Sunday, March 4, 2018

Carbon Cool

In 2009 a team of Engineering Students from Michigan State University traveled to a workshop organized by the Appropriate Technology Collaborative in Quetzaltenango, Guatemala. Their task: a refrigerator that can be built from locally available materials almost anywhere and run without power.

Design an adsorption refrigerator capable of maintaining a temperature between 2°C and 8°C that utilizes passive solar energy and can be built in developing countries. The team’s final product will be a clear and comprehensive set of instructions for building the device.
The students built a vaccine refrigerator that does not use electricity. It does not have any moving parts. You simply place it in the sun and it chills or freezes things.

This very remarkable machine runs on pyrolytic carbon. The char does not need to be food grade, as for biochar or activated carbon. It stays inside a closed loop. It could be cascade carbon from a variety of feedstocks. Its essential service is evaporative cooling. The total cost for the prototype was $917.39. Estimated worker cooperative production cost at the scale of three per month, including labor, would be under $300. Their report reads:
Based on the design decision matrices, a solar-powered adsorption refrigerator was selected for the design of the vaccine refrigerator. This refrigerator has no moving parts aside from a few valves. It uses no toxic materials, generally available materials, and should be simple to build and operate. The refrigerator has an intermittent cycle. It will “charge” during the day and remove heat from a cooling volume at night.

Some previously used adsorbent/refrigerant pairs used for solar adsorption refrigeration systems are zeolite and water, silica gel and water, activated carbon and methanol, activated carbon and ammonia, and activated carbon and ethanol. It has been determined that the performance of each pair depends greatly on the climate in which it is tested. Read More