How to use a property model
------------------------------------------------

The example below shows how to use a property model and display outputs for a state block. Property models allow
users to model the chemical and physical properties of simple systems without the use of unit models.

.. testsetup::
    
    # quiet pyomo logs
    import logging
    logging.getLogger('pyomo.core').setLevel(logging.CRITICAL)

    # quiet idaes logs
    import idaes.logger as idaeslogger
    idaeslogger.getLogger('idaes.core').setLevel('CRITICAL')
    idaeslogger.getLogger('idaes.core.util.scaling').setLevel('CRITICAL')
    idaeslogger.getLogger('idaes.init').setLevel('CRITICAL')

.. testcode::
    
    # Import concrete model from Pyomo
    from pyomo.environ import ConcreteModel

    # Import flowsheet block from IDAES core
    from idaes.core import FlowsheetBlock

    # Import solver from IDAES core
    from watertap.core.solvers import get_solver

    # Import NaCl property model
    import watertap.property_models.NaCl_prop_pack as props

    # Import utility tool for calculating scaling factors
    import idaes.core.util.scaling as iscale

    # Create a concrete model, flowsheet, and NaCl property parameter block.
    m = ConcreteModel()
    m.fs = FlowsheetBlock(dynamic=False)
    m.fs.properties = props.NaClParameterBlock()

    # Build the state block and specify a time (0 = steady state).
    m.fs.state_block = m.fs.properties.build_state_block([0])

    # Specify the state variables of the stream.
    feed_flow_mass = 1
    feed_mass_frac_NaCl = 0.035
    feed_mass_frac_H2O = 1 - feed_mass_frac_NaCl
    feed_pressure = 50e5
    feed_temperature = 298.15

    m.fs.state_block[0].flow_mass_phase_comp["Liq", "NaCl"].fix(
        feed_flow_mass * feed_mass_frac_NaCl
    )
    m.fs.state_block[0].flow_mass_phase_comp["Liq", "H2O"].fix(
        feed_flow_mass * feed_mass_frac_H2O
    )
    m.fs.state_block[0].pressure.fix(feed_pressure)
    m.fs.state_block[0].temperature.fix(feed_temperature)

    # Set scaling factors for component mass flowrates (variable * scaling factor should be between 0.01 and 100).
    m.fs.properties.set_default_scaling("flow_mass_phase_comp", 1, index=("Liq", "H2O"))
    m.fs.properties.set_default_scaling("flow_mass_phase_comp", 1e2, index=("Liq", "NaCl"))
    iscale.calculate_scaling_factors(m.fs)

    # "Touch" build-on-demand variables so that they are created. 
    # If these properties are not touched before running the solver, they will not be calculated 
    # and the output would only display their initial values instead of their actual values.
    m.fs.state_block[0].dens_mass_phase["Liq"]
    m.fs.state_block[0].conc_mass_phase_comp["Liq", "NaCl"]
    m.fs.state_block[0].flow_vol_phase["Liq"]
    m.fs.state_block[0].molality_phase_comp["Liq", "NaCl"]
    m.fs.state_block[0].visc_d_phase["Liq"]
    m.fs.state_block[0].diffus_phase_comp["Liq", "NaCl"]
    m.fs.state_block[0].enth_mass_phase["Liq"]
    m.fs.state_block[0].pressure_osm_phase["Liq"]

    # Create the solver object.
    solver = get_solver()

    # Solve the model and display the output.
    solver.solve(m, tee=False)
    m.fs.state_block[0].display()

A portion of the displayed output is shown below.

.. testoutput::

   Block fs.state_block[0]

     Variables:
       flow_mass_phase_comp : Mass flow rate
           Size=2, Index=fs.properties.phase_list*fs.properties.component_list, Units=kg/s
           Key             : Lower : Value : Upper : Fixed : Stale : Domain
            ('Liq', 'H2O') :   0.0 : 0.965 :  None :  True :  True : NonNegativeReals
           ('Liq', 'NaCl') :   0.0 : 0.035 :  None :  True :  True : NonNegativeReals
       temperature : State temperature
           Size=1, Index=None, Units=K
           Key  : Lower  : Value  : Upper  : Fixed : Stale : Domain
           None : 273.15 : 298.15 : 373.15 :  True :  True : NonNegativeReals
       ...