Is there a solid proven RMH design to use for scaling up or down.

Hi,

I've been looking at vids on YouTube and they are all made different. Some have insulated up stacks others don't, some are short up stacks others long. Some have no up stack at all just a long run till the exhaust stack.

I like seeing them all, but would like to know if there is a solid, proven design that is correct in all aspects of RMH design with measurements that I can use to scale the RMH up or down? Or perhaps a formula that can be used for scaling purposes?

For instance, if a proven design uses 6 inch pipe and a 55 gal drum and I want to make one at 1/6th scale or 1/8th scale what rules do I need to apply to ensure maximum and correct performance? Or it'd I wanted to upscale it say to an 8 or 9 or 10 inch pipe or cross it over to metric dimensions etc.

Also, is there a formula or rule of thumb to go by for the heating tube max length/diameter or what performance you can expect using xyz heat tube diameter length curves turn arounds etc?

I guess in short I'm looking for a sure fired way to figure out an expected performance level per scale and design.

tia,
- chase -

listen to Pauls podcast with Erica and Ernie (http://www.richsoil.com/permaculture/182-rocket-mass-heaters-permaculture-podcast-019/)
also, if you havent read this, this is a collection of all (most of) Pauls RMH stuff http://www.richsoil.com/rocket-stove-mass-heater.jsp

Chase, anything bellow 4 inches don't work. The lower limit is reached due to the boundary layer sticking too much to materials.

And stop watching youtube, it's full of shit!

They all say, "hey, look at my design, isn't that wonderfull? "

But never tell you about the failures! Some don't even know their build have failed, because it's been burned once or twice, and now is gathering dust in the back of the garage.

Simple rules to me;

If it's not insulated, it's not a rocket.

And if it has metal for the internal parts (feed tube, burn tunnel, heat riser) it will fail, no mater what! Usualy shortened in

Metal is doomed!

As for scaleabillity;

http://donkey32.proboards.com/thread/1170/tube-dimensions

This is actually quite an interesting thing - many things can't scale because of the laws of physics (and I hope I may be permitted a minor digression). JBS Haldane wrote a brilliant book "On Being The Right Size" about how biological organisms are constrained in how they can grow. One example is the size of leg bones in relation to the animal it can support. If you double the overall scale (height, length, breadth), you multiply the volume (and hence the weight) by EIGHT, yet the cross-sectional area of the leg would only go up by a factor of FOUR. This is one reason why (thank goodness) giant ants the size of elephants will never take over the world - they would simply collapse under their own weight. And it's why it's not the case that if a flea was the size of a human, it would be able to jump over the Empire State Building. It wouldn't even be able to move. It's a great wee book - I would recommend it.

But back to RMHs - you can probably play about with size within a range of maybe 20% plus or minus without sacrificing *too* much in terms of function, but once you're into the realm of orders of magnitude shift, then the physics is very different. If you have a very small system, you're unlikely to generate the pull through from the differential pressure caused by the column of hot air within the riser, for example. You'll also radiate the heat away from the bell much more quickly (greater surface area to volume), and conduction effects become much stronger than convection effects, again impeding the pump.

On the other hand, if you're going very small, you can play with TLUDs, which are ideal for this sort of caper

Chase Canade' : I totally agree with Max, With the recommendation that even a 4 inch Rocket Mass Heater RMH is an advanced build, try building a 6'' system
first, The Thermal mass bench that can be supported by a vertically fed J-Bend 4'' RMH is about the size of a love seat !

Ask a fire fighter when you scale your ducting size down by 1/2 you cut the sq. inches of flow area to a 1/4 and then your precent of circumferential surface area
is greatly increased, so laminar flow further reduces the volume of ether a liquid, a gas, or a plasma that can flow through your pipe !

Metal, specifically iron and even stainless steel will fail dramatically due to the high temperatures your RMH will work at . For more information you can google
"high Temperature Hydrogen Attack'' or ''Hydrogen/Steam Embrittlement'' !

There are a good set of proven plans available to you as a member See link below :


http://www.richsoil.com/email.jsp

On the new page note the box describing the free plans, and then sign up for the daily e-mail and our dastardly plans for world domination !

Hope this is Helpful and timely ! Big AL !

Yup... They are like proton skimmers in a way. (I was saying so in my other post.)

You can make a protein skimmer small, and they look cute, they work to a degree. But a small one.
They as well need to be a certain length to allow for molecules to be in contact, flow is critical etc etc. for it to truly do what is suppose to do.

And I was thinking the same might be the case with Rocket stoves and RMH's on my way to work after posting these questions.

I was hoping to model an idea I was playing with about these. And my idea was to go smaller. But miniaturize one first to be sure it would do and play with optional ideas for it.

I don't have the space for a 6 inch let alone a 4 inch model. (Circumstances/space/area to build that large, prevent such a build at this time)

I have to think about all that has been said... learn more, I can see that.

About metal. What about titanium?

Or hmmm, there is that insulation I was reading about the other day, Aerogel. Perhaps that could be worked into the mix somehow. (Thinking out loud)

Okay, so for the moment, my bubble has been burst... temporarily.

Back to the drawing board! And to check out the further knowledge via those links you all provided.

Thanks all.

- chase -

Chase, what are your space restrictions? What do you want to use it for exactly? Do you have a chimney?

Hi Chase, I wasn't kidding about TLUDs - if space is at a premium you can very easily construct one that can be adapted to a normal fireplace - as long as (and this is vital for any combustion system) you have a clear draught for your chimney, and I would always use a carbon monoxide monitor indoors. You'll not get a great deal of thermal storage from a TLUD, and fireplace-size ones will give you maybe 45 minutes from a kilo of wood pellets, but you'll get a nice flame and a talking point I'm trying to source a few heat resistant glass tubes to use as risers as I think they'd look great. I've also used a giant TLUD (yes, they do scale to some extent!) as a patio heater for outdoor parties in chilly NI, and with a few kilos of chipped dried willow, you get almost 90 minutes of excellent radiant heat, without burning off fossil fuels. The risers are metal, and yes, they are going to have a limited lifespan, but you can construct most out of paint tins, soup tins etc. Have fun and stay safe!

Satamax Antone wrote:Chase, what are your space restrictions? What do you want to use it for exactly? Do you have a chimney?

My goal is to make something that is truly backpackable.

Requirements would be,
Small, very small.
Light weight
Compact
No open flame
No smoke
(And yes I checked the TLUD - won't suit due to the upward and open flame)

Primary goal of the unit
Heat living space
Have a cook top
Heat 5gallons of water for use. (Hygiene, dishes etc)

My thought at the moment, well one thought I was tinkering with in light of the given info is...

Insulator for the riser would come from insight locale.
Underground heating of the primary sleeping area (tent floor) would come from a underground ditch style flue loop. Possibly a ditch with flat rocks over the top, with dirt over the rocks ending with an upright flue stack beyond the tent floor perimeter. Just a thought for something that could be built onsite.

Stove body locale would be under a tarp style over hang or within the vestibule area. Within the tent anywhere even under the vestibule makes me nervous but that is the point of this. To have access to the stove cooking without burning a hole in my tent, or melting it. Or catching it and myself on fire in the process. lol

Possible secondary loop to the water tank or possibly off the floor heat loop final exhaust flue stack..?. Since the water supply would be a gravity style water supply, I could have the exhaust flue be say 10 foot high with a 5 gal water supply at say, 8 foot. Considering that the average temp of the end of the exhaust flue is approximately 140 degrees Fahrenheit from what I've read, a portable shower as the water tank would work, it can handle higher temps. And since is flexible, I could just wrap the flue with it to heat it up.

Area to be covered.
My North Face VE 24 (25 is the new one) is approximately a 6 foot diameter.So a simple loop underground would be easy to make. I was hoping to go 2.5 inch max on the pipe diameter if I had to. 1.5 would have been nice though probably too small.

Smallest area, would be for my Cattoma single person. A single run under that one would work for heat. Even above ground run, since it's above the ground about cot height.

I have a military grade radiant /reflective (?) tarp. I wasn't to say it's 7x7 maybe, possibly bigger. Rated at -123° to +240 I think, some ridiculous spread in degrees, super hot to super cold. They cooked an egg on it while under it. Any way that should hold the heat nicely. And I figured the "stove" past would heat that area up. I'd be less afraid of catching it on fire than I would my tent(s) so that to me, it's the ideal place for the stove/cooking area.

I was also considering some sort of damper system to be able to shut one part/loop off if it got to hot in the tent but that's not going to be necessary , but on file if I change my mind.

And no, no chimney.

I hope this isn't a disappointing train of thought for you guys. Wish I had a house to put it in, or soms land to put the house on. A the moment, that's not my reality.

The idea of this being portable would be made highly plausible if the build was on locale and only the main parts packed in. Like the riser. The tank, and last rise in the flue is my thought.

What's your thoughts on this?

- chase -

Hi Chase, I don't think a RMH can be constructed to cover those bases - even large statics would struggle to stack all those functions. I think you need a nuclear thermal generator - that's why NASA didn't send Curiosity to Mars with a RMH

Gasification might be a way to go, but I think you'll need to split your burners and accept some degree of open (or contained) flame.
-Shane

(Note my nod to the Wheaton trademark of "I think" - like any scientist I love being proved wrong!)

Chase, what do you mean by backpackable?

Well, you could do things which could go towards your goal. But, if you moving everyday, you can't beat a swedish torch

https://www.youtube.com/watch?v=ydqGJEOz8VU

But i would give it another twist.

Basicaly, i would hold the three quaters with stones. piled around, and thoses, i wold put in the tent when hot and the torch has finished burning.

In this case, a heat riser made of metal is also an option for a rocket. As we're not talking about a thing to heat and cook , and not meant to be disassembled.

Your flat stone trench is a good idea. Along the lines of a roman hypocaust. That powered by a small rocket could do the trick. But you will need to build a chimney at the other end, may be out of stones and mud. You don't need much. What you need to find is a hump top. Not a hill but smaller. Dig a trench, covered with flat stones. Make a chimney out of stones, dropping down, to use the trench as a bell. At the other end, you dig a hole on the hill side. Make a rocket of some kind in there. So the rocket top is under the first flat stone.

Something along thoses lines.

http://www.thediyworld.com/DIY-Rocket-Stove-Make-Your-Own.php Insulate with some rockwool or superwool. And a trick to improve the draft and efficiency, as well as heat yourself. Carry another outer can and another inner can, that you put on top of the heat riser. Then you fill in between thoses two with stones. Which will heat up while you're cooking, and then bring thoses stones back in the tent when needed. May be more convenient than my first idea of using a swedish candle. There is plenty of ideas to be looked at. But heating stones while you're cooking or after, and bring thoses in seems a way to heat inside yoour tent.

@ Satamax

The TLUD did not go unappreciated, I'll be turning that style onto some that do have chimneys (existing fireplaces) that I have raved to about the RMH since learning about them.

As for your next post concerning the Swedish torch etc. I'll have to look more at what that post contains and links you provided, the ideas you put forth later tonight when I have more time.

But a quick skimming of the content, I did think of heating rocks, which is an old stand-by for heating sleeping areas in small tents or bedding.

As for splitting the work load, that may have to be done. May not. Not sure at this point. I'll post a couple vids when I return later today by someone that has been experimenting with Rocket stove design. His designs are much larger than I want to go, but he has some neat designs, if nothing else, deserve a look see at what he's doing.

- chase -

Chase Canade` : If true backpacking use is important to you this is a good tutorial on a Rocket (cook) Stove will -with out its insulating dirt- travel light, finding dirt when
you get where you are going is a simple as looking down ! Bon Chance' For the Good of the Craft Big AL

link below :

https://www.youtube.com/watch?v=yRLR07GRgvQ

@ Big Al - thanks, seen that one. The problem with that style or rather what I'm trying to get away from is the up draft flame.And I'll show you another DIY rocket in use on a camping trip. You might like it. It's a nice build. But I think the updraft tube in these styles needs to be longer... just my thinking from what I've seen of larger designs. Here's that vid:



@ Satamax,

Yeah, I'm familiar with the Swedish candle, didn't recognize the name but as soon as I saw the vid still shot I knew exactly what it was. Again, open flame. Though I thought of putting it in a can like the TLUD mentioned, and a second can over that. Filed the thought for later examination.

The latter part of your post follows my thought with the ditch. I could carry in a final flue. And in rethinking it, I'd only need maybe a 3 or 4 foot end rise...? Maybe less. As I could still warm the water. Which I've completely figured out how to go about it easily and make it very light and portable. That part anyway.

I've been thinking about this non stop. I've broken down each areas process of the RMH design and what each part is suppose to do. Hellos explaining it to others. Which btw, you're probably going to get a bunch of new members as I've told and continue to tell/talk about this to everyone stirring up interest.

I like the idea of the Mass section of an RMH, when camping I don't want a fire going 24 hrs a day to heat my tent. A three hour burn is shoo appealing. The trench idea is so doable. Provided there's enough rocks.

Your build up rocks around a rocket stove might just be a solution. I could carry them in an insulated bag into the tent area. And just let then sit in the bag, which would help hold/contain the heat. Let the heat escape from the top of the bag to heat the tent. After all, I'm not trying to heat a huge area in either tent.

The water... it's a solar water heater to begin with, designed to be movable. So I can heat it anywhere really along the heat source, so long as the heat is not too high. Then move it to any height needed. Adding a simple reflective insulator when heating it, will quicken the riser in water temp, as well as retain the temp for a longer duration.

As for a RMH in an existing fireplace. I thought about that some. The thing that many like about fireplaces is the ambiance the visual aspect of having a fire burn gives off. A window in the front of a fresh build RMH as one guy did, really address that visually pleasing aspect most like about a fireplace. For existing fireplaces, on could use the fireplace as is I guess for the visual when sitting in the room, The TLUD takes care of the heating during the night when the visual id's no longer needed. Then I saw this vid, (coming up next) of a rocket stove created by a metal artist in Japan I think? It's in Japanese so I'm being presumptuous that that is where he's located. Anyway, take a look at this vid of one of his rocket stoves. Then look at some of his other metal art work stoves. Really nice stuff.



This last video I'm going to post is one by the guy I was mentioning in my last post that has done a lot of experimenting with Rocket stove designs. He's located in, I think not sure, Russia...? Anyway he has like 30 or 40 designs he's posted vids on. This one shows several multifunctional designs.



In many of his vids he shows how to make the one in that video. But he fires them all up and explains what's going in each video.

Lastly, here is one that is about the size I was after for the main body off the stove itself. This guys build was unsuccessful but he realized why in the end.



I still think that a RMH can be scaled down. Maybe others have tried but I still think it can be done. Might not get the heat needed or worth it, but I think one can be successfully downsized. And the reason is this after thinking about what was said as to why it couldn't be scaled down past 4 inches. The reason was due to the volume of air, or the lack thereof. Can I be so bold as to suggest it may not be the volume of air that was needed to scale it down successfully, but rather the correct ratio...? If the ratio is correct, no matter the size, the principle should work. Just on a smaller scale. It's a thought I'm going to continue to think on at any rate. ie, I just gotta try it and see.

- chase -

I don't think the scaling issue is with the volume of air per se, but with the physics of boundary layers reducing the effective cross section while the relative heat loss from the enclosing surfaces increases. There is some limit to how much airspeed you can get in a small pipe with self-induced draft. If you make the entire combustion chamber from extremely low-mass insulating refractory fiber, it might work decently.

Chase Canade` : We have let a little confusion enter the picture There is a vast difference between the Rocket (Cook) Stove, and a Rocket Mass Heater RMH.,
visually the difference is the Barrel over a heat riser

While the Rocket Stove can be sized up and down, a true RMH that creates a powerful enough draft to suck flames sideways to the base of the Heat Riser is
extremely difficult to scale down, and certainly without supplemental draft the proper size for the thermal mass is about the size of a love seat

Many people have tried and failed to make a 4'' system, and is generally considered an advanced build that few ever attempt, mostly people with tiny houses.

Here is another Rocket cook stove clone that works very well and is a good stove for its weight IF to are camping and cooking for Two! link below :

https://www.youtube.com/watch?v=2mO3bfGrbso

You might like to look at kelly kettles for late fall any early spring camping

And no exploration of what is out there is complete with out a trip to Zenstoves.net The Great grandaddy of Cooking appliances D.I.Y./Other on the internet

Oh and concrete and all concrete blocks will rapidly fail when used regularly!

Also The RMH unlike the wood stove can never be operated safely with an inline damper, sooner rather than later it WILL Bite your Ass !

For the Good of the Crafts ! Big AL

Perhaps I'm getting confused or rather not understanding the "why" it (the RMH) can't be scaled down after seeing all these rocket stoves with flue channels after the initial burn area going up, down, S-curving this way and that before hitting the exit upright flue stack. And them being all different sizes.

I'm not grasping something apparently, I take it, it's within that chamber (the inverted drum over the insulated riser area) that is lending itself to my not understanding or thinking "why not?" when it comes to scaling it up or down.

Perhaps I'll have to eliminate that area in what ever I come up with. But keep the Mass part.

I could just have a down feed in a chamber with a cook surface just past the feed area, run a horizontal flue say 3 to 5 feet straight out, and either turn a single 90 degree on the horizontal under my tent, heating the Mass, then a final 90 to a 3 or 4 foot exit riser.

Or create something that would resemble a dual exhaust. Exhausts being on each side of the Mass. The whole horizontal system creating a "T" where the burn is at the bottom of the "T", connecting to the Mass at the top of the "T", (which would be under my tent" and two uprights at each end of the "T" top.

Hope you can follow that....?

One of your members built a hybrid out of a Military ammo box, let me locate the vid for you... Here it is:



He didn't show the lighting of it. So I'm curious as to how he got it going. And this design makes me a little nervous since the fire is shooting straight back into the tube. I picture hot pieces of wood being pulled far into the tube. But this and other horizontal designs do intrigue me.

For simply showing what I don't want to happen in light of your statement of how doing things wrong could bite you in the ass. Here was a way to heat a tent/shelter that the guy was experimenting with ideas that it went wrong. In building a small modified Dakota fire pit I'm his custom insulated tent. He inadvertently and unwittingly created a rocket stove in his design apparently. And well, you'll see what happens...



But this is where I my interest first started. Which led me to Rocket stove which led me to RMH's which led me here.

Years ago I saw the underground A/C which uses the earths natural cooling or rather, ambient temperature so many feet down, to cool homes. Like the RMH it uses a ducting loop. Only it is so many feet down and it goes back and forth under the house. As air is pushed through, it cools the air, whereby cooling the house. Beats using an A/C unit. The similarity being the loop and using stored energy. And that it's the part I'm trying to create.

A short burn, stored heat, released over time to heat my tent/living space. And a relatively small amount of water, 5 gallons. Oh and cook with. I don't see this as that hard to do. In theory anyway. Though in practice it seems like it's getting overly complicated. By my own hand I suppose.

I'm going to take a look at some ovens next. Some traditional ovens made of clay etc, use a mass and convection to cook with.

I feel confident that I can come up with something that I can easily pack in with, and with a minimal build accomplish what I'm trying to do. I just have to mix and match, connect the dots if you will, and the design will reveal itself to me.

Plus, I've been given a lot to think about here, with some good options.

That Zip Stove was cute, and works, but nahhh. But reminds me of how some are running fans and lights with that heat pump style generator. Those are pretty cool. Going to build one myself for sure


- chase -