Spatial Nonuniformity Research Articles

Modeling and Analysis of Temperature-Dependent Capacity Degradation in Large Format Lithium-Ion Batteries

The large-format lithium-ion batteries, widely used for electric vehicle applications, are generally characterized by spatial non-uniformities in temperature. The presence of thermal gradients and temperature-dependence of cell parameters are responsible for non-uniform degradation within the battery that leads to poor performance of the battery packs and also poses safety risks. In this work, we aim to develop a detailed physics-based simulation framework to model non-uniform, temperature-dependent capacity degradation within these large format batteries based on the classical pseudo two-dimensional (p2D) battery model. The electrochemical model will be coupled with degradation mechanisms to capture solid-electrolyte interface layer growth, reversible lithium plating, structural disintegration, and volume change within the electrodes on the cell level signatures and usable capacity over charge/discharge cycles. The effects of temperature inhomogeneities will be accounted in the multi-cell simulations at different operating temperatures for individual cells with dynamic currents and temperature and concentration dependent battery parameters as the model inputs.Overall, the primary focus of this study is to capture the effect of spatial temperature variation on battery capacity over cycles and help identify an improved design for the battery module. The model is implemented in an efficient equation-based form for the p2D model and degradation mechanisms with dynamic cell inputs using the mathematical modules in the finite element based solver, COMSOL Multiphysics. This approach enables an easier model development and analysis of the detailed physics and allows an easier implementation of any additional side reaction. The relative contributions of various fade modes have also been compared to understand their competitive interplay over cell cycles. The model predictions are validated with the available experimental data and in-house codes for each case. We believe that this simple yet detailed model can be further developed to be computationally feasible for adoption and implementation in a battery thermal management system.

Effect of defects in capacitance-voltage measurement of doping profiles in Ga2O3

We investigate the intermixing effects of doping profile and the carrier emission from deep levels in the capacitance-voltage measurement of the wide bandgap semiconductor material of β-Ga2O3. Specifically, we find that the spatial non-uniformity of doping measured under practical conditions is substantially contributed by artifacts due to carrier emission from deep levels. We develop a procedure to measure the hysteresis in cyclic capacitance-voltage experiments in dark and at room temperature for probing of the deep levels contributing to the apparent doping profile. Analysis of this hysteresis in the dynamic electrostatic framework of a Schottky junction containing deep levels enables more accurate determination of the doping density and its spatial distribution, and simultaneously the extraction of energy, density, and capture cross-section of the deep levels.

Evaluation of the feasibility of a multisource CBCT for maxillofacial imaging

Objective. The aim of this study was to investigate the feasibility of improving the image quality and accuracy of cone beam computed tomography (CBCT) by replacing the conventional wide cone angle x-ray tube with a distributed x-ray source array positioned in the axial direction. Approach. The multisource CBCT (ms-CBCT) design was experimentally simulated using a benchtop scanner with a carbon nanotube x-ray tube and a flat-panel detector. The source was collimated and translated in the axial direction to simulate a source array with a reduced cone angle for each beam. An adjacent scatter ratio subtraction (ASRS) method was implemented for residual scatter reduction. Several phantoms were imaged using the ms-CBCT and conventional CBCT configurations under otherwise similar conditions. The Requirements of the ms-CBCT design on the x-ray source and detector were evaluated. Main results. Compared to the conventional CBCT, the ms-CBCT design with 8 sources and ASRS significantly improved the image quality and accuracy, including: (1) reducing the cupping artifact from 15% to 3.5%; (2) reducing the spatial nonuniformity of the CT Hounsfield unit values from 38.0 to 9.2; (3) improving the contrast-to-noise ratio of the low contrast objects (acrylic and low density polyethylene inserts) against the water-equivalent background by ∼20% and (4) reducing the root-mean-square error of the HU values by 70%, from 420.1 to 124.4. The imaging dose and scanning time used by the current clinical CBCT for maxillofacial imaging can be achieved by current source and detector technologies. Significance. The ms-CBCT design significantly reduces the scatter and improves the image quality and accuracy compared to the conventional CBCT.

Identifying the Distribution and Frequency of Dust Storms in Iran Based on Long-Term Observations from over 400 Weather Stations

Middle Eastern countries suffer from dust events due to extended arid areas. Among them, Iran is a country experiencing a high record of dust events each year causing major environmental challenges. Although there are previous studies of the present situations of dust storm occurrences in Iran, most studies have analyzed the meteorological dataset in limited weather stations and areas in Iran. To understand the nationwide trends of the distributions and frequencies of dust storm events, comprehensive statistical evaluations of dust storm events, based on different dust categories, are required. Therefore, this study analyzes 12-year meteorological databases obtained at 427 stations in Iran to clarify the distribution of dust events and occurrence frequencies of the dust in a recent decade by classifying the dust events into suspended dust, rising dust, and dust storm. The highest record of the days belongs to rising dust, which surpassed 150 days per year, followed by suspended dust with over 100 days per year, and, finally, dust storms with a frequency of 30 days per year as annual statistics of dust events. In contrast, there were some stations that recorded minimal occurrences of dust events during the observation periods. To prove the spatial nonuniformity of the dust events, suspended dust events showed a distinct concentration in the western regions of the country, while rising dust tended to occur more frequently in the southern, eastern, and central parts of Iran. Accordingly, seasonal analyses indicate that the highest number of dust events occurred during the spring season, with the number of stations experiencing dust events being greater than during other seasons in all three categories. Nonetheless, annual analyses of dust events do not demonstrate any significant trends, with only 2012 having the highest record of dust events across all three categories. In terms of monthly analyses, dust events tended to increase from late spring to early summer in the suspended dust and rising dust categories. These analyses demonstrate the importance of studying numerous weather station datasets to clarify spatial trends of dust events with long-term variations.

High-speed measurement of thickness of a water film formed by a jet obliquely impinging onto a plate using an LED-induced fluorescence method

A transient thickness distribution measured with a high temporal resolution is elemental for exploring the flow characteristics and mechanism of a liquid film formed by an impinging jet. Therefore, this paper develops a high-speed Light-Emitting Diode-Induced Fluorescence (LEDIF) system based on the brightness measured directly above the liquid film. An Ultraviolet (UV) LED lamp is used to provide sufficient and continuous excitation light. Then, a system performance analysis proves that the system can continuously measure the global film thickness at a high acquisition frequency of 5000 Hz when the dye concentration is 200 mg/L. The influence of the irregularity of the excitation intensity, including the spatial non-uniformity, temporal instability, and long-term instability, on the measurement uncertainty is analyzed in detail. The analysis indicates that the system has an acceptable uncertainty of 10%. Compared with theoretical results, experimental results verify that the LEDIF system can accurately measure the global thickness of a liquid film formed by a water jet obliquely impinging onto a plate. An experimental investigation of the radial section of the raised zone demonstrates that the radial section changes from a sewing needle to an oval when the azimuth angle increases from 10° to 90°. Meanwhile, the dynamic contact angle exponentially decreases from 41.4° to 30.1°. A dynamic analysis of surface waves shows that the measured wave velocity decreases from 12 m/s to 1 m/s and the dominant frequency decreases from 1000 Hz to 10 Hz along the flow direction.

Mechanism causing the spatial distribution non-uniformity of the prompt optical crosstalk effect in G-APD cells of silicon photomultipliers

Mechanism causing the spatial distribution non-uniformity of the prompt optical crosstalk effect in G-APD cells of silicon photomultipliers

Left atrial hyper-strain in dyssynchronous hearts: potential driver for adverse left atrial remodelling

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Institute for Surgical Research, Oslo University Hospital. Introduction It was recently shown that left bundle branch block (LBBB) is associated with risk of developing atrial fibrillation. A potential mechanism is abnormal left atrial (LA) loading caused by LA dyssynchrony. Purpose To investigate if LBBB is associated with abnormal LA loading as reflected in non-uniform segmental strains. Methods In a prospective study of 143 heart failure patients with LBBB, myocardial strain was measured by speckle-tracking echocardiography prior to and after 7±2 months on cardiac resynchronization therapy (CRT). As indicated by brackets in the lower panels in the Figure, LA strain amplitudes were calculated as the difference between minimum and peak strain during the reservoir phase. Results In the Figure, the upper panel shows segmental and average LA strain traces in a representative LBBB patient. This patient illustrates marked spatial non-uniformity in strain amplitude between the interatrial septum and the LA lateral wall during the reservoir phase. For the entire study population, strain amplitudes were 19±9% (mean±SD) for the interatrial septum and 24±11% for the LA lateral wall (p<0.0001). In the quartile of patients with largest differences, strain amplitudes were 16±9 and 32±12%, respectively (p<0.0001). CRT abolished these differences (p = NS). Conclusions Patients with LBBB showed marked spatial non-uniformity of LA strains. Potentially, the excessive LA lateral wall strain amplitudes may stimulate atrial adverse remodelling. Future studies should investigate if abnormal LA strains may be a trigger mechanism for atrial fibrillation in patients with LBBB.

Experimental and numerical study of a circular OWC with a U-shaped duct for wave energy conversion in long waves: Hydrodynamic characteristics and viscous energy loss

This paper presents an experimental and numerical study of a pile-type circular oscillating water column device with a U-shaped duct (circular U-OWC) for wave energy conversion in long waves. In the experiments, the circular U-OWC model and a conventional OWC model of identical chamber dimension was compared in a wave flume under various wave conditions. Orifices of different sizes are used to simulate the power-takeoff (PTO). The pneumatic power, PTO damping coefficient, and the scattering of the incident waves are measured. A RANS equation based numerical model with a modified k-ω SST turbulence closure is validated using the experiment. The numerical model is utilized to investigate the spatial non-uniformity of the free surface inside the chamber, and the viscous energy loss in the U-shaped duct. It is found that for long waves, the circular U-OWC device is several times more efficient than a conventional OWC device, and the sloshing effect inside the pneumatic chamber is significantly reduced compared to a conventional OWC device. It is also found that a significant amount of energy entering the U-shaped duct is dissipated in viscous loss, recommendations on U-shaped duct design are given to help reduce the viscous loss of the device.

Iterative image reconstruction with polar coordinate discretized system matrix for optical CT radiochromic gel dosimetry.

Gel dosimeters are a potential tool for measuring the complex dose distributions that characterize modern radiotherapy. A prototype tabletop solid-tank fan-beam optical CT scanner for readout of gel dosimeters was recently developed. This scanner does not have a straight raypath from source to detector, thus images cannot be reconstructed using filtered backprojection (FBP) and iterative techniques are required. Iterative image reconstruction requires a system matrix that describes the geometry of the imaging system. Stored system matrices can become immensely large, making them impractical for storage on a typical desktopcomputer. Here we develop a method to reduce the storage size of optical CT system matrices through use of polar coordinate discretization while accounting for the refraction in optical CTsystems. A ray tracing simulator was developed to track the path of light rays as they traverse the different mediums of the optical CT scanner. Cartesian coordinate discretized system matrices (CCDSMs) and polar coordinate discretized system matrices (PCDSMs) were generated by discretizing the reconstruction area of the optical CT scanner into a Cartesian pixel grid and a polar coordinate pixel grid, respectively. The length of each ray through each pixel was calculated and used to populate the system matrices. To ensure equal weighting during iterative reconstruction, the radial rings of PCDSMs were asymmetrically spaced such that the area of each polar pixel was constant. Two clinical phantoms and several synthetic phantoms were produced and used to evaluate the reconstruction techniques under known conditions. Reconstructed images were analyzed in terms of spatial resolution, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), signal nonuniformity (SNU), and Gamma map passpercentage. A storage size reduction of 99.72% was found when comparing a PCDSM to a CCDSM with the same total number of pixels. Images reconstructed with a PCDSM were found to have superior SNR, CNR, SNU, and Gamma (1mm, 1%) pass percentage compared to those reconstructed with a CCDSM. Increasing spatial resolution in the radial direction with increasing radial distance was found in both PCDSM and CCDSM reconstructions due to the outer regions refracting light more severely. Images reconstructed with a PCDSM showed a decrease in spatial resolution in the azimuthal directions as radial distance increases, due to the widening of the polar pixels. However, this can be mitigated with only a slight increase in storage size by increasing the number of projections. A loss of spatial resolution in the radial direction within 5mm radially from center was found when reconstructing with a PCDSM, due to the large innermost pixels. However, this was remedied by increasing the number of radial rings within the PCDSM, yielding radial spatial resolution on par with images reconstructed with a CCDSM and a storage size reduction of 99.26%. Discretizing the image pixel elements in polar coordinates achieved a system matrix storage size reduction of 99.26% with only minimal reduction in the imagequality.

Increasing the Q-Contrast in Large Photonic Crystal Slab Resonators Using Bound-States-in-Continuum

Photonic-crystal surface-emitting lasers (PCSELs) have shown promise for large-area single-mode lasers. However, the difficulty in increasing PCSEL area while preserving single-mode operation has hindered the progress of achieving ultralarge-area PCSELs. The physical origin of the scaling challenge lies in the diminishing quality-factor (Q) contrast between the fundamental mode and higher-order modes as the lateral size of the crystal increases. Here, we show that the existence of bound states in the continuum (BIC) can overcome this challenge. The presence of BIC enables large and constant Q-contrast that is independent of the lateral size of the crystal. Such a Q-contrast should guarantee size-invariant single-mode operation, which is the key to realize ultralarge-area PCSEL. We develop an analytical theory to elucidate the underlying physics of the size-invariant Q-contrast enabled by BIC and verify it with full-wave simulations. Furthermore, we show that the Q-contrast can be further increased by introducing specific spatial nonuniformities. Our findings provide theoretical guidance and open new possibilities for designing ultralarge-area PCSEL.

Key physical topology features for optical backbone networks via a multilayer correlation analysis

A communication network is a multilayer network comprising various layered technologies, and the underlying physical topology is an important aspect that determines the upper bound of overall system performance, including total communication capacity, cost, and robustness. We expect that understanding the impact of the physical topology on system performance will lead to better optical communication network design in the future, and we thus focus on clarifying the relationship between physical topology features and system performance. There have been various studies on the relationship between topology features and overall network performance. For example, the average number of hops and the cluster coefficient are well known to change network properties in complex networks. From the perspective of optical communication networks, it is known that the algebraic connectivity and average path length are related to total network capacity, and these findings have been applied in physical topology design models. On the other hand, there have been no quantitative comparisons among various topology features, and the comprehensiveness of the population from which these features are extracted is insufficient. Hence, we have developed a multilayer (physical topology and layer 1) correlation analysis framework that enables a quantitative comparison of topology features. We use this framework to numerically examine the relationships between physical topology features and the total communication capacity, cost, and robustness of optical communication networks, including graph features (especially graph spectra) that have not been investigated. The results show that the Laplacian spectral radius and geodesic distance Laplacian spectral radius are strongly related to system performance, in addition to the conventional average number of hops, cluster coefficient, algebraic connectivity, and average path length. We confirm that these correlations hold for the different network sizes and spatial nonuniformity of real optical backbone networks in different countries and regions. The results show that the average path length and cluster coefficient, or the Laplacian spectral radius and geodesic distance Laplacian spectral radius, are important guidelines for physical topology design of real optical backbone networks.

Drifting Faraday patterns under localised driving

Physical systems undergoing spontaneous pattern formation are governed by intrinsic length scales that may compete with extrinsic ones, resulting in exceptional spatiotemporal behaviour. In this work, we report experimental and theoretical evidence that spatial nonuniformity sets Faraday-wave patterns in motion, which are noticeable in the zigzag and drift dynamics exhibited by their wave crests. We provide a minimal theoretical model that succeeds in characterising the growth of localised patterns under nonuniform parametric driving. Furthermore, the derivation accounts for symmetry-breaking nonlinear gradients that we show are the source of the drift mechanism, which comes into play right after the system has crossed a secondary bifurcation point. Numerical solutions of the governing equations match our experimental findings and theoretical predictions. Our results advance the understanding of pattern behaviour induced by nonuniformity in generic nonlinear extended systems far from equilibrium.

Behavioral simulations and experimental evaluations of stress induced spatial nonuniformity of dynamic bulk modulus in additive friction stir deposited AA 6061

Additive friction stir deposition (AFSD) is a rapidly developing solid-state additive manufacturing (AM) technology that enables the fabrication of customized products on a relatively large scale. The unique forge-liked process offers high quality products with refined equiaxed microstructure and exceptional mechanical performance. However, in AFSD, the spatially distributed mechanical properties within a deposited layer have not been established so far, due to the lack of a suitable large-scale mapping method. In the present work, an ultrasonic dynamic-elasticity mapping method was employed to map the distribution of physical properties in a AFSD 6061 Al. Strong spatial asymmetries in elastographies were mainly due to the residual stresses. The origin of the asymmetries was investigated through thermo-mechanical simulations of the AFSD process. It was observed that majority of the asymmetries were associated with the mechanical residual stresses instead of the symmetric thermal residual stresses during linear deposition of the AFSD process. However, the thermal residual stresses can be manipulated to become asymmetric with a 90° turn in the linear deposition path, due to the difference between the levels of cooling along the edges of the inner and outer corners. Hence, the mechanical and thermo-mechanical residual stresses can be additive or subtractive depending on the direction of the turns. Such numerically predicted behaviors were also experimentally observed on the AFSD fabricated samples by ultrasonic elastography. Furthermore, additional preliminary studies on multi-layer AFSD fabrications show the asymmetric mechanical stresses generated during the deposition process on different layers generate constructive or destructive interference which results to spatially variable dynamic bulk modulus depending on the deposition orientations of layers.

Design and characterization of a continuous solar simulator for photovoltaic modules with automatic I-V curve acquisition system

This paper presents the development, characterization, and testing of a continuous large-area solar simulator for PV modules with an automatic I-V curve acquisition system and the results of a CIGS PV module over 25 h of light soaking. The simulator was developed to perform the IEC 61215 stabilization test and automatic characterization of PV modules during indoor testing. The equipment records the I-V curves of the PV module at programmed time intervals so that the change in the electrical characteristics of the PV modules can be tracked over time. The test plane has an area of 1.2 × 2 m and an irradiance of 800 W/m2. The simulator was installed in a container and consists of 16 metal halide lamps of 1 kW each. The simulator is characterized by temporal instability, spatial non-uniformity, and spectral mismatch, resulting in CCB classification. The I-V curves of the tested PV module were measured every 30 s, with 200 I-V points per curve. The power change of the tested module occurs mainly in the first 12 min and stabilizes after about 5 h under the conditions selected for the test. The developed device can save significant resources compared to commercial continuous solar simulators. The ability to automatically track changes in PV module electrical parameters during light-soaking tests is presented in detail and provides important information for future work related to the development and characterization of solar simulators of this type.

Obtaining plasma parameters by Langmuir probes and optical emission spectroscopy in low-pressure DC plasma

The plasma environment in low-pressure systems allows coating different materials such as glasses, textiles, metals, etc. at the atomic level. Although vacuum coating is one of the best methods for thin film coating, the coating quality is closely affected by the spatial and temporal non-uniformities inside the reactor. Therefore it is quite important to determine the plasma properties within the chamber. The determination of plasma parameters such as electron temperature, electron excitation temperature, electron and ion densities can be realized using Langmuir probe systems, and by Optical Emission Spectroscopy (OES) by using Boltzmann plot method. Knowing such parameters can provide important information about specific reaction mechanisms, as well as it provides invaluable information that can increase reproducibility in various discharge process control in thin film coating. In this study, a homemade single Langmuir probe (s-LP) and a multiple Langmuir probe system (m-LP) were used to calculate electron temperature, electron density, saturation current, and plasma potential of the plasma at different pressures and at different voltages. One of the objectives of this work was to evaluate the electron temperature and ion density inside the plasma during a coating process. The second objective was to find the spatial change of electron temperature in the axial direction between cathode and anode by m-LP system including 8 independent tips. The last objective was to measure the axial plasma electron temperature distribution inside the vacuum chamber by using OES.

Biosensor Design for the Detection of Circulating Tumor Cells Using the Quartz Crystal Resonator Technique.

A new mass-sensitive biosensing approach for detecting circulating tumor cells (CTCs) using a quartz crystal resonator (QCR) has been developed. A mathematical model was used to design a ring electrode-based QCR to eliminate the Gaussian spatial distribution of frequency response in the first harmonic mode, a characteristic of QCRs, without compromising the sensitivity of frequency response. An ink-dot method was used to validate the ring electrode fabricated based on our model. Furthermore, the ring electrode QCR was experimentally tested for its ability to capture circulating tumor cells, and the results were compared with a commercially available QCR with a keyhole electrode. An indirect method of surface immobilization technique was employed via modification of the SiO2 surface of the ring electrode using a silane, protein, and anti-EpCAM. The ring electrode successfully demonstrated eliminating the spatial nonuniformity of frequency response for three cancer cell lines, i.e., MCF-7, PANC-1, and PC-3, compared with the keyhole QCR, which showed nonuniform spatial response for the same cancer cell lines. These results are promising for developing QCR-based biosensors for the early detection of cancer cells, with the potential for point-of-care diagnosis for cancer screening.

Investigation of the effect of microbial-induced calcite precipitation treatment on bio-cemented calcareous sands using discrete element method

Owing to the bio-geological origin, calcareous sands are characterized by irregular particle shapes and abundant internal pores. These weak soil structures undergo extensive particle breakage under specific stress conditions. In recent years, microbial-induced calcite precipitation (MICP), a green soil treatment technique, has been widely utilized to improve the mechanical properties of calcareous sands. The treatment effect of MICP on calcareous sands and the underlying mechanism are still relatively unclear owing to the complex microstructures of the sands. This study investigated the micromechanism of MICP treatment on calcareous sands via the discrete element method (DEM). First, a group of calcareous sand particles were individually treated via a proposed MICP process. Single-particle crushing tests were conducted on the MICP-treated calcareous particles and a control group of untreated calcareous particles. The experimental results were further used to verify and calibrate the DEM models and parameters. The DEM model of MICP-treated calcareous particles was established via a novel modeling technique using the commercial PFC3D platform, which considered the inter-particle bridging and intra-particle pore filling effects by MICP treatment. Through this method, a series of MICP-treated calcareous sand samples subjected to uniaxial compression were simulated. The effects of calcite content and its spatial non-uniformity on the compression behaviors of the bio-cemented calcareous sand samples were studied. The micromechanics in terms of crack propagation and distribution as obtained from DEM were investigated to elucidate the mechanism of the MICP treatment of calcareous sands.

Analysis and Control of Acoustic Modes in Cylindrical Cavities with application to Direct Field Acoustic Noise (DFAN) Testing.

It is well known that acoustic cavities have frequencies at which certain free-response 'modes' of propagation respond especially strongly. In the absence of significant damping, these cause peaks of high SPL in the frequency response as well as spatial non-uniformity and temporal ringing. The spatial non-uniformity is especially problematic since it means the room cannot be 'EQ'd' to compensate, since the SPL is different in different positions. This phenomenon has been studied extensively in the room acoustics literature and various strategies for mitigation proposed. Many of these make use of the theoretical mode shapes for a cuboid with a rigid boundary condition, since this is a common shape of room and a reasonable approximation for a solidly constructed wall. But modes exist for other shape spaces too. Of particular interest is the cylindrical cavity that is formed when large enclosing arrays of loudspeakers are used to perform high-intensity acoustic tests on space hardware. These possess problematic modes that can cause over-testing in some positions and under-testing in others. In this work, it is investigated how a simple FEM simulation can compute Q-factors for these modes and identify which will be problematic. How this might inform control system design is discussed.

A Detailed Analysis on Hydrodynamic Response of a Highly Stratified Lake to Spatio-Temporally Varying Wind Field

Wind is generally considered an important factor driving the transport and mixing processes in stratified enclosed systems such as lakes and reservoirs. Lake Abashiri is one of the instances of such a system. For these systems, typically, the temporally unsteady but spatially uniform nature of wind has been assumed for simplicity. However, the spatial non-uniformity of wind could significantly alter compound hydrodynamic responses. In this study, such responses were investigated under the continuous imposition of different inhomogeneous wind conditions by applying numerical models and integrated analysis. The resultant tracer transport in both uniform and non-uniform wind cases was insignificant for the total study period of 9 days. However, under the short interval of Ti, where Ti is the internal fundamental period, different behaviors of both surface particle transport and the internal wave field were identified. Particularly, surface mass transport responses to higher spatial wind variance were obviously different from those in the uniform case. In addition, internal wave spectra under strong wind magnitude, which has low spatial variances, became identical to that of uniform wind; however, there were some discrepancies in the non-uniform case in the wave spectra under the influence of weak-to-moderate wind of high spatial variances. The results could provide an in-depth understanding of the lake’s hydrodynamic response to inhomogeneous wind which could improve water management in lakes and reservoirs.

Catalytic reverse-flow oxidation process in reactors of various designs: Axial, side and tangential gas inlet

The study was dedicated to the mathematical modeling of the catalytic reverse-flow process in reactors of different design, e.g. in reactors with axial, side or tangential arrangement of reaction gas inlet/outlet streams. The oxidation of volatile organic compounds in the fixed adiabatic catalyst beds was considered, using toluene as an example contaminant. Three-dimensional fluid dynamics modelling performed by means of Comsol Multiphysics software showed the existence of the significant gradients of temperature, concentrations of reactants and fluid velocities along the bed radius; such gradients are neglected in the conventional one-dimensional models, usually used for simulation of reverse-flow processes. The spatial distribution of these parameters may be asymmetric in the reactors with asymmetric design. It was shown that efficiency of both toluene conversion and heat regeneration significantly decrease in reactor with side feeding of inlet mixture, finally resulting in lower thermal stability of the process with the significant (∼20%) decline of the maximum possible duration of the cycles between flow reversals compared to reactor with axial gas feeding. Vice versa, the tangential arrangement of gas inlet provides the visible (∼10%) increase of maximum cycle duration. Application of 3D modelling approach to development and optimization of catalytic processes becomes especially important in case of reverse-flow reactors where negative influence of various spatial non-uniformities may impose more significant influence on process parameters.