By the law of physics I've been told many times that black absords more heat the other colours. But by how much so, 1%, 10% or something really significant like 30%?

If you were to use a black server case instead of white how much difference would it make?
:confused:

No difference at all. Color only matters as far as *radiative* heat is concerned... ie, unless the inside of your case is hot enough to be visibly glowing it won't matter.

Computers are cooled almost totally by convection (of hot air), which is entirely unaffected by color. A slight effect is also due to heat being conducted away through the case, which means that a metal case *might* result in temperatures 1 or 2C lower than an identical plastic case.

So yes, black does absorb much more heat than other colors, but only in the context of radiation, so the effect on computers would be insignificant.

Originally posted by cperciva
unless the inside of your case is hot enough to be visibly glowing it won't matter.

remove the fan of your CPU and you will know the difference ;)

Actually in the case of cpu heatsinks there will be a difference, although not directly due to color. The surface properties of metal heatsinks vary significantly and have noticeable effect upon heat transfer; consequently two otherwise identical aluminium heatsinks which have been anodized to different colors could very easily show performance differences. Although which would be better is anyones guess.

Originally posted by MattF
By the law of physics I've been told many times that black absords more heat the other colours. But by how much so, 1%, 10% or something really significant like 30%?

If you were to use a black server case instead of white how much difference would it make?
:confused:


It would only make a real difference if you were shining heat lamps at your servers.

Originally posted by cperciva
Color only matters as far as *radiative* heat is concerned... ie, unless the inside of your case is hot enough to be visibly glowing it won't matter.
Why does it have to be visible to be radiative heat? ;)

Besides, the inside of any server/computer case is not black! So, why does that matter?

cheers,
:beer:

Originally posted by Mike the newbie
It would only make a real difference if you were shining heat lamps at your servers.

Don't tell me I'm the only one who does this?! :eek3:

lol!! It would prob. only make a difference if you put your servers outside on a hot summer day.

Originally posted by dektong

Besides, the inside of any server/computer case is not black! So, why does that matter?

Well if your CPU is glowing you'd probably want the inside to be black - so that it didn't reflect all the radiative heat back at your CPU, wouldn't you?

And if you really wanted to blow it, you could stick mirrors on the inside :D

It's not that black absorbs heat faster or better, it's that it holds and maintains the heat better. So yes, a black case would not be good. Anyone who wasnt sleeping in class would remember this from when you studied why pan makers make their pans black and why Arabians wear white in the desert. Go look at your cooking pans, are they black? Gee, wonder why.

They do make white cooking pans. If you have one, turn on two burners on your stove, put both a black pan and a white pan, put a little water in them and you can tell the difference of which heats faster. The water in the black pan will come to boil sooner. When it comes to electronics, you want whatever gets rid of the heat the best. White (or light colors) cases will lose the heat faster than black ones.

Wouldn't you want the case to reflect as much external heat as possible but absorb as much internal heat as possible? I'm thinking a white case that's black on the inside.

In an ideal situation you would be reducing the effect of external heat sources (white case), and drawing as much heat towards the edges of the case as possible, away from the processor (black inside of case, as the black lining would hopefully retain heat better than the processor). Then, of course, you actually want to dissipate as much heat out of the case as you can.

The problem with that is that the heat would be in stuck in there (yes, I know about cooling fans) and heat up the electronics. Just put in 10 fans and you won't have to give a ****!

Originally posted by Lawrence
Wouldn't you want the case to reflect as much external heat as possible but absorb as much internal heat as possible? I'm thinking a white case that's black on the inside.


Yes.... but. (there's always a but.) You need to look at this as a heat flow problem, i.e., what are the sources of heat and what are the sinks of heat; and how do you move the heat from the source to the sink.

Without going through all the engineering calculations, I would offer that the overwhelming majority of the heat is sourced inside the case by the electronics; and very, very little of the heat is sourced due to radiation heating of the case. The heat sink is everything outside the case.

So the question resolves to: how do you move heat from inside the case to outside the case. Convection (i.e., fans) is quick and easy and inexpensive). In a previous life, I had to design a box that was totally sealed because it had to run in a very contaminated environment. Low power components and cooling by conduction were the order of the day. IBM mainframes have used water-cooling. some of the older (ancient?) number crunchers actually had freon flowing through the circuit boards. etc., etc., etc.




In an ideal situation you would be reducing the effect of external heat sources (white case), and drawing as much heat towards the edges of the case as possible, away from the processor (black inside of case, as the black lining would hopefully retain heat better than the processor). Then, of course, you actually want to dissipate as much heat out of the case as you can.

The amount of heat you would dissipate due to what you describe would be neglible compared to the convection cooling provided by the fan.

Originally posted by Webdude
It's not that black absorbs heat faster or better, it's that it holds and maintains the heat better. So yes, a black case would not be good. Anyone who wasnt sleeping in class would remember this from when you studied why pan makers make their pans black and why Arabians wear white in the desert. Go look at your cooking pans, are they black? Gee, wonder why....


Black absorbs heat, white reflects heat. For radiation cooling, black radiates heat (i.e., cools) better than white. Do a search in the search engine of your choice, looking for "emissivity radiation cooling blackbody" and see what you find.

I'm no expert on this, but I was curious and decided to ask someone who has been involved with nuclear power for over 30 years, and is a high level manager at a nuclear facility in this area, among other things.

MattF
If you were to use a black server case instead of white how much difference would it make?

He says not much, although black would be the better choice.



cperciva
Color only matters as far as *radiative* heat is concerned... ie, unless the inside of your case is hot enough to be visibly glowing it won't matter. Computers are cooled almost totally by convection (of hot air), which is entirely unaffected by color... <SNIP> ...so the effect on computers would be insignificant

He said that although this statement is partially incorrect, in this context, due to the *amount* of difference, it wouldn't matter much. He'd pick the black, as I said above.



Lawrence
Well if your CPU is glowing you'd probably want the inside to be black - so that it didn't reflect all the radiative heat back at your CPU, wouldn't you?

Aside from the glowing thing, heh, he said you are correct and that you'd want the inside of the case to be black as well (as black absorbs heat better).



Webdude
It's not that black absorbs heat faster or better, it's that it holds and maintains the heat better.

He said this statement is not really accurate. Black absorbs and radiates heat better. Black does not 'hold' heat better, nor 'maintain' it better than white, the opposite is true.

So yes, a black case would not be good.

Due to the reasons above, he said this statement is not correct.

Anyone who wasnt sleeping in class would remember this from when you studied why pan makers make their pans black and why Arabians wear white in the desert. Go look at your cooking pans, are they black? Gee, wonder why.

They do make white cooking pans. If you have one, turn on two burners on your stove, put both a black pan and a white pan, put a little water in them and you can tell the difference of which heats faster. The water in the black pan will come to boil sooner.

He wonders what they teach kids in class these days :D About the cooking pans, he says you are correct, a black pan is prefered due to its ability to absorb heat better (from the heat source), and radiate heat better (to the food, or water in this case), than a white pan.

When it comes to electronics, you want whatever gets rid of the heat the best. White (or light colors) cases will lose the heat faster than black ones.

As you can probably guess, the last part is incorrect, a black case will absorb more heat from the hot inside, and radiate more heat out than a white case.



Mike the newbie
He says Mike is correct. :D

Go Mike!!!!

Originally posted by Chicken
I'm no expert on this, but I was curious and decided to ask someone who has been involved with nuclear power for over 30 years, and is a high level manager at a nuclear facility in this area, among other things.


Small world. 26 years ago I was designing emergency cool-down motors for nuclear power plants. :)

*gets out spray gun*

Hang on, gloss black, semi gloss or flat? :D

[QUOTE]Originally posted by cperciva
Actually in the case of cpu heatsinks there will be a difference, although not directly due to color. The surface properties of metal heatsinks vary significantly and have noticeable effect upon heat transfer; consequently two otherwise identical aluminium heatsinks which have been anodized to different colors could very easily show performance differences. Although which would be better is anyones guess. [/QUOTE

Black has shown to do very well, not sure if all are tested... but it seems to be the best so far.

For all practical purposes, it doesn't really make a difference.

Save your black spraypaint money and buy an extra fan. Or better yet, save it for your electric bill (Keeping a data center freezing cold ain't cheap here in Florida...) :stickout

Originally posted by Mike the newbie
Small world. 26 years ago I was designing emergency cool-down motors for nuclear power plants. :)

Guessing you've heard of Combustion Engineering, then ABB, now I believe owned by Westinghouse eh?

Originally posted by Lawrence
*gets out spray gun*

Hang on, gloss black, semi gloss or flat? :D

LOL, I forgot to ask him that, heh :D

Originally posted by Chicken


Guessing you've heard of Combustion Engineering, then ABB, now I believe owned by Westinghouse eh?

Yup. I knew of CE very well.