Problems with CFD RESULTS

[Anonymous]

I am simulating a box that has a few CCAs. The heat dissipation within the unit is approximately 10W. The box is fully sealed and there is air enclosed. There are only two cooling mechanisms one is conduction the other is convection. The results that I am getting do not seem to make sense as the model is predicting a temperature of 20°C as the hottest places. Something does not seem right and I cannot figure out what it is. The model is set up such that there is a big chassis containing a few CCAs that are mounted to the wall and then another subassembly is contained within this big box that have a few components. Could you please suggest possible issues. I have already refined my mesh, used Advection 5 Scheme, etc.

Thanks

[Jon.Wilde]

a few questions from me:

1. What is a CCA?
2. Do you have air set to variable?
3. What boundary conditions are you using to control the external temperature? (Film coeff is likely the most suitable)

There could be other issues though, it might just be worth sharing the model so we can troubleshoot it quickly 🙂

[Anonymous]

Jon,

Thanks for the reply back. CCAs stands for Circuit Card Assemblies. I have tried film coefficient setting it at 5 w/m2K and setting up the reference temperature at 21°C . The environment is at 20°C. I checked my mesh and when I ran the surface and edge diagnostic I did see that there were a few edges highlighted. So I went into geometry tools to fix the problem. It seems to me that the box contained in the chassis is not dissipating any heat due to the 15 to 20W heat. The temperature I get is 20.00067. Could you recommend possible causes? Unfortunately, I cannot share the model.

Thanks.

[Anonymous]

Also, I have set the air to variable. Does Auto desk become confuse when you have to fluid volume for me there is one that is inside the chassis and then there is another one inside the smaller box within the chassis.  Is this is a connectivity problems. When I ran my analysis I had checked if there were any interference issues, there were none. I do not have any inlets as this is a sealed box design.

[Jon.Wilde · Accepted solution]

Without the file, this will be tough (maybe impossible) but let's try.

Next guess - you have the wrong scale. Check the dimensions of the model in CFD and the units that CFD is using. My next guess is that this is HUGE compared to what it should be... 

[Anonymous]

Thanks Jon you were right it was the conversion problem. I brought the model from Creo and was assuming that CFD automatically makes the conversion from inches to meter or vice versa. But it did not seem to have done it. Appreciate your feedback. My results make a lot of sense now.

Thanks,

Sulman

[Jon.Wilde]

Glad we found it!

It should be automatic, weird that it was not. Maybe change the default CFD units within 'options', that might help.

Thanks,

Jon