The "Rocket Phase Change Heater"

Sorry, no working model This is just some toughts as I have it worked out so far.

The Rocket Phase Change Heater (RPCH)

In order to save space as would be needed in a Rocket Mass heater (RMH) I would like to use a phase change material in place of straight mass. The reasons for saving space are varied, but space saving should not be concidered just because it looks better. If the room is available, then a RMH will probably work better and be easier to operate and install. Also a large space needs the larger space for fuel burning in order to heat the space anyway. Also the larger the radiator the lower the temperature of the surface can be and still be effective.

I would think a RPCH would be about the size of a pot bellied stove and so good for a small cabin or even a boat. It may even fit in a trailer of at least 8 feet wide. The outside surface design temperature is quite low (200F max or so) adding safety in tight situations. It is interesting to note that a properly designed RMH mostly has quite a low surface temperature as well.

My phase change material of choice is tin. It's phase temerature is quite hot so there would have to be a layer of insulation between it and the room. It is hot enough that food could be cooked on it after the fire has gone out. Or it could heat an oven enough to cook in. Tin has been used successfully in solar applications for cooking after sunset after being heated by a 2 to 3 meter dish reflector.

As you can see from the drawing this is based on the cooking kind of Rocket stove as seen in some of the Aprovecho documents. The idea with the removable insulation is that the thickness can be increased or decreased in order to control the amount of heat being used to heat the room. The removable tin container in the middle could be used in another room in it's own insulated container and the resulting hole used as an oven with an insulating and reflective lid. The insulating lid when lifted leaves a cook top surface as well.

The disadvantages (that I can see so far ) are that it costs more to build than a RMH. That it becomes a stove and not a masonry heater and so falls under different rules. It may need to be fired more often and require more attention to operate too. As drawn, the exit temperature (wasted heat) is higher than I would like to see... more design needed. I am sure that as I collect materials and try it out I will think of more things This may be years before I get that far though.

It will be very interesting to follow the trajectory on this one, this is an area that will send me back to the books to keep-up with, but as the name says this is a change in phase not
a chemical reaction so if the system is made without impurities it should be capable of cycling an infinite number of times .

The prototype as drawn looks much like some of the Aprovecho cook stoves,but these units still take advantage of the lost heat that gets absorbed by the cooler cooking pot.
This allows the placement of a conventionally lower Rocket Stove-type exhaust chimney, and full use of the delta T, more thermal mass ,and use of a bell at a more remote location .
This chimney location should be marginally better at protecting from heat radiation/lose and inadvertent contact with the environment than the prototype as sketched .
What happens if/when the temperature equalizes, do we need that higher chimney and how often? Please excuse my off the top of my head thoughts Y.M.M.V.

I also like Erica Wisners Rocket Canning / Frying Stove - specifically the lower 1/2 of the barrel with an attached ' J-Tube ' which will also add stability!
It will also make it easier to feed ! Erica's sketch for this can be found at the forum thread of the same name ! - PYRO - magically yours Allen L>

Len, just a thing, which poped out of my mind right now. Use wax for the exhaust phase change. Just a thought.

The most space could be saved by using Na2SiO3·5H2O ( sodium metasilicate pentahydrate)
http://en.wikipedia.org/wiki/Phase-change_material#Thermophysical_properties_of_selected_PCMs

Lol. They got that at Wal-mart?

haha. I'd be careful with tin, too. It's not the healthiest of metals to come in contact with.