Harry Veeder wrote:
> A sound way to turn heat into electricity
>
> http://forum.physorg.com/index.php?showtopic=15401
>
>
> University of Utah physicist Orest Symko holds a match to a small heat
> engine that produces a high-pitched tone by converting heat into sound.
> Symko's research team is combining such heat engines with existing
> technology that turns sound into electricity, resulting in devices that can
> harness solar energy in a new way, cool computers and other electronics.
> Credit: University of Utah
>
> University of Utah physicists developed small devices that turn heat into
> sound and then into electricity. The technology holds promise for changing
> waste heat into electricity, harnessing solar energy and cooling computers
> and radars.
>
> Five of Symkos doctoral students recently devised methods to improve the
> efficiency of acoustic heat-engine devices to turn heat into electricity.
> They will present their findings on Friday, June 8 during the annual meeting
> of the Acoustical Society of America at the Hilton Salt Lake City Center
> hotel.
>
> Symko plans to test the devices within a year to produce electricity from
> waste heat at a military radar facility and at the universitys
> hot-water-generating plant.
>
> The research is funded by the U.S. Army, which is interested in "taking care
> of waste heat from radar, and also producing a portable source of electrical
> energy which you can use in the battlefield to run electronics" he says.
>
> Symko expects the devices could be used within two years as an alternative
> to photovoltaic cells for converting sunlight into electricity. The heat
> engines also could be used to cool laptop and other computers that generate
> more heat as their electronics grow more complex. And Symko foresees using
> the devices to generate electricity from heat that now is released from
> nuclear power plant <http://www.physorg.com/news100141616.html#> cooling
> towers.
>
> How to Get Power from Heat and Sound
>
> Symkos work on converting heat into electricity via sound stems from his
> ongoing research to develop tiny thermoacoustic refrigerators for cooling
> electronics.
>
> In 2005, he began a five-year heat-sound-electricity conversion research
> project named Thermal Acoustic Piezo Energy Conversion (TAPEC). Symko works
> with collaborators at Washington State University and the University of
> Mississippi.
>
> The project has received $2 million in funding during the past two years,
> and Symko hopes it will grow as small heat-sound-electricity devices shrink
> further so they can be incorporated in micromachines (known as
> microelectromechanical systems, or MEMS) for use in cooling computers and
> other electronic devices such as amplifiers.
>
> Using sound to convert heat into electricity has two key steps. Symko and
> colleagues developed various new heat engines (technically called
> "thermoacoustic prime movers") to accomplish the first step: convert heat
> into sound.
>
> Then they convert the sound into electricity using existing technology:
> "piezoelectric" devices that are squeezed in response to pressure, including
> sound waves, and change that pressure into electrical current. "Piezo" means
> pressure or squeezing.
>
> Most of the heat-to-electricity acoustic devices built in Symkos laboratory
> are housed in cylinder-shaped "resonators" that fit in the palm of your
> hand. Each cylinder, or resonator, contains a "stack" of material with a
> large surface area such as metal or plastic plates, or fibers made of
> glass, cotton or steel wool placed between a cold heat exchanger and a hot
> heat exchanger.
>
> When heat is applied with matches, a blowtorch or a heating element the
> heat builds to a threshold. Then the hot, moving air produces sound at a
> single frequency, similar to air blown into a flute.
>
> "You have heat, which is so disorderly and chaotic, and all of a sudden you
> have sound coming out at one frequency," Symko says.
>
> Then the sound waves squeeze the piezoelectric device, producing an
> electrical voltage. Symko says its similar to what happens if you hit a
> nerve in your elbow, producing a painful electrical nerve impulse.
>
> Longer resonator cylinders produce lower tones, while shorter tubes produce
> higher-pitched tones.
>
> Devices that convert heat to sound and then to electricity lack moving
> parts, so such devices will require little maintenance and last a long time.
> They do not need to be built as precisely as, say, pistons in an engine,
> which loses efficiency as the pistons wear.
>
> Symko says the devices wont create noise pollution. First, as smaller
> devices are developed, they will convert heat to ultrasonic frequencies
> people cannot hear. Second, sound volume goes down as it is converted to
> electricity. Finally, "its easy to contain the noise by putting a sound
> absorber around the device," he says.
>
> Studies Improve Efficiency of Acoustic Conversion of Heat to Electricity
>
> Here are summaries of the studies by Symkos doctoral students:
>
> -- Student Bonnie McLaughlin showed it was possible to double the efficiency
> of converting heat into sound by optimizing the geometry and insulation of
> the acoustic resonator and by injecting heat directly into the hot heat
> exchanger.
>
> She built cylindrical devices 1.5 inches long and a half-inch wide, and
> worked to improve how much heat was converted to sound rather than escaping.
> As little as a 90-degree Fahrenheit temperature difference between hot and
> cold heat exchangers produced sound. Some devices produced sound at 135
> decibels as loud as a jackhammer.
>
> -- Student Nick Webb showed that by pressurizing the air in a similar-sized
> resonator, it was able to produce more sound, and thus more electricity.
>
> He also showed that by increasing air pressure, a smaller temperature
> difference between heat exchangers is needed for heat to begin converting
> into sound. That makes it practical to use the acoustic devices to cool
> laptop computers and other electronics that emit relatively small amounts of
> waste heat, Symko says.
>
> -- Numerous heat-to-sound-to-electricity devices will be needed to harness
> solar power or to cool large, industrial sources of waste heat. Student
> Brenna Gillman learned how to get the devices mounted together to form an
> array to work together.
>
> For an array to efficiently convert heat to sound and electricity, its
> individual devices must be "coupled" to produce the same frequency of sound
> and vibrate in sync.
>
> Gillman used various metals to build supports to hold five of the devices at
> once. She found the devices could be synchronized if a support was made of a
> less dense metal such as aluminum and, more important, if the ratio of the
> supports weight to the arrays total weight fell within a specific range.
> The devices could be synchronized even better if they were "coupled" when
> their sound waves interacted in an air cavity in the support.
>
> -- Student Ivan Rodriguez used a different approach in building an acoustic
> device to convert heat to electricity. Instead of a cylinder, he built a
> resonator from a quarter-inch-diameter hollow steel tube bent to form a ring
> about 1.3 inches across.
>
> In cylinder-shaped resonators, sound waves bounce against the ends of the
> cylinder. But when heat is applied to Rodriguezs ring-shaped resonator,
> sound waves keep circling through the device with nothing to reflect them.
>
> Symko says the ring-shaped device is twice as efficient as cylindrical
> devices in converting heat into sound and electricity. That is because the
> pressure and speed of air in the ring-shaped device are always in sync,
> unlike in cylinder-shaped devices.
>
> -- Student Myra Flitcroft designed a cylinder-shaped heat engine one-third
> the size of the other devices. It is less than half as wide as a penny,
> producing a much higher pitch than the other resonators. When heated, the
> device generated sound at 120 decibels the level produced by a siren or a
> rock concert.
>
> "Its an extremely small thermoacoustic device one of the smallest built
> and it opens the way for producing them in an array," Symko says.
>
> Source: University of Utah
>
> http://www.physorg.com/news100141616.html
Other than the not exactly original idea to make these devices smaller,
I don't see what's new here.
M.
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