Reverse Osmosis (1D)

This reverse osmosis (RO) unit model
  • is 1-dimensional

  • supports a single liquid phase only

  • supports steady-state only

  • is based on the solution-diffusion model and film theory

  • assumes isothermal conditions

Degrees of Freedom

Aside from the inlet feed state variables (i.e. temperature, pressure, component flowrates), the RO model has at least 4 degrees of freedom that should be fixed for the unit to be fully specified.

Typically, the following variables are fixed, in addition to state variables at the inlet:
  • membrane water permeability, A

  • membrane salt permeability, B

  • permeate outlet pressure

  • membrane area or length or width

Model Structure

This RO model consists of 1 MembraneChannel1DBlock for the feed-side (feed_side.properties[t, x]), a StateBlock indexed by time and space for the permeate-side (permeate_side[t, x]), and a StateBlock for the final permeate at the outlet (mixed_permeate).

Sets

Description

Symbol

Indices

Time

\(t\)

[0]

Space

\(x\)

Normalized ContinuousSet [0 … 1] discretized by number of finite elements

Phases

\(p\)

[‘Liq’]

Components

\(j\)

[‘H2O’, ‘NaCl’]*

*Solute depends on the imported property model; example shown here is for the NaCl property model.

Variables

Refer to the Variables section in the 0DRO model.

Equations

Refer to the Equations section in the 0DRO model.

Class Documentation

class watertap.unit_models.reverse_osmosis_1D.ReverseOsmosis1D(*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

    dynamic

    Indicates whether this model will be dynamic or not. default - False. Membrane units do not yet support dynamic behavior.

    has_holdup

    Indicates whether holdup terms should be constructed or not. default - False. Membrane units do not have defined volume, thus this must be False.

    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.}

    property_package_args

    A ConfigDict 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 mass balance should be constructed, default - useDefault. Valid values: { MaterialBalanceType.useDefault - refer to property package for default balance type 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 - useDefault. Valid values: { EnergyBalanceType.useDefault - refer to property package for default balance type EnergyBalanceType.none - exclude energy balances, EnergyBalanceType.enthalpyTotal - single enthalpy balance for material, EnergyBalanceType.enthalpyPhase - enthalpy 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.}

    concentration_polarization_type

    Options to account for concentration polarization.

    default - ConcentrationPolarizationType.calculated

    Configuration Options

    Description

    ConcentrationPolarizationType.none

    Simplifying assumption to ignore concentration polarization

    ConcentrationPolarizationType.fixed

    Specify an estimated value for the concentration polarization modulus

    ConcentrationPolarizationType.calculated

    Allow model to perform calculation of membrane-interface concentration

    mass_transfer_coefficient

    Options to account for mass transfer coefficient.

    default - MassTransferCoefficient.calculated

    Configuration Options

    Description

    MassTransferCoefficient.none

    Mass transfer coefficient not used in calculations

    MassTransferCoefficient.fixed

    Specify an estimated value for the mass transfer coefficient in the feed channel

    MassTransferCoefficient.calculated

    Allow model to perform calculation of mass transfer coefficient

    transport_model

    Options to account for mass transfer model.

    default - TransportModel.SD

    TransportModel.SD”, “Solution-diffusion model for describing water and salt transport for most membrane types” “TransportModel.SKK”, “Speigler-Kedem-Katchalsky model for describing water and salt transport”

    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.}

    pressure_change_type Indicates what type of pressure change calculation will be made. To use any of the pressure_change_type options to account for pressure drop, the configuration keyword has_pressure_change must also be set to True. Also, if a value is specified for pressure change, it should be negative to represent pressure drop.

    default - PressureChangeType.fixed_per_stage

    Configuration Options

    Description

    PressureChangeType.fixed_per_stage

    Specify an estimated value for pressure drop across the membrane feed channel

    PressureChangeType.fixed_per_unit_length

    Specify an estimated value for pressure drop per unit length across the membrane feed channel

    PressureChangeType.calculated

    Allow model to perform calculation of pressure drop across the membrane feed channel

    friction_factor

    Options to account for friction factor correlations.

    default - FrictionFactor.flat_sheet

    Configuration Options

    Description

    FrictionFactor.flat_sheet

    Friction factor correlation for flat-sheet membrane modules

    FrictionFactor.spiral_wound

    Friction factor correlation for spiral-wound membranes

    area_definition

    Argument defining whether area variable should be spatially variant or not. default - DistributedVars.uniform. Valid values: { DistributedVars.uniform - area does not vary across spatial domain, DistributedVars.variant - area can vary over the domain and is indexed by time and space.}

    transformation_method

    Discretization method to use for DAE transformation. See Pyomo documentation for supported transformations.

    transformation_scheme

    Discretization scheme to use when transforming domain. See Pyomo documentation for supported schemes.

    finite_elements

    Number of finite elements to use when discretizing length domain (default=10)

    collocation_points

    Number of collocation points to use per finite element when discretizing length domain (default=5)

    has_full_reporting

    Level of reporting results. default - False. Valid values: { False - include minimal reporting of results, True - report additional properties of interest that aren’t constructed by the unit model by default. Also, report averaged expression values

  • 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:

(ReverseOsmosis1D) New instance

class watertap.unit_models.reverse_osmosis_1D.ReverseOsmosis1DData(component)[source]

Standard 1D Reverse Osmosis Unit Model Class.