[Python/Samples] Add Peridic CSTR example to Python module

Translated from the Matlab sample

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

@@ -0,0 +1,96 @@
+"""
+Periodic CSTR
+
+This example illustrates a CSTR with steady inputs but periodic interior state.
+A stoichiometric hydrogen/oxygen mixture is introduced and reacts to produce
+water.  But since water has a large efficiency as a third body in the chain
+termination reaction
+
+       H + O2 + M = HO2 + M
+
+as soon as a significant amount of water is produced the reaction stops. After
+enough time has passed that the water is exhausted from the reactor, the mixture
+explodes again and the process repeats. This explanation can be verified by
+decreasing the rate for reaction 7 in file 'h2o2.cti' and re-running the
+example.
+
+Acknowledgments: The idea for this example and an estimate of the conditions
+needed to see the oscillations came from Bob Kee, Colorado School of Mines
+"""
+
+import cantera as ct
+import numpy as np
+
+# create the gas mixture
+gas = ct.Solution('h2o2.cti')
+
+# pressure = 60 Torr, T = 770 K
+p = 60.0*133.3
+t = 770.0
+
+gas.TPX = t, p, 'H2:2, O2:1'
+
+# create an upstream reservoir that will supply the reactor. The temperature,
+# pressure, and composition of the upstream reservoir are set to those of the
+# 'gas' object at the time the reservoir is created.
+upstream = ct.Reservoir(gas)
+
+# Now create the reactor object with the same initial state
+cstr = ct.IdealGasReactor(gas)
+
+# Set its volume to 10 cm^3. In this problem, the reactor volume is fixed, so
+# the initial volume is the volume at all later times.
+cstr.volume = 10.0*1.0e-6
+
+# We need to have heat loss to see the oscillations. Create a reservoir to
+# represent the environment, and initialize its temperature to the reactor
+# temperature.
+env = ct.Reservoir(gas)
+
+# Create a heat-conducting wall between the reactor and the environment. Set its
+# area, and its overall heat transfer coefficient. Larger U causes the reactor
+# to be closer to isothermal. If U is too small, the gas ignites, and the
+# temperature spikes and stays high.
+w = ct.Wall(cstr, env, A=1.0, U=0.02)
+
+# Connect the upstream reservoir to the reactor with a mass flow controller
+# (constant mdot). Set the mass flow rate to 1.25 sccm.
+sccm = 1.25
+vdot = sccm * 1.0e-6/60.0 * ((ct.one_atm / gas.P) * ( gas.T / 273.15)) # m^3/s
+mdot = gas.density * vdot # kg/s
+mfc = ct.MassFlowController(upstream, cstr, mdot=mdot)
+
+# now create a downstream reservoir to exhaust into.
+downstream = ct.Reservoir(gas)
+
+# connect the reactor to the downstream reservoir with a valve, and set the
+# coefficient sufficiently large to keep the reactor pressure close to the
+# downstream pressure of 60 Torr.
+v = ct.Valve(cstr, downstream, K=1.0e-9)
+
+# create the network
+network = ct.ReactorNet([cstr])
+
+# now integrate in time
+t = 0.0
+dt   = 0.1
+
+tm = []
+y = []
+while t < 300.0:
+    t += dt
+    network.advance(t)
+    tm.append(t)
+    y.append(cstr.thermo['H2','O2','H2O'].Y)
+
+if __name__ == '__main__':
+    print(__doc__)
+    try:
+        import matplotlib.pyplot as plt
+        plt.figure(1)
+        plt.plot(tm, y)
+        plt.legend(['H2','O2','H2O'])
+        plt.title('Mass Fractions')
+        plt.show()
+    except ImportError:
+        print('Matplotlib not found. Unable to plot results.')