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722 posts

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Topic # 230761 12-Mar-2018 12:31
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I ask because the all-black axial heat transfer fan in my (very) hot roof space recently packed a sad: the plastic fan blade started slipping on its spline.

 

The company provided a free replacement but the new model fan motor and housing is all white.

 

Which made me wonder if the manufacturer had decided that white fan motors stay cooler than black, thus lessening the chance of the internal plastic fan blade softening enough to slip on it's shaft.

 

Even if the roof space is mostly dark.

 

Anyone?


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  Reply # 1973159 12-Mar-2018 13:01
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White will reflect more light, but I'm not sure about radiated heat.

 

 





Mike



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Ultimate Geek
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  Reply # 1973166 12-Mar-2018 13:11
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MikeAqua: White will reflect more light, but I'm not sure about radiated heat.

 

Yeah, that's what I thought. The motor is just a typical Chinese low-cost unit (although it's worked OK, and quietly, until the fan blade busted).

 

I don't see why they'd do the white finish unless there was a good reason.

 

He, the distributors don't seem to know why, either. Maybe it's just because it might show up better in the dark, LOL.


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  Reply # 1973180 12-Mar-2018 13:30
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Can't think it would make a lot of difference - unless the white one is made from materials that are more heat resistant.

 

If you bake a vanilla (white) cake and a Chocolate (Dark Brown) they pretty much both cook the same.





Nothing is impossible for the man who doesn't have to do it himself - A. H. Weiler

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  Reply # 1973248 12-Mar-2018 14:24
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robjg63:

 

If you bake a vanilla (white) cake and a Chocolate (Dark Brown) they pretty much both cook the same.

 

 

Nice analogy





Mike

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  Reply # 1973261 12-Mar-2018 14:42
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Yes, white will radiate more heat away. That is why it takes so long to get your toast to start toasting, but so little time for it to go from lightly toasted to burnt. The process accelerates as the toast darkens.










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  Reply # 1973272 12-Mar-2018 14:52
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robjg63:Can't think it would make a lot of difference - unless the white one is made from materials that are more heat resistant. If you bake a vanilla (white) cake and a Chocolate (Dark Brown) they pretty much both cook the same.

 

Baked in a black or white oven?


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  Reply # 1973274 12-Mar-2018 14:54
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gbwelly:

 

Yes, white will radiate more heat away. That is why it takes so long to get your toast to start toasting, but so little time for it to go from lightly toasted to burnt. The process accelerates as the toast darkens.

 

 

It'll reflect more radiant heat away.  In theory it'd probably radiate slightly less heat away (ie that produced internally by the motor) but that effect probably doesn't matter.

 

IIRC and only slightly off topic, I read an article recently about a NZ invention, a black paint which stayed much cooler than normal black paint as it selectively absorbed light from the visible spectrum, but reflected IR and UV.

 

 


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  Reply # 1973292 12-Mar-2018 15:15
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gbwelly:

 

Yes, white will radiate more heat away. That is why it takes so long to get your toast to start toasting, but so little time for it to go from lightly toasted to burnt. The process accelerates as the toast darkens.

 

 

Don't think that's correct. Black is both a better radiator and absorber of heat. That's why heatsinks are often anodised black.

 

 


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  Reply # 1973301 12-Mar-2018 15:32
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kryptonjohn:

gbwelly:


Yes, white will radiate more heat away. That is why it takes so long to get your toast to start toasting, but so little time for it to go from lightly toasted to burnt. The process accelerates as the toast darkens.



Don't think that's correct. Black is both a better radiator and absorber of heat. That's why heatsinks are often anodised black.


 



I agree, that would suggest brown bread would burn before white bread. I suspect it’s more to do with the water content of the bread. The process will accelerate as there is less water in the bread.

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  Reply # 1973381 12-Mar-2018 16:02
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Can anyone tell us for certain if colour effects reflection of radiant heat (as opposed to visible light)?





Mike

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  Reply # 1973387 12-Mar-2018 16:07
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MikeAqua:

 

Can anyone tell us for certain if colour effects reflection of radiant heat (as opposed to visible light)?

 

 

AIUI invisible infrared is the only 'colour' that warms you. 

 

 

 

 


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  Reply # 1973392 12-Mar-2018 16:25
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I thought that an object’s colour only affected the reflection/absorption of light in the visible spectrum. A hot object is radiating light in the infrared so the colour of the paint is not a factor.

I could be completely wrong however.

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  Reply # 1973400 12-Mar-2018 16:32
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I think that being a fan that is presumable running much of the time, the radiated and reflected heat (and therefore colour) is of little consequence. It has air moving past it much of the time, so the heat conducted to or from the air will be of greatest significance.

 

Therefore I reckon that assuming all other things are equal (eg same model fan of different colour) the fans will more or less the same temperature irrelevant of colour.


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  Reply # 1973402 12-Mar-2018 16:37
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tripper1000:

 

I think that being a fan that is presumable running much of the time, the radiated and reflected heat (and therefore colour) is of little consequence. It has air moving past it much of the time, so the heat conducted to or from the air will be of greatest significance.

 

Therefore I reckon that assuming all other things are equal (eg same model fan of different colour) the fans will more or less the same temperature irrelevant of colour.

 

 

Agreed!

 

 


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  Reply # 1973434 12-Mar-2018 17:21
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MikeAqua:

Can anyone tell us for certain if colour effects reflection of radiant heat (as opposed to visible light)?



Colour definitely affects radiated heat. I have a homemade central heating system in my house. The radiators are all old oil column heaters that I have modified. And I have spray painted them black just to increase the amount of heat that they radiate.

You can easily tell the difference comparing them to an unmodified electric oil column heater. Despite it being impossible for my radiators to get hotter than 100deg.





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