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Bruce Sutherland
United Kingdom
1547 Posts |
 Posted - 24/10/2017 : 15:51:51
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Regarding brake drum colour for best heat dissipation, my memory from school physics always advised that black was best.
If so, why not try a high temperature black exhaust manifold paint?
Bruce. (PB0564) |
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Ian Bowers
United Kingdom
937 Posts |
Posted - 24/10/2017 : 16:12:34
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Effective heat loss by radiation only takes place from low red hot conditions and above, at this point blackness assists radiative loss. Up to that point convection is the primary mode of heat loss. Air, from the action of driving and the rotating wheels provides a highly effective coolant. Fins help both rigidity and heat loss.
The major factor for maximising convection is avoiding insulating the drum with a heavy paint layer.
Ian Bowers
OD 6791
J3 3772 |
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Bruce Sutherland
United Kingdom
1547 Posts |
Posted - 24/10/2017 : 16:32:16
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Ian,
Whilst agreeing with your premise that heat loss/dissipation by the convective airflow round the brake drum will be greater than that of the (lesser) benefit of black-body radiation, are you able to say how much the insulating effect of a layer of black paint is/will be?
Most brake drum metals will corrode/rust if left without a protective (paint?) finish.
Bruce. (PB0564) |
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Ian Bowers
United Kingdom
937 Posts |
Posted - 24/10/2017 : 18:30:58
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Sorry, Bruce, I just don't have that information. However I am confident that a metallic paint (eg aluminium flake) will be more efficient than something like Hammerite, though the difference will almost certainly be quite small.
Ian Bowers
OD 6791
J3 3772 |
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O.Thomas
United Kingdom
755 Posts |
Posted - 24/10/2017 : 19:16:52
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| It's all to do with Stefan-Boltzmann law and Wien's Law. S-B law relates to the total energy radiated from a blackbody proportional to its fourth power of its temperature.Wiens law is the relationship between the wavelength of the maximum intensity a black body emits and its temperature . |
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Bruce Sutherland
United Kingdom
1547 Posts |
Posted - 24/10/2017 : 19:31:03
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Hi Olli,
I applaud your powers for Google searches  , but you forgot to mention Planck's law of black-body radiation.......tut, tut. 
But back to the 'job-in-hand', it most probably doesn't matter what colour you paint the brake drums to stop them corroding/rusting.
Bruce. (PB0564) |
Edited by - Bruce Sutherland on 24/10/2017 19:34:24 |
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george
United Kingdom
862 Posts |
Posted - 24/10/2017 : 20:56:30
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| I would guess that more people would worry about the ability of MMM brakes to generate heat than those that worry about dissipating heat from them. Geoff [with hydraulics AND ventilated drums] |
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Hamish McNinch
United Kingdom
108 Posts |
Posted - 24/10/2017 : 21:47:42
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Duh! Oliver didn't mentioned Planck's law because he was, quite correctly for the matter in hand, applying the Raleigh-Jeans Law in the low frequency case while, again quite correctly, referring to Wien at the higher end.
It's all pretty basic..... |
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Dow
United Kingdom
490 Posts |
Posted - 25/10/2017 : 05:41:02
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I'd heard about whine, and the short plank laws, but not the others ! Relates to thickness of material I think !
DD
Regards
David D |
Edited by - Dow on 25/10/2017 05:48:34 |
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Bruce Sutherland
United Kingdom
1547 Posts |
Posted - 25/10/2017 : 10:25:38
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OK! OK!
I bow to the superior Googlers’ and Wikipedias’ in their searches to understand the physics behind radiation from bodies……………….it’s a constant delight to find the depth of knowledge on this forum. 
Bruce. (PB0564) |
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Oz34
United Kingdom
2495 Posts |
Posted - 25/10/2017 : 11:23:40
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All this erudite discussion does nothing really to answer the OP question. I guess probably most Triple Ms had black drums originally and this is my preference. I had heard that the suppliers of the Alfin drums said they should not be painted and, while I can ask them if I decide to buy, I wonder if any member can suggest a REALLY valid reason why this should be so?
Confused of Lewes |
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coracle
United Kingdom
1885 Posts |
Posted - 25/10/2017 : 11:39:11
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If they are painted then no-one would notice them and thus the supplier would not benefit from the extra demand generated by those admiring them?
From the one who put C in oracle. |
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tonym
United Kingdom
651 Posts |
Posted - 25/10/2017 : 14:48:15
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| I am very happy when my drums are producing heat - it is when they are dead cold after the car has stopped a mere inch from the wall or car in front that I worry !! |
Edited by - tonym on 25/10/2017 14:49:27 |
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