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Anextensive experimental study of the kinetics of capillary risein borosilicate glass tubes of different sizes and cross-sectionalshapes using various fluid systems and tube tilt angles is presented.The investigation is focused on the direct measurement of dynamiccontact angle and its variation with the velocity of the moving meniscus(or capillary number) in capillary rise experiments. We investigatedthis relationship for different invading fluid densities, viscosities,and surface tensions. For circular tubes, the measured dynamic contactangles were used to obtain rise-versus-time values that agree moreclosely with their experimental counterparts (also reported in thisstudy) than those predicted by Washburn equation using a fixed valueof contact angle. We study the predictive capabilities of four empiricalcorrelations available in the literature for velocity-dependence ofdynamic contact angle by comparing their predicted trends againstour measured values. We also present measurements of rise in noncircularcapillary tubes where rapid advancement of arc menisci in the cornersahead of main terminal meniscus impacts the dynamics of rise. Usingthe extensive set of experimental data generated in this study, anew general empirical trend is presented for variation of normalizedrise with dynamic contact angle that can be used in, for instance,dynamic pore-scale models of flow in porous media to predict multiphaseflow behavior. [ABSTRACT FROM AUTHOR]

Reactivekinetics coupled with population balance model (PBM) andcomputational fluid dynamics (CFD) was implemented to simulate silvernanoparticles (AgNPs) formation in a microtubular reactor. The quadraturemethod of moments, multiphase model theory, and kinetic theory ofgranular flow were employed to solve the model, and the particle sizedistributions (PSD) were calculated. The simulation results were validatedby synthesizing AgNPs experimentally in an actual microtubular reactorfor comparison with the PSD. The results confirmed the effectivenessof the model and its applicability in predicting AgNPs formation andits PSD evolution in the microtubular system. Finally, benefitingfrom its superiority, in that the influence of reactive kinetics andfluid dynamics on particle evolution could be considered separately,the model was employed to verify predictions and inferred conclusionsin our previous works, which were difficult to verify through experiment. [ABSTRACT FROM AUTHOR]

Today development, design, and optimization of the various processes is carried out with the help of process simulators.The reliability of the results mainly depends on the quality of thethermodynamic model and the model parameters used. While gEmodels can be applied for calculation of the phaseequilibrium behavior of multicomponent systems using only binary experimentaldata, group contribution methods like UNIFAC or modified UNIFAC Dortmundallow prediction of the required thermophysical properties usingonly a limited number of group interaction parameters. For systemscontaining supercritical components equations of state like Soave–Redlich–Kwongor Peng–Robinson or group contribution equations of state (GCEOS)like the predictive Soave–Redlich–Kwong (PSRK) or thevolume-translated Peng–Robinson group contribution equationsof state (VTPR) can be applied. In different papers it was alreadyshown that VTPR is a very powerful thermodynamic model. In this papernew group interaction parameters for 192 group combinations are presented,so that the actual matrix now contains group interaction parametersfor 252 group combinations. In this paper predicted results of theVTPR group contribution equation of state are compared with the resultsobtained using modified UNIFAC Dortmund or the PSRK method. [ABSTRACT FROM AUTHOR]

Theetherification of biodiesel based glycerol with isobutene catalyzedby an ion-exchange resin (NKC-9) was studied in a stirred batch reactor.The effects of temperature, catalyst loading, and feed compositionon the product distribution were investigated. A kinetic model basedon Eley–Rideal mechanism was developed according to the experimentalresults. In this model, three consecutive etherifications and a dimerizationof isobutene were taken into account; isomers in the product werelumped as monoethers (ME), diethers (DE), and dimers of isobutene(DIB); glycerol and isobutene were thought to be adsorbed on the activesites of catalyst and the surface reactions were treated as the ratedetermine step; the acceleration function of ME to the reactions wasalso considered. The activities of components were employed in rateequations with the activity coefficients calculated by UNIFAC. Modelparameters including reaction and adsorption equilibrium constantsas well as rate constants were estimated. The model reliability wasvalidated through the prediction of glycerol conversion and etheryields under different conditions. [ABSTRACT FROM AUTHOR]

We critically examined a series of exact kinetic models for their ability to describe binding of a typical α-helical amphipathic peptide to lipid bilayers. Binding of the model peptide lysette-26 was measured through fluorescence resonance energy transfer from a Trp residue on the peptide to a fluorescently labeled acceptor lipid included in vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine. Experimental data was collected varying peptide and lipid concentrations over an order of magnitude. The kinetic models were fit to all the experimental data simultaneously. Of the four models examined, the simplest one that is sufficient to correctly describe the experimental data includes two coupled equilibria, one between peptide monomers in solution and bound to the lipid membrane, and a second one between lipid-bound peptides that oligomerize to form dimers. We found that individual kinetic binding curves are insufficient to distinguish among kinetic models of peptide binding to lipid bilayers but that a number of models can be excluded based on inspection of a simple set of experiments. [ABSTRACT FROM AUTHOR]

In our work, we focus on the Euler−Lagrange strategy to simulate bubbly flows and fast chemical reactions. We propose a film model to account for fast, multistep chemical reactions near the gas−liquid interface. A combination of such a film model with Euler−Lagrange simulations for bubbly flows has not been used before. Also, we account for micromixing effects with respect to chemical reactions in the liquid bulk by solving for the variance of the concentration field. To validate our model predictions for multiphase flow and reactive mixing, we compare our results with literature data and find excellent agreement. [ABSTRACT FROM AUTHOR]

Understanding hydrodynamics of liquid−solid fluidized beds is crucial in proper scale-up and design of these reactors. Computational fluid dynamics (CFD) models have shown promise in gaining this understanding. In this paper, a two-dimensional CFD model, using an Eulerian−Eulerian two-fluid model incorporating the kinetic theory of granular flow, is used to describe the liquid−solid two-phase flow in a liquid−solid fluidized bed. The predicted pressure gradient data and concentrations are found to agree with experimental data published in the literature. Furthermore, the model is used to investigate the influences of the superficial liquid velocity and the sold particle size on the distribution of solids concentration. The simulation results showed that the solids concentration has a relatively uniform distribution and high bed expansion with the increase of liquid velocity and decrease of particles sizes. Solids mean axial velocities decrease with the decrease in superficial liquid velocity. The static bed height plays a minor role on the effect of velocity and concentration distribution in numerical simulations of liquid−solid bubbling fluidized beds. [ABSTRACT FROM AUTHOR]

Methane hydrate, a potential future energy resource, is known to occur naturally in vast quantities beneath the ocean floor and in permafrost regions. It is important to evaluate how much methane is recoverable from these hydrate reserves. This article introduces the theoretical background of HydrateResSim, the National Energy Technology Laboratory (NETL) methane production simulator for hydrate-containing reservoirs, originally developed for NETL by Lawrence Berkeley National Laboratory (LBNL). It describes the mathematical model that governs the dissociation of methane hydrate by depressurization or thermal stimulation of the system, including the transport of multiple temperature-dependent components in multiple phases through a porous medium. The model equations are obtained by incorporating the multiphase Darcy’s law for gas and liquid into both the mass component balances and the energy conservation equations. Two submodels in HydrateResSim for hydrate dissociation are also considered: a kinetic model and a pure thermodynamic model. Contrary to more traditional reservoir simulations, the set of model unknowns or primary variables in HydrateResSim changes throughout the simulation as a result of the formation or dissociation of ice and hydrate phases during the simulation. The primary variable switch method (PVSM) is used to effectively track these phase changes. The equations are solved by utilizing the implicit time finite-difference method on the grid system, which can properly describe phase appearance or disappearance as well as the boundary conditions. The Newton−Raphson method is used to solve the linear equations after discretization and setup of the Jacobian matrix. We report here the application of HydrateResSim to a three-component, four-phase flow system in order to predict the methane produced from a laboratory-scale reservoir. The first results of HydrateResSim code in a peer-reviewed publication are presented in this article. The numerical solution was verified against the state-of-the art simulator TOUGH+Hydrate. The model was then used to compare two dissociation theories: kinetic and pure equilibrium. Generally, the kinetic model revealed a lower dissociation rate than the equilibrium model. The hydrate dissociation patterns differed significantly when the thermal boundary condition was shifted from adiabatic to constant-temperature. The surface area factor was found to have an important effect on the rate of hydrate dissociation for the kinetic model. The deviation between the kinetic and equilibrium models was found to increase with decreasing surface area factor. [ABSTRACT FROM AUTHOR]

The step response, including various startup procedures, in a three-phase microreactor of 2 mm internal diameter packed with nonporous particles of 100 μm is reported. We demonstrate that the bed behaves reproducibly through many cycles of operating conditions. Interestingly, we find that the different startup procedures have little effect on the steady state that is achieved. In other words, minimal hysteresis was observed, in sharp contrast to larger-scale reactors with larger particles where prewetting has a remarkable impact on the hydrodynamic behavior. The powder-packed beds have very high liquid saturation values, and prewetting is not needed. At least four liquid-residence times were needed to achieve stable pressure drop and dispersion values over the bed. This indicates that the hydrodynamic response into a stable operation may well be the limiting factor that determines the rate at which kinetic experiments can be performed in high-throughput equipment. [ABSTRACT FROM AUTHOR]