The IDAES Pressure Changer model represents a unit operation with a single stream of material which undergoes a change in pressure due to the application of a work. The Pressure Changer model contains support for a number of different thermodynamic assumptions regarding the working fluid.
Pressure Changer units generally have one or more degrees of freedom, depending on the thermodynamic assumption used.
Typical fixed variables are:
- outlet pressure, Pratio or ΔP,
- unit efficiency (isentropic or pump assumption).
The core Pressure Changer unit model consists of a single control volume (named ControlVolume0DBlock), a state block, containing the states, one Inlet Port (named inlet) and one Outlet Port (named outlet).
Pressure Changers contain the following Variables (not including those contained within the control volume Block):
| Variable | Name | Notes |
|---|---|---|
| Pratio | ratioP | |
| Vt | volume | Only if has_rate_reactions = True, reference to control_volume.rate_reaction_extent |
| Wmechanical, t | work_mechanical | Reference to control_volume.work |
| Wfluid, t | work_fluid | Pump assumption only |
| ηpump, t | efficiency_pump | Pump assumption only |
| Wisentropic, t | work_isentropic | Isentropic assumption only |
| ηisentropic, t | efficiency_isentropic | Isentropic assumption only |
Isentropic Pressure Changers also have an additional Property Block named properties_isentropic (attached to the Unit Model).
In addition to the Constraints written by the Control Volume block, Pressure Changer writes additional Constraints which depend on the thermodynamic assumption chosen. All Pressure Changers add the following Constraint to calculate the pressure ratio:
Pratio, t × Pin, t = Pout, t
The isothermal assumption writes one additional Constraint:
Tout = Tin
The isothermal assumption writes one additional Constraint:
Hout = Hin
The isentropic assumption creates an additional set of Property Blocks (indexed by time) for the isentropic fluid calculations (named properties_isentropic). This requires a set of balance equations relating the inlet state to the isentropic conditions, which are shown below:
Fin, t, p, j = Fout, t, p, j
sin, t = sisentropic, t
Pin, t × Pratio, t = Pisentropic, t
where Ft, p, j is the flow of component j in phase p at time t and s is the specific entropy of the fluid at time t.
Next, the isentropic work is calculated as follows:
Wisentropic, t = ∑pHisentropic, t, p − ∑pHin, t, p
where Ht, p is the total energy flow of phase p at time t. Finally, a constraint which relates the fluid work to the actual mechanical work via an efficiency term η.
If compressor is True, Wisentropic, t = Wmechanical, t × ηt
If compressor is False, Wisentropic, t × ηt = Wmechanical, t
The incompressible fluid assumption writes two additional constraints. Firstly, a Constraint is written which relates fluid work to the pressure change of the fluid.
Wfluid, t = (Pout, t − Pin, t) × Fvol, t
where Fvol, t is the total volumetric flowrate of material at time t (from the outlet Property Block). Secondly, a constraint which relates the fluid work to the actual mechanical work via an efficiency term η.
If compressor is True, Wfluid, t = Wmechanical, t × ηt
If compressor is False, Wfluid, t × ηt = Wmechanical, t
idaes.unit_models.pressure_changer
PressureChanger
PressureChangerData