Blackening Kettle Bottoms

[brewmonk]

do you think that the water staying at 212 gives the paint a "cool side" to help it not blister off?
you are having better luck with it than I did (not on a kettle).
let me know how the first few hours go, thanks.

 

[ChemE]

do you think that the water staying at 212 gives the paint a "cool side" to help it not blister off?
you are having better luck with it than I did (not on a kettle).
let me know how the first few hours go, thanks.

Absolutely I do. Sure, I'll keep this thread updated on that score.

 

[BrewMoreBeers]

i don't see how this could help decrease boiling time.

- all electric heat-stick guy.

SM=10

 

[ChemE]

This wouldn't help if you're using a heat stick. You need fire under your kettle for it to make a difference. In your case it would hurt since your boil kettle would radiate more heat to the room by having its emissivity increased.

 

[brewmonk]

well, for it to work on an electric rig, you have to paint the INSIDE!

 

[MadDwarf]

Do you guys think that we could skip weighing the propane tank. So long as it doesn't run empty, the gas output should be relatively constant. I'm thinking that simply measuring the time from start temp to ending temp would do it while running the burner wide open, given that the starting temps were the same and the burner cooled down to ambient each time.

Catt, since you're planning on running the tests on different days anyway, why not just top off the propane tank between the two runs so they both start at the same pressure? One more variable out of the equation.

I'm in favor of this mod overall - if nothing else, it makes me feel clever about not religiously cleaning soot off the bottom of my keggles.

 

[BrewMoreBeers]

well, for it to work on an electric rig, you have to paint the INSIDE!

that ought to make cleaning a snap...

 

[shortyjacobs]

Curing of the engine paint isn't too onerous or time consuming and can absolutely be done with household equipment. I used my oven since both my pots fit inside (though not at the same time).

1) Apply
2) Let cure 1-2 hours
3) Bake @ 200F for 30 minutes
4) Let cool 30 minutes
5) Bake @ 400F for 30 minutes
6) Let cool 30 minutes
7) Bake @ 600F for 30 minutes (here I only did 550F since my oven only goes that high)
8) Let cool 30 minutes

I was a little worried that the paint wouldn't take the heat but the blue flame was absolutely blasting on it and there was no damage.

Catt, I look forward to seeing your data. I do not think that the propane weight matters one iota I was just being thorough.

Damn. Anyone have a keggle sized oven?

 

[Catt22]

Hmmm. I think this will be a waste of a test. As soon as you are done, no matter the result, the obvious dropping pressure in the tank will be questioned, and it will be all for naught. Hate to be the naysayer, but it's inevitable, and rightfully so.

Not true. The vapor pressure will remain relatively constant so long as there is some liquid propane remaining in the tank. The vapor pressure of propane is a function of it's temperature. I will check the tank temperature and take measures to insure that it's reasonably close for each run. I will probably keep the tank in a tub of tap water before and during each test run. I plan to start with a full tank.

I just remembered that I have a four gallon SS kettle that should be large enough to give us some usable data. It will fit in my oven for the paint cure whereas my aluminum kettle would not. I also don't have to hunt it down as I would the aluminum one. The smaller kettle will shorten the test time too which I like a lot.

 

[Catt22]

Damn. Anyone have a keggle sized oven?

I would think that you could do the cure using a heat lamp or even a halogen shop light at close range. Might have to increase the exposure time some, but I bet it would work. You might also be able to turn the keg upside down on a propane burner to heat it up for the cure. Use an infrared thermometer to check the temperature.

 

[Catt22]

Catt, since you're planning on running the tests on different days anyway, why not just top off the propane tank between the two runs so they both start at the same pressure? One more variable out of the equation.

No need to top off the propane tank between runs. The vapor pressure of propane is a function of its temperature, the same as a tank of CO2. The pressure will remain constant so long as there is some liquefied propane (or CO2) remaining in the tank. I will take measures to keep the tank reasonably close to the same temp for each test run.

 

[Catt22]

do you think that the water staying at 212 gives the paint a "cool side" to help it not blister off?
you are having better luck with it than I did (not on a kettle).
let me know how the first few hours go, thanks.

That explains it. I've had terrible results using high temp paint. I tried it on engine headers and it went away in a short time. I tried it on a BBQ grill and it went away a little more slowly, but still did not last long. I thought this was a lost cause. It makes sense that the kettle bottom will be kept cooler by the liquid inside conducting heat away as fast as it is applied.

 

[passedpawn]

Not true. The vapor pressure will remain relatively constant so long as there is some liquid propane remaining in the tank. The vapor pressure of propane is a function of it's temperature.

Well damn that makes sense.

I have a large propane tank with a dial meter on the top of it that goes from "0 - 80". I always assumed that was pressure, but I guess that's not what it is. Hmmm.

 

[Catt22]

Well damn that makes sense.

I have a large propane tank with a dial meter on the top of it that goes from "0 - 80". I always assumed that was pressure, but I guess that's not what it is. Hmmm.

That probably is a pressure gauge, but the question would be what pressure is it reading. Is it on the regulator or the tank itself. Seeing that 80" (water column) is only about 2.9 psi, I suspect that the gauge is reading the regulated pressure supplied to the house. The internal tank pressure would always be much higher than 80" unless it were empty.

Additionally, regarding our test, the regulator would have the same output pressure regardless of how full the tank is or it's temperature assuming, of course, that the tank is not empty or extremely cold. The regulator would be doing what it's supposed to do and that is regulating the gas pressure to the burner. I guess that's why they call them regulators.

 

[passedpawn]

That probably is a pressure gauge, but the question would be what pressure is it reading. Is it on the regulator or the tank itself. Seeing that 80" (water column) is only about 2.9 psi, I suspect that the gauge is reading the regulated pressure supplied to the house. The internal tank pressure would always be much higher than 80" unless it were empty.

It's on the top of the tank itself, built into it, not on the regulator. The tank does not go to my house, it goes to a inground spa heater (I keep it turned off about 10 months of the year!). It is a big tank, perhaps 5 feet tall, and 2.5' diameter. I looked for units of measure on it and there were none (at least nothing obvious to me). Odd.

 

[Catt22]

It's on the top of the tank itself, built into it, not on the regulator. The tank does not go to my house, it goes to a inground spa heater (I keep it turned off about 10 months of the year!). It is a big tank, perhaps 5 feet tall, and 2.5' diameter. I looked for units of measure on it and there were none (at least nothing obvious to me). Odd.

Yes, very strange that the gauge has no units of measure indicated. You had said it registered from 0-80" and the only thing I could correlate that to would be inches of water column which is a common pressure unit of measure for natural gas, but not so much for propane AFAIK. The vapor pressure of propane ranges from 0 at -44 F to 204 psi at 110 F, so the 0-80 gauge doesn't make much sense, as it does not range high enough. You might ask your propane supplier about that when he next fills the tank. I can't imagine what it would be used for, unless perhaps it's not actually a pressure gauge. It might be a liquid level indicator of some kind.

 

[Catt22]

Hmmm. I think this will be a waste of a test. As soon as you are done, no matter the result, the obvious dropping pressure in the tank will be questioned, and it will be all for naught. Hate to be the naysayer, but it's inevitable, and rightfully so.

BTW, WTF's up with the very passive aggressive, "inevitable, and rightly so" comment? I see nothing anywhere in this thread that warrants that kind of a response.

 

[jezter6]

It's say it's just more the questional and confrontative (both seem to be not words according to Chrome) nature of the DIY forum.

Face it. Homebrewers will question EVERY scientific fact until they can prove it themselves, even if it's provided by someone with extensive credentials in their field.

 

[lincoln]

well, for it to work on an electric rig, you have to paint the INSIDE!

not exactly, that would help heat out of the kettle for an electric setup you would want the inside of the pot to be as polished as you could keep it.

but on a serous note, couldn't you shutter the burner to give you a carbon black coat to the bottom?

link

 

[Catt22]

It's say it's just more the questional and confrontative (both seem to be not words according to Chrome) nature of the DIY forum.

Face it. Homebrewers will question EVERY scientific fact until they can prove it themselves, even if it's provided by someone with extensive credentials in their field.

There's a huge difference between questioning a theory and stating that it would be a waste of time run a test and especially the, "and rightly so part". I'm a skeptic at heart myself and I often question the questionable. It's just my nature, but face it, there's no point in questioning a fact, if in fact, the fact is actually a fact. You might want to check the definition of a fact with your Chrome thingy. I'm skeptical that there would be an appreciable advantage to blackening the bottom of a kettle, but I'm also open minded enough to test the theory.

 

[passedpawn]

I don't want to be confrontational. I was merely stating that if you changed more than one variable the results would be doubted. I'm sure you agree.

Now if you don't think that you are changing more than one variable ( and you might be right there ) then go for it.

 

[Boerderij_Kabouter]

In general this community is not very quick to change. This idea make a ton of practical sense and is very likely a good idea. The only downfall is the difficulty in properly conditioning the paint. 99% of people who buy that engine paint at the big box store are wasting money because they do not properly heat treat the paint...

Anyway, I am sure this at least helps a few minutes per boil. Almost everyone on the planet called me an idiot here when I wanted to use SS for a chiller too... my how much difference a few years make.

Don't worry about the naysayers, they are always waiting in the wings.

 

[Catt22]

I don't want to be confrontational. I was merely stating that if you changed more than one variable the results would be doubted. I'm sure you agree.

Now if you don't think that you are changing more than one variable ( and you might be right there ) then go for it.

The only variable I planned to change was painting the kettle bottom black. I thought that was fairly clear from the start. Obviously, there is no way that as a DIY'er that I can have absolute control over every tiny little variable, but as I mentioned earlier, I'm looking for an appreciable gain and the small variances should not much affect the results. I would expect some variation in the results if multiple tests were run, but I doubt they would amount to much at all. Some over and unders would indicate to me that the blackened bottom would make very little difference. I want to see a significant gain to make it worth the bother. I would not be very impressed with a gain of only a couple of minutes.

 

[passedpawn]

The only variable I planned to change was painting the kettle bottom black. I thought that was fairly clear from the start. Obviously, there is no way that as a DIY'er that I can have absolute control over every tiny little variable, but as I mentioned earlier, I'm looking for an appreciable gain and the small variances should not much affect the results. I would expect some variation in the results if multiple tests were run, but I doubt they would amount to much at all. Some over and unders would indicate to me that the blackened bottom would make very little difference. I want to see a significant gain to make it worth the bother. I would not be very impressed with a gain of only a couple of minutes.

It might be better than you think. I'd do the test if you have the engine paint around. If it makes an appreciable difference, a ton of brewers will do it too!

I just want to repeat myself that I mistakenly thought that the pressure would drop significantly between boils, and thus the experiment would be skewed. Not the first time I was wrong. I think ChemE's idea and your effort to test it are commendable.

 

[vinyl_key]

Hmm, if anything comes of this, I might just have to paint the bottom of my keggle black.
Looking forward to some sort of result on this!

 

[ClaudiusB]

do you think that the water staying at 212 gives the paint a "cool side" to help it not blister off?

Correct
Look at the video below, same principal.

Almost everyone on the planet called me an idiot here when I wanted to use SS for a chiller too... my how much difference a few years make.

Now everybody needs Tri-Clover clamps too

Look at my latest brew kettle design Brutus 0.000001, testing phase



Cheers,
ClaudiusB

 

[bblack7489]

With 1000F I get 151 watts silver and 1950 watts black
With 2700F I get 3,500 watts silver and 45,000 watts black

Isn't this assuming that 100% of the heat transfer between the burner and the pot itself is coming from radiant heating?

Increasing the emissivity of the bottom of the pot only affects the heat transfer via radiant energy. Adding a coating of paint to an aluminum or stainless pot will decrease the heat transfer due to conduction. In this case that conduction comes from the temperature of the flame itself as well as the column of hot air coming up from the burner thanks to convection. So the issue is a function of the ratio of radiant heating to conductive / convective heating as well as the changes in conductivity and emissivity of the surface.

I would wager a pretty well educated guess that it will significantly decrease the boil time since the emissivity increases by such a large factor and the conductivity decreases by a relatively insignificant amount and since there's definitely a significant amount of radiant heating in the system. I'm really interested to see the actual results.

Ah heat transfer...takes me back...
http://en.wikipedia.org/wiki/Heat_transfer

 

[ChemE]

bblack,

I had stated before that I'm just calculating radiative heat gain and totally ignoring conduction which will remain essentially unchanged though we all know adding a few mils of engine paint will every so slightly decrease the overall heat transfer coefficient. I miss heat transfer too, great class. Now I have to brew beer to use what I learned in school since my job doesn't require it of me!

 

[ChemE]

On a side note, I'm betting those trying this out on stainless steel may not have nearly the results that those using aluminum pots will have. Polished stainless steel actually already has a fairly high emissivity of around 0.3 (ish depending on alloy etc) while aluminum starts life at 0.06 (ish). So us aluminum guys have much more to gain than the keggle guys. Still, my best engineering judgment tells me in a carefully controlled experiment the difference in emissivities will be detectable.

 

[Catt22]

I just want to repeat myself that I mistakenly thought that the pressure would drop significantly between boils, and thus the experiment would be skewed. Not the first time I was wrong. I think ChemE's idea and your effort to test it are commendable.

So then, what we have here is one of them non-problems. They are my favorite kind.

I'm still thinking that the difference in emissivity will be quite trivial and of little consequence relative to the overall heat input from the burner, but I may be wrong. What the change in emissivity means to me in practical terms is that more radiant heat will be absorbed by the black bottom and less reflected away.

Here's one for you guys to ponder. I've often wondered it the skirt on the kegs is interfering with optimum heating. My thinking is that there will be a bubble of hot gasses trapped under the kettle by the skirt and the even hotter gasses are being deflected to the sides by the bubble. IOW, would drilling a bunch of vent holes around the top of the skirt help reduce this effect and allow the hotter gasses better access to the kettle bottom. I'm very tempted to drill some vent holes and try this out. Now if someone will let me do it to their kettle so I won't have to risk screwing mine up we could find out. Will someone please volunteer for this experiment? Come on now, man up and get 'er done !!