CATALYTIC CONVERTER DESIGN FOR MINIMISATION OF COLD-START EMISSIONS

The axial catalyst distribution in a monolithic converter that minimises cold-start pollutant emissions is investigated numerically, under the constraint of fixed total catalyst surface area. Various warm-up mechanisms can be present during the transient period. The catalyst distribution affects greatly which mechanisms prevail. For the optimal distribution, a large amount of catalyst is required in the upstream section of the monolith This ensures that the hot spot is kept at the monolith inlet throughout the warm-up period, and hence heat transfer by convection dominates. A result of practical significance is that the evolution and the steady-state value of the temperature of the exhaust gas stream at the monolith inlet do not affect significantly the form of The optimal distribution. Even though the local catalyst surface area of the optimal distribution in the downstream section of the converter is reduced as compared to the uniform distribution, steady-state performance is not adversely affected. A converter with two-zones, each having a different but uniform catalyst loading is also examined. It is shown that such a design can closely approximate the optimal distribution. Finally, performance degradation due to sintering is shown to be more severe for The case of the uniform catalyst distribution.     

Design and characterisation of the staggered herringbone mixer

The staggered herringbone mixer was studied using computational fluid dynamics (CFD) and particle tracking methods. The positions of tracer particles as well as the stretching of a fluid element associated with each tracer particle were tracked using a fourth order Runge-Kutta integration scheme with adaptive time stepping. Striation patterns observed were in qualitative agreement with experimental work from literature. The computed stretch values were found to be log-normally distributed. The specific stretch per period for a spatially periodic flow was computed. This allows for an estimation of the required length for complete mixing by further accounting the penetration depth achieved by molecular diffusion. The microchannel lengths for complete mixing computed using the mean stretch were lower than those obtained experimentally. This was attributed mainly to the fact that the experimentally derived values were measured in the central 50% of the mixer cross-section where striation thickness reduction can be observed to be slower. Furthermore, the specific stretch per period represents the mean stretch value while in reality the stretch values are distributed log-normally. In the design of mixers, a conservative estimate of the required mixing length can be obtained by replacing the mean stretch per period with a value which represents the cut-off point for the lower 10% of the distribution. The design lengths computed using these values were slightly higher than experimental ones and found to exhibit the same trend with increasing Peclet number. The pressure drop at various Re was also investigated and was found to be slightly lower than that of an equivalent grooveless channel.     

Laminar natural convection in water near the density extremum along a vertical plate with sinusoidal surface temperature variation

Summary. The steady laminar boundary-layer flow along a vertical plate immersed in water at 4°C is studied. The plate temperature varies sinusoidally with x between 0°C and 8°C, where the density of water varies parabolically and is almost symmetrical about 4°C. The results are obtained with the direct numerical solution of the boundary layer equations taking into account the temperature dependence of all water thermophysical properties (, , and c_p). It is found that the amplitude of oscillation of temperature gradient and wall shear stress remains constant with x, in contrast to previous studies concerning fluids with constant thermophysical properties and linear density-temperature relationship, where the amplitude of these quantities changes with x. It was also found that there is an inner boundary layer near the plate with periodic characteristics and that the velocity boundary layer thickness increases with x.     

Aerobic Oxidation of Benzyl Alcohol in a Continuous Catalytic Membrane Reactor

Topics in Catalysis - A catalytic membrane reactor with a Au–Pd catalyst, impregnated at the inner side of the membrane, was studied in the catalytic oxidation of benzyl alcohol in flow. The...     

On the Use of Online Reparametrization in Automated Platforms for Kinetic Model Identification

Parameter estimation algorithms integrated in automated platforms for kinetic model identification are required to solve two optimization problems: i) a parameter estimation problem given the available samples; ii) a model‐based design of experiments problem to select the conditions for collecting future samples. These problems may be ill‐posed, leading to numerical failures when optimization routines are applied. In this work, an approach of online reparametrization is introduced to enhance the robustness of model identification algorithms towards ill‐posed parameter estimation problems.     

Catalyst preparation and deactivation issues for nitrobenzene hydrogenation in a microstructured falling film reactor

Hydrogenation of nitrobenzene to aniline in ethanol was performed continuously in a microstructured falling film reactor at 60 °C, 1–4 bar hydrogen pressure and residence time 9–17 s. Palladium catalyst was deposited as films or particles via sputtering, UV-decomposition of palladium acetate, incipient wetness or impregnation. Deactivation was observed and was particularly pronounced for the sputtered and UV-decomposed catalysts. Catalysts prepared through incipient wetness or impregnation were more stable and activity could be recovered by oxidation at 130 °C. The main causes of deactivation were determined to be deposition of organic compounds and palladium loss.     

Comment on “Microsystem Technologies, (2018) 24:4945–4953”

Microsystem Technologies - Some serious errors exist in the above paper.     

Identification of kinetic models of methanol oxidation on silver in the presence of uncertain catalyst behavior

Catalytic oxidation of methanol to formaldehyde is an important industrial process due to the value of formaldehyde either as a final product or as a precursor of numerous chemicals. The study of kinetics in this system is hindered by sources of uncertainty that are inherently associated to the nature and state of the catalyst (e.g., uncertain reactivity level, deactivation phenomena), the measurement system and the structure of the kinetic model equations. In this work, a simplified kinetic model is identified from data collected from continuous flow microreactor systems where catalysts with assorted levels of reactivity are employed. Tailored model-based data mining methods are proposed and applied for the effective estimation of the kinetic parameters and for identifying robust experimental conditions to be exploited for the kinetic characterization of catalysts with different reactivity, whose kinetic behavior is yet to be investigated.     

Comment on the Paper “Onset of Marangoni-Bénard Ferroconvection with Temperature Dependent Viscosity,C. E. Nanjundappa,I. S. Shivakumara,R. Arunkumar,Microgravity Sci. Technol. (2013) 25:103–112”

The present comment concerns some doubtful results included in the above paper.