Heat dissipation.

What is the general consensus re heat dissipation. I am building a B175 engine for trials, I am using a modified Fantic 200 cyl head which has a larger finned area etc, they can get hot during trials in the warm months and they are centre plug head. On the Fantic they were black, just wondering is it best to paint or get blasted to bare ally. ?? I will be painting the barrel and using a Suzuki TS185 piston. Thanks in advance....

It seemed the in-thing when I was racing half-a-century ago to paint hot bits with black-lead paint -- something to do with emissivity -- but in any case there´s an old saying Black is Beautiful, so why not?



Cheers!

...read Kirchoff´s Radiation Law -- on Google.

Interesting I had been considering the same thing for the engine I am working on....it is normal concensus that a black surface absorbs more radiated heat than a white surface, does that mean that conversely black will be better at heat emission. It should be easy enough to prove; get 2 identical lumps of metal, shine one, paint one black. Heat both up remove from heat and measure temperature decay, I may have a go at work tomorrow if I get time.

As JB said in theory matt black should be good.

My experience with aircooled cast iron Bantam trials motors is that larger finned/greater surface area cylinder has great benefit.
I have a modified BTW head with larger surface area; I acquired with some old racing bits, very carefully set up with 64mm bore, 10:1 compression, 1.0mm squish, ground to barrel without gasket, running 98 octane petrol, B7ES in winter B8ES in summer. I can put my gloved hand on head.
In summer here in NZ(24-28degrees), cast iron barrel creaks a bit, so I drink from CamelBak between sections and give it a squirt of temporary watercooling before next section!

My TY175 has just been rebuilt, I had barrel and head bead blasted and painted with fancy micron thin aviation coating used on DC3 barrells (they leave heads plain) wasn't dear if goes with a batch. My aero engineer mate says since changing from old thick baked enamel DC3 engines run cooler and have extended maintenance times.

Sounds good, as its so cold I am going to paint my living room radiator matt black....hope my good lady like it.

Very amusing Karim:-

We are all aware -- I believe -- that domestic radiators transfer heat out by conduction, which is surface contact with air moving across those surfaces because the warmed air rises moving the cold air across the heated surfaces... Domestic radiators are surface-finished in silver, light coloured or white for the reason of radiating heat out. End!

-- I don´t think it would make much difference if painted black -- I´d suggest you too, go and take a look at Google´s "Kirchoff´s Radiation Law" and prove the point before you go creating a domestic upset.

john bass wrote:

Very amusing Karim:-

We are all aware -- I believe -- that domestic radiators transfer heat out by conduction, which is surface contact with air moving across those surfaces because the warmed air rises moving the cold air across the heated surfaces... Domestic radiators are surface-finished in silver, light coloured or white for the reason of radiating heat out. End!

-- I don´t think it would make much difference if painted black -- I´d suggest you too, go and take a look at Google´s "Kirchoff´s Radiation Law" and prove the point before you go creating a domestic upset.

But isn't that what's needed from an engine "radiating heat out" and nothing to do with reflecting sun rays.
Bit of useless information I remember from my technical college days - Black paint is smoother than white due to finer pigments required to make black.

I will try and absorb kirchoffs law at some point but have never been much of a scholar, will stick to my practical experiment and let you know the results. Lots of different opinion here at work, the main point has been that all car radiators are black, is there a reason?
My previous flippant post is not intended to wind anyone up, least of all my good lady (fyi John, she is also a Bass). The radiator was a metaphorical one, I have a paraffin heater and its brown!.

Yeah! -- radiation is a bit confusing to a lot of people. Perhaps, CORRECTLY I should have said a domestic radiator CONDUCTS most of the heat out. That is, with its radiation out as a smaller contribution to keeping your goolies warm ...

I don´t want to get into the Kirchoff explanation (it´s a 150 years old anyway) all I want to say to finish this (for myself on here) is that you either understsand emissivity & absorptivity according to Kirchoff -- or you don´t. Obviously, You don´t if you´ve never read owt about it... He refers to a `Black Body´ as something perfect as his standard -- and unattainable in practice .. yet states that lamp-black and platinum-black approach the `Black Body´ closely. Comparing the emissivity table of 20 materials (in another write up) given and just taking two extremes:- polished aluminium has €*** of 0.04 at 60°F and 0.06 at 1000°F whereas for those same temperatures Lampblack Paint has 0.96 and 0.97 -- which means heat radiated into that polished aluminium cylinder head will get much hotter than a Lamp-Black painted one. I guess the old grate-blacking stuff was near enough the right gear...


I added this bit later: Black is NOT a colour. To say a person is "coloured" really meaning they are "black" is a misnomer. Black has no place on the chromasticisty chart where the refractions (made by spectrometer) of white light wavelengths are measured in Angstroms. Since black has no refraction wavelength -- or there´s never been a way of finding such -- there is no place for black to sit in the chromasticisty chart ....

Wearing white or black -- is a good idea -- in high ambient temperature because both do not absorb the radiated ambient heat but white does begin to do so at the higher temperatures -- see note below -- and at normal cylinder head temperature white would be radiating heat energy IN where black prevents that happening. And if you think of a steel object standing in a sauna it will be too hot to handle (several degrees above the sauna air temperaure) because of radiated heat IN whereas the same object standing in zero ambient air will actualy have a temperature UNDER zero and be freezing enough that if you put your wet tongue on it the tongue will stick there by frost. Perhaps Karim it is an experiment you would like to perform??
That is because the steel object radiates enough of its heat energy OUT to have its internal temperature drop a couple of degrees.

I´d really like Karim to prove that...!!

White paint works just as well at normal ambient temperature in that its € is also 0.96 at 60°F but drops to 0.71 at 1000°F .

What seems important is that the surface -- of say cooling fins -- is not polished and that a surface as you get with sand-casting is probably the most practical best. The electro-magnetic radiation wave-angles (that cause molecular activity in the material and hence increase temperature) are diffused by the multidinous angles of the bumps in the surface. Uh oh! I said that before... but I did not say that the bumps and cavities are much smaller than the normal grain of sand which is the case with matt black paint.

As for the wind-up bit Karim your comment did -- at first -- seem a bit that way but after a bit I appreciated the humour. And what do you mean your Boss has my surname, Bass??? -- maybe we are related and you ought to be showing a bit more respect for your older relative...

...eh! by the way I´m a bit short at the moment -- could you spare a few quid??

I know this is all TOO MUCH -- for most -- but maybe helpful to a couple....

Cheers!

***€ here is not Euro, it is Emissivity ....

PS -- 12 hours later -- don´t do it Karim -- NOT with your tongue, I mean -- it can cause permanent damage. Try wetting some other part of your body and make contact and it´ll stick....

Achtung -- achtung -- act-tongue!!

Why has Karim not replied .... Uh oh!!

"Too Late...!" she cried, "...`ee´s gorn and stuck hisself ter a steel post. I wonder what `ee was tryin´ ter prove?"!

About a year ago some kids were licking steel posts in a playground and got their tongues stuck by frost...

... it was on BBC World News here....

Yaaawwwnnn!

Busy building a house at the weekends, too busy to be out licking any poles.

She says you must be the uncle John that ran away with all the money from the family beer business.

Willing to offer up an alternate view, the metal post was not colder at all it is just that metal will conduct the heat away from your hand (or tongue, if the need takes you) much faster than air, thus making the metal feel colder. Likewise for your steel in a sauna, it feels hotter. You can walk across burning charcoal as it is a good insulator, if you walked across metal at the same temp you would burn your feet as it conducts it well, not because it is hotter.

How about sandblasted/casted heads working better than smooth polished heads simply because due to the irregularities there is a larger surface area to diffuse the heat?

On the funnier side, I work in a foundry and a couple of summers ago when it was very hot (well hot for UK) we went out and purchased a box of ice lollies for the guys. As there is no freezer at work someone had the bright idea of keeping the aforementioned lollies in the dry ice chest. Line up first unsuspecting work hardened foundryman: Take one lolly out of chest, unwrap lolly, wrap lips around lolly, run squeeling to the toilets with lolly stuck hanging from lips and top lip peeled. oops. No serious harm done, except to pride.

Disappointing Karim! I thought you said you´d do an experiment?

Sand blasting tends to make a surface smooth ...
The point of unsmooth -- very irregular surface -- is what emissivity is all about irrespective of colour of surface paint ...Fin -- End!!

Anyway I said I was finished with the subject -- in any case I was told on this web-site that 2 lines on any subject is quite enough....

Bad Uncle Perc it was who stole the family treasure...

Take care,

Cheers!

john bass wrote:

What seems important is that the surface -- of say cooling fins -- is not polished and that a surface as you get with sand-casting is probably the most practical best.

Agree sand blasting could be used to make a surface smoother, but surely not smoother than polished? More irregular the better it would seem equates to greater surface area.

It is shoddy that I have yet to try the heat/metal thing, but I will....buggers at work are keeping me working, it really is standing in the way of some good solid experimentation and bantam building.

sorry more than two lines, I will aim for succinct in future.

I guess no beer for either of us.

Last PS on this subject Karim because we´d got away from whether painting a cylinder head black makes a difference... -- onto really cold ice lollies ...

Licking the frozen flagpole and licking an ice lolly that´s super-cooled -- to have both frozen stuck is heat CONDUCTED away from the lip & tongue because of the large heat difference: tongue to steel and tongue to super cooled ice, tongue heat conducted away and ice forming from saliva -- which has agreement with what you said about the sauna and the steel FEELING very hot. A steel screw in a wooden platform in a sauna FEELS very hot because the steel to flesh conducts more heat than the wood to flesh although both are at the same temperature ....

So it comes down to heat transfer and some of that when tranferring heat from a hot to a cold body is by conduction and some by radiation and whether the surface be black or white (at normal temperature -- 20°c - these colours radiate and absorb the same amount of heat energy)

I finish by maintaining that a black painted cylinder head is better for heat dissipation than a highly polished aluminium one ....

Ahhmen!

PPS -- do some experiments!!

Cheers!

john could you explain about the theory on

"matt" black please.

regds Derek

Derek you are embarrassing me***. I just said I close up on this subject because we (Karim & I) got into digression plus I thought I had gone too far with being scientifically clever (cocky with it...!). My New Year´s resolution was to stop doing this clever stuff....

First look at what happens to white light. White light refracted by a spectrometer give us monochromatic, pure tone colours with measurable wavelengths of their rainbow frequencies -- at one end of the spectrum is Infra-Red and the other is Ultra Violet, both of which transmit radio wave type energy. When Prof Spencer was working on radar in 1936 his very low frequency radio wave making machine melted the candy bar in his pocket -- that led to him making the very first micro-wave oven which was too big to be a commercially viable domestic unit because it needed a cooling water supply to prevent it blowing up. So white light can be made into the colours of the rainbow and pastel shades by mixing...Black is not there. So according to the colour chart Black is no colour.

According to Kirchoff black is the standard by which to measure all materials for emissivity and absorption of light wave energy. In doing this he also discovered he could not get a Perfect Black and the nearest was lamp black. I take it that this was an oil lamp´s soot. As far as being matt goes it is that the soot particles are very small and spherical and as light radiated waves are extremely small they fit the theory very nicely and Kirchoff then did some really smart mathematics to prove that these light waves cannot transmit light energy either in or out of a material so coated with lamp black....

OK. So now imagine the surface is smooth (and shiny say Kirchoff and several of his clever mates ...) the light ray striking the surface of such a surface has some light rays reflected away and most refracted thro´ (hence absorbed into the material) such that the light energy causes molecular disturbance (like the microwave oven) within the matrial which increases the material´s temperature.

Now, the lamp-blacked surface consists of either embedded spheres or semi-spherical cavities which diffuse the light rays to refelect them several times across these curved surfaces at different angles of incidence to teh curves such as to reduce their energy and reflect them out -- back to where they came from -- thus defeating the transmission thro´ into the material. It must be appreciated that these spheres are extremely small and that when Kirchoff finished his mathematical exercise he had to say that lamp-black was not the "perfect black body" of his mathematical theory and that he didn´t think it existed as a know material of that time.

If anybody could prove that black emits a wavelength then poor old Kirchoff would definitely turn in his grave.
The discoverer would be awarded some fantastic medal....

In the meantime it was found that when comparing matt white paint with matt black paint there is -- reallistically -- no difference in radiation effect (in or out of a material) in the temperature range of 60°F to 500°F -- but above that the white´s emissivity decreases whereas black stays consistent,.

Phwew! Which means matt black would be better than white because of the cylinder head´s temperature...

Note: many houses in the tropics are painted matt white to keep cool -- so goes the Belief!!

So far Convention has not been mentioned nor gas nor carbon dioxcide. The latter we know belongs to global warming, gas has me worried and the former, Convention belongs to water-cooliong -- I think! Most cooling systems are a combination of conduction, convention and radiation -- SHMG....!!

***My Boss here says such a thing as embarrssing John-Boy is impossible.

Kryyysssttt! This is too long. After you´ve read it Derek I´ll delete it. Go well and keep well....

Cheers!

Hi John

"Phew" - so matt Black is best then! just adding paint to metal joint must be a quality joint for this to be so. !

thats all I have to say on that other than "I have copied it" !!!!!!

well also adding "I think its a brilliant piece of work, theory/facts and science all jumbled in with a bit of humer.

Thank you John & Karim!


Derek

Thanks Derek!

I forgot to say these light rays are travelling in parallel lines at the speed of light. Millions of them. So when they get disorientated by the molecules of soot (or whatever the matt-black is) they lose their effective energy.

Conversely, when the sun shines and a magnifying glass is held at its focal length from an inflammable substance the concentrating of the rays into a small hot spot is sufficient to cause fire to begin. Hopefully that proves the point ...??

That last bit: nothing to do with cylinder heads painted matt-black -- of course -- but might come in useful if you want to take up arson as a hobby instead of riding Old Hacks!!!

Never to be taken seriously Derek -- have a good day!



Cheers!

Hi John

just one last question, seems some of my replies have been distorted /changed even, and some more than others my when I read them back could not believe how different they were, so bad, now it seems I have been trolled, the culprit has been found too, all sorts of people involved not to mention the police. One thing I did notice they wear matt black as std uniform, for the same reason to keep cool (especially if fire bombed ? ) I was thinking (always dangerous) if i painted my tank mattt Black would it help the fuel keep cool, hence charge stay cool before its used, to stay dense, no affect or little on a cold day, but would think big effect on the denceity of the charge on a hot day!! "john" ?.

whats your thoughts john should we all paint our tanks matt plack for hot days, also have significant effect on front down pipe too and as you say the cylinder head also, while we are at it i to noticed yamaha painted all there barrels and crankcases matt plack ? for the same reason "john"?

Regds Derek

For years I wondered why cricketers wore whites and some Arabs in the desert wore white gear too whilst their woman were clothed in black -- and thought it be religious cogitations but now I know better -- both black and white keep the human body cooler than any other colour... at NORMAL ambient temperatures, that is...

The reason some well known motorcycle racing companies do things like painting parts matt black, change the fairing or give their rider new coloured leathers is more for rider and mechanic-team morale. The rider and mechanics thinks he has something really new that none of the others have and he consequently goes that tiny bit quicker....SHMG!!

Yes! it is possible that a matt black petrol tank*** would keep the fuel²²² cooler -- and slightly denser -- on a hot, bright-light day but more important -- I THINK! would be to keep the air cooler (oh pooh! now we will have matt black carbs appearing!!?) and that could be done by fresh-air boost or by water-injection:- both, maybe? being illegal.

I got involved with Toronto Research -- whilst biding my time in Canada -- and we almost had a 20%water 80% diesel running at Montreal but the project got canned. We were after reducing emissions and Toronto research claimed a high level of exhaust pollutant reduction and a 10% increase of horsepower. Remember that in the war aircraft ³³³ had water-injection boost for take-off on their (both sides) fighter aircraft ...

This idea of `fresh air-boost´ was laughed at and utterly rejected. I wanted to try it on Icarus-1 but decided against it because of 3 after-thoughts: One, was that I was track-testing and it should be done on a dyno to see positive results; Two, it is likely to cause a seizure and Three on shut down it would surely cause an oil-leak on throttle shut-down (not sure this would happen but it might do because of petroil-mix) ...

I must take another look at the formulae....

***still hoping that Karim would do the test -- remind him of No-Smoking on the job ...!!?

²²²² "... Fuel..." because it might be highly doped...?

³³³ you are too young for that statement to apply...!

Cheers!

Achtung!! Important!!

Came across an article by a specialist who said you should paint your device (a flat plate above a water tank) matt black to collect heat from the sun´s rays to warm your domestic water...***
Reverse of what I had said...

This same bloke though said that he´d done an experiment -- which Karim might have done for us -- that proved a silver painted, metal flask containing water kept the water warm longer than a similar matt-black painted, metal flask. He reckoned the silver coating reflected the heat back in whereas matt-black allowed the heat to flow out... Well it would, because the radiation -- relative the black surface -- would not be there.

Whilst this knocks hard on my theory of `...heat-radiated-in is lessened by matt black painted surface..." it does support a cylinder head being painted matt-black because it would transmit (... must be by conduction, I guess...??) the heat out from the hot cylinder head better than a silver-shiny one. With the head being matt-black it will reduce radiated heat from light being transferred in, as I said earlier, so I rest my case ... (I hope?)

What has to be remembered is that heat flows from a hot body to a cooler body -- NEVER the other way -- so with the cold fuel and warm day it would not be wise to paint the tank matt-black -- which is obvious because because the hot air transfers some its heat into the tank by conduction & convection (the latter when you think of air as a fluid....??)

So I´ll pack up going on about radiation, and stick to conduction & convection of heat... Much more simple....

Well, we all know that thermos flasks have silver painted inner flasks.


So the tank could have a double hull (like the Titanic!), the inner with silver finish, then an air gap to the outer cover (good insulation!) with that outer surface being being matt-black or any other colour....

Phwew!
Might start a new trend in motorcycle racing, Derek! Thermos-insulated fuel tanks and vans with fridges installed only for containing well-cooled fuel...!!?
Somehow I think that must have been tried?


Has anybody thought of hanging a wet towel near the carb such that with the airflow of frantic racing it cools the intake air??


***the flat plate was of steel. With the sun on the plate -- no matter what its paint colour -- it would eventually get hot and transfer heat into the water.

Hoping all this hasn´t been too confusing.
Cheers!