Comment on Copper

stoicmaverick@lemmy.world ⁨9⁩ ⁨hours⁩ ago

• resipsaloquitur@lemmy.cafe ⁨4⁩ ⁨hours⁩ ago

  Nice try. I’m not googling “copper pegging” again.

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  • Piemanding@sh.itjust.works ⁨31⁩ ⁨minutes⁩ ago

    That thing doesn’t make any sound so you gotta search “Copper Sounding” instead.

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• Contramuffin@lemmy.world ⁨6⁩ ⁨hours⁩ ago

  Was bored, so made a simulation to figure it out.

  TLDR: 592.2 seconds, or 9 minutes and 52.2 seconds. Very similar to the other comment, so it appears temperature differentials and heat loss to the air are somewhat minor effects compared to the sheer heat mass of the block

  Assumptions:

  • Copper’s heat conductivity is 400 W/m-K, and specific heat is 0.4 J/g-K, and density is 9000 kg/m^3, and these values do not change over the range of temperatures
  • Air’s heat transfer coefficient is 20 W/m^2-K and does not change over the range of temperatures
  • The surrounding air does not change in temperature and remains at room temperature (25 C)
  • The input wattage is actually 120 W and not just random marketing bullshit
  • The copper block’s size is 4 cm x 4 cm x 16 cm (same as other comment)
  • The temperature within the copper block differs only by the vertical axis; it is assumed that temperature does not change if you move horizontally into the block

  Modeling conditions:

  • The block is sliced into 100 equally-sized slices, stacked vertically.
  • 120 W is input directly into the bottom slice
  • Heat transfer is modeled between each slice
  • Heat loss into the air is modeled for each slice (top slice has more heat loss due to more contact with the air)
  • Heat changes are calculated per millisecond
  • Final time is calculated is the total number of milliseconds it takes for the bottom slice to reach a temperature greater than 100 C

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  • Piemanding@sh.itjust.works ⁨29⁩ ⁨minutes⁩ ago

    Did the model include some air movement by way of the fans on the case. That would be a fun thing to think about.

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  • stoicmaverick@lemmy.world ⁨3⁩ ⁨hours⁩ ago

    Well goddamn… Ok. Go ahead and dm me your home address, phone number, social and/or tax id number, the name of the street you grew up on, the name of your favorite teacher, the IMEI number of your cellphone, a high resolution set of your fingerprints, and a list of your three greatest fears, and I’ll get your sticker sent over as soon as I can.

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  • Bahnd@lemmy.world ⁨3⁩ ⁨hours⁩ ago

    You did the monster math.

    Respect.

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  • mnemonicmonkeys@sh.itjust.works ⁨5⁩ ⁨hours⁩ ago

    Numerical methods is cheating! Real men use PDE’s!

    /s of course, though I was kinda hoping you’d use PDE’s

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    • Contramuffin@lemmy.world ⁨5⁩ ⁨hours⁩ ago

      See, I thought about doing that, but then I realized: I don’t actually want to do that

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  • kahjtheundedicated@lemmy.world ⁨5⁩ ⁨hours⁩ ago

    Respect for taking the time to model that. Goes to show why heat sinks look the way they do, and not just big lumps of metal lol

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• KSPAtlas@sopuli.xyz ⁨9⁩ ⁨hours⁩ ago

  Let’s assume the dimensions of the copper block are 40mm40mm160mm (I’m not taking the heat spreader into account here)

  That results in a volume of 256000mm3, or 256cm3

  Copper (at 20C) has a density of 8.935 g/cm3, so that’s roughly 2.28736kg of copper

  Copper has a specific heat capacity of 384.603 J/(kg K)

  Using E=cm∆t, we can figure out that it would take ≈ 70378J of energy to heat the copper block to 100C, starting at 20C

  With a TDP od 120W, that means it would take 586 seconds to heat the block to 100C, or 9m46s

  This is probably way off but I was bored

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  • Rugnjr@lemmy.blahaj.zone ⁨52⁩ ⁨minutes⁩ ago

    This doesn’t seem to account for convection, which is presumably the entire point of a heat sink?

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  • SleeplessCityLights@programming.dev ⁨9⁩ ⁨hours⁩ ago

    Your napkin math is the best we have. We will make all decisions based on it.

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    • Napster153@lemmy.world ⁨4⁩ ⁨hours⁩ ago

      They will have entire hard drives explaining KSP Atlas’s shitty math in 3 thousand years…

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  • Contramuffin@lemmy.world ⁨8⁩ ⁨hours⁩ ago

    Hmm, I think at minimum calculus will need to be involved here. Because we can’t just assume that the heat is spread evenly in the copper - it’ll likely be hotter at the bottom, leading to thermal throttling earlier than expected. On the other hand, there’s going to be heat dissipation into the air, which will help cool the block somewhat

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    • Einskjaldi@lemmy.world ⁨6⁩ ⁨hours⁩ ago

      The conduction in copper is fast enough that there’s not much of a difference between the top and bottom.

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      • Contramuffin@lemmy.world ⁨5⁩ ⁨hours⁩ ago

        Copper conductivity is fast, sure, but it’s not fast enough to have equal temperatures at the top and bottom for such a big chunk of copper. That does affect the time to thermal throttle pretty significantly, actually. If we assume completely homogeneous temperatures across the block (ie, instantaneous heat transfer), according to my model, it’ll take 703 seconds to thermal throttle. With heat transfer, the time drops to 592 seconds - a difference of almost 2 minutes

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    • Eheran@lemmy.world ⁨5⁩ ⁨hours⁩ ago

      Heat transfer will not limit much, but heat loss should add a significant amount of time. How did you model that?

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      • Contramuffin@lemmy.world ⁨5⁩ ⁨hours⁩ ago

        I left another comment going into more detail about the model specifications, if you’d like to read into it. But briefly: I took the copper heat conductivity coefficient and the air heat transfer coefficient. I sliced the copper block into thin slices and modeled heat transfer between each slice, as well as heat transfer between each slice and the surrounding air.

        It seems that both heat transfer and heat loss do actually matter quite significantly, but they just cancel each other out almost entirely.

        If we assume instantaneous heat transfer, thermal throttling time goes up from 592 seconds to 703 seconds (almost 2 minute difference).

        If we assume no heat loss to the air, thermal throttling time goes down from 592 seconds to 500 seconds (about 1.5 minute difference).

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    • falcunculus@jlai.lu ⁨8⁩ ⁨hours⁩ ago

      Alright, what about a 4040160mm block of copper at 100C ?

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  • potpotato@lemmy.world ⁨9⁩ ⁨hours⁩ ago

    Account for convective loses into air?

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    • YerbaYerba@lemmy.zip ⁨8⁩ ⁨hours⁩ ago

      Its going to radiate a little bit too.

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