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44,115 Views 3 Replies Last post: Sep 29, 2010 2:17 AM by dirk_niemeier RSS
jitender.kumar Lurker 3 posts since
Sep 28, 2010
Currently Being Moderated

Sep 28, 2010 7:37 PM

Flotherm accuracy in natural convection

I am using flotherm for simulation of power supplies of various power range. For natural convection(without fan) power supplies, Flotherm doesnt predict temperature accurately. I performed some testing also. We measured the actual power dissipation for main components( Transformer, choke, Fet, Capacitor). After getting the actual power dissipation, i performed Simulation again and compre with actual temperature measurement. I got the difference of -10% to +18%. for me it is huge. It would be great if someone share their ideas.

 

Thanks

Jitender

dirk_niemeier Active 45 posts since
Oct 20, 2008
Currently Being Moderated
Sep 29, 2010 1:30 AM in response to: jitender.kumar
Re: Flotherm accuracy in natural convection

My two cents:

 

Radiation included?

Turbulence Model = Laminar (as long as you are sure it's laminar)?

Choke Modeling is IMHO often not so easy (material settings, losses in the core etc ...

Gridding ok (if in doubt raise an SR)?

Measurement "setup" in experiment and in simulation identical? I've seen lots of cases where the position of thermocouples and monitor points were not identical ... IR is also critical as in the experiment you have to open the chassis and in the FT model is very often closed ...

 

Cheers,

Dirk

dirk_niemeier Active 45 posts since
Oct 20, 2008
Currently Being Moderated
Sep 29, 2010 2:17 AM in response to: jitender.kumar
Re: Flotherm accuracy in natural convection

Low level stable is usually ok. Do you have some high conducting materials (Cu or matierial with k>k(Cu)) inside?

 

In [Solve/Overall Control] switch on the Field Error for Temperature and solve one more iteration. Visualize the Field Error: Where is it worst? For high conducting materials you often see some random (or even periodic) pattern in the solids in a very small intervall. That's what is causing the low level stability. But you should check ...

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