Maximum Viscosity Research Articles

Anomalously enhanced thermal conductivity of graphite-oxide nanofluids synthesized via liquid-phase pulsed laser ablation

Graphite-oxide (GO) nanofluids with enhanced thermal conductivity are successfully prepared using pulsed laser ablation in liquid (PLAL) of a graphite target in deionized water. The effects of laser frequencies are investigated on the variations of GO nanoparticles. The morphology, structure and composition of the nanoparticles are characterized using various spectroscopic techniques. During the PLAL process, graphite is oxidized to GO which is inherently hydrophilic, no surfactant is required in the preparation of nanofluid. The laser frequency significantly affects the size and morphology of the GO nanoparticles during laser ablation, leading to a profound variation in the thermophysical properties of the GO nanofluids. At the laser frequency of 10 Hz, the maximum thermal conductivity enhancement of 82% is achieved at a temperature of 50 °C while the maximum viscosity increment is recorded at a temperature of 30 °C. This study shows the great potential of the PLAL method in synthesizing GO nanofluid with anomalously enhanced thermal conductivity.

WITHDRAWN: Optimization of process parameters by Hybrid Taguchi-Grey Relational Analysis for thermal behaviours of lubricant oil of worm gearbox

In this research work, the major focus is given on thermal behaviours of lubricant oil of worm gearbox. In worm gearbox due to sliding motion between teeth's of worm and worm wheel cause friction energy loss. The friction energy loss is converted into heat energy and that heat energy is dissipated into lubricant oil of worm gearbox. The performance of lubricant oil is decreasing due to the rise in temperature which causes decreases in the overall performance of gearbox. To observe thermal behaviour of lubricant oil of worm gearbox Lubricant Heating Time (time required to increase the temperature of the oil from 35 °C to 50 °C) and the Viscosity of oil (at 50 °C) is taken as response parameters while Load on the worm wheel (L), Volume of oil (V) and Type of oil (T) are taken as process parameters. Every process parameter is varied at three dissimilar levels. Taguchi optimization technique (L9) is used for the optimization of experiments for this Minitab19 software is used. Grey Relational Analysis (GRA) is used to determine the optimum levels of process parameters. The optimum levels of process parameters for maximum Lubricant Heating Time and maximum Viscosity are L1V2T2 i.e. the lowest level of Load on the worm wheel, intermediate level of Volume of oil and Type of oil B. ANOVA is performed to determine the relative contribution of process parameters on Lubricant Heating Time. ANOVA results show that Type of oil is the maximum influence parameter (98.26%) followed by Load on the worm wheel (0.99%) and Volume of oil (0.72%) on Lubricant Heating Time. There exist an inverse relationship between oil viscosity and lubricant heating time.

Effect of pH on the Structure and Dynamics of Wormlike Micelles in an Amino Acid-Derived Surfactant Composition.

We studied the impact of pH as a thickening mechanism on the structure and dynamics of wormlike micelles in a mixture of sodium lauroyl sarcosinate (SLSar) and cocamidopropyl hydroxysultaine (CAHS). The viscoelastic properties were obtained using mechanical rheometry and diffusing wave spectroscopy, which provided access to a wide range of frequencies. By using a mesoscopic simulation method [Zou; Larson. J. Rheol. 2014, 58 (3), 681-721], characteristic micelle lengths and times were extracted including contour length, persistence length, entanglement length, reptation time, breakage time, breakage rate, and breakage rate constant. The interplay of pH-dependent reptation times (10-1000 ms) and breakage times (4-38 ms) leads to a minimum in the ratio of reptation time to breakage time of about 0.02 at pH 4.8. This minimum was closely associated with the sharp increase and decrease of the observed viscosity maximum at pH 4.8 in this system. These values may be contrasted with much longer breakage times (20-300 ms) that have been measured in more easily thickened sulfate-based systems. The low breakage times of the SLSar/CAHS system were attributed to the high and pH-sensitive breakage rate constants (0.01-0.17 ms-1 μm-1).

Computational study on nanoparticle shape effects of [formula omitted]-silicon oil nanofluid flow over a radially stretching rotating disk

This paper examines the shape effect of nanoparticles in the flow of Al2O3− silicon oil nanofluid around a rotating disk which extends radially. Magnetic field and radiation energy results are also added. In this research, five distinct shaped Al2O3 nanoparticles, sphere, brick, cylinder, platelet and blade have been used. All five distinct shaped nanoparticles are assumed to have equal diameter dp=45nm. Each form is suspended in equal volume. The related non-linear equations have been implied and reformatted by Von Karman transformations out under boundary layer conditions. The aforementioned non-linear differential equations is evaluated more by shooting testing method, including the Iterative Power Series (IPS) methodology. The progress of flow patterns with potential consequences for control parameters is mathematically dealt and presented graphically. The present analysis is validated comparing with the earlier described research. In fact, the nanofluid containing platelet-shaped nanoparticles seems to have the maximum dynamic viscosity and nanoparticles that are blade-shaped has the strongest thermal conductivity. Friction coefficient is found to be higher in the strength of magnetic field and when disk is radially stretched. Heat transfer rate is greatly enhanced on neglecting the magnetic field and radiation effects.

Starch digestibility and quality of cookies made from acid and heat-moisture treated sweet potato starch and wheat flour composites

Nowadays, resistant starch (RS) has been widely produced using the physical modification methods and applied for producing low-carb foods. In this study, quality and digestibility of cookies supplemented with 20% of native, heat–moisture treated, and citric acid and heat-moisture combined treated starches (NS, HS, and AHS, respectively) were investigated. Composite flours had lowered swelling index and increased water absorption values than did the wheat flour. Both maximum and final viscosities of the paste with 20% AHS substitution were significantly lower than those with 20% NS or 20% HS substitution. Resistant starch contents increased from 8.0% of the control cookie to 10.6%, 18.4% or 25.4% of the cookies substituted with 20% NS, 20% HS or 20% AHS, respectively. The cookie substituted with 20% AHS was a medium Glycemic Index (GI) food, whereas the cookie substituted with 20% NS or HS was the high GI food, similar to the control cookie. Although the cookie substituted with 20% AHS had lower volume than the control cookie, their sensory quality values were not significantly different. Thus, the combined acid and heat–moisture treated sweet potato starch could be substituted for 20% of wheat flour to increase the RS content and reduce the GI values of cookies as compared to those of the native or heat–moisture treated starch.

Nuclear Magnetic Resonance Diffusometry of Linear and Branched Wormlike Micelles.

Diffusion studies using nuclear magnetic resonance (NMR) spectroscopy were conducted on two model surfactant solutions of cetyltrimethylammonium bromide/sodium salicylate (CTAB/NaSal) and cetylpyridinium chloride/sodium salicylate (CPCl/NaSal). By increasing the salt-to-surfactant concentration ratio, these systems display two peaks in the zero-shear viscosity and relaxation time, which are indicative of transitions from linear to branched micellar networks. The goal of this work is to assess the sensitivity of NMR diffusometry to different types of micellar microstructures and identify the mechanism(s) of surfactant self-diffusion in micellar solutions. At low salt-to-surfactant concentration ratios, for which wormlike micelles are linear, the surfactant self-diffusion is best described by a mean squared displacement, Z2, that varies as Z2 ∝ Tdiff0.5, where Tdiff is the diffusion time. As the salt concentration increases to establish branched micelles, Z2 ∝ Tdiff, indicating a Brownian-like self-diffusion of surfactant molecules in branched micelles. This result indicates that NMR diffusometry is capable of differentiating various types of micellar microstructures. In addition, the self-diffusion coefficient of the surfactant molecules in linear and branched micelles are determined, for the first time, by comparing the existing restricted diffusion models and are shown to be much slower than the diffusion of proton molecules in the bulk. Moreover, in linear and moderately branched wormlike micelles, the dominant mechanism of surfactant self-diffusion is through the curvilinear diffusion of the surfactant molecules along the contour length of the micelles, whereas in the branched micelles, before the second viscosity maxima, the surfactant self-diffusion could arise from a combination of micellar breakage, exchange between micelles and/or the bulk.

Functional characterization of mango seed starch (Mangifera indica l.)

Mango agribusiness is an expanding activity in Brazil and produces a large volume of waste that are not reused. Mango seeds are one of the residues from fruit processing, and are a potential starch source. In the food industry, starch is used as a functional ingredient, allowing the preservation of important characteristics of foods. The objectives of this study were to extract starch from mango seed, and to characterize it in terms of its physicochemical, technological and rheological properties. Starch extraction involved washing, cutting, and milling the mango seeds. The extraction yield was 53.89% and the starch granules presented spherical to irregular ellipsoidal shapes with superficial grooves and average size of 20 µm. It had an initial paste temperature of 75.3 °C and a maximum viscosity of 706 BU at 88.1 ºC. The rate of syneresis, 1.51%, was considered low, which indicates a starch with good stability at low temperatures. In the texture profile it was found that there was a significant difference (p ≤ 0.05) in the texture profile of gels with sodium chloride, sucrose and citric acid added. The gel with emulsifier showed no significant difference in any of the parameters analyzed (hardness, cohesiveness and gumminess). The properties of the starch indicated great potential for use in food products.

Optimized formulation of thermoresponsive nanoemulsion-based gel for enhanced oil recovery (EOR) application

A thermoresponsive system of a nanoemulsion-based gel with favorable characteristics to enhanced oil recovery (EOR) application is presented. A full factorial design study with different formulations of thermosensitive nanoemulsion-based gels was performed to assess the influence of the oil chain length, concentration of polyethylene glycol (PEG 400) and concentration of oil on the rheological behavior of the system. A formulation with low viscosity at room temperature and high viscosity at the temperature of the oil extraction well was presented. Hexane (6-carbon chain), capric acid (10-carbon chain) and isopropyl myristate (17-carbon chain) were used in concentrations of 5%, 10%, 15% and 20% wt%, also varying the concentration of PEG 400 in 0%, 3%, 6% and 9% wt%. The thermosensitive polymer used was a mixture of Pluronic® F-127 and Pluronic® F-68 6:1 wt% at 4.7% concentration. The surfactants used were Tween 80 and Span 80 (HLB = 13) at 20%. The formulation containing 20% isopropyl myristate (IPM) without the addition of PEG 400 showed a better response, with an increase in viscosity of more than 38 times in relation to its viscosity at 25 °C, and the maximum viscosity was reached at 53 °C. This is a promising formulation for EOR technology.

Influence of VNIIMK 620 and Itil flax varieties on the rheological properties of wheat dough

The influence of the mass fraction of flax in the composite mixture on the state of the carbohydrate – amylase complex of the studied system was studied. It was found out that the maximum viscosity of the suspension and the rate of starch gelation in a mixture of wheat flour with whole-ground flax is lower than in the suspension, where the dispersed phase was wheat flour, but higher than that, where the dispersed phase is flax.
 The influence of flax on the rheological characteristics of wheat dough in the Chopin+ Mixolaba protocol was revealed. It is found out that with an increase in the mass fraction of flax in the composite mixture from 5 to 20%, the formation time of the test and its water absorption capacity increases, and the stability decreases. When the mass fraction of flax increases, the torque values at the extreme point of the function C2, which characterizes the dilution of the dough, increase; and at the point C5, which characterizes the retrogradation of starch, they decrease.

Influence of particle shape and sample preparation on shear thickening behavior of precipitated calcium carbonate suspensions

To more closely bridge the technological advent of shear thickening fluids with material applications, a well-defined sample preparation protocol is needed. In this work, preparation conditions have been studied for suspensions of precipitated calcium carbonate (PCC) particles by means of a 2k Factorial Experimental Design (DOE), with three center points, and as a function of PCC particle shape. Shear thickening maximum viscosity was the response variable and the corresponding analyzed factors were: particle concentration, stirring time, stirring speed and sonication time. Samples with rosette PCC particles exhibited a stronger shear thickening behavior in view of stronger frictional interactions and they also shear thicken at lower shear rates compared to samples with acicular PCC particles. In the case of acicular PCC particles, the shear thickening fluid that provided the highest maximum viscosity ηm was obtained with higher particle concentration, lower stirring speed and shorter sonication time, as acicular PCC particles align more easily in the flow direction. In the case of rosette PCC particles, ηm was achieved with higher particle concentration, longer stirring time and shorter sonication time. Finding optimal sample preparation conditions and particle shapes that take the most advantage of shear thickening behavior is very important for final applications.

Thermosyphon Flat Plate Collector with Nanodiamond-Water Nanofluids: Properties, Friction Factor, Heat Transfer, Thermal Efficiency, and Cost Analysis

Thermal efficiency, friction factor, heat transfer, and cost analysis of a flat plate collector operates with water-based nanodiamond nanofluids under thermosyphon (natural circulation) conditions are investigated experimentally at 0.2%, 0.4%, 0.6%, 0.8%, and 1.0% particle volume concentrations. The thermophysical properties of the working fluids are analyzed as well. Results show that the maximum thermal conductivity and viscosity enhancements are obtained by using 1.0 vol% concentration of nanofluid and found to be 22.86% and 79.16%, respectively, compared to water at a temperature of 60 °C. The maximum increases in Nusselt number are 19.53% and 36.17% using 1.0 vol% concentration of nanofluid compared to water at Reynolds number of 140 and 345, respectively. The maximum increases of friction factor are attained by using 1.0 vol% concentration of nanofluid and found to be 1.14 times and 1.25 times of water friction factor at Reynolds number of 143 and 345, respectively. The collector thermal efficiency increases from 57.15% using water to 69.85% using nanofluid with a concentration of 1.0%. The collector cost decreases approximately by 18.18% for 1.0 vol% nanofluid compared to water. The relative deviations of the equations developed to evaluate Nusselt number and friction factor are within ± 2.5%.

Towards a general understanding of the effects of hydrophobic additives on the viscosity of surfactant solutions

Small amounts of nonpolar additives can have a tremendous impact on viscosity and viscoelasticity of giant micelles and completely change macroscopic properties. The effect can be best understood with the establishment of complete salt curves by screening surfactant viscosity as a function of electrolyte concentration. From previous studies in micellar systems of sodium laureth sulfate (SLES) with fragrance molecules, two independent mechanisms could be identified, co-solvent type interactions leading to a decrease of the maximum viscosity, and co-surfactant type interactions that cause the salt curve shift to the left. Our studies here reveal two new mechanisms with different effects on the salt curve. In particular, with long-chain hydrocarbons from n-octane to n-tetradecane a right shift was observed, whereas with short-chain or cyclic hydrocarbons such as n-hexane or cyclohexane the maximum viscosity increases. The two effects are interpreted via an extension of a recently developed thermodynamic model where changes in viscosity can be rationalized by a rebalance of the relative concentration of the three co-existing microphases: endcaps, cylinders and branching points. The right shift is linked to a continuous transformation of giant micelles into microemulsions containing an internal fluid. On the other hand, viscosity at maximum scales with the generalized bending constant of the molecular film forming the three microphases of the surfactant system. The total of four proposed mechanisms of solute-surfactant interactions that can impact amplitude and position of salt curves are independent and of different origin, but they are all intimately linked to the location of the additives within the surfactant film: headgroup, micellar interface, surfactant tail region or micellar core. Further investigation will be necessary to understand the molecular driving forces that position nonpolar additives within micellar aggregates, which would be the key for successful prediction of their impact on macroscopic viscosity.

Thermal Efficiency, Heat Transfer, and Friction Factor Analyses of MWCNT + Fe3O4/Water Hybrid Nanofluids in a Solar Flat Plate Collector under Thermosyphon Condition

The heat transfer, friction factor, and collector efficiency are estimated experimentally for multi-walled carbon nanotubes+Fe3O4 hybrid nanofluid flows in a solar flat plate collector under thermosyphon circulation. The combined technique of in-situ growth and chemical coprecipitation was utilized to synthesize the multi-walled carbon nanotubes+Fe3O4 hybrid nanoparticles. The experiments were carried out at volume flow rates from 0.1 to 0.75 L/min and various concentrations from 0.05% to 0.3%. The viscosity and thermal conductivity of the hybrid nanofluids were experimentally measured at different temperatures and concentrations. Due to the improved thermophysical properties of the hybrid nanofluids, the collector achieved better thermal efficiency. Results show that the maximum thermal conductivity and viscosity enhancements are 28.46% and 50.4% at 0.3% volume concentration and 60 °C compared to water data. The Nusselt number, heat transfer coefficient, and friction factor are augmented by 18.68%, 39.22%, and 18.91% at 0.3% volume concentration and 60 °C over water data at the maximum solar radiation. The collector thermal efficiency improved by 28.09% at 0.3 vol. % at 13:00 h daytime and a Reynolds number of 1413 over water data. Empirical correlations were developed for friction factor and Nusselt number.

Effect of carrier fluid and particle size distribution on the rheology of shear thickening suspensions

We present a systematic rheological study on the fumed silica suspensions to understand the effect of particle and fluid parameters on the critical shear rate and shear thickening ratio. It was observed that removal of air bubbles and water contamination is crucial to prepare good shear thickening fluids. A careful sample preparation method was adopted to properly disperse the fumed silica particles in polyethylene glycol solution, and we achieved discontinuous shear thickening at low particle concentration. It was observed that the critical shear rate in shear thickening suspension is strongly influenced by both carrier fluid and particle concentration. However, the shear thickening ratio is mainly influenced by the particle parameters and the frictional forces between the particles. Increasing the amount of smaller particles in the suspension significantly decreases the maximum viscosity and shifts the onset of shear thickening to higher values of critical shear rates with much smaller shear thickening ratio. Further, a possible mechanism has been proposed based on the influence of carrier fluid and particle size distribution to explain the rheological behaviour of shear thickening suspension. Our study supports the theory of particle-particle frictional contacts as the main reason for the discontinuous shear thickening.

Design and evaluation of mucoadhesive in situ liposomal gel for sustained ocular delivery of travoprost using two steps factorial design

Travoprost (TRAVO) is a prostaglandin analog used to reduce the intraocular pressure (IOP) for patients suffering from glaucoma and ocular hypertension. The aim of the present study was the development of a novel in situ mucoadhesive ocular liposomal gel to prolong and improve therapeutic efficacy of TRAVO. With this purpose, liposomal formulations were prepared by implementing a full factorial design to study the effect of three factors; type of permeation enhancer (PE), PE concentration and the ratio of lecithin: cholesterol at two levels. The evaluated responses were entrapment efficiency (EE), vesicle size (VS), polydispersibility (PDI) and zeta potential (ZP). L6 (selected liposomal formulation), composed of 20% sodium deoxycholate (Na DOC) and lecithin: cholesterol at 4:1 ratio showed high EE (67.55%), suitable Ps and PDI (74.19 nm and 0.433) and ZP (−75.5 mv). L6 was incorporated in a second 31 × 21 design to study the effect of concentration of gellan gum (at three level) and carbopol 934 (at two levels) to develop in situ mucoadhesive gel. Selected liposomal in situ gel LISG2 (0.25% gellan gum and 0.5% carbopol 934), showed minimum release (18.2%) after 30 min and maximum release after 24 h (72.5%) and achieve maximum viscosity (4445cps) at physiological conditions, mucoadhesive force (0.438 N), with minimum viscosity (124 cps) at normal conditions. Selected LISG2 will be further in vivo evaluated for irritation and pharmacokinetic. TRAVO LISG was non irritant and showed improved bioavailability (higher concentration of TRAVO in aqueous humor) when compared to the marketed product, and showed more prolonged effect compared to liposomal formulation.

Preparation and property evaluation of a temperature-resistant Zr-crosslinked fracturing fluid

Compared with the traditional water-based fracturing fluid thickener guanidine gum, the price of synthetic polymer is relatively low, and the temperature resistance, shear resistance and viscoelasticity of the formed fracturing fluid are better. Therefore, the fracturing fluid formed by the crosslinking of HPAM and organic metal crosslinker will become one of the hot spots in the research of water-based fracturing fluid. In this paper, zirconium oxychloride, acetic acid and triethanolamine were used as raw materials to prepare organic Zr-crosslinked agent. The polymer gel was formed by crosslinking the organic Zr-crosslinked agent with the acrylamide copolymer KY-5S solution, and the viscosity of the gel with different concentrations was investigated. The performance of the fracturing fluid was evaluated through laboratory experiments. The results showed that the viscosity of the fracturing fluid remained above 100mPas at the shear rate of 170s−1 and after 2h of shear at 140°C. When the temperature was 20°C, the shear stress was 0.1Pa, and the frequency f varied from 0.1 to 10Hz, the elastic modulus of fracturing fluid was at least 11.6Pa, and the viscous modulus was at least 8.54Pa. At the temperature of 90°C, when the addition of glue breaker was 0.01wt%, the longest breaking time was 3h, and the maximum viscosity of breaking liquid was 4.05mPas. The damage rate of core permeability of glue breaker was about 13%. When the temperature was 25°C and the shear rate was 0–170s-1, the viscosity of fracturing fluid remained above 200mPas.

Ballistic Performance of Shear Thickening Fluids (STFs) Filled Paper Honeycomb Panel: Effects of Laminating Sequence and Rheological Property of STFs

In order to exploit future soft body armor to achieve a more comprehensive protection than just the torso part of the body, in this study, shear thickening fluids (STFs) with different rheological properties are fabricated by planetary mixer and three-roller mills to investigate the mixing process effect on the resultant rheological behavior. Rheological results indicate the critical shear rate and the maximum viscosity of STF are deeply influenced by the dispersion degree of nano-silica particles in PEG. These STFs are then filled into a paper honeycomb partition to prepare a STF-based protective structure. Different laminating sequences of the composite panels composed one STF structure layer and nineteen layers of Kevlar fabric are obtained by simply placing the STF structure at different positions in the composite panels. The ballistic tests are conducted according to the NIJ 0101.06—Type II standard using 9 mm Full Metal Jacketed Round Nose bullets. Our results show that the absorbed energy of the composite panel with STF that thickens at higher shear rate is higher compared to that using STF that thickens at a lower shear rate. It suggests the STF with higher critical shear rate would be optimally used in ballistic impacts. In addition, ballistic testing results confirm that the STF structure placed at the rear position can significantly contribute to the increase in impact resistance.

Co-slagging characteristics of coal and biomass ashes considering entrained flow slagging gasifier

This study systematically investigated the co-slagging characteristics of high-rank coal and biomass ashes considering entrained flow slagging gasifier. Despite favourable performance parameters, coal might not be feasible for entrained flow gasification because of not forming slag within the gasifier operating temperature (1200–1500 °C). To overcome this issue, co-gasification can be a potential solution, which simultaneously helps to reduce the carbon footprint and environmental impact. Hence, this study studied the feasibility of co-gasification of coal and biomass by testing co-slagging behaviour of bituminous coal and pine park biomass ashes. The slag viscosity is measured using a Brookfield DV-III Ultra rheometer coupled with a high-temperature furnace. Results show that pure coal ash does not form slag using the maximum furnace temperature of 1670 °C. However, co-slagging by 50/50 (wt./wt.) ratio of coal and biomass ash (PB50) significantly drops the slagging temperature due to the higher fluxing agents (i.e. CaO) in biomass ash. The temperature of critical viscosity was determined to be 1390 °C using PB50 ash, which maintained the maximum industrial viscosity limit of 25 Pa s up to the temperature of 1360 °C.

Thermoresponsive dynamic BAB block copolymer networks synthesized by aqueous PISA in one-pot

The incorporation of neutral hydrophilic monomer units in the hydrophobic B blocks of BAB copolymers produces transient networks exhibiting a thermoresponsive behavior with a maximum of viscosity in water.

Viscosity prediction and optimization of ZnO-coconut oil nanofluids using numerical simulation

The present study aimed at the prediction and optimization of ZnO-coconut oil nanofluid using numerical simulation. Two inputs, temperature, and nanofluid concentration, and one output (viscosity) were determined for simulation. The simulation was performed in the temperature range 35 to 55 and nanofluid concentration 0 to 0.48. The multivariant empirical model was developed and validated with the experimental data, and the results showed a good agreement. The model was further used for the optimization of process parameters such as temperature and nanofluid concentration with the objective of minimization and maximization of viscosity. The minimum viscosity was obtained at temperature (55 °C) and nanofluid concentration (0), while the maximum viscosity was obtained at temperature (35 °C) and nanofluid concentration (0.48).