A big component of our stove is its insulation.  Between the inner chamber (where combustion happens) and the outer walls is a lot of space.  If we simply left it empty, then hot air would move around and carry heat from the inside to the outer walls in much the same way your oven cooks food.

The obvious answer is to use insulation.  But what kind?  Often ceramics, sand, and earth come up.  It’s true that these would slow down the transfer of heat from the inner wall to the outer wall, but they do it by absorbing energy.  In scientific terms, they have a higher specific heat capacity than air which means that, for every degree they change, they absorb more energy.  This is helpful for safety, but it can actually decrease the efficiency of a stove.

In order to have an efficient stove, you need materials that don’t transfer heat very well–or, in other words, materials that are not very thermally conductive.  Air is actually pretty good with respect to this, but it’s a problem when it moves around freely.  Many of the best insulators simply work by trapping air in small pockets.  This is how down blankets work.

Our initial prototype used perlite, but it’s not readily available in Myanmar, so we’ve been exploring the possibility of importing it and other materials.  Ash is readily available and a pretty good insulator.  We’ve also been looking at special clay mixtures which are much lighter (and thus have a lower specific heat capacity) than normal ceramics.

As always, we’d love to hear from anyone with thoughts/advice on the manner!

A year ago, after we had just completed a prototype of a stove design we liked (it was literally made from an old metal trash can!) we decided to try adding a “pot skirt” to see how much it would improve our stove’s efficiency. We had read about these heat shields in other stoves before; the basic idea is to surround the pot on all sides with a thin metal shield that creates about an inch-gap for hot air to pass through. The pot skirt thus prevents heat from the stove from escaping to its surroundings, keeping it close to the walls of the pot and increasing the heating surface.

The idea sounded interesting, so we set to work building a prototype and testing it out! (My next post, “Frustrated by Frustums” will explain why our prototype is the shape it is-most pot skirts are actually just cylindrical.) The result was… WOW.

Adding the pot skirt cut down our rocket stove’s boiling time almost in half. The rocket stove itself was already able to boil water in maybe half the time it took an open flame, but with the pot skirt, we were boiling water at incredible speeds: up to a third of the time it takes to boil water on an open flame. Whatever we expected, I don’t think it was as drastic as this.

As great as it may sound though, our pot skirt idea still needs a lot of work. Adding that much material to our stove makes it more expensive and difficult to manufacture, not to mention clunky looking. Because it traps hot air, the skirt metal gets really hot too, posing a potential burn hazard to our customers. Our first prototype didn’t allow the cook to see the flame very well either (we fixed that issue by cutting out holes into the skirt).

Right now, we’re starting to explore new skirt designs, as well as some completely new concepts. One of the things we’d like to try is something similar to a “heat exchanger” which traps hot convective air at the bottom of the pot. The Jet Boil camping stove uses a mechanism like this. Such a design wouldn’t increase our heating surface area, but it will at least increase the concentration of hot air, which may be enough.

If you have any ideas about this engineering challenge, we’d love to hear them!

I believe that everyone deserves dignity.

Having dignity is empowering; it compels people to act, change, and even inspire others. Why? Because I believe this how humans were made to be. The designer’s challenge is to create products, services, experiences that create a culture of dignity through their use. Good design makes people feel like they count, and that their needs and fears are meaningful. It changes the way they see themselves—and the way they see others.

If all this sounds rather abstract and idealistic, it is. I wrestle with how to embed my designs with a sense of dignity all the time. One thing I do know: having a deep understanding of my customers and their needs is the only way to create systems that really promote a sense of dignity.

I am challenged by this (albeit strongly-worded) quote from Paulo Freire’s Pedagogy of the Oppressed:

“The oppressor is solidary with the oppressed only when he stops regarding the oppressed as an abstract category and sees them as persons who have been unjustly dealt with, deprived of their voice, cheated in the sale of their labor– when he stops making pious, sentimental, and individualistic gestures and risks an act of love… To affirm that men and women are persons and as persons should be free, and yet do nothing tangible to make this affirmation a reality, is a farce”.

How can our stove create a culture of dignity for all the people it touches? In my next post, I’ll talk a little more about this.