topic Battery Powered DC Power Supply - CFD Setup Questions in CFD Forum

Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Wed, 18 Feb 2015 20:00:42 GMT

I am trying to run a CFD simulation on a battery powered power supply. It is not possible to know how many Watts to assign to each component, but I do have a thermal camera and can measure component temperatures during battery discharge. Is it a valid technique to assign temperature as a boundary condition rather than Watts?

Re: Battery Powered DC Power Supply - CFD Setup Questions

Jon.Wilde — Wed, 18 Feb 2015 20:20:18 GMT

Hi,

The important question for me is, what is the overall goal of the analysis?

It is OK to do this but really only really if we suppress the batteries from the mesh/analysis so that we do not have internal boundary conditions.

Thanks,

Jon

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Wed, 18 Feb 2015 20:40:58 GMT

I need to create a reasonable thermal simulation of an existing product to use in the design of next generation products. Only a few components get hot during battery discharge; the rest are part of the charging circuit. I have calculated the wattage of one big resistor that is heating up, but I can't do those calculations for the transformer and transistors. With the thermal camera, I have taken the temperature of the hottest components. So I wonder if I can just assign those temperatures to the component faces. I can email the model to you if that will help you to help me set this up correctly.

Re: Battery Powered DC Power Supply - CFD Setup Questions

Jon.Wilde — Thu, 19 Feb 2015 10:29:43 GMT

Hi Mark,

Assigning temperatures should be fine, so long as you are aware that this value will remain 100% fixed. Do suppress these components from the mesh too.

This is unlike applying a volumetric heat load, where the component temperature will be defined by the heat lost to the surrounding solids and air.

What do you need to see as a result from this simulation? What will define a pass/fail for the design?

If you run into other issues, sure share the CFZ, no problem.

Kind regards,

Jon

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Thu, 19 Feb 2015 13:43:47 GMT

@wildej wrote:
Hi Mark,

Assigning temperatures should be fine, so long as you are aware that this value will remain 100% fixed. Do suppress these components from the mesh too.
This is unlike applying a volumetric heat load, where the component temperature will be defined by the heat lost to the surrounding solids and air.

What do you need to see as a result from this simulation? What will define a pass/fail for the design?

If you run into other issues, sure share the CFZ, no problem.

Kind regards,
Jon

Jon,

From your explanation, it sounds like I need to use heat generation vs. surface temperatures for the components. And that is the way I learned in the turorials. We will attempt to measure component Watts on the bench today.

As for pass/fail, we will be using the thermal data to aid us in future designs. This is a production unit we are trying to replicate in our CFD model.

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Thu, 19 Feb 2015 21:19:35 GMT

I would like to run this simulation in a test chamber at ambient temperature and at elevated temperature. Please check my setup and advise if there is a better way.

Re: Battery Powered DC Power Supply - CFD Setup Questions

Jon.Wilde — Fri, 20 Feb 2015 10:43:46 GMT

Hi,

Check out the guide here for the best setup. This is for a ground based unit - which it looks like you are running here. If not, there is another approach, that you'll find in the guide.

I would think that fixing the floor to 21C is going to heavily impact your results as it appears to be on top of the condition.

Best regards,

Jon

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Fri, 20 Feb 2015 14:59:26 GMT

Jon,

Thanks for the link. I'll try that setup on Monday.

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Wed, 25 Feb 2015 12:38:25 GMT

I am getting this error in my CFD model now. Is it a mesh problem?

Re: Battery Powered DC Power Supply - CFD Setup Questions

Jon.Wilde — Wed, 25 Feb 2015 13:13:40 GMT

Hi,

What changed between the previous analysis and this one?

What was in the output bar when this popped up?

One thought I did have - if this is to be table mountned - we might need to square off the edges of the case where it meets the table. Otherwise we are going to have some very skewed elements, or zero angles which are near impossible to mesh.

Kind regards,

Jon

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Wed, 25 Feb 2015 13:41:33 GMT

Jon,

Here is the output on the failed model:

Mark McGee
Senior Mechanical Engineer
Acuity Brands
770 860-3128

Re: Battery Powered DC Power Supply - CFD Setup Questions

Jon.Wilde — Wed, 25 Feb 2015 13:36:37 GMT

Hi Mark,

I am not sure that image worked OK.

Would you like to share the CFZ once more?

Thanks,

Jon

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Wed, 25 Feb 2015 13:40:46 GMT

Here is the output:

Re: Battery Powered DC Power Supply - CFD Setup Questions

Jon.Wilde — Wed, 25 Feb 2015 13:41:57 GMT

OK so this is past the meshing stage.

It says flow off as there is no fluid?

Is that right?

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Wed, 25 Feb 2015 13:42:50 GMT

Here is the CFD file:

https://drive.google.com/file/d/0B8KVvS6tGzv_cEJiWURMRXVKOUE/view?usp=sharing

Re: Battery Powered DC Power Supply - CFD Setup Questions

Jon.Wilde — Wed, 25 Feb 2015 14:00:03 GMT

Thanks.

What I posted above is your solution. What I think should be your air domain is set to be graphite. Change it to air-variable and you'll be all set!

Thanks,

Jon

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Wed, 25 Feb 2015 14:25:45 GMT

I'm back in business. Thanks Jon.

Re: Battery Powered DC Power Supply - CFD Setup Questions

Anonymous — Wed, 25 Feb 2015 17:54:14 GMT

Please review my setup. I am trying to model a test chamber (oven) so I can test this product at 55° C. I modeled the chamber and let Sim CFD create the air mass. I set the boundary conditions on the top surface of the air mass as shown in the image. It seems to run alright, but I want to know if there is a better way to model the oven.