Applying heat transfer boundary conditions
Greetings!
I have a solid containing a fluid (water tank, 100% filled). My question pertains to the heat transfer between the tank and its environment. Is there a way to apply boundary conditions like convection and solar radiation? |
heat flux from where to where?
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For instance, on the top surface of the tank we have heat gain from solar radiation (heat flux) and heat loss to the environment via convection. From what i understand, we can't apply two boundary conditions on the same surface. How should i approach this? Haven't found any example or tutorial where we have both convection and heat flux on the same surface...
Edit: I just realized that you cannot use a surface as a boundary condition and as an interface at the same time, something that perplexes things. I really need a comprehensive example. |
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Thank you for your answer!
Lets us ignore the first part of your answer for the time being. I'll figure out the specifics about CEL expressions later. What i've done so far is define a solid and a fluid domain, as well as their automatically generated solid-fluid interface. If i go ahead and insert a boundary condition in a surface, that surface will be subtracted from the solid-fluid interface. Naturally, if i do this (add boundary conditions) for all the surfaces within the interface, i'll end up without interface. Weird huh? On top of that, i have NO heat transfer between the domains. I've been "tinkering" for quite some time without results... |
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You can add heat fluxes to the interface boundary condition. This allows you to have an interface with additional heat input. I think this is what you want. Have a look at the interface boundaries on the domain level (not the interface condition by itself). |
I see....Each domain's interface provides a heat source option. How do i make the domains convect heat? I don't want just a steady heat flux.
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you have heat flow and heat flux option.
You can set one domain as heat source or select some faces and set them as heat source. Then you need buoyancy setting enabled for the fluid. For domain you can set heat as kW per m^3 and for a surface kW per m^2. Or you can specify a temperature. It is a good idea to create named objets in the mesher. I.e. name the domain or the surfaces in question something descriptive like heat source. Then they are easier to identify in the Preprocessor |
I apologize for taking a long time to answer. I' d like to thank both of you, for pointing me to the right direction. I have successfully run simple simulations (at least i think so), both steady and transient. Now my problem lies in simulating a partially filled water tank. Including a second fluid certainly perplexes things...
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Any help will be appreciated! |
Try the fluent forum.
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Convection is Flux = h(Twall - Tambient)
So if you have a heat flux you wish to apply on top of that the Flux = h(Twall-Tambient)+A where A is your additional heat flux. |
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Switch to CFX and it will work fine. Otherwise refer to post #11.
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Thanks again. For solving my problem, after studying much more, I came up with the following conclusion. If I define the environment around the top box for FLUENT, I will have two separate surfaces for applying the boundary conditions. Therefore I will have the heat flux for one of two surfaces and convection and radiation for the other one. Please see the attached, figure 1 shows the geometry I have already worked with and Figure 2 is the new one. The problem I have now is that the surfaces I want to apply boundary conditions for are predefined by FLUENT as interface, so I have no access to assign boundary conditions for them. so the question will be: Is there any way to convert interface to wall? If yes so, I will be able to follow my hypothesis. ThanksAttachment 43697
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This is what I do ready need, but how can I add heat fluxes to the interface boundary condition? Thanks in advance
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Let me quote post #11 for you:
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Either the no heat transfer result is correct or you set the simulation up wrong.
If you are in a flow regime when very little heat transfer occurs then it is correct that you don't see much heat transfer. This could be the case if the intermediate material has high thermal resistance or specific heat or many other factors. If the simulation is wrong then you set it up wrong. The most obvious thing is whether the interfaces between the fluids and solids are correct. If they are wrong it will stop heat transfer. Have a look at the non-overlap % reported in the output file. Also what do you mean by heat as kW/m3? Do you mean there is a volumetric heat source in there somewhere? Or is that the heat content of the incoming fluids? |
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