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Painting pot black
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James Klein
(jnklein21) - M

Locale: Southeast
Re: A couple of things on 01/03/2012 14:04:46 MST Print View

"That made sense to me because the hot gasses from the flame contact the pot directly, and the heat transfer is by convection/conduction not radiation."

Radiative heat xfer will occur as long as there is a temperature differencial btw the stove output & pot bottom AND there is nothing btw the two to block the radiation.

If there wasn't a temperature differencial the pot bottom would likely melt.
If there was something blocking the radiation you wouldn't be able to see the flame (though the combustion products probably block some of the infrared radiation).

Keith Selbo
(herman666) - F - M

Locale: Northern Virginia
Yeah but ... on 01/03/2012 15:36:37 MST Print View

There will be radiant transfer, but based on the results we've seen so far it is certainly not the dominant mode and likely doesn't justify painting the bottom of the pot black.

Rand Lindsly
(randlindsly) - MLife

Locale: Yosemite
Re: Re: Re: Re: thread on 01/03/2012 15:39:35 MST Print View

"I figure the faster the boil time the less fuel used.."

Ben's right in saying that this is not true.....but did I want to kinda explain it a little differently. If you pump heat out of the stove really really fast, the pot won't absorb the heat as fast as you are pumping it out. Quite a bit of that heat is lost to the atmosphere. The experiment you can perform to test this is to hold your hands near the top of the pot/windscreen. If you feel heat coming off, that is heat that is not going into boiling your water....and consequently fuel that is used to create the heat that isn't being put into your water/food. So, while it seems counter-intuitive, the faster the boil time, the MORE fuel is used.....because you are using a good bit of that to heat the campsite too.

Since he brought up the Caldera Cone, that is an example of a system that holds the hot stove exhaust next to the pot for longer, so when the system exhaust comes out the upper vents, it is not much hotter than the water in the pot. Pretty efficient.

...but I'm just a cottage guy....so clearly no innovation here....

Rand :-)

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: thread on 01/03/2012 15:57:13 MST Print View

You have to weigh canister before and after

Record temperature before and after

Carefully measure amount of water (weigh it is good)

Before and after wipe any condensation off the canister

Repeat several times to make sure it's consistent and you're not basing your opinion on some uncontrolled variable that you're not aware of

Measure black pot, not black pot, not black pot again, black pot again to cancel out any error due to canister being less full

etc.

if the difference between black measurements is as big as the difference between black and not black then you have to measure more to average or just conclude no measureable difference

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: thread on 01/03/2012 15:58:31 MST Print View

And it would be good to take pictures with ultra-fast "explosion" camera

Nevermind, that's a different thread : )

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Actual Results - Paint your pot bottoms on 01/03/2012 16:01:08 MST Print View

>"Would I benefit from painting the bottom black or soot up the bottom to help increase boil time??"

Cross-posted from another thread where this Q came up:

I'll write this up as a new thread in a few days with photos and all, but here's the punchline:

Four pots identical pots. One unpainted, three with different paint jobs.

Each timed on each of four different stoves. 1000 g of 4C water to a rolling boil.

Average (of 4 stoves) with no paint: 5:50 (350 seconds)

Average (of 12 runs, 3 pots on 4 stoves) with paint: 5:24 (324 seconds).

Saving 7-8% of your fuel for a 2 or 3 grams increase in weight? You'll come out ahead on the second liter you boil.

It's a no brainer - DO IT! Paint the bottom of your pot. Painting the sides didn't help or hurt in my set-up WITHOUT windscreens.

Caveats: These four stoves were propane stoves. I plan to re-run with white gas and with with alcohol. I suspect the effect will be greater with WG and less with alcohol, but we'll see.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: A couple of things on 01/03/2012 16:13:29 MST Print View

>"I've done a lot of stove experiments and found that the temperature rise is linear with time in almost every case"

Keith, I like that. A lot. During my wide versus narrow and painted versus unpainted tests, I did a lot of work to maintain constant starting temps, room temperature, etc. And just what is a "rolling boil" varies several seconds.

Whereas if I throw a thermocouple in the center of each pot and time a 10 degree temp rise (or record temp rise in one minute) and that captures everything I need to compare one set up to another and to calculate fuel savings.

Thanks

C Nugget
(nuggetwn)

Locale: Pacific Northwest
Re: Re: Re: Re: Re: thread on 01/03/2012 17:04:15 MST Print View

@ Ben experimentalist and beyond,

Thanks for simplifying some of the science for me. Very helpful to have things broken down a bit more. I will not given up when the jargon hits.

@ Randy,

Thanks for another view point and sarcasm on innovation. Haha! If I didn't already have a stove set up, I'd be interested in the caldera cone. I was looking for ways to improve upon it... I am curious about the boil times and fuel use of your set-up with my version pot(GSI pinnacle soloist).. though I believe my pot may be the problem. At the end of the day when your hungry you just wish the water would boil faster and for longer.

@ David,

Awesome testing data that is useful.. If I don't get rid of my pot it's going an infrared version of black... of course I'll be testing the boil times before and after that.. non-scientifically of course.

About your temp gauge.. I'm looking for a light weight way to test the air temp while hiking.. Would a non-contact infrared thermometer be a way to go?? I tire of looking at a 1.5" thermometer and guessing... but I can't help but wonder exactly. Any suggestions? Or, maybe just a longer thermometer.

Could you post the link to the thread for soot vs paint... Sorry bout the cross post.

thanks all y'all

Paul Wagner
(balzaccom) - F

Locale: Wine Country
size matters on 01/04/2012 22:49:08 MST Print View

Not being a scientist, I can't comment on some of the findings here---but I appreciate the info.

My wife is a professionally trained chef, who points out that it is important to match the size of the pot with the size of the burner for best results.

And now she will finally let me paint the bottom or our backpacking cook pot black!

Dirk Rabdau
(dirk9827) - F

Locale: Pacific Northwest
Re: Painting pot black on 01/04/2012 23:11:39 MST Print View

This thread reminds me warmly of time spent hiking in the company of engineers. I didn't understand a lot of what they discussed, but they were ecstatic to explain to a liberal arts kind of guy the finer points of thermodynamics. Truthfully, I think what I came to appreciate is that there is a lot of good in the world we owe to engineers.

I do really enjoy this thread. Thanks David and all for the explanation and supporting data. It's greatly appreciated.

Dirk

Keith Selbo
(herman666) - F - M

Locale: Northern Virginia
Re: Re: A couple of things on 01/05/2012 08:01:08 MST Print View

David,

Glad I could help especially because your findings are particularly interesting. The findings of other experimenters I've read have been most notable for their imprecision and have gone both for and against blackening.

I eagerly await your further findings.

Keith

Ryan Smith
(ViolentGreen) - F

Locale: Southeast
Re on 01/05/2012 10:41:21 MST Print View

Finally, now I know why my cookies burn on the bottom if bake them in dark pan. Sheesh.

Ryan

Ultra Magnus
(Ultra_Magnus) - F
Re: size matters on 01/05/2012 11:12:55 MST Print View

I've done some tests, though not scientific enough to post hard data, between my 1.3l ti pot and my Heineken pot (wide vs. narrow). With everything else being more or less equal, water boiled in the wide pot around 2 mins faster (9mins vs 11mins). But- the stove also burned out of fuel faster. I'd need to do more consistent controlled tests to collect enough data to get some consistent averages, before I could say what is exactly going on. I credit that to the larger pot reflecting more heat downwards, causing more thermal feedback to the stove (alcohol) increasing the rate of vaporization. I don't know how it would affect a canister stove, but then again, I can't say that I can recall anyone using a canister stove on a beer can pot anyway...

BM

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Measuring air temperatures on 01/05/2012 11:31:29 MST Print View

>"I'm looking for a light weight way to test the air temp while hiking.. Would a non-contact infrared thermometer be a way to go??"

Christy-Lynn: It wouldn't give you air temps. Opaque solid objects give off infrared that corresponds to their temperature. Shiny metal objects reflect the IR of their environment. Materials transparent in IR would allow IR to pass through them, but most glass and clear plastic is transparent in the visible but not in IR. (e.g. eyeglasses noticeably shield your eyeballs from the radiant heat from a campfire).

So a non-contact thermometer would give you an air-temp reading only if you pointed it some non-metalic object in the air (piece of paper or plastic or cloth). You'd want it to be out of the sun, so you could shoot the front or back of a companion's backpack or strap, depending on which one was in the shade.

Some digital watches have digital thermometers, but you'd want it off you wrist to get a decent air temp. And some are also alarms, altimeters, pulsemeters, etc. It's even a watch.

Some kitchen thermometers are digital and pretty small. And have a waterproof probe so you could also check water or snow-pack temps.

But I can't think of a lighter option than squinting at that 1.5" zip-pull / thermometer.

Ross P Hemphill
(rbimli) - F

Locale: PNW
a possible variable, etc on 01/05/2012 13:47:01 MST Print View

Just thought it worth mentioning that the height of the pot above the burner is a major variable in efficiency.

Also thought I should mention that you can make your own "Caldera Cone" for an arbitrary pot.

David Barnas
(Dave-a-roni) - F

Locale: Erie County
Wow! on 03/09/2014 07:39:48 MDT Print View

Wow this was nerdy fun, I seriously was interested in the scientific discussion going on here. I made a Heineken pot recently (from one I found in a recycling bin a few years ago) and noticed some people on YouTube were painting their pots black with high heat paint. I was wondering the reason for it and came across this. I just got schooled! Thanks everyone for all the work that went into this info :-)

Ryan Smith
(ViolentGreen) - F

Locale: Southeast
Re: Wow! on 03/09/2014 09:29:39 MDT Print View

Oh yeah David. There are A LOT of nerdy threads around here on all sorts of topics. Just search for your desired topic and you will find one eventually.

Ryan

David Gardner
(GearMaker) - M

Locale: Northern California
Re: Painting pot black on 03/10/2014 23:46:32 MDT Print View

Disclosure: I make and sell brushed aluminum beer can pots. Originally I brushed the cans for aesthetic reasons. I continue to brush them because of test results like those below.

One huge variable that is difficult to control is relative humidity, unless you have both a humidifier and a de-humidifier, and a hygrometer to measure it. I get a difference of about 30 seconds in boil times in 65% vs. 85% humidity.

At any rate, I did 5 boils each using the cans pictured below over the course of two and a half hours.

Same air, fuel and surface temperature: 63.5* F.
Same quantity of water: 500.0 grams (500.0 ml).
Same quantity of fuel: 12.62 grams (16.00 ml).
Same relative humidity: 68%
Doing it in a two and half hour period with no apparent change in the weather, I presume essentially the same atmospheric pressure as well.

"Boil" measured as 212* F with a digital thermometer.

I did one burn for the series of cans (one shiny, one black, one brushed), then a second burn in the same sequence, etc. Used a series of air-temperature ceramic tiles for the resting surfaces, to avoid any surface temperature variables.

Here are the results I got:

1. Shiny original can:

6:56 (416 sec)
7:02 (422 sec)
7:06 (426 sec)
6:58 (418 sec)
7:05 (425 sec)

Average = 421.4 sec = 7:01.4 min
Maximum deviation = 10 sec = 2.4%


2. Bottom of brushed can blackened to top of windscreen by soot from crappy de-natured alcohol brand (do NOT buy E-nrg alcohol, it burns dirty and stinks too):

7:20 (440 sec)
7:15 (435 sec)
7:24 (444 sec)
7:18 (438 sec)
7:22 (442 sec)

Average = 439.8 sec = 7:19.8 min

Maximum deviation = 9 sec = 2.0%


Clean brushed can:

6:36 (396 sec)
6:29 (389 sec)
6:38 (398 sec)
6:31 (391 sec)
6:40 (400 sec)

Average = 394.8 sec = 6:34.6 min

Maximum deviation = 11 sec = %2.8

I expected the brushed can to absorb heat faster than the shiny can, but I did not expect that the soot-blackened can would be slowest. I had thought that because it was black on the bottom, it should have been the fastest. Perhaps the soot acts as an insulator, or emits IR faster than it absorbs it (is that even possible?), or....?

I did not have any high-temp black paint to try a can with just the bottom painted black. Will try that soon, when I get the same air temperature and humidity. If I was really smart, there is probably some formula that lets you account for those variables and get comparable results, but I don't know what it is.

pots

[edited to add disclosure]

Edited by GearMaker on 03/13/2014 07:51:49 MDT.

Steve B
(geokite) - F

Locale: Southern California
Grill Paint and Esbit on 03/11/2014 19:36:23 MDT Print View

Just an aside from the good discussion, but Esbit burns hotter than high temperature grill paint can withstand, and the paint will bubble and get messy (even more messy than normal with Esbit)

Steve

Bob Gross
(--B.G.--) - F

Locale: Silicon Valley
Re: Grill Paint and Esbit on 03/11/2014 19:51:03 MDT Print View

I've seen high temperature grill paint that failed because it was never applied correctly. Some people just spray it on and let it dry before use. Most of the grill paint that I've seen has instructions that say to spray it on, let it dry, and then place it in your oven at a certain temperature to bake it on, and that cycle is repeated at another temperature. Then and only then is it ready to actually use.

--B.G.--