CyberTruck SS Heat

[Ogre]

Oddly enough, some interesting thoughts about this on discussion about BBQ grills.

I know grills and trucks aren't the same. Also I know the steel used in trucks isn't the same as cast iron, regardless....

Stainless:

• Heat up quickly – You don’t have to spend a lot of time preheating your grill before you put on the food.
• Don’t retain heat well – Stainless steel cools off quickly. It won’t maintain a decent cooking temperature once you’ve removed the heat source.

Cast Iron:

• Retain heat well – Cooking on cast-iron combines the benefits of stovetop cooking on a cast-iron pan with outdoor grilling. You’ll get a good sear where the grates touch the meat, and you’ll get great heat transfer. This helps you cook your food thoroughly when your charcoal is starting to die down.
• Transfer heat directly – Food that’s touching the surface of the grates will be well-seared. This is ideal for foods that only have to cook for a short amount of time but benefit from a darker outer layer.

So there you have it, stainless is likely to be less good at transferring heat (which confirms what @Delusional suggested above), and will heat up and cool off quicker.

Not quite sure how much of that applies when we're talking about solar heating versus a grill.

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[ajdelange]

This is neat, hadn't thought SS would be that different from regular steel.

It isn't. See the histogram in No. 7. Of the 19 steel types listed he chose the highest conductivity one to compare to stainless. Of the 19 ten, over half, including the two stainless and 8 others have conductivity in the 10 - 20 W/m-K range. He tried to hood wink you and evidently he succeeded.

But isn't it still going to radiate heat?

It does but just not as much as painted steel because paint has emissivity of aroud 0.95 whereas stainless the emissivity is appreciably lower than that. Mirror polished stainless (or any other metal) has emissivity close to 0. It can't re radiate any heat but it doesn't absorb any either. It's the finishes with mid range emissivity that can absorb enough but can't reradiate enough that get hot.

So you park in a sunny spot, the outside of your car is about 150 degrees. Doesn't burn you to the touch, but when you get into the car, you are sitting in a small oven surrounded by a shell of 3mm metal.

The reason the metal gets hot is because it cannot reradiate all the heat it absorbs to the outside at a temperature close to the ambient It has to be hotter to do that and come to equilibrium. The reason the metal doesn't burn you is because it doesn't contain that much heat (high density but low specific heat) and because your skin has low conductivity. Just as it doesn't radiate heat effectively to the outside it does not radiate to the inside,heat transfer to the inside is via conduction and, like your skin, the air space (and/or insulation which is, of course, mostly air space) has a high thermal impedance. Thus the sun beating down on the skin isn't what turns the inside of your vehicle into an oven. What does that is the visible sun light pouring in through the windscreen, windows and glass roof.

This would make it quite a bit harder to cool the cabin in the summer time.

Were your premise correct it would but your premise is not correct.

Usually I would just park in the shade, but since I'll probably pay too much money for the solar option, I'm going to want to park in the sun at least part of the time.

I made Mrs (bless her heart) wait for me in the hot sun for 3 hrs about a month ago. She was, if bored, at least comfortable at the cost of about 1 kW from the battery.

 

[ajdelange]

So there you have it, stainless is likely to be less good at transferring heat (which confirms what @Delusional suggested above), and will heat up and cool off quicker.

Which is, of course, why it is so widely used in, for example, brewing, steam kettles in commercial cooking, dairies and pharmaceutical plants etc.

Not quite sure how much of that applies when we're talking about solar heating versus a grill.

I think the main thing you are missing is that in a brewery or a kitchen or a car stainless is chosen not for its thermal properties but for its other properties in particular its strength, ability to resist corrosion. Brewers and chefs prefer and for years have used copper which is not as strong as steel or iron but easier to work with and which conducts heat 8 to 40 times better But there is a problem with it - low pH foods dissolve it. Tesla is trying to transfer structural load to an exoskeleton. I'm sure they would use titanium if they could but there are obvious problems with it (cost). Stainless will do just fine. There are nothing in it's thermal properties which make using it disadvantageous for Tesla (brewers and cooks do need to use a higher source temperature to transfer an equal amount of heat relative to copper).

 

[Crissa]

This would make it quite a bit harder to cool the cabin in the summer time.

Well, even if it's hot, the steel is radiating less into the cabin directly than the other steel...

...which is why there will be so much reflective glazing over the top.

-Crissa

 

[tmeyer3]

This is neat, hadn't thought SS would be that different from regular steel.

But isn't it still going to radiate heat?

So you park in a sunny spot, the outside of your car is about 150 degrees. Doesn't burn you to the touch, but when you get into the car, you are sitting in a small oven surrounded by a shell of 3mm metal.

This would make it quite a bit harder to cool the cabin in the summer time.

Usually I would just park in the shade, but since I'll probably pay too much money for the solar option, I'm going to want to park in the sun at least part of the time.

To the touch, yeah it'll burn you because it can store a lot of energy. But it's a terrible insulator. The plastic internal trimming will insulate far better than the steel will. But that's also true for aluminum. Aluminum body panels are far worse insulators then even SS, by an order of magnitude worse. Plenty of cars are just fine in aluminum. The only difference here is that SS will hold more heat.

It's going to radiate heat by being reflective more than anything else!

ALL cars are little ovens here the Mojave! It's pretty easy to fix. Get in, roll down ALL the windows, get up to speed, roll up the windows, crank that AC!
This is why it's common practice to crack you windows while parked. It is also why Tesla created dog and camp mode.

 

[Klaxon]

Well, the guys that are not fried in the regular vehicles made from black steel should not worry about the stainless cabs. Stainless steel, like majority of complex alloys, has much lower thermal and electrical conductivity than the low alloy steel or pure metall. You will be better protected from exterior heat. The lower conductivity among widely used metals have only titanium alloys.

 

[BillyGee]

Oddly enough, some interesting thoughts about this on discussion about BBQ grills.

I know grills and trucks aren't the same. Also I know the steel used in trucks isn't the same as cast iron, regardless....

Stainless:

• Heat up quickly – You don’t have to spend a lot of time preheating your grill before you put on the food.
• Don’t retain heat well – Stainless steel cools off quickly. It won’t maintain a decent cooking temperature once you’ve removed the heat source.

Cast Iron:

• Retain heat well – Cooking on cast-iron combines the benefits of stovetop cooking on a cast-iron pan with outdoor grilling. You’ll get a good sear where the grates touch the meat, and you’ll get great heat transfer. This helps you cook your food thoroughly when your charcoal is starting to die down.
• Transfer heat directly – Food that’s touching the surface of the grates will be well-seared. This is ideal for foods that only have to cook for a short amount of time but benefit from a darker outer layer.

So there you have it, stainless is likely to be less good at transferring heat (which confirms what @Delusional suggested above), and will heat up and cool off quicker.

Not quite sure how much of that applies when we're talking about solar heating versus a grill.

The other fun thing about high grade stainless compared to cast iron is that it has localized heating. If it's well made steel you have one end be red hot and touch the other end with a bare hand with no risks. Depending on thickness and level of insulation between the cabin and exterior it may even prove to be slightly better for thermal management than a normal car finish, but only slightly. I'd imagine that compared to the average car on a hot or cold day it'll be much the same unless you keep the climate control on in the cabin at all times.

 

[Ogre]

The other fun thing about high grade stainless compared to cast iron is that it has localized heating. If it's well made steel you have one end be red hot and touch the other end with a bare hand with no risks. Depending on thickness and level of insulation between the cabin and exterior it may even prove to be slightly better for thermal management than a normal car finish, but only slightly. I'd imagine that compared to the average car on a hot or cold day it'll be much the same unless you keep the climate control on in the cabin at all times.

Funny thing that, in a Tesla, climate control is on in the cabin at all times in the summer. It just resets to 105 degrees when you are away. Love that feature, though range will suffer if you leave it parked in the hot sun. Of course if you get solar...

 

[ajdelange]

To the touch, yeah it'll burn you because it can store a lot of energy.

The reason it can burn was explained in a previous post. While it doesn't store that much heat per cc it is, though configured as a thin sheet, conductive enough that the heat from a patch several cm away from where you touch it can reach you quickly because it is more conductive than you are. Thus you are effectively in contact with many cc of it.

But it's a terrible insulator.

People concerned with getting heat out of gear consider it an insulator but in fact it's a pretty good conductor. Again I emphasize, a much better one than you are which is why it can burn you (if it gets hot enough).

The plastic internal trimming will insulate far better than the steel will.

The plastic is an insulator true but its main job, in this regard, is to trap air which is a better insulator still.

But that's also true for aluminum. Aluminum body panels are far worse insulators then even SS, by an order of magnitude worse. Plenty of cars are just fine in aluminum. The only difference here is that SS will hold more heat.

Aluminum has thermal conductivity about 16 times that of stainless but air has conductivity 600 times worse so a few mm of air behind the metal, aluminum or stainless, will drop the temperature. It isn't the heat coming through the panels and trim that are heating the interior. It is the energy coming through the windows.

It's going to radiate heat by being reflective more than anything else!

Radiation is not reflection. This is not a nit. They are two entirely different mechanisms. Most of the suns energy is in the visible and NIR. When it strikes the metal a portion is reflected and the remainder absorbed. The absorbed part heats the metal and the metal will continue to get hotter and hotter until such time that it gets hot enough that the energy it radiates in the far infrared (black body radiation) equals the energy that it is absorbing in the visible and near infrared.

ALL cars are little ovens here the Mojave! It's pretty easy to fix. Get in, roll down ALL the windows, get up to speed, roll up the windows, crank that AC!
This is why it's common practice to crack you windows while parked. It is also why Tesla created dog and camp mode.

You don't even have to do that. Just turn on the A/C remotely about 10 minutes before you come out to the car and it will be comfortable. Of course this will cost you battery some of which you can save by cracking the windows (remotely) or by just opening the doors for a few minutes before you get in if there is a breeze.

 

[ajdelange]

The other fun thing about high grade stainless compared to cast iron is that it has localized heating. If it's well made steel you have one end be red hot and touch the other end with a bare hand with no risks.

As the thermal conductivity of cast iron is only about 3 times that of stainless this better be a loooong piece of stainless!

Depending on thickness and level of insulation between the cabin and exterior it may even prove to be slightly better for thermal management than a normal car finish, but only slightly. I'd imagine that compared to the average car on a hot or cold day it'll be much the same unless you keep the climate control on in the cabin at all times.

As I've said in at least three of these posts now it is not the conductivity of the metal in the skin that determines this but rather the thickness of the air layer beneath it that determines how much heat flows to the interior from the outside. Various steels vary in conductivity by less than an order of magnitude. Even with aluminum that is an order of magnitude and a half better than steels its easy to swamp that with a little air.

 

[tmeyer3]

The reason it can burn was explained in a previous post. While it doesn't store that much heat per cc it is, though configured as a thin sheet, conductive enough that the heat from a patch several cm away from where you touch it can reach you quickly because it is more conductive than you are. Thus you are effectively in contact with many cc of it.

People concerned with getting heat out of gear consider it an insulator but in fact it's a pretty good conductor. Again I emphasize, a much better one than you are which is why it can burn you (if it gets hot enough).


The plastic is an insulator true but its main job, in this regard, is to trap air which is a better insulator still.


Aluminum has thermal conductivity about 16 times that of stainless but air has conductivity 600 times worse so a few mm of air behind the metal, aluminum or stainless, will drop the temperature. It isn't the heat coming through the panels and trim that are heating the interior. It is the energy coming through the windows.


Radiation is not reflection. This is not a nit. They are two entirely different mechanisms. Most of the suns energy is in the visible and NIR. When it strikes the metal a portion is reflected and the remainder absorbed. The absorbed part heats the metal and the metal will continue to get hotter and hotter until such time that it gets hot enough that the energy it radiates in the far infrared (black body radiation) equals the energy that it is absorbing in the visible and near infrared.


You don't even have to do that. Just turn on the A/C remotely about 10 minutes before you come out to the car and it will be comfortable. Of course this will cost you battery some of which you can save by cracking the windows (remotely) or by just opening the doors for a few minutes before you get in if there is a breeze.

Was keeping it simple since it's all been covered multiple times. But thanks, sensei!

 

[CyberGus]

What the hell is that ghostly image?? Is that what they call "black body radiation"

 

[ajdelange]

Was keeping it simple since it's all been covered multiple times.

I appreciate that but each time I go at it I gain insight. On this last one I realized that what is going on in that piece of stainless steel is greenhouse effect!

 

[Ogre]

What the hell is that ghostly image?? Is that what they call "black body radiation"

Someone did a really weird photo edit on that picture and I'm not sure why. It's kind of funky and gross.

 

[ajdelange]

A couple of years ago he could have posted a picture of a "perfect black body" which we all would have enjoyed but that sort of thing is no longer politically correct along several lines.

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