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A novel averaging of the conservation equations for axial flow in packed beds is presented to express the momentum, continuity, and energy equations in terms of the cross‐sectional averages of concentration, temperature, and superficial velocity. The model integrates the radial fluctuations of the intrinsic variables into the partial differential equations of the model and presents a method for the design and analysis of catalytic reactors at a broad range of Reynolds numbers without the necessity of adjusting the operating conditions to minimize the impact of the radial profiles of velocity, concentration, and temperature. Since the control of the industrial reactors is dependent on the average values of the concentration and temperature, the model can be directly employed for design, optimization, and control processes with the added advantage of time and cost savings for both the numerical resolution and laboratory testing expenses. The model is limited to reaction systems with Péclet numbers of less than 700 with an average void fraction of εb for which the ratio of the bed length‐to‐particle diameter to particle Péclet number exceeds 0.3εb1−εb. The model was applied to the simulation of steam methane reforming (SMR). The results indicate that the average equations predict the responses of the SMR properly and thus the model could be reliably utilized for process design, operation, and control. [ABSTRACT FROM AUTHOR]

Due to scale effects, directly enlarging the size of the micromixer is an easy way to reduce the efficiency of mass and heat transfer in the continuous flow chemical process. It is urgently needed to solve the problem of mass and heat transfer efficiency of the scale‐up mixer. A scale‐up microfluidic mixer with a porous structure was designed to improve the mass and heat transfer efficiency using computational fluid dynamics (CFD) simulations. The effects of rotation angle, porosity, and baffle spacing were studied to optimize the mixer structure. Compared with the 1 mm mixer without structure, the scale‐up mixer has a higher mixing efficiency and an 80% reduction in energy consumption at Re ≥ 700. A Nusselt number was used to evaluate the heat transfer efficiency of the mixer during fluid heating. The results show that the porous baffle promotes the generation of secondary flow and enhances the heat transfer effect, making its Nu increase by three times compared with the unstructured mixer. The scale‐up microfluidic mixer with a porous structure can effectively improve the mass and heat transfer performance. This study can provide a reference for the design or development of a novel scale‐up mixer. [ABSTRACT FROM AUTHOR]

A novel method based on cup‐mixing concentration and superficial velocity is presented for the analysis of reactions in isothermal fixed‐bed reactors. It is founded on experimentally observed profiles of concentration and velocity so as to preserve the heterogeneity of a reaction system. The domain of application of the model includes reaction systems at lower Reynolds numbers and Péclet numbers of less than 700 with a void fraction of ϕ for which the ratio of the bed‐length‐to‐particle diameter to particle Péclet number exceeds 0.3ϕ1−ϕ. [ABSTRACT FROM AUTHOR]

Foam formation in porous media is a topic of growing scientific and industrial interest due to its range of applications, from daily life consumer products to oil recovery. Despite the work done so far on foams flowing through complex structures, such as rigid porous media, this subject still needs to be fully elucidated. An additional complexity to the problem arises when the porous medium is deformable, a situation which has only been faced, to our knowledge, from a modelling point of view. In this work, the investigation of foam formation in deformable porous media is carried out by using commercial sponges as a deformable porous media system, with special emphasis on the effect of confinement on foam bubble size distribution. Foam is formed by wetting the sponge with an aqueous surfactant solution and then squeezing the sponge either between two glass cover slides or between a plastic net and a cover slide. Our experimental data reveal that the latter system allows the formation of drier foams (ie, with lower liquid fraction, fL < 0.3), more similar to the ones obtained in dish‐washing applications. Moreover, the effect of sponge type, in terms of material and microstructure, on final foam is presented. Our results are of potential interest for the optimization of foams in complex structures, such as in deformable porous media. [ABSTRACT FROM AUTHOR]

Low-temperature steam reforming is an interesting alternative to traditional hydrogen production methods, making it possible to couple the reactor with solar heating. The main limitation in this process is imposed by thermodynamic equilibrium, which may be overcome by considering the use of a pre-reformer, in which equilibrium conversions are easily reached, followed by a membrane reactor, in which additional hydrogen production takes place along with its separation from the other products. This work is based on an overview of studies previously carried out by the same authors on the influence of pressure on the interplay between transport, permeation, and reaction in methane steam reforming membrane reactors and focuses on the behaviour of yield, defined as the ratio between the flow rate of hydrogen permeating across the membrane and at the inlet of the reactor. In the present work we show that all the curves depicting the yield, corresponding to a variety of operating conditions, can be rescaled onto a single master curve, thus providing the most compact representation of the reactor's performance. Furthermore, we show that the invariant scaling is robust with respect to changes of the reactor geometry. [ABSTRACT FROM AUTHOR]

Skin is a complex structured system primarily involved in Transdermal Drug Delivery (TDD). The outer s tratum corneum represents the main barrier to the entrance of external molecules. Nowadays, none of the recognized methods, used for the investigation of penetration processes, is able to give a complete overview of the transport mechanisms involved. Standard protocols are based on the use of human or animal skin samples, which are difficult and expensive to obtain. Here, we present a novel experimental setup to investigate TDD by using Confocal Laser Scanning Microscopy and image analysis. The methodology is based on diffusion experiments of fluorescent-labelled fluids (water, oil, and oil-in-water emulsions), in a model matrix. Using an agarose gel as model for a proof of concept, different penetration efficiencies were observed, suggesting an important role of both chemical composition and fluid microstructure on the transport mechanism. An adequate model system should be used to better mimic the stratum corneum morphology and properties. To this aim, several bicontinuous emulsion gels, obtained from an emulsification process, were preliminary formulated and suggested as model systems to mimic the stratum corneum. In this work, we define the key directions for the development of an innovative approach to study the penetration of formulations through the skin. [ABSTRACT FROM AUTHOR]

Experimental data on bed friction and solids transport in an open-channel flow at high bed shear are presented in this paper together with a discussion using analytical developments. Experiments were carried out using plastic particles transported in water above an erodible bed in a tilting flume. They confirmed that bed friction is affected by transport of solids for large bed shear stresses in the upper plane bed regime. Similarities in flow conditions were also observed between open-channel flows in steep slopes with intense solids transport, and stratified flows in slurry pipes. Furthermore, the experiments revealed two different sub-regimes for the upper plane bed regime in open channels. Formulae for the friction coefficient and the solids flowrate were proposed for an erodible bed with a developed shear layer. Measured velocity distribution indicated a linear velocity profile across a major part of the shear layer. [ABSTRACT FROM AUTHOR]

An adaptive discretization for population balance equations is presented. The method is combined with the multiphase CFD code STAR-CCM+ of CD-adapco. In order to account for the multidisperse nature of the flow the dispersed phase is split into M size groups; from the modelling point of view each group is a separate phase in every aspect but the name. The groups move with their own velocities and exchange mass, momentum, and energy with other groups and with the continuous phase. Size of a group is not prescribed a priori, but calculated from an additional scalar equation. A special procedure is designed to ensure that at each point all groups have the same volume fractions. As the particle sizes change due to coagulation and breakup, the discretization of the phase space adjusts itself to the new size distribution. Few groups suffice to predict the mean characteristics of the flow. [ABSTRACT FROM AUTHOR]

Reactive pore diffusion is an important process in automotive exhaust-gas aftertreatment modelling the overall conversion of pollutants. It features highly nonlinear source terms from chemical reactions coupled with transport processes. This work examines the application of model reduction by proper orthogonal decomposition. It is shown that this technique can be successfully applied to the system using separate bases for each species. Using a basis obtained for baseline conditions, predictions can be made for species profiles within a pore system for different conditions, potentially leading to significantly reduced computational requirements. [ABSTRACT FROM AUTHOR]

During steam assisted gravity drainage (SAGD) process, a steam chamber forms due to continuous steam injection. This chamber first moves upward to the top of the reservoir and then spreads sideways. The upward chamber displacement is one of the key factors for optimising the steam injection rate. It is necessary to determine the accurate chamber rise velocity for predicting the oil recovery rate. Recent experiments show that oil flow is coupled to water flow during three-phase gravity drainage in water-wet systems. In this paper, we argue that this type of flow coupling can be significant in SAGD operations. We extend Butler's [Butler, J. Can. Petrol. Technol. 1987, 26, 70] and Gotawala and Gates [Gotawala and Gates, Can. J. Chem. Eng. 2008, 86, 1011] analytic models for the rise of interfering steam chambers to account for three-phase flow and flow coupling. We also show the importance of flow coupling by solving a simple numerical example. We observe that by including three-phase drainage and the flow coupling at the steam finger edge, the vertical rise velocity of a steam chamber increases. Moreover, the rise velocity is very sensitive to the coupling term introduced in the new models. Even a small value of the coupling term increases the rise velocity significantly. Furthermore, we compare the model predictions with the values measured in six fields. [ABSTRACT FROM AUTHOR]

A pore-and-throat network including fractal-like roughness features along its surface is employed to simulate primary drainage and secondary imbibition by accounting for the quasistatic motion of menisci in pores and throats and varying the contact angle from 0° (strongly water-wet conditions) to 180° (strongly oil-wet conditions). The angle of sharpness of roughness features defines a range of contact angles within which the cross-section of the throat or pore is occupied completely by the one fluid and conditions of intermediate wettability are established. In contrast, outside this range, both fluids may coexist in a pore or throat. Such differences on the fluid distribution at the pore level affect strongly the capillary, electrical and hydraulic properties of the porous medium and are reflected in the capillary pressure, resistivity index and relative permeability curves. The simulator is used to calculate the aforementioned two-phase flow coefficients as the pore system transits from strongly water-wet or strongly oil-wet to intermediate-wet. The capillary pressure curves are always sensitive to the wetting state and the particular value of the contact angle. The relative permeability and resistivity index curves for secondary imbibition are grouped in families of curves which are sensitive mainly to the wetting state (water-wet, intermediate-wet/water-wet pores, intermediate-wet/oil-wet pores, oil-wet) rather than to the particular value of the contact angle. [ABSTRACT FROM AUTHOR]

An engineering model of a transient laminar flow from a pressurised vessel through a long microchannel under a condition of a rapid valve opening at a channel outlet is developed. A valve at the channel outlet, which is opening with a given speed, is modelled as a time-dependent boundary condition. Transient flows are investigated numerically by the method of characteristics. The calculations show that variations of pressure and velocity distributions along the channel over time, caused by a transient flow regime, decrease with a decrease in the channel diameter and the channel length, an increase in the time of valve opening and an increase in the fluid viscosity. © 2012 Canadian Society for Chemical Engineering [ABSTRACT FROM AUTHOR]

We report on extended computer simulations of the thermocapillary effect in a model liquid biphasic mixture by employing a nonequilibrium molecular dynamics (NEMD) technique. It maintains a constant temperature gradient in the simulated system. We discuss the methodology used and report, after a careful analysis of the uncertainties inherent to such simulations, first results. The main feature is a stable roll cell convection with flows from hot to cold in the vicinity of the interfaces. This basic pattern persists in systematic variations of the temperature gradients, the size of the simulated systems and several other parameters. We thus assume to be dealing with Marangoni flows (thermocapillary effect) at the microscopic level. © 2012 Canadian Society for Chemical Engineering [ABSTRACT FROM AUTHOR]