13 Replies Latest reply on Jan 26, 2015 4:41 PM by Frank Phelps

    Thermal simulation question

    Frank Phelps

      I am completely fresh and green to solidworks simulation.  I have watched a bunch of videos and have played around with setting up thermal simulations, but I have a question.  After I do a simulation with a circuit board and a heat sink the numbers I get back are around 1100 to 1600 Kelvin.  When doing the math this turns into around 1500 degree F.  Am I reading this chart wrong or does this sound like the error is in my setup.  Thanks in advance guys.

        • Re: Thermal simulation question
          Attilio Colangelo

          Are you using flow simulation or Solidworks SImulation (FEA)?  Either way it sounds like there is too much power (Watts) going into the model.  What are some of your parameters/boundary conditions?

          • Re: Thermal simulation question
            Bill McEachern

            This can happen if you have a small gap in one of the conductive paths. A gap is perfectly insulating no matter how small. As the other poster states it could be BC's that are not realistic for the situation you are anticipating.

            • Re: Thermal simulation question
              Frank Phelps

              I am using FEA solidworks simulation.  It is a very basic simulation I am running. Bill- It has a Square circuit board connected to a square heat sink via 4 circular post at the corners so there other than where it is making contact with the IC's there are some gaps.  Just to completely dumb down the whole process I made the "circuit board" out of silicon to simulate a board filled with IC's.  The heat sink is aluminum.  As far as the model taking in too much power,  I set it up to take in 165 watts.  This is the power wattage used for our compact modules.  Hope this provides some insight to my problem.  I will post some pictures when I am at my computer where those files are located.

                • Re: Thermal simulation question
                  Bill McEachern

                  Please explain how the heat goes from the source to ambient? is it by convection? Conduction? Radiation? Most likely convection for a heat sink. What is the convection coefficient applied to all the relevant surfaces of the heat sink? 165 W is a lot of power - you won't cool this with say natural convection of 10 W/m^2K - you will need forced of something not exceeding 125W/m^2K.

                • Re: Thermal simulation question
                  Frank Phelps

                  Bill- I think some stuff you hit on is pushing me in the right direction.   I am going to tweek some things this evening and get back to you ASAP. 

                  • Re: Thermal simulation question
                    Frank Phelps

                    Bill another quick question.  I am attempting Thermal simulation at home as we have been speaking about.  While at work I am also running Flow simulation.  My question lies with Flow Simulation.  While doing that how do I relay to Solidworks how many watts are going through IC's.  Is that something that only Standard simulation does?  Thanks for the insight.

                      • Re: Thermal simulation question
                        Bill McEachern

                        I assume you are using the full up Flow product and not the express product? You might want to run through the first 2 tutorials and then you will have a handle on it. The tutorial guide is typically in your install directory (C:\Program Files\SolidWorks Corp\SolidWorks Flow Simulation (2)\lang\english\Docs).It is applied as either a volume source or a surface source. hope that helps

                      • Re: Thermal simulation question
                        Frank Phelps

                        Bill- Thanks so much!

                          • Re: Thermal simulation question
                            Frank Phelps

                            Bill-  Do you know of any good books/articles on clearly understanding and defining the types of thermal loads used in Solidworks.  I have a good understanding convection and radiation and heat power, but stuff like the heat flux I am not really getting.  Is it simply the ambient temperature fluxing or?  Sorry for so many questions, but my 2-year degree in Engineering graphics didn't really go over much of this thermal simulation stuff.   Thanks again for the help.

                              • Re: Thermal simulation question
                                Bill McEachern

                                Any text book on heat transfer will get you up to speed. Flux is power - so it is in watts. Heat flux density is per unit of area. It shows where the high energy flux is - in a spatial plot what parts are moving the most energy.

                                  • Re: Thermal simulation question
                                    Frank Phelps

                                    Rude_and_Crude.JPG

                                    Bill_ This is very crude.  For all purposes, lets say that (A) is the computer enclosure (sheet metal), (B) is my IC's (Roughly 1/5 silicon) and heat producing chips, and (C) is the PCB board.  So for Setup Temperature would be the temperature of the surfaces of (A),(B), and (C).  I would apply convection to (A).  I would also apply radiation to (A) and (C).  Heat Power, Flux, and Temperature could be applied to (B).  So is one possible way to look at this that Radiation, Convection could be input data in a sense.  Heat Power, and Heat Flux could be output data to a sense.  The temperature would kind of be used as both depending on application? 

                                      • Re: Thermal simulation question
                                        Bill McEachern

                                        Hi Frank,

                                        You need to think it terms of paths. I will skip radiation for simplicity. The heat is generated in the center of the chip by some small chuck of silicon, it goes to the case surface (this resistance is usually available from the chip manufacturer - usually as a 2 resistor mode - see JEDEC for the various models that are used) where it either gets conducted along the board or it gets convected into the air in the enclosure. The air then convects it back into the wall of the enclosed into the wall of the enclosure where it gets conducted through the wall (assuming its a sealed enclosure). On the other side of the enclosure it is again convected away but this time by the ambient air. For the board path it goes along the board till it gets to the stand offs say (might be other avenues as well) goes via conduction to the case  and then the case wall then off to ambient via the air. Also the board will lose heat to internal convection and then to the case and out to ambient. In a Flow sim scenario you can just model it all directly and you will get probably a pretty good answer but even here you have to make some assumptions. If Sim though you need to apply convection coefficients on all the surface that it applies to mimic the paths where it occurs. So all these resistances, and the applied powers are used to solve for the temperature at every location in the solids. The temperatures are used to compute the fluxes. To get a good estimate here you need the average internal air temperature which you don't know. Usually one will design a system that one can analyze. IF you have a conduction tool - you would design a system that you can analyze with where uncertainties on convection can be managed.

                                        Good luck.

                                • Re: Thermal simulation question
                                  Frank Phelps

                                  Bill_Awesome!  Thanks so much for the insight.