Articoli di riviste: "Two-Phase Reactive Flow"

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Cheng, Cheng, e Xiaobing Zhang. "Numerical simulation of two-phase reactive flow with moving boundary". International Journal of Numerical Methods for Heat & Fluid Flow 23, n. 8 (28 ottobre 2013): 1277–90. http://dx.doi.org/10.1108/hff-11-2011-0242.

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Geiss, S., A. Dreizler, Z. Stojanovic, M. Chrigui, A. Sadiki e J. Janicka. "Investigation of turbulence modification in a non-reactive two-phase flow". Experiments in Fluids 36, n. 2 (1 febbraio 2004): 344–54. http://dx.doi.org/10.1007/s00348-003-0729-3.

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Rai, Nirmal K., e Tariq D. Aslam. "Evaluation of thermodynamic closure models for partially reacted two-phase mixture of condensed phase explosives". Journal of Applied Physics 131, n. 18 (14 maggio 2022): 185902. http://dx.doi.org/10.1063/5.0085208.

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One of the key fundamental issues that is crucial in the continuum modeling of reactive flow phenomena is the thermodynamically consistent description of reaction mixture properties. To define the mixture properties, thermodynamic closure rules that relate the properties of the individual reaction components to the mixture properties are required. In the context of reactive two-phase modeling approaches, various strategies to define the thermodynamic closures have been adopted such as pressure temperature (PT) equilibrium between the individual reaction components, pressure (specific) volume (PV) equilibrium, etc. The choice of closure rules determines the relative distribution of specific volume and energy across the reaction components that comprise the mixture. Therefore, depending on the choice of the closure, the mixture thermodynamic behavior can vary. The present work examines the effect of different closure approaches on the thermodynamic properties of the reaction mixture. The analysis is performed for a condensed phase HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) based plastic bonded explosive (PBX) 9501 explosive using four different thermodynamic closures, viz., PT equilibrium, PV equilibrium, volume temperature (VT) equilibrium, and pressure (P) equilibrium with reactants on an isentrope. The relative variations in the thermodynamic properties of the mixture are analyzed and compared under both compression and expansion loading regimes. It is shown that out of the four closure models, only PT equilibrium and P equilibrium closures lead to a thermodynamically accurate description of the mixture under both compression and expansion.

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Sengupta, Rajarshi, Mukul D. Tikekar, James V. Raj, Kris T. Delaney, Michael C. Villet e Glenn H. Fredrickson. "Phase-field simulations of morphology development in reactive polymer blending". Journal of Rheology 67, n. 1 (gennaio 2023): 1–14. http://dx.doi.org/10.1122/8.0000523.

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Reactive blending is an efficient method for synthesizing polymer blends. Industrially, this process is carried out in extruders, where the reacting polymers and the generated copolymer are subjected to high shear stresses. The dynamics of the process, and the resulting morphology is dictated by a coupling of the hydrodynamic forces in the extruder, the thermodynamic interactions between species, and the reaction kinetics on a complex interfacial manifold. We use phase-field simulations to quantify the evolution of the reactive blending process under an external shear flow. Specifically, we consider a model system of two homopolymers of equal length, which react via an end-coupling reaction to form a diblock copolymer of double the length. We compare the morphology development in two different initial geometries of the homopolymers—a cylindrical thread and a drop of one homopolymer in a matrix of the second. We investigate the effect of flow strength, measured by the shear rate, and reaction kinetics, quantified by a Damkohler number, on the progress of the reaction and morphology development. Cylindrical threads are susceptible to breakup via the Rayleigh capillary instability. We demonstrate that this instability can be suppressed by imposing shear along the direction of the thread and increasing the extent of the reaction. The reaction rate in this geometry is unaffected by shear imposed along the cylinder axis. Drops deform significantly under an imposed flow, eventually stretching to long cylindrical threads for sufficient shear rates. In the case of drops, shear stresses enhance the reaction rate by deforming the drop, enabling more homopolymers to come in contact at the expanded interface. We show that shear stresses significantly impact the morphology development and reaction dynamics in reactive polymer blending.

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Xue, She Sheng. "Modeling and Numerical Simulation of a Gas/Drop Flow". Applied Mechanics and Materials 444-445 (ottobre 2013): 1503–7. http://dx.doi.org/10.4028/www.scientific.net/amm.444-445.1503.

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To investigate the mechanism of TUSOG(Transverse Uniform Singlet Oxygen Generator), a two-phase, chemistry reactive flows model is established to describe the physical and chemical performances of Cl2/He mixed gases which transversely travels through a falling BHP(KOH,H2O2,H2O) droplets field, and the relevant numerical simulation is carried out. In the gas-phase model equations, the mass source term is determined by drop-absorbed chlorine and released singlet oxygen due to chemical reaction between drops and chlorine. An assumption is made that the BHP drops have equal sizes and fall vertically in equal speeds. The set of gas-phase control equations is solved by SIMPLEC scheme. The computational results agree well with the test results provided by relevant reference. It is found, that chlorine utility and singlet oxygen yield decreases with increasement of gas inflow speed, and increases with increasement of the speeds of falling drops, and the absorption of chlorine mainly takes place in the upstream reactive region.

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Cheng, Cheng, e Xiaobing Zhang. "Numerical investigation of two-phase reactive flow with two moving boundaries in a two-stage combustion system". Applied Thermal Engineering 156 (giugno 2019): 422–31. http://dx.doi.org/10.1016/j.applthermaleng.2019.04.061.

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Oliver, J. M. "Thin-film theories for two-phase reactive flow models of active cell motion". Mathematical Medicine and Biology 22, n. 1 (1 marzo 2005): 53–98. http://dx.doi.org/10.1093/imammb/dqh022.

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Hannebique, Gregory, Patricia Sierra, Eleonore Riber e Bénédicte Cuenot. "Large Eddy Simulation of Reactive Two-Phase Flow in an Aeronautical Multipoint Burner". Flow, Turbulence and Combustion 90, n. 2 (9 ottobre 2012): 449–69. http://dx.doi.org/10.1007/s10494-012-9416-x.

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Sin, Irina, Vincent Lagneau e Jérôme Corvisier. "Integrating a compressible multicomponent two-phase flow into an existing reactive transport simulator". Advances in Water Resources 100 (febbraio 2017): 62–77. http://dx.doi.org/10.1016/j.advwatres.2016.11.014.

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Keller, Tobias, e Jenny Suckale. "A continuum model of multi-phase reactive transport in igneous systems". Geophysical Journal International 219, n. 1 (25 giugno 2019): 185–222. http://dx.doi.org/10.1093/gji/ggz287.

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SUMMARY Multiphase reactive transport processes are ubiquitous in igneous systems. A challenging aspect of modelling igneous phenomena is that they range from solid-dominated porous to liquid-dominated suspension flows and therefore entail a wide spectrum of rheological conditions, flow speeds and length scales. Most previous models have been restricted to the two-phase limits of porous melt transport in deforming, partially molten rock and crystal settling in convecting magma bodies. The goal of this paper is to develop a framework that can capture igneous system from source to surface at all phase proportions including not only rock and melt but also an exsolved volatile phase. Here, we derive an n-phase reactive transport model building on the concepts of Mixture Theory, along with principles of Rational Thermodynamics and procedures of Non-equilibrium Thermodynamics. Our model operates at the macroscopic system scale and requires constitutive relations for fluxes within and transfers between phases, which are the processes that together give rise to reactive transport phenomena. We introduce a phase- and process-wise symmetrical formulation for fluxes and transfers of entropy, mass, momentum and volume, and propose phenomenological coefficient closures that determine how fluxes and transfers respond to mechanical and thermodynamic forces. Finally, we demonstrate that the known limits of two-phase porous and suspension flow emerge as special cases of our general model and discuss some ramifications for modelling pertinent two- and three-phase flow problems in igneous systems.

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Xue, Tao, Xiaobing Zhang e K. K. Tamma. "An in-depth study on the implementation aspect of unified time integrators in reactive two-phase flows with consistent time level". International Journal of Numerical Methods for Heat & Fluid Flow 29, n. 2 (4 febbraio 2019): 617–39. http://dx.doi.org/10.1108/hff-04-2018-0173.

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Purpose A consistent implementation of the general computational framework of unified second-order time accurate integrators via the well-known GSSSS framework in conjunction with the traditional Finite Difference Method is presented to improve the numerical simulations of reactive two-phase flows. Design/methodology/approach In the present paper, the phase interaction evaluation in the present implementation of the reactive two-phase flows has been derived and implemented to preserve the consistency of the correct time level evaluation during the time integration process for solving the two phase flow dynamics with reactions. Findings Numerical examples, including the classical Sod shock tube problem and a reactive two-phase flow problem, are exploited to validate the proposed time integration framework and families of algorithms consistently to second order in time accuracy; this is in contrast to the traditional practices which only seem to obtain first-order time accuracy because of the inconsistent time level implementation with respect to the interaction of two phases. The comparisons with the traditional implementation and the advantages of the proposed implementation are given in terms of the improved numerical accuracy in time. The proposed approaches provide a correct numerical simulation implementation to the reactive two-phase flows and can obtain better numerical stability and computational features. Originality/value The new algorithmic framework and the consistent time level evaluation extended with the GS4 family encompasses a multitude of past and new schemes and offers a general purpose and unified implementation for fluid dynamics.

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Zamuner, B., P. Gilbank, D. Bissières e C. Berat. "Numerical simulation of the reactive two-phase flow in a kerosene/air tubular combustor". Aerospace Science and Technology 6, n. 7 (novembre 2002): 521–29. http://dx.doi.org/10.1016/s1270-9638(02)01190-2.

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Bougamra, Ahmed, e Huilin Lu. "Interior Ballistics Two-Phase Reactive Flow Model Applied to Small Caliber Projectile-Gun System". Propellants, Explosives, Pyrotechnics 40, n. 5 (13 marzo 2015): 720–28. http://dx.doi.org/10.1002/prep.201400268.

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Shabanian, Jaber, e Jamal Chaouki. "Performance of a Catalytic Gas–Solid Fluidized Bed Reactor in the Presence of Interparticle Forces". International Journal of Chemical Reactor Engineering 14, n. 1 (1 febbraio 2016): 433–44. http://dx.doi.org/10.1515/ijcre-2014-0106.

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AbstractThe influence of interparticle forces (IPFs) on the hydrodynamics of a gas–solid fluidized bed was experimentally investigated with the help of a polymer coating approach. The results showed that the presence of IPFs in the bed can considerably change the hydrodynamic parameters. The tendency of the fluidizing gas passing through the bed in the emulsion phase increased with IPFs in the bubbling regime. The performance of a fluidized bed reactor was then studied through simulation of a reactive catalytic system using three different hydrodynamic models: (a) a simple two-phase flow model, (b) a dynamic two-phase flow model, and (c) a dynamic two-phase flow model, integrating the effects of superficial gas velocity and IPFs. The simple two-phase flow model was found to underestimate the reactor performance for catalytic reaction most likely due to the oversimplified assumptions involved in this model. Also, the simulation results showed that modification of the bed hydrodynamics due to IPFs resulted in a better performance for a bubbling fluidized bed reactor. This suggests that the hydrodynamic models should take into account the effects of superficial gas velocity and variation in the ratio of the magnitude of IPFs/hydrodynamic forces, due to any operational reason, to yield a more reliable evaluation of the performance of the fluidized bed reactor.

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Rashad, M., X. Zhang e H. El Sadek. "Interior Ballistics Two-Phase Reactive Flow Model Applied to Large Caliber Guided Projectile-Gun System". Advances in Mechanical Engineering 6 (12 febbraio 2015): 698032. http://dx.doi.org/10.1155/2014/698032.

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Jones, W. P., A. J. Marquis e D. Noh. "A stochastic breakup model for Large Eddy Simulation of a turbulent two-phase reactive flow". Proceedings of the Combustion Institute 36, n. 2 (2017): 2559–66. http://dx.doi.org/10.1016/j.proci.2016.06.033.

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Karadimitriou, N. K., V. Joekar-Niasar, S. M. Hassanizadeh, P. J. Kleingeld e L. J. Pyrak-Nolte. "A novel deep reactive ion etched (DRIE) glass micro-model for two-phase flow experiments". Lab on a Chip 12, n. 18 (2012): 3413. http://dx.doi.org/10.1039/c2lc40530j.

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Siratarnsophon, Piyapath, Vinicius C. Cunha, Nicholas G. Barry e Surya Santoso. "Interphase Power Flow Control via Single-Phase Elements in Distribution Systems". Clean Technologies 3, n. 1 (13 gennaio 2021): 37–58. http://dx.doi.org/10.3390/cleantechnol3010003.

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The capability of routing power from one phase to another, interphase power flow (IPPF) control, has the potential to improve power systems efficiency, stability, and operation. To date, existing works on IPPF control focus on unbalanced compensation using three-phase devices. An IPPF model is proposed for capturing the general power flow caused by single-phase elements. The model reveals that the presence of a power quantity in line-to-line single-phase elements causes an IPPF of the opposite quantity; line-to-line reactive power consumption causes real power flow from leading to lagging phase while real power consumption causes reactive power flow from lagging to leading phase. Based on the model, the IPPF control is proposed for line-to-line single-phase power electronic interfaces and static var compensators (SVCs). In addition, the control is also applicable for the line-to-neutral single-phase elements connected at the wye side of delta-wye transformers. Two simulations on a multimicrogrid system and a utility feeder are provided for verification and demonstration. The application of IPPF control allows single-phase elements to route active power between phases, improving system operation and flexibility. A simple IPPF control for active power balancing at the feeder head shows reductions in both voltage unbalances and system losses.

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Belhachmi, Z., Z. Mghazli e S. Ouchtout. "A coupled compressible two-phase flow with the biological dynamics modeling the anaerobic biodegradation process of waste in a landfill". Mathematical Modeling and Computing 9, n. 3 (2022): 483–500. http://dx.doi.org/10.23939/mmc2022.03.483.

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In this article, we present and study a new coupled model combining the biological and the mechanical aspects describing respectively the process of the biogas production and the compressible two-phase leachate-biogas flow during the anaerobic biodegradation of organic matters in a landfill, which is considered a reactive porous medium. The model obtained is governed by a reaction-diffusion system for the bacterial activity coupled with a compressible two-phase flow system of a non-homogeneous porous medium. We carry out the analysis and the numerical approximation of the model within a variational framework. We propose a full discrete system based on a second-order BDF-time scheme and P1-conforming finite element and we derive an efficient algorithm for the coupled system. We perform some numerical simulations in 2D and 3D examples in agreement with the theoretical analysis.

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Zaretskiy, Yan, Sebastian Geiger e Ken Sorbie. "Direct numerical simulation of pore-scale reactive transport: applications to wettability alteration during two-phase flow". International Journal of Oil, Gas and Coal Technology 5, n. 2/3 (2012): 142. http://dx.doi.org/10.1504/ijogct.2012.046318.

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Tatomir, Alexandru, Dejian Zhou, Huhao Gao, Alexandru-Nicolae Dimache, Iulian Iancu e Martin Sauter. "Modelling of kinetic interface sensitive tracers reactive transport in 2D two-phase flow heterogeneous porous media". E3S Web of Conferences 85 (2019): 07003. http://dx.doi.org/10.1051/e3sconf/20198507003.

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Fluid-fluid interfacial area plays an important role for mass- and energy-transfer processes across the interface which is relevant in several hydrogeological and engineering applications, e.g. enhanced oil-gas recovery, CO2 storage in geological formations, unconventional geothermal systems, contaminant removal, etc. Kinetic interface sensitive tracers were designed to determine the size of the interface between two fluids by undergoing hydrolysis at the fluid-fluid interface. This study investigates by means of numerical modelling the influence of heterogeneity on the KIS tracer breakthrough curves in six idealized scenarios (S1-S6). It is an extension of the previous work conducted in “one-dimensional” column experiments by Tatomir et al. (2018) [1]. The changes in interfacial area are created by inclusion of heterogeneities at the Darcy-scale. The results show that KIS tracers can be used in two-dimensional experimental setup and can provide information about the size and dynamic evolution of interfacial area. Therefore, this is a first step for the dimensioning of an experimental flume.

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Schwendeman, D. W., A. K. Kapila e W. D. Henshaw. "A study of detonation diffraction and failure for a model of compressible two-phase reactive flow". Combustion Theory and Modelling 14, n. 3 (9 luglio 2010): 331–66. http://dx.doi.org/10.1080/13647830.2010.489955.

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Schwendeman, D. W., C. W. Wahle e A. K. Kapila. "A study of detonation evolution and structure for a model of compressible two-phase reactive flow". Combustion Theory and Modelling 12, n. 1 (18 dicembre 2007): 159–204. http://dx.doi.org/10.1080/13647830701564538.

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Cheng, Cheng, e Xiaobing Zhang. "Numerical modeling and investigation of two-phase reactive flow in a high-low pressure chambers system". Applied Thermal Engineering 99 (aprile 2016): 244–52. http://dx.doi.org/10.1016/j.applthermaleng.2016.01.046.

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Bazdidi-Tehrani, Farzad, e Hamed Zeinivand. "Presumed PDF modeling of reactive two-phase flow in a three dimensional jet-stabilized model combustor". Energy Conversion and Management 51, n. 1 (gennaio 2010): 225–34. http://dx.doi.org/10.1016/j.enconman.2009.09.020.

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Akmal Zuhdi, Muhammad, e Faiz Husnayain. "Power Flow Analysis in Unbalanced Three-Phase Distribution Systems using Backward/Forward Sweep and Current Injection Methods". ELKHA 16, n. 2 (21 ottobre 2024): 107. http://dx.doi.org/10.26418/elkha.v16i2.82179.

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The electrical power distribution system is a part of the power system that distributes electricity from the transmission network to customers. In the distribution system, imbalances often occur due to the varying load profiles in each phase. This can cause voltage imbalances in the distribution system. This study aims to compare two power flow analysis methods, Backward/Forward Sweep and Current Injection. The study analyses the voltage and power loss conditions on each phase at each bus and line in the three-phase distribution system under unbalanced conditions. Simulations were conducted on two IEEE test buses, IEEE 19-Bus and IEEE 33-Bus with radial configurations. The power flow calculation results using the Backward and Forward Sweep method showed that in the IEEE 19-Bus system, the highest voltage drop percentage occurred on phase b at bus 19, at 3.14%, the highest voltage imbalance percentage occurred at bus 19, at 0.1409%, and the total active and reactive power losses were 7.352 kW and 3.164 kVAR. In the IEEE 33-Bus system, the highest voltage drop percentage occurred on phase c at bus 18, at 5.85%, the highest imbalance percentage occurred at bus 15, at 0.2077%, and the total active and reactive power losses were 19.107 kW and 8.22 kVAR. The percentage difference between the two methods used is less than one percent, indicating that both methods are sufficiently accurate in analyzing power flow in an unbalanced distribution system.

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LOGAN, J. DAVID, e THOMAS S. SHORES. "ON A SYSTEM OF NONLINEAR HYPERBOLIC CONSERVATION LAWS WITH SOURCES". Mathematical Models and Methods in Applied Sciences 03, n. 03 (giugno 1993): 341–58. http://dx.doi.org/10.1142/s0218202593000187.

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We study the existence of travelling reaction fronts connecting equilibrium states in the nonlinear reactive-convective system [Formula: see text] where r represents a given chemical reaction rate of a reversible reaction A⇌B, and f(u)=(2−u)(u−1) represents a nonlinear heat source. The original model equations for irreversible reactions and without sources were motivated by an analog of reactive flow and detonation processes posed by Fickett and Majda. It is shown that endothermic compressions exist for wave speeds c≥2 and in this case, a singular perturbation method is developed to find a two-term analytic approximation for the waveforms. For wavespeeds 0<c<c*<1, for some c*=c*(q), nonmonotonic travelling waves exist. These subsonic travelling waves have either an oscillating tail or a minimum occurring at a finite value, and they essentially represent exothermic rarefaction waves. In this latter case a singular line in the flow comes into play, and a method of analysis is developed based on desingularization of the phase plane equations.

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Peskova, E. E., e V. N. Snytnikov. "Mathematical Modelling of the Impact of IR Laser Radiation on an Oncoming Flow of Nanoparticles with Methane". Computational Mathematics and Information Technologies 8, n. 3 (8 ottobre 2024): 34–42. http://dx.doi.org/10.23947/2587-8999-2024-8-3-34-42.

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Introduction. The study is devoted to the numerical investigation of laser radiation’s effect on an oncoming two-phase flow of nanoparticles and multicomponent hydrocarbon gases. Under such exposure, the hydrogen content in the products increases, and methane is bound into more complex hydrocarbons on the surface of catalytic nanoparticles and in the gas phase. The hot walls of the tube serve as the primary source of heat for the reactive two-phase medium containing catalytic nanoparticles. Materials and Methods. The main method used is mathematical modelling, which includes the numerical solution of a system of equations for a viscous gas-dust two-phase medium, taking into account chemical reactions and laser radiation. The model accounts for the two-phase gas-dust medium’s multicomponent and multi-temperature nature, ordinary differential equations (ODEs) for the temperature of catalytic nanoparticles, ODEs of chemical kinetics, endothermic effects of radical chain reactions, diffusion of light methyl radicals CH3 and hydrogen atoms H, which initiate methaneconversion, as well as absorption of laser radiation by ethylene and particles. Results. The distributions of parameters characterizing laminar subsonic flows of the gas-dust medium in an axisymmetric tube with chemical reactions have been obtained. It is shown that the absorption of laser radiation by ethylene in the oncoming flow leads to a sharp increase in methane conversion and a predominance of aromatic compounds in the product output. Discussion and Conclusion. Numerical modelling of the dynamics of reactive two-phase media is of interest for the development of theoretical foundations for the processing of methane into valuable products. The results obtained confirm the need for joint use of mathematical modelling and laboratory experiments in the development of new resource-saving and economically viable technologies for natural gas processing.

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Ahusborde, E., e M. El Ossmani. "A sequential approach for numerical simulation of two-phase multicomponent flow with reactive transport in porous media". Mathematics and Computers in Simulation 137 (luglio 2017): 71–89. http://dx.doi.org/10.1016/j.matcom.2016.11.007.

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Raju, M. S., e W. A. Sirignano. "Spray Computations in a Centerbody Combustor". Journal of Engineering for Gas Turbines and Power 111, n. 4 (1 ottobre 1989): 710–18. http://dx.doi.org/10.1115/1.3240317.

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A hybrid Eulerian–Lagrangian method is employed to model the reactive flow field of a centerbody combustor. The unsteady two-dimensional gas-phase equations are represented in Eulerian coordinates and liquid-phase equations are formulated in Lagrangian coordinates. The gas-phase equations based on the conservation of mass, momentum, and energy are supplemented by turbulence and combustion models. The vaporization model takes into account the transient effects associated with the droplet heating and liquid-phase internal circulation. The integration scheme is based on the TEACH algorithm for gas-phase equations, the Runge-Kutta method for liquid-phase equations, and linear interpolation between the two coordinate systems. The calculations show that the droplet penetration and recirculation characteristics are strongly influenced by the gas- and liquid-phase interaction in such a way that most of the vaporization process is confined to the wake region of the centerbody, thereby improving the flame stabilization properties of the flow field.

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Gharde, Mr Rahul, e Dr Prashant Thakre. "“Enhance the Power Quality of the Smart Grid System by Using Advance UPQC.”". International Journal for Research in Applied Science and Engineering Technology 10, n. 5 (31 maggio 2022): 2778–85. http://dx.doi.org/10.22214/ijraset.2022.42837.

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Abstract: The UPQC is the grouping of a DVR and D- STATCOM which perform series, shunt compensating and phase shifting at the same time. This is capable to control the PQ with leading and lagging reactive and real power flow through a particular route with enhance the system stability. The salient options of UPQC device are its multiple management functions, like voltage management, transient stability improvement & damping oscillation. Voltage sag and swell compensation is important for secure system operation. This is a multivariable versatile AC transmission systems controller. In this work UPQC is excited by PV array with DC link capacitor. In the SG using PMU and flow meter, measures the phase and related data, from this data of analysis centralized controller determine the harmonics amplitude and phase. At fault condition UPQC mitigate the fault with simultaneous or individual operation of series-shunt converters. At the presence of harmonics this two converter works simultaneously and optimized the harmonics injected by the UPQC, the centralized controller calculates the switching angle for same magnitude with opposite phase harmonics and inject into the system. These two components eliminate each other and make the grid approximately harmonics free with mitigate the active and reactive power problem. Keywords: UPQC, DSTATCOM, DVR, PV array, Power Quality

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Zhou, Chongbo, Lingyi Guo, Li Chen, Xin Tian, Tiefeng He e Qinghua Yang. "Pore-Scale Modeling of Air–Water Two Phase Flow and Oxygen Transport in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cell". Energies 14, n. 13 (24 giugno 2021): 3812. http://dx.doi.org/10.3390/en14133812.

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Understanding multiphase flow and gas transport occurring in electrodes is crucial for improving the performance of proton exchange membrane fuel cells. In the present study, a pore-scale model using the lattice Boltzmann method (LBM) was proposed to study the coupled processes of air–water two-phase flow and oxygen reactive transport processes in porous structures of the gas diffusion layer (GDL) and in fractures of the microscopic porous layer (MPL). Three-dimensional pore-scale numerical results show that the liquid water generation rate is gradually reduced as the oxygen consumption reaction proceeds, and the liquid water saturation in the GDL increases, thus the constant velocity inlet or pressure inlet condition cannot be maintained while the results showed that at t = 1,200,000 iterations after 2900 h running time, the local saturation at the GDL/MPL was about 0.7, and the maximum value was about 0.83, while the total saturation was 0.35. The current density reduced from 2.39 to 0.46 A cm−2. Effects of fracture number were also investigated, and the results showed that for the fracture numbers of 8, 12, 16, and 24, the breakthrough point number was 4, 3, 3, and 2, respectively. As the fracture number increased, the number of the water breakthrough points at the GDL/GC interface decreased, the liquid water saturation inside the GDL increased, the GDL/MPL interface was more seriously covered, and the current density decreased. The pore-scale model for the coupled multiphase reactive transport processes is helpful for understanding the mechanisms inside the porous electrodes of PEMFC.

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Zhang, Xinying, Runze Fan, Miao Qi, Xinyi Zhao, Jin Zhang, Dehui Xu e Yanjie Yang. "Studies on a sinusoidally driven gas–liquid two-phase plasma discharge and its application to sterilization". AIP Advances 12, n. 11 (1 novembre 2022): 115218. http://dx.doi.org/10.1063/5.0100815.

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Atmospheric pressure cold plasmas are widely used in the biomedical field as evidenced by developments in recent years. In this study, a quartz tube-guided gas–liquid two-phase discharge has been configured with a hollow needle-water structure. The power source for the device was sinusoidal, and switching between a gas–liquid miscible discharge and a pure gaseous discharge was simple. It was discovered that the gas–liquid discharge was beneficial in terms of reactant species generation and reaction efficiency in terms of processing water. The types of particles, the physicochemical properties, and the concentrations of reactive oxygen and nitrogen species in the discharge were studied spectroscopically. The discharge was discovered to have high levels of H2O2 and NO2−, and the activated water was proven to be effective at sterilizing samples that were contaminated with micro-organisms. Key experimental parameters including the driving voltage and the air flow rate were optimized to achieve the best sterilization conditions. The membrane potential changes in the treated bacteria were also studied to explore the causes of bacterial inactivation. The results showed that the device exhibited a strong bactericidal effect for the gas–liquid mixed phase discharge operating at 17 kV for 5 min with a gas flow rate of 0.3 SLM. In addition, the present device offers enhanced sterilization efficiency relative to the efficiency of conventional plasma sterilization equipment and, therefore, has a wide range of applications.

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Kiełczyński, Piotr. "Relation between Mass Sensitivity and Complex Power Flow in Love Wave Sensors". Sensors 22, n. 16 (15 agosto 2022): 6100. http://dx.doi.org/10.3390/s22166100.

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In this paper, we investigate the connection between average power flows in Love wave waveguides with the mass sensitivity of Love wave sensors. In fact, loading with a Newtonian liquid gives rise to two extra power flows, in the transverse direction towards the loading Newtonian liquid. The first is an active power flow feeding viscous losses in the Newtonian liquid and the second is a reactive power flow that is responsible for the phase delay of the Love wave and consequently for the changes in phase velocity of the Love wave. Since loading with a lossless mass also leads to changes in the phase velocity, we assert that mass sensitivity Sσvp of Love wave sensors is connected to the average reactive power flow, in the transverse direction x2, bouncing back and forth, between the interior of the waveguide and the loading Newtonian liquid. Subsequently, we found the thickness of the effective surface layer of mass that is equivalent to loading with a semi-infinite Newtonian liquid. The analytical formulas developed in this paper are illustrated by the results of numerical calculations performed for an exemplary Love wave waveguide composed of a PMMA surface layer deposited on an ST-Quartz substrate.

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Sauni Camposano, Yesenia Haydee, Sascha Sebastian Riegler, Konrad Jaekel, Jörg Schmauch, Christoph Pauly, Christian Schäfer, Heike Bartsch, Frank Mücklich, Isabella Gallino e Peter Schaaf. "Phase Transformation and Characterization of 3D Reactive Microstructures in Nanoscale Al/Ni Multilayers". Applied Sciences 11, n. 19 (7 ottobre 2021): 9304. http://dx.doi.org/10.3390/app11199304.

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Reactive multilayer systems represent an innovative approach for potential usage in chip joining applications. As there are several factors governing the energy release rate and the stored chemical energy, the impact of the morphology and the microstructure on the reaction behavior is of great interest. In the current work, 3D reactive microstructures with nanoscale Al/Ni multilayers were produced by alternating deposition of pure Ni and Al films onto nanostructured Si substrates by magnetron sputtering. In order to elucidate the influence of this 3D morphology on the phase transformation process, the microstructure and the morphology of this system were characterized and compared with a flat reactive multilayer system on a flat Si wafer. The characterization of both systems was carried out before and after a rapid thermal annealing treatment by using scanning and transmission electron microscopy of the cross sections, selected area diffraction analysis, and differential scanning calorimetry. The bent shape of multilayers caused by the complex topography of silicon needles of the nanostructured substrate was found to favor the atomic diffusion at the early stage of phase transformation and the formation of two intermetallic phases Al0.42Ni0.58 and AlNi3, unlike the flat multilayers that formed a single phase AlNi after reaction.

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Salmerón, Patricio, Juan L. Flores-Garrido e Juan A. Gómez-Galán. "Instantaneous Reactive Power Theory in the Geometric Algebra Framework". Applied Sciences 13, n. 3 (30 gennaio 2023): 1796. http://dx.doi.org/10.3390/app13031796.

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In this paper, a new approach for instantaneous reactive power analysis in the geometric algebra (GA) environment is presented. The different formulations of the instantaneous reactive power theory (IRPT) proposed, to date, have been developed in three-phase systems. There, an instantaneous power variable, and two/three reactive power variables, all handled independently, were introduced. Thanks to GA, it is possible to carry out a global treatment where an instantaneous power multivector is defined. Thus, in the same multidimensional entity all the power variables are included. From the instantaneous power multivector, the instantaneous power current and the instantaneous reactive current are determined. It should be noted that in this mathematical framework there is no limitation on the number of phases, and the extension of the IRPT to the analysis of multi-phase systems appears in a natural manner. In this study, a systematic approach with the most relevant definitions and theorems corresponding to the proposed methodology has been established. Two practical cases of five-phase and three-phase systems have been included to apply the new established formulation.

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Radwan, Eyad, Mutasim Nour, Ali Baniyounes, Khalid S. Al Olimat e Emad Awada. "Direct control of active and reactive power for a grid-connected single-phase photovoltaic inverter". International Journal of Power Electronics and Drive Systems (IJPEDS) 12, n. 1 (1 marzo 2021): 139. http://dx.doi.org/10.11591/ijpeds.v12.i1.pp139-150.

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This paper presents a single-phase grid-connected photovoltaic system with direct control of active and reactive power through a power management system of a Photovoltaic inverter. The proposed control algorithm is designed to allow maximum utilization of the inverter’s available KVA capacity while maintaining grid power factor and current total harmonic distortion (THD) requirements within the grid standards. To reduce the complexity and improve the efficiency of the system, two independent PI controllers are implemented to control single-phase unipolar PWM voltage source inverter. One controller is used to control the power angle, and hence the active power flow, while the other controller is used to control the reactive power, and consequently the power factor by adjusting the voltage modulation index of the inverter. The proposed system is modelled and simulated using MATLAB/Simulink. The PV inverter has been examined while being simultaneously connected to grid and local load. Results obtained showed the ability of the PV inverter to manage the active and reactive power flow at, and below rated levels of solar irradiances; resulting in an increased inverter utilization factor, and enhanced power quality. The proposed system, was capable of operating at power factors in the range of 0.9 lead or lag for reactive power compensation purposes and delivered its power at a wide range of solar irradiance variations.

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Calcio Gaudino, Emanuela, Giorgio Grillo, Maela Manzoli, Silvia Tabasso, Simone Maccagnan e Giancarlo Cravotto. "Mechanochemical Applications of Reactive Extrusion from Organic Synthesis to Catalytic and Active Materials". Molecules 27, n. 2 (10 gennaio 2022): 449. http://dx.doi.org/10.3390/molecules27020449.

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In the past, the use of mechanochemical methods in organic synthesis was reported as somewhat of a curiosity. However, perceptions have changed over the last two decades, and this technology is now being appreciated as a greener and more efficient synthetic method. The qualified “offer” of ball mills that make use of different set-ups, materials, and dimensions has allowed this technology to mature. Nevertheless, the intrinsic batch nature of mechanochemical methods hinders industrial scale-ups. New studies have found, in reactive extrusion, a powerful technique with which to activate chemical reactions with mechanical forces in a continuous flow. This new environmentally friendly mechanochemical synthetic method may be able to miniaturize production plants with outstanding process intensifications by removing organic solvents and working in a flow mode. Compared to conventional processes, reactive extrusions display high simplicity, safety, and cleanliness, which can be exploited in a variety of applications. This paper presents perspective examples in the better-known areas of reactive extrusions, including oxidation reactions, polymer processing, and biomass conversion. This work should stimulate further developments, as it highlights the versatility of reactive extrusion and the huge potential of solid-phase flow chemistry.

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Ahmed, E., e Y. Huang. "Flame volume prediction and validation for lean blow-out of gas turbine combustor". Aeronautical Journal 121, n. 1236 (12 gennaio 2017): 237–62. http://dx.doi.org/10.1017/aer.2016.125.

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ABSTRACTLean Blow-Out (LBO) limits are critically important in the operation of aero engines. Previously, Lefebvre's LBO empirical correlation has been extended to the flame volume concept by the authors. Flame volume takes into account the effects of geometric configuration, spatial interaction of mixing jets, turbulence, heat transfer and combustion processes inside the gas turbine combustion chamber. For these reasons, LBO predictions based on flame volume are more accurate. Although LBO prediction accuracy has improved, it poses a challenge associated with Vfestimation in real gas turbine combustors. This work extends the approach of flame volume prediction based on fuel iterative approximation with cold flow simulations to reactive flow simulations. Flame volume for 11 combustor configurations were simulated and validated against experimental data. To make prediction methodology robust, as required in preliminary design stage, reactive flow simulations were carried out with the combination of presumed Probability Density Function (PDF) and discrete phase model (DPM) in Fluent 15.0 The criterion for flame identification was defined. Two important parameters—critical injection diameter (Dp,crit) and critical temperature (Tcrit)—were identified and their influence on reactive flow simulation was studied for Vfestimation. Results exhibit ±15% error in Vf estimation with experimental data.

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Baer, M. R., e J. W. Nunziato. "A two-phase mixture theory for the deflagration-to-detonation transition (ddt) in reactive granular materials". International Journal of Multiphase Flow 12, n. 6 (novembre 1986): 861–89. http://dx.doi.org/10.1016/0301-9322(86)90033-9.

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Panariello, Luca, Gaowei Wu, Maximilian O. Besenhard, Katerina Loizou, Liudmyla Storozhuk, Nguyen Thi Kim Thanh e Asterios Gavriilidis. "A Modular Millifluidic Platform for the Synthesis of Iron Oxide Nanoparticles with Control over Dissolved Gas and Flow Configuration". Materials 13, n. 4 (25 febbraio 2020): 1019. http://dx.doi.org/10.3390/ma13041019.

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Gas–liquid reactions are poorly explored in the context of nanomaterials synthesis, despite evidence of significant effects of dissolved gas on nanoparticle properties. This applies to the aqueous synthesis of iron oxide nanoparticles, where gaseous reactants can influence reaction rate, particle size and crystal structure. Conventional batch reactors offer poor control of gas–liquid mass transfer due to lack of control on the gas–liquid interface and are often unsafe when used at high pressure. This work describes the design of a modular flow platform for the water-based synthesis of iron oxide nanoparticles through the oxidative hydrolysis of Fe2+ salts, targeting magnetic hyperthermia applications. Four different reactor systems were designed through the assembly of two modular units, allowing control over the type of gas dissolved in the solution, as well as the flow pattern within the reactor (single-phase and liquid–liquid two-phase flow). The two modular units consisted of a coiled millireactor and a tube-in-tube gas–liquid contactor. The straightforward pressurization of the system allows control over the concentration of gas dissolved in the reactive solution and the ability to operate the reactor at a temperature above the solvent boiling point. The variables controlled in the flow system (temperature, flow pattern and dissolved gaseous reactants) allowed full conversion of the iron precursor to magnetite/maghemite nanocrystals in just 3 min, as compared to several hours normally employed in batch. The single-phase configuration of the flow platform allowed the synthesis of particles with sizes between 26.5 nm (in the presence of carbon monoxide) and 34 nm. On the other hand, the liquid–liquid two-phase flow reactor showed possible evidence of interfacial absorption, leading to particles with different morphology compared to their batch counterpart. When exposed to an alternating magnetic field, the particles produced by the four flow systems showed ILP (intrinsic loss parameter) values between 1.2 and 2.7 nHm2/kg. Scale up by a factor of 5 of one of the configurations was also demonstrated. The scaled-up system led to the synthesis of nanoparticles of equivalent quality to those produced with the small-scale reactor system. The equivalence between the two systems is supported by a simple analysis of the transport phenomena in the small and large-scale setups.

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Nie, Guo Zheng, Chun Liang Zhong, Lan E. Luo, Ren Long Zhou e Qiang Liu. "Effect of N₂ Flow on Microstructure, Mechanical Properties and Oxidation Resistance of CrN_x Coatings". Advanced Materials Research 750-752 (agosto 2013): 2117–20. http://dx.doi.org/10.4028/www.scientific.net/amr.750-752.2117.

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A series of CrNx coatings were deposited by direct-current reactive magnetron sputtering. The microstructure, the hardness and oxidation resistance of the thin films were characterized respectively with X-ray diffraction (XRD) and nanoindentor. The effect of N2 flow on the microstructure, the hardness and oxidation resistance was studied. It was found that the CrNx film has two phases, the conformation of hcp-Cr2N (hexagonal structure) and fcc-CrN (face-centered cubic). In CrNx film phase structure, with N2 flow increasing, there is the conformation of CrNx films transition from Cr2N to Cr2N and CrN mixed phase, the final CrN single-phase. A single phase of CrNx films has very high hardness while thin film as mixed phase showed a low hardness. CrN has better oxidation resistance with the oxidation resistance temperature of 500°C to 600°C compared to Cr2N. Comparison of Cr2N and CrN on the mechanical properties and oxidation resistance, CrN has better comprehensive performance for protective hard coatings.

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Ahusborde, Etienne, Michel Kern e Viatcheslav Vostrikov. "Numerical simulation of two-phase multicomponent flow with reactive transport in porous media: application to geological sequestration of CO2". ESAIM: Proceedings and Surveys 50 (marzo 2015): 21–39. http://dx.doi.org/10.1051/proc/201550002.

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Sin, Irina, Vincent Lagneau, Laurent De Windt e Jérôme Corvisier. "2D simulation of natural gas reservoir by two-phase multicomponent reactive flow and transport—Description of a benchmarking exercise". Mathematics and Computers in Simulation 137 (luglio 2017): 431–47. http://dx.doi.org/10.1016/j.matcom.2016.12.003.

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45

Paul, Biplab, Jun Lu e Per Eklund. "Growth of CaxCoO2 Thin Films by A Two-Stage Phase Transformation from CaO–CoO Thin Films Deposited by Rf-Magnetron Reactive Cosputtering". Nanomaterials 9, n. 3 (15 marzo 2019): 443. http://dx.doi.org/10.3390/nano9030443.

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The layered cobaltates AxCoO2 (A: alkali metals and alkaline earth metals) are of interest in the area of energy harvesting and electronic applications, due to their good electronic and thermoelectric properties. However, their future widespread applicability depends on the simplicity and cost of the growth technique. Here, we have investigated the sputtering/annealing technique for the growth of CaxCoO2 (x = 0.33) thin films. In this approach, CaO–CoO film is first deposited by rf-magnetron reactive cosputtering from metallic targets of Ca and Co. Second, the as-deposited film is reactively annealed under O2 gas flow to form the final phase of CaxCoO2. The advantage of the present technique is that, unlike conventional sputtering from oxide targets, the sputtering is done from the metallic targets of Ca and Co; thus, the deposition rate is high. Furthermore, the composition of the film is controllable by controlling the power at the targets.

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46

SHORT, M., I. I. ANGUELOVA, T. D. ASLAM, J. B. BDZIL, A. K. HENRICK e G. J. SHARPE. "Stability of detonations for an idealized condensed-phase model". Journal of Fluid Mechanics 595 (8 gennaio 2008): 45–82. http://dx.doi.org/10.1017/s0022112007008750.

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The stability of travelling wave Chapman–Jouguet and moderately overdriven detonations of Zeldovich–von Neumann–Döring type is formulated for a general system that incorporates the idealized gas and condensed-phase (liquid or solid) detonation models. The general model consists of a two-component mixture with a one-step irreversible reaction between reactant and product. The reaction rate has both temperature and pressure sensitivities and has a variable reaction order. The idealized condensed-phase model assumes a pressure-sensitive reaction rate, a constant-γ caloric equation of state for an ideal fluid, with the isentropic derivative γ=3, and invokes the strong shock limit. A linear stability analysis of the steady, planar, ZND detonation wave for the general model is conducted using a normal-mode approach. An asymptotic analysis of the eigenmode structure at the end of the reaction zone is conducted, and spatial boundedness (closure) conditions formally derived, whose precise form depends on the magnitude of the detonation overdrive and reaction order. A scaling analysis of the transonic flow region for Chapman–Jouguet detonations is also studied to illustrate the validity of the linearization for Chapman–Jouguet detonations. Neutral stability boundaries are calculated for the idealized condensed-phase model for one- and two-dimensional perturbations. Comparisons of the growth rates and frequencies predicted by the normal-mode analysis for an unstable detonation are made with a numerical solution of the reactive Euler equations. The numerical calculations are conducted using a new, high-order algorithm that employs a shock-fitting strategy, an approach that has significant advantages over standard shock-capturing methods for calculating unstable detonations. For the idealized condensed-phase model, nonlinear numerical solutions are also obtained to study the long-time behaviour of one- and two-dimensional unstable Chapman–Jouguet ZND waves.

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Eyenubo, OJ, e P. Oshevire. "IMPROVEMENT OF POWER SYSTEM QUALITY USING VSC-BASED HVDC TRANSMISSION". Nigerian Journal of Technology 36, n. 3 (30 giugno 2017): 889–96. http://dx.doi.org/10.4314/njt.v36i3.31.

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The HVDC technology can be represented by the combination of a Direct Current (DC) circuit with two power electronics converters, each one at a link terminal, for AC/DC and DC/AC conversion The principal characteristic of VSC-HVDC transmission is its ability to independently control the reactive and real power flow at each of the AC systems via the Point of Common Coupling (PCC). The active and reactive power is related to the power angle and the magnitude ofÂ voltage in the reference -frame selected such that the quadrature component will result in the ratio between the maximum fundamental peak phase voltage and the DC total voltagehttp://dx.doi.org/10.4314/njt.v36i3.31

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Murthy, G. V. K., Sowjan Kumar, B. Nagaraju, R. Shankar, C. Rajalingam e C. Rajaselvan. "Power Factor Compensation for a Single-Phase AC-DC Hybrid Micro-Grid". International Journal of Innovative Research in Engineering and Management 9, n. 5 (26 ottobre 2022): 327–30. http://dx.doi.org/10.55524/ijirem.2022.9.5.49.

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A single-phase AC-DC Hybrid Micro-Grid (HMG) power flow control strategy is modeled and simulated in this paper. Two AC and two DC zones are separated by a bidirectional interlinking converter (BIC) in the full bridge IGBT structure, which is a typical H-Bridge inverter/rectifier, in the proposed HMG system topology. Based on the DQ transformation theory, the BIC's switching pattern comes from one voltage loop (Vdc) and two power control loops. The transfer of both active and reactive power between the HMG and the public AC Grid is controlled by this control strategy. Additionally, this can be accomplished in either rectifying or inverting modes by utilizing the bidirectional converter. Matlab-Simulink is used to implement and test the simulation model.

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Pape, L., C. Ammann, A. Nyfeler-Brunner, C. Spirig, K. Hens e F. X. Meixner. "An automated dynamic chamber system for surface exchange measurement of non-reactive and reactive trace gases of grassland ecosystems". Biogeosciences Discussions 5, n. 4 (12 agosto 2008): 3157–219. http://dx.doi.org/10.5194/bgd-5-3157-2008.

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Abstract. We present an automated dynamic chamber system which is optimised for continuous unattended flux measurements of multiple non-reactive and reactive trace gases on grassland ecosystems. Main design features of our system are (a) highly transparent chamber walls consisting of chemically inert material, (b) individual purging flow units for each chamber, and (c) a movable lid for automated opening and closing of the chamber. The purging flow rate was chosen high enough to keep the mean residence time of the chamber air below one minute. This guarantees a proven efficient mixing of the chamber volume and a fast equilibration after lid closing. The dynamic chamber system is able to measure emission as well as deposition fluxes of trace gases. For the latter case, the modification of the turbulent transport by the chamber (compared to undisturbed ambient conditions) is quantitatively described by a bulk resistance concept. Beside a detailed description of the design and functioning of the system, results of field applications at two grassland sites are presented. In the first experiment, fluxes of five trace gases (CO2, H2O, NO, NO2, O3) were measured simultaneously on small grassland plots. It showed that the dynamic chamber system is able to detect the characteristic diurnal cycles with a sufficient temporal resolution. The results also demonstrated the importance of considering the chemical source/sink in the chamber due to gas phase reactions for the reactive compounds of the NO-NO2-O3 triad. In a second field experiment, chamber flux measurements of CO2 and methanol were compared to simultaneous independent eddy covariance flux measurements on the field scale. The fluxes obtained with the two methods showed a very good agreement indicating a minimal disturbance of the chambers on the physiological activity of the enclosed vegetation.

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50

Pape, L., C. Ammann, A. Nyfeler-Brunner, C. Spirig, K. Hens e F. X. Meixner. "An automated dynamic chamber system for surface exchange measurement of non-reactive and reactive trace gases of grassland ecosystems". Biogeosciences 6, n. 3 (18 marzo 2009): 405–29. http://dx.doi.org/10.5194/bg-6-405-2009.

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Abstract (sommario):

Abstract. We present an automated dynamic chamber system which is optimised for continuous unattended flux measurements of multiple non-reactive and reactive trace gases on grassland ecosystems. Main design features of our system are (a) highly transparent chamber walls consisting of chemically inert material, (b) individual purging flow units for each chamber, and (c) a movable lid for automated opening and closing of the chamber. The purging flow rate was chosen high enough to keep the mean residence time of the chamber air below one minute. This guarantees a proven efficient mixing of the chamber volume and a fast equilibration after lid closing. The dynamic chamber system is able to measure emission as well as deposition fluxes of trace gases. For the latter case, the modification of the turbulent transport by the chamber (compared to undisturbed ambient conditions) is quantitatively described by a bulk resistance concept. Beside a detailed description of the design and functioning of the system, results of field applications at two grassland sites are presented. In the first experiment, fluxes of five trace gases (CO2, H2O, NO, NO2, O3) were measured simultaneously on small grassland plots. It showed that the dynamic chamber system is able to detect the characteristic diurnal cycles with a sufficient temporal resolution. The results also demonstrated the importance of considering the chemical source/sink in the chamber due to gas phase reactions for the reactive compounds of the NO-NO2-O3 triad. In a second field experiment, chamber flux measurements of CO2 and methanol were compared to simultaneous independent eddy covariance flux measurements on the field scale. The fluxes obtained with the two methods showed a very good agreement indicating a minimal disturbance of the chambers on the physiological activity of the enclosed vegetation.

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