Heat Exchanger With Three Streams

The HeatExchangerWith3Streams model consists of a heat exchanger with three inlets, side_1 represents the hot stream, while side_2 and side_3 are cold streams. This model is a simplified generic heat exchanger model with lumped UA (the product of the overall heat transfer coefficient and the heat transfer area).

In a power plant flowsheet this model is used to represent an air preheater unit. This is because modeling the Ljungström type preheater is quite challenging since it involves not only the hot and cold gas streams but also the energy stored in and relased from the metal parts.

Degrees of Freedom

Aside from the inlet conditions, a 3 inlet heat exchanger model usually has six degrees of freedom, which must be fixed for it to be fully specified. Things that are frequently fixed are two of:

  • UA_side_2 - lumped overall heat transfer and heat transfer area of side 2

  • UA_side_3 - lumped overall heat transfer and heat transfer area of side 3

  • frac_heatloss - fraction of heat loss in the system

  • deltaP_side_1 - pressure drop in side 1

  • deltaP_side_2 - pressure drop in side 2

  • deltaP_side_3 - pressure drop in side 3

Model Structure

The HeatExchangerWith3Streams model contains three ControlVolume0DBlock blocks. The hot side is named side_1 and two cold sides are named side_2 and side_3. These names are not configurable. The sign convention is that duty is positive for heat flowing from the hot side to the cold side.

The control volumes are configured the same as the ControlVolume0DBlock in the Heater model. The HeatExchangerWith3Streams model contains additional constraints that calculate the amount of heat transferred from the hot side to the cold side.

The HeatExchangerWith3Streams has three inlet ports and three outlet ports. By default these are side_1_inlet, side_2_inlet, side_3_inlet, side_1_outlet, side_2_outlet, side_3_outlet.

Variables

Variable

Symbol

Index Sets

Doc

heat_duty

\(Q\)

time

Heat transferred (model includes 3 variables, one for each side)

UA

\(UA\)

None

lumped Heat transfer area and overall heat transfer coefficient

LMTD

\(LMTD\)

time

Log Mean Temperature difference, LMTD

Constraints

The default constraints can be overridden by providing alternative rules for the heat transfer equation, temperature difference, heat transfer coefficient, shell and tube pressure drop. This section describes the default constraints.

Heat transfer from hot to cold sides:

\[Q_{side\_1} * (1-frac_{heat\_loss}) = Q_{side\_2} + Q_{side\_3}\]
\[Q_{side\_2} = UA_{side\_2}\Delta T_2\]
\[Q_{side\_3} = UA_{side\_3}\Delta T_3\]

Temperature difference is:

\[\Delta T = \frac{\Delta T_1 - \Delta T_2}{\log_e\left(\frac{\Delta T_1}{\Delta T_2}\right)}\]

Note

DeltaT2 is a function of hot stream side 1 and cold stream side 2, and DeltaT3 is a function of hot side and cold stream side 3.

Class Documentation

class idaes.power_generation.unit_models.heat_exchanger_3streams.HeatExchangerWith3Streams(*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

  • default (dict) –

    Default ProcessBlockData config

    Keys
    dynamic

    Indicates whether this model will be dynamic or not, default = useDefault. Valid values: { useDefault - get flag from parent (default = False), True - set as a dynamic model, False - set as a steady-state model.}

    has_holdup

    Indicates whether holdup terms should be constructed or not. Must be True if dynamic = True, default - False. Valid values: { useDefault - get flag from parent (default = False), True - construct holdup terms, False - do not construct holdup terms}

    side_1_property_package

    Property parameter object used to define property calculations, default - useDefault. Valid values: { useDefault - use default package from parent model or flowsheet, PhysicalParameterObject - a PhysicalParameterBlock object.}

    side_1_property_package_args

    A ConfigBlock with arguments to be passed to a property block(s) and used when constructing these, default - None. Valid values: { see property package for documentation.}

    side_2_property_package

    Property parameter object used to define property calculations, default - useDefault. Valid values: { useDefault - use default package from parent model or flowsheet, PhysicalParameterObject - a PhysicalParameterBlock object.}

    side_2_property_package_args

    A ConfigBlock with arguments to be passed to a property block(s) and used when constructing these, default - None. Valid values: { see property package for documentation.}

    side_3_property_package

    Property parameter object used to define property calculations, default - useDefault. Valid values: { useDefault - use default package from parent model or flowsheet, PhysicalParameterObject - a PhysicalParameterBlock object.}

    side_3_property_package_args

    A ConfigBlock with arguments to be passed to a property block(s) and used when constructing these, default - None. Valid values: { see property package for documentation.}

    material_balance_type

    Indicates what type of material balance should be constructed, default - MaterialBalanceType.componentPhase. Valid values: { MaterialBalanceType.none - exclude material balances, MaterialBalanceType.componentPhase - use phase component balances, MaterialBalanceType.componentTotal - use total component balances, MaterialBalanceType.elementTotal - use total element balances, MaterialBalanceType.total - use total material balance.}

    energy_balance_type

    Indicates what type of energy balance should be constructed, default - EnergyBalanceType.enthalpyTotal. Valid values: { EnergyBalanceType.none - exclude energy balances, EnergyBalanceType.enthalpyTotal - single ethalpy balance for material, EnergyBalanceType.enthalpyPhase - ethalpy balances for each phase, EnergyBalanceType.energyTotal - single energy balance for material, EnergyBalanceType.energyPhase - energy balances for each phase.}

    momentum_balance_type

    Indicates what type of momentum balance should be constructed, default - MomentumBalanceType.pressureTotal. Valid values: { MomentumBalanceType.none - exclude momentum balances, MomentumBalanceType.pressureTotal - single pressure balance for material, MomentumBalanceType.pressurePhase - pressure balances for each phase, MomentumBalanceType.momentumTotal - single momentum balance for material, MomentumBalanceType.momentumPhase - momentum balances for each phase.}

    has_heat_transfer

    Indicates whether terms for heat transfer should be constructed, default - False. Valid values: { True - include heat transfer terms, False - exclude heat transfer terms.}

    has_pressure_change

    Indicates whether terms for pressure change should be constructed, default - False. Valid values: { True - include pressure change terms, False - exclude pressure change terms.}

    flow_type_side_2

    Flag indicating type of flow arrangement to use for heat exchanger, default ‘counter-current’ counter-current flow arrangement

    flow_type_side_3

    Flag indicating type of flow arrangement to use for heat exchanger (default = ‘counter-current’ - counter-current flow arrangement

  • initialize (dict) – ProcessBlockData config for individual elements. Keys are BlockData indexes and values are dictionaries described under the “default” argument above.

  • 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 overide the default behavior of matching the BlockData index exactly to the index in initialize.

Returns

(HeatExchangerWith3Streams) New instance

class idaes.power_generation.unit_models.heat_exchanger_3streams.HeatExchangerWith3StreamsData(component)[source]

Standard Heat Exchanger Unit Model Class

build()[source]

Begin building model

initialize(state_args_1=None, state_args_2=None, state_args_3=None, outlvl=0, solver=None, optarg=None)[source]

General Heat Exchanger initialisation routine.

Keyword Arguments
  • state_args_1 – a dict of arguments to be passed to the property package(s) for side 1 of the heat exchanger to provide an initial state for initialization (see documentation of the specific property package) (default = None).

  • state_args_2 – a dict of arguments to be passed to the property package(s) for side 2 of the heat exchanger to provide an initial state for initialization (see documentation of the specific property package) (default = None).

  • state_args_3 – a dict of arguments to be passed to the property package(s) for side 3 of the heat exchanger to provide an initial state for initialization (see documentation of the specific property package) (default = None).

  • outlvl – sets output level of initialisation routine

  • optarg – solver options dictionary object (default=None, use default solver options)

  • solver – str indicating which solver to use during initialization (default = None, use default solver)

Returns

None