7 Replies Latest reply on Jul 23, 2012 10:40 AM by Anthony Botting

    Understand Thermal Curve

    Jim Monti

      I have a simulation I am trying to construct. I have a heat source and a Heatsink. The heat source cycles 1.5Ws of power one second on and one second off. The opposite side of the heatsink will be simulated at a constant temperature.

       

      So the question is how do a represent the cycling of the heat source (one second "on", one second "off") during the simulation.

        • Re: Understand Thermal Curve
          Anthony Botting

          Hi Jim: You only need to define a "Transient" thermal analysis (go to Properties of the steady state analysis and change it to "transient"), if not already done, then when you edit definition of the heat source, there should be an option in the Property Manager to add a "time curve" to the source. You can key-in a curve to ramp the source power up and down over the time. Hope that helps! (BTW, welcome to the forums)- Tony

            • Re: Understand Thermal Curve
              Jim Monti

              Evening Tony,

               

              Saw a YouTube of yours on transient simulation. I see where you can do incremental sampling thru the simulation, but I don't see how you cycle the heat being generated by the assembly over time. Imagine an LED on a PCB attached to a Heatsink. You have a constant temperature on the back of the Heatsink. You turn the LED "on" and "off" repeatedly (1 second on, 1 second off, etc) every time power is applied the heat output approaches 1.5 watts, but the materials of the assembly obviously moderate the heating and cooling.

               

              I don't see, under the "thermal loads" section, where you make the intermittent application of the heat load. 

               

              Thanks for your time, and explanation.

               

              Jim

            • Re: Understand Thermal Curve
              Billy Wight

              Hi Jim,

               

                   I don't know the specifics of your problem, so I may be off here, but typically with a thermal analysis of a heatsink, you don't want to specify a constant temperature on the heatsink, you want to specify an ambient temperature and a convection coefficient on the outer surfaces of the heatsink.  Specifying a constant temperature will drastically over-estimate the performance of the heatsink (if you use ambient temperature).

                • Re: Understand Thermal Curve
                  Jim Monti

                  Thank you for the direction. I was just trying to get the time interval into the time curve, and get it to solve. Then go back and correct for the heatsink. I do have the ambient temperature specified, and will change the constant surface temp on the heatsink to a convection coefficient. Thanks.