Electric cars and cooling drag

[ME_Andy]

That may be the problem -- if you're looking at a Model S and a Porsche Taycan, you should probably be comparing against something with similar weights and 0-60 times. Similar power output, in other words.

On the lower end, if you look at, say, a Chevy Spark vs a Spark EV -- it's pretty obvious the EV has smaller grill openings.

Or Chevy Volt compared to Chevy Cruze. There are lots of examples of similar models where the EV version requires less airflow.

[ME_Andy]

Maybe a Dodge Viper is an apt comparison? Look at the honking grill on that thing.

https://www.dodge.com/content/dam/fc...ro-desktop.jpg

Or a Dodge Demon?

https://hips.hearstapps.com/hmg-prod...1539891230.png

[ME_Andy]

With that Tesla picture you showed -- yes, it has a large heat exchanger but it's not exposed to (much) airflow. There's a nose cone covering it.

[JulianEdgar]

Originally Posted by ME_Andy

With that Tesla picture you showed -- yes, it has a large heat exchanger but it's not exposed to (much) airflow. There's a nose cone covering it.

That's not how drag of heat exchangers is determined. The outlet area is of equal importance to the inlet area, for example.

(And did you see the two side heat exchangers?)

[JulianEdgar]

Originally Posted by ME_Andy

That may be the problem -- if you're looking at a Model S and a Porsche Taycan, you should probably be comparing against something with similar weights and 0-60 times. Similar power output, in other words.

On the lower end, if you look at, say, a Chevy Spark vs a Spark EV -- it's pretty obvious the EV has smaller grill openings.

Or Chevy Volt compared to Chevy Cruze. There are lots of examples of similar models where the EV version requires less airflow.

I don't have any data on other EVs. I do have data on other powerful cars (eg Porsche 911) and it has lower cooling drag than the Taycan - and by a lot.

As for regarding grille size as an indicator of percentage cooling drag - there is a lot wrong with that approach, which I why I like measured data.

But my main point is that the cooling drag of an EV is nowhere near zero (and has often been claimed here) and may in fact be higher than many internal combustion engine cars.

[Isaac Zachary]

Originally Posted by jakobnev

Interesting, could be because you have less temperature difference between the heat source and ambient. I don't know what temps motors are run at, but I know you wouldn't want your battery at 100⁰C.

Originally Posted by freebeard

The ICE engines are self-purging of most of the heat through the exhaust. The air (or Heaven forfend, water) cooling only has to handle the excess.

These are very good points. First of all a battery needs to stay around ambient temperature. But it's sure hard to keep something as cool as ambient temperature with a tiny radiator even if it doesn't create a lot of heat. That's because if it's hard to remove the heat it's easier for it to build up.

A greater temperature difference between radiator fluid and ambient air means you can get away with a smaller radiator. I remember reading somewhere that NASCAR vehicles get away with smaller radiators by using cleaver tricks to run higher engine and coolant temperatures.

And then there's the point that at least half the heat goes out the exhaust on an ICEV.

Now if batteries and inverters and such could run at +100°C/+212°F then they'd be much easier to cool.

[Piotrsko]

From what I understand, silicon dies used in computation control equipment can run up to 140f on the die but they go into thermal shutdown. The same for power silicon, only it gets there much faster. I also understand the junctions fail because of dissimilar material expansion basically flex fatigue

[ME_Andy]

Originally Posted by JulianEdgar

That's not how drag of heat exchangers is determined. The outlet area is of equal importance to the inlet area, for example.

I strongly suspect you're misapplying the formula. If there is no airflow over the heat exchanger (because it's covered by a nosecone), the windspeed would not be anywhere close to the vehicle speed. For the Model S, the airflow over the radiator appears to come from the fans.

Re. Porsche 911 vs Taycan -- the 911 is slower to 60 mph and the 911 is lighter, too.

There are some good points about electric motors running at lower temperatures than an engine!

Also interesting to note -- the Nissan Leaf has zero battery cooling. Ha!

[Piotrsko]

Originally Posted by ME_Andy

Also interesting to note -- the Nissan Leaf has zero battery cooling. Ha!

Andlook where that went

[aerohead]

PhD Joseph Katz shared some helpful numbers in 2017.
For his 'generic' automobile of Cd 0.355:
* ' cooling drag' was 0.024.
* 'engine bay' drag was 0.048.
* or, 0.072 combined!
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This would partially explain a BEV's drag advantage, as it can have an essentially 'ideal' belly pan, compared to an ICE variant of the same model.
* Underbody & Chassis is 0.085 for ICE.
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General Motors pubished Cd 0.36 for the SPARK ICE, and Cd 0.325 for SPARK EV.
Delta- 35-counts.
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The Coventry University Audi A2 measured:
* belly pan = 16.2-counts
* grille-block = 27.3-counts
* under wheel arch seal = 3.6-counts
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Chevrolet Division published for their 2013 Malibu:
* lower grille shutters = 7-counts
* closed upper grille = 7-counts
* center outboard belly pan = 10-counts
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The 2013 Dodge Dart radiator shutters were good for 0.005.
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Ford published that their 1st-gen Fusion cooling system carried a 0.025 penalty.
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100% grille-block on Spirit meant a delta- 0.027.
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I believe that Adrian Gaylard mentioned a Land Rover with a 0.048 cooling system.
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Hucho spoke of 2% drag cooling systems.
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The circa 2012 IVECO Class-8 ' Glider' Tractor has a non-aspirated cooling system, using bat-wing, heat-dissipating gap-filler panels behind the cab. ) My new Energy Star refrigerator uses this technology.
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There are other random numbers published. I don't have all that organized.