copper tubing

i saw a tv program about ice makers that gave me a thought

if you flatten copper tubing a bit before you wrap it around a rocket stove you'd get more contact area

if you can weld, a die could be made out of 3 pieces of steel with a forth used as a punch, a hefty hammer and you're in business

More benefit for less effort/expense might be to smear a touch of thermal grease onto the copper. This might also help prevent any galvanic corrosion of the steel.

Joel Hollingsworth wrote:
More benefit for less effort/expense might be to smear a touch of thermal grease onto the copper. This might also help prevent any galvanic corrosion of the steel.

that may work if the temp isn't a factor

and the expense

The grease I'm thinking of is silicone oil plus hexagonal boron nitride powder. It should be good up to a couple hundred C, which temperature would probably cause enough steam pressure to burst the relief. If the tubes boil dry after that, the grease doesn't release anything too nasty from over-temp: a tiny amount of fumed silica, but nothing toxic.

They use it inside automatic coffee makers, to connect the boiler tube to the hot plate under the carafe. That's lower pressure, I know, but a vaguely similar range of temperatures.

wardd wrote:
i saw a tv program about ice makers that gave me a thought

if you flatten copper tubing a bit before you wrap it around a rocket stove you'd get more contact area

if you can weld, a die could be made out of 3 pieces of steel with a forth used as a punch, a hefty hammer and you're in business

ice doesn't explode.  much.

steam does. dramatically.

Keeping copper pipe open, with no pinch points, helps avoid flash-steam problems.

That added surface area might replace 1 or 2 extra coils, but could cost you the entire coil (or personal injury etc) if it collapses the pipe enough to restrict flow.

Your die might let you create a consistent ellipse cross-section without collapsing the pipe.  With great care, it might even hold that shape when the coil is bent into place. 

This seems like a small performance tweak to a system that is still hobbling along like a 3-legged horse.  I'd like to see more experimentation with the safe, effective places to put the pipe within the rocket system before trying to refine the pipe's surface area. 

I think it might be possible to collect heat directly off the exhaust, by plumbing the pipe into the base of the barrel or nearby, in which case a round pipe would work just fine.

But maybe that's because I just spent $300 on copper pipe for Ernie to play with, and I sure don't want to create a kink in the middle by accident.

-Erica Wisner
http://www.ErnieAndErica.info

Erica Wisner wrote:
ice doesn't explode.  much.

steam does. dramatically.

Keeping copper pipe open, with no pinch points, helps avoid flash-steam problems.

That added surface area might replace 1 or 2 extra coils, but could cost you the entire coil (or personal injury etc) if it collapses the pipe enough to restrict flow.

Your die might let you create a consistent ellipse cross-section without collapsing the pipe.  With great care, it might even hold that shape when the coil is bent into place. 

This seems like a small performance tweak to a system that is still hobbling along like a 3-legged horse.  I'd like to see more experimentation with the safe, effective places to put the pipe within the rocket system before trying to refine the pipe's surface area. 

I think it might be possible to collect heat directly off the exhaust, by plumbing the pipe into the base of the barrel or nearby, in which case a round pipe would work just fine.

But maybe that's because I just spent $300 on copper pipe for Ernie to play with, and I sure don't want to create a kink in the middle by accident.

-Erica Wisner
http://www.ErnieAndErica.info

it's a minor point and the added efficiency may not be much but if it were to be done i would use tubing of greater diameter than the tubing going to and from so the cross section area remained the same

and filling the tubing with sand or ice helps prevent collapse

one way to help prevent steam explosion is to keep the water flowing even if you have to add a holding tank

have the inlet and exit in the holding tank and the heat coil as a separate circuit

the downside may be it takes longer to get hot water but there are a couple inexpensive  fixes for that if you're good  at fabricating

Ernie definitely uses a holding tank and continuous circulation in any water-heater he designs.  The possibility that water might stop moving in the heating coils makes us very, very nervous. 

Sounds like you have a good sense of what you want to do, and how to make it work.

Ernie reminds me that he's not on here giving advice (even though he has built water heaters and I haven't) because he doesn't want to feel responsible if someone gets hurt. He's seen too many experiments in water heating, literally blow up in people's faces.

So please be careful, take it slow, and good luck.

-Erica Wisner

Someone sent me this digram of where someone used copper.  Seams the only factor there ( and the reason I"m not using copper) is the fact that the stove gets so hot, it can weaken the copper.  I"m kinda afraid of it melting so I"m using galvanized...just to be sure.

http://www.flickr.com/photos/ryancdeuschle/sets/72157610150609041/

Re the galvanized pipe. 

this may be of no concern, but I do know that one reason wood stove chimney pipe is black and not galvanized is it can get hot enough to cause the zinc to give off gases and they are very bad to breath. Ditto on why one should be very careful if they weld galvanized metals.  Maybe your application does not get hot enough, but I thought I'd mention this as a potential safety issue.

Hmm, this is all very interesting and you all make some great points. Thanks so much for sharing. What about running the black pipe up and down the length of the barrel or incorporate it to run the length of the exhaust pipe either on the outside up against it or plumb it on the inside of the exhaust pipe. Also having the hot side of the water on a rise will always give you a natural movement although it might be a bit slow. Interesting to hear your results.

Foxfire7893 wrote:
Hmm, this is all very interesting and you all make some great points. Thanks so much for sharing. What about running the black pipe up and down the length of the barrel or incorporate it to run the length of the exhaust pipe either on the outside up against it or plumb it on the inside of the exhaust pipe. Also having the hot side of the water on a rise will always give you a natural movement although it might be a bit slow. Interesting to hear your results.

the water should be in a counter direction to that of the flow of heat

in other words the water should enter the coolest region and exit the hottest region

if i understand you want to make a loop of the water going from hot to cool several times, that would be less efficient

Paul talks with Ernie and Erica about rocket mass heaters in this podcast: rocket mass heater podcast

They talk about heating coils.

This is not specific to water heating, but a useful trick when working with pipe --- To curve pipe without kinking,fill it with sand first. The sand makes a sharp kink nearly impossible. Beach sand is easier to remove than sharp masonry grade stuff.