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

Locale: Silicon Valley
Re: Cooking on 12/29/2011 22:00:52 MST Print View

"Use spray paint intended for barbeque - readily available and cheap"

How much weight is that going to add?

--B.G.--

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Paint on 12/29/2011 23:01:17 MST Print View

Thomas:

I'd suggest just painting the bottom of the pot, not the sides at all.

There's a concept of "view angle": How much of your view sees hot versus cold objects.

For the pot looking down, 180 x 360 degrees, there's some pretty hot stuff - hot steel bits, campfire coals, etc. The objects around the bottom of the bottom are warmer than the pot so it should be black so it absorbs more radiant heat.

For the side of the pot, they look out at the same terrain and scenery and sky that we do. Most of the objects being ambient temperature, the clouds cooler, depending on their elevation and deep space on a clear day or night, quite cold (4 degrees Kelvin, I think). The sides' surroundings are colder than the pot, so it should be left shiny so it emits less heat.

A pot within a windscreen probably should be painted black up to the height of the windscreen. Let me puzzle out how to answer that particular question.

I suspect that painting the bottle black will help the most on a white gas stoves, less on a butane stove and much less on a alcohol stove. But I'll be testing that in a few days. I just bought four 4 identical stainless steel canisters as Walmart that are comparable in thickness and diameter to BP pots and I'll modify three of them in different ways and try them on different stoves.

So for now, if you're leaving for a thru hike tomorrow, I'd say: paint the bottom black. If you've leaving next week, I hope to have more definitive answers.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: Multipurposing saliva on 12/29/2011 23:38:36 MST Print View

BM said, "and the chrome tools stayed hot for a very long time."

That is a very astute observation and one that I am going to steal. I try to not give K-12 students and junior engineers an equation without giving real world examples. Black objects getting hotter in the sun is a common experience. I've used white lines to cross a parking lot barefoot on hot sunny days.

Black versus white or, more so, black versus shiny metal cooling more quickly is less commonly noticed. But is just as true.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
Re: Re: Cooking on 12/29/2011 23:50:40 MST Print View

"Use spray paint intended for barbeque - readily available and cheap

How much weight is that going to add?"

negligible

even for gram wienie

paint layer is very thin

C Nugget
(nuggetwn)

Locale: Pacific Northwest
thread on 12/30/2011 02:35:49 MST Print View

Awesome!! I look forward to more results :) giggling too... Who needs Discovery Channel when you have a forum like this!!! Would different metals react the same or??? Thinking Titanium vs. Anodized Aluminium.. or is thickness more of a priority? What about the non-stick coating inside the pot some make the inside shiny and some(ceramic) make it flat black.. Would that affect it as well?? Would a larger surface area on the bottom of the pot increase heating as well?? What about verses a more slender tall pot of the same volume?

I sense a can of worms... but interesting... must be a forum on some of this...

-christy

C Nugget
(nuggetwn)

Locale: Pacific Northwest
this thread on 12/30/2011 02:35:49 MST Print View

sorry bout the double post...

It was slow loading!!!

ooops

Edited by nuggetwn on 12/30/2011 02:38:56 MST.

Tim Zen
(asdzxc57) - F

Locale: MI
d on 12/30/2011 11:14:08 MST Print View

d

Edited by asdzxc57 on 01/25/2012 17:37:06 MST.

Ben H.
(bzhayes) - F

Locale: So. California
Re: thread on 12/30/2011 11:22:44 MST Print View

David -

I am surprised that white paint would have an emissivity of 0.95 in the IR spectrum. When I saw that you got similar results with white and black I thought there was room for improvement, but perhaps not. You could stick a thermocouple on the pan and confirm your results.

Christy - The type of metal certainly plays a significant role. Anodized coatings are what a lot of satellites use to control radiative properties of parts. There is no convection in space, so radiation really does dominate. I wouldn't think the radiative properties inside the pan play a significant role. Temperature gradients are low and convection dominates.

In terms of pot shape, you have to realize that radiation from the stove will go in all directions. The more area "visible" to the hot flame/burner the more radiation will be absorbed. Likewise putting reflective surfaces (like a windscreen) in the areas you don't want to get hot will increase the amount of heat absorbed by the pot.

James Klein
(jnklein21) - M

Locale: Southeast
Re: Re: Re: Ask and you shall receive on 12/30/2011 11:47:58 MST Print View

Thomas, good quick and dirty test and thanks for the heads up on the cheap IR thermometers.

I would say that we care plenty about visible emissivity for the bottom of a cook pot -- probably on par with how much we care about IR emissivity -- the flame does have a color after all.

I would go for black, high temp paint.

Andrew F
(andrew.f) - F - M

Locale: San Francisco Bay Area
Re: Painting pot black on 12/30/2011 11:58:36 MST Print View

One other easy way to get your pot black is to cook over a wood fire. No paint required.

Andrew

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: Re: thread on 12/30/2011 12:21:04 MST Print View

Ben: You sound like a rocket scientist. I clean up after them (Lockheed, perchlorate in the groundwater, etc).

>"Anodized coatings are what a lot of satellites use to control radiative properties of parts." Is that to increase emissivity? Metals work like a mirror (hence their use in mirrors). I'm guessing metal oxides work like paint pigment (hence their use as paint pigments!) and are close to black-body behavior, but you tell me.

I did stick a thermometer on the pan, it just wasn't a mercury thermometer. It was a patch of spit. The spit that straddled the white and black sections evaporated in the same way, at the same rate. Red was a bit different. Unpainted was much different in that it went faster and actually boiled a bit. So unpainted was definitely hotter for having less radiant cooling. But white and black paint - the ones I used - had the same IR emissivity at 8um (peak radiation from 100C metal). Would expect them to have similar IR emissivity at 2um (peak radiation from a 1000C flame/steel)?

I'll be testing four identical pots against each other to boil water. I'll have one unpainted, one black and one white, among other modifications. And I'll test them over white gas, natural gas, propane, butane and alcohol. I think radiant contribution could vary a lot over that range of fuels, but we'll see. My plan is to start with ice water as an easily acheivable constant starting point (removing the ice just before the test).

After an initial round on unpainted / white / black and seeing how different fuels compare, I hope to focus on maybe propane (cheaper) if it parallels butane behavior and get into heat fins and fixed wind screens.

I suspect one outcome of this is that I'll know enough to make "The Spaghetti Pot From Hell" with the color, fins and integral windscreen to cut boiling time in half on the home stove.

Ben H.
(bzhayes) - F

Locale: So. California
Re: Re: Re: thread on 12/30/2011 13:32:47 MST Print View

Indeed I am a rocket scientist! Though I work mostly with LO2/LH2 rockets, so I don't think I am responsible for any of your messes :)

Yup, you got oxides down as far as I understand their use (I don't work a lot in radiation though).

What I meant by adding a thermocouple is to measure the emissivity. Difference in temperature from the thermocouple and IR thermometer gives you a good indication of emissivity. If there is a good match, there is not much point exploring alternative coatings.

What you plan on doing sounds an awful lot like what I imagine Jetboil did when developing their system.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Cleaning up your mess on 12/30/2011 13:39:54 MST Print View

>"I work mostly with LO2/LH2 rockets, so I don't think I am responsible for any of your messes"

Ben: Yep, anything you spill is gone in 3 seconds. One way or another!

ChemE Berkeley, 20+ years working with Civils and Geos (they do rocks, dirt and concrete) so I do all the wires, pipes, motors, bio, and chem. You?

Paul Ashton
(PDA123) - F

Locale: Eastern Mass
little or no difference in boil time on 12/30/2011 15:52:42 MST Print View

Hiram Cook made some empirical tests of coated and uncoated pots for boil time. Found no significant difference. Check them out on youtube

David Goodyear
(dmgoody) - MLife

Locale: mid-west
paint? on 12/30/2011 16:43:49 MST Print View

Why paint,

+ 1 on letting nature do it for you. Go for a blackened bush pot with a healthy coating of creosote. Better for the environment that the crap coming out of a spray can. :)


All in fun,

Dave

P.S. I realize that I probably can't hike in California - as I would be importing the toxins bonded to the bottom of my pot.

C Nugget
(nuggetwn)

Locale: Pacific Northwest
Re: Re: thread on 12/30/2011 18:25:03 MST Print View

Ben..

Sorry my science is not up to snuff for this thread and some things are going above my head. I am keen to be enlightened though.

To help me understand...
An aluminium pot would be thicker after being anodized? But the anodized process would help heat the pot faster or slower? Or, the function of anodizing a pot more to harden metal(making it safer to eat from) and create a non-stick benefit instead of increasing one's boil time?

So taller pots with a narrower base would take longer to reach boil time than a wider base pot of the same volume and type of metal because of a lower surface area on the bottom? Am I on the right track or lost in space?

I have a tall pot (http://www.rei.com/product/784114/gsi-outdoors-pinnacle-soloist-cookset) and noticed that the alcohol stove flame seems to creep around the edges. I left it behind last trip for a lighter wider pot but missed the ease of use of mine.. (I did a very non-scientific test between the two and the lighter wider pot won out for boil time). If tall pots take longer to boil then why are they on the market??

Is there any way to help with the efficiency of a tall pot and alcohol stove?? I figure the faster the boil time the less fuel used.. but maybe this is not the case either.. Would I benefit from painting the bottom black or soot up the bottom to help increase boil time?? Or... would some kind of collar work in addition to my windscreen to help in heat exchange. Or... perhaps I should just look at getting a wider based pot.. :(

My stove: ThermoJet MicroLite (where the pot stand is the windscreen)

Trying to convert discussion data to real life works for my cooking set-up... Ak!!

-christy

Ben H.
(bzhayes) - F

Locale: So. California
Re: Re: Re: thread on 01/03/2012 10:43:44 MST Print View

Hey Christy,

I'll do my best to answer your questions. One thing to realize is the science can only get you so far. Science can point you in the right direction, but in the end it is the real life data that matters.

"An aluminium pot would be thicker after being anodized?"

The anodizing process reacts the top layer of aluminum to form a hard aluminum oxide. It should have a pretty negligible affect on thickness of the pot. Anodizing has many useful properties as you mentioned, but in terms of this discussion anodizing can change the optical properties of the pot. A nice black anodized pot should absorb more radiant heat from the stove. The confusing part though is, it is not really important how black it appears in visible light. What is important is how black it is in the infrared spectrum. In general things that are more visibly black are also more black in infrared, but note in David's tests the white paint was "as black" as the black paint.

"So taller pots with a narrower base would take longer to reach boil time than a wider base pot of the same volume and type of metal because of a lower surface area on the bottom? Am I on the right track or lost in space?"

yes and you are on the right track.

"If tall pots take longer to boil then why are they on the market?? "

People like the form factor of the tall narrow pot.

"Is there any way to help with the efficiency of a tall pot and alcohol stove??"

I believe a lot of windscreens increase the efficiency of heat captured from a flame. Many people are happy with their caldera cone.

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

if you are only talking about the pot side of the equation that is true. To make thing more confusing, if you are talking about the stove the the opposite is true. The pot is able to capture more of the heat from a nice low flame. As a result, a stove that pumps out the heat, will use more fuel (per cup of boiled water) than a stove that pumps out less fuel. The hot stove will get the water boiling faster but use more fuel doing it.

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

I think David's test would indicate the answer is "yes"

"Or... would ...."

I am sorry I don't have enough practical knowledge on the subject to say what would help you the best. Painting the pot is pretty easy... designing an effective heat exchanger would be more challenging.

"Or... perhaps I should just look at getting a wider based pot."

I have read enough anecdotal evidence on these forums to say that is probably the case. :)

Don't get frustrated by all the science. I am an experimentalist and by that I mean I believe the science is useful for understanding experimental results and for guiding future experiments. The actual experiments are what leads to better stove/pot/windscreen combinations for real world use. Best of luck, and let me know if you have any other questions. I love to get nerdy!

David Olsen
(oware)

Locale: Steptoe Butte
Tarp color and heat loss/retention on 01/03/2012 10:59:47 MST Print View

How will similar mechanics work with tarp fabric?

Say you want a tarp that stays cooler in hot sun. I've experimented and have some
answers, but always learn something from this group.

Dark color, light color, what would you scientists expect and what have you
engineers found?

Keith Selbo
(herman666) - F

Locale: Northern Virginia
A couple of things on 01/03/2012 11:17:23 MST Print View

The guy at minibull design tested blackened vs natural pots and found no significant difference in boil times. 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.

Measuring boil time wastes a lot of time. I've done a lot of stove experiments and found that the temperature rise is linear with time in almost every case (wood stoves being the exception). That means that you really only need to measure the temperature rise over a fixed time interval to get degrees per second. No need to wait for a boil or control the starting temperature to make your comparisons.

Edited by herman666 on 01/03/2012 12:24:31 MST.

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

Locale: Silicon Valley
Re: Tarp color and heat loss/retention on 01/03/2012 11:18:22 MST Print View

"How will similar mechanics work with tarp fabric?"

You want it to be cooler in hot sun. Make the top surface reflective aluminum.

--B.G.--