# Heat transfer through a composite wall

Hi, friends. I’m new at this forum and I would like you to help me to try to solve the following:

I’ve been looking forward tutorials or information about how to simulate the heat transfer through a composite wall for calculating the heat loss but I haven’t found anything. So I’m going to explain what I did during the attempts to simulate this and maybe someone could tell me what’s wrong:

1- I drew the wall in 3D as you could see below:

The wall is composed by: 1/2 foot of brick, 36 cm of reinforced concrete and 2 cm of mortar.

2 - I meshed the wall and all were right.

3 - Then, I choosed a ‘heat transfer - advanced’ analysis whose properties I choosed were ‘Steady-state’ and ‘Non-linear analysis’.

4 - I started defining the materials with its respective thermal conductivity, density and specific heat. I assigned the materials that compose the wall to the volumes but here I found the first trouble: I don’t know how to define the Ris (Internal thermal surface resistance [m^2K/W]) and Res (External thermal surface resistance [m^2K/W]) so I omit that and just defined the volume of the room with the properties of air at 25 ºC.

5 - After the material assignment, I defined the boundary conditions but just the temperature because my goal is that SimScale could ‘tell’ me (calculate) the heat loss with an internal temperature of 25 ºC (293,15 K) and a outdoor one of 0 ºC (273,15 K) for what I defined the internal surface as the room’s surface in contact with the wall, and the external surface as the 1/2 foot of brick’s surface.

6 - Finally, I created a new run and after some minutes the result is:

‘The solution matrix is not factorable. This might be caused by an unconstrained rigid body motion or by overconstrained degrees of freedom due to multiple linear relations at at least one node.’

I hope someone could help me because that’s important for my air-conditioning project and I would be really grateful and happy to learn this.

Thank you in advance to this great community.

After a quick look it seems the error comes from the fact that you did not connect the different volumes using contacts. You have to define a thermal contact between two solids to allow heat transfer between them. You can check out this Thermal Analysis of a PCB Board of my colleague @ahmedhussain18 that shows how to use contacts in a heat transfer analysis.

As a side note, if you do not have any nonlinearities present, like material parameters that are temperature dependent, you should rather use the linear thermal analysis. That will reduce runtime and also behave more stable.

Best,
Richard

Thanks @rszoeke for your quick answer. I will try out as you say and I hope to solve it. I will left feedback with any newness. When you make the reference to ‘this project’ I don’t get a link so, could you send me again this one, please?

Thank you again.

Thanks, it’s updated.

I have just try it out but I think I did the contacts wrong because the Run has failed again. I saw the Thermal Analysis of a PCB which you show me but that isn’t the same because it only had 1 contact so it’s easy but instead the wall has many different contact surfaces and I don’t understand which are the master and slave.

Also, I have no clear ideas about how to define the Boundary conditions in the analysis: Temperature and Heat flux. So I’m a bit confused.

Thank you @rszoeke

You need to define bonded contact between each body in your simulation. So, in this case it requires three bonded contact sets to be defined. You can see this in the file I shared. In contact, typically the master is the larger surface, or the more course mesh, or is the flattest surface. In your model all the surfaces are flat, about the same size, and have about the same mesh on them, it really does not matter which one is the master and with one is the slave.

It looks like you applied the temperatures correctly and your part has no heat flux the way you defined it.

Please let me know if you have any other questions.

Christopher

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GREAT! I’m really thankful to you @cjquijano . I’ve succeeded simulating what I want and that’s really fine. The copy you have made of my project has been very useful for me and I appreciate that a lot.

The only doubt I have is the parameters you have introduced in the ‘Simulation Control’, this is: ‘Number of computing cores’ and ‘Maximum runtime’. I don’t understand why you have changed that and that was one of the troubles I had along with the defining process of the contacts which you have explained me fine.

Nothing more but telling you thank you again for you support. Best regards, friend.

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Hi @adripgarcia96, the Simulation Controls were changed more out of habit than anything else. I wanted to ensure the simulation would run the first time so that is why I changes the number of cores and the maximum run time. your actual setting probably would have worked fine.

Thank you again @cjquijano , I’m happy you have solved me the troubles and now I understand the ‘Thermal’s simulation’.

Best regards from Spain.