Acoustic Stove Could Aid Third World

type size: [A] [A] [A]

May 25, 2007 — An appliance being designed for developing communities in Africa and Asia not only generates electricity, but also cooks and cools using acoustic technology.

The "Stove for Cooking, Refrigeration and Electricity," or SCORE, could help improve the health and quality of life for the two billion or so people in the world who cook over open fires. When used in enclosed places, smoke from such fires can cause health problems. 

And these stoves are notoriously inefficient. A person can spend two hours a day collecting wood to burn in a fire that is so wasteful that 93 percent of the energy generated, literally, goes up in smoke.

"We make the burning more efficient so that they use less wood and have more time to spend on other things like education," said Paul Riley, the project director at the University of Nottingham in the United Kingdom.

The efficiency comes from a technology known as thermoacoustics, which produces sound waves from heated gas and then converts them to electricity.

Here's how it works: wood is placed inside the stove and burned. The fire heats compressed air that has been pumped into specially shaped pipes located inside the stove's chimney and behind the stove.

The heated air begins to vibrate and produce sound waves. Inside the pipes, the noise is 100 times louder than a jet taking off. But because the pipes are stiff and do no vibrate, the sound waves have nowhere to go. So outside the pipe, people hear only a faint hum.

The sound waves vibrate a diaphragm located at the end of the pipe. The diaphragm is attached to a coil of metal wires that sit inside a magnet. As the wire coil vibrates — about 50 times per second — it generates an electrical current, which is captured by wires and converted to the proper voltage.

The stove has electrical sockets, where the homeowner can plug in, for example, a mobile phone for charging. Or she can sell the electricity as a phone-charging service.

"In Bangladesh, people could use the electricity to power lights, radio or educational equipment, for example, computers," said professor Choudhury Mahmood Hasan, chair of the Bangladesh Council of Scientific and Industrial Research in Dhaka.

For refrigeration, the heated, compressed air is sent through a different part of the pipe, where sound waves cause the air to expand. As it expands, it cools to a temperature that can produce ice. It takes about two hours of stove use to produce enough ice that will keep the fridge cold for 24 hours. But homeowners have the option of producing more ice to sell for income.

Riley and his team want to involve local universities to train a labor force that can build and manufacture most of the parts needed to make the stove. In five year's time, they hope to be churning out about 1 million stoves a year that each sell for $30 to $40.