch chains, respectively. Batch filtration experiments showed that xanthan gum solution corresponded to a more rapid flux decline trend, and specific filtration resistance (SFR) of xanthan gum (2.32 × 1015 m-1 kg-1) was over 10 times than that of carrageenan (2.21 × 1014 m-1 kg-1). It was found that, xanthan gum possessed a more disordered structure and a rather higher viscosity (15.03 mPa·s V.S. 1.98 mPa·s for carrageenan). Calculation of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed higher adhesion energy of xanthan gum (-42.82 my m-2 V.S. -23.26 mJ m-2 for carrageenan). Scanning electron microscopy (SEM) analyses showed that xanthan gum gel layer had a more homogenous structure and rigid polymer backbone, indicating better mixing with water to form a gel. As verified by heating experiments, such a structure tended to contain more bound water. According to this information, Flory-Huggins lattice theory was introduced to build a bridge between polymeric structure and SFR. It was revealed that branch structure corresponded to higher chemical potential change during gel layer formation, and higher ability to carry bound water, resulting in higher filtration resistance during filtration process. This work revealed the fundamental thermodynamic mechanism of membrane fouling caused by polysaccharides with different structure, deepening understanding of membrane fouling.

Effect of flaxseed oil double emulsion with tea polyphenol on the gel characteristics, antioxidant property and water mobility in reduced‐fat pork batter

SummaryThe changes in gel characteristics, rheology and antioxidant properties, microstructure and water mobility were studied to investigate the potential use of flaxseed oil double emulsion to replace pork back‐fat (25%, 50%, 75% and 100%) in reduced‐fat pork batter. The flaxseed oil double emulsion (pH 6.0) was made of 20 mL 0.5% tea polyphenol solution (w/w), 20 mL flaxseed oil, 60 mL 4% whey protein (w/w) and 400 mL 2% Arabic gum solution. The result showed that the TBARS, L*, and a* values of pork batter significantly decreased (P < 0.05) when the flaxseed oil double emulsion replacing the pork back‐fat was ≤50%. Meanwhile, the pH, emulsification stability, hardness, springiness, gumminess, chewiness, cooking yield and G′ at 80 °C significantly increased (P < 0.05). In addition, the mobility of water in cooked batter first decreased and then increased (P < 0.05) with increasing flaxseed oil double emulsion. In addition, the microstructure of cooked pork batter with 50% flaxseed oil double emulsion has a continuous, tighter and regular structure, with the pores being smaller and more uniform. Overall, the replacement of pork back‐fat with flaxseed oil double emulsion at 50% reduced‐fat content could improve the quality of pork batter.

Improved mixing of viscoelastic fluids by the use of hysteresis effect

A non-conventional mixing strategy utilizing the hysteresis effect of propeller jets in viscoelastic xanthan gum solutions was evaluated through decolorization mixing time experiments. The experiments consisted of capturing and analyzing the images of the flow patterns illustrated by a fast acid-base indicator reaction in a rectangular tank equipped with a side-entering propeller. A non-subjective image processing method using average color was compared with the literature. The steady operation using the axial flow pattern was found more effective than the one using the semi-radial flow pattern. The time-periodic operations with appropriate combinations of both flow patterns significantly enhanced mixing, whereas an inappropriate combination extended the mixing time. The unsteady mixing concept using the hysteresis effect shortened the mixing time, even when the propeller was operated at a reduced rotational speed. Hence, the mixing strategy utilizing the hysteresis effect can reduce mixing time and power consumption simultaneously.

Evaluation of natural polymer for mobility control in carbon utilization and geo-storage applications

Underground CO2 injection is susceptible to bypass, viscous fingering, and premature breakthrough which reduces the efficacy of CO2 storage. Hence, this work explores the usage of a natural polymer (Guar Gum) for promising control in mobility of injected CO2 in subsurface. Guar gum solutions of varying concentration (500–4000 ppm) were prepared in deionized (DI) water, and CO2 absorption (by pressure decay method) tests were performed at varying pressure (2–20 bar). CO2 absorption experiments were performed by pressurized CO2 in a stirring pot and kept the confined gas (pressure reduces as gas molecules get entrapped in the body of fluid) till equilibrium pressure (no further decrease in pressure) was reached. Rheological analysis confirmed that increasing polymer concentration yielded an increase in viscosity. This increase in viscosity showed two effects on CO2 absorption; (1): reduced CO2 absorption (in polymer solutions, compared to pure water) and (2): higher retention of entrapped CO2 inside the body of polymer solution. Maximum CO2 retention (≈9 h) was observed in 4000 ppm solution. Furthermore, pH and temperature tolerance tests indicate superior stability of guar gum solutions for pH >3 and temperature <75 °C. This study proposes the use of natural polymer as mobility control agents in geo-sequestration of CO2.

Study on cavern evolution and performance of three mixers in agitation of yield-pseudoplastic fluids

The hydrodynamic performance of three mixers (single shaft central mixer (SSC), single shaft off-centred mixer (SSO), dual shaft off-centred mixer (DSO), was investigated in the mixing of yield-pseudoplastic fluids (xanthan gum solutions) in the laminar regime. To explore and determine the efficiency of three mixers, both numerical and experimental approaches were adopted. The fluid rheology was described by the Herschel–Bulkley rheological model. Computational fluid dynamics was employed to simulate the apparent viscosity distribution, mixing time, and the flow pattern inside the stirred tank. The developed model was validated through experimentally measured torque. The influence mechanism of the rotational speed and fluid rheology on the cavern evolution was explored deeply. The performances of three mixers in this work were compared at the constant power input and fluid rheology with respect to the flow pattern, mixing time, and mixing efficiency. The results verify that the faster the rotating speed, the greater influence of the fluid rheology on the cavern evolution, and the more uniform apparent viscosity distribution. Moreover, the mixing time decreases continuously as the increasing power consumption per unit volume, and the dimensionless mixing time of DSO mixer was nearly 42.8% and 6.1% shorter than that of SSC and SCO mixer at the same Reynolds number, respectively. According to the mixing efficiency criteria, these data also revealed that DSO was more efficient than SSC and SSO.

Physicochemical, rheological and structural characterisation of Bene gum exudates from Pistacia eurycarpa Yalt

Bene gum was investigated for its physicochemical and structural properties in comparison to gum arabic and gum tragacanth. Elemental analysis of the Bene gum sample revealed sodium and potassium content to be 57.21 and 0.95 ppm, respectively. According to the rheological properties, all gum solutions exhibited non-Newtonian, shear-thinning in the concentration of 1% (w/w). Both storage modulus G′ and loss modulus G″ of all gums demonstrated elastic properties. The GC–MS analysis of dichloromethane extract confirmed the presence of eight constituents and α-pinene is the predominant constituent. The NMR spectra of the gum sample showed resemblance in individual sugar ingredients and the specific patterns of gum were observed. FTIR spectra of the studied gums displayed the presence of the same functional groups in the three gums. XRD studies revealed the amorphous nature of Bene gum. DSC and TGA thermograms were characteristic for each gum. Major thermal transitions were determined.

Iron Oxide Magnetic Nanoparticles with a Shell Made from Nanosilver-Synthesis Methodology and Characterization of Physicochemical and Biological Properties.

The interest in magnetic nanoparticles is constantly growing, which is due to their unique properties, of which the most useful is the possibility of directing their movement via an external magnetic field. Thus, applications may be found for them as carriers in targeted drug delivery. These nanomaterials usually form a core in a core–shell structure, and a shell may be formed via various compounds. Here, nanosilver-shelled iron oxide magnetic nanoparticles were developed. Various reaction media and various Arabic gum (stabilizer) solution concentrations were investigated to verify those that were most beneficial one in limiting their agglomeration as much as possible. The essential oil of lavender was proposed as a component of such a medium; it was used alone or in combination with distilled water as a solvent of the stabilizer. The particle size was characterized by dynamic light scattering (DLS), the chemical structure was characterized via FT-IR spectroscopy, the crystallinity was characterized by X-ray diffraction (XRD), and the surface morphology and elemental composition were verified via the SEM-EDS technique. Moreover, UV-Vis spectrophotometry was used to verify the presence of the shell made of nanosilver. Importantly, the particles’ pro-inflammatory activity and cytotoxicity towards L929 murine fibroblasts were also characterized. It was demonstrated that a 3% stabilizer solution provided a preparation of Fe3O4@Ag particles, but its stabilizing effect was not sufficient, as a suspension with micrometric particles was obtained; thus it was necessary to apply 4 h of sonication for their crushing. Next, the oil/water reaction medium was verified as beneficial in terms of nanoparticle formation. In such reaction conditions, the formation of particle agglomerates was strongly limited, and after 15 min of sonication a suspension containing only nanoparticles was obtained. The presence of a nanosilver shell was confirmed spectrophotometrically via XRD and SEM-EDS techniques. Importantly, the developed nanomaterials showed no cytotoxicity towards murine fibroblasts and no pro-inflammatory activity.

Studies on the storage stability of betacyanins from fermented red dragon fruit (Hylocereus polyrhizus) drink imparted by xanthan gum and carboxymethyl cellulose

Red dragon fruit is rich in health-benefited betacyanins that are susceptible to degradation. The present study was to improve the fermented red dragon fruit drink (FRDFD) betacyanins stability by incorporating hydrocolloids solution of xanthan gum (XG, 0.15–0.30%, w/v) and carboxymethyl cellulose (CMC, 0.3–0.5%, w/v) to produce Improved-FRDFD-dH2O. Results revealed the viscosities of all samples were significantly increased as the hydrocolloids concentration increased. All the samples’ pH, aw, total soluble solids (TSS) and betacyanins content were not significantly affected by the hydrocolloids solution added. After four-week storage (25 °C), the formulation of 0.3% XG and 0.5% CMC had significantly reduced the betacyanins degradation from 60.55% to 30.66%. Meanwhile, all samples added with 0.3% XG and 0.3–0.5% CMC remained no significant change in viscosity, pH, aw and TSS after storage. These conclude the hydrocolloids solution of 0.3% XG and 0.5% CMC successfully stabilise the betacyanins in the FRDFD at 25 °C over four-week storage.

Effect of Silica Nanoparticles in Xanthan Gum Solutions: Evolution of Viscosity over Time.

The effect of silica nanoparticles (NP-SiO2) in xanthan gum (XG) solutions was investigated through the analysis of viscosity profiles. First, hydrocolloid XG solutions and hydrophilic NP-SiO2 suspensions were characterized individually through rheological measurements, with and without salt (NaCl). Then, nanofluids composed of XG and NP-SiO2 dispersed in water and brine were studied through two different aging tests. The addition of nanoparticles was shown to produce a slight effect on the viscosity of the fresh fluids (initial time), while a more remarkable effect was observed over time. In particular, it appears that the presence of NP-SiO2 stabilizes the polymer solution by maintaining its viscosity level in time, due to a delay in the movement of the molecule. Finally, characterization techniques such as confocal microscopy, capillary rheometry, and Zeta potential were implemented to analyze the XG/NP-SiO2 interaction. Intrinsic viscosity and relative viscosity were calculated to understand the molecular interactions. The presence of NP-SiO2 increases the hydrodynamic radius of the polymer, indicating attractive forces between these two components. Furthermore, dispersion of the nanoparticles in the polymeric solutions leads to aggregates of an average size smaller than 300 nm with a good colloidal stability due to the electrostatic attraction between XG and NP-SIO2. This study proves the existence of interactions between XG and NP-SiO2 in solution.

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.

Investigation of the drag reduction of hydrolyzed polyacrylamide–xanthan gum composite solution in turbulent flow

AbstractIn this paper, the rheological properties, drag reduction properties, and flow field characteristics of hydrolyzed polyacrylamide (HPAM) solution, xanthan gum (XG) solution, and HPAM–XG composite solution were analyzed to explore the synergistic effect of flexible and rigid polymer. The experimental results show that the viscoelasticity and shear thinning of the composite solution are significantly enhanced compared with single‐component solution, which indicates that the rigid XG has an effect on the viscoelasticity of the flexible HPAM solution. Compared with the single‐component solution, the drag reduction rate of HPAM–XG composite solution is higher, and the mean flow field of HPAM–XG composite solution changes less after being sheared for 300 minutes, which means that not only the drag reduction effect of composite solution is better, but also the shear resistance. Compared with single‐component solution, the mean velocity distribution of the composite solution moves upwards most obviously in the logarithmic layer, the peak of velocity fluctuation in the main flow direction of composite solution is higher, the suppression degree of normal velocity fluctuation is deepened, and the corresponding vorticity intensity is also reduced. These changes in the flow field characteristics explain the reason for the drag reduction gain of the composite solution.