Cook Stove

Blog Post – Cook stove

A few weeks ago we were presented with the challenge of designing a charcoal cook stove to be used in Nicaragua.  The goal of the stove would be to reduce the harmful emissions and gasses that currently fill homes as a result of cooking.  By virtue of the charcoal its self, the emissions are reduced, so we needed to design a stove that would have the same or better cooking capacity and efficiency when compared to the current wood stoves that are used. 

Initially, we developed a few main categories to focus our design efforts:

·      Good heat control

·      Effective ash disposal

·      Multi-purpose cooking surface

·      Solid structure

·      Aesthetically pleasing

In order to create a successful stove, it was determined that we would need pick a specific point we wanted to focus on, and leave the rest to become details around that point. 

Some of our original brainstorming.

Knowing that aesthetics are an important factor in a product’s success rate in the third world, we chose to focus on a stove that would appear large and powerful, but be efficient and ensure that the entire physical stove had a purpose.  We began with a very simple box design that would be large enough to hold two pots.  Given the fact that the current Nicaraguan cook stoves have the capability of cooking two pots at once, we felt that having only one cooking surface would be viewed as a down-grade and not amply used.  Furthermore, once we determined that there would be room to cook two separate items, we decided to make a stove with two different cooking surfaces.  One surface would be for pots and large items that cannot fall through a grated surface, and the other would be a solid surface, like a hot plate, on which people could cook tortillas, or keep things away from the flame if necessary.  Because there were two distinct cooking surfaces, we also wanted to be able to isolate one surface if only one pot was being cooked.  To do this, we needed to split the large box into two smaller compartments.  By simply putting a metal divider down the middle of the stove, we figured we could accomplish this task.  Thus, in choosing to focus on the aesthetics, we had already began to incorporate other important factors. 

            Once we had a basic design, a box-like structure that had a multi-purpose cooking surface, there were two other main points we had to consider.  Heat flow, and ash disposal are two points that could either make or break the functionality of our stove.  With inadequate heat flow, the stove would be inefficient, and people would have to burn more charcoal than necessary to cook, thus increasing the gaseous emissions, and giving people a product that is not as good as what they currently have.  Additionally, if the ashes are not contained properly, people are left with a mess in their kitchen and an unsanitary and unpleasant eating environment.  To tackle the problem of heat flow, we wanted to make sure that the charcoal was close to the cooking surface and only small amounts of useable heat escaped.  Our initial thinking was that having a box structure would be relatively good at insulating, and if the charcoal was close to the surface, it was almost guaranteed that all possible heat was being captured.  So given that we would not have a problem with insulation, we wanted to have a way to change the temperature of the stove, by letting some of the heat escape.  We sketched different doors that would slide along the side of the stove, with adjustable heights to let more or less air out, then we moved to vents that would be around a half inch on each portion of the stove, but we determined that the construction of the vents would be too difficult, and very hard to replicated or repair.  We concluded that we would have quarter circle doors that would rotate 90 degrees to reveal a quarter circle hole in the side of the stove.  In the final design and testing phases, we found that our vision did not match our product, and heat flow (in terms of insulation) was in fact the weakest element of our design. 

The problem of Ash disposal was definitely our most heavily deliberated and very unclear in our initial design.  Our original box shape did not incorporate any form of stand, or collection mechanism for the ashes.  We originally were thinking that the ash would just fall out of the bottom, but we weren’t sure where it would go.  As we observed other stove designs, both online and in the class room, we quickly realized that having a box sitting on the ground, with no airflow from the bottom, and no place for the ashes to fall would be a problem.  We spent some time thinking about different mechanisms, like trays, and collection bins; however, we encountered many trade offs between the difficulty to manufacture these items and the minor function they would serve.  So we went back and asked ourselves if it was truly necessary to have a way of cleanly disposing the ashes.  Obviously we all agreed that we couldn’t just have them flying everywhere, they would have to be contained, but it would be okay if they just fell to the ground.  Then we determined that there would be bricks available in Nicaragua, and it would be reasonable to assume everyone has access to bricks.  Thus, we would use bricks to elevate our stove, form a base, and a closed area in which the ashes would fall. 

Our final sketch:

The sketch has vents, as opposed to quarter-circle doors for increased airflow.

   

         

As we moved on to our cardboard sketch, we realized how limited we were in terms of our ability to connect materials, meaning that the stove would have to be held together by rivets so everything would have to be at right angles with extra material to make the folds.

Before we began to build or stove, now named the Power Stove 2, (PS2), we determined the made our final detentions and chose to have the sides composed of two pieces of sheet metal with a piece of Masonite in the middle for extra support and insulation.

Dimensions:                                       Materials:

2 feet long                                          Sheet metal; around the sides and the alternative cooking surface

1 foot wide                                         Masonite; around the side

6 inches wide                                    Chicken wire; top and bottom grates

                                                            Metal rods; to support the pot on the top grate

                                                            Rivets; to hold the stove together

Cost of stove;

Sheet metal:

Used approximately 72 inches X 14 inches for the base, 2(10X10) for the cooking surface; costs approximately $0.02 for 1 square inch; used 1208 square inches, costs $24.16

Masonite:

Used approximately 72 inches X 5 inches for insulating the sides; costs approximately $0.02 for 1 square inch; used 360 total inches

$7.2

Chicken Wire:

Used 12 inches X 24 inches for both the top and bottom grates, so there were a total of 2(12 X 24) square inches; costs $0.005, half of a penny, per square inch, total of 576 square inches

$2.88

Metal Rods

Used a total of 84 inches (7 feet) of metal rods that were 1/8 inch in diameter; cost is $0.63 per foot of rod

$4.41

Rivets

Used a total of 20 rivets

$1.28

Total cost of our stove = $39.93

Our final design consist of two layers of sheet metal, 6 inches tall, with a piece of Masonite in-between.  There are two vents on the front of the stove that can be opened or closed as much or as little as one wishes.  The vents are large enough to add charcoal to the fire without needing to take off the top grate.  There is one piece of sheet metal in the middle of the stove that serves as a divider between the two sections of the stove, to ensure that if one is only using half of the stove, only one half of the stove will be heated.  The bottom of the stove is simply one sheet of chicken wire attached to the base of the sides that have been folded over to allow the pieces of the stove to fit together properly.  The chicken wire is attached to the stove by woven small wire.  The top grate is completely removable.  It consists of a piece of chicken (1 foot by 2 feet) wire with 10-inch metal rods attached (by weaving the rods through the wire) at approximately 4-inch increments.  On one half of the top, however, there are two pieces of 10 X 10 inch sheet metal sandwiched together with rivets that serve as an alternative-cooking surface for items like tortillas. 

The final design of our stove was much larger than we had anticipated.  The stove can definitely hold any sized pot, and will be able to support it, however, it may be slightly inefficient for heating up small pots.  The bottom is very open and there is a lot of airflow, so all of the heat is not funneled upwards toward the desired location.  Thus, the vents were not entirely necessary for airflow, however, they were very good for accessing the charcoal & fire without needing to take the entire stove apart.  When we tested our stove, we loaded the charcoal through the vents and re-lit the flame using the vents while our pot was still sitting on the stove.  Shortening the body of the stove would have also made the stove more efficient, seeing that the charcoal would be closer to its targeted destination.  Our brick base did adequately contain the ashes (although there were hardly any to contain) and having the bricks along the sides of the stove served as an extra layer of insulation and support.  Overall, our stove successfully supported the pot and would have (most likely) done an adequate job boiling the water, if the weather was more like Nicaragua.  Aesthetically, we succeeded in producing a powerful-looking product, one that looks like it will function well and is desirable to have as an object in one’s home.  We have a multi-purpose cooking surface and effective ash disposal.  The only point for which we were slightly off the mark was the effective heat control.  We thought we were going to need a way to lower the heat, but it turns out that we now need a way to keep it hot!