How can i adjust thermal fluid settings from an THB-Bus? (Simscape Thermal Liquid)

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Hello everybody,
I am currently facing some problems modelling a district heating network. In the model I use both Simulink (Carnot Toolbox) and Simscape Thermal Liquid. In the attached Screenshot you can see how I planned to model the crossover from a THB-Bus to physical properties. Basically all I want to do is adjust the fluid settings pressure, temperature and massflow by the data given in the THB-Bus.
At the beginning this works out for temperature and pressure but when I try to adjust the massflow (Controlled Mass Flow Rate Source (TL)) both properties (T and p) increase dramatically. At least the massflow is just right afterwards.
I am very thankful for any kind of ideas!

Answers (1)

Sarah McElman
Sarah McElman on 18 Nov 2020
Hi Johannes,
I understand that you'd like to adjust the values of the pressure, temperature, and mass flow rate in a single line independently based on input signals, but when you change the mass flow rate, the changes in pressure and temperature are unexpected.
Which version of Matlab are you using? Without being able to verify the values in your model, I can't say for certain what the issue is, but I have a few questions and suggestions:
0) How different is the response from what you're expecting?
1) Is the behavior replicated when substituting a pump block, such as the Fixed-Displacement (TL) block?
2) Try adding a pipe block after the Controlled Mass Flow Rate (TL) block. This adds a dynamic component (another differential equation) that "softens" the model/solver response.
3) At the moment, your model is very stiff - check that you're using the most appropriate solver. See this page from our documentation more information:


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