CyberTruck SS Heat

Foxx

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All that being said………I remember the old slides at McDonald’s playgrounds when I was a child. I may still have some burn scaring on my backside 😲. I’m sure it won’t get that hot in the sun since the steel isn’t as polished. It will get pretty hot though for sure.
 

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Very highly polished SS wont get as hot as less polished because highly polished reflects all the energy striking it. The recipe for high temperature is a dull surface and low emissivity.
 

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Very highly polished SS wont get as hot as less polished because highly polished reflects all the energy striking it. The recipe for high temperature is a dull surface and low emissivity.
So CT steel will get hotter.. it just won’t feel hotter to the touch as polished steel would, right?
 

ajdelange

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This thread proposes two hypotheses;
1)Steel painted a dark color will get hotter than the unpainted CT skin
2)The CT skin won't feel hot because there are some other steels that have higher thermal conductivites.

Pages and pages of discussion and a couple of crude experiments have shown both these hypotheses to be incorrect. Thus the skin of the CT can get hotter than a painted steel sheet depending on the color of the paint and surface roughness and it will feel hotter too.
 

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So CT steel will get hotter.. it just won’t feel hotter to the touch as polished steel would, right?
It'll be hot. Ask the few delorian owners on the forums....

The recipe for high temperature is a dull surface and low emissivity.
I think you meant high emissivity? Emissive is the opposite of reflective.

In general, metals feel colder or hotter to the touch than other materials at the same temperature because they're good thermal conductors. This means they easily transfer heat to colder objects or absorb heat from warmer objects. The SS exterior is no different.
 

tmeyer3

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Emissive and reflective are perpendicular.

-Crissa
Oh, fair enough. I was just thinking, emissivity + reflectivity = 1. That doesn't make them "opposites" I guess haha
 

ajdelange

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A perfect black body has emissivity of 1. That means you plug the wavelength and temperature into the Planck formula and multiply the result by 1 to get the flux radiated. A non Planckian radiator (such as a piece of stainless steel) will have an emissivity of less than one and radiate, at a given wavelenth, less flux than that predicted by the Planck law by a factor which is the emissivity. The relationship between emissivity and reflectance is complicated by the fact that lots of materials have a high reflectance at visible wavelength but high emissivity at the long wavelenths where the Planck curve peaks at these temperatures of about 300 K. Thus you can't really tie emissivity and reflectivity together. White paint, black paint and a sheet of glass all have about the same emissivity but dramatically different reflectivity at visible and LIR wavelengths.

Yes, metals feel hot or cold to the touch because of their high conductivity. This whole discussion got kicked off by the claim that SS has a low conductivity than some other steels and wouldn't, therefore, feel like a metal. I explained (or tried to) that while there are metals that have conductivities much higher than that of SS the conductivity of SS is higher than the conductivity of uman bodies and that, therefore, it will feel like a metal.
 

Dids

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Aj is wrong about shiny getting less hot. Typically a dull surface has higher emissivity than a shiny one. Yes shiny has higher reflection but it's not enough to overcome the larger drop in emissivity. Weathered stainless emissivity is 0.8 which is pretty high.
Yes the shiny surface will get hotter slower than the matte, but the mechanism that allows the matte to absorb radiation also allows for it to emit radiation once it is hot.
The shiny surface will have to get very hot before it emits shorter wavelength higher energy radiation than the matte surface.
On the feels hot... conductivity and mass of the material make the biggest difference. In other words a shiny black car made of iron will feel hotter than a dull stainless steel Cybertruck.
 
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LDRHAWKE

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Personally I am not worried about which surface or color is hotter; black, red, yellow, white or bare stainless. I am simply going to click on my iPhone five minutes before I get in the car and tell it to cool down or warm up to 75 degrees before I get in….😊
 

Rockvillerich

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This has probably been covered but mildly concerned about the skin getting really hot in direct sunlight. Luckily there won’t be any door handles to access the vehicle but wanted to get others thoughts about this. Boondocking in the desert sun of ~100 degrees would make touching the vehicle unlikely. I know there has been talk of wraps for the truck but I like the SS look and want to keep it simple.
This will not be quite as big a problem in the cold of winter but if cold enough your skin could stick to the surface when touching I suppose. Of course I’m talking below zero temps.
Thanks!
This has probably been covered but mildly concerned about the skin getting really hot in direct sunlight. Luckily there won’t be any door handles to access the vehicle but wanted to get others thoughts about this. Boondocking in the desert sun of ~100 degrees would make touching the vehicle unlikely. I know there has been talk of wraps for the truck but I like the SS look and want to keep it simple.
This will not be quite as big a problem in the cold of winter but if cold enough your skin could stick to the surface when touching I suppose. Of course I’m talking below zero temps.
Thanks!
Guess I'll have to paint mine olive drab.
 

ajdelange

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It's all well and good to talk about the theory and give one's opionions as to what will happen in a particular set of circumstances but of course we don't know what the emissivity or reflectivity are going to be for the metal used to surface the CT. Also keep in mind that radiation isn't the only way the skin can cool. Convection will cool it as surely as IR emission will. Here's a plot based on models used by the construction industry used to calculate the temperature of roofing materials to asses their suitability.
NoWind.jpg


The numbers on the curves are estimates of the surface temperature (°C) of materials exposed to sunlight as a function of the materials reflectivity and emissivity in the absence of any air movement.. As we have stated throughout shiny and emissive materials will stay the coolest. What the curves show is the dramatic decrease in temperature as the reflectivity increases for a given emissivity. Thus polishing stainless dramatically reduces its temperature in sun. OTOH for highly reflective materials higher emissivity doesn't effect surface temperature so dramtically but for materials with low reflectivity it does. I'd say the ouchless region is the region to the right of the 50 °C curve.

This next curve shows the effect of winds in the range of 4 - 13 mph. The ouchless range is obviously larger.

4to13Mph.jpg
 

cybercamper

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Dids has explained everything well in his latest post. A lot of us (older folks) have noticed shiny chrome bumpers get very hot to the touch in direct sun.

I'll pitch in $.02: even though SS has a significantly (5x) lower thermal conductivity than painted steel, the difference is insignificant when it comes to the heat passing into your fingertips.
Plastic Thermal conductivity is about 1000x lower, and that is enough to notice a big difference in "burning" fingertips.

"Pickling" the SS could be a way to achieve the best of all worlds. A very shiny CT will be quite annoying for other drivers to look at depending on the sun angle, etc.


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"Aj is wrong about shiny getting less hot. Typically a dull surface has higher emissivity than a shiny one. Yes shiny has higher reflection but it's not enough to overcome the larger drop in emissivity. Weathered stainless emissivity is 0.8 which is pretty high.
Yes the shiny surface will get hotter slower than the matte, but the mechanism that allows the matte to absorb radiation also allows for it to emit radiation once it is hot."
 
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