How to setup a simple RO model

The example below shows how to setup and initialize a simple RO unit model.

# Import concrete model from Pyomo
from pyomo.environ import ConcreteModel
# Import flowsheet block from IDAES core
from idaes.core import FlowsheetBlock
# Import NaCl property model
import proteuslib.property_models.NaCl_prop_pack as props
# Import utility tool for calculating scaling factors
from idaes.core.util.scaling import calculate_scaling_factors
# Import RO model
from proteuslib.unit_models.reverse_osmosis_0D import ReverseOsmosis0D


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

# Add an RO unit to the flowsheet.
m.fs.unit = ReverseOsmosis0D(default={"property_package": m.fs.properties})

# Specify system variables.
m.fs.unit.inlet.flow_mass_phase_comp[0, 'Liq', 'NaCl'].fix(0.035)  # mass flow rate of NaCl
m.fs.unit.inlet.flow_mass_phase_comp[0, 'Liq', 'H2O'].fix(0.965)  # mass flow rate of water
m.fs.unit.inlet.pressure[0].fix(50e5)  # feed pressure
m.fs.unit.inlet.temperature[0].fix(298.15)  # feed temperature
m.fs.unit.area.fix(50)  # membrane area
m.fs.unit.A_comp.fix(4.2e-12)  # membrane water permeability
m.fs.unit.B_comp.fix(3.5e-8)  # membrane salt permeability
m.fs.unit.permeate.pressure[0].fix(101325)  # permeate pressure

# Set scaling factors for component mass flowrates.
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'))

# Calculate scaling factors.
calculate_scaling_factors(m)

# Initialize the model.
m.fs.unit.initialize(optarg={'nlp_scaling_method': 'user-scaling'})