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FEA Thermal Stress Factor of Safety Question

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  1. May 16, 2013 #1
    Hi Guys

    I'm analysing a heat exchanger based on an existing commercial model in SolidWorks Simulation. The same materials etc have been applied to it in the Static analysis.

    Deflection on the heat exchanger is very small. The one thing that baffles me though is how, regardless of even when I increase the wall thickness considerably, the factor of safety whenever I apply a temperature to the heat exchanger is always really small.

    The factor of safety is calculated based on Maximum von Mises stress and yield strength as a default.

    Are the FOS results I'm getting actually quite realistic? I have a feeling that something is quite wrong here. If you would concur, could anybody explain to me why? It seems there is very little improvements that can be made besides actually changing the temperature.

    Thanks for any help you can offer.

    David
     
  2. jcsd
  3. May 16, 2013 #2
    I don't have access to SolidWorks right now but as far as I remember there is a twist to the factor of safety. It exists in two versions, one where smaller is better, and one where bigger is better. I imagine you might be using the first
     
  4. May 16, 2013 #3
    Hi

    That's not the case with this one. As the temperature is reduced the factor of safety gets higher. It just gives baffling results considering I've based it off an existing commercial heat exchanger.

    If I could find a paper somewhere that explains why it might not be the best indicator I could explain it away but I've not found anything online pertaining to this.
     
  5. May 16, 2013 #4

    SteamKing

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    You say your FOS is "really small". What does this mean exactly? Can you provide an example?

    The details of your analysis are not provided. What is the purpose of your analysis? Are you trying to determine the deflection of a component or the stress in a component? What sort of loads are imposed on the exchanger?

    Are you using some sort of design code (e.g., AISC or ASME) to evaluate the FOS of the unit? Remember, the more detail you provide about your problem helps to obtain better responses.
     
  6. May 16, 2013 #5
    The stainless steel reaches temperatures of up to 140 degrees celcius. The actual deflection in the model is a fraction of a mm. However, it also plots a factor of safety throughout the model. The FOS for nearly the whole model is 0.5, 0.9 if I change it to tensile strenght rather than yield strength (obviously not ideal). I am determining both the stress and the deflection. The thermal data was imported from a CFD simulation.

    As far as I'm aware the FOS is designed to tell me whether or not the component will fail, like calculating a FOS on a simply supported beam. I'm new to thermal analysis on SolidWorks FEA simulation.

    I'm just wondering how calculating thermal stress next to yield/tensile strength is different to normal pressures/forces is different, if it is even different in the first place anyway.

    I should have given more details to begin with, sorry about that.



    "You say your FOS is "really small". What does this mean exactly? Can you provide an example?

    The details of your analysis are not provided. What is the purpose of your analysis? Are you trying to determine the deflection of a component or the stress in a component? What sort of loads are imposed on the exchanger?

    Are you using some sort of design code (e.g., AISC or ASME) to evaluate the FOS of the unit? Remember, the more detail you provide about your problem helps to obtain better responses."
     
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