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Old   May 4, 2016, 07:15
Default conjuagte heat transfer simulation
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Chaitanya
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hello,
I am new to CFX and currently working on CFX tutorials provided. I am doing the conjugate heat transfer simulation and have some doubts about this.
I want to fix a temeprature in one sub-domain at intial time t=0. At later stages i expect conduction through the solid and convection provided by the fluid/gas to reduce the temperature in this fixed sub-domain region.
Thus, I cannot use the fixed boundary condition in the sub-domain.
what are the possibilities to model this ?
I do not have any expression/table to input values. I just know some fixed value at intial time.

Regards
Chaitanya
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Old   May 4, 2016, 07:53
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You can first make a static analisis with a fixed temperature on that surface and other BCs, to obtain body temperatures than go to transient CHT to cool the bodies down with convection.

You first need to somehow get the energy into the body (transiently or staticly) to than disipate it out.
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Old   May 4, 2016, 10:16
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makes sense. Can I link the output of the static analysis as an input BC to dynamic analysis. ?
If yes, please suggest a link / tutorial to do so.
thanks for inputs.
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Old   May 4, 2016, 21:04
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This sounds like you simply define the initial condition of the solid block. It is not a boundary condition but an initial condition. For the initial condition you can define any temperature distribution you like, and this applies to both steady state and transient simulations.
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Old   May 24, 2016, 09:46
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Quote:
Originally Posted by ghorrocks View Post
This sounds like you simply define the initial condition of the solid block. It is not a boundary condition but an initial condition. For the initial condition you can define any temperature distribution you like, and this applies to both steady state and transient simulations.
Can I define initial temperature only on a surface on the domain.?
I cannot create a subdomain, because only one surface of the entire domain is the source of heat and dissipating heat into the body. !!
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Old   May 24, 2016, 12:03
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It would be great if you could describe your modeling situation better. If you are modeling a conjugate heat transfer problem, I assume you have multiple domains, at least one solid domain, correct ?

When you refer to sub-domain, are you referring to the solid domain, or a region of space within any of the domains previously defined ? For a solid domain, you can always initialize it in the domain panel. For the latter, you still initialize it in the domain panel, but you will write an expression that sets the initial value in the sub-domain of interest (see inside()@MyRegion), and other values elsewhere.

Initial conditions only make sense for the volume, not the boundaries. Therefore, the confusion from your description.

Hope the above helps,
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Old   May 24, 2016, 12:22
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Thanks for your interest.
I am modeling a cooling channel for a Drilling tool and trying to optimize the temperature Profile for the Drilling tool.
So the Maximum tmeperature is just generated along a surface in the Drilling.
I am using air flow through this cooling channel.
So , I Need to set the Initial condition of the cutting tool, which is a surface at some temperature.
pic1.PNG

The Color marked in red has high temperature profiles. I have 3 Domains, 1 solid and 2 for each of the cooling channels.

I hope, I make my question understandable
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Old   May 24, 2016, 16:59
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Ok.. Let us assume the problem is steady state first, therefore, the initial condition are irrelevant since they only aid convergence and not the final result.

From what I understood, the heating of the tool comes from an external source; therefore, it is a temperature specified heat transfer boundary condition on the solid domain.

Run it until convergence. You should be good for it.

Now, if you need to know how long it takes to cool it from a hot state to the steady solution , you must change the model to transient, set the new external temperature and repeat.

Hope the above helps,
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Old   May 24, 2016, 17:21
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That helps. A lot.
I am more interested in the time it takes for cooling and also how the temperature varies with time of the cutting edge which generates heat during the drilling process.
I do not know how to apply the BC for unsteady case... because in this case the external temperature is generated for only a surface...
Does it make sense to create one more solid domain that would be the workpiece which is been cut, and apply the temperature, initial conditon on this surface. ?
I am basically having troubles how to deal with temp. Initial BC for unsteady case!!
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Old   May 25, 2016, 08:28
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Now we are getting somewhere.

My advice is that you use a heat flux boundary condition, and let the temperature of the surface be computed. That is, for a given rotation speed, drill bit geometry, drill bit material and cut material there will be a certain amount of heat to be dissipated into both materials and the surrounding fluid (say air). The fraction of heat into the cutting tool is the one you should be imposing as a boundary condition.

Have you done the literature research of heat transfer modeling of cutting tools ? Here is a quick link

https://smartech.gatech.edu/bitstrea...00405_mast.pdf

but you should dig deeper before attempting anything further.

Good luck
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Old   May 25, 2016, 08:42
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Thanks for the link. I admit I did not read much, like 10-15 papers.!! I will get back after reading through this..
Thanks a lot for your inputs!!
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Old   June 1, 2016, 04:00
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I went through the book and some other literature about heat transfer modeling. Now, I can do a thermal analysis for to determine the temperature of the drilling surface. But, most of the literature I found do not have the observe the time required for cooling.
I want to know, whether its possible to link the output/result file of the thermal model as an initial BC for my unsteady state simulation.
Basically,I want to link the thermal output simulation as a BC condition for my CFX simulation.
Can this be done ?
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