Flash Unit ========== The IDAES Flash model represents a unit operation where a single stream undergoes a flash separation into two phases. The Flash model supports multiple types of flash operations, including pressure changes and addition or removal of heat. Degrees of Freedom ------------------ Flash units generally have 2 degrees of freedom. Typical fixed variables are: * heat duty or outlet temperature (see note), * pressure change or outlet pressure. Note: When setting the outlet temperature of a Flash unit, it is best to set control_volume.properties_out[t].temperature. Setting the temperature in one of the outlet streams directly results in a much harder problem to solve, and may be degenerate or unbounded in some cases. Model Structure --------------- The core Flash unit model consists of a single ControlVolume0DBlock (named control_volume) with one Inlet Port (named inlet) connected to a Separator unit model with two outlet Ports named 'vap_outlet' and 'liq_outlet'. The Flash model utilizes the separator unit model in IDAES to split the outlets by phase flows to the liquid and vapor outlets respectively. The Separator unit model supports both direct splitting of state variables and writing of full splitting constraints via the `ideal_separation` construction argument. Full details on the Separator unit model can be found in the documentation for that unit. To support direct splitting, the property package must use one of a specified set of state variables and support a certain set of property calacuations, as outlined in the table below. ==================================== =================================== State Variables Required Properties ==================================== =================================== **Material flow and composition** ------------------------------------------------------------------------ flow_mol & mole_frac flow_mol_phase & mole_frac_phase flow_mol_phase & mole_frac_phase flow_mol_phase & mole_frac_phase flow_mol_comp flow_mol_phase_comp flow_mol_phase_comp flow_mol_phase_comp flow_mass & mass_frac flow_mass_phase & mass_frac_phase flow_mass_phase & mass_frac_phase flow_mass_phase & mass_frac_phase flow_mass_comp flow_mass_phase_comp flow_mass_phase_comp flow_mass_phase_comp **Energy state** ------------------------------------------------------------------------ temperature temperature enth_mol enth_mol_phase enth_mol_phase enth_mol_phase enth_mass enth_mass_phase enth_mass_phase enth_mass_phase **Pressure state** ------------------------------------------------------------------------ pressure pressure ==================================== =================================== Construction Arguments ---------------------- Flash units have the following construction arguments: * property_package - property package to use when constructing Property Blocks (default = 'use_parent_value'). This is provided as a Property Parameter Block by the Flowsheet when creating the model. If a value is not provided, the Holdup Block will try to use the default property package if one is defined. * property_package_args - set of arguments to be passed to the Property Blocks when they are created. Additionally, Flash units have the following construction arguments which are passed to the Holdup Block for determining which terms to construct in the balance equations. ========================= ================= Argument Default Value ========================= ================= dynamic False include_holdup False material_balance_type MaterialBalanceType.componentPhase energy_balance_type EnergyBalanceType.enthalpyTotal momentum_balance_type MomentumBalanceType.pressureTotal has_phase_equilibrium True has_heat_transfer True has_pressure_change True ========================= ================= Finally, Flash units also have the following arguments which are passed to the Separator block for determining how to split to two-phase mixture. =================== ================= Argument Default Value =================== ================= ideal_separation True energy_split_basis EnergySplittingType.equal_temperature =================== ================= Additional Constraints ---------------------- Flash units write no additional Constraints beyond those written by the ControlVolume0DBlock and the Separator block. Variables --------- ============== ================================================== Name Notes ============== ================================================== heat_duty Reference to control_volume.heat deltaP Reference to control_volume.deltaP ============== ================================================== Flash Class ----------- .. module:: idaes.models.unit_models.flash .. autoclass:: Flash :members: FlashData Class --------------- .. autoclass:: FlashData :members: