# Feedwater Heater (0D)¶

The FWH0D model is a 0D feedwater heater model suitable for steady state modeling. It is intended to be used primarily used with the IAWPS95 property package. The feedwater heater is split into three sections the condensing section is required while the desuperheating and drain cooling sections are optional. There is also an optional mixer for adding a drain stream from another feedwater heater to the condensing section. The figure below shows the layout of the feedwater heater. All but the condensing section are optional.

Feedwater Heater

## Example¶

The example below shows how to setup a feedwater heater with all tree sections. The feedwater flow rate, steam conditions, heat transfer coefficients and areas are not necessarily realistic.

import pyomo.environ as pyo
from idaes.core import FlowsheetBlock
from idaes.unit_models.heat_exchanger import (delta_temperature_underwood2_rule,
delta_temperature_underwood_rule, delta_temperature_lmtd_rule)
from idaes.property_models import iapws95
from idaes.unit_models.power_generation import FWH0D

def make_fwh_model():
model = pyo.ConcreteModel()
model.fs = FlowsheetBlock(default={
"dynamic": False,
"default_property_package": iapws95.Iapws95ParameterBlock()})
model.fs.properties = model.fs.config.default_property_package
model.fs.fwh = FWH0D(default={
"has_desuperheat":True,
"has_drain_cooling":True,
"has_drain_mixer":True,
"property_package":model.fs.properties})

model.fs.fwh.desuperheat.inlet_1.flow_mol.fix(100)
model.fs.fwh.desuperheat.inlet_1.flow_mol.unfix()
model.fs.fwh.desuperheat.inlet_1.pressure.fix(201325)
model.fs.fwh.desuperheat.inlet_1.enth_mol.fix(60000)
model.fs.fwh.drain_mix.drain.flow_mol.fix(1)
model.fs.fwh.drain_mix.drain.pressure.fix(201325)
model.fs.fwh.drain_mix.drain.enth_mol.fix(20000)
model.fs.fwh.cooling.inlet_2.flow_mol.fix(400)
model.fs.fwh.cooling.inlet_2.pressure.fix(101325)
model.fs.fwh.cooling.inlet_2.enth_mol.fix(3000)
model.fs.fwh.condense.area.fix(1000)
model.fs.fwh.condense.overall_heat_transfer_coefficient.fix(100)
model.fs.fwh.desuperheat.area.fix(1000)
model.fs.fwh.desuperheat.overall_heat_transfer_coefficient.fix(10)
model.fs.fwh.cooling.area.fix(1000)
model.fs.fwh.cooling.overall_heat_transfer_coefficient.fix(10)

model.fs.fwh.initialize()
return(model)

# create a feedwater heater model with all optional units and initialize
model = make_fwh_model()


## Model Structure¶

The condensing section uses the FWHCondensing0D model to calculate a steam flow rate such that all steam is condensed in the condensing section. This allows turbine steam extraction rates to be calculated. The other sections are regular HeatExchanger models. The table below shows the unit models which make up the feedwater heater, and the option to include or exclude them.

Unit Option Doc
condense Condensing section (FWHCondensing0D)
desuperheat has_desuperheat Desuperheating section (HeatExchanger)
cooling has_drain_cooling Drain cooling section (HeatExchanger)
drain_mix has_drain_mixer Mixer for steam and other FWH drain (Mixer)

## Degrees of Freedom¶

The area and overall_heat_transfer_coefficient should be fixed or constraints should be provided to calculate overall_heat_transfer_coefficient. If the inlets are also fixed except for the inlet steam flow rate (inlet_1.flow_mol), the model will have 0 degrees of freedom.

See FWH0D and FWH0DData for full Python class details.