9 Replies Latest reply on Feb 10, 2016 7:49 PM by Joaquin Bascon

    Simple Thermal Analysis

    Joaquin Bascon

      Hi everyone!

       

      I'm having a simple variable over time thermal analysis which consist in one Al cylinder with a cool focal point at its bottom. I have added natural convection due to air (10w/m^2k and 293k) at the top and lateral faces, a cool point at its bottom (263k) and initial ambiental temperature in all its faces (293k)

       

      I don't know what's the mistake as the results aren't coherent because Solidworks shows that after 120s the temperature at the top is 238k. I insert a photo.

       

      Beforehand thank you very much!

       

      **SOLUTION**

       

      Siavash Khajehhasani:

      Hi Joaquin,

      I forgot to mention it at the beginning that the initial temperature has to be specified for the whole solid body and not at the faces. Accordingly, please modify the initial temperature setup and if you have any issue to select the solid body use Filters (F5).

      Please let me know if you find this helpful.

      -Siavash

        • Re: Simple Thermal Analysis
          Siavash Khajehhasani

          Hi Joaquin,

          Here is my initial guess regarding your simulation: 1) if you apply a cool point of 262K at the bottom face, what is the necessity of defining an initial temperature over there? 2) whatever reasonable temperature behaviour that you are looking for "may not" happen in the specified period of 120sec; accordingly, considering a wider time range is recommended; since natural convection effect could be slow depends on problem description.

          -Siavash

            • Re: Simple Thermal Analysis
              Joaquin Bascon

              Hi Siavash,

              Firstly, thank you very much for your answer. According with your points:

              1) You're right, but I have change this and it still the same.

              2) Yes, I know, but for me it's interesting what happend at all periods.

              I don't know why SW keep showing that a less temperature at the top face than at the bottom face, where the cool point is... Not only at the 120s but also in all periods.

              I'm going to post screenshots of each of my inputs.

              Greetings!

              (Sorry but my SW is in Spanish, but the process is the same)

               

              1º)

              1.JPG

              2º)

              2.JPG

              3º)

              3.JPG

              4º)

              4.JPG

              5º)

              5.JPG

              And this is the result at 60s. 263k at the bottom face and 137 at the top...

              6.JPG

            • Re: Simple Thermal Analysis
              Siavash Khajehhasani

              Hi Joaquin,

              I forgot to mention it at the beginning that the initial temperature has to be specified for the whole solid body and not at the faces. Accordingly, please modify the initial temperature setup and if you have any issue to select the solid body use Filters (F5).

              Please let me know if you find this helpful.

              -Siavash

              • Re: Simple Thermal Analysis
                Siavash Khajehhasani

                Hi Joaquin,

                That's right; in fact, Aluminum 1060 with thermal conductivity of 200 w/m.k is a good thermal conductor compared with other metals such as steel.

                Cheers,

                -Siavash

                • Re: Simple Thermal Analysis
                  Amit Katz

                  Just from curiosity, is this for a real problem or is it academic? I'm wondering why you set 10W/m^2-K as your coefficient of convection. How did you calculate that number?

                    • Re: Simple Thermal Analysis
                      Joaquin Bascon

                      Hi Amit,

                      First of all, I tell you that many years ago that I don't do any problem about thermal analysis, therefore it's probably that I'm wrong. At this moment is only to practice, nevertheless it will be a real problem but I suppose with different Al alloy. About the number that I've chosen is a random number, I remember that I calculated a similar number in some problems. But in real life I will use the Newton Law:

                      \frac {dQ} {dt} = h A_{s} ( T_{s} - T_{\inf} )

                        • Re: Simple Thermal Analysis
                          Amit Katz

                          I ran a similar analysis to your using the Flow Simulation tool, and in my case the bar cools a lot more quickly. This is what the results look like at steady state:

                           

                          Capture.PNG

                           

                          Here's a plot of the average temperature of the top surface over time:

                          Capture.PNG

                           

                          As you can see, in this simulation it only took about 30 seconds to lower the surface by 10K, rather than 60 seconds like you saw. The surface temperature stabilizes after about 200 seconds. The calculated heat transfer from the surfaces that are exposed to warm air is 3.825W, and the surface area is 0.028m. Using 30K for the temperature difference that gives a heat flux of approximately 4.5 W/m^2-K, only half of what you had in your thermal simulation.