[Simscape:thermal liquid] Pressure increasing without reason...

Hello,

I am trying simscape and I am having an issue on a rather simple system. I am using the library "thermal fluid" to model a system of a pressure source + pipe with the pipe exchanging heat to another body (thermal mass).

I would like in the end to see the temperature of the body and the temperature of the fluid (water) converging toward the same value as it should...

However, when I am simulating, I can see the pressure of my fluid (scope absolute pressure) rising and rising again until it crashes around 5e7 Pa. I cannot understand how the pressure is increasing that much... The pipe provide the exact pressure loss to compensate the pressure source (as the scopes show) and the temperature is evolving too slowly to cause such increase of pressure. I even get the problem if my body is at the same temperature of my fluid initially.

I attached the file for anyone willing to help me on this matter. Maybe I overlooked something basic.

Best,

Sylvain Mathonnière

[Jens Lünenstraß]

Hey Sylvain,

i'm experiencing the same problem. Just started with Simscape, building up a simple system and the pressure is always crossing the boundaries. Did you found a solution to this problem?

Best,

Jens

Edit: I did find a solution to my problem:

1. Open the block called 'thermal liquid settings'
2. Go to 'Density'
3. Set 'Density parameterization to 'Reference Density'
4. Set 'Constant isobaric thermal expansion coefficient' to zero

Simulate!

This worked for me. This way you ignore the influence of the temperature on the density, but as the density is varying only between 958kg/m^3 and 999kg/m^3 between 0 °C and 100 °C, you shouldnt't get into too much trouble.

Answer 1

[Sylvain Mathonniere]

So I checked a bit more the issue and it seems the pressure is just increasing following the change of temperature.

If the temperature of the fluid decreases, then the pressure of the fluid decreases as well (and hit an error like "too low pressure".

I am therefore looking at a way to decrease this built-in pressure but with no success so far... I used a pressure relief valve that I got from the simulation the example "ssc_tl_hydraulic_fluid_warming" but it does not work and just relieve the pressure drop on the pipe.

My main question is how can I maintain the absolute pressure of my fluid constant inside of my system ?

I attached the file in question as well as a picture of the model.

PS: it seems that setting the isobaric thermal expansion coefficient equal to 0 does the trick but I would prefer a physical solution.