Condensors white or silver?

You don't know by looking but you can tell by feeling. In all the cases below, white and light colors don't absorb or radiate heat like black does.

I don't think so, but maybe under some special laboratory conditions. Can you show me any example from real life where that is true.

You just make light of all my examples below, but they are similar to the refrigerator condensor in the original question. If you want metal, just put a piece of white painted metal next to black painted metal in the sun and you'll see the same thing.

What are you saying? That the sun doesn't emit IR? Not so. Or that visible light causes heat? Of course it does, when it's absorbed by something,, and that alone is one reason black things absor and radiate more heat than white.

If he wanted to paint his awning whte, that would help a little.

Reply to
micky
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White

Reply to
Doug

No, you really can't. You can pull a piece of aluminum foil directly out of the oven but don't try it with a cast iron pan.

Wrong. Visible color has nothing to do with it's performance in the infrared.

I *KNOW* so. Some materials are transparent in the infrared and opaque in the visible range, just like some materials are red, or yellow. What matters is the emissivity at the wavelength(s) of the incident radiation.

Other than the fact that the sun has a significant visible component, you're wrong.

I've only said it a dozen times now. Perhaps you can read it if I put it in all CAPS?

WHAT MATTERS IS THE EMISSIVITY OF A MATERIAL AT THE WAVELENGTH(S) OF THE INCIDENT RADIATION.

Idiot...

...doubled down.

WRONG, unless they're incandescent!

Some, because there is visible light in sunlight, but I've already said that. Perhaps you should READ.

Reply to
krw

Gold? WRONG again.

Out of gold? WRONG! Use aluminum or silver.

Reply to
krw

You're dragging in thermal capacity Everything before this was about two things of the same nature of different colors. Not something that is 3/8" thick with something that 1/100" of an inch thick.

That doesn't contradict what I said. I didn't compare color and IR but the effect of black on both.

I asked for an examples from real life. and you don't even give an example from a laboratory.

This is not what you were saying in the sentence I asked about. That read. "Well, you do know that the sun emits energy in the visible range, right?" I presume you were trying to make one of the two possible points I could think of, but you don't reply civilly to either of my choices.

You separated the line above from what follows. Here it is restored:

"glowing or white with heat. " No. It doesnt' require that.

Reply to
micky

No, *you* are dragging it in by saying that your senses can determine this stuff. They can't.

"Black" is a color which you can only sense in the visible range. You're not making any sense.

Good grief! There are examples everywhere. Have you ever seen colored glass? It is transparent at some wavelengths but not (absorbs at) others. That's why it's colored. The same thing happens at infrared vs. visible. The lens on your TV remote control is opaque in the visible range but is transparent at infrared. There are millions of such examples. THINK!

There are two points. In sunlight, the color does make some difference because the sun emits radiation in the visible range. HOWEVER, the 'fridge's radiator does NOT incandesce so its color is meaningless. It could be any "color". I suppose you've seen anodized aluminum heat sinks? A blue one is no less efficient than a black one (IIRC, blue anodizing is actually better).

You're as wrong as you can be. The "color" only matters at the wavelengths being radiated. For a 'fridge's coils,that's *NOT* in the visible range.

Reply to
krw

e:

ote:

If the color of a fridges coils exposed to the sun doesn't matter, then explain how a white roof results in a cooler house than a black roof.

Reply to
trader4

There are two conversations going on here. I've already said that the sun has a visible component, many times. The reason that the coils in the back of a refrigerator are black is *NOT* because what we see as black is a better radiator.

Reply to
krw

rote:

some in direct

Then all the experts who agree that home radiators, for example, radiate more heat when painted black instead of white are wrong? Do you agree or disagree that a home radiator painted black will radiate more heat than one painted white? And if you agree, then how can it not be because black is a better radiator?

Reply to
trader4

Certainly. The performance in the visible range is *no* guarantee of the performance outside the visible range.

Disagree, as stated. It doesn't matter a whit what it's performance is in visible light.

Bad assumption => faulty conclusion, as usual.

Reply to
krw

Regardless of the ir absorption qualities, black will probably never be less than white. I see the point. It's easy enough to check which material is going to get hotter in sunlight, I mean radiation.

Greg

Reply to
gregz

Let's try to pin this down a bit. A condenser (or any heat radiator I can think of) is for shedding heat. Heat is shed via IR radiation, conduction, and convection. Conduction and convection don't care about color. Condensors/radiators are normally shaded, so don't absorb solar visible light heat - color won't matter if it's shaded. There's something called emissivity of IR radiation. Depending on what/who you read, emissivity depends on color. Never found a good answer from the internet. But my understanding is that color is inconsequential for common condensors/radiators. It's just bling. Because conduction/convection is doing virtually all the work in moving the heat. So good airflow/fluid flow around the condensor/radiatior is worth a thousand times more consideration than IR emission. The funny part with home radiators is the arguments against using silver or gold paint because of emissivity. Every home radiator I've ever had was painted silver and worked just fine. Maybe it could have been more efficient with a different color. But maybe not. Because conduction is as important as emissivity. It would be expensive to get NASA engineers in to make the measurements. I never bothered with that. NASA has the answers to all this with their space radiators. I've read they use some wildly expensive materials to get best results.

Reply to
Vic Smith

Again, there are two discussions going on here. First, which will get hotter in sunlight. Black may get hotter because there is significant energy in the visible range (IIRC the peak is in the green/yellow region). There is far more, integrated over the entire EM spectrum, outside the visible range, so black will not necessarily be hotter. Certainly this can be measured with a thermometer (your hand isn't going to do it).

The other issue is whether black makes a better radiator for a 'fridge. This is *not* true because there is no visible light being emitted so it doesn't matter one bit what the color is in the visible range. There just isn't any radiation there. The emissivity at the black-body temperature of the widget matters, not its emissivity in the visible range.

Reply to
krw

:

The question at hand was obviously not whether the color of a condensor makes a difference for a fridge in general. The question was whether the color of a fridge condensor that is outside, EXPOSED TO SUNLIGHT, makes a difference.

Stormin: "If a refrigerator is used outdoors, in the summer. The condensor on the back, is black tubing. As we know, black absorbs heat from the sun shine, which makes the compressor work harder. "

Now, it seems you agree that white will reflect more of the sunlight. At the same time, white paint and black paint will both allow about the same radiation from the condensor. That means with white you radiate virtually the same amount of heat out, but because it's white, it reflects a lot of heat from the sun that it would absorb if it were black. Ergo, if the condensor was painted white instead of black, it would transfer virtually the same amount of heat via radiation, but it would be heated less by the sun.

And I also totally agree with Vic that the overwhelming heat transfer from the condensor is via convection, not radiation. So, again, which condensor is going to be more efficient? A black one that has to not only get rid of heat from the fridge mainly via convection, but also the additional heat from the sun? Or a white one, that has less heat absorbed from the sun? I vote for white.

Finally, I think the overall effect on efficiency of the fridge from the color of the condensor with sun shining on it is still probably small in the grand scheme of things.

Reply to
trader4

One vote, white.

To further refine the question. Maybe a white sun shade, about a foot out, would be workable. Plenty of air flow available.

Christopher A. Young Learn more about Jesus

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The question at hand was obviously not whether the color of a condensor makes a difference for a fridge in general. The question was whether the color of a fridge condensor that is outside, EXPOSED TO SUNLIGHT, makes a difference.

Stormin: "If a refrigerator is used outdoors, in the summer. The condensor on the back, is black tubing. As we know, black absorbs heat from the sun shine, which makes the compressor work harder. "

Now, it seems you agree that white will reflect more of the sunlight. At the same time, white paint and black paint will both allow about the same radiation from the condensor. That means with white you radiate virtually the same amount of heat out, but because it's white, it reflects a lot of heat from the sun that it would absorb if it were black. Ergo, if the condensor was painted white instead of black, it would transfer virtually the same amount of heat via radiation, but it would be heated less by the sun.

And I also totally agree with Vic that the overwhelming heat transfer from the condensor is via convection, not radiation. So, again, which condensor is going to be more efficient? A black one that has to not only get rid of heat from the fridge mainly via convection, but also the additional heat from the sun? Or a white one, that has less heat absorbed from the sun? I vote for white.

Finally, I think the overall effect on efficiency of the fridge from the color of the condensor with sun shining on it is still probably small in the grand scheme of things.

Reply to
Stormin Mormon

So far, so good. Conducion does care about paint, though. It's an insulator, to some degree or other. ;-)

At least in the first order, yes.

It doesn't depend on color at all. Snow has a very high emissivity, for instance.

Color doesn't. Some materials, of course, have definite colors and that may change emissivity. IIRC, blue anodizing is slightly better than other colors, not because it's blue, rather because of the specific process/chemicals used.

Yes.

Yes.

The paint will reduce conduction (insulation), and therefore convection. Bad idea, except that protecting the surface from corrosion will usually offset the insulation.

Convection and conduction don't work well in space. ;-)

Reply to
krw

There were two discussions getting mixed together.

That was the original issue, yes, which I answered quite early in the thread (shade it). Like every thread on the Usenet, it went in various directions, including what was the best color for a radiator.

Like always, you put words in people's mouth and then claim victory when they're not correct. Go for it. You will anyway.

I've said that all along. Please do read the thread before making such an ass of yourself.

I'd vote for shading it. Neither black nor white will be satisfactory. Any paint will just add to the problems.

I think you might be wrong. The higher the delta-T the higher the hill the heat has to be pumped.

Reply to
krw

Shade the coils.

Reply to
krw

ote:

Which of course does not answer the direct question. I mean here you are arguing science, so why not give the actual answer to the direct question?

Like every thread on the Usenet, it went in various directions,

I have not put words in anyone's mouth. I just believe I definitively answered the actual question posed by Stormin.

There you go again, getting nasty for no reason. All I said was I agreed with Vic. Apparently you do too, so why the attitude?

And there you go again, as usual, redirecting away from the question if black or white makes a difference.

That's interesting for two reasons. One is that by inference, you apparently agree that for Stormin's stated problem, white versus black does make a difference, though it's small. But as usual, you can't just man up and say so.

And second you obviously have not seen the results of experiments done with central AC units where the compressor/condensor was placed in direct sun versus shade. There was negligible difference in energy used because like the fridge they are highly dependent on the surrounding air temp, not the sunlight falling on the coils.

Reply to
trader4

Actually, it did.

I did. The binary answers weren't sufficient.

You're a liar but that's nothing new, either.

More lies. ...to be expected.

No, that's the right answer. You're just looking for an excuse to cause trouble. Again.

I said that, dumbass. Good Lord, you're stupid!

Go away, idiot.

Reply to
krw

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