Reactor Interactions#
Reservoirs#
A reservoir can be thought of as an infinitely large volume, in which all states are predefined and never change from their initial values. Typically, it represents a vessel to define temperature and composition of a stream of mass flowing into a reactor, or the ambient fluid surrounding the reactor network. In addition, the fluid flow exiting a reactor network has to flow into a reservoir. In the latter case, the state of the reservoir, except for its pressure, is irrelevant.
Python Usage
In Python, a reservoir can be defined using the Reservoir
class.
Flow Devices#
A flow device connects two reactors and allows mass flow from an upstream reactor (1) to a downstream reactor (2). Different kinds of flow devices are defined based on how the mass flow rate is determined.
A reactor can have multiple inlets and outlets. For the inlets, arbitrary states can be defined by setting a reservoir as the upstream reactor. Fluid with the current state of the reactor exits the reactor at the outlets.
Valves#
A valve is a flow device with mass flow rate that is a function of the pressure drop across it. The mass flow rate is computed as:
with
corresponding to a linear dependence of the mass flow rate on the pressure difference.
The pressure difference between the upstream (1) and downstream (2) reactor is defined
as
Valves are often used between an upstream reactor and a downstream reactor or reservoir
to maintain them both at nearly the same pressure. By setting the constant
Python Usage
In Python, a valve is implemented by class Valve
; Valve.valve_coeff
property; Valve.time_function
property; and Valve.pressure_function
property.
Mass Flow Controllers#
A mass flow controller maintains a specified mass flow rate independent of upstream and downstream conditions. The equation used to compute the mass flow rate is
where
Unlike a real mass flow controller, a Cantera mass flow controller object will maintain the flow even if the downstream pressure is greater than the upstream pressure. This allows simple implementation of loops, in which exhaust gas from a reactor is fed back into it through an inlet. But note that this capability should be used with caution, since no account is taken of the work required to do this.
Python Usage
Mass flow controllers can be implemented in Python using the
MassFlowController
class. The MassFlowController.mass_flow_coeff
property can be used to set MassFlowController.time_function
property can be used to set
Pressure Controllers#
A pressure controller is designed to be used in conjunction with a primary flow controller, typically a mass flow controller. The primary flow controller is installed on the inlet of the reactor, and the corresponding pressure controller is installed on on outlet of the reactor. The mass flow rate of the pressure controller is equal to that of the primary mass flow rate, plus a small correction dependent on the pressure difference:
where
Python Usage
Pressure controllers can be defined in Python using the PressureController
class. The primary flow controller can be set using the
PressureController.primary
property; PressureController.pressure_coeff
property; and PressureController.pressure_function
.
Walls#
In Cantera, a wall separates two reactors or a reactor and a reservoir. A wall has a finite area, may conduct or radiate heat between the two reactors on either side, and may move like a piston.
Walls are stateless objects in Cantera, meaning that no differential equation is integrated to determine any wall property. Since it is the wall, or piston, velocity that enters the energy equation, this means that it is the velocity, not the acceleration or displacement, that is specified. The wall velocity is computed from
where
The total rate of heat transfer through all walls is:
where
where
Python Usage
In Python, walls are defined using the Wall
class.
Reacting Surfaces#
In case of surface reactions, there can be a net generation or destruction of
homogeneous, gas phase species. The molar rate of production for each homogeneous phase
species
Mass fraction-based reactors#
The total mass production rate for homogeneous phase species
where
For each surface species
where
Mole-based reactors#
In the case of mole based reactors,
and the conservation equation for each surface species
These equations for
Python Usage
In Python, reacting surfaces are defined using the ReactorSurface
class.