5 Replies Latest reply on May 3, 2007 8:56 PM by Vince Adams

    Steady State Initial Temperature

    Kevin Spradley
      All,
      I am trying to complete a simple steady state thermal analysis. However, I would like to use an initial temperature for theassembly.  When I pick Temperature from the Load/Restraintsection, the only option available is just Temperature.  So, Iselect all my components and set them to a temperature. However, the results are all at that temperature with nothermal gradiants across the part.  If I remove thetemperature load/restraint, I get the gradiant, but the overallsteady state temp can not be correct.  


      How can I define a steady state initial temperature for myassembly?


      Thank you,
      Kevin
        • Steady State Initial Temperature
          David Arthur
          Kevin,
          You can't apply initial conditions for a steady state problem. "Initial" implies there is a time component to the study. You can only apply boundary conditions in a steady state problem. The temperature B.C. sets the face selected to a constant temperature (isothermal). In a steady state problem, if you apply a temperature to one surface of a part and dont have any heat transfer in or out, the entire part will eventually reach the temperature that is applied to the surface. The temperature B.C. for a steady state thermal analysis will be used for isothermal conditions like boiling water on one side of a heat exchanger.

          Hope this helps.
            • Steady State Initial Temperature
              Kevin Spradley
              Thank you for the reply.  Let me describe my assembly andanalysis setup briefly.  

              Imagine I have a flat Al panel.  On 1 side, I have a heat fluxof 1380 W/m2 into the surface.  This surface also radiates tosurface-to-ambient seeing a 3 K background.  the rear surfaceof the panel is a plain surface-ambient radiator seeing a 3 Kbackground.  I understand that after some time, a steady stateresult will be calculated.  However, I was under theimpression that you could start your solid body at sometemperature, and this would affect the overall steady statesolution.  
                • Steady State Initial Temperature
                  David Arthur
                  Kevin,
                  Sounds like you may need to to a transient analysis if you want to see how initial temperature effects your system. I'll be honest though, I don't do much thermal at work. We are mostly fluid dynamics and mechanics of materials. I'm going off memory of heat transfer in college. Maybe someone with more thermal backgroud can offer some guidance.

                  David
                    • Steady State Initial Temperature
                      Kevin Spradley
                      David,
                      Thank you again.  I too do not do a lot of thermal analysishere at work, but I am trying to learn.  We have others thatare excellent, but due to time constraints and such, we are tryingto get more people involved.  I am an optics guy by study andtrade.  We are planning on using the steady state results asthe input to our transient analysis.  

                      This is not my main problem right now.  I am not evenachieving the thermal gradient profile that is expected. Everything is going to one temperature, and this can not beright based on the input parameters.  

                      Again, thank you for insight.  
                        • Steady State Initial Temperature
                          Vince Adams
                          Steady-state means steady state and is independent of initial conditions. Your gradient problems may be due to improper conduction across bonded contact conditions. If your system can Zip up and it is still an issue (I realize this posting was from February!) go ahead and send it to me or you can try your VAR tech support as well.

                          I'm sure there's a simple explanation...