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Steam-Assisted Cracking of n-Dodecane in a Packed-Bed Reactor for Hypersonic Thermal Management

JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 2021年第4期35卷 696-707页

作者： Smith, Bradley J. Ervin, Jamie S. Reitz, Thomas L. Univ Dayton Mech & Aerosp Engn Dayton OH 45469 USA US Air Force Res Lab Wright Patterson AFB OH 45433 USA

Heat removal capacity of catalytically cracked supercritical n-dodecane as a jet fuel analogue in a cylindrical packed-bed reactor is examined. Fuel cracking is endothermic, and can be used in designing a potential hypersonic vehicle thermal management system. In this work, n-dodecane endotherm and product distributions were examined using a platinum catalyst on a ceramic support matrix. Although many previous fuel studies have used catalyst coated tubes, this study made use of a solid catalyst structure in a packed bed to distribute the catalyst throughout the fuel flow in order to provide more surface catalyst sites. The packed-bed reactor was treated as an ideal plug flow reactor, which assumes catalytic reactions that are radially uniform across the reactor diameter. Additionally, water was added to study its mitigation effect on coke formation and deposition on the reactor catalyst. Many previous jet fuel studies have either used a catalyst to aid in endothermic thermal management or have focused on water addition to reduce coke formation. This study combines these approaches. A catalyst is used to initiate endothermic reactions at lower temperatures than would ordinarily be achieved by thermal cracking alone, in conjunction with steam addition to mitigate coking. The packed-bed catalyst configuration provides catalytic action even as temperatures increase and thermal cracking becomes dominant, thereby enhancing the chemical heat sink. Water addition also provided coking mitigation, although with an associated decrease in dodecane conversion, and, hence, heat sink capability.

关键词： Thermal Management Catalysis Heat Exchangers Vehicle Thermal Management Jet Fuel Endothermic Reactions Heat of Formation Surface Thermocouples Fuel Pyrolysis simple algorithm

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Manninen's mixture model for conjugate conduction and mixed convection heat transfer of a nanofluid in a rotational/stationary circular enclosure

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INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW 2021年第5期31卷 1662-1694页

作者： Hoseininejad, Faraz Dinarvand, Saeed Yazdi, Mohammad Eftekhari Islamic Azad Univ Cent Tehran Branch Dept Mech Engn Tehran Iran

Purpose This study aims to investigate numerically the problem of conjugate conduction and mixed convection heat transfer of a nanofluid in a rotational/stationary circular enclosure using a two-phase mixture model. Design/methodology/approach Hot and cold surfaces on the wall or inside the enclosure (heater and cooler) are maintained at constant temperature ofT(h)andT(c), respectively, whereas other parts are thermally insulated. To examine the effects of various parameters such as Richardson number (0.01 = Ri =100), thermal conductivity ratio of solid to base fluid (1 =K-r= 100), volume fraction of nanoparticle (0 = phi = 0.05), insertion of conductive covers (***) around the heater in a different shape (triangular, circular or square), segmentation and arrangement of the conductive blocks (***) and rotation direction of the enclosure on the flow structure and heat transfer rate, two-dimensional equations of mass, momentum and energy conservation, as well as volume fraction, are solved using finite volume method and Semi-Implicit Method for Pressure Linked Equations (simple) algorithm. Findings The results show that inserting C.C around heater can increase or decrease heat transfer rate, and it depends on thermal conductivity ratio of solid to pure fluid. Also, it is found that by the division of C.B and location of its portions in a horizontal configuration, heat transfer rate reduces. Moreover, it is observed that external heating and cooling of the enclosure causes enhancement of heat transfer relative to that of internal heating and cooling. Finally, results illustrate that under the condition that cylinders rotate in the same direction, the heat transfer rate increases as compared to those that rotate in the opposite direction. Hence rotation direction of cylinders can be used as a desired parameter for controlling heat transfer rate. Originality/value A comprehensive report of results for the problem of conjugate conduction and mixed convection heat transf

关键词： simple algorithm Conductive blocks Conjugate conduction and mixed convection Manninen's two-phase model Rotational stationary circular enclosure

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The assessment of two different pollutants dispersion from a coal-fired power plant for various thermal regimes

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JOURNAL OF ENVIRONMENTAL HEALTH SCIENCE AND ENGINEERING 2021年第1期19卷 959-983页

作者： Issakhov, Alibek Mashenkova, Albina al Farabi Kazakh Natl Univ Alma Ata Kazakhstan Kazakh British Tech Univ Alma Ata Kazakhstan

In this study, numerical simulations of the movement and emissions dispersion of two pollutants (sulfur dioxide(SO2) and carbon dioxide(CO2)) into the atmospheric boundary layer were considered under natural atmospheric conditions. To test the numerical algorithm and to select the optimal turbulent model, the test problem was solved numerically. The obtained computational data were compared with measurement data and values from the computation of other authors and the SST k-omega model illustrated the closest values to the data from the experiment, this is achieved by modifying the boundary condition for turbulent kinetic energy. The tested computational algorithm was used to characterize the emissions process of two pollutants from two chimneys of the Ekibastuz SDPP and the distribution of CO2 and SO2 in the air flow field in natural air condition. For this task, four various velocity variations were considered, as well as several various thermal variations (temperature inversion, constant temperature and decreasing temperature by the height). From the obtained computational results, it should be noticed that different environmental temperature conditions extremely impact the distribution of pollutants CO2 and SO2 in the atmospheric surface layer, so at constant temperature conditions, the species for all velocity variations have nearly identical species profile.

关键词： CO2 and SO2 pollutants dispersion simple algorithm Jet in crossflow Reynolds averaged Navier-Stokes (RANS) Different thermal regimes

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Modeling of Coupled Heat and Mass Transfer in a Trapezoidal Porous Bed on a Grid

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Open Journal of Fluid Dynamics 2023年第1期13卷 1-15页

作者： Kokou N’Wuitcha Gagnon Koffi Apedanou Yendoubé Lare Kossi Napo Laboratoire sur l’Energie Solaire Groupe Phénomènes de Transfert et Energétique (LES-GPTE) Faculté des Sciences Université de Lomé Lomé Togo Laboratoire sur l’Energie Solaire Chair Unesco Faculté des Sciences Université de Lomé Lomé Togo

We investigate heat and mass transfer in an isosceles trapezoidal cavity, filled with charcoal considered as a granular porous medium. The Darcy-Brinkman-Forchheimer flow model is coupled to the energy and mass equations with the assumption of non-thermal equilibrium. These equations are discretized by the finite volume method with an offset mesh and then solved by the line-by-line method of Thomas. The coupling between pressure and velocity is obtained by Semi-Implicit Method for Pressure Linked Equations. (simple) algorithm. The results show that the temperature in the cavity increases when the inclination angle of the sides walls decreases. The 15° inclination is selected as being able to offer better thermal performance in the cookstove combustion chamber.

关键词： Heat and Mass Transfer Isosceles Trapezoidal Cavity Porous Medium Finite Volume Method simple algorithm

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Numerical Study of Viscoplastic Flows Using a Multigrid Initialization algorithm

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algorithmS 2023年第1期16卷 50-50页

作者： Maazioui, Souhail Kissami, Imad Benkhaldoun, Fayssal Ouazar, Driss Mohammed VI Polytech Univ Modeling Simulat & Data Anal MSDA Lot 660-Hay Moulay Rachid Ben Guerir 43150 Morocco Univ Sorbonne Paris Nord LAGA UMR 7539 F-93430 Villetaneuse France Mohammed V Univ Rabat Mohammadia Sch Engn Dept Civil Engn Hydraul Syst Anal Lab Rabat 10090 Morocco

In this paper, an innovative methodology to handle the numerical simulation of viscoplastic flows is proposed based on a multigrid initialization algorithm in conjunction with the simple procedure. The governing equations for incompressible flow, which consist of continuity and momentum equations, are solved on a collocated grid by combining the finite volume discretization and Rhie and chow interpolation for pressure-velocity coupling. Using the proposed solver in combination with the regularization scheme of Papanastasiou, we chose the square lid-driven cavity flow and pipe flow as test cases for validation and discussion. In doing so, we study the influence of the Bingham number and the Reynolds number on the development of rigid areas and the features of the vortices within the flow domain. Pipe flow results illustrate the flow's response to the stress growth parameter values. We show that the representation of the yield surface and the plug zone is influenced by the chosen value. Regarding viscoplastic flows, our experiments demonstrate that our approach based on using the multigrid method as an initialization procedure makes a significant contribution by outperforming the classic single grid method. A computation speed-up ratio of 6.45 was achieved for the finest grid size (320 x 320).

关键词： viscoplastic flows simple algorithm multigrid finite volume method Navier-Stokes equations

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Combustor Development and Performance Analysis for Recuperated Microturbine Application

Combustor Development and Performance Analysis for Recuperat...

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AIAA Propulsion and Energy Forum / IEEE Electric Aircraft Technologies Symposium (EATS)

作者： Liu, Yize Nikolaidis, Theoklis Gamil, Abdelaziz Madani, Seyed Hossein Sarkandi, Mohammad Cranfield Univ Cranfield MK43 0AL Beds England Samad Power Ltd Milton Keynes MK11 3JB Bucks England

ISBN: (数字)9781624106118

ISBN: (纸本)9781624106118

In recent years, increased attention is paid to the microturbine MGT as a promising technology for combined heat and power (CHP) applications. An MGT has advantages of high reliability, high efficiency, lower manufacturing and maintenance costs, reduced vibration and noise levels, and clean emissions. Recuperation can further increase efficiency by recycling the heat from the turbine exhaust and preheating the air for combustion via a heat exchanger. Such a system will be realized by designing a combustion chamber that can meet various design and operability requirements. This paper presents an overview of the combustor development and provides CFD analysis on combustor performance and emissions. A single tubular combustor is designed, and the direct injection mode is applied to mitigate the autoignition and flashback risks resulting from the high preheating temperature. Heat transfer and cooling analysis indicate that ceramic liner is capable of tolerating high temperature using effusion cooling. Studies of flow characteristics, temperature field, pressure loss, and pattern factor are provided in detail. The effects of design parameters and methods (i.e., fuel-air mixture strength, cooling hole angles, dilution hole design approaches) are also discussed. Finally, the use of biomass is investigated and shows that it has the potential to achieve a high combustion efficiency and low emissions for the recuperated microturbine application.

关键词： Gas Turbine Combustor Combustor Design Flamelet Generated Manifold Combustion Chambers Heat Transfer Analysis Fuel Air Mixture Renewable Energy Heat Exchangers Thermodynamic Properties simple algorithm

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Numerical study of the thermo-energy of a tubular heat exchanger with longitudinal baffles 4

Numerical study of the thermo-energy of a tubular heat excha...

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4th International Conference on Materials and Environmental Science (ICMES)

作者： Salhi, Jamal-Eddine Zarrouk, Tarik Salhi, Najim First Mohammed Univ Lab Mech & Energy Fac Sci Oujda 60000 Morocco

The work undertaken in this paper presents a computational study of the flow and heat transfer characteristics in a tubular heat exchanger with longitudinal baffles attached to its inner wall, which is maintained at a constant temperature Tw = 343 k. This study is carried out for a Reynolds number, Re ranging from 2 x 104 to 3 x 104, and was devoted first to the case of a smooth tube (without baffles), then to the case of a tube provided with longitudinal baffles of rectangular cross-section, and finally to the case of a tube provided with longitudinal baffles of triangular cross-section. The system of equations governing the thermohydraulic phenomenon consists of the continuity equation (for mass conservation), the NavierStokes equations (for momentum conservation), and the first principle equation (for energy conservation). The system of equations thus formulated is a hyperbolic system, which has been solved numerically over the entire domain, using the finite volume approach for its discretization, and the two-equation model (K-e) for the modeling of turbulence terms. The simple algorithm is thus used to overcome the problem of velocity-pressure coupling. To meet the needs of aerothermal users. The two fields, thermal and aerodynamic, were analyzed, the friction factor, the Nusselt number, and the thermal efficiency. Finally, the study undertaken was finalized by comparative analysis to identify the relevant parameters in the aerothermal phenomenon and deduce the optimal form to be proposed to aerothermal energy users. The results obtained show that the longitudinal inclusion of the rectangular section baffles improves the thermal performance by 32.37% for the triangular section, and by 44.37% for the case of rectangular section baffles. (c) 2021 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the Fourth edition of the International Conference on Materials & Environmental Science.

关键词： simple algorithm Baffle Nusselt number Heat transfer Cfd Friction factor

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Numerical simulation of lid driven flow based on finite volume method 23

Numerical simulation of lid driven flow based on finite volu...

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Proceedings of the 2023 4th International Conference on Machine Learning and Computer Application

作者： Lishan Jia Qingyi Mo School of Aeronautical Engineering Civil Aviation University of China China

ISBN: (纸本)9798400709449

At present, the computing power of computers has been greatly improved, which has led to the rapid development of computational fluid dynamics (CFD) technology. Computational fluid dynamics technology is widely used in fluid research work, so CFD software has played a huge role in solving problems such as fluid flow and heat transfer, successfully applied in various fields of science and technology. In this paper, to understand the computational principle of the mainstream CFD software in the simulation of fluid, aiming at the two-dimensional steady-state convective diffusion problem, taking the classical lid driven flow in computational fluid mechanics as an example, the analysis includes the establishment of the fluid governing equation by the finite volume method on the staggered grid to discretize the governing equation. At the same time, by using the simple algorithm to solve the discrete control equation, the simulation of the lid driven flow field is realized by programming. The simulation results are in line with reality, and the accuracy and reliability of the algorithm are tested. It provides a reference for understanding the principle of fluid simulation by CFD software and developing more efficient and accurate digital simulation methods on this basis.

关键词： CFD Finite volume method Lid driven flow simple algorithm Staggered grid

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The effect of using multichannel twisted tape and nanofluid on the absorber tube's heat transfer and the efficiency of a linear parabolic solar collector

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SUSTAINABLE ENERGY TECHNOLOGIES AND ASSESSMENTS 2022年第PartD期52卷

作者： Mustafa, Jawed Alqaed, Saeed Sharifpur, Mohsen Husain, Shahid Najran Univ Coll Engn Mech Engn Dept POB 1988 Najran 61441 Saudi Arabia Univ Pretoria Dept Mech & Aeronaut Engn Pretoria South Africa China Med Univ China Med Univ Hosp Dept Med Res Taichung Taiwan Aligarh Muslim Univ Dept Mech Engn Zakir Husain Coll Engn & Technol Aligarh 202002 Uttar Pradesh India

One of the most important tools for using solar energy is parabolic solar collectors (SCs). To improve the performance of these collectors, creating rotation in the fluid flow by placing twisted tape or helical paths inside the tube is an effective passive method. In this study, the role of three-and four-channel twisted tapes in increasing the rate of heat transfer (RHT) inside the collector adsorbent tube containing water-copper oxide nanofluid and its effect on energy and exergy efficiencies has been investigated numerically. Finite volume method, simple algorithm and SST k-w turbulence model for solving the equations. The study was conducted for Re = 20000-80000. Numerical results indicated that the highest Nusselt number was related to nanofluids with a volume fraction of 4% in Reynolds number of 80,000, equal to 54.7. Furthermore, the highest coefficient of thermal performance of three-channel twisted tape occurs in Reynolds of 80,000 with a volume fraction of 4%. Moreover, the best efficiency of SCs is related to nanofluid flow with Reynolds of 80,000 and volume fraction of 4%, which is equal to 26%. Furthermore, nanofluid with a volume fraction of 4% has the highest exergy efficiency.

关键词： Solar collector Nanofluid Turbulence Multichannel twisted tape simple algorithm SST k-w model

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Numerical simulation of separated flow past a square cylinder based on a two-fluid turbulence model

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JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 2022年 231卷

作者： Malikov, Z. M. Madaliev, M. E. Acad Sci Uzbek Inst Mech & Seism Stabil Struct Fergana Uzbekistan Ferghana Polytech Inst Fergana Uzbekistan

The paper presents the numerical results of the transverse flow around an infinite square beam based on the twofluid turbulence model for the Reynolds number Re = 21400. This problem has a periodic solution, so the nonstationary system of equations of the turbulence model was solved. For the difference approximation of the initial equations, the control volume method and the computational grid arranged in a checkerboard pattern were used. Coarse, fine, and condensed computational grids were used in the work. Their influence on the numerical results is shown. The simple procedure was applied to correct the velocity through pressure. For the numerical implementation of the equations of the two-fluid model, the two-step Peaceman-Rachford scheme was used. In the work, instantaneous and averaged results for longitudinal and transverse velocities, pressure, pressure coefficient and turbulent stresses are obtained. These results are presented in the form of profiles, as well as in the form of dependences on time and distance in the longitudinal direction. The instantaneous and averaged flow patterns are also presented. The obtained numerical results are compared with the experimental data and the results of other known turbulent models. It is shown that the two-fluid model describes this turbulent flow well.

关键词： Navier Stokes equations Separated flow Control volume method Two-fluid model simple algorithm

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