Reactor Model Research Articles

Analysis of the Vibration Characteristics and Vibration Reduction Methods of Iron Core Reactor

Series iron core reactors are one of the most commonly used electrical equipments in power systems, which can limit short-circuit currents and suppress harmonic waves from capacitor banks. However, the vibration of the reactor will not only generate noise pollution but also diminish the service life of the reactor and jeopardize power system safety. In order to reduce the vibration noise in the core disc region of the reactor, the vibration characteristics of a core reactor are calculated by modifying the anisotropy parameters of the Young’s modulus of the core disc lamellar structure and introducing the core magnetostriction effect based on the simulation analysis method of electromagnetic and mechanical coupling. A detachable single-phase series core reactor model is established, and the validity of the simulation calculation is measured and verified. At the same time, from the perspective of improving the air gap size of the series core reactor and the arrangement of electrical steel sheets, the corresponding iron core vibration reduction scheme is given. The average vibration reduction in the reactor is about 11.6% after comprehensive improvement according to the vibration reduction scheme, which provides an effective method for realizing the vibration and noise reduction in the reactor.

Experimental investigation and 2D mathematical modelling of copper foams packed with Rh-Al2O3 catalysts for the intensification of methane steam reforming

Efficient heat transfer is a crucial factor in the design of compact methane steam reformers for delocalized hydrogen production. The use of copper packed foams was proposed few years ago by our group to strongly intensify heat transfer in these systems, allowing the design of small-scale units with minimal radial temperature gradients. In this study, a new experimental campaign was performed to demonstrate the concept potential under industrially relevant heat fluxes and to establish an experimental foundation for validating a 2D mathematical model of the process. Copper open-cell foams were packed with a Rh/Al2O3 egg-shell catalyst and loaded into a 29.5 mm diameter tubular reactor, which was heated using a lab-scale oven. By leveraging the combined benefits of enhanced heat transfer, granted by the copper foam, and the high activity of the Rh-based eggshell catalyst, experiments were successfully performed at gas hourly space velocities (GHSV) ranging from 10 to 30 Nm3/h/kgcat, with heat duties of up to 9 MW/m3. These experiments lead to a methane conversion close to thermodynamic equilibrium while maintaining limited radial gradients within the system (maximum 20 °C across the mid-radius). A predictive pseudo-heterogeneous 2D reactor model was developed and validated against experimental data. The model accurately captured the observed trends in temperature profiles and outlet concentrations, and can be utilized for optimized design, paving the way for the development of efficient small-scale hydrogen production units.

Using Total Monte Carlo with hybrid calculation methods for constructing the covariance matrix of a neutron spectrum: Applications in spectrum adjustment

A new calculation scheme has been developed to improve the quality of covariance matrices of a-priori neutron spectra. A high quality covariance matrix is essential for guiding the adjustment of the a-priori calculated neutron spectrum to experimental dosimetry measurements in a physically realistic way. This new calculation scheme incorporates state-of-the-art hybrid deterministic/Monte Carlo methods and does not rely on prior knowledge of correlations between the different energy groups. The ADVANTG code was used to generate weight-windows for the full MCNP reactor model of the High Flux Reactor (HFR) in Petten, the Netherlands. This then allowed Total Monte Carlo (TMC) calculations to be performed with very low statistical uncertainties. A detailed demonstration of applying these covariance matrices to spectrum adjustment is also provided by utilising an algorithm adopted from the STAY’SL program. We have used the example of the HELIOS irradiation experiment performed at the HFR to demonstrate the approach here, but the flexibility of the method means it may be applied universally to neutron spectra calculated anywhere.

Development of a multiphase chemical reactor network method as a tool for simulating biomass gasification in fluidized beds

In the near future, biomass is expected to be a key resource for fulfilling clean energy requirements. The predictive modeling of biomass conversion in industrial systems is still challenging due to the multi-scale nature of the processes involved, including complex chemical reactions. To provide a detailed description and analysis of these reactions and their coupling to transport phenomena in large-scale systems, this work introduces a multiphase reactor network method incorporating efficient solution algorithms for engineering reacting systems. The method developed includes a novel multiphase solid–gas perfectly stirred reactor (sPSR) model capable of handling solid- and gas-phase reactions as well as heterogeneous reactions, in a fully coupled way. The sPSR approach, which is included in reactor networks with various levels of complexity, improves the analysis and understanding of physical and chemical phenomena occurring in gasifiers. Steam and air gasification experiments are analyzed using the new approach and fundamental differences and effects are revealed. Major findings include the importance of solid–gas coupling, char conversion reactions, and water–gas shift (WGS) reaction catalysis due to bio-ash. In addition, increasing the complexity of the reactor network achieves a better reproduction of the mixing behavior. The capability of handling complex reactor networks with detailed kinetics paves the way for efficient designs and improved reactors.

A comprehensive study on physics-based simulation combined multi-objective optimization of capacity decay and voltage loss of Vanadium redox flow battery

This paper proposes physics-based simulation combined multi-objective optimization approach for reduction of both capacity decay and voltage loss of Vanadium redox flow battery. In this approach, firstly, a physics-based-electrochemical model for a single-cell VRFB is developed based on the dynamic plug flow reactor model and is used to obtain capacity decay and voltage loss under various conditions. Simulation studies were then conducted to investigate the effects of electrolyte flow rate and electrode fiber diameter on the VRFB performance. The capacity decay in VRFB relies mainly on the vanadium ions’ variation between two half-cells. The variation in the long-term cycle is fundamentally due to the electrolyte transfer across the membrane. The lower electrolyte flow rate, as well as electrode fiber diameter, can reduce the capacity decay as the electrolyte’s velocity across the membrane decreases. However, the lower electrolyte flow rate and electrode fiber diameter increase the voltage loss considering open circuit voltage loss, activation overpotential, and concentration overpotential. Finally, a novel optimization framework combined with simulation and the meta-heuristic algorithm is introduced to reduce both capacity decay and voltage loss in VRFB simultaneously. The proposed multi-objective method shows a significant reduction of both capacity decay and voltage loss.

Optimal rule based fuzzy-PI controller for core power control of nuclear reactor

In this paper, an optimal rule based fuzzy proportional integral controller is proposed to control the core power of the molten salt breeder reactor (MSBR) model. Firstly, a nonlinear MSBR model is considered. It is then linearized using the perturbation linearizing approach, and the transfer function of the linearized MSBR system is established. Secondly, an optimal Fuzzy-PI control structure is formulated where a PI controller is set as the principal controller for the MSBR model and a fuzzy control system is used to adjust the PI controller parameters during any disturbance in the MSBR. The rule base system of the fuzzy controller is optimized with a reshaped class topper optimization algorithm. Finally, the optimized Fuzzy-PI controller tests under a variety of conditions. Furthermore, the Nyquist stability approach is used to analyze the stability of the closed loop MSBR model.

An updated functional-group-based approach to modeling the vacuum residue oil gasification kinetics

Gasification of heavy petroleum residues can convert low-value feedstock to hydrogen-rich syngas, which can further be used for power generation and/or chemical production. The present work proposed an updated functional-group-based approach (FGMech) to modeling the gasification of a vacuum residue oil (VRO), which is helpful for better understanding the detailed kinetics of the gasification and improving gasifier performance. Elemental, average molecular weight (AMW) and nuclear magnetic resonance (NMR) analyses were conducted experimentally to characterize VRO, including elemental composition, average molecular formula and the functional group distribution, which were further used for model construction. A lumped mechanism for VRO devolatilization was constructed based on the updated FGMech approach: stoichiometric parameters of stable gases, tars and char were obtained from experiments, while those of radicals were based on the multiple linear regression (MLR) correlations; thermodynamic and kinetic parameters were derived from Benson group additivity method and rate rules, respectively. A merged detailed model was adopted for describing the conversion of gases and tars, and a global model was used for char. To test the reliability of the present model approach, Orimulsion gasification experiments from literature were simulated using an integrated perfectly stirred reactor (PSR) and plug flow reactor (PFR) model. It shows that the present model can reasonably predict measured results under various equivalence ratios, and has better performance on the prediction of CH4 compared with most literature models. Based on model analyses, syngas comes from the conversion of C2H4, H2S, CH4 and char in different gasification stages. Benzene, toluene, naphthalene and 1-methylnaphthalene are initial tar species considered in the devolatilization of the VRO. They can undergo hydrogen abstraction acetylene addition (HACA) and C3H3/C5H5 addition reaction pathways to produce large PAHs.

Investigating the impact of modeling assumptions and closure models on the steady-state prediction of solar-driven methane steam reforming in a porous reactor

In this work, the effect of different modeling assumptions and closure models — frequently considered in the literature of solar thermochemical reactors and closely-related areas — is investigated. The application of different modeling assumptions and closure models may strongly affect the results accuracy and compromise a meaningful comparison across literature works. The following is herein investigated: (i) the role of upstream and downstream fluid regions to the two-phase reactor region; (ii) relevance of species and gas-phase thermal diffusion mechanisms; (iii) reaction heat accounted for in gas- or solid-phase energy balance equations; (iv) local thermal equilibrium (LTE) vs. local thermal non-equilibrium (LTNE) models; (v) model dimension (one-dimensional vs. two-dimensional axisymmetric models); (vi) local volumetric convection heat transfer correlations; and (vii) effective solid thermal conductivity correlations. The relevance of this work extends well beyond the current application (methane steam reforming in a volumetric solar reactor), since similar models and assumptions have also been widely applied for predicting the performance of volumetric solar absorbers and dry reforming solar reactors. The results show that an upstream fluid region should be considered while applying inlet first-type boundary conditions and diffusion transport in the corresponding governing equations to ensure full-conservation and simultaneously to account for developing profiles upstream the reactor inlet section. For the operating conditions considered, species diffusion and gas-phase heat conduction are particularly relevant at the reactor centerline but with a negligible integral effect. A significant difference in the reactor performance is observed while accounting for the reaction heat from surface reactions in the solid- or gas-phase energy balances — for the lowest inlet gas velocity herein considered, the thermochemical efficiency (methane conversion) is approximately equal to 70.8% (76.3%) and 77.3% (84.7%) assigning the reaction heat to the gas- and solid-phase energy balances, respectively. LTE model results are strikingly different from the results obtained with the LTNE model considering the reaction heat accounted for in the gas-phase energy balance but not significantly different from the results computed with the LTNE model with the reaction heat assigned to the solid-phase energy balance. One-dimensional reactor modeling provided with an average concentrated solar heat flux value results in a similar average performance as that given by a two-dimensional model but fails to predict the high temperatures observed at reactor centerline — for the lowest inlet gas velocity, the difference between the maximum solid temperatures predicted by one- and two-dimensional models is about 340K.

Calculation of neutron-induced radiation damage to gold and lutetium-aluminium microstructures using MCNP6.2

Interaction of particles and photons with materials in extreme radiation environments like the nuclear reactor may lead to basic alterations in the microstructural properties of crystalline solids. These changes accumulate over time into defects on the macrostructure translating to changes in the material's physical and mechanical properties. Studying the level of damage in the materials requires a good prediction of damage using statistical approaches like Monte Carlo simulations. This study aims to calculate the level of damage to Gold (Au) and Lutetium-Aluminium (Lu-Al) due to neutron irradiation, owing to the applications of the materials in reactor technology and other extreme radiation environments. Neutron fluxes, displacement per atom (dpa) rates, and heat deposition expected during irradiation were calculated with Monte Carlo N-particle transport code, MCNP6.2, using the SAFARI-1 research reactor model. The total neutron flux incident on gold and Lutetium-Aluminium was 2.26×1011 ncm−2s−1 and 6.94×1012 ncm−2s−1 respectively, while the dpa rate in Au and Lu-Al was estimated to be 1.96×10−7 s−1 and 6.56×10−5 s−1. The calculated neutron dpa rates and fluence for the materials suggest an elevated level of damage to the microstructure of the materials.

Computational fluid dynamics modeling of a discrete feed atomic layer deposition reactor: Application to reactor design and operation

Novel transistor fabrication methods such as area-selective atomic layer deposition (AS-ALD) are crucial to improving nanopatterning, which is essential for facilitating transistor stacking in semiconducting wafers. However, transistor surfaces are subjected to nonuniformities during the initial AS-ALD adsorption reactions that are attributed to steric hindrance effects. To minimize the role of steric hindrance generated by an oversaturation of reagent on the substrate surface, a discrete feed method is proposed for an ALD reactor configuration where reagent is introduced in short pulses through a perpendicular delivery system. An optimal reactor configuration is developed by modifying the inlet geometries of the reactor to ensure ideal fluid dynamics conditions (e.g., minimal vortices, radial flow distribution) are achieved. Detailed computational fluid dynamics simulations demonstrate the performance of the new reactor configuration and operational strategy.

Research on 750kV Reactor Vibration Based on Electromagnetic-mechanical Field Coupling Finite Element Model

The vibration signal characteristics of a 750kV shunt reactor with high voltage level and high vibration amplitude is one of the important indexes to evaluate the operating condition of the reactor. Since the high level of safe operation with Ultra-high voltage power equipment, it is challenging to collect long-term and extensive vibration signal data under safe operating conditions. This paper establishes the electromagnetic-mechanical field coupling finite element model (FEM) of a 750kV shunt reactor under a COMSOL open-source simulation environment. The resonance effect of magnetostriction of the iron core and the Maxwell forces between the iron core discs on the reactor structure is analyzed. The vibration distribution and typical frequency characteristics of each part of the 750kV shunt reactor are analyzed to provide a reference for the research of vibration fault diagnosis of Ultra-high shunt reactor.

Numerical schemes for a moving-boundary convection-diffusion-reaction model of sequencing batch reactors

Sequencing batch reactors (SBRs) are devices widely used in wastewater treatment, chemical engineering, and other areas. They allow for the sedimentation and compression of solid particles of biomass simultaneously with biochemical reactions with nutrients dissolved in the liquid. The kinetics of these reactions may be given by one of the established activated sludge models (ASMx). An SBR is operated in various stages and is equipped with a movable extraction and fill device and a discharge opening. A one-dimensional model of this unit can be formulated as a moving-boundary problem for a degenerating system of convection-diffusion-reaction equations whose unknowns are the concentrations of the components forming the solid and liquid phases, respectively. This model is transformed to a fixed computational domain and is discretized by an explicit monotone scheme along with an alternative semi-implicit variant. The semi-implicit variant is based on solving, during each time step, a system of nonlinear equations for the total solids concentration followed by the solution of linear systems for the solid component percentages and liquid component concentrations. It is demonstrated that the semi-implicit scheme is well posed and that both variants produce approximations that satisfy an invariant region principle: solids concentrations are nonnegative and less or equal to a set maximal one, percentages are nonnegative and sum up to one, and substrate concentrations are nonnegative. These properties are achieved under a Courant-Friedrichs-Lewy (CFL) condition that is less restrictive for the semi-implicit than for the explicit variant. Numerical examples with realistic parameters illustrate that as a consequence, the semi-implicit variant is more efficient than the explicit one.

Evaluation of neutron radiation damage on gold microstructure using MCNP

The effects of radiation interaction with materials have been studied over the years on metals, semiconductors, and other alloys. The result of these interactions constitutes microstructural effects, like point defects, dislocation loops, and void swellings. The accumulation of these defects results to damage on the macroscopic scale. This study is aimed to predict the magnitude of radiation damage in gold sample due to neutron irradiation. Neutron flux, displacement-per-atom rate, as well as heat deposition, were calculated in MCNP6.2, using the SAFARI-1 reactor model. The total neutron flux and dpa rate in the gold sample were determined to be 2.262 × 1011 n.cm−2.s−1 and 5.209 × 10−7 s−1 respectively. Also, the total heat deposition due to neutrons and photons was 2.515 × 10−6 W.g−1 and 0.513 W.g−1, respectively. Hence, the predicted neutron dpa and flux for the gold sample in this study suggest a heavy damage regime.

2D CFD simulations of flow and reaction during carbon dioxide methanation: A spatially resolved channel plate reactor study

Carbon dioxide methanation is a way of storing excess electrical energy as grid compatible gas. Spatially resolved channel plate reactor experiments were used to validate competing reactor (1D, 2Dx-z) models. Parallel exothermic carbon dioxide methanation and endothermic reverse water gas shift reactions were considered. The kinetic model, where the rate determining step is between an oxygenated complex (HCOO*) and an active site (*), was used in 2Dx-z CFD simulations for six laminar inflow conditions and variations in pressure, temperature, H2/CO2 ratio, methane, and steam co-feeds. The performance is improved by decreasing flowrate, and increasing H2/CO2 ratio, pressure, and temperature. Co-feeding methane has a negligible effect on reactor performance. However, co-feeding steam significantly reduces performance. At relatively high conversions, differential rates are obtained. This is due to the negligible dependence of the rate of carbon dioxide conversion with the equilibrium term of the reverse water gas shift reaction. With these studies, a link between the reaction mechanism and reactor performance is established at conditions relevant to power-to-gas applications.

Modeling and simulation of a micro gas-cooled nuclear reactor using Modelica

Highly compact micro nuclear reactors, which offer extensive energy benefits across ocean, land, space, and sky applications, have recently emerged as a popular research topic within the international nuclear industry. Due to its excellent inherent safety characteristics, the gas-cooled graphite-moderated reactor with TRISO fuel has attained extensive attention. Nonetheless, micro-reactors exhibit a high degree of system integration, characterized by the tight coupling and mutual constraints among various system functions. Conventional discipline-specific decoupled design patterns find it challenging to tackle the complexity arising from multi-disciplinary couplings. In response, this paper investigates the application of Modelica, a multi-domain unified modeling language, to construct models for several subsystems, encompassing the reactor, energy conversion system, and control system. This approach aims to enhance support for cross-disciplinary design. The accuracy of the reactor core model was verified by high-fidelity CFD simulation results, demonstrating a good agreement. Further investigations were then conducted on the safety and operational characteristics of the whole system. Typically, two simulations were conducted on the Gas cooled micro nuclear reactor (GCMR) design: one focused on an anticipated transients without scram accident scenario and the other on load-following operation. The simulation results demonstrated that the reactor possesses excellent inherent safety, even during extreme accidents. In such scenarios, the reactor is able to achieve shutdown solely through the negative reactivity resulting from increased core temperature. Furthermore, considering the heat accommodated in the reactor system and the constantly generated decay heat, a passive air-cooling mechanism has been investigated and successfully demonstrated with the model. The reactor also exhibits good load-following performance, which can be achieved by simply adjusting helium inventory (or pressure) and control drum position, while maintaining constant core temperature and power generation efficiency. These results can be leveraged to provide guidelines for further detailed designs of the GCMR.

Hybrid mechanistic and neural network modeling of nuclear reactors

An accurate and efficient model is the foundation for dynamic characteristics analysis and control design of nuclear reactors. Nevertheless, the widely-used mechanistic models of nuclear reactors inevitably have some deviations from the actual reactors due to inaccurate model parameters and model assumptions. This paper proposes a hybrid mechanistic and neural network modeling method for nuclear reactors to eliminate or minimizing these deviations. The high-efficiency point reactor kinetics model was adopted as the mechanistic reactor core model, and the simulation results obtained using the commercial program RELAP5 were taken as the reference operational data, based on which the reactivity feedback in the mechanistic model that is difficult to be accurately determined during reactor operations was calibrated using a genetic algorithm optimized BP neural network. Dynamic simulation results of a Generation III large pressured water reactor under three typical reactivity change transients show that the core power and outlet coolant temperature obtained with the hybrid model match much better with the reference results than those of the mechanistic model, demonstrating that the hybrid modeling method can improve the accuracy of the mechanistic reactor model effectively. This study can provide a valuable reference for accurate and efficient modeling of complex systems.

Solar-driven multichannel membrane reactor for hydrogen production from ammonia decomposition

Solar-driven ammonia decomposition is one of the most promising carbon-free pathways to release hydrogen from ammonia. Enhancing the heat and mass transfer processes within an ammonia decomposition membrane reactor is crucial to improve the hydrogen production rate. The multichannel reactors can reduce hydraulic diameters by raising the number of channels while the lateral surface areas of reactors keep the same, which can enhance heat and mass transfer without enlarging re-radiation losses. In this paper, a solar-driven multichannel membrane reactor for ammonia decomposition is proposed, which is promising to improve the conversion without deteriorating the efficiency. Models are developed to simulate the proposed multichannel membrane reactor under solar irradiation. A multichannel membrane reactor with three Pd membrane channels is designed and built. Experiments have been conducted to validate the reactor model. With the validated model, two consecutive parametric studies have been conducted for catalyst volume decreasing and increasing scenarios, respectively. The results show that enlarging permeation area by increasing membrane channels is worthwhile to improve the conversion although the catalyst volume decreases. Under the same solar flux and inlet ammonia properties, a six-channel membrane reactor can achieve a conversion of 0.76, while a single-channel membrane reactor can only achieve a conversion of 0.49. Additionally, the maximum temperature difference within the six-channel reactor is 47 °C lower than that within single-channel membrane reactor, which is favorable for the Pd membrane operating temperature range.

Retraction Note: A systematic study on simulation and modeling of a solar biogas reactor.

Retraction Note: A systematic study on simulation and modeling of a solar biogas reactor.

Kinetic modeling and experimental verification of a swirl flocculation-enhanced reactor: A case study of coal chemical wastewater pretreatment

In this study, a swirl flocculation-enhanced reactor (SFR) was designed to address the problems of high dosage and poor pollutant removal in the pretreatment process of coal chemical wastewater (CCW). The effects of different height-to-diameter (H/D) ratios, stirring speed, and impeller length on SFR flow field were analyzed by computational fluid dynamics (CFD) simulation. The optimal H/D and operating condition of SFR were determined by comparing and analyzing fluid velocity, eddy viscosity, and turbulent kinetic energy. Then the lab-scale SFR was manufactured to conduct agglomeration tests. The results showed that the flocculation effect was the best when the H/D ratio of SFR is 8:5 and the mixing blade length was at 3/10 of the reactor as well as 180 r/min of agitating rate. The removal rates of oil, suspended solids (SS), chemical oxygen demand (COD) and phenol in CCW could reach 73.43%, 87.88%, 78.63% and 65.20%, respectively. In addition, the plausibility of SFR design was further validated by the fact that the reagent dose was reduced by 50–60% and the removal rate was increased by 20–30% in comparison with the beaker flocculation experiment. The SFR flow field flocculation enhancement mechanism was analyzed. It is expected that the reactor designed in this work, has a wide range of industrial applications in the CCW treatment.

A Review: Membrane Reactor for Hydrogen Production: Modeling and Simulation

A membrane reactor is a multifactional vessel used for H2 production. Hydrogen's three spectrum colors are dependent on carbon present. Two types of membrane with high permeability to hydrogen (polymeric and metallic) Hydrogen is produced in two systems: conventional reactors and membrane reactors (which separate and purify hydrogen in a single vessel). There are many types of membrane reactors according to design (catalytic membrane reactor (CMR), fixed bed reactor (FBMR), fluidized bed reactor (FBMR), etc. The transport mechanism of H2 through the membrane by a "sorption-diffusion mechanism" and the government equations that are used for membrane reactor modeling and simulation, such as continuity, momentum, mass, and heat transfer equations of the CMR, and the thickness of the membrane. These equations are solved by MATLAB, COMSOL, and the Finite Element Method to simulate the MR at different parameters: rate of conversion, rate of sweep gas, temperature, pressure, rate of H2 permeation through a membrane, and activity of the catalyst. We summarized theoretical studies for membrane reactors, including the operation conditions, type of hydrocarbon feed, type of production method, kind of catalyst, and heat effect.