Two scientists in India have produced a tiny voltage in a small electrical
circuit by blowing gas across a mat of carbon nanotubes and doped semiconductors.
This result arises from two physical effects.
First, in the Bernoulli effect, gas rushing past a surface produces
pressure differences along streamlines, which in turn can produce a
temperature gradient along a material sample.
Second, in the Seebeck effect, a temperature gradient (the far ends
of the material being at different temperatures) can generate a voltage
difference across the sample.
In the experiment of Professor Ajay.K. Sood and his graduate student
Shankar Ghosh at the Indian Institute of Science (Bangalore) gas is
blown over a mat of carbon nanotubes as well as doped silicon and germanium.
With a small sliver of germanium as a sample, a voltage difference of
650 micro-volts was generated. The power flow amounted to 43 nano-watts.
This doesn't sound like much power, and the researchers have not yet
determined whether the effect could be scaled up (a no-moving-parts
carbon nanotube/doped-semiconductor generator of electricity), but one
definite near-term application would be in a new type of gas flow velocity
sensor for research in problems of turbulence or aerodynamics.
Compressed air was used to produce the tiny amount of electricity,
but even human breath blown at the inclined sample produced a measurable
result of several micro-volts. (Sood
and Ghosh, Physical Review Letters, 20 August 2004; firstname.lastname@example.org,