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Oscillating eddies help meter gas.

The frequency with which a flag flaps in any given breeze relates to the weight of its fabric. So "if you can tell me how rapidly a flag waves, I can give you a very good estimate of how much the flag weighs or how big it is," says Hassan Nagib of the Illinois Institute of Technology (IIT) in Chicago. Researchers at the school have tapped this principle to design a new residential gas meter.

Unlike current gas meters, the new IIT model contains no moving parts. Indeed, only the metered gas moves. As it enters the meter, the gas slams into a closed, triangular chamber. Finding no exit, the gas stream splits in two and doubles back, creating two counter-rotating vortices. As these whirling eddies push against one another, each alternately grows and shrinks in a pattern of pulsing oscillations.

"Why these oscillations occur was part of Hussein Mansy's Ph.D. thesis," explains David R. Williams. Mansy worked with Williams in the new meter's initial design. A tiny microphone listens for the oscillations -- the gas equivalent of a flapping flag -- and a microprocessor maintains a running tally of each pulse, which corresponds to a unit of methane consumed.

While the new digital devices should simplify installation and long-distance meter reading, size is the main advantage. "The gas industry is sensitive to the fact that its meters are ugly," Williams says. "So we tried to make ours small enough to hide between the studs in an apartment wall." One unit now undergoing tests measures just 50 cubic inches, 1/15th the volume of standard gas meters, notes Carl Griffis of the Chicago-based Gas Research Institute (GRI), which is helping finance development of the new meter. GRI has funded Alnor Instrument Co. in Skokie, Ill., to produce a few more units by year's end for testing to establish the meter's reliability.
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Title Annotation:Technology
Author:Raloff, Janet
Publication:Science News
Article Type:Brief Article
Date:Nov 23, 1991
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