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5487 results in Thermal-fluids engineering

Page 77 of 275

  • 1 - Thermodynamic and Single-Phase Flow Fundamentals

  • from Part One - Two-Phase Flow
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 3-37

  • Summary

    Fundamentals of thermodynamics and single-phase flows are reviewed. Equilibrium phase diagrams for pure substances and binary fluid mixtures, and metastable states for pure liquids and vapors are discussed. The transport equations and closure relations for single phase flows are presented. Thermodynamic properties of vapor-noncondensable mixtures, and transport properties of pure substances and fluid mixtures are discussed. Gaskinetic theory-based methods for the estimation of transport properties of ideal gases are presented. The universal turbulent boundary layer velocity and temperature profiles are reviewed. Convective heat and mass transfer are then discussed, including the effects of transpiration. Nine solved example problems, and ten end-of-chapter problems are provided.

  • 17 - Choking in Two-Phase Flow

  • from Part Two - Boiling and Condensation
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 643-677

  • Summary

    Physical phenomena in a choked flow are explained. Velocity of sound and critical discharge rate in single-phase flows are derived. Generic expressions are derived for velocity of sound and critical discharge in homogeneous two-phase flows and flows with velocity slip. The derivation details of widely used critical discharge models, including include the homogeneous-equilibrium isentropic model, the models of Moody (1965) and Henry and Fauske (1971), are reviewed. The RETRAN code’s empirical curve fits to the predictions of the latter three models for critical discharge of water are presented. The Omega Parameter Method (OPM), a simple and fast technique for estimation of critical discharge based on homogeneous-equilibrium flow assumption, is discussed. Choked flow is small flow passages, cracks and slits, is discussed. Non-equilibrium mechanistic modeling of choked two-phase flow, a technique based on iterative numerical solution of 1D conservation equations and searching for choking conditions, is discussed. Five solved example problems and 15 end-of-chapter problems are provided.

  • 4 - Two-Phase Flow Regimes – I

  • from Part One - Two-Phase Flow
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 135-161

  • Summary

    Two-phase flow regimes, and empirical flow regime prediction methods and flow regime maps are discussed in this chapter. The major two-phase flow regimes in adiabatic vertical and horizontal flow passages are described. Classical flow regime maps, including the flow regime maps of Hewitt and Roberts (1969), Baker (1954), and Mandhane et al. (1974) are presented and discussed. Flow regimes in rod bundles are reviewed, and flow regime prediction methods in thermal hydraulics codes that are used for the simulation of nuclear reactor coolant systems are discussed. The flow regime transition models of the RELAP5-3D computer code are presented. Two-phase flow regimes in curved flow passages are discussed. Two-phase flow regimes and their hydrodynamic aspects in helicoidally coiled flow passages are discussed in detail, in view of the increasing application of such flow passages in heat evaporators and steam generators. Nine end-of-chapter problems are provided.

  • 16 - Internal-Flow Condensation and Condensation on Liquid Jets and Droplets

  • from Part Two - Boiling and Condensation
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 590-642

  • Summary

    Flow regimes in condensing flows, and widely used flow regime maps are discussed. Empirical correlations for important regime transitions are presented. Widely-used pure-vapor condensation heat transfer correlations are discussed for vertical and horizontal passages. Models for condensation in horizontal pipes are reviewed. The effect of noncondensables on condensation heat transfer is discussed. Direct contact condensation is discussed, and widely-used models for condensation on subcooled liquid jests and droplets are reviewed. Mechanistic models for condensation in annular flow regime are reviewed. Flow regimes and pressure drop in minichannels and microchannels are reviewed. Condensation heat transfer in small channels is discussed, and several widely-referenced predictive methods are reviewed. Condensation in helically coiled flow passages, and relevant empirical correlations are discussed. The physics of internal flow condensation of binary vapor mixtures are discussed, and a method for the solution of the relevant 1D conservation equations based on the Couettere flow film model is demonstrated. Eight solved example problems and 20 end-of-chapter problems are provided.

  • 5 - Two-Phase Flow Modeling

  • from Part One - Two-Phase Flow
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 162-198

  • Summary

    Two-phase flow model transport equations are discussed. Local-instantaneous single-phase conservation equations and interfacial balance relations are presented in general mathematical forms. We then focus on 1D flows, and principles of flow area-averaging are reviewed. Using a simple and heuristic approach based on applying mass, momentum and energy balances on a slice of a flow channel, tractable model conservation equations are derived. These include mass, momentum, and energy conservation equations for homogeneous-equilibrium two-phase flow model; and phasic (i.e., separately for gas and liquid phases) mass, momentum and energy conservation equations for separated flow (two-fluid) model. The conservation equations are first derived for pure (single component) fluids, and are then expanded to two-component fluids. The interfacial processes (heat, mass, momentum transfer, virtual mass effect) are discussed for the separated-flow model. Two-fluid model equations for multi-dimensional flows are presented, followed by a simple method for the numerical solution of steady, 1D conservation equations. Three solved example problems and 14 end-of-chapter problems are provided.

  • 3 - Two-Phase Mixtures, Fluid Dispersions, and Liquid Films

  • from Part One - Two-Phase Flow
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 96-134

  • Summary

    Liquid-gas two phase mixtures, dispersions of small particles of one fluid in another, and the behavior of liquid films are discussed. The mathematical bases of time, volume, flow area, and composite averaging of two-phase flow properties are reviewed. Mixture and phase average properties are discussed. Flow area-averaged properties are presented, including void fraction, phase-intrinsic and superficial velocities, slip ratio, and thermodynamic properties. The hydrodynamic phenomena in a highly turbulent flow field that contains microparticles of one phase suspended in another fluid are discussed. The Kolmogorov theory of small turbulence scales is presented, followed by the discussion of the break-up and coalescence phenomena of suspended fluid micro particles. Size classification for flow passages is discussed, and various widely-used criteria for the definition of conventional, mini and microchannels are presented. The hydrodynamics and transport phenomena in falling liquid films are discussed, and useful empirical correlations for both laminar and turbulent films are presented. Six solved example problems, and 13 end-of-chapter problems are provided.

  • 12 - Flow Boiling

  • from Part Two - Boiling and Condensation
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 404-471

  • Summary

    Two-phase flow regimes, and boiling flow regimes in vertical and horizontal heated flow passages are first reviewed and discussed. Flow patterns and heat transfer in subcooled boiling are discussed, and mechanistic models as well as empirical correlations for onset of nucleate boiling (ONB) and onset of significant void (OSB), also referred to as net vapor generation (NVG), are discussed. Several widely used correlations for nucleate boiling are presented and discussed. Hydrodynamic aspects and pressure drop in subcooled flow boiling are discussed, followed by a review of partial boiling regime and empirical correlations for fully developed subcooled and saturated boiling heat transfer. Two-phase flow instability in flow boiling systems is reviewed, and several instability mechanisms are discussed. Flow boiling of binary liquid mixtures is reviewed and several widely used methods for the prediction of boiling heat transfer coefficients in binary liquid mixtures are presented. Flow boiling in helically coiled flow passages is reviewed and several relevant correlations are presented. Seven solved example problems and 26 end-of-chapter problems are provided.

  • 11 - Pool Boiling

  • from Part Two - Boiling and Condensation
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 357-403

  • Summary

    The pool boiling curve and pool boiling regimes are discussed. Heterogeneous bubble nucleation, bubble ebullition process (bubble waiting and growth periods, bubble departure) are reviewed and important relevant models are discussed. Several heat transfer correlations for nucleate boiling regime are reviewed. The hydrodynamic theory of boiling is discussed and related models for critical heat flux, minimum film boiling temperature, and film boiling on horizontal surfaces are presented and discussed. Predictive methods for film boiling on vertical surfaces and horizontal cylinders are presented. Pool boiling in binary liquid mixtures is reviewed. The physical processes involved in boiling of zeotropic mixtures, which render the boiling heat flux in such mixtures to be lower than pure liquids, are discussed. Several widely-used correlation for nucleate boiling heat transfer in binary liquid mixtures are reviewed. Critical heat flux in binary liquid mixtures is also discussed, and several method for the prediction of critical heat flux are reviewed. Five solved example problems and 12 end-of-chapter problems are provided.

  • 2 - Gas–Liquid Interfacial Phenomena

  • from Part One - Two-Phase Flow
  • S. Mostafa Ghiaasiaan, Georgia Institute of Technology
  • Book:
    Two-Phase Flow, Boiling, and Condensation
    Published online:
    01 February 2019
    Print publication:
    11 January 2017, pp 38-95

  • Summary

    Gas-liquid interfacial phenomena are discussed. Surface tension and its relation to interfacial pressure jump are discussed, and static and dynamic contact angles are reviewed. Interfacial force balance and the effect of surface tension nonuniformity are then briefly discussed, followed by a discussion of thermocapillary effect and the role of disjoining pressure in thin liquid films. Mass transfer phenomena at a liquid-gas interphase are discussed, including the predictions of kinetic theory for evaporation and condensation of pure substances. Interfacial equilibrium and transport of sparingly soluble gases are discussed. Semi-empirical treatment of interfacial heat and mass transfer, and the application of convective heat and mass transfer coefficients are discussed. Linear instability and interfacial waves are discussed. Rayleigh-Taylor and Kelvin-Helmholtz instabilities, and instability of gaseous jets are then derived and discussed. Waves at the surface of small bubbles and droplets, and the growth of small vapor bubbles surrounded by superheated liquids are reviewed. Seven solved example problems, and 19 end-of-chapter problems are provided.

Page 77 of 275