[Python] Add example demonstrating use of class Quantity

interfaces/cython/cantera/examples/reactors/mix1.py

@@ -11,6 +11,9 @@ mechanism, species are matched by name. If the upstream reactor contains a
 species that is not present in the downstream reaction mechanism, it will be
 ignored. In general, reaction mechanisms for downstream reactors should
 contain all species that might be present in any upstream reactor.
+
+Compare this approach for the transient problem to the method used for the
+steady-state problem in thermo/mixing.py.
 """
 
 import cantera as ct

interfaces/cython/cantera/examples/thermo/mixing.py

@@ -0,0 +1,35 @@
+"""
+Mixing two streams using `Quantity` objects.
+
+In this example, air and methane are mixed in stoichiometric proportions. This
+is a simpler, steady-state version of the example ``reactors/mix1.py``.
+
+Since the goal is to simulate a continuous flow system, the mixing takes place
+at constant enthalpy and pressure.
+"""
+
+import cantera as ct
+
+gas = ct.Solution('gri30.xml')
+
+# Stream A (air)
+A = ct.Quantity(gas, constant='HP')
+A.TPX = 300.0, ct.one_atm, 'O2:0.21, N2:0.78, AR:0.01'
+
+# Stream B (methane)
+B = ct.Quantity(gas, constant='HP')
+B.TPX = 300.0, ct.one_atm, 'CH4:1'
+
+# Set the molar flow rates corresponding to stoichiometric reaction,
+# CH4 + 2 O2 -> CO2 + 2 H2O
+A.moles = 1
+nO2 = A.X[A.species_index('O2')]
+B.moles = nO2 * 0.5
+
+# Compute the mixed state
+M = A + B
+print(M.report())
+
+# Show that this state corresponds to stoichiometric combustion
+M.equilibrate('TP')
+print(M.report())