Model Perfectly conducting fluid pipe simscape

Hi Everyone,

Im trying to model a cooling system in Simscape. From some experimental data I want to input a heat load of 4 kW, and at some other point I want to have a radiator with a cooling rate of 611 W / Kelvin, with an outside temperature of 50 degrees (meaning if the fluid is 50 degs nothing happens, and if it is 60 degrees, It cools with 10*611 W). How best to model this? Im using pipes at the moment with a controlled heat flow rate source for the heat source, and a pipe with a convective heat transfer block for the cooler. The stabilization temperature seems to vary if I change the pipe length, surface area etc which makes sense, but I just want the pipe to just have a ideal conduction if you know what I mean.

I know something is wrong since it does not match the experimental data, even though the values are derived from it.

Answer 1

[Umar]

Hi Jelmer,

I think the issue is that your Pipe (TL) blocks are adding their own thermal mass and heat transfer, which is why the steady-state temperature changes when you modify pipe geometry. The pipes are being too "realistic" when you just want ideal conduction. Here is quick solution to your problem. For the 4 kW heat input connect your Controlled Heat Flow Rate Source to a Thermal Mass block first (set it to fluid_volume × density × specific_heat), then connect that to your pipe network via the thermal port (H). Now, for the 611 W/K radiator: Instead of using a pipe with convective transfer attached, connect a Convective Heat Transfer block directly between your pipe's thermal port (H) and a Controlled Temperature Source at 50 degrees centigrade. Set the heat transfer coefficient to 611 W/(m^2.K) with area = 1 m^2 to get exactly 611 W/K. For connecting pipes, I would make them thermally neutral by setting very short lengths (0.1 m), turning off "Dynamic compressibility" and "Fluid inertia", and setting the Nusselt number really low (0.001). Afterwards, you should see at steady state: 4000 W = 611 W/K × (T - 50 degrees centigrade), so T should stabilize at 56.55 degrees centigrade regardless of pipe geometry. In addition to that, I can even suggest simpler alternative, if you don't need fluid dynamics, skip Thermal Liquid entirely and just use regular Thermal blocks: a Thermal Mass for your fluid, a Heat Flow Rate Source (4 kW), and a Convective Heat Transfer block (611 W/K) to a 50 degrees centigrade source. This completely avoids the pipe complications.

The key is separating your thermal behavior (thermal mass + heat transfer) from the flow circuit (pipes just move fluid without participating in heat transfer).

Hope this helps!

[Jelmer]

Thank you, this worked. The only problem was that the pipe with a described heat transfer coefficient was giving very strange values (still transferring almost no heat, leading to the temperature infinitely increasing). I used a Constant volume chamber like Zifeng suggested instead of a pipe and it worked perfectly.

[Umar]

Hi @Jelmer,

Glad to hear that your problem is resolved.

Answer 2

[Yifeng Tang]

Use a Constant Volume Chamber of represent to coolant volume in your radiator. Connect a thermal resistance block to the H port and set the resistance value to 1/611 [K/W]. I believe that's all you need.

[Jelmer]

Thank you, indeed using a constant volume chamber is a better approach than a pipe for my problem.