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not_important
International Hazard
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High power ultrasonic generators (or even audio frequency) cause cavitation, this is not boiling in the same sense as happens when you heat water.
The pressure wave from the sound source drops the pressure in a region so microscopic bubbles expand, or with high enough intensities pulls the liquid
apart forming a pocket of vacuum. In either case the liquid does evaporate into the low pressure bubble, which removes some energy from the adjacent
fluid. But the pressure wave soon reverses, collapsing the bubbles with the generation of heat. The bulk liquid does not cool down, indeed it heats
up from the energy being pushed into it.
Humidifies don't 'boil' the bulk water through cavitation, they atomise the surface of it. This can be done by flowing a film of water across a
vibrating sheet which disperses the water as very fine droplets. Alternatively they can use enough energy to do the same thing at the surface of bulk
water. If you wish you can think of it as cavitation happening at the water's surface, but it's not boiling into vapour but being broken into
droplets.
These droplets evaporate as they diffuse into the surrounding atmosphere, which does generate cooling. However this cooling occurs where the mist of
droplets evaporates, not in the bulk liquid.
Again, the energy for these effects comes from the sonic energy pushed into the liquid, not from the liquid's basic thermal energy. The fluid heats
up from the sound energy being shoved into it,
The high voltage in CRT displays generally comes from the flyback circuit, meaning it's tied to the horizontal deflection. The HV section is tuned to
work optimally at that frequency, and generally is designed to produce only a very low current; as a safety feature many designs will shut down if too
much current is drawn.
The excitation frequency and output impedance of the voltage source must be matched to the transducer used. Wrong frequency means little or no
output, and possible damage to the signal source. Wrong impedance means the same thing, if the transducer needs high voltage then too low drive
voltage means weak output; too high drive voltage means excessive current draw with damage to driver and/or transducer a distinct possibility.
http://www.kronjaeger.com/hv/hv/src/fly/index.html
You've not discussed how you hope to reject the heat you extract. You talk about hundreds of watts of heat, a low IC case temperature - say 50 C, and
eexpect to reject this into the 20 C atmosphere.
[Edited on 22-7-2009 by not_important]
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Shingoshi
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The heat is pumped outside...
Quote: Originally posted by not_important  | High power ultrasonic generators (or even audio frequency) cause cavitation, this is not boiling in the same sense as happens when you heat water.
The pressure wave from the sound source drops the pressure in a region so microscopic bubbles expand, or with high enough intensities pulls the liquid
apart forming a pocket of vacuum. In either case the liquid does evaporate into the low pressure bubble, which removes some energy from the adjacent
fluid. But the pressure wave soon reverses, collapsing the bubbles with the generation of heat. The bulk liquid does not cool down, indeed it heats
up from the energy being pushed into it.
Humidifies don't 'boil' the bulk water through cavitation, they atomise the surface of it. This can be done by flowing a film of water across a
vibrating sheet which disperses the water as very fine droplets. Alternatively they can use enough energy to do the same thing at the surface of bulk
water. If you wish you can think of it as cavitation happening at the water's surface, but it's not boiling into vapour but being broken into
droplets.
These droplets evaporate as they diffuse into the surrounding atmosphere, which does generate cooling. However this cooling occurs where the mist of
droplets evaporates, not in the bulk liquid.
Again, the energy for these effects comes from the sonic energy pushed into the liquid, not from the liquid's basic thermal energy. The fluid heats
up from the sound energy being shoved into it,
The high voltage in CRT displays generally comes from the flyback circuit, meaning it's tied to the horizontal deflection. The HV section is tuned to
work optimally at that frequency, and generally is designed to produce only a very low current; as a safety feature many designs will shut down if too
much current is drawn.
The excitation frequency and output impedance of the voltage source must be matched to the transducer used. Wrong frequency means little or no
output, and possible damage to the signal source. Wrong impedance means the same thing, if the transducer needs high voltage then too low drive
voltage means weak output; too high drive voltage means excessive current draw with damage to driver and/or transducer a distinct possibility.
http://www.kronjaeger.com/hv/hv/src/fly/index.html
You've not discussed how you hope to reject the heat you extract. You talk about hundreds of watts of heat, a low IC case temperature - say 50 C, and
eexpect to reject this into the 20 C atmosphere.
[Edited on 22-7-2009 by not_important] |
This post of yours was very informative. However I should also inform you there will be either an external condenser or radiator to dispense with the
heat of the system. The heat will not be kept inside the case. This will be the only "breach" in the environment, with bulkhead fittings providing for
the transfer of coolant in and out of the case.
Now, I'll read the rest of your post.
Shingoshi
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Shingoshi
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I admit, I don't know a thing about this!!
| Quote: Originally posted by stygian | | I recently caught the notion that one could potentially use antenna ferrites as a magnetostrictive element submersed in a reaction mixture in a vessel
surrounded by a coil. No idea how magnetostrictive said common ferrites are, and corrosion resistance would surely be an issure, but it was an idea.
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So I'm probably asking a stupid question. But since you mentioned the use of antennas, I was wondering if an antenna could be placed directly in the
liquid? There are antennas specifically designed for marine use, which I believe would deal with the issue of corrosion. Could a UHF antenna be used
as the radiator in this case? I could easily get one and mount it in the bottom of my coolant chamber. What would it take for an antenna to drop it's
energy into the liquid?
Shingoshi
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not_important
International Hazard
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You are assuming that those antennas show magnetostrictive properties, to start with. If it does, then it needs to be acoustical impedance matched to
the liquid to effectively couple the energy. That's why many ultrasound probes have a tapered horn, to better match the transducer to the liquid.
Also note that ultrasound is often used for cleaning, and stripping coatings off of objects. I think that you will find that those antennas have
plastic coatings...
As for cooling, from http://home.att.net/~Berliner-Ultrasonics/uson-4a.html#cooli...
| Quote: | | one problem that also plagues researchers is that the energy imparted to liquid samples rapidly translates into heat, raising the temperature of the
sample and degrading the components. The most obvious solution (another pun?) is to reduce the intensity of sonication, often quite unacceptable;
another is to place the sample vessel (test tube, beaker, etc.) in a cooling bath. |
Other useful links there include http://home.att.net/~Berliner-Ultrasonics/uson-4a.html#usfou... and ULTRASONIC CAVITATION http://home.att.net/~Berliner-Ultrasonics/uson-0.html#AL1V
I think that you will find the best way to do evaporative cooling is to pick the fluid and operating pressure to give boiling at the desired
temperature, and to provide a surface that encourages boiling as small bubbles as you want to avoid formation of a film of gas between the liquid and
the surface to e cooled.
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Shingoshi
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Location: Salem, Oregon
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I think I'm going to abandon this idea...
| Quote: Originally posted by not_important | You are assuming that those antennas show magnetostrictive properties, to start with. If it does, then it needs to be acoustical impedance matched to
the liquid to effectively couple the energy. That's why many ultrasound probes have a tapered horn, to better match the transducer to the liquid.
Also note that ultrasound is often used for cleaning, and stripping coatings off of objects. I think that you will find that those antennas have
plastic coatings...
As for cooling, from http://home.att.net/~Berliner-Ultrasonics/uson-4a.html#cooli...
| Quote: | | one problem that also plagues researchers is that the energy imparted to liquid samples rapidly translates into heat, raising the temperature of the
sample and degrading the components. The most obvious solution (another pun?) is to reduce the intensity of sonication, often quite unacceptable;
another is to place the sample vessel (test tube, beaker, etc.) in a cooling bath. |
Other useful links there include http://home.att.net/~Berliner-Ultrasonics/uson-4a.html#usfou... and ULTRASONIC CAVITATION http://home.att.net/~Berliner-Ultrasonics/uson-0.html#AL1V
I think that you will find the best way to do evaporative cooling is to pick the fluid and operating pressure to give boiling at the desired
temperature, and to provide a surface that encourages boiling as small bubbles as you want to avoid formation of a film of gas between the liquid and
the surface to e cooled.
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I'm looking into something else to do the job. Something which I know will work, but only needs some modification for my purposes.
Shingoshi
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12AX7
Post Harlot
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Ferrites are only very slightly magnetostrictive (ppm level?). Enough that they whine when driven with an audio frequency (like 10kHz), but in
general, not enough to do anything with. And instead of lots of current to swing the voltage, you need lots of voltage to swing the current --
efficiency is still low. Piezoelectrics probably have the best electrical efficiency, after proper motors (i.e., a voice coil).
I did once crack a high-mu ferrite toroid when it reached saturation. Broke into very regular bits, perpendicular breaks, regularly spaced. Never
seen it happen again, could've been internal stresses that helped.
Tim
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Texium
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