2528df0f75
These changes make it unnecessary to copy header files around during the build process, which tends to confuse IDEs and debuggers. The headers which comprise Cantera's external C++ interface are now in the 'include' directory. All of the samples and demos are now in the 'samples' subdirectory.
76 lines
2.9 KiB
Python
Executable file
76 lines
2.9 KiB
Python
Executable file
#################################################################
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print """
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Tutorial 4: Chemical Equilibrium
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"""
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#################################################################
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# To set a gas mixture to a state of chemical equilibrium, use the
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# equilibrate method.
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#
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from Cantera import *
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g = GRI30()
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g.set(T = 300.0, P = OneAtm, X = 'CH4:0.95,O2:2,N2:7.52')
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g.equilibrate('TP')
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# The above statement sets the state of object 'g' to the state of
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# chemical equilibrium holding temperature and pressure
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# fixed. Alternatively, the specific enthalpy and pressure can be held
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# fixed:
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g.set(T = 300.0, P = OneAtm, X = 'CH4:0.95,O2:2,N2:7.52')
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g.equilibrate('HP')
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# Other options are
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# 'UV' fixed specific internal energy and specific volume
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# 'SV' fixed specific entropy and specific volume
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# 'SP' fixed specific entropy and pressure
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g.set(T = 300.0, P = OneAtm, X = 'CH4:0.95,O2:2,N2:7.52')
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g.equilibrate('UV')
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print g
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g.set(T = 300.0, P = OneAtm, X = 'CH4:0.95,O2:2,N2:7.52')
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g.equilibrate('SV')
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print g
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g.set(T = 300.0, P = OneAtm, X = 'CH4:0.95,O2:2,N2:7.52')
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g.equilibrate('SP')
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print g
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# How can you tell if 'equilibrate' has correctly found the
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# chemical equilibrium state? One way is verify that the net rates of
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# progress of all reversible reactions are zero.
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# Here is the code to do this:
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g.set(T = 300.0, P = OneAtm, X = 'CH4:0.95,O2:2,N2:7.52')
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g.equilibrate('HP')
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rf = g.fwdRatesOfProgress()
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rr = g.revRatesOfProgress()
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for i in range(g.nReactions()):
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if g.isReversible(i) and rf[i] <> 0.0:
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print ' %4i %10.4g ' % (i, (rf[i] - rr[i])/rf[i])
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# If the magnitudes of the numbers in this list are all very small,
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# then each reversible reaction is very nearly equilibrated, which
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# only occurs if the gas is in chemical equilibrium.
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# You might be wondering how 'equilibrate' works. (Then again, you might
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# not, in which case you can go on to the next tutorial now.) Method
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# 'equilibrate' invokes Cantera's chemical equilibrium solver, which
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# uses an element potential method. The element potential method is
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# one of a class of equivalent 'nonstoichiometric' methods that all
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# have the characteristic that the problem reduces to solving a set of
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# M nonlinear algebraic equations, where M is the number of elements
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# (not species). The so-called 'stoichiometric' methods, on the other
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# hand, (including Gibbs minimization), require solving K nonlinear
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# equations, where K is the number of species (usually K >> M). See
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# Smith and Missen, "Chemical Reaction Equilibrium Analysis" for more
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# information on the various algorithms and their characteristics.
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#
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# Cantera uses a damped Newton method to solve these equations, and
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# does a few other things to generate a good starting guess and to
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# produce a reasonably robust algorithm. If you want to know more
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# about the details, look at the on-line documented source code of
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# Cantera C++ class 'ChemEquil.h' at http://www.cantera.org.
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