PEM fuel cells thermal and water management fundamentals
(eBook)

Preface -- List of figures -- List of tables -- Nomenclature --

1. Introduction -- 1.1 Energy challenges -- 1.2 Fuel cells and their roles in addressing the energy challenges -- 1.3 PEM fuel cells -- 1.3.1 PEM fuel cell operation -- 1.3.2 Current status of PEM fuel cells -- 1.3.3 Thermal and water management --

2. Basics of PEM fuel cells -- 2.1 Thermodynamics -- 2.1.1 Internal energy and the first law of thermodynamics -- 2.1.2 Enthalpy change -- 2.1.3 Entropy change and the second law of thermodynamics -- 2.1.4 Gibbs free energy and thermodynamic voltage -- 2.1.5 Chemical potential and Nernst equation -- 2.1.6 Relative humidity and phase change -- 2.2 Electrochemical reaction kinetics -- 2.2.1 Electrochemical kinetics -- 2.2.2 Electrochemical mechanisms in PEM fuel cells -- 2.2.3 Linear approximation and Tafel equation -- 2.3 Voltage loss mechanisms and a simplified model -- 2.3.1 Open circuit voltage (OCV) -- 2.3.2 Activation loss -- 2.3.3 Ohmic loss -- 2.3.4 Transport voltage loss -- 2.3.5 Current-voltage (I-V) curve and operation efficiency -- 2.3.6 Role of water and thermal management -- 2.4 Chapter summary --

3. Fundamentals of heat and mass transfer -- 3.1 Introduction -- 3.2 Conservation equations -- 3.2.1 General forms -- 3.2.2 Mass and momentum conservation -- 3.2.3 Energy equation -- 3.2.4 Species transport equation -- 3.3 Constitutive equations -- 3.3.1 A lattice model -- 3.3.2 Fourier's law and Fick's law -- 3.4 Scaling and dimensionless groups -- 3.4.1 Scaling and dimensionless equations -- 3.4.2 Dimensionless groups -- 3.5 Chapter summary --

4. Water and its transport in the polymer electrolyte membrane -- 4.1 Introduction to the polymer electrolyte membrane -- 4.2 Ion transport and ionic conductivity -- 4.2.1 Proton transport -- 4.2.2 Ionic conductivity correlations -- 4.2.3 Ionic conductivity measurement -- 4.3 Water transport in polymer electrolyte membranes -- 4.3.1 Transport mechanisms -- 4.3.2 Water holding capacity -- 4.4 Water quantification using neutron radiography -- 4.5 Ion transport in cathode catalyst layers -- 4.5.1 Variation in water content in catalyst layers -- 4.5.2 Proton transport in cathode catalyst layers -- 4.5.3 Multiple-layered cathode catalyst layers -- 4.6 Chapter summary --

5. Vapor-phase water removal and management -- 5.1 Mass transport overview -- 5.2 Diffusion -- 5.2.1 Diffusivity -- 5.2.2 Molecular versus Knudsen diffusion -- 5.2.3 Diffusion in GDLs -- 5.3 Species convection -- 5.3.1 Flow modeling with constant-flow assumption -- 5.3.2 Flow formulation without the constant-flow assumption -- 5.3.3 Convection in GDLs -- 5.4 Pore-scale transport -- 5.4.1 Stochastic material reconstruction -- 5.4.2 Pore-scale transport modeling -- 5.4.3 Pore-level phenomena -- 5.5 Transient phenomena -- 5.5.1 Transient terms and time constants -- 5.5.2 Transient undergoing constant voltage or step change in voltage -- 5.5.3 Transient undergoing constant current or step change in current -- 5.6 Water management between a PEM fuel cell and fuel processor -- 5.6.1 Water balance model -- 5.6.2 Effect of the steam-to-carbon ratio -- 5.7 Chapter summary --

6. Liquid water dynamics and removal -- 6.1 Multiphase flow overview -- 6.1.1 Modeling multi-phase flows -- 6.2 Multiphase flow in GDLS/CLS -- 6.2.1 Experimental visualization -- 6.2.1.1 X-ray imaging -- 6.2.1.2 Neutron radiography -- 6.2.2 Multiphase mixture (M2) formulation -- 6.2.2.1 Flow equations -- 6.2.2.2 Species transport -- 6.2.2.3 Model prediction -- 6.2.3 Carbon paper (CP) versus carbon cloth (CC) -- 6.2.4 Spatially varying properties -- 6.2.4.1 Through-plane variation in the GDL property -- 6.2.4.2 In-plane property variation and the effect of land compression -- 6.2.4.3 Microporous layers (MPLs) -- 6.3 Multiphase flow in gas flow channels (GFCS) -- 6.3.1 Experimental visualization -- 6.3.2 Two-phase flow patterns -- 6.3.3 Modeling two-phase flow -- 6.3.3.1 The mixture model -- 6.3.3.2 Two-fluid modeling -- 6.4 Water droplet dynamics at the GDL/GFC interface -- 6.4.1 Force balance on a spherical-shape droplet -- 6.4.2 Droplet deformation -- 6.4.3 Droplet detachment -- 6.4.3.1 Control volume method -- 6.4.3.2 Derivation using the drag coefficient (CD) -- 6.5 Chapter summary --

7. Ice dynamics and removal -- 7.1 Subfreezing operation-overview -- 7.2 Ice formation -- 7.2.1 Water transport and conservation -- 7.2.2 Three cold-start stages -- 7.2.2.1 First stage: membrane hydration -- 7.2.2.2 Second stage: ice formation -- 7.2.2.3 Third stage: ice melting -- 7.3 Voltage loss due to ice formation -- 7.3.1 Spatial variation of the oxygen reduction reaction (ORR) -- 7.3.2 The ORR rate under subfreezing temperature -- 7.3.3 Oxygen profile in the catalyst layer -- 7.3.4 Voltage loss due to ice formation -- 7.3.5 A model of cold-start cell voltage -- 7.4 State of subfreezing water -- 7.5 Chapter summary --

8. Thermal transport and management -- 8.1 Heat transfer overview -- 8.1.1 Heat transfer and its importance -- 8.1.2 Heat transfer modes -- 8.1.2.1 Heat conduction -- 8.1.2.2 Convective heat transfer -- 8.1.2.3 Heat radiation -- 8.1.3 Heat transfer in porous media -- 8.2 Heating mechanisms -- 8.2.1 The entropic heat -- 8.2.2 Irreversibility of the electrochemical reactions -- 8.2.3 The Joules heat -- 8.3 Steady-state heat transfer -- 8.3.1 One-dimensional (1D) heat transfer analysis -- 8.3.2 Two-dimensional (2D) heat transfer analysis -- 8.3.3 Numerical analysis -- 8.3.3.1 Macroscopic model prediction -- 8.3.3.2 Pore-level heat transfer -- 8.4 Transient phenomena -- 8.4.1 General transient operation -- 8.4.2 Transient subfreezing operation -- 8.4.2.1 Temperature evolution and voltage loss -- 8.4.2.2 Activation voltage loss -- 8.4.2.3 Ohmic voltage loss -- 8.5 Experimental measurement of thermal conductivity -- 8.6 Cooling methods -- 8.6.1 Heat spreaders cooling -- 8.6.2 Cooling by air or liquid flow -- 8.6.3 Phase-change-based cooling -- 8.7 Example: a thermal system of automotive fuel cells -- 8.7.1 A lumped-system model of a PEM fuel cell -- 8.7.2 Bypass valve -- 8.7.3 Radiator -- 8.7.4 Transport delay -- 8.7.5 Fluid mixer -- 8.7.6 Cathode intercooler -- 8.7.7 Anode heat exchanger -- 8.8 Chapter summary --

9. Coupled thermal-water management: phase change

9.1 Introduction to phase change

9.2 Vapor-liquid phase change: evaporation and condensation

9.2.1 Vapor-phase water diffusion and heat pipe effect

9.2.2 GDL de-wetting

9.2.3 GDL de-wetting and voltage loss

9.2.4 A general definition of the Damkohler number, Da

9.2.4.1 Local heating and vapor-phase removal

9.2.4.2 A specific Damkohler number

9.2.4.3 Liquid-free passages

9.2.4.4 2D numerical simulation

9.3 Freezing/thawing

9.3.1 Temperature spatial and temporal variation

9.3.2 Non-isothermal cold start

9.3.3 Freezing/thawing and degradation

9.4 System-level analysis of coupled thermal and water management

9.4.1 Flow rates of species and two-phase flows

9.4.2 Energy balance

9.5 Chapter summary.