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The Stored Energy Dance (Octovalve)

Discussion in 'Battery Discussion' started by SageBrush, Feb 2, 2021.

  1. SageBrush

    SageBrush REJECT Fascism

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    I was thinking about the beauty of the Octovalve after I watched a Bjorn Nyland video that showed the car using heat accumulated in the battery after a Supercharging event to keep the cabin warm.

    *Sweet!*, thought I, but that takes an hour or two and in the meantime the battery is hotter than ideal.
    Could the motor(s) be an interim heat sink ? how much heat capacity do they have ?
    Are there other heat sinks that can be utilized, or added to the system ? Perhaps a PCM ? Or a larger anti-freeze reservoir ?
     
  2. Brando

    Brando Active Member

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    octo as you know = 8
    consider 8 heat sources in a Tesla
    I can't imagine any sources Tesla engineers missed.
     
  3. SageBrush

    SageBrush REJECT Fascism

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    #3 SageBrush, Feb 2, 2021
    Last edited: Feb 2, 2021
    Sink, not source.

    ---
    The 'octo' name comes from the unit having 4 inputs and 4 outputs. To balance flow, an input is matched to an output. This allows up to a theoretical 2^4 = 16 pairings. IIRC, Tesla uses twelve.
     
  4. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Well-Known Member

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    Maybe they could have a built-in kettle.
     
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  5. CYBER_Y

    CYBER_Y Member

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    Are all 8 used for heat? Are any used for cooling?
     
  6. mongo

    mongo Well-Known Member

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    Thermal mass of the pack is huge ~85wH/C , there is nothing in the car that can offset that (in a storage way) significantly.
    https://patentimages.storage.googleapis.com/58/eb/22/870827f4b9f611/US20190070924A1.pdf
    Motor wants to be cool (winding less resistivity, electronics like cool).
    It would require 73 kg of pure water (no antifreeze) to equal the thermal mass (1C up for 1C down).
     
    • Informative x 1
  7. Needsdecaf

    Needsdecaf Member

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    Ya'll are making me re-live my 8:00 AM thermodynamics classes with Professor Ulucacli and I don't like it one bit.
     
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  8. mongo

    mongo Well-Known Member

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    Sorry, I tried to keep it at the Chem 101 level :)
     
  9. SageBrush

    SageBrush REJECT Fascism

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    Fair enough.

    PCM ?
    It would not be necessary to suck all the heat out of battery -- just get it off the 50C+ plateau into the low 40s C

    And we could always call on the heat pump if we wanted more heat transfer than a heat exchanger provides.
     
  10. rypalmer

    rypalmer Active Member

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    That's significant - 2.55kWh of equivalent energy assuming a 30ºC swing - even more considering the efficiency of the heat pump. But it would be interesting to do the math on the electrical energy lost due to heat harvesting for the cabin.
     
  11. Brando

    Brando Active Member

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    a continuum from (-) ... cold ... io ... hot ... (+)

    HeatPump moves heat from one place to another place
     
  12. mongo

    mongo Well-Known Member

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    Watch out, you don't get to multiplly the pack heat energy by the heat pump coefficient of performance, there is only 2.55kWh of heat available. Rather, the amount of energy the heat pump needs to use to move the pack heat is divided by the COP (add added to the total).
     
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