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.
Blackening Kettle Bottoms
- Thread starter ChemE
- Start date
Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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
Well-Known Member
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.
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.
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.
ClaudiusB
Well-Known Member
Correct
Look at the video below, same principal.
Boerderij_Kabouter said:
Now everybody needs Tri-Clover clamps too
Look at my latest brew kettle design Brutus 0.000001, testing phase
Cheers,
ClaudiusB
bblack7489
Well-Known Member
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
OP
OP
ChemE
Well-Known Member
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!
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!
OP
OP
ChemE
Well-Known Member
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.
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 !!
My thoughts on that have been that they will "catch" hot air convection currents and keep them on the bottom side of the pot, instead of it just shooting out and going up the side of the pot/keg
I've always thought the best thing to do with that SS tube that runs down into every keg is to solder it to the bottom, and then drill out the center on the bottom. That way the heat can run up the middle and add significant surface area for heating. I've thrown away 4 of them because I'm electric, but if I had a gas burner I'd weld that tube to the middle.
OP
OP
ChemE
Well-Known Member
Anyone have some FEA software they enjoy playing with? Though perhaps CFD would be more appropriate here.
That is a proven way to increase boiler efficiency and it is used extensively in industrial boilers. The only downside I can see doing that to a home brew kettle would be that the tube would get in the way and not be worth the inconvenience. We are not super heating a boiler, so there's not so much to gain it seems and our boil times are relatively short.
Yes, but is that what actually happens. The trapped bubble will be giving up its heat to the kettle bottom. The much hotter gasses coming off the burner will be deflected by the bubble. Obviously, there will be considerable turbulence directly below the kettle, but the question is could the heat flow be improved with vents. IOW, are the hottest gasses actually reaching the kettle bottom in the most efficient way. Some certainly are, but is it the optimum configuration with or without vents. I would ask why most standard kettles (not kegs) do not have some type of a skirt built in for improved efficiency?
I recall someone on HBT cutting a vent section out of the rear of their keggle skirt to allow for the exhaust gasses to flow out improving heat efficiency.
Found it, Kladue's idea,
Is it OK to link someone else's photo? Hope he don't mind. If so let me know and I'll delete it.
Found it, Kladue's idea,
Is it OK to link someone else's photo? Hope he don't mind. If so let me know and I'll delete it.
Oooh I didn't think about that. I'm all for increasing energy efficiency. I might make slots in my keggle *and* paint the bottom black!
All in the name of saving a few bucks on propane...
I think it's OK to link to photos posted in other threads. I wouldn't worry about it at all.
I must check with Kladue and find out if there was a noticeable improvement. I've decided to go ahead and vent mine. I think I will drill 1" holes about 270 degrees around the skirt, leaving only the front of the skirt intact where the valve and hose port is located. Probably space them at about 3" intervals. I should probably do a timed test before and after to see if there is much of a difference. Should be interesting.
First, i have no idea if this is the way it works but, if hot gas rises wouldn't the skirt trap the hottest gas letting the the cooler gas escape form the bottom? Turbulent flow may make a right proper mess of that, also the hot gas up the side may also help in heat transfer, hmmm....... time to test
Not really. Check out Kladue's posts on this subject. His experience indicates that it's much more efficient to vent the skirt.
Imagine inverting your kettle on the burner and trying to heat the bottom from the inside. Without venting it somehow near the top, it would not be very effective at all. Obviously, this is taking it to an extreme, but it demonstrates the basic principle. Initially, yes the skirt would trap the hottest gasses, but they won't remain hot for long and not nearly as hot as the incoming gasses from the burner. The problem is that the incoming hotter gasses will have to somehow displace the cooler gasses above and this won't happen very efficiently without a vent. Turbulent flow is probably not the best condition either as the bottom of the kettle would then be exposed to a mix of both hotter and cooler gasses. Some degree of turbulent flow would be unavoidable and a completely laminar flow unachievable. The best we could hope for would be a somewhat laminar flow of hot gasses over the kettle bottom where they would give up heat and then exit through the vent(s). I'm purely speculating, but this seems to make sense to me. I plan to give it a try soon. I'll post back with my results. I may do a before and after venting comparison to help determine just how much of an improvement, if any, the venting makes. I hope that it does not reduce the efficiency as the modification would be difficult to reverse. I'm trusting Kladue's opinion on this as I proceed.
KillerKellers
Well-Known Member
Its not bad to quote other photos or other people, but its usually best to also link the source for reference. I, for one, would be interested in reading about Kladues experience with venting the skirt.
Here's a direct quote from Kladue on the topic: "Folks would be suprised to find out that putting a vent opening in the keg skirt and reducing the flame level gets a lot more done than having the flames roll up the sides of the keg."
You can find it in this thread under Post #3 : https://www.homebrewtalk.com/f51/i-have-another-burner-question-132332/
Found that with only a quick search. I'm sure there's more somewhere.
Agreed. I would have given a reference if I could have. I had a vague idea of the source and found the photo through a search of Kladue's past post's which led to his photos.
In hindsight, I should have PM'd him and asked if he would mind.
I would be very interested to hear the results of venting the skirt and blackening the kettle bottom on heating times. I'd like to be more propane efficient, but time is even more important to me.
I just started doing double batches with a keg and it takes me about 8 hours vs. 4 with my 8 gal aluminum pot. I haven't timed it, but heating the water to strike temp takes a few hours for me. I need to find a better way...I've got a better burner on the way and I'm thinking of switching to a 20gal aluminum pot as well....
I just started doing double batches with a keg and it takes me about 8 hours vs. 4 with my 8 gal aluminum pot. I haven't timed it, but heating the water to strike temp takes a few hours for me. I need to find a better way...I've got a better burner on the way and I'm thinking of switching to a 20gal aluminum pot as well....
Stand by for the test later today. I have a converted keg that I will be using for the test.
The first test will be on an SQ-14 burner without vents in the keg skirt. I will be bringing 6 gallons to a boil and I will track the time.
The second test will use the same equipment, but I plan to drill six 1" holes in the keg skirt on the back side of the keg. I have not yet decided on the exact number of holes or the spacing yet, but I will give that some thought while I am running the first test.
I will adjust the burner for optimum air/fuel mix and a high flame level, but probably not full throttle. I will turn shut the burner down using only the tank valve. This will leave the regulator setting untouched between tests. That's the only way I can think of to be sure that the flame levels are equal for each run.
I expect that the improvement will be quite dramatic. I am not blackening the kettle bottom for this test. The only change will be the vents in the skirt.
The first test will be on an SQ-14 burner without vents in the keg skirt. I will be bringing 6 gallons to a boil and I will track the time.
The second test will use the same equipment, but I plan to drill six 1" holes in the keg skirt on the back side of the keg. I have not yet decided on the exact number of holes or the spacing yet, but I will give that some thought while I am running the first test.
I will adjust the burner for optimum air/fuel mix and a high flame level, but probably not full throttle. I will turn shut the burner down using only the tank valve. This will leave the regulator setting untouched between tests. That's the only way I can think of to be sure that the flame levels are equal for each run.
I expect that the improvement will be quite dramatic. I am not blackening the kettle bottom for this test. The only change will be the vents in the skirt.
-TH-
Well-Known Member
Be aware of the auto shut off device in the propane tank. Mine always seems to trigger if I try to open the tank valve when the regulator is already open.
I have anticipated that possibility. I think I can avoid tripping the surge valve by opening the tank valve very slowly.
bja
Well-Known Member
You just need to make sure the regulator is off before you turn the tank on. I always turn the regulator off before I turn the tank off.
I do not want to turn the regulator off for these tests. That was the whole point in shutting down with the tank valve and not the regulator. I want the regulator to remain at the same setting for both tests. The SQ-14 is equipped with an adjustable pressure regulator. It does not have a separate needle valve for flame control as the fixed pressure regulators have. I'm trying my best to limit the variables for this test. The burner flame level is crucial.
Actually, the recommended way to shut down a burner is to turn the tank valve off first and the appliance valve secondly. I know this is counter intuitive, but that's how the experts say to do it. It's the reverse when firing up, ie open tank valve first, then the appliance valve.
Similar threads
