Peter Davey Heater

[ramset]

directional arrays [not dipole[though this maybe what thrapp has in his bowl] use a set distance  determined by wave length to aim the energy [focus][increase directional power   this distance is a portion of the transmitted wave    EM DEVICES [member here] would know alot more than me    its been many years but i will look thru my stuff on this    Chet    PS a parabolic array[in series][microwaves are examples of parabolic transmitters] is not something that is done [but definitely seems one half of thrapps gizmo] also one half of davies device

[devrimogun]

directional arrays [not dipole[though this maybe what thrapp has in his bowl] use a set distance  determined by wave length to aim the energy [focus][increase directional power   this distance is a portion of the transmitted wave    EM DEVICES [member here] would know alot more than me    its been many years but i will look thru my stuff on this    Chet    PS a parabolic array[in series][microwaves are examples of parabolic transmitters] is not something that is done [but definitely seems one half of thrapps gizmo] also one half of davies device

Maybe you or Hartiberlin could invite him into the topic.

[storre]

From the drawings and photos what I can see is that the smaller half sphere sticks further out but it is because it is mounted inside the bigger one 4-5mm outwards. So I believe that the lengths are almost the same. Make further investigations.

I could not find the link for the cavity heater with motor sorry. Just forget about it for the moment.

I think that your guesses on the frequencies could be correct. For the moment the best thing to do is to use about the same sizes and same shapes as the old man it seems like you got the way to adjust the inner one to a certain multiple of 50 (by grinding) but the other adjustment is a bit more tricky as what exactly is the tuning going to be made for?

Do you have an idea on that?

@ devrimogun:

As you said the tuning of the 2 bells should be easy. I know I can do it by ear because I've done a lot of piano tuning but it could be done using a computer or other device. The other parameter is the distance between the 2 bells. My feeling is that it just needs to be at a distance such that the node of the vibrations coming off the bells hit the opposite bell with the node of the wave. I think though it would be much easier to just mount the upper bell on a post that is a screw and fix a nut on the top bell. This way you could wind up and down the outer bell and change the distance in a very controlled way. Just wind up to increase the distance between the bells and wind down to decrease. Finer thread on the screw would make for finder adjustments. The screw would either have to be non metal or if using a metal post/screw then it would have to be hollow so the inner bell could be attached to another post (could be metal) that fits inside the post. Then just insulate the inner pole that secures to the inner bell from the outer bells post/screw. It should be a tight fit. Then just screw up and down and wait for the sweet spot by testing the speed of the water boiling. Once the water boils instantly then that's the spot.

I personally will try to make or find a teflon screw and drill it open to make it a thick tube basically with threads on the outside. Then the inner bell will be attached permanently to a metal rod that fits tightly in the drilled out teflon screw. The outer bell would have a nut welded to it so it can be screwed up and down to find the right distance. I don't see it as a tuning to get this distance. The only things that are tuned as far as frequency is concerned are the 2 bells. The distance between the bells we can start as a guesstimate using the photos. It appears to be about a 1/4" but I would start close and wind out or the opposite. The right spot will cause instant boiling.

@ ramset:

I agree about the standing wave but I think this will all be easier by just trial and error. When the distance is found it will be apparent by the speed of the water boiling. The adjustment can be done easily using the screw method I wrote about above.

@ all:

This second tuning I think is what's confusing everyone because I don't think he is referring to tuning in the musical sense like he is with the bells. Peter(?) is saying tuning in the sense of tweaking and I imagine that is how he did it also, unless he was also a math genius and calculated the distance ;-)

[armagdn03]

The answer is seen in any stringed instrument, or tuning fork. For example, take 2 tuning forks of the same LENGTH and hit just one of them. Put that vibrating one near the other and the second one will start to vibrate also. You can also use a tuning fork of double the frequency and get the same effect. Take a guitar and strike the low E string (top string) without touching the others. Now stop the string you just stuck and listen to the high E (thinnest string) and it will be vibrating also even though it is at twice the frequency of the low E that you struck. Octaves (doubling or halving of the frequency demonstrates this the best. Take a wind chime and another wind chime exactly half the length of the first. Strike the bigger one and then put it near the one half it's length and then stop the big one from vibrating. The smaller one will be vibrating also even though it was never physically touched. All the same principle.

In this heater the electricity (mains) are oscillating at 50Hz. These bells Peter uses can't be 50Hz because they are too small. I guess them to be 800Hz or 1600Hz which are just octaves of 50Hz.

Someone here asked how to tune bells. Just like wind chimes, the smaller the bell the higher the frequency so start with something a little lower frequency than 1600Hz and then grind it down until you get to 1600Hz. If using 60Hz mains then the bells would need to be 1920Hz.

Then these bells will be vibrating in octave relation with the mains and you just need to adjust the distance between the two bells to find the sweet spot where the waves coming off each bell strike the other bell so as to not dampen IT'S vibration.

Same theory as to why you suspend a wind chime from a particular distance from the end so you hold it only on the node of the wave so you don't dampen the wave that is traveling up and down the wind chime.

Or think of it like two children swings but slow it down to visualize it. A swing (pendulum) will have a natural frequency determined by it's length. If you want to use the most minimal energy to continue the swing swinging then you need to push at the same frequency as this natural frequency of the swing.

With the 2 bells vibrating both at 1600Hz (in the case of 50Hz mains) and distanced from each other so the node of the waves strikes the opposite bell at exactly the right time and you make the water very hot very fast :-)

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.

[ramset]

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