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Model 3 to not have traditional radiators

Discussion in 'Model 3' started by ratsbew, Nov 22, 2015.

  1. ratsbew

    ratsbew Member

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    According to the leaks in this article, the Model 3 will not use traditional radiators and heat exchangers since they cause high drag. It sounds like they will use the front "nose cone" area as a heat exchange surface. Perhaps there will be liquid cooling channels milled into the back surface of these surfaces to allow hot coolant to be cooled. Here are a couple of bullet points for discussion.

    • There may be radiators in the rear bumper for auxilliary cooling during supercharging
    • The air conditioner needs its own heat exchanger (rear also?)
    • Will there be an auxiliary air inlet in the front that can open during high demand?
    • Will it be dangerous to have a hot bumper? How hot could the bumper be?
    • What is the energy and noise penalty for using fans vs ram air for the AC at highway speed?
    • Can this method actually provide enough cooling?
    • Will paint color have an impact on powertrain cooling due to solar heating and emissivity differences?
     
  2. Saghost

    Saghost Active Member

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    The air conditioner needs to be able to dump heat overboard, yes - it doesn't necessarily follow that it needs a separate heat exchanger.

    With the Model S (and actually the Volt in different ways,) the HVAC is tied in to the battery system heating/cooling. I wouldn't be terribly surprised to see Tesla extend this, and have a single heat transfer zone to the outside (replace the hood?) that uses a liquid coolant which is heated by the battery, motor/power electronics and A/C (most likely in that sequence, I'd guess) when the car is too hot, and shifts heat among the element in cooler weather (the Model S already does some of this, it can use drive motor/inverter waste heat to assist in warming the cabin in winter I believe.)

    An auxiliary inlet is an interesting thought - if they go with the whole hood as the transfer surface as I was suggesting, they could add ducts that route air through finned passages along the underside and exhaust near the windshield for high demand and are blocked at lower demands. This would also eliminate the bumper question - they could add fans to pump air through the finned ducts while stationary and stick with a single integrated assembly.

    Can it provide enough cooling? That's convective heat transfer modeling you're talking about, and we need some assumptions to answer it. Here's a quick primer on convection with some calculators:

    Convective Heat Transfer

    Tossing numbers into their calculator and using their chart, if you assume 40C air (~104F, typical really hot day,) 90C for the hood radiator (don't want it actually boiling, this is maybe already too hot since it could hurt someone,) a 3 m^2 hood, and a transfer coefficient of 40 (trying to use the chart, I think this is around the right number for a car driving on the highway (the last number on their chart is about 36, at around 20 m/s - about 45 mph,) I came up with around 6 kW of heat transfer.

    That's plenty for drive motor loads - the current Mdoel S and Volt systems are 85-90% efficient, so 6 kW would be equivalent to an average of 40 kW of drive power over the long term. I'm not really sure how much heat dissipation an A/C system needs. The Volt can get over 4 kW of power draw cooling off initially in the summer heat (I suspect the S is similar, but I don't have data,) and since it has to dump all of that power and the cabin thermal load, it can probably overwhelm the capacity during initial cool down.

    However, the normal running load is much lower even on a hot day - this is where your cooling ducts come into play again. To handle surge loads like cooling off on a summer day or climbing a mountain while towing something, you'd open the ducts and possibly turn on the fans. During normal operation after cooling off, passive transfer through the aerodynamic shell should be plenty, without getting hot enough to do any harm.

    It's actually a pretty clever idea for an EV with their reduced heat transfer needs, especially if they can make the double sided approach with ducts and fans work. Might make the traditional Frunk smaller or harder to access, though. :)
    Walter
     
  3. ratsbew

    ratsbew Member

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    Instead of having forced air running through the body panel, would it not be simpler and more effective to just open a valve in the coolant loop to a regular finned heat exchanger with a fan? A simple, small, & cheap radiator could easily dump an extra 10kW of heat if the primary is saturated. My thought was to place these at the rear of the car. In theory....the warmed air could provide thrust....yeah, I know, an inconsequential amount, but kind of interesting.
     
  4. Saghost

    Saghost Active Member

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    You certainly could use a separate conventional radiator for the high load occasions, but that's a lot of extra weight/space/drag. Getting thrust from the system requires careful modeling and design to a single operating point or group of points - probably not practical with the wide range of amounts of heat transfer the car might need.

    The beauty of the approach I was suggesting is that the panel is the finned radiator - the same single set of coolant paths heats both the outer face of the panel and the couple inches of fins extending down from it. These fins are the typical approach for an air cooled engine or electronics box - I haven't run numbers, but I'm pretty sure it'll be less weight and drag than a stand-alone radiator.
    Walter
     
  5. Zarwin

    Zarwin Member

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    #5 Zarwin, Nov 22, 2015
    Last edited: Nov 22, 2015
    Totally agree, also one of the biggest cooling loads is supercharging on a hot day, though with the car stationary, cooling options neither rely on nor benefit from airflow over the vehicle. This is the most aggressive cooling I've ever experienced my car do:

    Tesla louvers opening when supercharging - YouTube
    Hot Tesla supercooling while supercharging - YouTube (Warning, loud)
     
  6. woof

    woof Model S #P683 Blue 85 kWh

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    It appears that in the Model S the largest heat removal requirement comes when Supercharging, and the car is stationary at that time. So the need that radiators be in the front to take advantage of the natural air movement when the car is moving forward is moot...the radiators can be anywhere in the car, in any orientation, as fans are required to force the air movement over them anyway.
     
  7. AudubonB

    AudubonB Mild-mannered Moderator Lord Vetinari*

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    The dT electric motors that make use of the Seebeck Effect are ridiculously inefficient, but inasmuch as they still do create some electricity, perhaps some of the excess heat can be scavenged for incremental battery charging.

    For those of you who missed out on thermodynamics, here's a wiki on the Seebeck Effect: Thermoelectric effect - Wikipedia, the free encyclopedia.


    I've absolutely no idea if the problems of low voltage charging, of cost versus effect, or any other problems make this unusable, but, hey!, that's what this forum is for.
     
  8. evp

    evp Nerd

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    Not entirely inconsequential. The P51 Mustang seems to get net thrust out of its belly radiator. Meredith effect - Wikipedia, the free encyclopedia
     
  9. tga

    tga Active Member

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    And that engine can make a heck of a lot of waste heat! (supercharged V-12, up to 1700hp)
     
  10. aronth5

    aronth5 Long Time Follower

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    "Model 3 will not use traditional radiators" which implies the Model S does which is a stretch.
    I think what will be interesting to see is how Tesla changes the non-traditional radiator used in the Model S to either be cheaper to make and/or more efficient for the Model 3.
     
  11. S'toon

    S'toon Knows where his towel is

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    What about when it's winter on the Canadian Prairies and it's -35 degrees out?
     
  12. yobigd20

    yobigd20 Well-Known Member

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    when I first read the title of the thread, I thought it said "Model 3 to not have traditional cupholders" ... can't wait to see if the Model 3 will have cupholders or if it'll be a complete disaster like the MS.
     
  13. aronth5

    aronth5 Long Time Follower

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    So are your cupholders always half empty or half full? I tend toward the half full:smile:
     
  14. MassModel3

    MassModel3 Member

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    alwaysfull_fullpic.jpg
     
  15. Olle

    Olle Member

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    Meredith effect radiator would be awesome. Forward propulsion and cooling at the same time. Just the thought of stuff like that makes me want the car even more.
    Imagine how cool(!) it had a little jet outlet in the tail.
     
  16. mknox

    mknox Well-Known Member

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    I'd say they're twice as big as they need to be :wink:
     
  17. Olle

    Olle Member

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    additional question: since air resistance is lower in high temperatures, would these hot body panels generate less drag?
     
  18. Saghost

    Saghost Active Member

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    I'm not an expert in the exact application here, but from the more general work with ramjets you probably need to have a duct designed for the right expansion ratio based on the amount of heat you're putting in and the airspeed. That's the problem, here, because for an EV that amount will vary wildly - there's even a good chance the car will be taking heat out under some operating conditions.

    In any case, small amounts of power can only result in small amounts of thrust - I'll be surprised if the cost, drag, and weight of a ramjet duct actually prove to be worthwhile for the resulting thrust.
     
  19. Ardie

    Ardie Member

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    As nice as it is to consider the Teslaleak stating that "the Model 3 will not use traditional radiators" means that the car will have some kind of new kind of heat exchanger devices -- like ones that are actually part of the car's hood/door/floorboards/etc., as if they said "the Model 3 will use new-technology heat exchangers." But I am of the mind that the statement can be translated more like "the Model 3 will have conventional technology finned radiators, but they won't be located where they've always been."

    As we all know, radiators are draggy devices. Racing cars in the past used to place their heat exchangers onto the sides of the cars, where the 200 mph slipstream would be more than adequate in washing all that excess heat away. It required a huge surface area, and there was no car door to deal with, so it was possible. But not in a family sedan. Rooftop? Maybe, but there are too many of us who want a sunroof that gives a view of something other than Ethylene Glycol swimming over our heads.

    But other ideas to reduce efficiency and performance have placed the typical design finned heat exchanger(s) in a place where its *already* draggy -- behind the wheels. In the front, its problematic because you want to use that space for legroom. But the rear wheels, now you've got something. Those cavities behind the rear wheels were only part of the trunk storage area, and were not used for much more than stashing some various electronic stuff, or the gas cap and filler tube, or me squirreling away a spare quart of oil in there. Putting the radiators behind the rear tires is a lot more doable in an electric car since the heat-to-disperse is not generated in the engine bay anymore. No long pipes of hot stuff going to the rear of the car. No cold stuff going all the way back up front. The battery temp control system doesn't have to be in the front, and neither does the people temp control system.

    So maybe we'll see the Model 3's radiator(s) behind the rear tires.

    -- Ardie
     
  20. Olle

    Olle Member

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    first question how avoid filing them with mud from the tires?
     

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