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
Blackening Kettle Bottoms
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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.
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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.
![Craft A Brew - Safale S-04 Dry Yeast - Fermentis - English Ale Dry Yeast - For English and American Ales and Hard Apple Ciders - Ingredients for Home Brewing - Beer Making Supplies - [1 Pack]](https://m.media-amazon.com/images/I/41fVGNh6JfL._SL500_.jpg)
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.
bja
Well-Known Member
Update, but need to drill the vent holes and run the second part of the test.
Trial with six gallons in the kettle and the start temperature at 82 F. Burner adjusted to moderate flame level. Turned it up to the point where the flames are just at the point just short of where they begin to lift off the burner ports. Adjusted the air/fuel mix for a clean burn. This flame level is not full blast, but about where I normally set it for the boil. I could have turned it up considerably higher, but IMO running the burner that high wastes a lot of fuel.
So, without the vent holes I reached a boil at 31 minutes from a starting temp of 82F. That's a gain of 4.2 degrees F per minute. The heating rate was very nearly linear from the 5 minute point forward.
I will be drilling the vent holes and running the second test shortly.
Trial with six gallons in the kettle and the start temperature at 82 F. Burner adjusted to moderate flame level. Turned it up to the point where the flames are just at the point just short of where they begin to lift off the burner ports. Adjusted the air/fuel mix for a clean burn. This flame level is not full blast, but about where I normally set it for the boil. I could have turned it up considerably higher, but IMO running the burner that high wastes a lot of fuel.
So, without the vent holes I reached a boil at 31 minutes from a starting temp of 82F. That's a gain of 4.2 degrees F per minute. The heating rate was very nearly linear from the 5 minute point forward.
I will be drilling the vent holes and running the second test shortly.
Thanks for doing this test. I guess after you test the vent holes you could paint the bottom black. And that would test the original theory of the thread. But that is much more work.
Waiting anxiously with my hole saw...
Waiting anxiously with my hole saw...
Fail !!
So, I cut the vent holes and ran the test again. It took 1/3rd longer to reach boiling. Total time to boiling was 41 minutes and the heating rate was only 3.2 degrees per minute. I was quite disappointed to see these results, however. I was expecting exactly the opposite or at least a push with no difference. Keep in mind that these runs were done with the flame at a moderately high level. The results may have been different had I been running the burner wide open, but that's only a hunch and I'm not at all sure which way it would go.
I would like to paint the keg bottom black, but I have no way to cure the paint properly. I would need a huge oven to do it right. No way will it fit in my kitchen oven.
So, in light of this test, I would say to forget venting the keg skirt. There is one nice thing about the vent holes. You can see the flame better when adjusting the burner. Looks like you could poke an igniter through one of the holes when lighting the burner.
I did my best to keep all of the variables the same. I can't think of anything that could have screwed up the tests, so until someone else gives it a go and comes up with different results, it's looking bad for the vent mod.
I'm still planning to paint my 4 gallon kettle bottom and run some tests with that, so the show ain't quite over yet.
So, I cut the vent holes and ran the test again. It took 1/3rd longer to reach boiling. Total time to boiling was 41 minutes and the heating rate was only 3.2 degrees per minute. I was quite disappointed to see these results, however. I was expecting exactly the opposite or at least a push with no difference. Keep in mind that these runs were done with the flame at a moderately high level. The results may have been different had I been running the burner wide open, but that's only a hunch and I'm not at all sure which way it would go.
I would like to paint the keg bottom black, but I have no way to cure the paint properly. I would need a huge oven to do it right. No way will it fit in my kitchen oven.
So, in light of this test, I would say to forget venting the keg skirt. There is one nice thing about the vent holes. You can see the flame better when adjusting the burner. Looks like you could poke an igniter through one of the holes when lighting the burner.
I did my best to keep all of the variables the same. I can't think of anything that could have screwed up the tests, so until someone else gives it a go and comes up with different results, it's looking bad for the vent mod.
I'm still planning to paint my 4 gallon kettle bottom and run some tests with that, so the show ain't quite over yet.
shortyjacobs
Well-Known Member
I was afraid this would happen, but also afraid to speak out against it with the volume of (circumstantial) evidence for it. I didn't see how vent holes could help more heat transfer. Think you can weld your holes back together?? I still think the black paint thing has good viability, but I'm afraid to try to cure it on my keggle....(maybe with one of those bazooka heaters for garages????)
Or maybe spot weld wome stainless channel (may have to make the channel by cutting out one side of square tubing ?) vertically over and rising up from the holes to force the flames from the holes to stay in contact with the keg for a foot or so up the side? Note - I don't have any kegs to look at to see if that is even possible, so I probably don't know what I'm talking about.
I probably won't bother covering the holes. I kind of like the convenience of being able to easily view the flame level without standing on my head. It looks like I may be using a little more propane, but i think I can just turn up the burner some and it won't take any longer to reach a boil. One odd thing I noticed when running this test. The rate of heat gain decreased as the water temperature increased. The rate was quite stable on the first run. I logged the time and temp at five minute intervals for both tests. I have no explanation for this difference.
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