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Articles 1 - 30 of 46
Full-Text Articles in Engineering
Determination Of Surface Heating Distribution To Establish Targeted Thermal Tnvironments In Industry Hydrothermal Autoclaves, Hongmin Li, Guo-Xiang Wang, Edward Evans
Determination Of Surface Heating Distribution To Establish Targeted Thermal Tnvironments In Industry Hydrothermal Autoclaves, Hongmin Li, Guo-Xiang Wang, Edward Evans
Dr. Guo-Xiang Wang
This article presents a method for the determination of the heat flux distributions to establish the desired growth environments in autoclave reactors. The algorithm consists of three submodels including the inverse natural convection of the fluid, the inverse heat conduction in the metal wall, and the heat conduction in the insulation layer. The technique is employed to obtain the heat flux distributions that establish the same growth environment as the one predicted by the two-dimensional isothermal wall model. Based on the results, practical heater designs are proposed to improve the growth environments in such industry growth vessels.
Flow Of Solution In Hydrothermal Autoclaves With Various Aspect Ratios, Hongmin Li, Edward Evans, Guo-Xiang Wang
Flow Of Solution In Hydrothermal Autoclaves With Various Aspect Ratios, Hongmin Li, Edward Evans, Guo-Xiang Wang
Dr. Guo-Xiang Wang
A good understanding of the natural convective flow in hydrothermal autoclaves is essential for the control of the growth rate and the quality of the grown crystals. This paper presents a numerical simulation of turbulent natural convection in industry-size autoclaves with various aspect ratios. A simplified 2D axisymmetric model was developed. Numerical results were obtained for autoclaves with aspect ratios ranging from 2 to 20. Results show typical two counter-flow cells in both the bottom and upper chambers. Heat conduction through the baffle is negligible. Detailed analyses and discussions are presented to characterize the bulk flows in the upper chamber …
Zwitteration Of Dextran: A Facile Route To Integrate Antifouling, Switchability And Optical Transparency Into Natural Polymers, Bin Cao, Linlin Li, Haiyan Wu, Qiong Tang, Bingbing Sun, He Dong, Jiang Zhe, Gang Cheng
Zwitteration Of Dextran: A Facile Route To Integrate Antifouling, Switchability And Optical Transparency Into Natural Polymers, Bin Cao, Linlin Li, Haiyan Wu, Qiong Tang, Bingbing Sun, He Dong, Jiang Zhe, Gang Cheng
Dr. Jiang Zhe
This communication reports a facile method for zwitteration of dextran with carboxybetaine (CB), which integrates superior antifouling properties, switchability between zwitterionic and cationic forms, as well as enhanced optical transparency into one polysaccharide material. This study provides a new avenue for generating multifunctional zwitterionic CB materials in situ.
Single-And Multi-Hole Baffles-A Heat Transfer And Fluid Flow Control For Hydrothermal Growth, Edward Evans, Hongmin Li, Guo-Xiang Wang
Single-And Multi-Hole Baffles-A Heat Transfer And Fluid Flow Control For Hydrothermal Growth, Edward Evans, Hongmin Li, Guo-Xiang Wang
Dr. Guo-Xiang Wang
Hydrothermal solution growth is an important technique to grow high-quality single crystals. An autoclave, a closed cylindrical low-carbon steel vessel, is used to grow the large size crystals. A baffle located at the median height divides an autoclave into two chambers. Previous numerical studies indicate that the buoyancy-driven flow within an autoclave is very sensitive to the temperatures on the wall established by the heating. Baffles are required to establish the conditions for growth of high quality single crystals. This paper presents a numerical study of the effects of various baffles on the fluid flow and temperature fields in an …
Natural Convection Flow Structures And Heat Transfer In A Model Hydrothermal Growth Reactor, Hongmin Li, Minel Braun, Edward Evans, Guo-Xiang Wang, Govind Paudel, Jason Miller
Natural Convection Flow Structures And Heat Transfer In A Model Hydrothermal Growth Reactor, Hongmin Li, Minel Braun, Edward Evans, Guo-Xiang Wang, Govind Paudel, Jason Miller
Dr. Guo-Xiang Wang
Due to the experimental difficulties brought about by high pressure and temperature growth conditions, flow and heat transfer in industrial hydrothermal autoclaves for the growth of single quartz crystals have been studied mostly numerically. To date, most of the numerical models and associated results are not experimentally validated; only qualitative validation data from experiments done during actual crystal growth production is partly available. In this study, the authors used a model simulated reactor represented by an enclosure with two lower half sidewalls uniformly heated while the upper half sidewalls are uniformly cooled. Flow structures in the reactor are qualitatively visualized …
A Three-Dimensional Conjugate Model With Realistic Boundary Conditions For Flow And Heat Transfer In An Industry Scale Hydrothermal Autoclave, Hongmin Li, Edward Evans, Guo-Xiang Wang
A Three-Dimensional Conjugate Model With Realistic Boundary Conditions For Flow And Heat Transfer In An Industry Scale Hydrothermal Autoclave, Hongmin Li, Edward Evans, Guo-Xiang Wang
Dr. Guo-Xiang Wang
This paper presents a conjugate heat transfer model for industry size hydrothermal autoclaves. The electric heating on the wall outside surfaces is represented by constant heat fluxes. The circumferential heat flux deviation is introduced for the asymmetric factors from the surroundings. The results indicate that the temperature at the solution/wall interface is far from uniform. Circumferential temperature deviation is large enough to establish an asymmetric flow. To accurately simulate flows in industry autoclaves, one needs to use the conjugate model. The growth environment in current industry autoclaves, however, can be improved by establishing a uniform temperature on the wall/solution interface.
Three-Dimensional Flow Of Solution In An Industry-Size Hydrothermal Autoclave Subjected To Non-Uniform Heating Effects Of A Baffle On Flow And Temperature Separation, Hongmin Li, Guo-Xiang Wang, Edward Evans
Three-Dimensional Flow Of Solution In An Industry-Size Hydrothermal Autoclave Subjected To Non-Uniform Heating Effects Of A Baffle On Flow And Temperature Separation, Hongmin Li, Guo-Xiang Wang, Edward Evans
Dr. Guo-Xiang Wang
Hydrothermal growth takes place in a closed cylindrical container called an autoclave. Natural convection flow of an aqueous solution at a high temperature and a high pressure carries the nutrient. The high temperature growth condition and the natural convection flow are maintained by two independently controlled electrical heaters on the outside of the autoclave. In practice, the heating is circumferentially non-uniform. Many theoretical and numerical studies, however, assume axially symmetric heating conditions. This paper presents a numerical analysis of the three-dimensional heat transfer and fluid flow with a non-uniform heating condition. The analysis is based on an industry-size autoclave with …
One-Step Production Of Long-Chain Hydrocarbons From Waste-Biomass-Derived Chemicals Using Bi-Functional Heterogeneous Catalysts, Cun Wen, Elizabeth Barrow, Jason Hattrick-Simpers, Jochen Lauterbach
One-Step Production Of Long-Chain Hydrocarbons From Waste-Biomass-Derived Chemicals Using Bi-Functional Heterogeneous Catalysts, Cun Wen, Elizabeth Barrow, Jason Hattrick-Simpers, Jochen Lauterbach
Jason R. Hattrick-Simpers
n this study, we demonstrate the production of long-chain hydrocarbons (C8+) from 2-methylfuran (2MF) and butanal in a single step reactive process by utilizing a bi-functional catalyst with both acid and metallic sites. Our approach utilizes a solid acid for the hydroalkylation function and as a support as well as a transition metal as hydrodeoxygenation catalyst. A series of solid acids was screened, among which MCM-41 demonstrated the best combination of activity and stability. Platinum nanoparticles were then incorporated into the MCM-41. The Pt/MCM-41 catalyst showed 96% yield for C8+ hydrocarbons and the catalytic performance was stable over four reaction …
Integrating Top-Down And Bottom-Up Scaffolding Tissue Engineering Approach For Bone Regeneration, M. Ramalingam, Esmaiel Jabbari, S. Ramakrishna, A. Khademhosseini
Integrating Top-Down And Bottom-Up Scaffolding Tissue Engineering Approach For Bone Regeneration, M. Ramalingam, Esmaiel Jabbari, S. Ramakrishna, A. Khademhosseini
Esmaiel Jabbari
No abstract provided.
Effect Of Surfactants And Cosurfactants On The Phase Separation Temperature And Volatility Of Methanol/Hydrocarbon/Water Blends, Michael Cheung
Effect Of Surfactants And Cosurfactants On The Phase Separation Temperature And Volatility Of Methanol/Hydrocarbon/Water Blends, Michael Cheung
Dr. Michael Cheung
The effects of several surfactants and cosurfactants on the phase separation temperature and Reid vapor pressure of methanol/hydrocarbon/water blends were investigated.
Polymerization Of Microstructured Aqueous Systems Formed Using Methyl Methacrylate And Potassium Undecenoate, Michael Cheung
Polymerization Of Microstructured Aqueous Systems Formed Using Methyl Methacrylate And Potassium Undecenoate, Michael Cheung
Dr. Michael Cheung
No abstract provided.
Formation Of Polymeric Foams From Aqueous Foams Stabilized Using A Polymerizable Surfactant, Michael Cheung
Formation Of Polymeric Foams From Aqueous Foams Stabilized Using A Polymerizable Surfactant, Michael Cheung
Dr. Michael Cheung
Polymerization of foams formed by purging with nitrogen an aqueous precursor system made up of a polymerizable surfactant, a monomer, and a cross-linking agent yielded stable polymeric foams. The precursor system for foaming contained hydrophobic components (methyl methacrylate as monomer and ethylene glycol dimethacrylate as cross-linking agent) in water and was stabilized using the polymerizable surfactant potassium acrylamidostearate. The phase-behavior study for the precursor system was conducted followed by an investigation of the stability of the foams obtained on purging with nitrogen. Sonicating the precursor systems during the process of purging with nitrogen gas followed by polymerization resulted in aqueous …
Effects Of Heptanoic And Oleic Acid On The Phase Separation Temperatures Of Methanol/Hydrocarbon/Water Mixtures, Michael Cheung
Effects Of Heptanoic And Oleic Acid On The Phase Separation Temperatures Of Methanol/Hydrocarbon/Water Mixtures, Michael Cheung
Dr. Michael Cheung
The efficacy of heptanoic and oleic acids as phase separation temperature depressants for methanol/hydrocarbon/water blends was examined.
Characterization And Polymerization Of Middle-Phase Microemulsions In Styrene/Water Systems, Michael Cheung
Characterization And Polymerization Of Middle-Phase Microemulsions In Styrene/Water Systems, Michael Cheung
Dr. Michael Cheung
The products of photopolymerizing middle-phase microemulsions containing sodium dodecyl sulfate as a surfacant, styrene as a monomer, NaCL or NaSCN as electrolyte, and either 2-pentatol or a combination of 5-hexene-1, 2-diol and sodium styrenesulfonate as a cosurfacant were characterized by using differential scanning calorimetry, gel permeation chromatography, and scanning electron microscopy (SEM).
Microstructured Polymers Via Photopolymerization Of Non-Aqueous Organized Solutions, Michael Cheung
Microstructured Polymers Via Photopolymerization Of Non-Aqueous Organized Solutions, Michael Cheung
Dr. Michael Cheung
Structurally organized solutions containing monomers in an ethylene glycol (EG) medium were formed and polymerized to produce polymeric solids with various morphologies, and also unique thermal and mechanical properties. Previous research had demonstrated the formation of microemulsions in an aqueous medium containing methyl methacrylate (MMA) and acrylic acid (AA). However, the non-aqueous mixtures of MMA and AA with EG did not yield conventional microemulsions. Molecularly dispersed solutions were formed in the bulk of the phase diagram, while compositions closer to the demixing line exhibited critical behaviour. This paper presents the first account of the use of mixtures exhibiting critical behaviour …
Formation Of Porous Polymeric Structures By The Polymerization Of Single-Phase Microemulsions Formulated With Methyl Methacrylate And Acrylic Acid, Michael Cheung
Dr. Michael Cheung
No abstract provided.
Acid And Base Effects On The Morphology Of Composites Formed From Microemulsion Polymerization And Sol--Gel Processing, Michael Cheung
Acid And Base Effects On The Morphology Of Composites Formed From Microemulsion Polymerization And Sol--Gel Processing, Michael Cheung
Dr. Michael Cheung
Phase behaviour studies were performed for microemulsions, containing organic monomers (methyl methacrylate and acrylic acid), inorganic monomer (tetraethoxy silane (TEOS)), a cross linking agent (ethylene glycol dimethacrylate) and water, stabilized by a cationic surfactant, cetyltrimethylammonium bromide. Single phase transparent microemulsions were formed over a considerable portion of the composition domain. The effects of an acid, hydrochloric acid (HCl), and a base (NH4OH) on the gel times were studied and the catalytic action of acid and base on the overall sol–gel reaction was analysed. Organic/inorganic polymer composites were obtained from the hydrolysis and polycondensation reactions of TEOS (sol–gel process) and polymerization …
Light Scattering Study Of Polymer Network Formation In A Supercritical Diluent, Michael Cheung
Light Scattering Study Of Polymer Network Formation In A Supercritical Diluent, Michael Cheung
Dr. Michael Cheung
We have undertaken a study of the benefits of using near-critical and supercritical fluids in synthesizing microcellular foams. In this study, we use dynamic light scattering to study the formation of the polymer network directly in near-critical and supercritical freon-22. The polymer system studied is ethylene-glycoldimethacrylate+methylmethacrylate. We have previously obtained microcellular foams by direct polymerization in this system and this study elucidates the gelation process by tracking the correlation length of the inhomogeneities as a function of reaction time from the monomeric state to the gel transition.
Effects Of Precursor Composition On Pore Morphology For Thermally Polymerized Acrylic Acid/Methyl Methacrylate-Based Microemulsions, Michael Cheung
Effects Of Precursor Composition On Pore Morphology For Thermally Polymerized Acrylic Acid/Methyl Methacrylate-Based Microemulsions, Michael Cheung
Dr. Michael Cheung
Thermal polymerization has not been extensively studied as a technique for the polymerization of bicontinuous microemulsions. Other more rapid techniques have been employed such as visible- and UV-initiated polymerization. However, the industrial preparation of porous solids would be facilitated by the use of the cheaper and simpler thermal polymerization. The effects of changing composition of the precursor on the resulting matrix morphology for thermally polymerized microemulsions were studied. The factors examined were the surfactant loading of the aqueous phase, the aqueous to organic phase ratio, the monomer ratio of the organic phase, and the cross-linker content of the organic phase. …
Modeling Of Leakage In Liquid Surfactant Membrane Systems, Michael Cheung
Modeling Of Leakage In Liquid Surfactant Membrane Systems, Michael Cheung
Dr. Michael Cheung
The stability of double emulsions or liquid surfactant membranes, an important topic in liquid membrane extraction processes, was investigated. The percentage of liquid membrane leakage which reflects the stability of the liquid surfactant membranes was measured as a function of time using sodium hydroitide as a tracer. Water-in-oil emulsions were prepared with SOLTROL 220, an isoparaffinic solvent, and solvent extracted neutral oils—S100N and S500N. A stochastic model for droplet formation under the conditions of isotropic turbulence was developed. It assumes the presence of complete randomness in the process of emulsification. The mean growth rate obtained from this model is in …
Microcellular Polymeric Materials From Microemulsions: Control Of Microstructure And Morphology, Michael Cheung
Microcellular Polymeric Materials From Microemulsions: Control Of Microstructure And Morphology, Michael Cheung
Dr. Michael Cheung
The effect of a crosslinking agent on the formation of porous solids by polymerizing microemulsions formulated with monomers was investigated. Phenomenological studies were carried out to evaluate the possibility of controlling the morphology of the porous polymeric materials by using precursor microemulsions having a distinct microstructure. A microemulsion system, containing methyl methacrylate (MMA), acrylic acid (AA), the crosslinking agent ethyleneglycol dimethacrylate (EGDMA), water, and sodium dodecylsulfate (SDS) as surfactant, was studied. An identical surfactant-free system, formed using the same monomers, crosslinking agent, and water, but without surfactant, was also studied. Microemulsion samples from both these systems, having a water in …
Sonochemical Destruction Of Chlorinated C1 And C2 Volatile Organic Compounds In Dilute Aqueous Solution, Michael Cheung
Sonochemical Destruction Of Chlorinated C1 And C2 Volatile Organic Compounds In Dilute Aqueous Solution, Michael Cheung
Dr. Michael Cheung
No abstract provided.
A New Pdms Macromonomer Stabilizer For Dispersion Polymerization Of Styrene In Supercritical Carbon Dioxide, Michael Cheung
A New Pdms Macromonomer Stabilizer For Dispersion Polymerization Of Styrene In Supercritical Carbon Dioxide, Michael Cheung
Dr. Michael Cheung
Free radical polymerization of styrene in supercritical CO2 requires addition of a surfactant to produce polystyrene (PS) in high conversion and molecular weight with well-defined particle sizes. In this work, we examined a new stabilizer that can provide effective stabilization for the polymerization of styrene. A commercially available poly(dimethylsiloxane) macromonomer has been employed as a stabilizer for dispersion polymerization of PS in scCO2. The reactions were conducted in a 225-mL stainless steel autoclave over the temperature range 60–80°C and under pressures of 1,500 to 3,000 psi. After 2–12 h of polymerization, the conversion determined by gravimetrical method was between 20 …
Light Scattering Study Of Oil-In-Water Microemulsions: Corrections For Interactions, Michael Cheung
Light Scattering Study Of Oil-In-Water Microemulsions: Corrections For Interactions, Michael Cheung
Dr. Michael Cheung
No abstract provided.
Characterization Of Microporous Polymeric Materials: Pore Continuity And Size Distribution Via Thermal Analysis, Michael Cheung
Characterization Of Microporous Polymeric Materials: Pore Continuity And Size Distribution Via Thermal Analysis, Michael Cheung
Dr. Michael Cheung
Polymerization of single-phase microemulsions produces microporous solid materials. The surface morphology of the polymer solids, after drying, was examined using scanning electron microscopy (SEM). The microstructure of the precursor microemulsion is preserved to a considerable extent on polymerization, at least in a qualitative sense. The microstructure within the bulk of the polymers was characterized by the shape of drying-rate curves determined using thermogravimetric analysis. The results reveal that bicontinuous microemulsions yield polymers with an open-cell structure whereas microemulsions with less than 20% water content form closed-cell structures. The pore size distribution (PSD) of the aspolymerized solids was obtained using a …
Effect Of Preparation Parameters On Leakage In Liquid Surfactant Membrane Systems, Michael Cheung
Effect Of Preparation Parameters On Leakage In Liquid Surfactant Membrane Systems, Michael Cheung
Dr. Michael Cheung
The stability of double emulsions or liquid surfactant membranes, which is an important topic in liquid membrane extraction processes, was investigated. The percentage of liquid membrane leakage which reflects the stability of the liquid surfactant membranes was measured as a function of time using sodium hydroxide as a tracer. Water-in-oil emulsions were prepared with SOLTROL 220, an isoparaffinic solvent, and solvent-extracted neutral oils, S100N and S500N. The surfactant studied was Span 80 (sorbitan mono-oleate). The influence of microdroplet volume fraction, surfactant weight percent, agitation speed, and emulsifying device on leakage was studied using a half fraction of 24 experimental design. …
Polymerization Of Single-Phase Microemulsions: Dependence Of Polymer Morphology On Microemulsion Structure, Michael Cheung
Polymerization Of Single-Phase Microemulsions: Dependence Of Polymer Morphology On Microemulsion Structure, Michael Cheung
Dr. Michael Cheung
Polymerization of monomer-containing single-phase Winsor-IV microemulsions was studied and the morphology of the polymer obtained was found to be related to the structure of the microemulsion. The hydrophobic component of the microemulsions was formed with methyl methacrylate together with ethylene glycol dimethacrylate. Methacrylic acid was found to be effective as a polymerizable cosurfactant and was used in formulating the microemulsions, together with sodium dodecyl sulfate which was used as the surfactant. The structure of the single-phase microemulsion was found to vary with change in composition of the system. At concentrations of aqueous surfactant solution below 20%, a droplet structure of …
Sonochemical Destruction Of Chlorinated Hydrocarbons In Dilute Aqueous Solution, Michael Cheung
Sonochemical Destruction Of Chlorinated Hydrocarbons In Dilute Aqueous Solution, Michael Cheung
Dr. Michael Cheung
No abstract provided.
Ultrasound Assisted Emulsion Polymerization Of Methyl Methacrylate And Styrene, Michael Cheung
Ultrasound Assisted Emulsion Polymerization Of Methyl Methacrylate And Styrene, Michael Cheung
Dr. Michael Cheung
In this article, we report on the effect of using ultrasound during emulsion polymerization. This work differs somewhat from that previously reported in that ultrasound is used in conjunction with conventional initiators. The aim is to observe the changes in the nature of polymerization and the synthesized polymer. In this work, reaction conditions and compositions typical of conventional emulsion polymerization are used. Azo-bisisobutyronitrile and potassium per sulfate are the initiators used. The initial indication is that the rate of polymerization and the final conversion are higher when ultrasound is introduced into the polymerization system. This effect is more pronounced at …
Effects Of Pressure, Temperature, And Ph On The Sonochemical Destruction Of 1, 1, 1-Trichloroethane In Dilute Aqueous Solution, Michael Cheung
Effects Of Pressure, Temperature, And Ph On The Sonochemical Destruction Of 1, 1, 1-Trichloroethane In Dilute Aqueous Solution, Michael Cheung
Dr. Michael Cheung
There is an increasing interest in the application of high intensity ultrasound as an advanced oxidation technique. In this study, 1,1,1-trichloroethane (TCA) is the compound being subjected to ultrasonic irradiation. The study focuses on the effects of pressure (0.103–0.241 MPa), temperature (6–19.4°C) and pH (3.96–12.5). Optimum conditions of treatment are discerned from the results of the experiments based on a center composite design. The results show that about 98% of TCA can be removed in 1 h of treatment (starting concentrations average 80 mg/l). Also, experiments indicate that the initial concentration does not affect destruction rate in this system. Optimum …