Flashlights Polished vs. Coated

[ViReN]

Hey Good work

I also feel that a flashlight Sand Blasted & HA type III (like Fenix L2P, Civictor V1) would have better emissivity as compared with smooth/glossy HA type III / HA type II lights (Mag LED for instance)

Sand Blasted light having More surface area...

but at the same time, for hand heat transfer, smooth would be preferred, as it will offer greater contact surface with hand (some thing like polished lights)

So "NewBie", will it be safe to say that P1 sized / smaller lights should be polished (to offer greater skin contact surface area) and L2P/Nuwai QIII sized would be better off with a Sand Blasting and HA type III coating?

ViReN

 

[NewBie]

Thanks very much for taking the time to set up and document the demonstration. I'm sorry I missed the post with the calculation. I've always thought about radiative transfer as dominating only at relatively high temperatures, but I see now that's not true if the convective transfer is bad enough.

I did spot one error in your analysis, the C - to - F conversion. The conversion factor is exactly 9/5 (the ratio of the degree sizes), so

a 17.4 degree C change is a 31.32 degree F change, not 63.32
a 20 degree C change is a 36 degree F change, not 68.

Great job - thanks!

c_c

Oops, I was doing multiple things at once- running on autopilot, my bust there!


***THANK YOU VERY MUCH!!!***


Aluminum, highly polished and degreased 0.027
Aluminum, (6061-T6) highly polished 0.031
Aluminum, highly polished 0.039
Aluminum, semi-polished 0.05
Aluminum, rough surface 0.07
Aluminum, sand blasted, 0.21
Aluminum, anodized 0.776
Aluminum, Hard Anodize, Type III 0.835 to 0.856

Brass, highly polished 0.03
Brass, polished 0.10
Brass, rubbed with 80-grit emery 0.20
Brass, dull and tarnished 0.22
Brass, oxidized 0.61

Bronze, polished 0.10
Bronze, porous + rough 0.55

Cadmium, polished .02

Chrome, polished 0.09 to 0.10
Black Chrome 0.62

Copper, highly mirror polished, 0.008
Copper, polished 0.05
Copper, burnished 0.07
Copper, oxidized 0.65
Copper, heavily oxidized 0.78
Copper, oxidized to black 0.88

Gold, highly polished 0.02

Iron, shiny, etched 0.16
Iron, cast, polished 0.21
Iron, cast, oxidized 0.64

Lead, shiny 0.08
Lead, gray 0.28
Lead, oxidized 0.63
Lead, red oxide powder 0.93

Nichrome, Clean 0.65
Nichrome, Oxidized 0.60 – 0.85

Nickel, polished 0.05
Nickel, no polish 0.11
Nickel, oxidized 0.37
Black Nickel 0.66

Platinum, shinny 0.05
Platinum, Black 0.93

Rhodium, polished 0.03
Rhodium Flash (0.0002" over 0.0005" Ni) 0.10 to 0.18

Silver, high end observatory telescope mirror type finish, fresh, 0.01
Silver, highly polished 0.02 to 0.03
Silver, polished 0.08

Stainless Steel, buffed 0.16
Stainless Steel, sandblasted 0.440
Stainless Steel, oxidized at 800°C 0.85

Steel, polished 0.07
Steel, fresh rolled 0.24
Steel, red rust 0.69
Steel, oxidized 0.79
Steel, rough surface 0.96

Silicon Carbide 0.80 to 0.95

Titanium, high polish, 0.04
Titanium Alloy C110M, Polished 0.08 to 0.19
Titanium Alloy C110M, Oxidized at 1000F 0.51 to 0.61
Titanium(6AL-4V) bar, as received (oxidized) 0.472
Titanium(6AL-4V) bar, polished, not brilliant 0.10

Zinc, highly Polished 0.02
Zinc, Lightly Oxidized 0.11



Lampblack, 0.95
Candle soot, 0.95
Graphite, rough cut across grain, 0.98
Charcoal powder 0.96
3M Black Velvet #9560 1.0
Martin Black Velvet Paint 0.94
Krylon regular Flat Black 0.95
Krylon regular Gloss black 0.91
Sherwin Williams White Paint (A8W11) 0.87
Sherwin Williams White Paint (F8WJ2O3O) 0.82
Krylon regular Flat White 0.95

Paints with specific pigments:
Blue, Cu2O3 0.94
Black, CuO 0.96
Green, Cu2O3 0.92
Red, Fe2O3 0.91
White, Al2O3 0.94
White, Y2O3 0.90
White, ZnO 0.95
White, MgCO3 0.91
White, ZrO2 0.95
White, ThO2 0.90
White, MgO 0.91
White, PbCO3 0.93
Yellow, PbO 0.90
Yellow, PbCrO4 0.93
Paints, Aluminum 0.27 to 0.67
10% Al 0.52
26% Al 0.30
Dow XP-310 0.22
Gum Varnish (2 coats) 0.53
Gum Varnish (3 coats) 0.50
Cellulose Binder (2 coats) 0.34

Ice, smooth 0.97
Ice, rough 0.98

 

[Sixpointone]

Whereas I do not pretend to know much on a technical level of lights, I find this experiment to be most interesting. Thanks for taking the time to both conduct and share them.

 

[Moat]

More cool (pun?) stuff, Newbie - thanks!

As a motorcycle mechanic back in the early 80's, I used to do some custom painting of Aluminum engine castings (sandblast prepped heads, cylinders, crancases and sidecovers) with a paint specifically designed for heat dissapation - Kal-Guard Engine Kote, IIRC. Nice stuff - looked good (grey-ish flat black), and was quite durable. Always wanted to do some kind of "before-after" running-temp measurements, never got around to it. Looked great on my beloved Yammie XS650 and (yes - silly but ...) yellow '72 Honda CT90's engines!

I do imagine that, at some point in coating thickness, the insulative effect of the paint layer would diminish it's effect at radiating...?

Considering the durability and good thermal emissivity of HA - and it's minimal ~10% disadvantage over paint - HA looks like the way to go, really. Probably black?

(edit to add) - Looks like Kal-Guard still manufactures a line of similar coatings - for guns or general industrial use

 

[chesterqw]

lowtec, we should not coat the aluminum in contact with the luxeon itself as heat in transfered as conduction and not radiation.i believe HA don't conduct heat as well as aluminum itself with no coating.

why the aluminum rod with the black surface is cooler is because a black surface will radiate(or absorb) infrared radiation better then a white/sliver/shiny surface.

 

[NewBie]

Tonight, I hooked up a 90 CFM fan (I'm not sure of the airflow at the test subjects, the fan just moves that much) and decided to take some measurements, to see if the black coating would reduce the thermal tranfer in air:

Ambient temperature was 20.5C


It appears as though the coating has no effect when there is a lot of forced air blowing on the lights.

 

[amarv12]

Very cool experiment. :goodjob:

 

[Raybo]

Newbie never ceases to amaze me, he has more knowledge and ambition than I ever hope to have.

Ray

 

[Stuart B]

Very cool thread.

When I build my bike light I think this thread will be handy. Sometimes you need your light when you are stopped, anythign that helps them stay cooler with out excess heatsinking that isn't required on the move is great.

Stu

 

[leukos]

Interesting, but rarely do I use a flashlight that is not in my hand or exposed to the elements. I can see the implications for other applications though.

 

[Concept]

Cheers Newbie, another great job.

 

[elgarak]

I'm with leukos on this one. Nice experiment, but little relevance to most application of us. If a small flashlight is held in the hand, it does not lose the heat primarily by radiation. Most of it is transfered by direct heat conduction into the hand.

 

[asdalton]

I'm with leukos on this one. Nice experiment, but little relevance to most application of us. If a small flashlight is held in the hand, it does not lose the heat primarily by radiation. Most of it is transfered by direct heat conduction into the hand.

I doubt that "most" heat is transferred this way, unless you are encircling the flashlight tightly with your whole hand. The way I hold flashlights, only the tips of a few fingers are touching the surface, and usually near the tail (where the surface is coolest anyway).

 

[srvctec]

I doubt that "most" heat is transferred this way, unless you are encircling the flashlight tightly with your whole hand. The way I hold flashlights, only the tips of a few fingers are touching the surface, and usually near the tail (where the surface is coolest anyway).

Ditto. That's just what I was thinking. I never hold a flashlight inside of my clenched fist- which would make for the best heat transfer. I'm usually holding it by the tail end or cigar style to easily operate the tailswitch.

BTW, great thread Newbie!

 

[NewBie]

Well, I did some more checking, and found that my airflow is not quite uniform over the area. What I did find, that is even in extremely strong airflow, the black one was always the same or a bit cooler than the semi-polished bare one.

Then it occured to be to move the two a bit closer together, to make the airflow more the same. I also moved the air source further from the test subjects, and in this case, it is off to the left side of the picture. I ran two tests, one with the polished one at the top of the photo, and then switched their positions, and ended up with the same answers. I also tried several different spacings between them, in case the polished one radiated enough to effect the black one, or vice versa. I didn't find enough difference to notice. Anyhow, even in airflow, the black one is actually consistently cooler.

For the pictures, I placed the meter near the test subjects, just during the picture taking, to get a better close-up.


Semi-kind of Polished one:

Black one:

 

[McGizmo]

Newbie,
Thanks for this thread and your investigation. I recall when I first joined here, thermal discussions were more prevalent and the comments were that among the three means of thermal relief, conduction, convection and radiation, radiation was the least significant. You have shown radiation to play a part greater than one would assume but I suspect there is also the question of its role being relative to the presence or absence of the other means? If you were to sit both samples down on a nice thick slab of Al or copper, would you see the delta you see with them sitting in free and unmoving air? If you were to elevate the humidity level, would this delta remain as high?

Someone posted back then about a motorcycle head that when highly polished would keep the piston from seizing but a rough cast head would cause the piston to seize. I would assume that this is due to a difference in air flow over the surface and means of thermal relief based on the air cooling. Is forced air cooling in the category of conduction or more like enhanced convection?!?

 

[chevrofreak]

I'm planning on building an LED reading lamp one of these days and it seems like this info could be a big benefit to me for that. Thanks!

 

[NewBie]

On the head front with blowing air, it sounds like in the rough cast case, the rough surface was increasing the thickness of the boundary air layer, reducing the effect of air cooling, a very well known effect. Engineers often will create turbulent air flow on purpose, to help scrub the boundary layer. But you have to be careful with turbulent air flow, as it can greatly decrease the amount of air passing thru, and if you go too far, you'll actually reduce the effective cooling. I've even seen laminar airflow work better, and from experience, it seems there is a sweetspot between the two. Another effect that happens, when the air is not forced thru an area, is what is known as flow bypass, where there is enough resistance or back-pressure to airflow, that the air takes a route around the heatsink. Either one of those effects (which are somewhat related), is likely what was actually going on.

Humidity here is about 58%. The effects of humidity, and all the rest of this stuff is in many beginning mechancial engineering books, and is dealt with deeper in the thermodynamics portion of mechanical engineering. Some people even make a whole life long career in this area. There are a number of software suites that will help predict the outcomes under various scenarios, and one of the more common ones that is specialized for cooling/heating is made by Flomerics:
http://www.flomerics.com/

However, in most environments (7-94% humidity, 15-60C) humidity has a negligble effect on heat sink performance.

It is interesting to note, that the chimney effect is greater when the object has a high emissivity (such as black).

These pieces that I tested were large enough to be similar to some flashlights offered on CPF.

I didn't really consider setting them down directly on metal, as it is rare for me to find metal to sit my light down on the forest/mountains.

As the light gets much longer, like a Mag 4D, when it is oriented vertical, the chimney effect helps more.

Higher altitudes also reduce the cooling effect of air, it it thinner. As little as 5,000 ft can cause a forced air heatsink to become 10% less effective.

I also ran the air test to see how that contributes, see my last post.

The optimum mix varies depending on the environment, but it looks pretty obvious that a higher emissivity surface due to a very thin layer doesn't hurt in any case.

However, it looks that the surface coating has a large effect on the flashlight temperature when it is not held in the hand. And as I mentioned before, the forced liquid cooling of the human hand can have a very substantial effect, if you are not wearing gloves.

 

[3rd_shift]

bttt..
I just remembered something. :thinking:
It would seem that old black stoves were indeed black for a reason.
This appears to indeed be an older technology rediscovered and updated. :thumbsup:

 

[CM]

I love these experiments--chock full of useful info. The temperature differentials are not what I would have expected. :thumbsup:









































Anyone able to get Newbie's fingerprints off the picture :nana: