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Surface Source - Fixed Temperature?

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Old   April 24, 2014, 12:19
Default Surface Source - Fixed Temperature?
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Rob
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Hello CFD-online forum,

I performed a quick search of the forum for "surface source" only to find a very limited selection of topics. Nothing seemed to address my issue. I feel pretty certain that someone will be able to answer my question!

I am using SolidWorks Flow Simulation 2014.

Is it possible to constrain a surface heat source to a specified temperature? Why is the temperature specification missing from the Surface Source feature?

This appears to make (physical) sense in my head, although perhaps I'm overlooking something quite simple...

Say I have an metal cube involved in a CHT problem. I'm interested in determining the temperature distribution in the cube if five of the sides are subject to forced convection. To the sixth side is affixed a [insert a heat source here: a combustion chamber, TEG, heat exchanger, extended surface geometry subject to some other flow, etc.] such that I can safely assume that the heated surface of the cube takes on the temperature of the provider of that heat. And, as you may have guessed, I am not interested in modelling the intricacies of that heat source. How would you go about modelling such a scenario in SWFS?

For now, my solution would be to create a very thin solid body in perfect thermal contact with the cube and apply a Volume Source feature with a specified constant temperature to that thin body. Is this the best approach? Are there any physical concerns (i.e. concerns with this model accurately representing the real-life scenario) when approaching a problem in this way?

Thanks for the help!
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Old   May 6, 2014, 09:28
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Boris Marovic
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Hi Rob,

Yes, but you have to specify it in the "Boundary Condition" rather than under "Surface Source". So just like specifying an inlet or outlet you can specify a wall type of that condition in which you can define conditions such as roughness different from the one set in the general settings to selected surfaces as well as heat transfer coefficient and a temperature or just a wall temperature.
Maybe a little bit confusing.

I hope this ends your search,
Boris
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Old   May 6, 2014, 10:26
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Boris,

Thank you for the reply. You are absolutely correct; imposing a constant-temperature boundary condition for a wall that bounds a fluid subdomain is definitely possible.

However, what if that wall lies elsewhere? In conjugate heat transfer problems, it is often the case that a heat source is acting on a fluid subdomain "at a distance" if that wall is separated from the subdomain by virtue of some material.

If you try imposing a boundary condition on such a wall in Flow Sim, you will receive an error, as the wall does not bound the fluid subdomain. Specifically, it will appear as a rebuild error, and the message will read "[nameOfFace] is not laying on the boundary between solid and fluid region."

I probably didn't make it clear in my first post that such a case was the one I was interested in. Sorry!
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Old   May 6, 2014, 11:15
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Oh, I understand.
You have an internal simulation with a body in a distance to the actual considered model under flow conditions such as a hot engine in a distance to a pipe with a flow thought but only the pipe flow should be cosidered. Is that correct?

But even in that case, as long as both bodies are inside the computational domain, the wall condition can be defined as outer wall which basically means it is not in contact with a fluid even if there is no fluid in between the two bodies the wall has then a defined temperature but you might want to activate radiation as that is then the only way to transfer the heat from the surface to the other component.

Consider the tutorial example "Radiative Heat Transfer". Set it to internal and deactivate the "heat conduction in solids only" setting in the general settings. You need to move the one part of the sphere to have a surface contact with the other part so you have an internal volume. You can delete or deactivate the heat source in the sphere so now you have fluid in the sphere but none around it. You can then apply a wall heat source as outer wall on the large disc and it works. If you have radiation activated it will radiate onto the sphere, if not then there is no heat transfer between the two bodies.

Does that help?
Boris
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Old   May 6, 2014, 12:00
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Boris,

Thanks again for the assistance.

I think I may have failed to make the situation clear; it's actually simpler than the situation you're describing!

Let's say we have a solid block of material with a hollow "tunnel" within the block. The tunnel has two exposed openings.



Let's call one opening the inlet and the other, the outlet. Within this cavity will flow a fluid of interest. The fluid subdomain will encompass the cavity that snakes within the block. Our fluid subdomain is totally encompassed by walls; thus, we will run an internal flow analysis.

If I would like to apply a heat source to the opposite side of this block, I must insert a Source feature in Flow Sim. I cannot impose a boundary condition as the face of this block lies outside of the fluid subdomain. Any heat transferred to the fluid is by virtue of conduction through the solid.

No Flow Sim problems so far. Applying a boundary condition to the heat source wall results in an error - expected, as it lies outside of the fluid subdomain. Applying a surface source feature to the wall does indeed result in a CHT system and the solid (and thus the fluid) exhibits a thermal gradient.

My question is this: why isn't the constant-temperature specification available for the Surface Source feature? It's available for the Volume Source feature, and it seems odd to me that it's missing from Surface Source.
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Old   May 7, 2014, 06:38
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Ok, a sketch makes it all much clearer :-)
The reason why it is not in surface source is simple because the developers didn't do it that way. I know it might be confusing in this case of a surface temperature while a volume temperature is under volume source.
I cannot speak for the developer who initially did it this way or why it was done like this as it is like this for many years.
However, you need to specify a "Boundary Condition" with the type of "wall" and the wall type "outer wall". Here you can specify the temperature of the wall as well as a different wall roughness and a heat transfer coefficient.

Maybe they did it because it is a wall boundary condition and not a source in that way and wanted to include it in the boundary condition feature and maybe later in the early development years they saw the need for a surface source but the wall temperature was already in the other feature so they left it. However, you will need the boundary condition feature as described above and If you use an internal simulation with heat conduction and the whole model is inside the computational domain (make sure the reset the computational domain to be sure) then it should be possible to define such an "outer wall" type wall with a specified temperature.

I'll try to do a screenshot of an example.

Boris
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Old   May 7, 2014, 07:00
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This image shows the outer wall setting and the outer wall, as the name suggests, does not need a fluid domain contact such as the regular wall type.

Boris
Attached Images
File Type: png wall2.png (25.5 KB, 13 views)
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Old   May 7, 2014, 09:46
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Boris,

Wow. How simple. How did I overlook that third option each and every time?! You literally gave me the answer in an earlier post and I failed to realize it.

Now it's clear why your mind starting going in the direction of complex radiation models: you must have assumed the answer you were providing was too simple! I'm off to a good start on this forum...

Thank you so much for the information. That was very helpful!

As an aside: is there a SW Flow Sim user manual? I have three documents (and I had to dig for all of them in my file system) for use as Flow Sim references: a Tutorial manual (full of helpful tutorials), a Technical Reference (Information on underlying software mechanics and physics, and their corroboration) and a Solving Engineering Problems document (an interesting read with advanced topics and advice). However, I wouldn't call any of these documents a "user manual," outlining the function of each feature and tool in Flow Sim, one by one.

If I have a question about a feature in ANSYS, for example, I open up the (Fluent) user manual, hit Ctrl + f and search for the function name / a keyword. The document contains every single tool, menu, GUI and CLI function, etc., so if it's not in there, it's probably not in the software.

Is there such a manual for Flow Sim? That way, I don't have to resort to wasting other users' time with silly questions.
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Old   May 9, 2014, 02:25
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Hi Rob,
I'm glad, I thought I am missing something in your case.

Yes, of course. In every feature such as boundary condition or window that you open like for the engineering database or the solver run, you have a question mark somewhere in the window like the one in my screenshot right next to the header name "Boundary Condition". Simply click on it and you are already in the help related to that specific feature in which all the settings are explained on what they mean. If you want to know more about a certain parameter or option you can also search in that help by going to the search or index part of the help and type in anything you are looking for and it should find some related topics in which it is mentioned.

However, if you have any question that might not be clear to you from that help, feel free to come back to the forum ;-)

Boris
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Old   May 9, 2014, 14:14
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Boris,

Yet another simple answer to a simple question. Thank you for being awesome.

Perhaps it's because I couldn't access the tutorials via the SW menus (as you would access them for other SW software modules; that is, via Help > SolidWorks Tutorials) that I just assumed that the only way to access reading material for Flow Sim was by digging around in the file system. I've literally never once clicked on one of those little question marks. How funny.

Thanks again for everything!
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