SimScape-Model of a Reverse Osmosis Plant

Hello everyone,

I am planning on creating a model of a simple reverse osmosis plant using SimScape Fluids.

Therefore i have to create an custom membrane component in simscape to simulate the split of the waterflow within the membrane module.

The split of the water depents on the pressure and the concentration of salt in the waterflow. I have already found one thesis where someone has done such a custom element. He used a hidden domain for the salt concentration.

https://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=8906434&fileOId=8906435

Now my question is, is it possible to customize the standard IL Fluid domain to incorporate the salt concentration, or should i do it as show in the other thesis? Or is it maybe the easiest way to build a simulink model for the salt concentrations in combination with the simscape model for the fluid dynamics of the plant?

Answer 1

[Aravind]

Hi @Niklas Humberg,

You can indeed customize the salt concentration in the Isothermal Liquid (IL) Fluid domain. In MATLAB R2024b, the Isothermal Liquid domain in Simscape includes support for seawater as one of the isothermal liquids. This uses the seawater model described at https://web.mit.edu/seawater/.

To use the seawater model within the IL domain of Simscape, follow these steps:

1. Open the Simulink library browser and navigate to “Simscape/Fluids/Isothermal Liquid/Utilities”. Insert the “Isothermal Liquid Predefined Properties (IL)” block.
2. Double-click on the inserted block to open the block parameters.
3. From the dropdown menu for the “Isothermal Liquid” parameter, select the “Seawater (MIT Model)” option.
4. Enter the desired salt concentration in the “Dissolved salt mass fraction” parameter.

For more detailed information, you can refer to the official MathWorks documentation at this link: https://www.mathworks.com/help/hydro/ref/isothermalliquidpredefinedpropertiesil.html.

Hope this helps!

[Niklas Humberg]

Thank you so much for your quick response! This already helps a lot!

After you set the desired salt concentration in the properties, is it static or can it vary throughout the model? For example if the concentration rises in a membranelement or if two waterflows with different concentrations mix in a process?

[Aravind]

Hello @Niklas Humberg,

The salt concentration you aim to maintain will remain constant within each unique isothermal liquid circuit. Simscape does not automatically handle changes in concentration when two water flows are mixed. You will need to manage this aspect when defining the membrane. If you attempt to connect more than one "Isothermal Liquid Properties (IL)" block within the same isothermal liquid circuit, it will result in an error. For more details, you can refer to the official documentation here: https://www.mathworks.com/help/simscape/ug/troubleshooting-simulation-errors.html#brbwgs1-1.

As an alternative, you can create a custom component to mix two fluid flows. For guidance on this, you might find this MATLAB Answer helpful: https://www.mathworks.com/matlabcentral/answers/2054879-simscape-thermal-liquid-domain-custom-component-mixing-element.