Peter Davey Heater

[storre]

Ah, I love it when someone actually thinks a problem through instead of making guess work of the situation! Storre is correct, the beat frequency created by two frequencies of similar, but slightly different frequencies would be the most logical way to get ressonance out of such a small apparatus.

One "mystery" solved, now why the need for spacing?

Two possible answers, one the capacitance varies with distance, though I believe this is less likely the correct reason,
the other, that with varying distance, the physical position of peaks and nodes changes, for an example of why this is rather important lets take a look at a property called Thin Film Interference. you will all be familiar with this if you think of the differing colors in soap bubbles or an oil slick on water, both deal with varying distances between two surfaces.

Those in the know with optics will probably know of a property called thin film interference, which is taken advantage of in order make non reflective lenses. The premise is simple, if you have two separate layers, one glass and one your film, and say you want to cancel the blue end of the spectrum at 440nm for the wavelength, you will need to find a film that has the proper thickness to do so. So without going into the whole math of the situation, what you want happening is to have the  correct spacing between the top of the film and the top of the glass, if done correctly, you will have the peak of the reflection off of the glass being 180 degrees out of phase with the trough reflecting off of the film, when you do this, you get cancellation, and you see no reflection in the blue end of the spectrum for a particular wavelength of light.

An example can be found easily on the web
http://physics.bu.edu/py106/notes/Thinfilm.html

so what use is this? well, if you were to space it correctly you would have constructive wave interference rather than destructive, you would have peak meet peak, and you would have amplification, and if this amplification occurs at the beat frequency of the bells (In acoustics, a beat is an interference between two sounds of slightly different frequencies, perceived as periodic variations in volume whose rate is the difference between the two frequencies) then you have yourself a water boiling device.

Good explanation of the spacing. I couldn't figure out how to explain it. The best analogy I could come up with was to image to pendulums (our 2 bells).

If they are both exactly the same frequency and kept at that frequency by a common pusher (the mains) then the 2 pendulums positioned like such \/ at one position and /\ at the other position need to be spaced so they exactly hit each other at the node or zero energy point. If they are two close then they will start to dampen the others movement and if they are too far apart they might have weaker effect. Of course we are talking about the waves propagating through the water but waves all have a length that is dependent on it's frequency so it has to be a set distance or at least a set possible few distances since the waves would be very small and you could choose another node.

[storre]

Storre so the bells have a known resonance? then you tune [with the screw ] SWEET!! nice idea     Chet  PS what is the mains[HTZ] where you live

60Hz - Yes every bell, tube has a set frequency that is totally determined by it's size. Make it shorter and the frequency will go up so start with something a little larger than you need and test the frequency, grind a little and retest until it's perfect. I'm sure Peter did it by ear. It's so easy if you have any sort of musical ear.

[Nali2001]

Well I might be able to give some points out. Most of this stuff I learned from contact with Jan Pajak who had an active contact with Davey.
Anyway the 'inner' dome is indeed smaller. And the spacing is kinda around 4mm between each dome. But that is not so key, since it is different in every system due to the frequency distance tuning. One aspect also it that only ONE dome is actually ?tuned? to 50hz (well not really, since it is a harmonic of 50hz actually) not both. The second dome is more of a 'reflector' for the 'waves' same as the walls in your bathroom. Another thing is that the dome is not tuned to 50 hz but to a harmonic of that 50 hz. This is because it is impossible to realistically make a bell that small that has a self resonance of 50 hz. It has to be so hyper thin that it is highly impractical. I have checked this with a bell making company. I asked them if they could make a 50mm diameter dome bell with a 50hz self resonant frequency. They told me that it ?could be done? but  indeed that it then needs be  so thin that it can only be made of titanium to give it any strength at all. So in the Davey heater the dome is far above 1000hz probably, but tuned (sanded down) to a matching harmonic of 50hz. And after all that you need to fine tune the distance between each dome while in operation.

Domes can be made by spinning a sheet of metal on the lathe:
http://www.youtube.com/watch?v=Gwrk0SwDJhI

Steven

[storre]

Well I might be able to give some points out. Most of this stuff I learned from contact with Jan Pajak who had an active contact with Davey.
Anyway the 'inner' dome is indeed smaller. And the spacing is kinda around 4mm between each dome. But that is not so key, since it is different in every system due to the frequency distance tuning. One aspect also it that only ONE dome is actually ?tuned? to 50hz (well not really, since it is a harmonic of 50hz actually) not both. The second dome is more of a 'reflector' for the 'waves' same as the walls in your bathroom. Another thing is that the dome is not tuned to 50 hz but to a harmonic of that 50 hz. This is because it is impossible to realistically make a bell that small that has a self resonance of 50 hz. It has to be so hyper thin that it is highly impractical. I have checked this with a bell making company. I asked them if they could make a 50mm diameter dome bell with a 50hz self resonant frequency. They told me that it ?could be done? but  indeed that it then needs be  so thin that it can only be made of titanium to give it any strength at all. So in the Davey heater the dome is far above 1000hz probably, but tuned (sanded down) to a matching harmonic of 50hz. And after all that you need to fine tune the distance between each dome while in operation.

Domes can be made by spinning a sheet of metal on the lathe:
http://www.youtube.com/watch?v=Gwrk0SwDJhI

Steven

Good to find out the inner bell is just a reflector. I wonder why he made it longer in the few pictures I've seen. That is what made me think it was the same frequency but knowing it's just a reflector simplifies it and also means it will probably work just as well with the phase on the outer bell and neutral on the inner so as not to need 110v on each phase. We have that here (same type as the use in NZ) so if necessary I can put a 110v on each bell but most of my house is just wired 110v/0v

Thanks for the video link. I'm wondering what using stainless steel will make. It's easier than getting brass where I am.

Once I get this working with the size bell he used, it will be interesting to make one with the next harmonic octave. His bells I think are 1600Hz so the next size bigger would be 800Hz and might be more efficient for larger quantities of water.

[NewAge]

I wonder if it is possible to calculate the exact size of the bell so that it matches the 50Hz?