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myfjok
Posts: 4
Registered: ‎09-09-2012
Accepted Solution

Transient heat-dissipation problem

474 Views, 6 Replies
09-10-2012 02:02 AM

Here we got a case to calculate the component's temperature rise time when put it into a hot air tunnel. Attached please find the cae model. It will be get diverged after several time steps. It is highly appreciated if anybody could do me some favor to check the model and kindly give your comments.

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wildej
Posts: 927
Registered: ‎08-25-2011

Re: Transient heat-dissipation problem

09-10-2012 05:35 AM in reply to: myfjok

Hi,

 

If you have a subscription account with us I can create a case and take a look for you?

 

Kind regards,

Jon



Jon Wilde
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Product Support
wildej
Posts: 927
Registered: ‎08-25-2011

Re: Transient heat-dissipation problem

09-10-2012 05:37 AM in reply to: wildej

Also, I did try to take a peek at your file but I cannot open it..



Jon Wilde
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Member
myfjok
Posts: 4
Registered: ‎09-09-2012

Re: Transient heat-dissipation problem

09-10-2012 07:33 PM in reply to: wildej

Hi Jon,

 

Thanks for your prompt response. I'm from TE Connectivity (Tyco Electronics) and using CFdesign version2011. I archived the cfz file using split zip files due to the large file size. Can you please try to rename the files as below?

A2V1_support01.zip --> A2V1_support.z01

A2V1_support02.zip --> A2V1_support.z02

Then you will be able to open the file A2V1_support.zip, which contains the cfz file.

Please be noted that I created 3D modeling using SpaceClaim.

Any problem please let me know. Thank you again for your kind support!

 

Best regards,

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Product Support
wildej
Posts: 927
Registered: ‎08-25-2011

Re: Transient heat-dissipation problem

09-11-2012 07:47 AM in reply to: myfjok

I see, thanks.

 

The model is overconstrained. Remove all the temps on the large box apart from the base - this will be the air inlet.

Then place a p=0 and a film coeff on the top (5W/m.K at ambient +1  this (+1) helps keep the plume stable).

 

This is what we call the 'chimney approach'.

 

Try steady state first, to verify all is OK, then use transient. Probably going to need a smaller timestep too.

Do not have too many save intervals maybe 30-50 over an entire analysis as a maximum.

Unless you are particular worried about exact save points, you could improve stability but running with Intelligent Solution Control on.

Use the Mixing Length turbulence model - probably going to be the best here.

 

See how that goes.

 

Jon



Jon Wilde
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Member
myfjok
Posts: 4
Registered: ‎09-09-2012

Re: Transient heat-dissipation problem

09-12-2012 08:00 PM in reply to: myfjok

Many thanks for your attention and comments.

I found a paper from your website. http://www.cfdesign.com/en/Support/CustomerPortal/AnswerSystem/KnowledgeBase.aspx?solutionID=5013000...

For my case, I think it should belong to internal vented case. But if I created the external air block as well, I should use chimney approach, as you mentioned. Thus, could you please advise:

1) For this case, is it necessary to create the external air block?

2) If I created the external air block, is it necessary to specify the film coefficients to the exterior surfaces?

3) If I created the external air block, how to set the turbulance?

 

Furthermore I made several trials (steady state solution) to monitor a point temperature varied by different settings (see attachment). The result variance is quite large. Could you please give your suggestion also on this?

 

Thank you very much for your great support!

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Member
myfjok
Posts: 4
Registered: ‎09-09-2012

Re: Transient heat-dissipation problem

09-12-2012 08:11 PM in reply to: wildej

In addition, I have set the boundary condition and solver parameters according to your suggestion. It does work and the stability has been improved. Thanks!

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