Jan 21, 2008 at 2:24 pm #1226846
Got time for some tinkering this afternoon as the monsoon stopped work outside. Here's my new Kelly Kettle:
Using 11g of methanol in the tealight pot, it raised 1 pint of 12C cold tapwater to 88C in around 15 mins. A long time I know, but what else do you have to do on dark winter evenings?
I'm hoping that when my nion arrives, and I replace the steel potstand with an alloy catfood can, I'll have the same weight, and achieve the boil with 1/2oz of fuel.
In the meantime, I tried it out on the 5oz woodstove that I also made this afternoon:
That boiled a lot quicker. :-)
I've thought of a couple of improvements such as shoving a square section tube with the corners turned to give 1" dia across corners inside the chimney to increase the heating area, and making a more effective burner shroud/ kettle stand.
Please could someone who knows the math figure the efficiency on the current prototype for me – thanks.Jan 21, 2008 at 5:15 pm #1417053
Tim MarshallBPL Member
please give us the dirty details. what cans how did you seal the water chamber. i need those details!!
by the way, great job!!Jan 21, 2008 at 5:32 pm #1417059
The bottle is just a cheap 0.5 litre aluminium drinks bottle I bought from the local camping store. The chimney is made from 0.75mm wall thickness 1" diameter aluminium tube I got from ebay.
How you weld the two together is an art and a trade secret ;-)
I got enough tube to make quite a few of these so if there's enough interest stateside, I'll make a boxfull and send 'em over to someone who can distribute them. That way, we can keep the shipping costs reasonable.Jan 21, 2008 at 6:16 pm #1417063
@maynard76Locale: New England
Now if you can only make one of these:
Ive seen both the thermette and kelly kettle, I think this design is beter. You can cook while boiling water and it holds more water.
AND..I would be interested in one of your gassifier stoves!Jan 21, 2008 at 6:44 pm #1417069
Hmmm. 4pint capacity and weighs *THREE POUNDS*!!!
Just get 4 of my 1 pint models and save 2/3ds of the weight. ;-)
I don't like the look of the handle either, no way my knuckles are going that close to a copper pot full of boiling water! The original Kelly Kettle is better thought out I reckon. How do you mean cook while you boil anyway? You can get potstands and grills for Kelly Kettle fire boxes too…
The stove is so simple to make. I used a standard beans tin for the inner, a syrup tin for the outer, and a small beans tin for the pot stand. Add in a bit of mesh for the grate, then it's just a can opener, a couple of drills, a pair of tinsnips and away you go.
There are other people out there who will make a much neater job, I just hacked away for an hour or so, and never got the ruler or dividers out of the toolbox. I can't be bothered making a perfect job of a limited life item like this.Jan 21, 2008 at 7:15 pm #1417075
@maynard76Locale: New England
Well of caorse I was comparing it to the original kelly kettle which has less capacity than it ;) I really didnt look at the weights because they are both out of the question for backpacking.
I just saw the grill/potstands for the kettle, I dint see those before- the Thermette comes with a very stable one -(which is part of its quoted weight)-
The people I know who have one never complained about its handle but I can see your point.
Do you have a pot stand for your kettle ?Jan 21, 2008 at 7:27 pm #1417078
> Do you have a pot stand for your kettle ?
It's in the photo on the scales with the insulation stood inside it. It's steel, and primarily for the stove when using a pan, but worked ok upside down on the ground with the tealight stove inside and the kettle on top. I plan to improve the design when my nion stove arrives.
Edited to add: I could put the current stand on top of the kettle and fry on it while the kettle is boiling, I'll test how the impeded flue affects performance. Thanks for the idea!
> I just saw the grill/potstands for the kettle, I dint see those before
Pricey and a bit of an afterthought I reckon.
I made my lightweight kettle for weekend bivy trips where boiling water is all that's required. For longer trips with unplanned food resupplys a pan and woodstove is more versatile.Feb 5, 2008 at 12:34 pm #1419237
do you get the water in and out through the little hole shown in the first photo? I cant really see the need for more efficient use of fuel with free fuel such as wood, at least if it costs weight. The pot I use with my home made woodstove weighs 30 gram. Is there other advantages to a kelly kettle?
I suppose the secondary air jacket on my woodstove fits that description. I claim less smokey and more stable combustion as well as increased efficiency.
I just was forced by circumstance ( not being able to find a gas canister for the first 2 days in the Canaries) to heat water in a jetboil with solid fuel tablets. I think the jetboil boils 50% more water per tablet like it does with gas. By the way I live in England.Feb 20, 2008 at 6:28 am #1421228
>do you get the water in and out through the little hole shown in the first photo? I cant really see the need for more efficient use of fuel with free fuel such as wood, at least if it costs weight. The pot I use with my home made woodstove weighs 30 gram. Is there other advantages to a kelly kettle?
Hi Derek, My new design has a much larger opening for the water to be poured into, and a lid to close it with. Availability of wood isn't always good in the british climate and terrain, I know, I live there too. So my new design is for alcohol only, and it's pretty efficient at 53%, using just 12ml of fuel to boil half a litre of water. The unit weighs 82g including the stove, but I can make a lighter one around 40g which is only slightly less efficient.
The main advantage of a kelly kettle is it's wind resistance. Most alcohol burner/ pot combinations struggle in blustery conditions, but my kettle design is fully insulated and unaffected by wind. When you add the weight of a good windshield/pot stand to a pepsi stove, pot and lid, it adds up to more than the kettle by some margin.Feb 20, 2008 at 7:45 am #1421237
I totally see the point of a Kelly kettle with Alcohol. Would fins in the chimney to improve heat exchange eficiency even more be a good idea? If it works you could make more?Feb 20, 2008 at 7:51 am #1421238
sorry I read the original post long enough ago to have forgotten that you already had "fins" of a kind in mind.Feb 20, 2008 at 12:25 pm #1421278
Yep, just scored some 20mm square tube to make the chimney insert with. Also considering some thin aluminium plates on the outside of the chimney immersed in the water to increase surface area there too. This should be worthwhile when combined with the peltier driven accelerator fan I'm working on for the 'fast boiler' model. I'll post back with progress.Feb 20, 2008 at 12:55 pm #1421282
@vickrhinesLocale: Central Texas
Yep. The "fins" can be nothing more complicated than a strip of steel from a "tin" can (aluminum will melt) twisted along its length and jambed into place. Fins on the inside (in the water) might help as well but they would have to be fastened to the inner (chimney) wall somehow and that sounds like too much trouble. Silver solder (pure silver – no lead) might be the best way.Feb 20, 2008 at 4:14 pm #1421324
Hi Vick, I'll just press fit the fins to the outside of the chimney, ensuring a good contact area between them. I've never been able to get solder of any type to take to aluminium, and lumiweld won't work on such thin sections. Vertical fins are preferable, so as not to impede the convection currents in the heating water.Feb 21, 2008 at 2:13 am #1421389
I would have thought that sheet pressed in across the diameter might be better than a square in a circle. I would have thought the centre of the square would mostly carry the heat, whilst really you want the heat by the cylinder walls. Vicks twisted sheet sounds a good idea too. Its that core of hot gases in the centre, away from the boundary layer, that I would have inserted fins into.
I would have thought too, that the bottleneck in the heat transfer process is the gas to metal surface not the water to metal surface, so that fins in the water would not help.Feb 21, 2008 at 8:50 am #1421402
aluminium will not melt if the fins are well enough bonded to the walls and not too long, or too thin. That is one disadvantage of the thin twisted sheet it probably would have to not be Aluminium. but aluminium is the ideal material for fins. Perhaps a thicker and therefore untwisted Al plate, or a series of vertically shorter plates on different diameters.Feb 21, 2008 at 9:21 am #1421409
@vickrhinesLocale: Central Texas
The twisted strip is used in most gas hot water heaters. The purpose of the strip is not to absorb heat and conduct it to the tank, but rather to produce more complicated, i.e., higher pressure and slower, flow of hot gas. IOW, the gas is in contact with the side walls of the tank longer. This configuration also produces more complete combustion in all but gas stoves, as long as there is enough oxygen in the mix. The reason the strip has to be steel (or titanium) is that when additional combustion occurs, it happens in the high pressure zones along the strip and heats the strip past what aluminum can handle.Feb 21, 2008 at 2:44 pm #1421445
"higher pressure and slower, flow of hot gas"
Nice call Vick… yeah, slowing the hot gasses down will help the heating be more efficient as it increases heat transfer time… one could argue that impeding the flow of air by pluggin the top slightly might help, but then it concetrates the slowing at the top rather than all the way through the chimney like Vick has illustrated would be good.Feb 23, 2008 at 5:04 am #1421679
The problem I've found with slowing the gases down is that the stove doesn't get enough air through to give complete combustion. It's a trade off, you can lower the number of jets and have the boil take longer with more efficiency, or up the throughput and get a faster boil but use more fuel to do it. I think that getting just over a pint to boil in a bit under 9 minutes is around the right compromise, and using just 12g of fuel indicates the efficiency is pretty good.
My current design recovers heat in the exhaust gases quite well without inhibiting gasflow, but at the expense of additional weight and complexity. I'm working towards a compromise design which will use a simpler method of heat recovery with less weight. I'm going to try a slightly smaller diameter copper chimney with fins in the water. Copper transfers heat twice as well as aluminium so the finning would be worthwhile and the smaller diameter should minimise heat waste without the need for hard to fit interior fins. I'd like to find thinner walled tube than that used for mains pressure water plumbing though, copper is HEAVY!
Derek: I agree that the square tube is not ideal, but I've sized it so that it requires folds pressing into the faces of the tube to produce a smaller centre passage with larger volume paths up the sides of the chimney tube. Just for fun I'm also going to try a small fan driven by a tiny motor powered from a peltier unit above the chimney exhaust to see if I can force the throughput needed for choke free combustion whilst getting increased gas/metal contact area.
Vince: A spiral would be nice but getting a tight fit so the heat transfers to through the chimney wall as well as the system benefitting from the slower passage of gas is tricky. I remember seeing a free dangling twisted strip in a flue which jiggled around to slow the flow/ditribute the heat more randomly. I'm just concerned about the stove not getting enough air with the slowed down flow above the combustion chamber. Maybe the peltier driven fan will help.
Thanks for everyones input, research-build-test continues.Feb 23, 2008 at 6:18 am #1421682
A square with kinked sides does sound good. I would have thought that the heat transmission through Al and Cu would be very good and the boundaries are the problem. Gas to metal, maybe fin to tube if you dont get it right, and metal to water. I would estimate the temperature drop across the gas to metal to dwarf the other two, but I would have guessed that temp drop of transmission through the wall thickness of the tube would be smaller still. I would not want the extra weight of Cu just to halve that tiny loss. Cu melts at a higher temperature, so it could be a fallback for the finsFeb 23, 2008 at 7:24 am #1421690
Mine is coming along ok. I'll be trying the tubular heat exchangers to see how well they transfer heat. They are easily removed and will ballow back and forth testing with and without the tubes. Tubes are thin wall brass. Weight means nothing at this time of testing for heat exchange theory.
The bottle holds 2 cups nicely. Look forward to testing and sharing the results.
</center>Feb 24, 2008 at 12:10 pm #1421856
Looks very nice Dan. Looking forward to hearing about how well the tubes work. What I've noticed is that the flame is reluctant to split, and tends to pick one path or another, but maybe the different gasflow of your setup will give different results.
A minor tweak to the height of my exhaust heat recovery system above the chimney has produced quite an improvement on my max efficiency model. Maybe reducing the gap has increased the venturi effect increasing gas velocity. Anyway, it's still using 12g of alcohol to boil half a litre or just over a U.S. pint, but the time taken has dropped from 8.45 to exactly 7 minutes. Result!
Also tested my peltier and mini DC motor which arrived in the post today. Works like a charm over my gas lighter with a small glass of water on top to cool it, so I'll be playing with that on my next design which will be for speedier boiling times. Now to make a fan blade…Feb 24, 2008 at 2:55 pm #1421873
My first results are these:
I used 2 cups of 70 degree water to start. 1/2 ounce/15ml denatured, performed the test in my 40 degree garage.
Water boiled at 21 min. and continued for an additional 5 min. then flame out. Bottle was insulated with some paper wipes. 210 degree temperature held until flame out.
My tests tomorrow will be in the kitchen with better insulation around the bottle. I'll reduce the fuel down to 11ml and see if I can still get a boil.
Then I'll remove the brass tubes and see what the results are.Feb 24, 2008 at 3:56 pm #1421883
Good first result Dan. Looks like you may get down to the same 12g of fuel I'm using. What sort of stove were you using which burned for such a long time on 1/2oz of fuel?
Did you try turning the lights out to see if you were getting a flame path up each tube?
What is the wall thickness of your chimney tube?
I found that under sheltered conditions, insulation made surprisingly little difference, though with the longer run your current setup requires, it may help more.Feb 25, 2008 at 11:45 am #1422011
I tried another test yesterday in my garage under same teperatures. I wrapped the pot with aluminized bubble wrap of the windsheild sun visor kind.
I used 11ml of fuel this time to see how well it would do. The water temp got up to 185 degrees fahrenhite until flame out at 21 min.
Flames do not come out the top of tubes.
I'll get a wall thickness of the chimney tube for you and post some photos also.
The burner I'm using is made of 2 tea candle tins It is shown in the attached photos. It was made for the stove that I called the Stiletto.
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