Improve the Haber process

See if ultrasonic cavitation can be used to fixate atmospheric Nitrogen less expensively than the Haber process.

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The Haber process converts Hydrogen (from natural gas) and atmospheric Nitrogen into ammonia. It supplies a reliable source of nitrogen for fertilizers and is responsible for quadrupling agricultural crop yields in the last century. The process uses 1% of all energy worldwide, as it sustains roughly 40% of the population.

The process runs at 400°C and pressures of 200 atmospheres, and is energy intensive. The compressors and reaction vessels are wildly expensive and wear out over time, a great deal of energy is used for compression and heating, and the resulting yield is only about 15%.

Using ultrasonic cavitation, it may be possible to create the conditions for nitrogen fixation in a simpler manner, and using simpler equipment.

For this project I intend to design and build a system capable of ultrasonic cavitation within a reaction vessel, see if it's possible to convert Nitrogen and Hydrogen into ammonia, and see if this can be done more efficiently than Haber.


A home-built ultrasonic system that can be used for:

  • Ultrasonic mixing
  • Drilling
  • Plastic welding
  • Ultrasonic levitation
  • Sonochemistry
  • Installing metal inserts (in plastic)
  • Experimentation and exploration of cavitation

And to change the world:

  • See if ultrasonic cavitation can fixate Nitrogen less expensively than the Haber-Bosch process

All project information will be open source: schematics, plans, build instructions et. al. will be available on GitHub under the MIT license for the hobbyist to construct their own ultrasonic system.

Additionally, experimental procedures exploring the Haber process will be described in enough detail to allow other researchers to recreate the experiments.

Current Status

I have a working home-built ultrasonic system and demo videos for several of the design goals.

The existing system does levitation, mixing, cavitation, and sonochemistry. Demo videos are in the links section, which should be in the left column of this page.

The system can be built by hobbyists, the power level is adequate for the purpose, it's reasonably safe for casual use, and not difficult to set up and operate. It will power transducers up to 120 watts.

The system will melt plastic, but as yet I haven't been able to get the melt to appear between two sandwiched pieces (welding), or to surround a metal insert. Welding and installing inserts still appear to be achievable goals.

For Nitrogen experiments, I have a Hydrogen generator, a Nitrogen generator, a gas collection system, a mass flow controller, and a reaction vessel. (And a working ultrasonic system that produces cavitation.)

Making Ammonia from Nitrogen

Ultrasonic reaction chamber

The project description gives a good overview of the problem to be solved.

Fixing atmospheric Nitrogen into ammonia (or any other nitrogen-based compound) would reduce the cost of fertilizer worldwide, allowing us to feed more people at less cost, and globally reduce the amount of energy used.

Per calculations in my previous build log, the Haber process produces 17 grams of ammonia using over half a million joules of energy. For comparison, that much energy will run a 100 watt incandescent bulb for over 90 minutes.

That's the number to beat: generate 17 grams in 90 minutes, using 100 watts or less.

Ultrasonic fixation of Nitrogen has been tried before, but my methods are different:

  1. I'm using a parabolic reflector to focus the ultrasonic energy to a high level, and
  2. I'm directly sonicating a bubble instead of relying on dissolved gases

No previous experiments (as far as I can tell) have used this type of setup, so this is unexplored territory.

I'll be experimenting with Nitrogen fixation for the next few years. This is science, there's no guarantee this will work, and it may not work before the end of the contest.

The video below shows cavitation in the reaction chamber.

System Design

The system is a high voltage power supply driving an ultrasonic transducer from eBay.

An Arduino Nano sets the frequency and pulse width of a UC3525 PWM chip, whose output controls a half-bridge power driver that switches 12 volts across the 5 Volt winding of a scavenged ATX power transformer. The output (around 300 volts) drives the transducer.

The actual power delivered to the sample depends on how close the frequency is to the resonant frequency of the transducer. For off-resonance impedance of 1000 ohms, the delivered power is 84 watts at full modulation. At resonance (25 ohms), the supply will reduce the PWM to limit the output to the rated capacity of the transducer, to a maximum 120 watts.

The switcher and driver/ATX output circuits:

Driver circuit

MIT License

This project is released under the MIT license (details here), which means you can do anything you like with the information except patent it.

You can add this to your proprietary project, and doing so will not change your license model.

You can add this to your open source project and doing so will not change your license model.

You can sell this, or make money from a project which incorporates...

Read more »

  • 1 × Ultrasonic Transducer Available from eBay for under $20.
  • 1 × 100mm of 6061 aluminum rod To make a tuned aluminum horn. About $10 on eBay.
  • 2 × ATX power supply One supply for power, one to scavenge the SMPS transformer
  • 1 × Arduino nano Control board interface
  • 1 × UC3525 Pulse width modulator IC
  • 1 × MCP4161 10K Digital potentiometer
  • 1 × MCP4131 50K Digital potentiometer
  • 1 × AD9833 Sin/Square/Triangle generator, About $6 on eBay
  • 1 × ACS712 Hall effect current sensor
  • 1 × PCB, assorted passives Standard fare for an electronics project

View all 11 components

  • Reboot / Restart

    Peter Walsh10/27/2016 at 17:57 1 comment


    • Back from vacation, project is on
    • Working on new circuits/boards
    • Anyone have suggestions for storing/generating Hydrogen?
    • New resonance measuring board in the works

    I took a vacation from the project for about a year, and as part of that I entered the HAD prize with another project (lasercut optics bench) and did a lot of kayaking. The prize project won one of the interim prizes, so that worked out pretty well. The prize money will go towards this project.

    Meanwhile I've been doing research and running down some ideas, and I came up with a new and interesting approach. It's a rather obscure, little-known effect that has not been explored in the literature. Those are the best kind!

    It may be a way to get around the activation energy requirement at room temperature. If it works out, it would be a legitimate advancement worthy of a paper at least.

    I don't want to outline the method quite yet, because it would be easy for some grad student somewhere to "scoop" me on the process: they have access to lots of equipment, while I have to build things up from scratch.

    I am working on the project with renewed vigor, but not focusing on ultrasonic cavitation. The new idea uses ultrasonics indirectly, but it'll be awhile before I can piece together the equipment needed. I have to build some specialized electronics first.

    I have ordered initial PCBs from China, which have arrived (ye gods, PCB boards are cheap!), populated one board, and am using it as an exploration tool to build up more complicated boards.

    (IOW, the board is the raw amplifier, I'll add more electronics, make a new board, and repeat, testing and tuning at each step.)

    If all goes as planned, the system might lead to a new tool that hackers can build. More on that later.

    Also, I purchased a Nitrogen tank and regulator, so using Nitrogen is now much easier.

    I'm still planning on making Hydrogen, which is a pain but Hydrogen can be dangerous and it's easy to make (drop some Aluminum into acid or base). I can reduce the risk by making only as much as needed for testing.

    I'm planning to install a much better ventilation system, should be adequate for small gaseous samples.

    Anyone have suggestions or better ideas for working with Hydrogen?

    I have a new resonance finder circuit that I built into an arduino shield, and I'm casually building up the software for it. It's a semi-portable probe that lets me measure the resonant frequency of transducers and horns. Makes it easy to mill down the horns.

    I haven't uploaded specs or images yet, because ultrasonics are 'kinda tangential to the project right now.

    Dealing with the touchscreen interface is a pain - the display shares I/O pins with the touchscreen, so the touchscreen default Arduino library doesn't work with the display.

    Had to rewrite the 'damn thing from scratch. Still working on that, leisurely.

  • A leisurely blog

    Peter Walsh12/30/2015 at 03:46 2 comments


    The delete image formatting bug, described below, is preventing me from making blog entries.

    I'll pick this up again once it's fixed.

    • is pants
    • Still working on project
    • Got a neat mug for Christmas
    • Back of the envelope calculation is pants

    I have just now discovered that pressing the delete key removes image formatting (float left/right, resize) and size information - when the cursor is positioned anywhere within the post.

    This means that if I discover a typo and want to correct it, pressing the delete key anywhere in the text will remove image formatting tags throughout the post.

    I really wish HAD had implemented one of the various standards, instead of rolling their own system. It's really difficult to interleave text and images in a pleasing manner, and viewing text on a differently-sized monitor makes my careful formatting look like crap.

    The DocuWiki standard, or the MarkDown standard, or even html tags have specific renderings that can be relied upon, and they could have imported an open-source rendering library for any of these standards and saved months of work, debugging, and bug response.

    Still working on the project

    I'm still working on the project. I haven't been idle, I just haven't been blogging about it. Also the holidays came and went (both of them), and I was still a little fried from the contest.

    At this point, I'm 'kinda blocked by the image formatting bug described above.

    I got this for Christmas. The diagram is the bond activation energy for the conversion of Nitrogen and Hydrogen into Ammonia. Ignore the huge images - keeps deleting the image size information.

    Back of the envelope calculation


  • Vacation's over - back to work

    Peter Walsh11/02/2015 at 02:14 0 comments


    • Project vacation is over
    • Diary-style blogs are an interesting motivational technique
    • Original reaction chamber doesn't work as hoped
    • Three new chamber designs in the works
    • Some new "secret sauce" things to try
    • Looking into bubble-sonoluminescence

    Vacation is over

    As mentioned in a previous blog, I took a month vacation from the project to decompress. Keeping up with the Hackaday prize was good in that it held me to a schedule, but bad because the schedule tended to overrule my quality of life.

    Future blog posts will come less frequently - I'm hoping for one a month from now on.

    Public blogging as a motivational technique

    As a scientist-type I'm used to keeping a notebook of experiments, calculations and whatnot. I didn't see the value of this until I actually started doing it - and now I can't imagine doing anything without it. I actually keep 3 notebooks for different categories of my studies: one for the Haber thing, one for tool development, and one for all other projects. Now that I'm doing it, the psychological/motivational benefits of notebook'ing are obvious.

    I've come to wonder if keeping an online "diary" has similar benefits. Here I am writing "dear diary" updates, knowing that 111 people are interested enough to follow my progress and 51 thought it was worthy of a skull.

    Putting yourself in front of people like that has to have an effect on motivation.

    Most science is done in a lab by individuals, and the only others who know what's happening are the lead scientist and perhaps a few team members. The world only finds out when results are published, and if the experiments fail it's not all that embarrassing.

    With the internet we have the opportunity for "performance" science, where a researcher does his thing in front of an audience, and has to show results or get boo'ed off the stage.

    As an added extra, if the audience can throw suggestions and comments at the researcher, answering and defending against objections would more clearly crystallize the concepts in the researcher's mind.

    It's an interesting situation.

    I think I'll continue with the diary-style blogs for awhile and see where it leads.

    As mentioned previously, I expect to be looking into the Haber process for the next couple of years, so this will be an (anecdotal) "experiment-within-an-experiment".

    Reaction chamber doesn't work as hoped

    After much fiddling with bubbles in the reaction chamber, I've concluded that the chamber is not a good design. Currents and eddys within the liquid make it impractical to hold a bubble in the right place.

    The instability is probably due to having an area of focused energy surrounded by a chaotic buffer area. The transducer horn makes a focused rectangular "duct" of pressure within the water, but areas outside the duct are free to flow. This causes currents and eddies which are large enough to grab any bubble and throw it around the chamber willy-nilly.

    So for the next step I'm making new chambers.

    Three new chambers in the works

    One chamber will be acrylic in the shape of the focused duct, with no outside areas to swirl around. Basically, a rectangular chamber with the same profile as the (rectangular) horn end.

    For the second design, I found a pair of Aluminum cylinders at the scrapyard and turned down the inner diameters to the size and shape of the transducer 1:1 horn.

    When filled with water, the cylinders should make a resonance chamber in the form used by researchers. This should let me reproduce experiments from published research.

    The advantage of this type of chamber is that it's easy to tune: simply raise or lower the transducer until the chamber acoustics match the transducer.

    The disadvantage is that you can't see directly into the chamber. I can probably get around this by mounting the chamber on a glass plate and looking through the bottom. A future post will tell whether this...

    Read more »

  • Call for collaborators

    Peter Walsh09/29/2015 at 00:03 0 comments


    .) Call for collaborators

    .) Didn't make the cut

    .) New board design should be better

    .) New reaction vessel should be... interesting

    .) Entropy and the Haber process

    Call for collaborators

    If you'd like to join the project, ask to join my GitHub groups: Sonicators, for people who want to develop and build the system, and/or AmineGroup, for people who want to design and conduct experiments (of any type, not just ammonia ones).

    Or contact me through the

    Didn't make the cut

    The project didn't make it into the next round of the contest. This is a little disappointing, but also a relief - keeping up with the contest requirements takes a fair amount of time and constant stress.

    I'm now free to proceed at a more leisurely pace.

    The intent of the project was to build a system capable of exploring ultrasonic chemistry, and I've done that. I now have 3 systems capable of ultrasonic processing, and can easily make more if needed.

    A big thanks to everyone following the project and who gave feedback and support with skulls and such. I really appreciate the interest, and I hope you enjoyed the build log dialogs.

    Since the project focus will now be on chemistry (and not electronics), I'll be adding build logs at a slower pace, and probably using the GitHub wiki instead of the Hackaday system. I find the Hackaday system very difficult to use, and the results aren't really easy for others to view.

    New board design should be better

    I had frozen the electronics for purposes of the contest: it did all the things I needed it to do, there was no compelling reason to change it.

    Since then, I've come up with some new features that shouldn't be too hard to implement - some things that make the board easier to build, some convenience features, and some for a more robust project.

    1) The board as designed allows the user to sweep the frequency and determine the resonance point of the transducer/horn using a separately plugged input. Having this sweep without plugging/unplugging the transducer would be a convenient feature to have. I think the appropriate choice would be to use a relay on the transducer output that automatically switches the transducer between the low-voltage sweep and the high-voltage power output as needed.

    2) The current design requires a center-tapped SMPS transformer. These are available but uncommon (about 10% of all ATX supplies I've looked at), and being able to use a single-winding device would allow the user to use any transformer of suitable power. Using a pre-made class-d amplifier might accomplish this. A pre-built class-d smplifier board on eBay for around $30 (more or less, depending on power) might suffice, and would reduce the amount of soldering the user has to do.

    3) A higher voltage power supply makes everything easier: the trace widths for 10 amps (12 volts) is around half an inch, which are nigh impossible to route on a board. Printer or laptop power supplies in the 20-40 volt range are available for thin money on eBay ($10). This would allow the circuit board to use thinner traces. Also, the higher input voltage means a higher transducer output voltage, so the system could push more power through an off-resonance transducer.

    All told, the driver board will go through another rev of design, and V2.0 will be easier to build, easier to use, and more robust.

    New hardware has been ordered - waiting for delivery.

    New reaction chamber

    Now that I've got an ultrasonic system, it's time to do some experiments!

    I've discovered that holding a bubble underwater is a hard problem, partly due to physics and partly due to currents in the reaction chamber.

    To get around the latter, I've been mulling over some new reaction chamber designs.

    A type of horn called a "barbell" is sometimes used for ultrasonic processing. It's tuned to the resonant frequency of the transducer, and the weighted ends vibrate back and forth, as expected.

    Additionally, most ultrasonic...

    Read more »

  • Fixing Nitrogen, first attempts

    Peter Walsh09/26/2015 at 22:46 2 comments


    .) Would you purchase an ultrasonic kit?

    .) Kit quick sketch

    .) Making (and holding) a bubble underwater is a hard problem

    Would you purchase a kit?

    My goal for the project was to have a system for exploring the Haber process, which I now have.

    The specs and design files are in the repository, but the project isn't trivial. There's some expertise needed in assembling the electronics, designing and tuning the horn, and setting up the system. Also, a builder would have to make a PCB and purchase components in single quantity from several vendors.

    I was wondering if there's any interest in a kit. I could purchase parts in batch quantities and parcel them out for people to assemble. The kit (listed below) would include a PCB, all components, a transducer, aluminum stock for a horn, and a pre-programmed Nano. The cost would be about $200, which is 4x the cost of materials.

    This is not something I'm planning to do. Sales and marketing is tedious, and I'd much rather be doing experiments and building things.

    ...but if there's enough interest I might be convinced.

    If you would probably purchase a kit 6 months from now for $200, please leave a response below. I'll decide based on the number of responses.

    Kit quick sketch

    A "quick sketch" of what I think would go into the kit. The specifics aren't important (to answer the question), it's just to get a feel for the amount of interest.

    The kit would contain:

    • A PCB
    • All components
    • A pre-programmed Arduino Nano
    • The SMPS power transformer
    • One transducer
    • One 4" length of aluminum rod

    The user would need to:

    • Supply a project enclosure
    • Supply a power supply
    • Make mounting hardware (lasercut acrylic pieces)
    • Turn the rod into a horn, depending on the application
    • Assemble the PCB

    As an alternate kit, levitation doesn't require a horn or tuning. A kit demonstrating ultrasonic levitation would include everything you need, including mounting hardware and power supply, for about the same price (4x the material cost.)

    Making (and holding) a bubble underwater is a hard problem

    Generating and holding bubbles underwater at the end of a tube is hard, due to the dynamics of surface tension.

    Suppose you are holding a large bubble and a small bubble at the ends of a connected tube, by pinching the tubes shut.

    Which of the following happens when you stop pinching the tubes and allow the pressure to equalize?

    1. The large bubble gets smaller, the small one gets bigger
    2. The large bubble gets bigger, the small one gets smaller
    3. The bubbles stay the same

    As it happens, the force due to surface tension is in inverse proportion to the radius, which means that the smaller bubble has a higher pressure (on the inside) than the bigger bubble. The small bubble will contract while the bigger one expands.


    Next consider a tube immersed in water.

    The small surface area across the end of the tube requires a high pressure to start a bubble.

    If the volume of the tube is large relative to the volume of the bubble, then pushing out the bubble will not appreciably change the tube pressure. The tube air is effectively at constant pressure.

    Since a bigger bubble requires less pressure, the constant pressure in the tube tends to overinflate the bubble, eventually causing it to break off and float away. If the pressure is high enough to start a bubble, it's high enough to inflate and eject a bubble.

    So to hold a bubble at the end of a tube, you need to immediately back off on the pressure once the bubble starts to form. This is hard for a human, and pretty much impossible for a computer. I need another method of generating and holding bubbles under water.

    I've got some ideas to try.

    Maybe I don't need to actually *hold* the bubble in place, maybe I can break off a bubble and let it float up into the cavitation focal point. Maybe I can "catch" the bubble on a plate or something. Maybe I can generate the bubble with the tube pointing down instead of up.

    Yep - this is science. Keep trying...

    Read more »

  • Post-contest update

    Peter Walsh09/21/2015 at 21:55 0 comments

    .) New Git repository with everything: hardware, electronics, software

    .) PCB layout is complete, available in GitHub

    .) Sample boards ordered from OSH Park, I should have them October 7th, more or less.

    The new GitHub repository has everything so far: all the hardware files, the schematics, and the software.

    The only thing missing is the PCB layout, only because I'm having so much trouble getting it done with Kicad. This will probably get sorted in the next day or two, then the layout will go up as well.

    The repository is here:

    (NB: Having NO problems with GitGui whatsoever. Git is awesome!)

    PCB layout is complete, the board files are available in the repository.

    The board was ordered from OSH park, I should get the prototypes back around October 7th, more or less, then I can see if populating the board will result in a working system.

    OSH Park has a wonderful interface! It's completely seamless, and very informative. E-mails are sent informing me of the status and predicted dates for delivery and such. Really neat!

    Three boards are $123. Yikes!

    After some googling, I've decided that a 5-board run from a low-cost site on eBay puts the board at around $10. That's a lot better, and I can optimize the board for a better price.

    The original plan was to use an ATX power supply box as a project enclosure, but there's a lot of unused space on the board, and components are only on one side. I could easily chop $25 off of the OSH price.

  • Big Data Dump

    Peter Walsh09/20/2015 at 23:25 2 comments


    .) September contest video is ready

    .) Chemistry is an experimental science

    .) Making diamonds with ultrasound

    .) Copper nanoparticle emulsions

    .) Graphene emulsions

    .) Making an air bell

    .) All the stuff

    .) New schematic update

    September contest video

    The contest video for September is up on the project page.

    The video quality isn't the best: the camera is crooked, the lighting has dark and light bands (why?), moving objects (my hands) have jagged edges, the dialog has mistakes, and the scenes are poorly spliced.

    But it explains the problem (to be solved) to a non-technical audience, and has a good overview of the system and how to build it.

    It probably should place more emphasis on what the system can be used for rather than the Haber aspects (mixing, drilling, levitation, etc.). I hope it's clear to the judges that this can be used for more than just exploring Haber.

    I'm hoping that the video quality really doesn't matter, as advertised. Other contest project videos seem more polished.

    Chemistry is an experimental science

    Chemistry is very much an experimental science.

    For a clear example, note that chemists had predicted graphene to be impermeable to water. The holes in a carbon hexagon structure are too small to pass water molecules, so graphene should act as a water barrier.

    It doesn't.

    In fact, not only does water pass through graphene, it acts as if the graphene isn't there. This has many potential applications, not least of which is desalinization...

    but my point is that Chemistry often doesn't predict the outcome of an experiment.

    It's not that Chemists don't know the underlying principles, it's more a case of not knowing *which* underlying principle will dominate. As the graphene paper shows, it was only after the experiment was performed that chemists went in and re-analyzed the situation, and figured out why graphene was water permeable.

    That's good news for us hackers. There's a lot of interesting chemistry waiting to be discovered, and some of it will be accessible if you have an ultrasonic system to play with.

    Such as...

    Making diamonds with ultrasound

    Graphite-to-diamond transformation induced by ultrasound cavitation

    Summary: Ultrasonic cavitation of graphite suspended in oil produces diamond grit. Although the researchers used a 1000 watt ultrasonic system, the actual chamber energy density was only 80W/cm^2.

    This Hackaday project entry can produce that energy density.

    Copper nanoparticle emulsions

    Synthesis of copper nanoparticles by two different methods

    A recently discovered (2005, I believe) chemical reaction uses copper chloride and ascorbic acid to make copper nanoparticles. Copper chloride is readily available, and ascorbic acid (vitamin C) is available on eBay for pennies.

    I've actually tried this, it's trivial. You get a precipitate of finely-divided copper lining the bottom of your flask, and the particle size is determined by the reaction temperature. You can "tune" the reaction to generate whichever size of particle you need.

    This would make a conducting ink, except that copper forms a surface oxide that's non-conductive. The nanoparticles are small and have such enormous surface area that the oxides reduce conduction and the result has little or no conductivity. Pressing the particles - as with a spoon - mashes them together and reduces the surface area. You can make PCB traces this way.

    See "Copper Nanoparticles for Printed Electronics: Routes Towards Achieving Oxidation Stability" for more info.

    An ultrasonic system can make an oil/water emulsion that will last for days.

    Would an oil emulsion of copper nanoparticles have any use?

    Graphene emulsions

    On the subject of emulsions, note that graphene suspensions can be made with a blender and soap.

    Would this process benefit from sonification?

    Would an emulsion of oil and graphene have useful properties?

    Making an air bell

    The gas collection system was the last piece I needed for the project...

    Read more »

  • Random update

    Peter Walsh09/09/2015 at 20:11 0 comments

    .) Reaction chamber v3.0

    .) Complete list of components, $50 total cost

    .) Trying a "bubble plate"

    .) Capturing bubbles in a standing wave works... 'sorta

    Reaction chamber, v3.0

    The tube holder for the reaction chamber was a bit unwieldy, so I added mounting tabs to the back plate of the reaction chamber and changed the lid as needed.

    The new version holds the tube firmly in place, and has extra mounting holes for future use.

    The chamber layout is now based on a specific thickness and vendor for acrylic (Plaskolite, 5.75mm), so it's easy for anyone to cut out and assemble.

    To use a different thickness you'll have to resize the tabs and notches - if I get time after the contest maybe I'll make a parametric program that generates the pattern based on the thickness the user has available.

    Completed list of components

    The project components are complete and final (I hope!). All chips are listed, except I glossed over minor electronic things like passives and XOR gates and such.

    The final list of components are:

    • 1 × Ultrasonic Transducer (Available from eBay for under $20).
    • 1 × 100mm of 6061 aluminum rod (To make a tuned aluminum horn. About $10 on eBay).
    • 2 × ATX power supply (One supply for power, one to scavenge the SMPS transformer).
    • 1 × Arduino nano (Control board interface).
    • 1 × UC3525 Pulse width modulator IC.
    • 1 × MCP4161 10K Digital potentiometer.
    • 1 × MCP4131 50K Digital potentiometer.
    • 1 × AD9833 Sin/Square/Triangle generator (About $6 on eBay).
    • 1 × ACS712 Hall effect current sensor.
    • 1 × PCB, assorted passives.
    • 1 × Transducer mount (made from wood or acrylic, or whatever).

    With parts from eBay the whole system costs around $50, not counting the 2 ATX supplies.

    Bubble Plate

    Holding a bubble at the end of the gas inlet tube is proving to be problematic. There's a fine line between having a bubble and either a) no bubble, or b) releasing a bubble.

    I want the bubble held stationary, so I machined a concave depression into the head of a small bolt. This will attach to the gas inlet tube and serve as a catcher plate for released bubbles. This way I can position the bubble with the plate and not have to worry about keeping it at the end of the tube.

    UPDATE: It works well enough, but isn't sturdily mounted to the gas tube - it keeps flipping over. Oh well - it's a nut & bolt, shouldn't be to hard to figure out a mounting bracket.

    Capturing bubbles in a standing wave

    Thinking about ultrasonic levitation, I got to wondering if the reverse was possible. Can a standing wave capture a bubble under water?

    It turns out it can. I was able to get a bubble to "hover" above a reflecting plate for about a minute before it wandered off.


    I don't have a picture because it's hard to place the bubble in just the right position. Several times I positioned the bubble, only to have it fly away a few seconds later. It was definitely hovering for those few seconds, however.

    This really isn't the right horn or the right way to do this. If I get some time I'll play around some more later. Maybe a horn with a slight depression would arrange the energy to better capture the bubble.

    The speed of sound in water is 1482 m/s, the frequency is 28,000 hz, so the half wavelength is 26.46 mm.

    Position a flat horn any multiple of this distance over the reflecting plate to get standing waves.

  • Things are progressing

    Peter Walsh09/03/2015 at 03:27 0 comments

    Quick update:

    .) Home made rheoscopic fluid works

    .) The driver board satisfies all system requirements

    .) New hardware, new board design is coming along

    .) Fixed an issue with board current on USB connections

    .) Fixed an Arduino Nano windows driver problem

    .) Hope to try making ammonia "real soon now"...

    Home made rheoscopic fluid

    Finely ground mica mixed with water makes "rheoscopic fluid" which shows currents and eddies in swirling water. Powdered mica is available in the makeup section of eBay in various colors.

    The result is a sort of silky, swirly mixture that makes long lines that follow the current patterns. It's hard to explain, but there's lots of images on google that show the effect.

    I only used a tiny amount of mica because I wanted to keep the water transparent. The fluid works, I can see the current patterns, it just wasn't very informative.

    Ah well - this is science. I suppose this is an example of "Hackaday Fail". Still, the home made rheoscopic fluid seems to work well enough.

    Board works, all requirements met

    As mentioned in my previous log, the new board is stable up to 150 watts.

    Some things could be improved (I have a list), but in its current state the board satisfies all design requirements for the project. I could use it as is, or cautiously make some upgrades.

    I have 4 hardware improvements that should be straightforward. My plan is to get these working on a proto-board, then do schematic capture and and have PCBs made.

    Too many chips, not enough power

    A standard USB connection can supply a maximum of 100 mA of current. The AD9850 sine generator requires 76 mA, and the board also has an Arduino, an FT232 converter, and at least 2 power LEDs.

    So it came as no surprise that the components were struggling with the limited amount of power available.

    The solution is to power the circuit from the ATX 5V line, and of course the "smart power circuit" on the arduino board will have none of it, so the quick solution is to cut the red wire on a USB cable.

    The cheap Chinese knockoff Nano "smart switch" circuit doesn't work well. I can't run the 12 V line to the arduino onboard regulator either, but I may not need it - see below.

    Nano windows driver problem

    The Arduino Nano windows device driver was causing a lot of problems.

    With the Nano sending output to a serial window, after awhile the mouse would go wild - the pointer would move and select things seemingly at random.

    The only way around it was to reboot the computer, at which point you would get another hour or two of development until the mouse went wacky. This hampered development quite a bit.

    I finally discovered the cause: the system identifies the serial port as a microsoft mouse product, so in addition to being a serial port the device was being installed as a mouse!

    This is a problem with the Chinese knockoff driver CHSER340.exe. I can't find Nano's with real FTDI chips any more - nowadays everyone uses the knockoff USB interfaces.

    The solution is to disable the unwanted mouse in the hardware manager. Assuming you don't actually *have* a "Microsoft Serial Ballpoint" or other serial mouse, this should fix the problem.

    It turns out this is a known windows problem.

    AD9833 is cheaper and simpler

    One of the 4 proposed improvements is to use an AD9833 sin/square/triangle generator, which only needs 5 mA.

    Additionally, the squarewave output reduces the component count and complexity of the circuit: a single XOR can turn the squarewave into short pulses needed by the UC3525 PWM chip, and double the frequency which is *also* needed by the UC3525 PWM chip.

    Curiously, a development board on eBay costs less than the chip itself.

    Specifically, the AD9833 chip costs $10 on DigiKey (quantity: 1), but a breakout board with the chip, a 25 mHz crystal, and decoupling capacitors is only $6.99 on eBay. Go figure.

    If I use the dev board as a component, this reduces cost and reduces the number of SMD components...

    Read more »

  • I have done it! Qapla'

    Peter Walsh08/31/2015 at 01:46 1 comment

    Finally, a solution!

    I have driven electrons into resonance, and I can hear the lamentations of their women! Bwahahaha!

    .) I have a solution to the problem that has been vexing me for weeks.

    .) I'm confident I can make working boards (PCB layout, etc.)

    .) The new driver is simpler and less expensive

    .) The new driver can power transducers from 20 kHz through 40 kHz.

    .) The new board will include measure and tune functionality, previously on a separate board

    Statement of the problem

    The UC3525 PWM controller uses an RC for timing. This is an analog frequency generator, and is subject to (frequency) drift from factors such as noise and temperature variations.

    To compensate, the R of the RC circuit uses a digital pot controlled by a microprocessor. In theory, the micro adjusts the pot as needed to make the output frequency match the requested frequency.

    This worked on paper and in prototype. The micro reliably kept the output within 1 Hz of the requested frequency with no transducer attached.

    For outputs greater than 50 watts however, the noise affected the control and measurement systems, causing the frequency to drift faster than the control algorithm could keep up.

    As the frequency swept around, the transducer would go into and out of resonance, which varied the power faster than the power tracking system could compensate.

    So to summarize, the system couldn't maintain a stable frequency or power output.

    Digital frequency FTW

    The new circuit uses an AD9850 to generate extremely accurate frequencies with 32-bit resolution. This solves all of the horn tuning problems caused Arduino generated frequencies: The Arduino only makes square waves and at poor resolution, the AD9850 solves both of these problems.

    In a previous build log I noted that the SG3525 has a SYNC input that can slave chips to an external frequency. (And apparently no one has ever used this feature.)

    On a whim I routed the extremely accurate AD9850 output to the SYNC input and... it works! It's completely stable to over 150 watts.

    The SYNC input is thus digital, with noise immunity per the static discipline.

    It's also "set and forget", so the micro no longer needs a frequency-following system, or even a frequency *measuring* system. This greatly simplifies the software.

    And as a bonus, the AD9850 goes from DC to 2MHz, which means the system should run other transducers such as the 20 kHz and 40 kHz types.

    There's some devil in the details, but I feel confident I can design a board that's simple, stable, and easily controlled.

View all 37 project logs

Enjoy this project?



mario.lutz wrote 11/19/2016 at 10:25 point

one last thing, if you like the AD5934, then you should take a look at the following Evaluation board. It's about 50 bucks but it's a complete solution. You could even just use it for tuning your horn.

CN-0349 Fully Isolated Data Acquisition System Evaluation Board, Analog Devices

  Are you sure? yes | no

mario.lutz wrote 11/19/2016 at 10:10 point

just one more note. You may want to look at this. 

Basically it's the whole output stage of your project on Ebay. Also quite cheap. 

"Mini 150W DC-AC 12V To 110V 220V Step-up Transformer Boost Module Inverters O2A5"

  Are you sure? yes | no

mario.lutz wrote 11/19/2016 at 09:58 point

very interesting project. Good you came back to it.

I had an idea. Please take a look at the AD5933/AD5934. These are impedance converters or also used as network analyzers.

They can be used to make a frequency sweep, single frequency or step up/down frequencies with an internal DAC

The important thing is they also measure the feedback frequency with an internal ADC, calculate the DFT and give you real/imaginary numbers that you can calculate to magnitude/phase. 

What you can do with it is a frequency tracking if you get the feedback of the horn (let's say via a ferrite ring in the secondary and some opamp circuit to make a current to voltage conversion) 

This can compensate for resonance frequency changes due to the medium that affects the horn.

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Michael Vowles wrote 11/02/2015 at 05:07 point

Fascinating project mate, looking forward to updates!

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DeepSOIC wrote 08/26/2015 at 14:09 point

I see a problem. Speed of sound in water is 1484 m/s. Dividing that by 40khz, I get a wavelength of 37 mm (almost 1.5 inches). It's hard to tell how large a pieces do you have, but they don't look much larger than the wavelength to me. So, I'm afraid, there can't be planar waves put into water by that rectangular piece. It is rather close to a point source.

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Peter Walsh wrote 09/03/2015 at 02:10 point

If I read your note correctly, you're looking at the width of the horn and not it's length.

The length is tuned to 1/2 wavelength, and with the end stuck in a water bath the vibrations of the horn generate longitudinal waves, not transverse waves.

Essentially, rather than generate waves across the width of the horn the waves are generated into (and out of) the water. It's the path length in the water that is the wavelength, not the width of the horn.

An air cannon works on the same principle: take a drum with a hole in one side, and hit the other side. The "pulse" of air travels a great distance without dissipation, even though the speed of sound would imply a wavelength of 10 meters.

If I'm analyzing this correctly. Is there something I am missing?

  Are you sure? yes | no

DeepSOIC wrote 09/03/2015 at 19:54 point

The story of air cannon isn't goverened by wave propagation, but rather by hydrodynamics. For example, the pulse of air travels with the speed of the pulse (the speed of air flow through the hole), determined by how hard you hit the drum, and not by speed of sound, which doesn't depend on amplitude to certain extent. If your device is supposed to work like that, well... OK.. I didn't think of that =)

It is just that I was taught that a plane wave must be much wider in cross section than its wavelength, otherwise it won't be a plane wave, it will diverge quickly. Although I think, it still can be, if it is traveling in a (narrow) pipe. But I don't know for sure.

  Are you sure? yes | no

Peter Walsh wrote 09/13/2015 at 23:11 point

I've been thinking about your question and looking around the net for papers and such... and can't find anything relevant or definitive.

I don't have an answer, except to note that ultrasound tends to not spread out much in the air - it's more like a flashlight beam than a sound wave.

If the same effect happens in water, then the pressure nodes should travel in straight lines and should be able to be focused.

In any event, if it doesn't work I have other things to try. I might have this wrong, but it's not catastrophic if it is.

  Are you sure? yes | no

DeepSOIC wrote 09/14/2015 at 08:43 point

OK. Note that at the same 40 kHz, wavelength in air is 7.5 mm. Although, I have to admit, those ultrasonic sonars are really small (about equal the wavelength, although I have no idea, what frequency they operate at), yet are quite beamy.

  Are you sure? yes | no

DeepSOIC wrote 09/14/2015 at 08:51 point

A randomly chosen ultrasonic rangefinder works at 42 kHz, and has a beam width of about 35 degrees

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DeepSOIC wrote 09/14/2015 at 08:53 point

And by the way, good luck with your project! I hope my feedback was constructive!

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dimsml2008 wrote 08/13/2015 at 06:53 point

Apparently people all over the world try to find a better way to make ammonia. Here is a different approach I have found, maybe you can use it somehow?

Plus I remember there were cavitation water heaters. They are used by snakeoil salesmen to preach "overunity", which is bullshit, but at least they really use cavitation to heat water. Maybe they can also be used unstead of ultrasound transducers? Not sure if they can reach the levels of energy density needed, though.

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Peter Walsh wrote 08/18/2015 at 22:30 point

I remember reading about that paper when it came out.

Unfortunately, I don't have publication access, I have to drive to Boston to use the MIT library when I want to view a paper, so I extrapolate from the abstract because to read the article costs $217.

I don't recall why, but my impression of the abstract was that the process wasn't viable for mass production. I think it had to do with the catalyst (Fe3O4) changing forms or being poisoned by oxygen in the molten electrolyte. Or something.

This is not to say that the process isn't interesting or that it can't be developed into a viable system, just that I didn't think that Licht has slam-dunk solved the problem.

His (Prof. Licht's) website is interesting - he's doing a comprehensive study of electrolytic reactions using molten salt electrolytes, and one process reclaims atmospheric CO2 to make useful compounds (with the input of energy).

His paper was published about a year ago. If his ammonia process was the complete solution, it would be a lot more public and a lot more popular than shown on his website. That's not conclusive of course, but it's suggestive.

It's likely his process needs more development before it's economically viable.

For generating ultrasound, ultrasonic cleaner transducers on eBay are really cheap. The transducers have to be resonant to within some narrow spec (within 200 hz of 28000 hz, for instance), and the ones that are "out of spec" don't work in cleaners but are perfectly usable by us. I've got several that are 300-400 hz away from the rated frequency, but are otherwise stable and entirely usable.

It's also relatively easy to start and stop an electronic circuit and control and measure the power used, and easier for the hobbyist to solder a board than to mill out a mechanical cavitator.

So... it's an interesting approach, and one that might find use in an industrial process if you need a specific power regime and targeted output, but for the contest it's easier to just purchase a transducer.

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Peter Walsh wrote 08/19/2015 at 06:23 point

Hah! I found a copy of the paper online.

If my reading of his results are correct, his system created 1 mole of ammonia using roughly a million joules of energy. Per my previous calculations, the Haber process uses half a million joules per mole, and to be more effective you have to beat the Haber process.

(And also his system seems to poison or otherwise use up the catalyst in the process, as I expected.)

His process is certainly interesting and bears looking into. If it can be developed it might provide a good substitute for Haber.

His paper is buried in this document: Technical 8-10-15.pdf

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Swagnar wrote 07/15/2015 at 13:45 point

This is really smart. Would this work for the Ostwald process?

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Peter Walsh wrote 08/04/2015 at 04:42 point

Sorry for the late reply :-)

If I can read into your question a little, you're not asking if this will replace the Ostwald process per-se, you're asking if cavitation can make oxides of Nitrogen instead of, or in addition to, ammonia (the Ostwald process makes nitric acid from ammonia).

Any process that fixates Nitrogen less expensively than Haber would achieve the goal, so a pathway that involves oxides of Nitrogen would also be a success.

The limiting factor in the Haber process is entropy: making ammonia from nitrogen is an exothermic reaction that reduces entropy. At room temperature the released energy compensates for the reduction in entropy, but then the reaction can't ignite. At temperatures high enough to ignite the reaction, the released energy no longer compensates for the reduced entropy, so the reaction isn't favored.

I haven't calculated the Ostwald entropy/energy totals ('been dealing with the contest), but it looks like the 1st step is massively exothermic and also increases entropy, so that step would be strongly favored. It may be that cavitating a mixture of Nitrogen, Hydrogen, and Oxygen can bypass or at least alleviate some of the entropy deficit, making it more likely to fixate Nitrogen.

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Alex Rich wrote 05/29/2015 at 11:48 point

This is cool, when are you going to stick the horn in some water?  The video of the 2kW horn is crazy, looks like electrical arcing in the water almost.

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Peter Walsh wrote 05/31/2015 at 20:48 point

I've got toughly 2 months until the first culling [of the HAD prize], and maybe 4 good demos available. If I use them all up at the beginning, the project won't be fresh or novel during the culling! :-)

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Peter Walsh wrote 08/11/2015 at 20:20 point


(This horn is specific to the project with a relative large endpoint surface area. A horn with a smaller tip would be more impressive. About 50 watts of output.)

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[this comment has been deleted]

Alex Rich wrote 08/05/2015 at 00:21 point

This is cool as hell.  If nothing else you've made the world's most inefficient water heater!  Really though, despite the minimal amount of chemistry I understand behind it, this is such a  neat idea.  Keep it up.

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Zander Horn wrote 05/28/2015 at 22:39 point

This is a fascinating concept which I haven't really had the chance to consider until now, but some back of the envelope calculations indicate to me that you will have some difficulty making ammonia. I'm going to use your numbers just to make things easier, but your estimates of the bubble pressure are a bit on the high side and the bubble temperature on the lower end of what literature suggests.

Firstly going from 200 atm to 2000 atm will give you a reaction rate 10000 greater than conditions of the usual implementation of the Haber process and an equilibrium constant 3.16 times higher. However the reaction is also exothermic, considering an increase in temperature from 400°C to 5000°C gives a reaction rate 771 million times slower as per the Arrhenius equation. The associated equilibrium constant as per Van 't Hoff would be 56 million times smaller!

These figures are exactly what makes the fixation process so difficult in the first place, the conditions required are just quite difficult. In the case of the Haber process the reaction rate is somewhat improved at high temperature with the addition of a catalyst (which you have not yet documented to use) to reduce the activation energy, however this still results in a terrible equilibrium constant, which is why the continuous removal of ammonia in the Haber process is so effective.

Lastly you must consider that the conditions you are using (presence of water, high temperature and pressure) are much more ideal for the production of nitrogen oxides, benefiting from being both endothermic and benefiting from Le Chatelier's Principle.

Regardless, I look forward to you proving or disproving my theoretical calculations.

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Peter Walsh wrote 05/31/2015 at 04:53 point

Your comment is the best yet on this subject. I hope you'll stick around and in about a month we can have a conversation about thermochemistry. Hopefully I'll be experimenting with gases then, and be able to take measurements, post graphs, and we can discuss.

Could you explain your reasoning for the Arrhenius equation? By my reading, the reaction rate is a negative exponential which is normally small but approaches 1 with increasing temperature. This would be consistent with an increase of temperature generating a larger number of high-energy particles in a gas, resulting in a higher likelihood of attaining the transition state.

The problem, as you pointed out, is the change in entropy. That's a completely different aspect which is a different discussion, and indicates which way the reaction goes. Regardless of the direction, I was under the impression that higher temperatures meant higher reaction rates.

Once the system is running I've got a couple of things I want to try, which I think of as "secret sauce". People keep guessing parts of the secret sauce, and making oxides of nitrogen is one of the things I want to try. Fixing Nitrogen is the goal, and it doesn't have to be ammonia specifically.

I have responses to your back-of-the-envelope calculations, but I'd like to hold off for a month or so to get fully immersed in the chemistry. Right now I'm dealing with electronics and plumbing.

  Are you sure? yes | no

Zander Horn wrote 05/31/2015 at 16:43 point

My mistake on the Arrhenius equation! It's been a while since I've done thermochemical calculations, you're quite right that the reaction rate increases with temperature, by the factor that I stated it would decrease, but the equilibrium shifts to the left with the temperature increase.

Entropy plays a role along with the enthalpy in the form of the Gibbs free energy. I'm currently on holiday, but when I get back home I'll check up my equations and run a simulation to give something more concrete than my initial educated guesses.

  Are you sure? yes | no

Peter Walsh wrote 05/31/2015 at 20:42 point

Your profile lists you as a chemical engineer. I'm more of a physics guy, and having someone to bounce ideas off of and who can talk from experience would be a great asset.

I don't know how involved you want to get, but if it's of any interest I would be totally on board with co-authoring a paper if there are any results of note.

Think about it. Enjoy your vacation - let's pick up on this in a couple of weeks.

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Andre Esteves wrote 05/03/2015 at 23:12 point

Fascinating. Even if it doesn't work you will be helping set a good sonochemistry setup for other experiments and the rest of us. Kudos!

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Thomas Shaddack wrote 04/23/2015 at 00:07 point

Random thought. What about a homemade magnetostrictive transducer? In WW2 the transducers used Rochelle salt or later ammonium dihydrogen phosphate (USA) or quartz (Japanese) piezo transducers, or magnetostrictive transducers based on nickel tubes (Germany, later also Japan who got the designs from guess who) or iron-aluminium alloy (Japan as alternative to nickel). (More modern designs use lead zirconate titanate for piezo, or advanced alloys like Terfenol-D or Galfenol.)

Ancient WW2-era designs should be available online as at least sketches/blueprints and ballpark figures for driving voltages and powers. The projectors were typically hundreds of watts to several kilowatts of power, in the ballpark of what can be useful for sonochemistry. And nickel tubes or tapes may be easier to find than special high-power crystals, be more robust, and be easier to shape. (Unless the dimensions and weight of the high-power transducer become prohibitive for small-scale use, which I am not certain about.)

Germans used some quite nice nickel-based magnetostrictive designs.

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Peter Walsh wrote 04/23/2015 at 19:29 point

I am totally on board with making my own tools. :-)

Transducers are not hard to come by, they're on eBay in powers up to about 120 watts. These are Langevin types with ceramic piezo centers, and can be had at nominal cost. The 100-watt range suits a lot of hobbyist applications: plastic welding, levitation, mixing, and basic experimentation.

I don't know how hard it would be to build a transducer, but in the spirit of the competition I have to "change the world", so I'm trying to optimize towards more people having access. I don't think I can beat a 100 watt tuned-frequency transducer for $40.

The hard part is getting a power supply and tuned horn. The supplies sold on eBay are junk, and no one has published a good hacker-friendly circuit for this. (Lindsay Robert Wilson's circuit comes close.) The horn requires a lathe and some theory. I'm hoping to describe the theory in enough detail and examples so that anyone with a lathe could build one.

Even so, I'd like to eliminate the lathe as a requirement. Lathes are common, but not by any means universal.

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KeyGhost wrote 04/14/2015 at 10:37 point

Great update :) keep them coming.

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Thomas Shaddack wrote 04/13/2015 at 23:54 point

What about staying in gas phase and using microwave plasma? That way we'd get the same high temperature needed for the reaction, but only the electrons would be heated while the nuclei that take the bulk of thermal energy would stay cold. Look at the relevant publications, there are quite some out there.

Both microwave-assisted chemistry and sonochemistry are fascinating areas.

  Are you sure? yes | no

Peter Walsh wrote 04/15/2015 at 21:09 point

That's a very good thought.

When I started this project (several months before the contest announcement) I made a list of all the possible ways that might work and then researched and analyzed each one for likelihood of success. Microwaves was one approach, and I decided that it would be unlikely to succeed.

Rather than a detailed response, I'm thinking of putting your question up as a blog entry along with my analysis, and using it as a springboard for discussion among the followers. I'll create a couple of "background information" posts first, then we can let everyone discuss it & see if I've made an error in the analysis.

(And I'm always eager to talk to people about Nitrogen fixation)  :-)

Is that OK with you?

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butterfly wrote 04/05/2015 at 01:43 point

been done quite some time ago:

  Are you sure? yes | no

Peter Walsh wrote 04/15/2015 at 20:59 point

Many people have studied the efficiency of ultrasonic nitrogen fixation, the paper you cite is only one of many. This paper, and all the others, does not deter me from "checking it out".

I have some things to try which other people have not thought of, to be revealed (hopefully dramatically) in a future post.

Chemistry is very much an experimental science, which means that you can never be 100% certain that something will work (or not work) based on theory - you just have to "try it" and see what happens.

(The basic principles are well known, but you can never be certain which principle will dominate in any one experiment. If you're doing something for the first time - not recreating someone else's work - there's a fair chance of finding something unexpected.)

Also, there's value in constructing and documenting the setup in a way that others can duplicate. Having more eyes on the problem will increase the likelihood of finding a better solution.

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Jarrett wrote 04/02/2015 at 21:36 point

You had me at "ultrasonic cavitation"

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zakqwy wrote 03/12/2015 at 15:29 point

Interesting project! Cavitation is a fascinating process. I'd definitely focus on proving out a lab-scale process before you try to optimize anything. Be careful with the ingredients (and resulting product, if successful)!

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