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Flow Sim help needed - thermal chamber simulation

Question asked by Keith Mulhern on Nov 12, 2020
Latest reply on Nov 12, 2020 by Bill McEachern

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I'm attempting to recreate a thermal chamber that we use for testing electronic devices.

Quick rundown of model setup:

- Chamber is fully modeled with 20"^3 plenum with 250CFM convective fan at the rear.

- Fan is modeled as an internal fan with an inlet aperture at the top of the chamber and outlet at the bottom (which successfully represents the convective flow).

- Fluid subdomain set as 55C to represent ambient temperature.

- Electronic device outputs ~50W in thermal dissipation.

- No boundary conditions applied (chamber walls are non-conductive adiabatic).

The problem I'm having is that the device simulation internal temperatures - as well as those of the outer case - are ~20C higher than the physical test (thermo-couples are applied to various key locations during testing). The physical chamber would naturally counteract the device dissipation by cooling the fan air to maintain the 55C ambient, but the problem I'm having is that I'm unsure on how to represent that phenomenon in the model.

All suggestions welcome.

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Bill McEachern Nov 12, 2020 3:21 PM

Lots of options. You could add a volume, disable it, put a duct around it, put an internal fan against it, and give the volume a fixed temperature, and have all air come out at the target temp.....there are other ways. Give it a whirl and see how it goes. You could also use a negative power equal to the input power.....depends on specifics....

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Keith Mulhern @ Bill McEachern on Nov 12, 2020 4:07 PM

Thanks Bill - appreciate the feedback. Not completely clear on the additional volume approach; the air temp coming from the fan would need to be a lower temp than the ambient to maintain the 55C, in order to overcome the device output. Would the extra volume element be a heat sink of sorts? Regarding the negative power suggestion; does that entail a calculation to apply a 50W equivalent negative temperature to the airflow?

I've tried a direct fan airflow onto the unit (not representative of the physical chamber), and that does help, but I'm trying to replicate the physical test as closely as possible for future simulations.

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Bill McEachern @ Keith Mulhern on Nov 12, 2020 5:28 PM

When u disable some volume (look in component control) it be comes a fluid volume and you then tell it to be a variety of things like a heater, a cooler, a fixed temp block of magic, pourus media, etc. This volume, if say you apply a negative power it becomes an air cooler.

Hope that helps. The first few tutorials in the documentation are worth doing. Also, test chamber can be a bit tricky. Modelling them like they work is the way to go.

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Bill McEachern Nov 12, 2020 3:21 PM
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Lots of options. You could add a volume, disable it, put a duct around it, put an internal fan against it, and give the volume a fixed temperature, and have all air come out at the target temp.....there are other ways. Give it a whirl and see how it goes. You could also use a negative power equal to the input power.....depends on specifics....
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- Keith Mulhern @ Bill McEachern on Nov 12, 2020 4:07 PM
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  Thanks Bill - appreciate the feedback. Not completely clear on the additional volume approach; the air temp coming from the fan would need to be a lower temp than the ambient to maintain the 55C, in order to overcome the device output. Would the extra volume element be a heat sink of sorts? Regarding the negative power suggestion; does that entail a calculation to apply a 50W equivalent negative temperature to the airflow?
  
  I've tried a direct fan airflow onto the unit (not representative of the physical chamber), and that does help, but I'm trying to replicate the physical test as closely as possible for future simulations.
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  - Bill McEachern @ Keith Mulhern on Nov 12, 2020 5:28 PM
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    When u disable some volume (look in component control) it be comes a fluid volume and you then tell it to be a variety of things like a heater, a cooler, a fixed temp block of magic, pourus media, etc. This volume, if say you apply a negative power it becomes an air cooler.
    Hope that helps. The first few tutorials in the documentation are worth doing. Also, test chamber can be a bit tricky. Modelling them like they work is the way to go.
    Like • Show 0 Likes0
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Flow Sim help needed - thermal chamber simulation

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