Fluid Mechanics Aspects of Fire and Smoke Dynamics in Enclosures

Description

This book provides essential understanding of flows in fire and smoke dynamics in enclosures, covering combustion, heat transfer and fire suppression in more detail than other introductory books. It moves from the basic equations for turbulent flows with combustion, through a discussion of the structure of flames, to fire and smoke plumes and their interaction with enclosure boundaries. This is then applied to fire dynamics and smoke and heat control in enclosures. This new edition provides considerably more on the fluid mechanics of the effect of water, and on fire dynamics modelling using Computational Fluid Dynamics. Presents worked examples taken from practical, everyday fire-related problems Covers a broad range of topics, from the basics to state-of-the-art computer simulations of fire and smoke-related fluid mechanics, including the effect of water Provides extensive treatment of the interaction of water sprays with a fire-driven flow Contains a chapter on Computational Fluid Dynamics, the increasingly popular calculation method in the field of fire safety science The book serves as a comprehensive guide at the undergraduate and starting researcher level on fire and smoke dynamics in enclosures, with an emphasis on fluid mechanics. Cover Half Title Title Page Copyright Page Table of Contents Preface Authors Chapter 1 Introduction 1.1 The Candle Flame 1.2 The Importance of Chemistry, Heat Transfer and Fluid Mechanics in Fires 1.2.1 Chemistry 1.2.2 Heat Transfer 1.2.2.1 Flame, Smoke Plume and Surroundings 1.2.2.2 Heat Transfer at the Level of the Fuel Surface 1.2.2.3 Enclosure Effect on Heat Transfer 1.2.3 Fluid Mechanics and Turbulence 1.3 Combustion and Fire 1.4 Fire Modelling References Chapter 2 Turbulent Flows with Chemical Reaction 2.1 Fluid Properties – State Properties – Mixtures 2.1.1 Fluid Properties 2.1.1.1 Mass Density 2.1.1.2 Viscosity 2.1.1.3 Specific Heat 2.1.1.4 Conduction Coefficient 2.1.1.5 Diffusion Coefficient 2.1.2 State Properties 2.1.2.1 Pressure 2.1.2.2 Temperature 2.1.2.3 Internal Energy 2.1.2.4 Enthalpy 2.1.2.5 Entropy 2.1.2.6 Equation of State 2.1.3 Mixtures 2.2 Combustion 2.2.1 Chemical Reaction 2.2.2 Thermodynamics 2.2.2.1 Enthalpy 2.2.2.2 Temperature 2.2.3 Chemical Kinetics 2.3 Transport Equations 2.3.1 Conservation of Mass 2.3.2 Momentum Equations 2.3.3 Conservation of Energy 2.3.3.1 Convection 2.3.3.2 Conduction 2.3.3.3 Radiation 2.3.4 Transport of Species 2.3.5 Mixture Fraction 2.4 Bernoulli 2.5 Hydrostatics 2.6 Buoyancy 2.7 Non-Dimensional Numbers 2.7.1 Fluid Properties 2.7.2 Flow Properties 2.7.3 Scaling Laws 2.8 Turbulence 2.8.1 Reynolds Number 2.8.2 Reynolds Averaging 2.8.3 Turbulence Modelling 2.8.3.1 Energy Cascade 2.8.3.2 Turbulent Scales 2.8.3.3 Turbulence Modelling 2.9 Boundary Layer Flow 2.10 Internal Flows – Pressure Losses 2.11 Entrainment 2.12 Impinging Flow 2.13 Evaporation 2.14 Pyrolysis References Chapter 3 Turbulent Flames and Fire Plumes 3.1 Flammability 3.1.1 Flammability Limits – Threshold Temperature 3.1.2 Addition of Gases 3.1.3 Flammability of Liquid Fuels 3.2 Premixed Flames 3.2.1 Laminar Premixed Flame Structure 3.2.2 Laminar Burning Velocity 3.2.3 The Effect of Turbulence 3.3 Diffusion Flames 3.3.1 Laminar Diffusion Flame Structure 3.3.2 The Effect of Turbulence 3.3.3 Jet Flames 3.4 Extinction of Flames 3.4.1 Premixed Flames 3.4.2 Diffusion Flames 3.5 Fire Plumes 3.5.1 Free Fire Plumes 3.5.1.1 Average Flame Height 3.5.1.2 Temperature Evolution 3.5.1.3 Kelvin–Helmholtz Instability 3.5.1.4 The Effect of Wind 3.5.1.5 Transition from Buoyancy-Driven to Momentum-Driven Jets 3.5.1.6 Correlations 3.5.2 Interaction with Non-Combustible Walls 3.5.3 Interaction with Non-Combustible Ceiling 3.5.4 The Effect of Ventilation 3.5.4.1 Reduced Oxygen at Ambient Temperature 3.5.4.2 Oxygen-Enriched Fire Plumes 3.5.4.3 Vitiated Conditions 3.5.5 Fire Whirls 3.6 Flame Spread 3.6.1 Flame Spread Velocity – a Heat Balance 3.6.1.1 Opposed Flow Flame Spread over a Thermally Thick Fuel 3.6.1.2 Opposed Flow Flame Spread over a Thermally Thin Fuel 3.6.1.3 Concurrent Flow Flame Spread over a Thermally Thick Fuel 3.6.1.4 Concurrent Flow Flame Spread over a Thermally Thin Fuel 3.6.2 Gas-Phase Phenomena 3.6.3 Horizontal Surface 3.6.3.1 Natural Convection 3.6.3.2 Concurrent Airflow 3.6.3.3 Counter-Current Airflow 3.6.4 Vertical Surface 3.6.5 Inclined Surface 3.6.6 Parallel Vertical Plates Configuration 3.6.7 Corner Configuration References Chapter 4 Smoke Plumes 4.1 Introduction 4.2 Axisymmetric Plume 4.2.1 Theory and Mathematical Modelling 4.2.1.1 Description of the Configuration 4.2.1.2 Conservation Equations of Mass, Momentum and Energy 4.2.1.3 Model Development under the Boussinesq Approximation 4.2.1.4 List of Assumptions 4.2.2 Experiments 4.2.2.1 Hot Air Plumes 4.2.2.2 Smoke Plumes from Fires 4.3 Line Plume 4.3.1 Description of the Configuration 4.3.2 Conservation Equations 4.3.3 Experimental Studies 4.3.4 Transition from Line to Axisymmetric Plume 4.4 Wall and Corner Interaction with Plumes 4.4.1 Detailed Example: Line Plume Bounded by an Adiabatic Wall 4.4.1.1 Conservation Equations 4.4.1.2 Experiments 4.4.2 General Correlations for Wall and Corner Configurations 4.5 Interaction of a Plume with a Ceiling 4.5.1 Description of a Ceiling Jet 4.5.2 Alpert’s Integral Model 4.5.3 Simplified Correlations 4.5.3.1 Alpert 4.5.3.2 Motevalli 4.5.3.3 Heskestad and Yao 4.5.4 Additional Considerations 4.5.5 Smoke Layer Build-up in a Room 4.6 Balcony and Window Spill Plumes 4.6.1 Balcony Spill Plumes 4.6.2 Window Plumes 4.7 Scaling Laws and Buoyant Releases 4.8 Exercises 4.8.1 Analytical Solution for the Line Plume Problem 4.8.1.1 Problem Description 4.8.1.2 Suggested Solution 4.8.2 Design of a Reduced-Scale Helium/Air Mixture Experiment of a Car Fire in a Tunnel 4.8.2.1 Problem Description 4.8.2.2 Suggested Solution References Chapter 5 Fire and Smoke Dynamics in Enclosures 5.1 Some Fundamentals on Flows through Openings 5.2 Growing Fire 5.2.1 Fire Source 5.2.1.1 Fuel-Controlled Growing Fire 5.2.1.2 Ventilation-Controlled Growing Fire 5.2.2 Smoke Dynamics 5.2.3 Flows Through Openings 5.2.3.1 Horizontal Openings 5.2.3.2 Vertical Openings 5.2.4 Natural and Mechanical Ventilation 5.2.5 Zone Modelling 5.3 Fully Developed Fire 5.3.1 Fire Source 5.3.2 Smoke Dynamics 5.3.3 Flows Through Openings 5.3.3.1 Horizontal Openings 5.3.3.2 Vertical Openings 5.3.4 Natural and Mechanical Ventilation 5.3.5 Zone Modelling 5.4 Large Compartments 5.5 Fires in Well-Confined Enclosures 5.6 Backdraft References Chapter 6 Driving Forces in Smoke and Heat Control 6.1 The Importance of Fluid Mechanics 6.2 Buoyancy – The Stack Effect 6.3 Fire-Induced Buoyancy 6.4 The Effect of Wind 6.5 Pressurization 6.6 Natural Ventilation 6.7 Mechanical Ventilation 6.7.1 Vertical Ventilation 6.7.2 Horizontal Ventilation 6.7.2.1 Tunnels 6.7.2.2 Other Underground Structures 6.8 Smoke Extraction 6.9 Positive Pressure Ventilation 6.10 Air Curtains 6.11 Exercises References Chapter 7 Impact of Water on Fire and Smoke Dynamics 7.1 Individual Water Droplet 7.1.1 Droplet Dynamics 7.1.2 Mass Transfer 7.1.3 Heat Transfer 7.1.3.1 Conductivity within the Droplet 7.1.3.2 Convective Heat Transfer 7.1.3.3 Radiative Heat Transfer 7.1.3.4 Energy Balance 7.1.4 Exercises 7.2 Sprays of Water Droplets 7.2.1 Characterization of the Injection 7.2.2 Spray Angles and Shapes 7.2.3 Atomization and Break-Up 7.2.4 Angular Distribution of Water 7.2.5 Droplet Size Distribution 7.2.6 Dilute Sprays and Dense Sprays 7.2.7 Spray-Induced Momentum 7.2.8 Experimental Characterization of Water Sprays 7.3 Applications of Water Sprays and Interaction with a Fire-Driven Flow 7.3.1 Interaction with Smoke 7.3.1.1 Smoke Cooling 7.3.1.2 Smoke Logging 7.3.1.3 Smoke Blocking 7.3.2 Interaction with the Flame 7.3.2.1 Cooling the Flame Zone Directly 7.3.2.2 Dilution Effect and Inerting 7.3.2.3 Blowing Effect and Oxygen Displacement 7.3.2.4 Attenuation of Thermal Radiation Using Water Mist 7.3.3 Interaction with the Fuel 7.3.3.1 Fuel Wetting and Blanketing 7.3.3.2 Special Care with Liquid Fuels 7.3.4 Interaction with the Sprinklers: Sprinkler Skipping 7.4 Interaction of Water Sprays with Smoke and Heat Control Systems References Chapter 8 Introduction to Fire Modelling in Computational Fluid Dynamics 8.1 Introduction 8.2 Laminar Diffusion Flames 8.2.1 Instantaneous Transport Equations 8.2.2 Combustion Modelling 8.2.2.1 Infinitely Fast Chemistry 8.2.2.2 Finite-Rate Chemistry 8.3 Turbulence Modelling 8.3.1 DNS 8.3.2 RANS 8.3.2.1 Standard k - ε Model 8.3.2.2 RNG k - ε Model 8.3.2.3 Realizable k - ε Model 8.3.2.4 Cubic k - ε Model 8.3.3 LES 8.4 Turbulent Non-Premixed Combustion 8.4.1 Infinitely Fast Chemistry with a Presumed PDF 8.4.1.1 Flame Sheet Model 8.4.1.2 Chemical Equilibrium Model 8.4.1.3 Steady Laminar Flamelet Modelling (SLFM) 8.4.2 Finite-Rate Chemistry 8.4.2.1 Eddy Break-Up (EBU) Model and Eddy Dissipation Model (EDM) 8.4.2.2 Eddy Dissipation Concept (EDC) 8.4.2.3 Conditional Moment Closure (CMC) 8.4.2.4 Transported PDF Models 8.5 Radiation Modelling 8.5.1 Models for Radiative Transfer 8.5.1.1 The P-1 Radiation Model 8.5.1.2 The Finite Volume Method (FVM) 8.5.2 Models for the Absorption Coefficient 8.5.3 Turbulence Radiation Interaction (TRI) 8.6 The Soot Problem 8.6.1 Soot Nature, Morphology and General Description of Its Chemistry 8.6.2 Importance of Soot Modelling 8.6.2.1 Sootiness and Radiation 8.6.2.2 Interaction of Soot with Carbon Monoxide 8.6.3 The Sootiness of Fuels 8.6.3.1 The Laminar Smoke Point Height 8.6.3.2 The Threshold Sooting Index (TSI) 8.6.4 Soot Modelling 8.6.4.1 Laminar Flames 8.6.4.2 Detailed and Reduced Chemistry Models 8.6.4.3 Models Describing Inception, Coagulation, Surface Growth and Oxidation 8.6.4.4 The Laminar Smoke Point (LSP) Model 8.6.4.5 Fuel Conversion Model 8.6.4.6 Turbulent Flames 8.7 Basics of Numerical Discretization 8.7.1 Discretization Schemes 8.7.1.1 Description of a 1-D Example 8.7.1.2 Explicit Scheme 8.7.1.3 Implicit Scheme 8.7.2 Initial and Boundary Conditions 8.7.3 Properties of Numerical Methods 8.7.3.1 Consistency 8.7.3.2 Stability 8.7.3.3 Convergence 8.7.3.4 Conservativeness 8.7.3.5 Boundedness 8.7.4 Pressure-Velocity Coupling 8.7.5 The Importance of the Computational Mesh 8.8 Boundary Conditions 8.8.1 Fire Source 8.8.1.1 Gaseous Fuel 8.8.1.2 Liquid Fuel 8.8.1.3 Solid Fuel 8.8.1.4 Turbulence Inflow Boundary Conditions 8.8.2 Walls 8.8.2.1 Velocity 8.8.2.2 Temperature 8.8.3 Open Boundary Conditions (Natural Ventilation) 8.8.3.1 Velocity and Scalars 8.8.3.2 Pressure 8.8.4 Mechanical Ventilation and Pressure Effects 8.8.4.1 Fixed Velocity 8.8.4.2 Fan Curves and Pressure Effects 8.9 Examples of CFD Simulations 8.9.1 Non-Reacting Buoyant Plume 8.9.1.1 Test Case Description 8.9.1.2 Simulation Set-Up 8.9.1.3 Results 8.9.2 Hot-Air Plume Impinging on a Horizontal Plate 8.9.2.1 Test Case Description 8.9.2.2 Simulation Set-Up 8.9.2.3 Results 8.9.3 Free-Burning Turbulent Buoyant Flame 8.9.3.1 Test Case Description 8.9.3.2 Simulation Set-Up 8.9.3.3 Results 8.9.4 Over-Ventilated Enclosure Fire with Natural Ventilation 8.9.4.1 Test Case Description 8.9.4.2 Simulation Set-Up and Results 8.9.5 Over-Ventilated Enclosure Fire with Mechanical Ventilation 8.9.5.1 Test Case Description 8.9.5.2 Simulation Set-Up and Results 8.9.6 Interaction of a Hot-Air Plume with a Water Spray 8.9.6.1 Test Case Description 8.9.6.2 Simulation Set-Up 8.9.6.3 Results 8.9.7 Underventilated Enclosure Fire with Mechanical Ventilation 8.9.7.1 Test Case Description 8.9.7.2 Simulation Set-Up 8.9.7.3 Results 8.9.8 Fire Spread Modelling 8.9.9 Conclusions References Index