The closed reactor model can consider two modes of operation: given pressure and given volume. These act as the global constraints.

Given pressure, closed reactor model

When the pressure of the Multiphase Closed Reactor is specified, the given reactor pressure is applied to all phases

(9–13)

The reactor volume is considered as the sum of all phase volumes

(9–14)

Given volume, closed reactor model

When the volume of the Multiphase Closed Reactor is specified, this overall volume constraint is applied to the gas phase, that is

(9–15)

And the reactor pressure is then calculated from the gas-phase equation of state. For the bulk-phase volumes, the differential form of Equation 9–11 is used. Note that, in the specified equation, individual species density is a function of the phase temperature.

Open reactor model

For the open reactor model, outflow rate appears as an extra variable in the system of equations for gas and for each bulk-phase. The pressure is the same for all phases and is given as input. For each phase either the volume or the outflow rate can be solved for. In the Chemkinimplementation, you can specify one of these variables for each bulk phase and solve for the other. The gas-phase volume is then implied (gets constrained) through the specified total volume of the reactor and the outflow rate of the gas phase is solved for.