4 Replies Latest reply on Feb 6, 2014 3:36 PM by Jared Conway

    Floworks Accuracy

    Abraham Azar III
    Abraham Azar III Feb 6, 2014 10:05 AM

      To All,

       

      We recently purchased Floworks and are using it to thermally model an electronics project.  Before we start using it for any projections on this design, we're testing its accuracy on small experiments.

       

      Right now I've got a 3 Ω resistor burning 3 Watts attached to a heatsink.  I've entered heat generation, thermal resistance (measured and calculated), ambient air conditions etc.

      I'm quite sure I have all of the initial conditions as close to reality as possible.

      Unfortunately I cannot get the results to get any closer than 10°C below what I am physically measuring (Calc = 40°C, Meas = 30°C).

       

      Have any of you guys gotten floworks to produce highly accurate results (i.e. ±2.5°C) or is it always off or is there some major variable that is easy to miss that would influence the results?

       

      Thanks in advance  -  Bram

        • Re: Floworks Accuracy
          Jared Conway
          Jared Conway Feb 6, 2014 10:38 AM (in response to Abraham Azar III)

          I've been within 0.5 deg in some sims. But we spent a lot of time making sure that the settings exactly matched the physical.

           

          Have you included radiation?

           

          Have you done mesh convergence?

           

          Have you considered that there will be some discrepancy between physical and numerical such that you have looked at trends to see that trends are correct and that the discrepancy may just be a constant to keep track of as an assumption between designs?

          • Re: Floworks Accuracy
            Mark Keown
            Mark Keown Feb 8, 2014 4:27 PM (in response to Abraham Azar III)

            Brian,  Getting the fidelity between simulation and what you have on the bench is a mission.  Is the problem with the test or simulation or both?

            Bench or Heat chamber consideration that you may think make no difference but do:

            - Solar from windows

            - The building HVAC moving air.  Look a JEDEC specifications testing boards.

            - The heat chamber fan

            - Radiation from ancillary equipment

            - The UUT is on a table or bench

            - Proper ambient air temperature measurement

            - I the component temperature method verifiable.

             

            Simulation:

            - Add radiation as mentioned - but what is the proper emissitivity and absorption?

            - Add the bench or support features

            - Add and air velocity match bench or heat chamber

            - Add heat chamber walls and fan...

             

            How dose the temperature compare with calculations using basic heat transfer?

             

            You need to experiment with the lab test setup and the simulation until satisfied that both are robust.  Tweak simulation until it matches the bench test.  Then for the next equipment build you will have a process and confidence.

             

            See:

            EIA/JESD51-2 or newer..