Guest Post by Willis Eschenbach
This one is for fun and also for real. The theme of this post is “There’s never enough time.” I worked in the villages of the developing world off and on for a number of years. A recurring issue is the inefficiency of most stoves. The simplest is the “three stone” variety, made with three stones to put the pot on.
Figure 1. An obviously ancient three-stone fire with a modern cookpot in Tanzania. Photo Source
This is hugely wasteful of fuel, particularly in lands where wood and even branches and twigs are scarce. Among my known defects is that I’m an inventor. Over the years I’ve worked on making and designing a variety of stoves to try to improve stove efficiency. As a result, in one of my peregrinations around the web a few days ago I was intrigued to stumble across the “Kelly Kettle”.
The Kelly Kettle was used in Ireland by the shepherds to brew their cuppa tea. Here’s one at work on a beach somewhere.
Figure 2. Kelly Kettle cooking on a beach. Note the fire coming out the chimney.
The brilliance of the plan is that the water in the kettle surrounds the fire. I looked at that, and my inventor’s soul rose to the fore, and I thought “Man, I could make the radical Dutch Oven using that plan. Here’s what I think it might look like.
Figure 3. What I call the “Magic Cookpot”. Note the split (two part) lids, one of which has been removed, flipped over, and laid on the ground for clarity. Lids will have handles in the final version.
And here’s a cross-section:
Figure 4. Cross-section of Magic Cookpot without the lids.
No good to throw away waste heat, so the Kelly Kettles have a pan-holder that fits in the chimney to allow you to cook another pot of food on top.
Figure 5. Kelly Kettle with cookpot. Source.
Looks good to me, so here’s my version of the same. This would allow you to cook soup or stew and have a frypan on top …
Figure 6. Potholder inserts into chimney of Magic Cookpot.
OK, advantages of this plan:
• Efficiency, efficiency, efficiency. Even without cooking anything on the top, this will heat water with less fuel than any design I’ve ever seen.
• Cost. Because the stove and the cookpot are one, you don’t need to buy both.
• Portability. It can be moved easily.
• Adaptability. It can use a variety of fuels, including a propane burner.
• Speed. It will heat water fast.
As I mentioned, the theme of this post is the theme of life—there’s never enough time.
In a perfect world, I’d take this idea and run with it and make a big difference in the amount of wood burned around the planet. I don’t have time, I have a bunch of other projects going on. But I’d hate to see this idea die, it’s a really good one that could make a big difference. So I figure I’ll cast the idea free on the web, make a gift of it to the world of stoves, and see what becomes of it out in the greater marketplace of ideas.
How could this rough plan be improved? It needs a damper to control the draft, and some kind of flap to control the air intake. You could probably increase the heat transfer (fire to liquid) by putting some spiral fins up the chimney. This would increase the surface area and transfer extra heat to the cookpot.
In any case, there it is, and I encourage anyone with the time and energy to become the champion of the idea. You’ll make a name for yourself and have women blessing you all around the planet. All it needs are a couple of sharp Brazilian or Indian or Chinese (or European or American) college students who’d like to make a difference in the world.
w.
Is there a practical way to produce electricity from a pot?
http://www.alternative-energy-news.info/waste-heat-to-electricity/
As a boy growing up in fifties/sixties Scotland I was in awe of steam engines.
clipe says:
May 10, 2011 at 2:04 pm
Is there a practical way to produce electricity from a pot?
From your link:
http://www.alternative-energy-news.info/waste-heat-to-electricity/
This was one of those content free press releases I find so dissatisfying.
“Thermoelectric devices designed by Bergfield and Stafford can generate power that can lit a 100 Watt bulb or increase car’s efficiency by 25%.”
Yeah? Cool. How much does it weigh and how much heat is required?? It only exists as a computer simulation, but just supposing it really can increase a car’s efficiency by 25%, let’s think how much power they are claiming to convert and how efficient the process would have to be.
Cars are pretty inefficient to start with, so improving that situation by 25% might not be all that exciting. Added to which a good percentage of the waste heat is normally used to keep the car’s occupants warm on cold days, leaving less for conversion into electricity.
The current best solid state thermoelectric generators cost a lot for small returns. I’ll await developments with some resignation.
I’m no engineer, but looking at figure 4, the cross section, it looks like the shape of the firebox might be optimised a bit – maybe made into a shape that’s a section of a sphere so it would naturally concentrate the heat of the fire into the centre of the firebox. Of course you’d have to then have some holes in that sphere section, probably with sliding covers so that you could control and optimise the volume of air flow through the firebox and perhaps add additional fuel to a flagging fire.
Granted it would increase the complexity of any casting, provided you were contemplating manufacturing this as a cast piece…
I love this!! And you have published it to the world meaning that it can’t possibly be patented. Now anyone can make this and help the world instead of one greedy person getting all the money.
Let’s not forget the immortal Trangia stove. Weighs nothing, works outside in a storm, no moving parts, runs on alcohol. I’ve used my two for over thirty years. They don’t wear out, and I can simmer as well as boil. Top converts to a frying pan!
I wonder if a sturdier household version wouldn’t help in poor and remote areas. If we can run Prince Charles’ Aston Martin on alcohol, we should be able to cook rice with the stuff.
kbray in California says:
May 10, 2011 at 12:41 pm
I agree, but there is such a thing as “appropriate technology”. As I said above, you can wait for the gummint to bring you clean water and cheap cooking technology … or you can roll your own.
w.
Willis Eschenbach says:
May 10, 2011 at 3:50 pm
you can wait for the gummint to bring you clean water and cheap cooking technology … or you can roll your own.
Quite right. And speaking of which:
http://greensteamengine.com
Ubercool 70% efficiency with the recondensing and distilling rig too.
Heat transfer fins. Into the fire box {flame path} protruding from the fire box directly into the water. Force the heat to spiral upward. The stew pan needs vertical heat transfer fins into the stew, and vertical heat transfer fins into the flame {heat path}.
I just love my Bushbuddy stove which has much of the efficiency Willis talks about:
http://www.bushbuddy.ca/indexs.html
Dont know if anyone picked up on this !! In your bottom pot section, you need to have 2 x removable pots (shaped in a 1/2 donut shape each) that fit in and are removable. You cant cook inside the actual heating unit iteself because cleaning this thing will be too hard, so you have to have insertable pots that fit inside.
Hi Willis
Like many here, I have used the Thermette for years – available in two models – one tin the other copper.
My copper one is very thin-walled, so every now and then it gets a huge dent in it that drastically reduces the water capacity – but I discovered that compressed-air reshapes it nicely.
Tragically though, the Thermette has soldered joints – it’s not the first time – and I’m sure it won’t be the last when I’ve let it boil dry and had to spend hours gently resoldering
How do you propose to make your device waterproof and free of such problems?
Andy
Hey Tallbloke, great photos.
I’ve built several alcohol stoves, and a couple of wood stoves – but I never tried one of these. Do you have build instructions of your stove, or just the photos?
Thanks for the ideas!
Willis, keep the original design. The mods might be on the base to reverse the flange out for stability and possibly making manufacturing a little easier. Cast Iron might be the material of choice as it has proven to stand up to the rigors of being cookware. And instead of a fancy radiator to maximize the heat area, turn groves inside and outside of the chimney with would increase the surface area.
And the benefit of cast iron is that all the thermite junkies could fix their broken Willis’ with it. 😀
In our home, we have a middle aged, attractive lady to make cold food and liquid warmer. How she does it is her business, but she is very good at it. She is also more shapely than a chip heater and does not smoke. We have not had to think about this before, but I think we would call it “civilisation”.
There was a time in history when all countries had about the same degree of civilisation. The differences we see now are a direct consequence of political decisions including warfare.
If funds are to be expended, they would best go into showing individuals everywhere the ideals of self-respect, self-sufficiency, altruism, pride in self-advancement. We won’t get there by taking farming land to grow potions to power motor cars.
Martin Hale says:
May 10, 2011 at 3:10 pm
Agreed. This is a first crude unit. Further refinements will occur.
I’ve never considered anything but cast iron for this. If it’s made out of thin metal it’ll burn through and be harder to make. The cookpot should be castable as a single piece, although you might want to separate out a firebox that you could lift the pot off of the firebox. Complexity of the casting (within reason) doesn’t increase cost beyond the increased cost of mold-making.
w.
Jarryd Beck says:
May 10, 2011 at 3:42 pm
You got the plan exactly. Now it just needs someone who is sandcasting and making cast iron cookpots to modify their design slightly …
w.
AndiC says:
May 10, 2011 at 5:49 pm
Cast iron … so it’s just like a cast iron stove, doesn’t need to have water in it.
w.
http://www.trangia.se/english/
I neglected to post a link before. I’d love to buy a new Trangia but the old ones won’t wear out, and there’s nothing to break or malfunction if you are using alcohol. I have the Trangia Mini for indoors and in-tent, the storm-cooker for outside. I’ve faced the storm-cooker into high wind and rain and it actually boils better than with no wind. Why not engineer a larger, more solid version? I’d love to own one for domestic purposes when there are blackouts and picnics. Of course, Willis’ idea is a great one, and the storm-cookers vent system may be encumbered by patents.
That said, it’s so utterly simple, patents may not restrict much.
As mentioned above, these kettles use the same design as typical gas fired water heaters (or maybe it’s vice versa).
I would not think that cast iron would be a suitable material to use. The secret to heating the water quickly is the quick transfer of heat through the sheet metal. Cast iron has more mass, requiring more btus of energy in order to heat it before it begins heating the water. Additionally, the thickness (mass) of the cast iron will result in higher temperatures of the cast iron inside the flue, which will further reduce thermal transfer efficiency.
In other words, I would stick with the sheet metal versions, perhaps with the addition of an exterior insulating barrier of some sort.
AndiC says: “…Tragically though, the Thermette has soldered joints – it’s not the first time – and I’m sure it won’t be the last when I’ve let it boil dry and had to spend hours gently resoldering.”
Uh, don’t you mean brazed? I hope you’re not using solder in any wetted joints. Lead, and all that.
Too much good stuff here to comment on all of it. I’ll just cite Tallbloke, Hultquist, Shanghai Dan, and John Johnston, in addition to Willis, for their fascinating comments. There are others, but I haven’t time to list them all.
One negative aspect: A friend of mine who was employed by a global do-gooder organization worked on a device intended for use in third-world countries where the poverty level made lives short and miserable. It would have helped hundreds of thousands. The project was a failure–not for engineering reasons, but for economic reasons: the level of bribery necessary to import such devices made it impractical to proceed. It must never be assumed that “redistributing wealth” and throwing money at undeveloped countries will improve the lives of their citizens. Graft is a bottomless pit.
One more comment:
(1) I agree that cast iron is the best material. It’s durable, a better heat conductor than stainless steel, and cheap, plus it holds heat well for nighttime heating, where needed.
(2) Avoid hard-to-clean fins or other accessories. Make any spiral internals removable and easily replaceable.
(3) Avoid nesting parts in the heat conduction path, unless they are really necessary and carefully designed. Any air gap will impede heat conduction significantly. If the gap is wet, steam may form, with consequent bumping problems.
(4) Consider developing a mantle holder that clips onto the top of the chimney, as in a kerosene lantern. This could provide light at night, if made strong enough to permit removal and handling, or cheap enough for frequent replacement.
(5) Consider allowance for embedded cast-in serial numbers to reduce theft.
(6) Stick to one piece construction, if possible, also for anti-theft purposes.
(7) An alternative project would be a reusable, fast-release mold for local manufacture of ceramic cookers at reduced cost. Be aware, however, that the collapse of an unreinforced ceramic chimney or firebox could be dangerous.
(8) Don’t use any overseas manufacturer that has a habit of putting lead in its alloys or ceramic products, or melamine in its milk.
Doug: got any pictures?
An interesting source of ideas here. I have been considering a similar problem for boat heating because it seems that to buy anything “off-the shelf” I have to spend more than I paid for the boat! I had considered putting an inexpensive parafin (kerosine) greenhouse heater inside something like a kelly kettle vented through a chimmney in the cabin roof. The chimney was formed around a copper or aluminium archimedes screw in good contact with the thin copper chimney to increase the effeciency of what is in effect a heat exchanger/chimney combination. Add in a pressure relief valve and a small 12V in line pump on a radiator loop taking the hot water around the boat and hey presto! We have an inexpensive boat heating system. Adding in a samovar tap and we have hot water on demand! Seems there is a first world business opportunity here also.
eco-geek
Ron Dean says:
May 10, 2011 at 6:06 pm
Hey Tallbloke, great photos.
I’ve built several alcohol stoves, and a couple of wood stoves – but I never tried one of these. Do you have build instructions of your stove, or just the photos?
Thanks for the ideas!
Hi Ron,
I haven’t written up instructions for constructing the ultralight kettles I make. One day I’ll make the time. Basically, the trick for the small one relies on the fact that the diameter of the body of an energy drink can is the same as the diameter of the neck of a standard size beer can. So if you cut the inside edge of the lid of the beer can out, you can fit the energy drink can to it and roll/press the flange left by the removed lid to make it watertight. It’s tricky, the failure rate is high, and it requires patience and dexterity. I did a four year engineering craft apprenticeship as a teenager.
Some people just epoxy it in place, but I make no recommendation about that, as some others don’t like the idea of the epoxy being in contact with the water you drink. Annealing the aluminium near the joint first helps. The completed kettle weighs 30 grams.
It takes a good deal of experimenting to get the vapourisation rate of the mini penny stove right for an efficient burn too, and this varies according to the altitude you use the stove at, and the ambient temperature. I’m still working on perfecting an adjustable stove, but I found a neat way to get a limited range of adjustability. I drill the jet holes in a pattern such that by changing the rotational orientation of the kettle relative to the stove, the proximity of the folded chimney flutes to the flame jets affects the amount of heat reflected back onto the stove. I make the stoves out of 40mm diameter lip balm pots. They weigh 4 grams complete. The priming ring is press fitted after cutting from the bottom edge of the energy drink can.
Nothing goes to waste. 🙂
The other big advantage of using the central chimney design is that you can extend a removeable chimney through the hut roof. The health hazards of cooking over charcoal indoors are alleviated. It increases the health hazard of setting fire to the roof though, a mesh spark arrester is recommended.