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This work reports theoretical studies of flow behaviour in a monolith outlet zone for different Reynolds numbers covering laminar and transitional/turbulent flow regimes. Monolith type substrate is the core part of the automotive catalytic converter. Due to computational limitations, most numerical models of the converter represent the monolith as a continuum, averaging the effect of the solid and the open space on the flow. This strategy is useful to study the macro-structure of the flow, however, it does not capture the exact behaviour of an actual honeycomb type structure, especially at its entrance and exit. In this work, which is a continuation of the publication by Cornejo et al. (2018), a series of 3D LES and RANS simulations are performed using different discrete channel geometry to study and quantify the velocity fluctuations of flow leaving a monolith. The results show that above a certain Reynolds number the instability of the flow after the monolith is significant, leading to turbulence generation. The velocity fluctuations are mainly explained by the flow past the outlet of the monolith, and their magnitude is related to the Reynolds number based on the thickness of the walls between channels. An expression for this critical Reynolds number has been designed and verified against numerical simulations. Parametric studies are carried out to illustrate the influence of the Reynolds number on the appearance of flow fluctuations at the outlet zone of the monolith. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive multiscale study of the turbulence inside of an automotive monolith using a porous medium approach and a representative group of single channels. A series of RANS simulations of an axisymmetric model of the whole converter and a 3D model of a representative group of single channels is combined to study the turbulence at different scales.Results of simulations are validated against experimental data published in the literature. Good agreement is achieved. Results of simulations reveal that although the continuum porous media model produces good agreement with experimental velocity profiles after the monolith, it does not describe accurately the effects of turbulence inside the monolith. Literature reports that a transition from turbulent to laminar at the beginning of the monolith channels impacts significantly the performance of the whole converter, but, at the same time, it is usually neglected, due the complexity that it adds to the problem. According to the results from the single channels, there is a smooth decay of the turbulence viscosity inside the monolith, that does not appear using the traditional models of porous zones. This decay can be achieved at the converter scale, via the addition of a damping term for the turbulence to the κ -equation of the RANS model. [ABSTRACT FROM AUTHOR]

A catalytically active particulate filter with a first order catalytic reaction taking place inside the filter walls is investigated by numerical simulation. The conversion efficiency for different channel geometries and operating conditions is systematically studied as a function of the governing dimensionless parameters. It is found that the conversion efficiency of a catalytically coated wall flow filter is very close to that of an ideal plug flow reactor over the full range of realistic operating conditions. Only in a range of intermediate residence times, the filter reactor shows some diffusion limitation which leads to conversion efficiencies slightly below that of the plug flow reactor. In all cases, these deviations from ideal conversion behaviour are below 15%. If the filter and the open monolith are compared at identical operating conditions and channel geometries, for fast reactions, the filter reactor shows higher conversion efficiency than the open monolith, since in this case the open monolith becomes strongly mass transfer limited. However, there can be a small range of conditions where the monolith is slightly more efficient than the filter. The reason for this effect is that due to the thinner washcoat layer the onset of mass transfer limitation in the coated monolith is shifted to higher reaction rates, compared to the filter reactor. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a preliminary study about the performance of a new hybrid adsorption bed, for CO2 capture from flue gases by Electric Swing Adsorption (ESA), was performed. The hybrid adsorption bed tested consists in an activated carbon honeycomb monolith with zeolite 13X particles packed inside its channels. The dynamic behaviour of the adsorption bed was evaluated by performing breakthrough experiments. The amount of CO2 adsorbed was the double when compared with employing the activated carbon monolith only, even when the content of zeolite is only 18%. ESA experimental cycles were tested. Purity of 46.6% was obtained while capturing 81.4% of the fed CO2 with a six-step ESA cycle. The obtained purity means an enrichment of the feed stream of 5.8 times. The experimental energy consumption is still high due to the mass transfer zone limitations. Solving this problem will allow decreasing the energy consumption more than five times which means that the process can present competitive energy consumption when compared with existing technology. [Copyright &y& Elsevier]

Abstract: The importance of accurately measuring gas diffusivity in porous materials has led to a number of methods being developed. In this study the Temporal Analysis of Products (TAP) reactor and Flux Response Technology (FRT) have been used to examine the diffusivity in the washcoat supported on cordierite monoliths. Herein, the molecular diffusion of propane within four monoliths with differently prepared alumina/CeZrO x washcoats was investigated as a function of temperature. Moment-based analysis of the observed TAP responses led to the calculation of the apparent intermediate gas constant, K p , that characterises adsorption into the mesoporous network and apparent time delay, τ app , that characterises residence time in the mesoporous network. Additionally, FRT has been successfully adapted as an extensive in situ perturbation technique in measuring intraphase diffusion coefficients in the washcoats of the same four monolith samples. The diffusion coefficients obtained by moment-based analysis of TAP responses are larger than the coefficients determined by zero length column (ZLC) analysis of flux response profiles with measured values of the same monolith samples between 20 and 100°C ranging from 2–5×10−9 m2 s−1 to 4–8×10−10 m2 s−1, respectively. The TAP and FRT data, therefore, provide a range of the lower and upper limits of diffusivity, respectively. The reported activation energies and diffusivities clearly correlate with the difference in the washcoat structure of different monolith samples. [Copyright &y& Elsevier]

Abstract: A comprehensive experimental and modeling study of selective catalytic reduction of NOx with NH3 was carried out on Fe-ZSM-5 and Cu-chabazite (CHA) catalysts. The experiments reveal that Cu-CHA catalyst has a higher NH3 storage capacity and activity for NH3 oxidation and standard SCR compared to Fe-ZSM-5. The NOx reduction activity on the Fe-ZSM-5 catalyst was found to be strongly dependent on the NO2 feed fraction in contrast to Cu-CHA catalyst for which NOx conversion was much less sensitive to NO2. In the presence of excess NO2, both N2O and ammonium nitrate were produced on both catalysts although Fe-ZSM-5 catalyst had a higher selectivity towards these byproducts compared to Cu-CHA. For different feed conditions (NO2/NOx=0–1), Cu-CHA was a more active NOx reduction catalyst at lower temperatures (<350°C) while Fe-ZSM-5 was more active at higher temperatures (>400°C). Global kinetic models were developed to predict the main features of several SCR system reactions investigated experimentally. The models account for NH3 adsorption, NH3 oxidation, NO oxidation, standard SCR, fast SCR, NO2 SCR, ammonium nitrate formation and its decomposition to N2O, N2O decomposition and N2O reduction by NH3. The 1+1 dimensional reactor model accounts for potential washcoat diffusion limitations. The model accurately predicts the steady state NOx and NH3 conversions and the selectivity of the different products formed during these reactions. The model was used to predict the performance of standard and fast SCR reactions on combined systems of Fe- and Cu-zeolite monolithic catalysts which were found to have higher NOx conversion activity over a wider temperature range than with individual Fe- and Cu-zeolite catalysts as reported in our earlier study (Metkar et al., 2012b). Among various configurations of the combined catalysts, either a single brick made up of a dual-layer catalyst with a thin Fe-zeolite layer on top of a thick Cu-zeolite layer or a sequential arrangement of short Fe-ZSM-5 brick followed by longer Cu-CHA brick resulted in high NOx removal efficiency over a wide temperature range of practical interest. [Copyright &y& Elsevier]

Abstract: In this paper, the dimensionless reaction rate density of a two-dimensional channel with catalyst on its boundary was maximized by optimizing its aspect ratio H/L. Order of magnitude expressions in the limit of small H/L and in the limit of large H/L were developed and then intersected to predict the optimal aspect ratio and maximum reaction rate. Numerical simulations were performed and the results corroborated very well with the scale analysis. The results showed that the optimal design of microreactors depends on the Schmidt number (Sc), the Bejan number (Be) and the Catalyst number (Ct). Correlations based on those numbers are proposed. The analysis was performed for steady-state laminar flows, using the dilute species assumption and a first order kinetic expression. [Copyright &y& Elsevier]

Abstract: The filtration of gas/(kaolin-kerosene) suspension flows in monolith reactors was monitored using electrical capacitance tomography. Two flow modulation modes (fast and semi-fast) were compared to constant-throughput feeds of the suspension in a quest for strategies for the reduction of fines accumulation. The effects of initial distribution of liquid suspension and superficial velocities, and base-pulse time splitting of flow modulation were found to affect both the structure of deposition and the amount of deposited fines. One major finding concerned dampening of liquid hydrodynamic waves generated in flow modulation which could severely limit implementation of self-cleaning fast-modulation strategies of monolith reactors subject to filtration of suspensions. [Copyright &y& Elsevier]

[Display omitted] • M1@Cordierithe structured catalyst for the ODHE process is successfully prepared. • A CeO 2 inter-layer is introduced to improve the M1 catalytic performance without decrease of ethylene selectivity. • M1@CeO 2 @Cordierithe structured catalyst shows an excellent ethylene productivity and long-term stability in ODHE process. The phase-pure M1 MoVNbTeO x catalyst was successfully coated on cordierite monolith by PVP-sol binder solution. In order to improve the activity of structured catalyst, an M1@CeO 2 @Monolith layered structure was further prepared through a two-step procedure: (i) Coating CeO 2 layer on monolith by sol–gel method, then (ii) coating the M1 on CeO 2 @Monolith. The M1@CeO 2 @Monolith structured catalyst exhibited superior catalytic performance and stability for ODHE reaction. At 400 °C, ethane conversion (X C2H6) ∼ 60% and ethylene selectivity (S C2H4) ∼ 85% with a space time yield of ethylene (STY) ∼ 0.9 kg C2H4 /kg cat /h (normalized to M1 ∼ 1.05 kg C2H4 /kg cat /h) have been achieved for the M1@CeO 2 @Cordierite structured catalyst, while the M1@Monolith has only about X C2H6 ∼ 40%, S C2H4 ∼ 92%, and STY ∼ 0.64 kg C2H4 /kg cat /h. In summary, these results inspired the catalyst design for ODHE process, presenting great potential for industry practice. [ABSTRACT FROM AUTHOR]

Abstract: It is shown that a mapping of precomputed rate data can be used to implement efficiently detailed surface mechanisms into reactor simulations. The procedure is demonstrated using a surface mechanism for oxidation on platinum (11 surface species, 19 reactions). It is found that a spline representation based on 7000 data points reproduces the effective conversion rates with an error of less than 0.5%. To demonstrate the potential of the approach a 3D model of a monolith channel including the irregularly shaped washcoat is implemented in a commercial CFD program. A steady state solution of this model takes 20s on a 1.5GHz Pentium computer. This corresponds to a speed up of three orders of magnitude compared to the solution of the same model coupled to a full numerical solution of the surface chemistry. [Copyright &y& Elsevier]

Abstract: The effects of grafting conditions on the properties of a novel cation-exchange cryogel by grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) onto polyacrylamide-based cryogel (pAAm cryogel) using potassium diperiodatocuprate (Cu(III) solution) as initiator were investigated experimentally. The basic cryogels were saturated with the initiator solution followed by the solution of monomers to get the expected sulfo groups under various grafting conditions, such as concentrations of monomers and initiator, graft reaction time, graft temperature and the volume ratio of Cu(III) to NaOH. The results showed that these factors influenced the liquid dispersion behaviors and the flow resistance as well as the protein binding capacity of the grafted cryogels. Protein binding capacity increased with the increase of concentration of AMPSA and Cu(III), the graft temperature and the graft reaction time in a wide range under the present conditions. Compared with these factors, the volume ratio of Cu(III) to NaOH in the initiator solution in the considered situations had a relatively weaker influence on the cryogel microstructures and protein binding capacity. The maximum binding capacity of lysozyme reached 2.5mg/mL cryogel in these grafted cryogels. [Copyright &y& Elsevier]

The present work investigates the influence of gas and liquid flow rates on inlet liquid distribution across monoliths operating in gas–liquid cocurrent downflow mode. Gas and liquid superficial velocities range from 0 to 68 and 1.4 to 8.5cm/s, respectively. Gas–liquid distribution was studied using a packed bed liquid distributor and a pipe distributor for the aforementioned range of operating conditions. To determine the liquid distribution over the monolith, gravimetric, time-averaged liquid collection method was applied using a customized collector apparatus. Quantification of the distribution is reported using a suitably defined maldistribution factor. For each liquid velocity, gas velocities are varied and corresponding maldistribution factors are calculated. The results are reported in view of the varying operating conditions. [Copyright &y& Elsevier]

Abstract: The hydrodynamic behavior of trickle bed and monolith reactors experiencing deposition from fines-contaminated feed flows was studied to assess the potential aptitude of monolith to be an alternative for disability of trickle bed reactors under filtration condition. Beds with equal collection surface area were subjected to single-pass suspension and air flows to study the influence of filtration for different gas and liquid superficial velocities. It was found that for equivalent gas and liquid velocities, specific deposits in trickle bed are up to two times more than in monolith. [Copyright &y& Elsevier]

The use of stereolithography is well suited for the fabrication of a monolithic photocatalyst for cleaning of air contaminated by volatile organic compounds (VOCs). In this paper we present the influence of the geometry of the monolith on the reactor''s efficiency. Our aim is to develop a model that describes the basic phenomena, which are involved, i.e., light absorption, hydrodynamic and transfer processes and the reaction kinetics. Three different geometries of the monolith reactor have been tested: mixer (), crossed channels (), and star geometry (). It appears that the geometry has practically no influence on the external mass transfer rate but has a great influence on the kinetics of photocatalysis. The model will be used to predict and optimize the photocatalytic behaviour and to scale up the results to an industrial reactor. [Copyright &y& Elsevier]

Abstract: Transient two dimensional (2-D) and three dimensional (3-D) single channel models (SCMs) describing transport of into a NaZSM-5 film and kinetics for reactions forming nitrate species were developed. The film consisted of a continuous thin layer of inter-grown NaZSM-5 crystals supported on a cordierite monolith support. The 2-D model which included a comprehensive transport model was developed for studying the adsorption kinetics, whereas the more rigorous 3-D model was used to provide a better picture of radial and axial concentration and velocity variations in the monolith channel and the film. The overall adsorption–desorption mechanism, consisting of two competing reaction schemes for nitrate formation, was sufficient to predict the dynamic development of surface nitrate species. The simulation results showed that the adsorption is strongly influenced by transport resistance in the NaZSM-5 film. Also, the effective diffusion of in the NaZSM-5 film is apparently surface nitrate concentration dependent. [Copyright &y& Elsevier]

This paper describes an approximation method for the estimation of effectiveness factors in porous catalysts that have reactions with non-linear kinetic models. The reaction rate expression is expressed as a combination of two asymptotic solutions based on a local concentration, leading to an approximate rate function containing four parameters. The effectiveness factors computed with the approximated rate are shown to be close to the values calculated from the real rate function for a variety of non-linear LHHW type models. The advantage of the approximate method is that a given set of four parameters, which can easily be calculated, uniquely identifies an effectiveness factor. This observation enables the construction of a table from which the effectiveness factor can be readily extracted during reactor simulation, thus resulting in a decrease in computational effort. [Copyright &y& Elsevier]

Solvent freezing crystallization is a crucial step to the satisfactory formation of homogenous and interconnected supermacropores within cryogels during the preparation of supermacroporous cryogel beds via cryo-copolymerization. In this work, the freezing characteristics of an aqueous solution system containing acrylamide (AAm), -methylene-bis-acrylamide (MBAAm) and allyl glycidyl ether (AGE) for the production of polyacrylamide-based cryogels were investigated experimentally under various cooling conditions. Freezing curves of solution of under various concentrations were measured to determine the corresponding values of freezing point temperature and the actual initial solvent crystallization temperature . The effects of freezing rate and monomer concentration on and were addressed. The results showed that the freezing rate had a limited effect on when the freezing rate was very low under the present work. At the same time, changed randomly in a certain range with monomer concentration and freezing rate, while decreased with the increase of monomer concentration under freezing condition at a constant freezing rate. Based on these results, the in-column freezing behaviors of 7% (w/w) aqueous solution of reactive system initiated by ammonium persulfate (APS) and N,N,,-tetramethylethylenediamine (TEMED) under different freezing-temperature variation conditions were measured to reveal the actual solvent crystallization processes occurring within the column during the cryo-copolymerization. The properties of these cryogels were also measured and discussed. [Copyright &y& Elsevier]

Abstract: One of the developments in separation technologies by adsorption is the use of new shaped structured materials offering some attractive properties rather than pellet or extrudates behavior. Monolithic adsorbents have actually been studied in a wide range of applications. It is the purpose of this work to report the behavior of a square honeycomb monolith containing zeolite 4A crystals inserted by extrusion. Adsorption equilibrium of pure gases was measured at 423 and in a Rubotherm microbalance, and data were in agreement with commercial extrudates data. Diffusivity coefficients of propylene were determined by uptake curves at low pressures; and . These values are three orders of magnitude smaller than that of previous data measured in commercial extrudates due to partial blocking of the micropores of the zeolite with one of the materials used in the monolith preparation. A complete mathematical 3D-distributed parameter model for fixed-bed adsorption of dilute streams in monoliths composed of materials with bidisperse structure was developed. A more simplified model in 1D was also used for description of adiabatic bulk adsorption. Breakthrough curves of propylene diluted in helium at three different partial pressures (1.5, 5.6 and ) were measured to validate both models. [Copyright &y& Elsevier]

Abstract: The monolith bed is one of the promising catalytic reactors for a number of chemical gas–liquid–solid processes. In the present work, liquid saturations for five different monoliths have been investigated experimentally in a cold-flow unit with a reactor diameter of 5.0cm. The influences of gas and liquid flow rates and of the direction of two-phase flow on liquid saturation were examined. The results indicate that the direction of flow has no significant influence on liquid saturation for proper gas–liquid distribution. The experimental results are in good agreement with predictions of the drift flux model using the distribution parameter proposed by Ishii (ANL Report ANL-77-47, 1977) along with the assumption of zero drift velocity. In preliminary experiments, gamma-ray computed tomography (CT) has been successfully applied to measure time-averaged liquid distribution over the monolith cross-section in a selected condition. The employment of a nozzle-type distributor provides an almost uniform liquid distribution over the monolith substrate. It is demonstrated that CT is a viable technique for studying two-phase flow in laboratory-scale monolith reactors. [Copyright &y& Elsevier]

Abstract: This paper describes a method for the determination of effectiveness factors in a monolith washcoat of non-uniform thickness. The method is based on the previously reported slice concept, in which the monolith is divided into a series of slices, each of which is analysed using a one-dimensional approach. In each one-dimensional slice, an apparent characteristic length is used to compute the Thiele modulus. In the approach described here, the apparent characteristic length is determined by conducting a single two-dimensional simulation for a first-order reaction in the kinetically controlled region. The characteristic length is then calculated from the flux at the surface using an analytical solution. Results are shown for the idealized circular washcoat in a square channel, as well as for a real washcoat in a square channel and a sinusoidal shape. Results for first-order and LHHW kinetics show good agreement between the one-dimensional approximation and the true solution. Both average and local effectiveness factors can be calculated within acceptable range for monolith reactor simulations. [Copyright &y& Elsevier]

Abstract: Honeycomb structures made of highly thermal conductive materials (e.g. certain metals) have been proposed as attractive catalyst supports with enhanced heat transfer properties. Recently prototypes of such materials have become available, enabling experimental investigations on their heat transfer properties, including packaging into tubes. This work is focused on the heat transfer performance of conductive monolith structures packaged into heat exchanger tubes. Several parameters such as monolith material structure and properties and packaging tolerances are investigated. Heat transfer coefficients on the order of and higher were measured. The results are analyzed applying a detailed model based on a fundamental understanding of the relevant phenomena. It is demonstrated that it is necessary to consider the variations of the thermal expansion of the monolith and the tube over the length of the monoliths. By including thermal expansion, the model is in excellent agreement with the experimental results without the need of any fitting parameter. The results are used to develop some design guidelines. In addition some implications of the heat transfer performance for the relevant applications in multitubular reactors as well as some new potential application areas are discussed. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental study on the impact of channel shape to gas–liquid catalytic reactions inside small reaction channels (1–2mm size). The channel shape is a unique design parameter offered by a structured catalyst/reactor. Comparative reaction testing of square channels vs. circular channels is conducted under various flow conditions in a gas/liquid co-current down flow mode. Hydrogenation of olefins and toluene saturation over the Ni/-alumina monolith catalyst module are used as model reactions. The gas/liquid feed is directly delivered into one, single channel in the monolith catalyst module in order to eliminate any gas/liquid distribution problem. It is found that for the 2-mm channel size, the circular shape gives a catalytic conversion activity two to five times higher than the square-shaped channel. The dramatic activity enhancement is believed resulting from better gas/liquid/catalyst contacting in the circular channel than in the square channel. The degree of activity enhancement due to the channel shape decreases as the channel size is reduced from 2 to 1mm, because the catalyst utilization is increased with decreasing the channel size. This finding suggests that catalyst utilization in the three-phase reactor can be largely affected by the non-uniformity of flow structure at particle size scale. [Copyright &y& Elsevier]

This paper reports the results of a numerical investigation of the diffusion and reaction in the washcoat of a catalytic monolith reactor. Both idealized shapes and real geometries are tested. It is shown that for non-uniform washcoat thickness, the Sherwood number varies along the channel/washcoat interface. The internal diffusion resistance, expressed in terms of an effectiveness factor, cannot be represented in terms of a unique curve using the generalized Thiele modulus approach. The most significant deviation occurs when the washcoat has the greatest variation in thickness. The internal diffusion affects the magnitude of the external mass transfer resistance. Three factors significantly affect the rates and role of mass transfer. These are (1) the washcoat thickness, (2) the channel radius, including its non-uniformity around the channel, and (3) the angular diffusion in the washcoat caused by variable thickness. [Copyright &y& Elsevier]

A global optimization analysis of a general class of perforated monolithic bed reactors is presented for the case of an isothermal first-order reaction and for laminar flow conditions. The resulting design rules indicate how a given amount of catalyst material should best be perforated or distributed in space as a function of the available inlet pressure. It is shown that the influence of the different process variables (k,ΔP,Vcata,Cin/Cout,Dmol, Sreac) on the reactor productivity and on the optimal bed design can be grouped into a single dimensionless number E. This number also allows to discuss the sensitive relation between the total and the volumetric productivity of single bed reactors in a very general, compact manner. Two different perforated monolithic bed designs, a slit pore bed (SPB) and a cylindrical pore bed (CPB) are considered. It is found that, when there is an excess inlet pressure (i.e., for E≪1), the optimal catalyst layer thickness is given by φ=0.3–0.5 and that the optimal pore diameter is in both cases 1.4–1.45 times smaller than the catalyst layer, independently of the internal catalyst diffusivity (Dint) and the other process variables. When the available inlet pressure is limiting (E>10−4), and when the absolute reactor productivity is more important than the volumetric productivity, it is found that much more open structures, with much wider pores are needed, i.e., perforated beds show the same behavior as packed beds, where the occurrence of a pressure-drop limitation also induces a shift from the use of full particles to the use of hollow extrudates. [Copyright &y& Elsevier]

The maximally attainable productivity of perforated monolithic bed reactors has been compared to that of the traditional packed bed of spheres for the case of laminar flow conditions and first-order isothermal reaction kinetics. Using the E number established in Part I, it could be shown in a very condensed, yet fully quantitative way that the maximal gain in total reactor productivity which can be obtained by switching from the tortuous pore system of the packed bed of spheres (large flow resistance) to the straight-running flow-through pores of a perforated monolithic bed (minimal flow resistance) typically is 25–40%. Much larger gains in total productivity can be obtained by using highly open-porous beds. Whether this high porosity is achieved using a perforated monolithic bed, a packed bed of hollow extrudates or a structured fibre-mesh bed is then only of secondary importance. The E number also allows to quantify the potential gain and the range of applicability of the more advanced reactor designs proposed in the past years (e.g., the parallel passage reactor). It could now be shown that the productivity gain of these advanced concepts can even amount up to a factor of 100. As these gains are to be realized in beds with ultra-small flow-through pores, the present study also provides a strong quantitative argument for the current research on (micro-)structured reactor beds. [Copyright &y& Elsevier]

Solid-acid catalysts are attractive replacements for processes using conventional homogeneous catalysts. In the esterification of an alcohol with a carboxylic acid, however, the side product water strongly inhibits the activity of a solid-acid catalyst. Since an esterification is an equilibrium limited reaction, full conversion is not possible unless one of the products is removed. A novel reactor type, utilizing a solid-acid catalyst coated monolith, is presented in which water can be removed from the liquid reaction mixture by means of reactive stripping. In this manner the inhibition is eliminated and complete conversion can be reached. The advantages of this reactor concept are demonstrated by both experiments and reactor modeling. [Copyright &y& Elsevier]

We consider the problem of flow in a tube with an exothermic surface reaction and show that the azimuthally symmetric steady-state can lose stability giving rise to patterned states with nonuniform concentration and temperature profiles. The primary cause for this transport limited pattern formation is the slow relative rate of heat and mass diffusion compared to surface reaction. Patterned states in which the temperature and concentration profiles vary in the azimuthal direction, can exist (or coexist with symmetric states) for all values of the fluid Lewis number (Lef) though the patterned states are more pronounced and exist in a wider range of parameter space when Lef<1. We analyze a three-dimensional model of catalytic monolith and develop analytical criteria for identifying the parameter regions in which patterned states exist. These criteria indicate that patterned states are formed whenever the local balance equations have multiple solutions and the characteristic reaction time is much smaller compared to the heat/mass diffusion time. Examination of the numerical values of the various parameters shows that most catalytic monoliths and combustors may operate in the region in which a large number of patterned states may exist. It is also found that when nonuniform and three-dimensional temperature and concentration fields exist, there can be hot spots in which the temperature exceeds the adiabatic temperature even when Lef=1. [Copyright &y& Elsevier]

• A fully predictive multiscale pressure drop model for monolith substrates is presented. • Excellent agreement with experimental velocity profiles was observed. • The model works for several channel shapes and substrate void fractions. • The methodology has general applicability to substrates with other channel shapes. This paper presents a detailed physics based model for the pressure drop through a honeycomb substrate for several channel shapes and void fractions. A CFD-based computational model of a single channel is used to study the pressure drop when flow is entering, passing through and leaving the substrate. An extensive set of 3D computational experiments covering square, hexagonal and triangular channel cross-sections, void fractions from 0.39 to 0.84 and channel Re from 95 to 1284 is used. It is shown that altering the void fraction changes the pressure drop at the inlet and outlet of the substrate, however, its effect on the friction factor inside the substrate is minor. The resulting model can be used either as a semi-empirical lumped model for pressure drop and in 3D full-scale simulations with a porous medium representing the substrate. A validation for the velocity profile in a full scale monolith with experimental data available in the literature is carried out and an excellent agreement is observed. The proposed model significantly improves the prediction of the flow distribution across the substrate, which has remained unaddressed historically by existing models and is the most important effect required to make accurate predictions of heat distribution, conversion efficiency and others in full-scale simulations. [ABSTRACT FROM AUTHOR]