The Solution

An Intermediate Technology

From the data gathered by previous Cal Poly student groups, in addition to our own research, we've deduced the best materials from which to assemble our food storage device. This device is very cheap, and requires no electricity, so already it has the potential to be much more effective than a refrigerator in Sierra Leone, where there is very little electric power. It bridges the gap between traditional methods of storing foods and modern refrigeration technology. This is why we refer to it as an "intermediate technology".

The device consists of three parts: a protective, thermally insulating outer container, an inner airtight container, and a desiccant (hydrophilic drying agent). For additional cooling, one may bury the entire assembly partially underground.

For the outer protective container, one may use a clay pot, a steel can, or any strong container with similar thermal properties.
For the inner airtight container: a Ziploc or similar bag works best. These can be nested inside each other if a better seal is needed.
As desiccant: Silica gel packets are the best choice.

Although previous students found that Calcium Chloride is the most effective desiccant in terms of ability to reduce the level of humidity, we chose to use Silica gel packets instead.

This is mainly due to the health risk. Calcium Chloride is quite toxic, while Silica gel, although dehydrating, is much safer.

Additionally, Calcium Chloride comes in bulk powder form and would require an additional material to package, and thus an extra cost. This material is also only available in bulk quantities, and we could not find any for sale in Africa. Meanwhile, Silica gel is readily available in places that sell packaged foods.

The final reason that we chose Silica gel over Calcium Chloride was that Silica gel is easily rechargeable. It can be recharged when placed in a baking sheet in an oven set to 275 degrees Fahrenheit for one hour. This should work in a pot or pan as well, as long as the temperature does not exceed 275 F. (This is the high end temperature suggested by silica gel manufacturers). More tests should be done to discover the best way to recharge these packets using as little technology as possible.

Another possible design that we scrapped was the option of using aluminum oxide bags for the airtight container. Although they allow much less moisture to permeate the bag, they would not provide a noticeable improvement in the function of the device. Most of the humidity enters the bag when it is opened for cooking purposes, rather than passively through the material. Additionally, AlOx bags are not currently being sold (to the best of our knowledge), so we would have to manufacture them ourselves.