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Turbulent Multiphase Flows with Heat and Mass Transfer von Borghi, Roland (eBook)

  • Erscheinungsdatum: 11.12.2013
  • Verlag: Wiley-ISTE
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Turbulent Multiphase Flows with Heat and Mass Transfer

Numerous industrial systems or natural environments involve multiphase flows with heat and mass transfer. The authors of this book present the physical modeling of these flows, in a unified way, which can include various physical aspects and several levels of complexity. Thermal engineering and nuclear reactors; the extraction and transport of petroleum products; diesel and rocket engines; chemical engineering reactors and fluidized beds; smoke or aerosol dispersion; landslides and avalanches − the modeling of multiphase flows with heat and mass transfer for all these situations can be developed following a common methodology. This book is devoted to the description of the mathematical bases of how to incorporate adequate physical ingredients in agreement with known experimental facts and how to make the model evolve according to the required complexity. Contents Part 1. Approach and General Equations 1. Towards a Unified Description of Multiphase Flows. 2. Instant Equations for a Piecewise Continuous Medium. 3. Description of a "Mean Multiphase Medium". 4. Equations for the Mean Continuous Medium. Part 2. Modeling: A Single Approach Adaptable to Multiple Applications 5. The Modeling of Interphase Exchanges. 6. Modeling Turbulent Dispersion Fluxes. 7. Modeling the Mean Gas–Liquid Interface Area per Unit Volume. 8. "Large Eddy Simulation" Style Models. 9. Contribution of Thermodynamics of Irreversible Processes. 10. Experimental Methods. 11. Some Experimental Results Pertaining to Multiphase Flow Properties that Are Still Little Understood. Part 3. From Fluidized Beds to Granular Media 12. Fluidized Beds. 13. Generalizations for Granular Media. 14. Modeling of Cauchy Tensor of Sliding Contacts. 15. Modeling the Kinetic Cauchy Stress Tensor. Part 4. Studying Fluctuations and Probability Densities 16. Fluctuations of the Gas Phase in Reactive Two-Phase Media. 17. Temperature Fluctuations in Condensed Phases. 18. Study of the PDF for Velocity Fluctuations and Sizes of Parcels. About the Authors Roland Borghi is Professor Emeritus at Ecole Centrale Marseille in France and works as a consultant in the space, petrol and automobile sectors. His research activities cover fluid mechanics, combustion and flames, and multi-phase and granular flows. He was a member of the CNRS scientific committee and a laureate of the French Academy of Science. Fabien Anselmet is Professor at Ecole Centrale Marseille in France. His research activities focus on the turbulence of fluids and its varied applications in industry and in fields linked to the environment. With a unified, didactic style, this text presents tangible models of multiphase flows with heat and mass transfer with attention to various levels of complexities. It addresses thermal engineering and nuclear reactors, extraction and transport of petroleum products, diesel engines and rocket engines, chemical engineering reactors and fluidized beds, smoke or aerosol dispersion, and landslides and avalanches. Engineers, researchers, and scientists will appreciate the discussions of modeling principles, flows and granular media, and fluctuations around averages.

Produktinformationen

    Format: ePUB
    Kopierschutz: AdobeDRM
    Seitenzahl: 320
    Erscheinungsdatum: 11.12.2013
    Sprache: Englisch
    ISBN: 9781118790199
    Verlag: Wiley-ISTE
    Serie: ISTE
    Größe: 19803 kBytes
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Turbulent Multiphase Flows with Heat and Mass Transfer

Introduction

I.1. The significance of multiphase flows and their modeling

Many industrial systems bring into play, in one way or the other, multiphase media involving the combination of liquids and gases, non-miscible liquids, fluids and solids.

Nuclear reactors (whether they use boiling or pressurized water) possess a cooling circuit where, in certain parts of this circuit, a mixture of water and vapor circulates, with water vapor forming on contact with hot walls needing to be cooled and drops of liquid water forming on contact with cold walls needing to be heated. Numerous other thermal engineering facilities possess this type of circuit for transferring heat, in order either to use this energy elsewhere or simply to prevent the machinery from being destroyed by the heat.

The extraction and transportation of oil products is done using conduits within which media are flowing with two or more phases: liquids of different densities and viscosities, gases and even solids. Problems of icing in aeronautics (on the leading edges of wings or ailerons or in Pitot tubes, etc.) also necessitate studying a humid air medium with drops of water flowing in the immediate vicinity of the wall. The short-distance transport of pulverulent materials such as wheat, sawdust and grain is done by blowing air loaded with these solid particles through ducts.

In liquid-fuel rocket engines used in space launchers, as well as in diesel engines, the combustion chamber contains a mixture of vaporizing droplets and combusting gases that give off a considerable release of heat in an astonishingly small volume. A combustible or oxidant liquid, or a mixture of both, is injected in tiny droplets into the combustion chamber, where these drops vaporize and the vapors can burn together, in a steady regime in a rocket engine and in a periodic regime in cycles of a diesel engine.

Fuel burners in glassworks furnaces, or vapor generators in thermal power stations, also inject jets of droplets of fuel into the zone of reacting gases. They produce not only heat and burned gases, but also smoke in which very small particles of carbon are dispersed, and the control of these particles is critical; they allow high heat transfers via radiation in furnaces, but can lead to significant air pollution from chimney exhaust.

Chemical engineering uses several types of gas - liquid reactors at controlled temperature, which are intended to produce specific chemical products rather than heat. Liquid and gaseous reactants are mixed as effectively as possible in order to be able to allow various chemical reactions at the interface between phases. Many chemical reactors also use a catalyst, which is most often in the form of a solid dispersed phase, and these reactors therefore bring multiphase flows into play.

Fluidized beds are currently the most effective devices for burning coal: air is blown forcefully through a highly dense dispersed solid phase composed of particles of dolomite and small particles of coal, enabling exchanges of energy among these three phases, which then causes and maintains chemical reactions. The energy released by combustion produces water vapor by the intermediary of a heat exchanger, the tubes of which can be closer to the combustion zone. The system not only enables adequate homogeneity of the temperature field but also maintains this temperature at around 1,300 K by a voiding the overproduction of NO, while stabilizing combustion at the same time. In addition, dolomite absorbs sulfur and reduces SO2 emissions. There are also recirculating fluidized beds in which solid phases are entrained by the gas phase, recovered at the exit and reinjected at the entry to perfect combustion, even in the highest mass flow rate conditions. These are also easily transposable for the combustion of different types of combustibles, ranging from gas mixtures to various types of waste. Fluidized b

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