looking at the all matt black prototype and remembering that the heat from batteries and posibly even the A/C system are supposed to dissapate all excess energy from micro colant channels threwout the vehicles outer skin.
is anyone else concerned that this will be impossible to achieve on a hot day in direct sunlight. ive reserved the Sol white color just for that reason and was considering painting/wrapping the upper side of the car between the solor cells to help whith heat dissipation.
as far as the increas in drage from a radiator, i would prefer the simplicity and reliablilty especially in hotter climates where it may prove better for batery degradation and charging speed.
I hear you Riley. My reservation is silver in color for the same reason.
How about we lobby for flaps, one in the roof and another in the "hood" of the car that only open when the batteries, interior, and/or solar panels get too hot.
The temperature-activated flaps would allow natural convective heat transfer to remove the heat when parked and dynamic convective heat transfer when moving.
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automatic flaps that open when needed is a great idea, i think the best location would probably be under the vehicle behing the rear most battery pack. it doesnt need to be a large radiator and the idea of having micro tubes dissapating heat is an awesome idea. if these tubes can actively cool the solar cells to increase efficiency would make more sense to me.
Riley:
Thanks for the shout out.
I don't want to dampen your creative process, but placing temperature-activated vents under the vehicle, especially if the vent led to a micro tube air-to-air heat exchanger, might tend to get clogged with road dirt.
Thoughts?
@Tom Kruer many motercycles place their radiator directly behind the front tire and regular cleening is needed to maintain thermal effiency. that could be a problem if the apteras radiator is tucked behind a flap under the vehicle. getting crammed full of mud while overlanding would be devistating. unfortunatly the apteras super sliperry desighn has backed it into a thermal corner. I cant think of any reaonable options to this dilemma.
@Riley:
Obviously, you see my point about road debris.
Thus the reasoning behind suggesting placement of the proposed temperature-activated vents for the micro tube heat exchangers on the roof and hood.
Repeating, we are trying to mitigate the problem of efficiency loss when the batteries, solar panels (below), and motors get too hot. (Assuming the experts at Aptera have not already come up with a solution).
The Thermo classes we had in school taught that natural convention can be very effective at removing heat... if air is allowed to flow. Therefore, when our cars are sitting in the hot sun recharging, some air flow over an air-to-surface micro fin heat exchanger mounted to the back side of the solar cells might help.
When we are cruising down the highway on a hot day, just a little dynamic air convection flow over a heat exchanger could help cool the motor, motor controller, and passengers.
Using a heat pipe to transfer the heat from the motor, etc. up to the same air stream of the roof vents could make for a system with no moving parts, other than the vents.
And I am thinking the vents would only have to open a millimeter or two with the exhaust out the tip of the "tail" (or whatever the aft of a wingless animal is called).
Aptera's low drag means lower cooling requirements when driving*, since there's less motor power draw, which means less power flow heating the battery.
Power flow is higher than that while grid-charging, but at that time the vehicle is stopped so if more cooling is required, a retractable radiator that extends out into ambient air would be much less problematic. However a simple A/C-to-battery-coolant heat exchanger would be smaller, lighter, completely enclosed (zero added air drag), & has far fewer moving parts.
*Ball-parking heat-creating power flow: I'm pretty sure I saw that Aptera range specs are based on the EPA test cycle which has an average speed of about 35mph (about 20 city & 50 highway). Divided by the 10mi/kWh spec, that's only 3.5kW, which is only 53% of the 6.6kW from charging at most public L2 chargers.
@Kiteboarder, I understand your point but must ask for support of your claim that a retractable radiator, and A/C to battery coolant heat exchanger has less parts than a fixed grill in the tail and a small, vent (perhaps of shape memory alloy) at the top edge of the windshield.
When moving, the air and heat flows from front to back. When stationary and charging, the air and heat flows from back to front (or from the lower to higher points).
Thanks for reading my post, but if you take another look you'll see that I didn't "claim that a retractable radiator, and A/C to battery coolant heat exchanger has less parts than" anything.
I claimed that "a simple A/C-to-battery-coolant heat exchanger ... has far fewer moving parts." compared to a retractable radiator.
My 500e has a small one of those battery coolant heat exchangers, circled in the picture below, with I believe 1 moving part (coolant flow valve). I've paid very close attention to it, & even in 113F, driving at highway & city speeds & immediately L2 charging, it has never activated.
The radiator/fan have always been sufficient. The most battery cooling I've ever seen is high coolant flow, & high fan speed about 3 times in over 5 years.
All that is on a car with about 250% as much battery-heating current flow while driving as an Aptera. & the exact same charging current flow on any public L2 I've ever seen, since those have all matched the Fiat's maximum 6.6kW.