Charles Xie

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  • in reply to: scaling up the Solar Updraft Tower #283

    Charles Xie
    Keymaster

    Thanks for your interest in Energy2D. The simulation depends also on the boundary. A flow that is stable in a small box may not be in a large box, vice versa. I will take a further look once I get some free time.

    in reply to: Simulation of foam insulated hot water pipe system #273

    Charles Xie
    Keymaster

    Hi Guy:

    I looked at your model and I don’t know what is wrong. Can you elaborate?

    Thanks,
    Charles

    in reply to: Minimum dimension #266

    Charles Xie
    Keymaster

    Many users have requested supporting a material library. Unfortunately, I have very limited time and I am maintaining this software in my spare time. It is not funded by anyone since about five years ago.

    Hopefully it will continue to exist.


    Charles Xie
    Keymaster

    I can reproduce your problems. Not sure if this is caused by a huge distortion of the grid cells (400 times larger in the horizontal direction than in the vertical direction). I will keep looking.

    in reply to: Minimum dimension #263

    Charles Xie
    Keymaster

    Expanding the grid size would cause the simulation to slow down by N^2. So this is currently locked. But I agree there should be such an option in the future.

    in reply to: Minimum dimension #261

    Charles Xie
    Keymaster

    That is right. Since the computational grid is 100×100, you can’t set the size of a component below 1/100th of the size of the window. If you could, it would be ignored by the engine.

    in reply to: Minimum dimension #257

    Charles Xie
    Keymaster

    PS: Don’t forget to set the time step to be small to be compatible with the micron scale. Otherwise you will get a fatal error.

    in reply to: Minimum dimension #255

    Charles Xie
    Keymaster

    This is done. See the attached image.

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    in reply to: Minimum dimension #254

    Charles Xie
    Keymaster

    I am just back from running a workshop. I will find some time to change the lowest dimension allowed in the program. Thanks for your encouragement!

    in reply to: Minimum dimension #252

    Charles Xie
    Keymaster

    I will look into this. I didn’t expect users who would use this at micron scale.


    Charles Xie
    Keymaster

    Hi Will:

    Sorry for the delay in responding. Can you annotate your model a bit so that I can understand what you are trying to accomplish?

    Charles

    in reply to: Completely insulated object? #243

    Charles Xie
    Keymaster

    Please do.

    I am also working on an app based on FLIR ONE (literally as I am replying your questions). So we have overlapping interest.

    in reply to: Completely insulated object? #241

    Charles Xie
    Keymaster

    Of course you are correct, Stefano. This problem is related to the relatively large grid cells used by default in Energy2D (100×100). If we can reduce the size, the effect can be reduced, but I suspect we can’t get rid of it completely as this is the side effect of numerical simulation based on discretization. A numerical solution is always only an approximation.

    You may notice that the leaking only happens at the interface. Although the medium has zero conductivity, in reality does it really prevent the layer from getting any energy through the contact? What would happen to the molecules of such a hypothetical (and non-existent) medium at that interface do when they are in contact with a heat source? The physicist part of me would say they would heat up no matter what. Otherwise, this would be an open violation of fundamental laws.

    So this offers an “explanation” for the numerical problem if that comforts us.

    • This reply was modified 2 months, 2 weeks ago by  Charles Xie.
    in reply to: Completely insulated object? #233

    Charles Xie
    Keymaster

    Good question. I confirmed this with your model.

    Now, if the specific heat of the square is larger than or equal to that of the ambient, we can find out that the thermometer will read almost the same value or slightly smaller as initial.

    The interesting thing happens whenever the specific heat of the ambient is larger than that of the square–the thermometer starts to register a lower value. But it eventually stops dropping further and settles at a certain temperature. The larger the specific heat of the ambient is, the lower the final temperature is. Which is exactly what you reported here.

    The reason, I figured, is because of the boundary layer effect. When you have a layer that has a huge heat capacity next to the square, it will draw some energy from the square into it. The zero conductivity of the ambient stops the flow of energy through the ambient, but it doesn’t necessarily prevent the energy from getting into the contact layer.

    I attached a screenshot of a revised model and the actual model file for your reference.

    Hope this helps.

    • This reply was modified 2 months, 2 weeks ago by  Charles Xie.
    • This reply was modified 2 months, 2 weeks ago by  Charles Xie.
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    in reply to: How to to simulate an unheated cross-ventilated space? #228

    Charles Xie
    Keymaster

    How about this one? Not a heat-driven one, but I use a 4m/s fan.

    The particle speeds are not 4m/s, though, perhaps because of the air drag.

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