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This study presents a new model to predict the additional pressure drop for series-arranged misaligned monoliths, relevant for high-flow industrial applications. Long reactor tubes often contain multiple short monoliths, leading to extra pressure drops as the flow enters and leaves multiple monoliths. Existing models address aligned monoliths, but this research considers misalignment, where extra pressure drop is higher. Channel Reynolds from 50 to 320, spacings from 0.1 to 20 channel diameters, and several void fractions are investigated using a discrete channel model. Results indicate a significant impact of misalignment on extra pressure drops in closely spaced monoliths due to flow collisions. A correction factor model that adapts to misalignment is proposed, starting from large values for closely spaced channels and decreasing as spacing increases. The proposed model aligns with discrete channel data and phenomenological behavior of aligned channels both in trend and magnitude, showing an R2 above 0.93. • Innovative model for pressure drop correction in misaligned monoliths. • Accounts for a wide range of Reynolds numbers and gap lengths. • Demonstrates a significant impact of misalignment on pressure drop. • Validated against discrete channel CFD data and real-world behavior. [ABSTRACT FROM AUTHOR]

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 is concerned with the modeling of the pressure drop through monolith honeycombs. Monolith substrates are promising for the intensification of catalytic processes, especially because of their low back-pressure. There have been several improvements in the modeling of monolith reactors during the last decade, most of them focused on a single substrate configuration, while research in multiple substrates in a single reactor is still sparse. One example is the so-called "minor losses", such as those because of the flow entering and leaving a substrate. Both phenomena interact when two monoliths are placed close in series, and the extra losses produced by them may become relevant when relatively short monoliths are used. In this paper, a spatially resolved computational model of monolith channels arranged in series is used to compute the extra pressure drop because of the flow leaving one substrate and entering the next one downstream. Several Reynolds numbers and spacing lengths for the channels between substrates are investigated. According to the results, for close-coupled monoliths, the inlet and outlet effects produce a negligible pressure drop compared to that in a single monolith configuration. This phenomenon can be accounted for by introducing a correction factor. The magnitude of the correction factor depends on the channel's Reynolds number, diameter, and spacing length. A model for such a factor is proposed. The model accurately predicts the trend and magnitude of the correction factor. [ABSTRACT FROM AUTHOR]

This paper reports an investigation of heat and mass transfer coupled with fluid flow inside monolith honeycomb substrates. Many important aspects of multiscale models of a monolith are investigated. Three common geometrical representations of monolith channels are tested, and their advantages and disadvantages are analysed. A detailed computational model and a large set of computational experiments, covering a broad range of substrate void fractions, channel Reynolds numbers and heating rates is used. Results assuming constant and temperature-dependent fluid properties are reported and compared. At a high heating rate, assuming constant fluid properties leads to a significant error in the estimation of Nusselt and Sherwood numbers in the entry region. At a constant wall temperature and a high heating rate, there is a minimum in the Nusselt curve that classical models are not able to describe. Hence, a novel correlation that shows excellent agreement with channel data is presented together with a methodology to fit it. Additionally, empirical models to estimate the placement and value of the minimum Nusselt are proposed. These results contribute significantly to the improvement of lumped parameter multiscale models of monolith catalytic reactors. • Entry Nusselt numbers for a monolith channel are analysed with realistic conditions. • Nusselt number depends on Reynolds number, inlet geometry and variable properties. • Improved correlations for developing flow Nusselt numbers is developed. [ABSTRACT FROM AUTHOR]

• RANS and LES models used for turbulent flow modelling in a monolith. • The resulting pressure drop, power spectrum and flow regime are analysed. • RANS predicts a small fraction of the turbulence entering the channels to decay rapidly. • LES predicts a total dissipation of the turbulence before the flow enters the channels. • RANS predicts steady flow and LES predicts pulsating flow after turbulence decay. This paper reports the pressure drop through a monolith for turbulent and laminar flow. A computational model of a monolith channel together with the open sections before and after it is used. Simulations at several channel Reynolds numbers, and assuming laminar and turbulent flow approaching the substrate are considered. Reynolds average Navier Stokes (RANS) and large eddy simulation (LES) are used as flow models in the cases with turbulence. The resulting pressure drop, power spectrum and flow regime are analysed. RANS predicts a decay of the turbulence as the flow approaches the substrate, a small fraction of the turbulence effectively entering the channels to decay rapidly, then steady flow from that point. On the other hand, LES predicts a total dissipation of the turbulence before the flow enters the channels; however, the flow remains unsteady along the entire substrate, in a sort of pulsating regime. Despite the significant differences in the flow regime, both models predict a marginal influence of the upstream turbulence on the total pressure drop. The dominating frequencies of the pulsating flow inside the channels were found to be comparable to the ratio of the channel velocity over the channel diameter, therefore, to the channel Reynolds number. [ABSTRACT FROM AUTHOR]