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1.
Non‐Newtonian rheology can have a significant effect on mixing efficiency, which remains poorly understood. The effect of shear‐thinning rheology in a Taylor‐Couette reactor is studied using a combination of particle image velocimetry and flow visualization. Shear‐thinning is found to alter the critical Reynolds numbers for the formation of Taylor vortices and the higher‐order wavy instability, and is associated with an increase in the axial wavelength. Strong shear‐thinning and weak viscoelasticity can also lead to sudden transitions in wavelength as the Reynolds number is varied. Finally, it is shown that shear‐thinning causes an increase in the mixing time within vortices, due to a reduction in their circulation, but enhances the axial dispersion of fluid in the reactor. 相似文献
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The influence of the emulsification process on the microstructure and physical stability of model water‐in‐oil‐in‐water (W/O/W) emulsions formulated with a green solvent and a mixture of amphiphilic copolymers as emulsifiers was investigated. Emulsions were prepared by applying a homogenization step with a rotor‐stator device followed by high‐pressure homogenization. Viscous flow tests, transmitted light optical microscopy, globule size distribution (GSD), and multiple light scattering (MLS) measurements were carried out. The GSDs obtained were the result of a recoalescence due to overprocessing and the coalescence of inner droplets with the outer water phase. MLS detected a main destabilization mechanism by creaming. The passing of the emulsion through a high‐pressure homogenizer (HPH) significantly delayed the creaming process. 相似文献
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Water‐in‐oil‐in‐water (w/o/w) multiple emulsions are considered that could be suitable components of functional dairy products. Such emulsions enable the preparation of low‐calorie products, encapsulation of bioactive components or microorganisms, and their protection during digestion. Because of the large phase interface, w/o/w emulsions are thermodynamically unstable. Therefore, their preparation and stabilization requires specific conditions. This review describes a potential industrial application of w/o/w emulsions in dairy products in detail and summarizes the value, preparation, stabilization, and evaluation of w/o/w emulsions in a dairy system. 相似文献
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Laboratory investigations have been undertaken to assess the suitability of heavy oil‐in water emulsions for pipeline transportation. The emulsions contained 65% oil in water and were prepared using polyethoxy nonylphenol surfactants. Two methods were employed for simulating the shear process which accompanies pipeline flow: a bench scale stirred vessel and a rotated pipe toroid. The progress of the emulsions towards inversion, at which point the oil becomes the continuous phase, was followed by measuring the surfactant concentration in the aqueous phase using liquid chromatography. At inversion the surfactant concentration falls below the threshold level required to sustain an oil‐in‐water emulsion. The experiments showed that the lifetime of the emulsion depends upon the initial surfactant dosage, the solids content of the oil, the intensity of shear and the nature of the shear process. Laminar flow was found to be less desirable than turbulent flow. 相似文献
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The effect of added solids on the rheology of oil in water emulsions was investigated. The range of the oil concentration, solids free basis, was (0-70%) and the solids volume fraction was (0-0.16). The solids mean diameter was 45 μm and it was about four times larger than the oil droplets. In the absence of added solids, non-Newtonian behaviour was observed for oil concentrations above 40%. The added solids increased the emulsion viscosity in a manner similar to the addition of solids to a homogeneous fluid. The rheological data of all the emulsion-solids mixtures investigated were correlated as relative viscosity versus solids volume fraction, where the relative viscosity is defined as the ratio of the emulsion-solids mixture viscosity to the solids-free emulsion viscosity. In the case of non-Newtonian systems, the emulsion-solids mixture viscosity and the solids-free emulsion viscosity were calculated at the same shear stress. The Barnea and Mizrahi viscosity correlation was found to fit the data well. 相似文献
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《分离科学与技术》2012,47(9):2111-2120
Abstract Six dendrimers with the same polyamidoamine (PAMAM) basic structure but different terminals/generations were synthesized by divergent method. The dendrimers were studied by surface tension measurement at the air‐water interface. The demulsification performance for oil/water (O/W) simulated crude oil emulsion and crude oil extract directly from field was investigated. The experimental results indicate that the three dendrimers terminated with ester groups were insufficient demulsifiers for crude oil emulsion. However, the three dendrimers terminated with amine groups exhibited excellent demulsification performance for O/W emulsions. As demulisifers, amine based dendrimers were superior to the commercial polyether ones (SP‐169 and BP‐169). The possible mechanisms for the nanocontainer effects of the dendrimers, through either surface adsorption or internal encapsulation, were discussed. 相似文献
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In this study, the viscosity reduction of heavy oil has been investigated through the formation of oil‐water emulsion using a bio/chemical emulsifier mixture. Four bioemulsifiers from indigenous Rhodococcus ergthropolis and Bacillus licheniformis strains were used to stabilize a highly‐viscous oil‐in‐water emulsion. The Taguchi method with an L9 orthogonal array design was used to investigate the effect of various control factors on the formation of the oil/water emulsions. An emulsion with lowest viscosity was formed using ACO4 strain. The substantial stability of the oil‐in‐water emulsion allows the heavy oil to be transported practically over long distances or remain stationary for a considerable period of time prior to utilization. As the result of Taguchi analysis, the temperature and concentration of the emulsifier had a significant influence on viscosity reduction of the emulsion. 相似文献
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María Jerez Francisco J. Deive Jorge Sineiro María J. Núñez 《European Journal of Lipid Science and Technology》2011,113(11):1402-1411
In this work, the ability of pine bark procyanidins to hinder oxidation in bulk corn oil and corn oil‐in‐water‐emulsion has been investigated. A preliminary characterisation of the obtained aqueous (AF) and organic (OW) fractions and subfractions suggested a very polar character and showed that both fractions possess remarkable antioxidant activity when minimum concentrations of 2 mg/mL are used. OW fractions and subfractions derived from both pine varieties were able to inhibit oxidation in oils. More specifically, two organic subfractions were the most efficient for retarding the degradation process, with levels of 62% and 50% after 8 days of treatment, respectively. Organic subfractions obtained from both varieties of pine also rendered possible inhibition levels in oil‐in‐water‐emulsions up to 80% after 4 days of oxidation, more than 3 times higher than the levels provided by tocopherol, a well‐known model commercial antioxidant, which confirms the excellent antioxidant potential of procyanidins from pine bark. Practical application: Lipid deterioration leads to losses in quality and nutritional value and to the development of off‐flavours in many foodstuffs. One way to overcome this drawback is by using antioxidants of natural origin, which is a subject of a great scientific and industrial interest, reflected by the growing number of papers and patents published during the last years. Since aqueous and organic fractions obtained from Pinus pinaster and Pinus radiata bark turned out to be an adequate source of procyanidins in previous investigations of our group, their possible antioxidant role in model lipid systems was investigated. This approach entails also another benefit in terms of waste valorisation, since pine bark is a typical residue of agroforestal industries. 相似文献
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The performance of several combinations of a wall scraping impeller and dispersing impellers in a coaxial mixer operated in counter‐ and co‐rotating mode were assessed with Newtonian and non‐Newtonian fluids. Using the power consumption and the mixing time as the efficiency criteria, impellers in co‐rotating mode were found to be a better choice for Newtonian and non‐Newtonian fluids. The hybrid impeller‐anchor combination was found to be the most efficient for mixing in counter‐rotating or co‐rotating mode regardless of the fluid rheology. For both rotating modes, it was shown that the anchor speed does not have any effect on the power draw of the dispersing turbines. However, the impeller speed was shown to affect the anchor power consumption. The determination of the minimum agitation conditions to achieve the just suspended state of solid particles (Njs) was also determined. It was found that Njs had lower values with the impellers having the best axial pumping capabilities. 相似文献
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For the configuration optimization of plate heat exchangers (PHEs), the mathematical models for heat transfer and pressure drop must be valid for a wide range of operational conditions of all configurations of the exchanger or the design results may be compromised. In this investigation, the thermal model of a PHE is adjusted to fit experimental data obtained from non‐Newtonian heat transfer for eight different configurations, using carboxymethylcellulose solutions (CMC) as test fluid. Although it is possible to successfully adjust the model parameters, Newtonian and non‐Newtonian heat transfer cannot be represented by a single generalized correlation. In addition, the specific heat, thermal conductivity and power‐law rheological parameters of CMC solutions were correlated with temperature, over a range compatible with a continuous pasteurization process. 相似文献
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Surfactant Concentration,Antioxidants, and Chelators Influencing Oxidative Stability of Water‐in‐Walnut Oil Emulsions 
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下载免费PDF全文 Jianhua Yi Wenbin Dong Zhenbao Zhu Ning Liu Yong Ding David Julian McClements Eric Andrew Decker 《Journal of the American Oil Chemists' Society》2015,92(8):1093-1102
Effects of surfactant concentration, antioxidants with different polarities, and chelator type on the oxidative stability of water‐in‐stripped walnut oil (W/O) emulsions stabilized by polyglycerol polyricinoleate (PGPR) were evaluated. The formation of primary oxidation products (lipid hydroperoxides) and secondary oxidation products (hexanal) decreased with increasing PGPR concentrations (0.3–1.0 wt% of emulsions). Excess surfactant might solubilize lipid hydroperoxides out of the oil–water interface, resulting in the decreased lipid oxidation rates in W/O emulsions. At concentrations of 10–1000 μM, the polar Trolox demonstrated concentration‐dependent antioxidant activity according to both hydroperoxide and hexanal formation. The antioxidant efficiency of the non‐polar α‐tocopherol was slightly reduced at the higher range of 500–1000 μM based on hydroperoxide formation. Both ethylenediaminetetraacetic acid (EDTA) and deferoxamine (DFO) at concentrations of 5–100 μM reduced the rates of lipid oxidation at varying degrees, indicating that endogenous transition metals may promote lipid oxidation in W/O emulsions. EDTA was a stronger inhibitor of lipid oxidation than DFO. These results suggest that the oxidative stability of W/O emulsions could be improved by the appropriate choice of surfactant concentration, antioxidants, and chelators. 相似文献
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Abdelilah El‐Abbassi Marcos A. Neves Isao Kobayashi Abdellatif Hafidi Mitsutoshi Nakajima 《European Journal of Lipid Science and Technology》2013,115(2):224-231
Argan oil is well known for its nutraceutical properties. Its specific fatty acid composition and antioxidant content contribute to the stability of the oil and to its dietetic and culinary values. There is an increasing interest to use argan oil in cosmetics, pharmaceutics, and food products. However, the formulation of highly stable emulsions with prolonged shelf life is needed. In this study, argan oil‐in‐water (O/W) emulsions were prepared using microchannel (MC) emulsification process, stabilized by different non‐ionic emulsifiers. The effects of processing temperature on droplet size and size distribution were studied. Physical stability of argan O/W emulsions was also investigated by accelerated stability testing and during storage at room temperature (25 ± 2°C). Highly monodisperse argan O/W emulsions were produced at temperatures up to 70°C. The obtained emulsions were physically stable for several months at room temperature. Furthermore, emulsifier type, concentration, and temperature were the major determinants influencing the droplet size and size distribution. The results indicated that a suitable emulsifier should be selected by experimentation, since the interfacial tension and hydrophilic–lipophilic balance values were not suitable to predict the emulsifying efficiency. Practical applications: MC emulsification produces efficiently monodisperse droplets at wide range of temperatures. The findings of this work may be of great interest for both scientific and industrial purposes since highly stable and monodisperse argan oil‐in‐water emulsions were produced which can be incorporated into food, cosmetic, or pharmaceutical formulations. 相似文献
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R.B. Krone 《Chemical Engineering Communications》1983,22(3):161-180
The lack of success of existing theories in describing viscosity of molecular liquids appears to be due to at least two difficulties. The mechanisms of viscous momentum transfer have not been identified, and the thermal motions of molecules can not be described until the spatial arrangement of molecules in a shearing liquid is known. This paper presents the results of an effort to identify the mechanisms of viscous momentum transfer. A model is proposed and a relation is derived from it that precisely fits viscosity data for a wide variety of Newtonian liquids. The effects of the spatial distribution of thermal motions and of intermolecule attraction are represented as parameters together with a Debye-like temperature. Values of these parameters are found from fitting the relation to published data. The parameters are found to be sensitive to molecular weight and to molecular configuration. Frequencies of interaction of molecules in the direction of the velocity gradient are of the order E 10 s -1. Abrupt shifts in these parameters with increasing temperature are found for paraffins at temperatures slightly above their melting points that are interpreted as disaggregation of molecules. Other abrupt shifts in the parameters at high temperatures for mercury and alcohol are interpreted as a change in the momentum transfer mechanism. Correlation of the parameters of the relation with molecular properties promises to provide predictive value. The relation provides a framework for further theoretical development. 相似文献
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R.B. KRONE 《Chemical Engineering Communications》2013,200(3-4):161-180
The lack of success of existing theories in describing viscosity of molecular liquids appears to be due to at least two difficulties. The mechanisms of viscous momentum transfer have not been identified, and the thermal motions of molecules can not be described until the spatial arrangement of molecules in a shearing liquid is known. This paper presents the results of an effort to identify the mechanisms of viscous momentum transfer. A model is proposed and a relation is derived from it that precisely fits viscosity data for a wide variety of Newtonian liquids. The effects of the spatial distribution of thermal motions and of intermolecule attraction are represented as parameters together with a Debye-like temperature. Values of these parameters are found from fitting the relation to published data. The parameters are found to be sensitive to molecular weight and to molecular configuration. Frequencies of interaction of molecules in the direction of the velocity gradient are of the order E 10 s ?1. Abrupt shifts in these parameters with increasing temperature are found for paraffins at temperatures slightly above their melting points that are interpreted as disaggregation of molecules. Other abrupt shifts in the parameters at high temperatures for mercury and alcohol are interpreted as a change in the momentum transfer mechanism. Correlation of the parameters of the relation with molecular properties promises to provide predictive value. The relation provides a framework for further theoretical development. 相似文献
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Coupled mass and heat transfer between a cone and a non‐Newtonian fluid was studied when the concentration level of the solute in the solvent is finite (finite dilution of solute approximation). Convective heat and mass transfer between a laminar flow and a stationary cone and between a rotating cone and a quiescent fluid is investigated. Solutions of both problems are found in the form of the dependencies of Sherwood number vs. Reynolds and Schmidt numbers. Coupled thermal effects during dissolution and solute concentration level effect on the rate of mass transfer are investigated. It is found that the rate of mass transfer between a cone and a non‐Newtonian fluid increases with the increase of the solute concentration level. The suggested approach is valid for high Peclet and Schmidt numbers. Isothermal and nonisothermal cases of dissolution are considered whereby the latter is described by the coupled equations of mass and heat transfer. It is shown that for positive dimensionless heat of dissolution, K > 0, thermal effects cause the increase of the mass transfer rate in comparison with the isothermal case. On the contrary, for K < 0 thermal effects cause the decrease of the mass transfer rate in comparison with the isothermal case. The latter effect becomes more pronounced with the increase of the concentration level of the solute in a solvent. 相似文献
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Kamal Hariri Samer Al Akhrass Christelle Delaite Patrick Moireau Gérard Riess 《Polymer International》2007,56(10):1200-1205
The system N‐vinyl‐2‐pyrrolidone (VP)/polydimethylsiloxane diglycidylether (PDMS‐DGE) is a typical example of an oil‐in‐oil emulsion formed by two non‐miscible liquids, where both phases are polymerizable in a ‘one‐pot’ procedure by two distinct reaction mechanisms. These oil‐in‐oil emulsions were characterized by their stability and by the particle size of the dispersed VP phase. Non‐aqueous dispersions (NADs) are obtained in a first step by free radical polymerization of the dispersed VP phase. The reaction kinetics, studied as a function of the initiator type and concentration, show that the polymerization rate is mainly influenced by the partition coefficient of the initiator between both phases. The NAD particle size could be tailored from a micrometer to a nanometer range by in situ formation of PVP‐PDMS graft copolymer. Hydrophilic–hydrophobic two‐phase materials can be obtained by polycondensation, in the presence of polyamines, of the epoxy‐functionalized PDMS continuous NAD phase. Copyright © 2007 Society of Chemical Industry 相似文献