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Acoustic Gas Compressor / Expander

Generate sound to compress gas, or expand gas to harness sound
  [vote for,

This idea can be used for compression of gases, pumping of liquids, or turning a fluid pressure differential into electrical power.

First, gas compression / liquid pumping:

Take two pipes, and connect them in an acute V shape. At the point where the axes of the pipes intersect, place a high efficiency piezoelectric speaker.

At the other end of each pipe, place a valve which can be efficiently opened and closed at the frequencies that the PZ speaker can most efficiently produce sound (Somewhere around 1MHz, I think), and which can pass a good amount of fluid through when opened. These valves would be opened and closed by linear PZ actuators.

I'm thinking the valves would be similar to the valve in an auxetophone, but there might be something more modern and efficient.

Have the speaker make sound at high volume and at it's optimal efficiency, and the valves open and close at that same frequency.

The phase of the speaker relative to the intake valve is continuously adjusted so that the low pressure portion of each sound wave reaches the valve as the valve opens, and the high pressure portion of each sound wave reaching the valve as the valve closes.

The phase of the output valve relative to the speaker is also continuously adjusted, but so that the high pressure portion of the wave reaches the valve as the valve opens, and the low pressure portion of the wave reaches the valve as the valve closes.

The maximum possible pressure difference between input and output will hopefully come close to the amplitude of the sound waves.

The reason why dynamic adjustment is needed is because the speed of sound in a fluid changes as that fluid's temperature changes.

For converting a fluid pressure differential into electrical energy:

Opening and closing the input valve (particularly with a pressure differential across it) will of course produce sound waves.

A portion of each sound wave will bounce off of the piezoelectric mic and continue to the output valve; a portion of each sound wave striking the mic gets converted to electricity. Some of the sound, of course, will bounce off, but that's not particularly harmful here, as some of the bounced sound will go back to the input valve, and then return here, and some of the sound will go to the output valve, then return here.

The output valve for the expander will do what the input valve did in compressor/pump; namely bounce back the high pressure part of each sound wave, while being open for the low pressure part of each sound wave. Since energy is being removed (not added) by the PZ speaker, the pressure of the low pressure part of the sound wave will be higher than the fluid pressure beyond the valve.

For converting liquid pressure into electricity (or for pumping liquids), it should be possible to get pretty good efficiency with a single stage.

For converting gas pressure into electricity (or for compressing a gas), multiple stages will be necessary for efficiency.

What's the big deal? The extremely small number of moving parts, and the direct-to-electricity aspect.

Let's suppose we want to build a toy steam engine using this tech: there are two valves and a speaker for the feedwater pump, then the boiler, and two valves and a piezoelectric mic for the expander, then a condenser. If we want a compound steam engine, each additional stage of expansion requires one additional mic and one additional valve.

The PZ speaker and mics need no seals, and thus should last longer than the rest of the system. The valves could be given permanent hydrophobic coatings, which would allow the water / steam to act as a lubricant, which would allow the valves to last for a very long time too.

There is a downside: our toy steam engine has no visibly moving parts, makes no audible sound (humans can't hear the 1MHz vibrations), and can't spin a wheel unless we hook up the output to an electric motor. Thus, it's not an exciting toy to look at.

goldbb, Jul 20 2011

Los Alamos web page about thermoacoustics http://www.lanl.gov...coustics/index.html
[j paul, Jul 21 2011]


       Are you sure about the efficiency?
Zimmy, Jul 21 2011

I am posting a link to a Los Alamos web page about thermoacoustics, i'm no expert but it might work better than using piezo.
j paul, Jul 21 2011

       Bun for making me look up auxetophone.
RayfordSteele, Jul 21 2011

       A mechanical valve that operates at 1 MHz ?
VJW, Jul 21 2011

       j_paul, although acoustics are definitely involved, and compression of a gas generates a temperature rise, and thus "thermo-" is involved, this idea is totally unrelated to other thermoacoustic devices.   

       VJW, the auxetophone (invented in 1906) had a valve which could operate at a high enough speed to produce a wide range of human-audible frequencies, and with a century of engineering improvements between then and now, I think it might be possible.   

       For that matter, I would expect that the auxetophone's valve's design should be able to work -- namely, take two plates, create small openings through both plates (the openings must line up, of course), mount one plate in a fixed manner, and use power to move the other plate.   

       The size of the holes would of course need to be small enough so that the displacement of the PZ will suffice to open and close the valve, and lubrication would be needed to minimize the amount of energy needed to open and close the valve.   

       Since PZ linear actuators have a range of motion of about 90 μm, the holes would need to be about this size. I'm fairly certain it would be possible to manufacture holes this size in a pair of plates. As for lubrication... I'm not really certain. Ceramics, maybe?
goldbb, Jul 28 2011


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