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What is the value of the enthalpy of formation for diatomic oxygen under standard conditions?
What is the value of the enthalpy of formation for diatomic oxygen under standard conditions?
What does the equation for absolute enthalpy represent?
What does the equation for absolute enthalpy represent?
At what reference temperature and pressure is standard enthalpy defined?
At what reference temperature and pressure is standard enthalpy defined?
What is the bond dissociation energy of O2 at standard state?
What is the bond dissociation energy of O2 at standard state?
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What does the sensible enthalpy change represent in the context of absolute enthalpy?
What does the sensible enthalpy change represent in the context of absolute enthalpy?
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Which of the following elements has an enthalpy of formation of 0 at standard state?
Which of the following elements has an enthalpy of formation of 0 at standard state?
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Which statement correctly describes enthalpy of formation?
Which statement correctly describes enthalpy of formation?
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What is the enthalpy of formation of atomic nitrogen (N) at standard conditions?
What is the enthalpy of formation of atomic nitrogen (N) at standard conditions?
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What is the relationship between the enthalpy of reaction and the enthalpy of combustion?
What is the relationship between the enthalpy of reaction and the enthalpy of combustion?
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In the steady-flow reactor, what must occur for the temperature of products to be the same as that of the reactants?
In the steady-flow reactor, what must occur for the temperature of products to be the same as that of the reactants?
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In the equation $q_{cv} = H_{prod} - H_{reac}$, what does $q_{cv}$ represent?
In the equation $q_{cv} = H_{prod} - H_{reac}$, what does $q_{cv}$ represent?
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When calculating ∆hR on a per-mass-of-fuel basis, which formula is used?
When calculating ∆hR on a per-mass-of-fuel basis, which formula is used?
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What equation represents the mixture molecular weight of an ideal gas mixture?
What equation represents the mixture molecular weight of an ideal gas mixture?
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What is the effect of stoichiometric combustion conditions on reactants?
What is the effect of stoichiometric combustion conditions on reactants?
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Based on the enthalpy values provided, what is the calculated enthalpy change ∆HR?
Based on the enthalpy values provided, what is the calculated enthalpy change ∆HR?
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Which equation describes the relationship between total pressure and partial pressures in an ideal gas mixture?
Which equation describes the relationship between total pressure and partial pressures in an ideal gas mixture?
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How is the partial pressure of the ith species in a gas mixture defined?
How is the partial pressure of the ith species in a gas mixture defined?
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Which statement best describes complete combustion in a steady-flow reactor?
Which statement best describes complete combustion in a steady-flow reactor?
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What does the term 'enthalpy of combustion' specifically refer to?
What does the term 'enthalpy of combustion' specifically refer to?
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What is the formula to calculate the mixture entropy of ideal gases?
What is the formula to calculate the mixture entropy of ideal gases?
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In ideal gas mixtures, how is the specific enthalpy calculated?
In ideal gas mixtures, how is the specific enthalpy calculated?
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If the standard state is defined at 1 atm, how is the entropy of the ith species related to its partial pressure?
If the standard state is defined at 1 atm, how is the entropy of the ith species related to its partial pressure?
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What is the relationship between latent heat (enthalpy) of vaporization and constant pressure?
What is the relationship between latent heat (enthalpy) of vaporization and constant pressure?
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What does the equation for specific energy transfer in a system typically depend on?
What does the equation for specific energy transfer in a system typically depend on?
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Study Notes
Combustion Fundamentals
- Combustion is a key process in many modern technologies, accounting for approximately 85% of global energy use.
- It converts chemical energy to thermal or propulsive force.
Combustion Applications
- Gas turbines and jet engines
- Rocket propulsion
- Piston engines
- Guns and explosives
- Furnaces and boilers
- Materials processing (e.g., carbon black production, fullerenes, nano-materials)
- Forming of materials
- Fire hazards and safety
Combustion Processes
- Combustion is a complex interaction of physical (fluid dynamics, heat and mass transfer) and chemical (thermodynamics, chemical kinetics) processes.
- Energy, mass, and momentum transport are key physical processes.
- Thermal energy conduction, species diffusion, and gas flow are consequences of chemical energy release.
Relevant Subject Areas
- Thermodynamics: Includes stoichiometry, gas and gas mixture properties, enthalpy of formation, enthalpy of reaction, equilibrium, and adiabatic flame temperature.
- Heat and Mass Transfer: Includes heat transfer by conduction, convection, and radiation, and mass transfer.
- Fluid Dynamics: Includes laminar flows, turbulence, effects of inertia and viscosity, and combustion aerodynamics.
- Chemical Kinetics: Focuses on the application of thermodynamics to reacting systems to determine equilibrium composition and adiabatic flame temperature.
- Additionally, understanding rates of chemical reactions is necessary for accurate modeling of combustion.
Primary Combustion Research Literature Sources
- Combustion and Flame journal
- Combustion Science and Technology journal
- Combustion Theory and Modelling journal
- Progress in Energy and Combustion Science (review journal)
- Proceedings of the Combustion Institute (Biennial Combustion Symposia)
- Combustion, Explosions, and Shock Waves journal (translated from Russian).
Fundamental Definitions
- Chemical Reactions: involve rearrangement or exchange of atoms between colliding molecules.
- Reactants: substances entering a reaction.
- Products: substances produced in a reaction.
- Atom conservation follows reactions. Molecular conservation does not.
Amount of Substance/Mole Numbers (mol)
- One mole of a compound corresponds to 6.023 x 1023 particles (atoms, molecules, or chemical species).
- Avogadro's constant: 6.023 x 1023
- Mole fraction (Xi) of species i is the ratio of the number of moles of species i to the total number of moles in the mixture.
- Mass fraction (Yi) of species i is the ratio of the mass of species i to the total mass of the mixture.
Molar or Molecular Mass (Mi)
- Molar or molecular mass (also known as molecular weight) is the mass of one mole of a substance.
- Units are g/mol. Examples: CH4 = 16 g/mol, H2 = 2 g/mol, O2 = 32 g/mol.
Mean Molar Mass (M)
- Mean molar mass represents an average molar mass of a species mixture.
Ideal Gas Equation of State
- PV = nRT where P = pressure, V = volume, n = number of moles, R = ideal gas constant (8.314 J/mol K), and T = temperature.
- Real gas equations (e.g., van der Waals, Peng-Robinson equations) are necessary for conditions near or above critical temperatures and pressures.
Basic Flame Types
- Premixed flames (Laminar / Turbulent)
- Non-premixed flames (Diffusion) flames (Laminar / Turbulent)
- Partially premixed flames (Laminar / Turbulent)
Stoichiometry
- Stoichiometric flame - Complete fuel consumption
- Fuel-rich system- Excess fuel
- Fuel-lean system- Excess oxidiser
- Common air compositions (O2 + 3.762 N2) for combustion reaction calculations
Stoichiometry (Cont'd)
- Air-to-fuel ratios are important in combustion calculations.
- Equivalence ratio (Φ) calculates the combustion proportion of reactants
Laminar (Turbulent) Non-premixed Flames
- Fuel and oxidizer mix in the combustion process.
- A candle flame is often described as a laminar non-premixed or diffusion flame.
Thermodynamics/Thermochemistry
- Basic property relations for ideal gas and ideal gas mixtures
- First law of thermodynamics
- Enthalpy (heat of reaction), adiabatic flame temperature
- Chemical equilibrium
Calorific Equations of State
- Relates enthalpy and internal energy to temperature and pressure.
- Key for calculating changes in enthalpy and internal energy related to combustion
- Ideal gas assumption simplifies relations
- Specific heats (Cv and Cp) values are important for calculation purposes
Ideal Gas Mixtures
- Mole fraction (Xi) and mass fraction (Yi) in mixtures are fundamental for determining the composition of combustion gases.
- Mixture molar mass is used for extensive property calculations
- Partial pressures
Latent Heat (Enthalpy) of Vaporization
- Heat required to vaporize a unit mass of liquid at a constant pressure
- The Clausius-Clapeyron equation describes the relationship between vapor pressure and temperature for phase changes
First Law of Thermodynamics
- Conservation of energy is fundamental; expressed as the change of energy within a system equal to heat transfer and work done
- Total energy is the sum of internal energy, kinetic energy, and potential energy of the system.
Constant Pressure/Volume Adiabatic Flame Temperatures
- Heat transfer (at constant pressure/volume) within a system is used for adiabatic flame temperature calculations
- The enthalpy of the reactants (at initial state) equals absolute enthalpy of the products (at final state).
- Calculating these temperatures requires knowledge of the reactants and products compositions, and applying the energy conservation equations.
Chemical Equilibrium
- Combustion products are not always a simple mixing
- Relevant in determining the overall stoichiometry
- Identifying the conditions under which components would exist will help to determine the species present
Real Combustion Products
- Products of real combustion reactions include multiple components and species, due to dissociation of major species into minor species.
Second-Law Considerations
- Key for chemical reactions
- Adiabatic reaction vessel - Constant volume (V) where only temperature and pressure change
- Second law condition requires the entropy change to be greater than or equal to 0
Gibbs Function
- Useful for determining the equilibrium at constant T and P.
- Helps calculate equilibrium by establishing a condition to meet.
- Gibbs free energy determines the natural conditions of equilibrium.
Water-Gas Equilibrium
- Important consideration for lean or rich combustion conditions
- Describes the simultaneous presence of CO and H2, considered as incomplete combustion products
- Relationships are used to calculate the mole fractions of products in the system
Global Mechanisms
- Simplistic models for complex reactions; useful in engineering approximations.
- Useful for combustion calculations; however, have limitations
- Single/Multiple step expressions
Nitrogen Oxide (NO) Kinetics
- NO forms, primarily, from multiple processes
- Equilibrium
- Reaction rates, and the related mechanisms need to be considered to better understand combustion reactions and products
Chemical Kinetics
- Study of chemical reaction rates.
- Reaction orders (first, second, third)
- Rate coefficients
- Mechanisms of reaction - Elementary reaction steps
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