Alternating polarity to dislodge gas

[Darrell]

That sounds like a great project and can't wait to see the performance. Keep us updated to the progress. "D"

[AnActualPhysicist]

Also, need to find out if we can use ultrasonic frequencies to generate cavitation in the liquid and thus aid the formation of bigger bubbles as is being done in ultrasonic cleaning systems.

Hi! This is my first time posting here, I am a senior physics major about to graduate from college.

Just thought I'd point out that using ultrasonic generators could be extremely dangerous. If it is at a resonance frequency of your container, bubbles could be trapped at the wave antinodes and heated to many thousands of degrees. This would provide an ignition source inside the generator, which is obviously a very bad idea!

If you watch the liquid while the unit is running, you will notice that the water is moving. What you are seeing is the magnetic pull of the oxygen and hydrogen particles.

This is very unlikely. While water molecules are polar at the small scale, on the macro scale they are neutral, and therefore experience no net force from an electric field.

[AnActualPhysicist]

http://www.youtube.com/watch?v=oY1eyLEo8_A

I made one of those a little over a year ago. It has nothing to do with the charge of water. In fact you can make that type of generator with nearly any liquid.

[AnActualPhysicist]

Ok, so how do you explain the phenomena?

Basically the buckets at the bottom and cans the water pours through have a very small capacitance. As the water starts to fall through the two nozzles, any tiny initial charge imbalance becomes amplified in a feed back effect. This is because the initial charge imbalance puts a voltage on the cans, which are switched as shown in the video. This voltage induces opposite charges to build up in the corresponding nozzles, which fall into the opposite water buckets.

The effect is an exponentially increasing voltage in the system, at least until it discharges. By exponential I mean literally exponential, as in the exponential function. The system is described by the simple differential equation dQ/dt=C*Q, where C is some constant.

This effect has nothing to do with the dipolar nature of water. It's just surface charge, meaning any liquid can be used. Water is used in the demonstration simply because it is convenient (i.e. doesn't make a mess).

[RTJ_Nair]

Ultrasonics are currently used extensively for cleaning and the principle behind is to induce cavitation. We are talking about power in the range of just 30 to 50 watts and not something too much to cause an explosion. I do have a small ultrasonic cleaner that could hold about 250ml of water and have been using it since some time for cleaning mechanical parts including small metal plates.

There are 3 cases to research regarding the alternating current application in a cell,

Duty cycle=50% (to start with)

CASE-1
The gating frequency between 0.5 to 10Hz.
PWM=1 to 10KHz (find resonance here ?)
Alternating Frequency=0 ie; no reversal of current direction and is unidirectional.

CASE-2
The gating between 0.5 to 10Hz
PWM=10Hz to 500Hz
Alternating current Frequency=10Hz to 500Hz synced for forward and reverse polarity with the PWM within a gate pulse ie 50% of the time period (to find resonance here or could be difficult ?).
Note: The frequency is low taking into consideration the commutation delay and the cell time constant ie amount of retention time needed to regain cell activity when current is reversed.

CASE-3
The gating between 0.5 to 10Hz
PWM=1 to 10KHz
Alternating Frequency=0.5 to 100Hz, synced to alternate with every gate cycle ie the current pulses will flow in one direction during the first rising edge gate pulse and then reversed during the second rising edge gate pulse and continues alternately (find resonance here ?).

RTJ Nair

[AnActualPhysicist]

Well, if you're running it under 10kHz then chances are you won't have any resonances. Generally resonances will occur above 20kHz because that's where you start to have excited resonance states, which grow in number very quickly.

I'm just concerned that if you actually induce bubble trapping and thus cavitation, that the extreme heat generated in the localized volume could eventually ignite all of the gas, which would be nasty. As far as I know wattage isn't a good indicator of when this will happen (although obviously it helps).

http://en.wikipedia.org/wiki/Sonoluminesence

[RTJ_Nair]

Not true, resonance depends on the cell structure/construction (plates, tubular, spiral..etc)...if you scan youtube, u will find many instances to corroborate this fact. In short, it is a function of the cell capacitance, its ohmic resistance and your fabricated inductor design and also whether you want to run a parallel or series circuit configuration. I have read people saying something between 3 to 5 KHz for their cell designs. Also, I don't foresee any ignition risks at this low frequency and power.

I am at the final stages of development. Have done the dry-cell part, circuit layout (microcontroller based) and currently modifying the software code. I have completely changed my strategy, ie from a current-driven-cell to a voltage-driven-cell. Hence, I might have to redo the cell construction altogether. My vague guess is that a tubular cell might perform better as far as resonance is concerned.

Check the below youtube link about ultrasonics,

http://www.youtube.com/watch?v=1kpswB6Ae-o

RTJ Nair

[AnActualPhysicist]

Check the below youtube link about ultrasonics,

http://www.youtube.com/watch?v=1kpswB6Ae-o

RTJ Nair

That effect he's seeing, where "the bubbles collide" is an indication that he is setting up a standing wave in the container. That is exactly what I'm concerned about. Bubbles in a standing wave tend to experience volume fluctuations on the order of 100-1000 times. During compression, the gases inside can be heated to well over 10,000 degrees F.

By the way, you can calculate the resonance frequencies and excited modes using spherical harmonics, or cylindrical harmonics as the case may be. Even if it doesn't exactly match the shape of your container, you can still get a pretty good idea of which frequencies might be dangerous. I.e. try to avoid any eigenfrequencies of the system.

http://en.wikipedia.org/wiki/Spherical_harmonics
http://en.wikipedia.org/wiki/Cylindrical_harmonics

I would have very serious reservations about copying this - at the very least don't run the ultrasonics at a frequency where you see this effect taking place.

[AnActualPhysicist]

Not true, resonance depends on the cell structure/construction (plates, tubular, spiral..etc)...if you scan youtube, u will find many instances to corroborate this fact. In short, it is a function of the cell capacitance, its ohmic resistance and your fabricated inductor design and also whether you want to run a parallel or series circuit configuration.

Just thought I'd add that while electrical resonance may depend on capacitance, inductance, and resistance, mechanical resonance does not. Mechanical resonance depends on the geometry of the vessel and the speed of sound in the medium. And the effect with bubbles you are seeing there is a purely mechanical resonance.

[Madsceintist]

Just my two cents, but you can only put so much logic and pinned down physics on this with HHO, you can definitely over think and miss something !! The type of fluid you use does make a difference in different ways. Different resistance. Ease of flow. And contaminants, which changes resistance. That experiment wouldn't work if the water was just dripping due to the lack of flow of electrons. The faster the water the faster the spark occurs. I would think that the spark would increase in voltage as well.