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Hi

but do you not have the HeatTransfer - Conjugated Heat Transfer - laminaror turbulent flow NITF ?

I do believe if you are careful with the couplings, you should be able to compose your other physics to the same effects as NITF for the dependent variables is equivalent to SPF + HT, remains to know how the fields are coupled internally ;)

The main isuse with fluids and heat is that you take into account both heat transport and conduction, it's easy to forget one ;)

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Good luck
Ivar

Hi Ivan,

Thanks for your response.
I double checked and we do not have the heat transfer module. Therefore no conjugate heat transfer.
I am trying to use two-phase laminar flow with heat transfer in solids and heat transfer in fluids.
I'm having a hard time with the boundary conditions trying to mimic natural convection to ambient air.
Any input would be appreciated.

Thanks for your help.

Selin

Hi

try something like the following weak expression on your bounary:

my_h*(Text-T)*test(T)

where my_h [W/m^2/K] is the heat transfer coefficient, Text hte external temperature and T the dependent variable for the temperature field

Pls check carefully, among other the sign to be sure you "cool" and are not "heating" your boundary if T>Text

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Good luck
Ivar

Hi Ivan,

I tried a very simple rectangular microchannel with a heat source downstream. Just to understand if I can do laminar spf, heat transfer in fluids and heat transfer in solids without conjugate heat transfer analysis.
I do get some velocity results, the fluid temperature does not change (which should b/c of the solid heat source).
I do not know what I'm missing.
Sometimes I do get the following error:

Cannot evaluate expression
Failed to evaluate variable.
-variable mod1.ht2.gradTx
-Geometry: 1
-Domain: 1
Failed to evaluate expression.
-expression mod1.ht2.gradTx
-Plot: arwv1 (arrow volume)

I'd appreciate it if you can take a look at my model (please find attached).
Note that I removed the mesh and the results to make the file smaller.

Thanks a lot!

Selin

Hi

first you do not need to "zip" a mph, its already a "zipped" file you will not gain anything like that ;)

in your model you have 2 HT physics, each with a different "T" that is getting complex. You can define only 1 HT and include 2 Heat transfer nodes, one for the solid and one for the fluid under the same HT. Then you have only 1 T and its much easier and logical to link your model

Now HT + SPF is in fact NITF physics, that is precooked for you, if you have access to that one (check the doc)

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Good luck
Ivar

Hi,

Thanks so much for the reply. Unfortunately we do not have NITF. That's probably one of the reasons I'm struggling with this model. I will define 1 HT (does it matter solid or fluid?) and try with 2 different temperature boundary conditions.

Once again thank you.

Selin

Hi

mostly there is a "master and a slave domain", if the solid heats the fluid, start with "solid", if the opposite use "fluid", for my version I can add a sub node in HT of Fluid or Solid, then you can mix. But this could be linked to the modules I have. If you do not have that I'm not sure what is the best, needs some thinking, as you cannot really model a fluid with a "solid" interface

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Good luck
Ivar

Hi Ivar, I contacted you yesterday regarding a similar problem. Thanks for the response. Two issues remain unfortunately. To recap:

I tried to solve for heat transfer due to flow from a head containing a micro-nozzle to a substrate plate. At first, I used the rarified gases slip model coupled to both a heat transfer for fluids and heat xfer for solids. The calculation failed and I then simplified to one heat xfer model taking into account both phases, but again to no avail.

I finally relied upon the conjugate heat xfer model which worked, however I was relegated to using only a laminar flow option for my fluid flow. I'm quite sure the model is not accurate as Knudsen diffusion has to be taken into account at these low pressures and tiny dimensions. If you can direct me as to how to include the rarified gases models alongside the conjugate heat transfer, I would really appreciate it.

How can I include rarified gases in such a model? Should I use nonisothermal flows? Also, the model would throw errors if I started with cold boundary conditions and proceeded to flow heated gas through the channel. I tried more complicated step functions so the computer would accept my values, but it didn't work. As such, I could not view the time evolved temperature change as the substrate went from cold to hot. Instead, I would have to start with a hot substrate and let it equilibrate to room temperature before flowing the gas onto the substrate, which gave me an artificially hot blanket above the substrate. Any suggestions? Many thanks! I would attach the mph file, but it is too large.