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Front Velocity (front + velocity)

Distribution by Scientific Domains

Polymers and Materials Science	42%
Chemistry	42%

Selected Abstracts

Design of a thermally balanced membrane reformer for hydrogen production

AICHE JOURNAL, Issue 10 2008
David S. A. Simakov
Abstract Hydrogen production by autothermal methane steam reforming in a catalytic fixed bed membrane reactor has been analyzed and simulated. The two-compartment reactor indirectly couples the endothermic steam reforming with methane oxidation, while hydrogen is separated by a permselective Pd membrane. Simulations of the reactor, using published kinetics, map the acceptable domain of operation and the optimal set of operating parameters. The simulations exhibit slow-moving thermal fronts and the steady-state operation domains bounded by stationary fronts, separating domains of upstream and downstream-moving fronts. Front velocity depends on thermal coupling and hydrogen separation. An analytical approximation for the thermal front velocity in a thermally balanced reactor has been developed. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source]

Frontal polymerization with monofunctional and difunctional ionic liquid monomers

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 13 2007
Zulma Jiménez
Abstract For the first time, we studied frontal polymerization with ionic liquid monomers. We synthesized a series of compounds from the neutralization reaction between trialkylamines (tributylamine, trihexylamine, trioctylamine, and (2-dimethylamino)ethyl methacrylate) and acrylic or methacrylic acid. For the ionic liquids prepared from the unreactive amines, frontal polymerization could not be achieved without the addition of a diacrylate. With the addition of a diacrylate, the front velocities were slower than for dodecyl acrylate (with the diacrylate), a compound of comparable molecular weight. Monomers prepared from the (2-dimethylamino)ethyl methacrylate could support frontal polymerization alone but the front velocities were lower than dodecyl (meth)acrylate. These results are contrasted with recent results of Jiménez et al. for room temperature kinetics. Finally, the polymers prepared were comparable to those prepared by batch curing at 75 °C except for the monomethacrylate ionic liquid, which lost some tertiary amine by dissociation and evaporation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2745,2754, 2007 [source]

Directions of preferential flow in a hillslope soil, 1.

HYDROLOGICAL PROCESSES, Issue 4 2005
Quasi-steady flow
Abstract Preferred infiltration is mainly perceived as vertically down whereas subsurface storm flow is thought to occur parallel to slopes. The transition from vertical to lateral flow in a layered hillslope soil is the focus of the contribution. Transient flow is assumed to move as a wetting front. Three time-domain reflectometry (TDR) wave-guides, each 0·15 m long, were mounted in the shape of a truncated tetrahedron with its peak pointing down. Each wave-guide focuses the front velocity along its axis. The three front-velocity vectors are decomposed into their x, y and z components, which are then assembled to the resultant velocity vector. The volume density flux of preferred flow is the product of the front velocity and the mobile water content. The latter is the amplitude of transient soil moisture measured with each wave-guide. The resultant vector of the volume flux density is computed similarly to the velocity vector. The experimental approach allows for the rapid assessment of transient flows without relying on the variation of water potentials. The experiments indicate that the directions of the resultant vectors of velocity and volume flux density can be estimated if the moisture variations of the three TDR wave-guides are strongly correlated during the passing of the wetting front. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Profiling of injection velocity for uniform mold filling

ADVANCES IN POLYMER TECHNOLOGY, Issue 1 2006
Xi Chen
Abstract Uniform melt front velocity is recommended for injection mold filling to minimize the part nonuniformity. A method of profiling the injection velocity for such a uniform mold filling is presented in this paper. Based on a neural network model developed for estimating the melt flow length from online measurable variables, the profiling problem is transformed into an optimization to minimize the difference between the predicted melt flow length and a given ramp. The rate of the ramp determines the rate of the melt front velocity traveling in the cavity during filling. Experiments with different molds show that the proposed method is effective in profiling the screw injection velocity to achieve a uniform mold filling. © 2006 Wiley Periodicals, Inc. Adv Polym Techn 25: 13,21, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20054 [source]

Design of a thermally balanced membrane reformer for hydrogen production

Frontal free-radical copolymerization of urethane,acrylates

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2006
Ting Hu
Abstract We report the first synthesis of urethane,acrylate copolymers via free-radical frontal polymerization. In a typical run, the appropriate amounts of the reactants (urethane,acrylate macromonomer and 2-hydroxyethyl acrylate) and initiator (ammonium persulfate) were dissolved in dimethyl sulfoxide. Frontal polymerization was initiated by the heating of the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self-propagate throughout the reaction vessel. Once it was initiated, no further energy was required for the polymerization to occur. The dependence of the front velocity and front temperature on the initiator concentration was investigated. The front temperatures were between 55 and 65 °C, depending on the persulfate concentration. Thermogravimetric analysis indicated that the urethane,acrylate copolymers had higher thermal stability than pure frontally prepared polyurethane. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3018,3024, 2006 [source]

Investigation of redox initiators for free radical frontal polymerization

POLYMER INTERNATIONAL, Issue 8 2009
Huan Yu
Abstract BACKGROUND: The reaction temperature for frontal polymerization (FP) initiated by redox initiators can be greatly decreased compared with FP initiated by peroxide initiator and disulfide initiator. We report the synthesis of poly(hydroxyethyl acrylate)s via free radical FP using benzoyl peroxide (BPO)/N,N -dimethylaniline (DMA) and ammonium persulfate (APS)/N,N,N,,N,-tetramethylethylenediamine (TMEDA) couples as redox initiators at ambient pressure. RESULTS: The results show that unlike the phenomenon of bubbles and ,fingers' when using BPO alone, a self-sustaining and stable front can be obtained when the [DMA]/[BPO] ratio is higher than 1 (mol/mol). A slight increase of the DMA (or TMEDA) reductant concentration causes a marked decrease of front temperature to 53 °C (or 61 °C). CONCLUSION: We investigated the effects of the ratio of the oxidant to the reductant and the initiator and monomer concentrations on certain parameters of FP: formation of bubbles, front velocity and front temperature. This opens the way to the potential development of FP using more appropriate monomers with low boiling points. Copyright © 2009 Society of Chemical Industry [source]