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International Association of the Properties of Water and Steam IAPWS-95

International Association of the Properties of Water and Steam IAPWS-95#

Accurate and thermodynamically consistent steam properties are provided for the IDAES framework by implementing the International Association for the Properties of Water and Steam’s “Revised Release on the IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use.” Non-analytic terms designed to improve accuracy very near the critical point were omitted, because they cause a singularity at the critical point, a feature which is undesirable in equation oriented models.

The IAPWS-95 property package is the same as the generic Helmholtz EoS model with the pure_component option set to "h2o" Please see the general Helmholtz documentation for more information.

Iapws95StateBlock Class#

class idaes.models.properties.iapws95.Iapws95StateBlock(*args, **kwds)#
Parameters:

  • rule (function) – A rule function or None. Default rule calls build().

  • concrete (bool) – If True, make this a toplevel model. Default - False.

  • ctype (class) –

    Pyomo ctype of the block. Default - pyomo.environ.Block

    Config args

    parameters

    A reference to an instance of the Property Parameter Block associated with this property package.

    defined_state

    Flag indicating whether the state should be considered fully defined, and thus whether constraints such as sum of mass/mole fractions should be included, default - False. Valid values: { True - state variables will be fully defined, False - state variables will not be fully defined.}

    has_phase_equilibrium

    Flag indicating whether phase equilibrium constraints should be constructed in this state block, default - True. Valid values: { True - StateBlock should calculate phase equilibrium, False - StateBlock should not calculate phase equilibrium.}

  • initialize (dict) – ProcessBlockData config for individual elements. Keys are BlockData indexes and values are dictionaries with config arguments as keys.

  • idx_map (function) – Function to take the index of a BlockData element and return the index in the initialize dict from which to read arguments. This can be provided to override the default behavior of matching the BlockData index exactly to the index in initialize.

Returns:

(Iapws95StateBlock) New instance

Iapws95StateBlockData Class#

class idaes.models.properties.iapws95.Iapws95StateBlockData(*args, **kwargs)[source]#

IAWPS95 State Block class.

Iapws95ParameterBlock Class#

class idaes.models.properties.iapws95.Iapws95ParameterBlock(*args, **kwds)#
Parameters:

  • rule (function) – A rule function or None. Default rule calls build().

  • concrete (bool) – If True, make this a toplevel model. Default - False.

  • ctype (class) –

    Pyomo ctype of the block. Default - pyomo.environ.Block

    Config args

    default_arguments

    Default arguments to use with Property Package

    pure_component

    (str) Pure component for which to calculate properties

    phase_presentation

    Set the way phases are presented to models. The MIX option appears to the framework to be a mixed phase containing liquid and/or vapor. The mixed option can simplify calculations at the unit model level since it can be treated as a single phase, but unit models such as flash vessels will not be able to treat the phases independently. The LG option presents as two separate phases to the framework. The L or G options can be used if it is known for sure that only one phase is present. default - PhaseType.MIX Valid values: { PhaseType.MIX - Present a mixed phase with liquid and/or vapor, PhaseType.LG - Present a liquid and vapor phase, PhaseType.L - Assume only liquid can be present, PhaseType.G - Assume only vapor can be present}

    state_vars

    The set of state variables to use. Depending on the use, one state variable set or another may be better computationally. Usually pressure and enthalpy are the best choice because they are well behaved during a phase change. default - StateVars.PH Valid values: { StateVars.PH - Pressure-Enthalpy, StateVars.PS - Pressure-Entropy, StateVars.PU - Pressure-Internal Energy, StateVars.TPX - Temperature-Pressure-Quality}

    amount_basis

    The amount basis (mass or mole) for quantities default - AmountBasis.mole Valid values: { AmountBasis.mole - use mole units (mol), AmountBasis.mass - use mass units (kg)}

  • initialize (dict) – ProcessBlockData config for individual elements. Keys are BlockData indexes and values are dictionaries with config arguments as keys.

  • idx_map (function) – Function to take the index of a BlockData element and return the index in the initialize dict from which to read arguments. This can be provided to override the default behavior of matching the BlockData index exactly to the index in initialize.

Returns:

(Iapws95ParameterBlock) New instance

Iapws95ParameterBlockData Class#

class idaes.models.properties.iapws95.Iapws95ParameterBlockData(component)[source]#

IAWPS95 Parameter Block class

Example#

The Heater unit model example, provides a simple example for using water properties.

from idaes.models.properties import iapws95
import pyomo.environ as pe # Pyomo environment
from idaes.core import FlowsheetBlock, MaterialBalanceType
from idaes.models.unit_models import Heater

# Create an empty flowsheet and steam property parameter block.
model = pe.ConcreteModel()
model.fs = FlowsheetBlock(dynamic=False)
model.fs.properties = iapws95.Iapws95ParameterBlock(
  phase_presentation=iapws95.PhaseType.LG,
  state_vars=iapws95.StateVars.PH
)

# Add a Heater model to the flowsheet.
model.fs.heater = Heater(
  property_package=model.fs.properties,
  material_balance_type=MaterialBalanceType.componentTotal
)

# Setup the heater model by fixing the inputs and heat duty
model.fs.heater.inlet[:].enth_mol.fix(4000)
model.fs.heater.inlet[:].flow_mol.fix(100)
model.fs.heater.inlet[:].pressure.fix(101325)
model.fs.heater.heat_duty[:].fix(100*20000)

# Initialize the model.
model.fs.heater.initialize()

Since all properties except the state variables are Pyomo Expressions in the water properties module, after solving the problem any property can be calculated in any state block. Continuing from the heater example, to get the viscosity of both phases, the lines below could be added.

mu_l = pe.value(model.fs.heater.control_volume.properties_out[0].visc_d_phase["Liq"])
mu_v = pe.value(model.fs.heater.control_volume.properties_out[0].visc_d_phase["Vap"])

For more information about how StateBlocks and PropertyParameterBlocks work see the StateBlock documentation.

References#

International Association for the Properties of Water and Steam (2016). IAPWS R6-95 (2016), “Revised Release on the IAPWS Formulation 1995 for the Properties of Ordinary Water Substance for General Scientific Use,” URL: http://iapws.org/relguide/IAPWS95-2016.pdf

Wagner, W., A. Pruss (2002). “The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use.” J. Phys. Chem. Ref. Data, 31, 387-535.

Wagner, W. et al. (2000). “The IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam,” ASME J. Eng. Gas Turbines and Power, 122, 150-182.

Akasaka, R. (2008). “A Reliable and Useful Method to Determine the Saturation State from Helmholtz Energy Equations of State.” Journal of Thermal Science and Technology, 3(3), 442-451.

International Association for the Properties of Water and Steam (2011). IAPWS R15-11, “Release on the IAPWS Formulation 2011 for the Thermal Conductivity of Ordinary Water Substance,” URL: http://iapws.org/relguide/ThCond.pdf.

International Association for the Properties of Water and Steam (2008). IAPWS R12-08, “Release on the IAPWS Formulation 2008 for the Viscosity of Ordinary Water Substance,” URL: http://iapws.org/relguide/visc.pdf.

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