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osmotically_assisted_reverse_osmosis_1D.rst

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Osmotically Assisted Reverse Osmosis (1D)

This osmotically assisted reverse osmosis (OARO) 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
  • assumes the feed-side flows in the forward direction
  • assumes the permeate-side flows in the backwards direction
.. index::
   pair: watertap.unit_models.osmotically_assisted_reverse_osmosis_1D;osomtically_assisted_reverse_osmosis_1D


.. currentmodule:: watertap.unit_models.osmotically_assisted_reverse_osmosis_1D

Degrees of Freedom

Aside from the feed-side and permeate-side inlet state variables (i.e. temperature, pressure, component flowrates), the OARO model has at least 4 degrees of freedom that should be fixed for the unit to be fully specified. Unlike RO, which only accounts for concentration polarization on the feed side, the OARO model includes a structural parameter variable, which is used to calculate the membrane-interface concentration on the permeate side.

Typically, the following variables are fixed for the OARO model, in addition to state variables at the inlet:
  • membrane water permeability, A
  • membrane salt permeability, B
  • membrane area
  • structural parameter

On the other hand, configuring the OARO unit to calculate concentration polarization effects, mass transfer coefficient, and pressure drop would result in 6 additional degrees of freedom. In this case, in addition to the previously fixed variables, we typically fix the following variables to fully specify the unit:

  • feed-side spacer porosity
  • feed-side channel height
  • permeate-side space porosity
  • permeate-side channel height
  • feed-side Reynolds number or water mass recovery

Model Structure

This OARO model consists of a separate MembraneChannel1DBlock for the feed-side and the permeate-side of the OARO unit.

  • The feed-side includes StateBlocks indexed by time and space (feed_side.properties[t, x]) which are used for mass, energy, and momentum balances, and additional StateBlocks for the conditions at the membrane interface (feed_side.properties_interface[t, x]).
  • The permeate-side includes StateBlocks indexed by time and space (permeate-side.properties[t, x]) which are used for mass, energy, and momentum balances, and additional StateBlocks for the conditions at the membrane interface (permeate-side.properties_interface[t, x]).

Sets

Description Symbol Indices
Time t [0]
Inlet/outlet x ['in', 'out']
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 :any:`0doaro_variables` section in the 0D OARO model.

Equations

Refer to the :any:`0doaro_equations` section in the 0D OARO model.

Class Documentation