1 Chemical thermodynamics Flashcards
What does chemical thermodynamics deal with?
The description of the equilibrium states of reacting multicomponent systems
What are global performance parameters?
- heat
- power output
How can global performance parameters be estimated?
By assuming thermodynamic equilibrium
Which effect does the big amount of nitrogen have in the air?
It reduces
the combustion temperature
because of the expenditure of thermal energy used to heat it up during the course of burning.
Which measures can be taken for applications requiring intense burning
use of
- oxygen enriched air
- pure oxygen
Representative components of gaseous fuels
- hydrogen (H2)
- carbon monoxide (CO)
- light hydrocarbons (HC)
Representative components of liquid fuels
heavier hydrocarbons and alcohols
Representative components of solid fuels
- carbon
- coal
- wood
- metals
What does the combustion intensity between a fuel and an oxidizier depend on?
It depends on their relative concentrations
When is a reaction fuel lean?
< 1
Practical HC reactants (not necessarily gaseous)
- alkanes (paraffins)
- alkenes (olefins)
- acetylenes (alkynes)
- diolefins (two CC)
- napththenes (cycloparaffins or cyclanes)
- aromatics
- alcohols
Characteristics of napththenes
- C(m)H(2m)
- single-bond
- saturated
- closed rings
Characteristics of aromatics
- C(m)H(2m-6)
- single-bond
- double-bond alternate in position
Characteristics of alcohols
- R-OH
- C(m)H(2m+1)OH
What does the first law of thermodynamics state?
For a closed system, the heat added to the system is used to increase its intenral energy and to perform a certain amount of work
How many modes of reversible work exist?
One : pdV
How can the state of a single-component thermodynamic system be characterized?
By two independent variables: S and V (second law of thermodynamics)
How do you deal with multicomponent systems?
The same species in different phases is treated as different thermodynamic species by considering phase transition as a chemical reaction
Does the presence of inerts in the system affect the equilibrium constant?
No, but it needs to be accounted for, when the partial pressures are related to either the molar fraction or the mass fraction.
How do you consider solid carbon in the product for HC/air mixtures?
- Assume C(s) is present, then check the sign of C(s)
- Assume there is no C(s), check partial pressure of C(g) If the calculation shows that the partial pressure of the gaseous carbon exceeds the equilibrium vapor pressur of carbon, then condensation and solid carbon must exist.
Which indicator lets you estimate if solid carbon is likely to be formed?
Equivalence ratio.
For <1, there exists enough oxygen for complete conversion, implying that carbon, or soot emission, usually observed only for rich mixtrues.
What does the composition depend on in a fuel lean composition according to major-species- model?
It does NOT depend on T, P
It just depends on equivalence ratio