Initial Stage Of Mixing Research Articles

Diffusion mechanisms of convective instability in liquid and gas mixtures

AbstractA review of publications on stability of mechanical equilibrium of multicomponent mixtures in gases and liquids under non‐isothermal and isothermal conditions is given. Studies where diffusion in binary and multicomponent mixtures led to the occurrence of instability of mechanical equilibrium of the system have been analyzed. The main attention is paid to the description of approaches predicting the areas where there are increasing convective disturbances, as well as the determination of the spectrum of thermophysical parameters where the contribution of convection to heat and mass transfer is negligible. At the same time, the problems determining the role of diffusion, thermodiffusion, and double diffusion mechanisms in the separation of mixture components at the boundary of convective instability were given priority in the description. The results of investigations related to the study of the evolution of flows arising due to instability at the initial stage of mixing were also discussed.

Investigating PCM encapsulated NaOH additive for set-on-demand in 3D concrete printing

This study investigates the print head activation of an encapsulated additive to attain on-demand setting in 3D concrete printing for buildability enhancement. Sodium hydroxide (NaOH) is considered as a set accelerating additive, and it is encapsulated using a phase change material (PCM). The encapsulated NaOH is added during the initial mixing stage and the mix is heated at the print head to release the NaOH, which subsequently reacts with cementitious materials to attain the on-demand setting of the printed layer. The dosage of NaOH was varied from 0 to 5 wt% of the cement to determine the optimum dosage for buildability enhancement. The results showed that the static yield strength of the printable concrete after the print head activation increased with the NaOH dosage, however, this has resulted in reducing the compressive strength of the mixes. The fresh and hardened properties of the mixes with encapsulated NaOH were compared with the mix with nano-clay to assess two buildability enhancement approaches (set-on-demand vs traditional). It was found that the buildability enhancement using nano-clay was limited by pumpability constraints, whereas the activation of encapsulated NaOH was limited by compressive strength reductions.

Point-to-Point Efficient Grafting Improved Compatibility of Boron-Based Fuel-Rich Propellants.

Due to the high mass calorific value, boron powder is widely used in energetic material systems such as solid propellants and ignition powders. Especially, boron powder has very broad application prospects in the field of fuel-rich propellants. However, due to the cross-linking reaction between the boric acid contained on the surface of boron powder and an adhesive called hydroxylated polybutadiene (HTPB), the viscosity of the propellant mixture system increases sharply, which seriously affects the preparation of the propellant. In this paper, "click chemistry" is intended to be used to graft the functional groups on the surface of boron powder to reduce the viscosity of the boron powder and HTPB in the initial mixing stage. In addition, a rheometer was used to test the viscosity of the boron powder and the HTPB system. The test results showed that compared to the viscosity of the raw boron powder system at 24.1 Pa·s, the mixing termination viscosity of the grafted sample was 17.1 Pa·s, a decrease of 29.0%.

Solvent Controls Nanoparticle Size during Nanoprecipitation by Limiting Block Copolymer Assembly.

Control of the properties of nanoparticles (NPs), including size, is critical for their application in biomedicine and engineering. Polymeric NPs are commonly produced by nanoprecipitation, where a solvent containing a block copolymer is mixed rapidly with a nonsolvent, such as water. Empirical evidence suggests that the choice of solvent influences NP size; yet, the specific mechanism remains unclear. Here, we show that solvent controls NP size by limiting block copolymer assembly. In the initial stages of mixing, polymers assemble into dynamic aggregates that grow via polymer exchange. At later stages of mixing, further growth is prevented beyond a solvent-specific water fraction. Thus, the solvent sets NP size by controlling the extent of dynamic growth up to growth arrest. An a priori model based on spinodal decomposition corroborates our proposed mechanism, explaining how size scales with the solvent-dependent critical water fraction of growth arrest and enabling more efficient NP engineering.

WAYS TO MANAGE THE QUALITY OF NANOCRETE

"This article presents an integrated approach to the design of the concrete composition, which contains a combination of various types of modification of the concrete mixture by introducing a hyperplasticizer based on polycarboxylate ether, as well as reinforcing fibers (anisotropic additive), activation of aggregates, binders and mixing water. It is shown how the reinforcement of concrete cement stone with fibers reduces the formation of shrinkage cracks and increases its frost resistance, and polycarboxylate nanoparticles significantly reduce the amount of water used and the drying time of the material, making the steam treatment stage optional. The article presents the mechanism of action of the hyperplasticizer, the test results of samples-beams and samples-cubes at the age of 28 days, as well as the result. As a result of the action, polycarboxylate particles are adsorbed on the surface of cement grains, repel each other and set the cement mortar in motion. With the help of this approach, a condition is created for the formation of a cement stone nanostructure of various functional actions with the help of nanoparticles already at the initial stage of mixing."

Study on Flow Distribution and Structure Optimization in a Mix Chamber and Diffuser of a CO2 Two-Phase Ejector

This paper establishes a mathematic model of a CO2 two-phase ejector to investigate flow distribution in the components of a mixing chamber and diffuser. The suction chamber was modeled using the characteristic line method to describe the development process of the supersonic expansion wave, and the mixing chamber, as well as diffuser models, were built based on the double-flow model. The reliability of the model was verified by experimental data. The distributions of flow parameters along the axis of the mixing chamber and diffuser were analyzed under different expansion ratios of the ejector. Structure optimizations of the mixing chamber and diffuser were conducted. The results showed that the primary flow temperature gradually increased along the axis of the mixing chamber and diffuser, but the Mach number distribution decreased for a certain ejector expansion ratio. The temperature and Mach number of the secondary flow showed the opposite trend. Moreover, at the initial stage of mixing, the fluid pressure increased rapidly, and the Mach number of the primary flow decreased rapidly. The gas-phase fraction of primary flow increased gradually in the mixing chamber and was stable in the diffuser. When the length–diameter ratio of the mixing chamber was about 10.8–12, it was beneficial to mix uniformity, and when the expansion angle of the diffuser was 4–6°, the ejector had a better ejector efficiency.

Temporal and spatial variation characteristics of soil mechanical composition after aeolian soil improvement by soft rock in Mu Us sandy land

Based on the field experiment of compound soil with volume mixing ratio of soft rock and sand of 1 : 1, 1 : 2, 1 : 5 from 2010 to 2018, the spatio-temporal characteristics and development trend of the mechanical composition of the compound soil with different proportions were studied. The driving factors of the good development of potato growth-compound soil mechanical composition were also explored. Results showed that there was a significant positive correlation between silt-clay mass fraction and cultivation years, the annual variation rates of silt-clay mass fraction were 3.02, 3.90 and 4.11% in 1 : 1, 1 : 2, and 1 : 5 of compound soil. At the initial stage of mixing, clay and silt contents of the compound soil in different proportions were 1 : 1 > 1 : 2 > 1 : 5, and 9 years after planting, clay and silt contents were 1 : 5 > 1 : 2 > 1 : 1, potato growth promoted the development of 1 : 5 compound soil mechanical composition more significantly. The downward migration of silt and clay content in the 0-30 cm surface soil made a relatively dense argic horizon in the 30-40 cm soil layer, which effectively prevented water and fertilizer downward movement and the migration of fine particles in the surface soil. After years of planting, the thickness of the sandy land plow layer has increased to 45 cm, and the three-proportion compound soil mechanical composition developed to a good condition suitable for crop growth, and did not need to be compounded again after many years. Bangladesh J. Bot. 50(3): 865-872, 2021 (September) Special

Numerical evaluation of contaminants mixing uniformity in a full-scale test chamber with mixing fan

Most existing models and standards for volatile organic compounds emission assume that contaminants are uniform in the testing devices. In this study, a three-dimensional transient numerical model was proposed to simulate the mass transport process based on a full-scale test chamber with a mixing fan, and the airflow field and contaminants concentration distribution were obtained within the chamber under airtight and ventilated conditions. The model was validated by comparing the numerical results with experimental data. The numerical results show that the contaminant source position and the airflow field characteristics have significant impact on the contaminant mixing, and the fan rotation has an important role in accelerating mixing. In the initial mixing stage, the concentration distribution is obviously uneven; as the mixing progresses, it gradually reaches acceptable uniformity except for some sensitive regions, such as high concentration region at the injection point of the contaminants and low concentration region at the air inlet. To ensure test accuracy, the monitor should avoid above sensitive regions; and some special regions are recommended where contaminant concentration uniformity can be reached sooner. The ventilated chamber results indicate that the mixture of contaminants in the chamber is actually better than the results shown by conventional test method.

Compressive Strength and Workability of Cement Mortar Containing Recycled Asphalt Pavement

This article presents the compressive strength and workability of cement mortar (CM) containing recycled asphalt pavement (RAP) as fine aggregate replacement. The effect of the RAP replacement, water to cement ratio, curing time, and aggregate water absorption on compressive strength and flow workability are reported. The results show that the mixing water and mixing time play a significant role in the compressive strength and unit weight of CM containing RAP. The RAP has a higher water absorption and slower rate of water absorption than those of sand. The flow workability of CM increases with RAP replacement due to the unabsorbed water at the initial mixing stage. The main negative factors that affected the compressive strength of CM containing RAP as a fine aggregate replacement are revealed. The unabsorbed water at the initial state of mixing before hardening causes increased flow workability and decreased compressive strength. The findings from this research will promote the mix design approach of CM containing RAP as a fine aggregate replacement, for moving toward increased applications of recycled materials in a sustainable manner in civil engineering construction.

Investigation on the dispersion mass transfer in the interface between silicone oil and water

In this work, the dispersion mass transfer of the silicone oil-water mixture, especially the material dispersion process in the silicone oil/water interface was studied. Adopt a combination of macro test methods and microscopic test methods, the Cryo-scanning electron Microscope (Cryo-SEM) and the Transmission Electron Microscope (TEM) were introduced into the work of this paper respectively. The interface region between the dispersed phase and the continuous phase in the silicone oil-water mixture was investigated by the Cryo-SEM, the boundary of pure silicone oil droplets was studied by the TEM. Moreover, a simple and practical silicone oil-water interface characteristic measuring instrument (ICMI) has been designed and made for the measurement of properties in the silicone oil-water mixture interface. The results show that the silicone oil boundary is continuous and free of other impurities, and the interface presents a three-layer structure of “silicone oil-associated matter-water”, the Cryo-SEM images show the associated matter formed a layer of shell structure at the interface. The ICMI measurements show that the formation of the associated matter will lead to a rapid increase in interfacial pressure, while the associated matter migration will lead to rapid relaxation of the interface, and the relaxation effect is greater than the diffusion effect. This study shows that the dispersion mass transfer between silicone oil and water are consists of two interrelated stages: in the initial stage of mixing, continuous liquid phase splitting produces a large number of droplets, the diameter of the droplet group has a centralized distribution law, and there exists a sole clockwise circulation in the droplet. In the second stage, a kind of associated matter is formed by molecular aggregation in the interface area between the dispersed phase and the continuous phase, the associated matter contains both the silicone oil component and the water component. The formation and migration of the associated matter will result in a compression and relaxation effect of the interface. This manuscript provided a useful study for observing the oil/water interface with an electron microscope.

Effects of polymerized sulfur on rheological properties, morphology and stability of SBS modified asphalt

The objective of this study was to investigate effects of polymerized sulfur on viscosity functions, morphology and storage stability of SBS modified asphalt, as compared to elemental sulfur. Viscosity functions including complex viscosity, steady flow viscosity and dynamic viscosity were measured by dynamic shear rheometer (DSR) and Brookfield viscosity rheometer. The morphology and microstructure of modified asphalt were observed using fluorescence microscopy and Fourier Transform Infrared spectroscopy (FTIR). The results revealed that the increment in viscosity of modified asphalt containing polymerized sulfur was slower than that of elemental sulfur. Vulcanization rate decreases with the increase of polymerized sulfur, i.e. delayed vulcanization effect. In morphology, large polymer domains progressively transform to the fine dispersed SBS phase with smaller dimensions as the elongation of mixing time; whereas a fine polymer phase was found for elemental sulfur at the initial stage of mixing, which is significant evidence of delayed vulcanization. Moreover, the FTIR results verify the decrease of unsaturation of poly-butadiene block and the formation of CS bond. Viscosities of asphalt with polymerized sulfur were always lower than those of elemental sulfur and decreased with the increase of polymerized sulfur content. SBS phase domain vulcanized by polymerized sulfur is larger than that of elemental sulfur and tends to become larger with the increase of polymerized sulfur content. Lastly, SBS modified asphalt with higher level of polymerized sulfur shows the improved storage stability.

Destabilization of Emulsion Formed During Aqueous Extraction of Peanut Oil: Synergistic Effect of Tween 20 and pH

AbstractTo destabilize the emulsion formed during aqueous extraction processing (AEP) of peanuts, Tween and Span series surfactants (Tween 20, Tween 80, Span 20, and Span 80) were used alone or in combination to break the emulsion. Results indicate that only Tween surfactants had a pronounced demulsifying effect that was dependent on Tween concentration and system pH. When 1.2 wt% Tween 20 aqueous solution was used for oil extraction at pH 10.0, the highest free oil yield was achieved at 76.1 %, which was similar to the oil recovery of using proteases as a destabilization agent. The results obtained using a model emulsion system containing peanut oil and Tween 20/peanut protein isolates (PPI) showed that when Tween 20 and PPI coexisted in extraction medium at pH 10.0, the dynamic interfacial tension and droplet size distribution curves were very similar to those when Tween 20 was used alone, suggesting that Tween 20 dominated at the interface, instead of PPI. Destabilization of the model emulsions relied on three important factors: inclusion of Tween 20 at the initial mixing stage, high pH, and a gentle mixing speed. A synergistic destabilization mechanism of using Tween 20 at high pH during AEP was proposed. The discovery of Tween 20 as an effective demulsifier significantly contributes to the development of AEP of oilseeds.

(Invited) Computational Design of Coatings, Interfaces, and Nano-Structures for Si Based Electrodes

The chemical composition and mechanical properties change of coating materials, interfaces, and Si itself during lithiation and delithiation process imposed a grand challenge to design coating/Si nanostructure as an integrated electrode system. In our work, reactive force field (ReaxFF) parameters for Li-Si-Al-O-F were developed along with a new algorithm to simulate lithiation and delithation processes with different rates. With the reactive dynamics simulations, we were able to simultaneously track and correlate the lithiation-delithiation rate, compositional change, mechanical property evolution, stress distributions, and fracture. Interesting insights were obtained from these studies. For example, it was found that the lithiation rate during the initial mixing stage increases exponentially with vacancy concentrations in Si; and it was discovered the self-accelerating Li diffusion in Al2O3 coating forms a well-defined Li concentration gradient, leading to an elastic modulus gradient, which effectively avoids local stress concentration and mitigates crack propagation. A new mechanics model based on these varying properties was developed to determine how to stabilize the coating with a critical size ratio.

Vacancies in Si Can Improve the Concentration-Dependent Lithiation Rate: Molecular Dynamics Studies of Lithiation Dynamics of Si Electrodes

The study of lithiation dynamics is important because it affects both stress generation and rate performance of electrodes for Li-ion batteries. This topic becomes more crucial for Si anodes because its high capacity is accompanied by dramatic volume and structural changes, which lead to mechanical fracture, capacity loss, and limited cycle life. To provide fundamental insights into the lithiation dynamics, determine the rate-limiting process of lithiation, and investigate the effect of concentration on Li diffusivity, molecular dynamics along with reactive force field was used to simulate the lithiation process of both amorphous and crystalline Si electrodes. The local Li concentration evolution shows that lithiation dynamics can be characterized as occurring in two stages: an initial mixing stage followed by a subsequent random walk diffusion stage. The Li diffusion is demonstrated to be concentration-dependent as Li diffuses faster with higher Li concentration, opposite to many intercalation compounds....

Quantifying magma mixing with the Shannon entropy: Application to simulations and experiments

We introduce a new quantity to petrology, the Shannon entropy, as a tool for quantifying mixing as well as the rate of production of hybrid compositions in the mixing system. The Shannon entropy approach is applied to time series numerical simulations and high-temperature experiments performed with natural melts. We note that in both cases the Shannon entropy increases linearly during the initial stages of mixing and then saturates toward constant values. Furthermore, chemical elements with different mobilities display different rates of increase of the Shannon entropy. This indicates that the hybrid composition for the different elements is attained at different times generating a wide range of spatio-compositional domains which further increase the apparent complexity of the mixing process.Results from the application of the Shannon entropy analysis are compared with the concept of Relaxation of Concentration Variance (RCV), a measure recently introduced in petrology to quantify chemical exchanges during magma mixing. We derive a linear expression relating the change of concentration variance during mixing and the Shannon entropy.We show that the combined use of Shannon entropy and RCV provides the most complete information about the space and time complexity of magma mixing. As a consequence, detailed information about this fundamental petrogenetic and volcanic process can be gathered. In particular, the Shannon entropy can be used as complement to the RCV method to quantify the mobility of chemical elements in magma mixing systems, to obtain information about the rate of production of compositional heterogeneities, and to derive empirical relationships linking the rate of chemical exchanges between interacting magmas and mixing time.

Behavior of dissolved aluminum in the Huanghe (Yellow River) and its estuary: Impact of human activities and sorption processes

Dissolved aluminum (Al) is a sensitive tracer for biogeochemical cycles in the ocean. There has been a dramatic decline in water and sediment fluxes into the sea from the Huanghe because of climate change and human activities. Water–Sediment Regulation Schemes (WSRSs) have been implemented annually to flush trapped sediments from the upstream watercourse and reservoirs of the river. Monthly observations to investigate the behavior of dissolved Al in the lower reach of the Huanghe were carried out from November 2008 to December 2010. During 2009, daily observations were made to assess the impact of the ninth WSRS on the lower reach of the Huanghe and three cruises were carried out in the Huanghe Estuary in 2009 (prior to, during and following the WSRS). The monthly concentrations of dissolved Al ranged from 25 nM to 362 nM (average 90 nM) in the lower reach of the Huanghe. Assessment of the seasonal variation of dissolved Al showed that the highest concentrations occurred in summer and the lowest in winter: these corresponded to the variations in water discharge and sediment loads, which were controlled by WSRS events. During the ninth WSRS events in 2009 the daily runoff and sediment load increased from 200 m3/s to 3600 m3/s and from 0.1 g/L to 5 g/L, respectively. The concentration of dissolved Al increased from 180 nM to 600 nM (average 380 nM) in less than 20 days, which were equivalent to 43% of the annual Al flux into the Bohai. Exchange between dissolved and particulate Al, investigated using a simple sorption model based on the distribution coefficient (Kd), was approximately 106 mL/g in the Huanghe. The average concentrations of dissolved Al in the Huanghe Estuary prior to, during and following the WSRS were 243 nM, 238 nM and 186 nM, respectively. The comparable concentrations of dissolved Al in the Huanghe Estuary prior to and during the WSRS indicate that removal processes occurred in the initial stages of mixing in the estuary. The Al–salinity relationship and laboratory mixing experiments demonstrated that dissolved Al has a non-conservative behavior in the Huanghe Estuary, where a significant loss (20–50%) occurred. The mechanism of removal of dissolved Al in the Huanghe Estuary was adsorption onto suspended particulate matter and salt-induced flocculation. These observations suggest that human activities (e.g. the WSRSs) and sorption processes dominate the geochemical interactions of Al in the Huanghe and its estuary.

A new sol–gel processing routine without chelating agents for preparing highly transparent solutions and nanothin films: engineering the role of chemistry to design the process

The great sensitivity of titanium alkoxides to hydrolysis makes their sol–gel transformation very fast and thus difficult to control. A method was proposed to alleviate this drawback. Preparation of highly transparent solutions and nanothin films is another objective of the present research. Employing nanoemulsion method and optimizing the processing conditions, a clear solution of well-dispersed nanosized particles was obtained. With the proposed process BaTiO3 precursor sols and nanothin films with enhanced optical transparency towards the visible were prepared. The optimal formulation of the sol consists of acetic acid, barium acetate, 2-propanol, TTIP and deionized water with 6:1:1:1:150 M ratios, respectively. It was found that the reduction of the temperature in the initial stage of mixing of precursors controls the size of the forming species and accordingly improves the stability and transparency of the sol. The results also showed that the applied modifications and optimizations significantly downsize the particles within the sol to the nanometric scale and accordingly result in a significant improvement in the optical response of the products.

Description of internal microstructure of agglomerated cereal powders using X-ray microtomography to study of process–structure relationships

Agglomerated food powders are made from native particles which are assembled to form grains. The present investigation seeks to contribute to a better understanding of the three-dimensional internal morphology of food agglomerates (i.e. different couscous grains made from durum wheat semolina under different agglomeration process conditions) by means of microscopic methods (size, compactness) and X-ray micro-computed tomography (XMT), to bring understanding of the process–structure relationships. The three-dimensional internal morphology of food agglomerates was evaluated by means of X-ray micro-computed tomography (XMT), using a tabletop system with a resolution of several micrometers. XMT was considered to evaluate the internal porosity (or void fraction) as well as the size and spatial distribution of pores inside the grains. Closed porosity values ranged between 0.005 and 0.011. Diameter of internal pores was found to range between 13 and 155μm which contribute to control mainly their end-properties. The experimental results were discussed to develop a better knowledge of the process–structure relationships for food agglomerates based on wheat powders, produced by wet agglomeration process. We demonstrated that the shearing conditions during the initial mixing stage significantly contribute to the internal structure characteristics of agglomerates. The cooking treatment is found to largely improve the mechanical strength of the agglomerates.

Studies on Morphology Evolution of Polypropylene/Poly (Ethylene-co-1-octene) Blends at Different Shear Rates

The transient state of the phase morphology of polypropylene with poly(ethylene-co-1-octene) blends during melt mixing are investigated by the pattern analysis of scanning electron microscope (SEM). The results show that morphology develops mainly at the initial stages of mixing. During the intermediate mixing stage, a dynamic equilibrium is established between breakup and coalescence of domains. The mixing time required for reaching equilibrium stage reduces as shear rate increases. The fractal analysis indicates that the development of the dispersed phase during melt mixing process evolves with dynamical self-similarity partly through the competitions of break-up and coalescence of dispersed phase.

Synthesis of Highly Active and Thermally Stable Nanostructured Pt/Clay Materials by Clay-Mediatedin SituReduction

Novel and intriguing one-pot in situ method for the preparation of nanostructured Pt-clay materials under simple conditions is reported. In this synthesis, an inorganic clay mineral such as synthetic hectorite ("Laponite XLG") or natural montmorillonite ("Kunipia F") serves as a mild and effective reducing agent for Pt ions, which is uncommon for such a clay system, and also acts as an outstanding stabilizer for the resulting Pt nanoparticles. In aqueous solution, exfoliated colloidal clay platelets forms complex with Pt ions in the initial stage of mixing. Devoid of any organic dispersants or external reducing agents, subsequently, the Pt nanoparticles (3-6 nm) generated by clay-assisted in situ reduction of Pt ions successfully anchored onto the clay nanoplatelets. The Pt-clay material features a very high surface area (312 m(2) g(-1)) and has excellent catalytic activity, as was kinetically evaluated via the reduction of 4-nitrophenol with NaBH(4). After drying, this remarkably stable nanocomposite is completely redispersible in water and displays extreme thermal stability (up to 500 °C). On the basis of these results, this synthetic strategy is anticipated to be a very simple, economical, and green approach for the synthesis of nanostructured Pt-clay materials.