steam engine

[plasma]

I'm planning on increase the capacitance tell its large enough for all the water to turn to steam or hydrogen/oxygen, I think getting up to 90uF should give a more accurate picture of the input.
Ive got ltspice will check this out just in case, each capacitor of the cap bank is 450Vac, 320Vdc about.
Cheers

Attached sicmatic, the green is across inductor.

[Twospoons]

Based on your 0.25ml of water you are going to need a very big capacitor to vaporize it all.
With a specific heat of 4.2J/g/K its going to take ~84J just to heat from room temp to 100C.
Then to turn that into steam, the latent heat of vaporization is 2260 kJ/kg, or 2260 J/g, meaning another 565J to turn 0.25ml of 100C water into 100C steam.

That's over 3000uF at 640V.

And that's assuming 100% efficiency too, so your cap is going to have to be bigger still.

Did you run the math before you started this project?

[plasma]

Its not just joule heating, there's electysis and then the return of some of the energy on recombation.
There's also increase in pressure with no volume change which gets converted to heat.
Is it local or global heating, all at 100 degrees or local pockets at 300.
Its not exactly easy.

[plasma]

The Scr and parts arrived, I use a 12V source to trigger the Scr by shorting a connection.
This is the component used https://www.digikey.co.nz/product-detail/en/vishay-semiconductor-diodes-division/VS-70TPS16PBF/VS-70TPS16PBF-ND/2632107 .
The inductor measures about 3uH , the two resistor equal 44ohm with a diode just in case anode shorts to gate.
The salt gap makes about the same noise as before.

[plasma]

Building a new salt gap to test more Joule's on. Running some numbers on the design with conserve variables.
vthroat =sqrt(2*k/k+1*R*Tthroat) =395m/sec
R =461 for water vapor
Tthroat=300
k=1.3
V1 =R*T1/p1 = 0.27
p1 = 505000
Vthroat =V1*(k+1/2)^1/k-1 =1.10
Athroat =mVthroat/vthroat = 2.78mm2 for the size of the hole, the chamber will be 20mm ID with the inner electrode 12mm. I plan to fibreglass one end of the pipe, and weld flat bar over the other.
I'll be getting more caps next week, the Scr and resistors don't get hot, I was worried that I might exceed the wattage of the gate, did notice when I got a good contact to switch the Scr on, it resulted in a larger shot.

The sounds a mulfed but a blue arc can be seen inside.

Changed my cap bank to 2 in series 4 in parrellel given 60uF 30J at 1000V.
I added the salt water read 4 ohms across the gap and fired it, it made a small pop sound.
I think that I can measure the resistance across the gap to get approximately the mL in the chamber. The chamber has a slightly larger ID than the previous but should work with more energy.

[plasma]

The chamber above didn't workout, there was to much salt water for a given resistance.
I've moved back to the pic attached, it has 0.5mL and I plan to modify it so I can inject water into the gap.
I upgraded the wiring on the cap bank, its getting to the stage were ear muffs are compulsory.

The last picture is the injector idea, gravity feed at first, but a slow continuous flow from a pump should work.

I'm thinking that maybe 4 of the above feeding into a central tube might be better than one large chamber and a lot of energy.

[plasma]

Tested out a system to have salt water fill up the gap between electrodes, it works well, the problem is the connection from the wire to the electrodes, it arcs when fired.
The back pressure when fired delays the topping up, but after a shot it froths at the exit between electrodes.

The third picture shows the froth, a lot of small bubles. Upgraded the charging circuit by parrellel more capacitor, it now takes 2 seconds to reach full charge on the bank.
The latest shot must have cleared a blockage, the water flows quicker into the gap.

[plasma]

I check the numbers on the choke to limit A/uS it was to low which probably have shown up later with longer pulses. Got 30 turns on 25mm pipe.

The Scr seems to be turning off prematurely, there's still 200 V on the cap bank, I though that would be enough to supply 150mA holding current?

I thought that maybe the charging circuit was raising the voltage on the cap bank, but increase to 4uF doesn't seem to change the value.

I probably should have noticed it early, it charges to -536V then after the discharge goes to 106V, this is with a 50% voltage divider.
I tried adding a diode after the choke for the Scr but didn't do much, its probably the choke between charge circuit and cap bank.

[davekni]

Yes, if the R of your salt gap is low enough, then the L/C will ring past 0V.  You can calculate the resonant frequency of your cap bank combined with the inductor, then calculate the impedance of the L or C.  They'll be the same impedance except for phase at resonance.  If the salt gap resistance is lower, then expect the voltage reversal.  (Salt gap resistance will change as the solution heats, so only a scope trace could verify the real situation.)

[plasma]

Do you think it would be a good idea to put a diode in reverse across the SCR?
If I increase the size of the capacitor bank it should lower the reverse voltage?

My DMM can't read inductor that low but it should be about 5-6uH, with 75uF I get 0.28ohms for impendence at 8217Hz and last I checked the salt gap should be 3-5ohms, would that be accurate for 200V?

[davekni]

A diode across the SCR is a good idea.  That way all the energy will end up in the salt gap, and the charging circuit doesn't need to start from a reverse voltage.  Another option is to put a diode across the capacitor.

Your calculations look good.  The salt gap resistance is clearly dropping during the discharge, perhaps forming an arc.  Resistance must be dropping to ~0.28 ohms.  The effect of more capacitance is hard to predict, as that will also change the salt gap resistance during the discharge.

[plasma]

Thanks Davekni

About 8 years ago on www.4hv.org there was a thread were someone had Ali foil in a barrel with a little water, the video showed a lot of reaction out the non closed end.

I tried rolling up small Ali balls and placed them in the chamber, the Ali turned to AlOH after a shot and aloud noise.
I have patched up the chamber to fix leaks and a slightly larger volume, guessmate 2mL.

I should be getting some more caps to take it 90uF 45J and some 6A diodes.

The Gibbs free energy of water is 237kJ/mol 13.1kJ/g which is a lot for a small amount, hoping other elements or salts can lower the input.

I'm going to try some different salts, and look at Ali foil more.

[plasma]

At the moment I have 45J going through the salt gap, firing sprays water 1-1.5m.
The Ali foil makes it more vigorous with the smell of burnt Al, not sure if its from air trapped or oxygen from the water. Al2O3 has 1532kJ/mol on formation, with 30g/mol for Al, its twice the mole mass, but 4 times the energy of water. Finding a way to pump it between the electrodes is going to be a problem.
The water getting sprayed out I think is the sudden production of hydrogen and oxygen, I don't think its local effects of water turning to steam.
I've added diodes across the Scr but it didn't have any effect to reverse voltage on the capacitor bank which has stumped me.

[Twospoons]

I've added diodes across the Scr but it didn't have any effect to reverse voltage on the capacitor bank which has stumped me.

Not surprising at all. By the time the current goes to zero the caps will have some reverse charge, and a lot of the water in your gap will be gone leaving an open gap full of mist. Any arc will rapidly extinguish once the current is low enough - the plasma will cool rapidly with all that atomised water. At that point there is no longer a conduction path for the caps and they will retain their reverse charge.
What you need is a reverse diode across the caps - that way the residual energy in your inductor will end up dumped in the water gap, rather than cycling back into the caps.

[davekni]

Hydrogen and oxygen production is insignificant compared to heat/steam.  The potential for electrolysis is 1.23V.  At 1kV initial, 500V average, at best  1.23V / 500V = 0.246% of the energy is going into electrolysis.

As Twospoons said, the salt gap must be non-conductive at the end.  With the diode across the SCR, the remaining reverse cap voltage is also across the salt gap.  Even a relatively-small conductivity in the gap would discharge the caps before long.

Diodes across the caps is likely what you want given the salt gap's lack of conductivity.  The diodes will conduct a bit more current for longer placed across the caps, but there's likely still plenty of margin in their 10ms surge rating.

[Twospoons]

Hydrogen and oxygen production is insignificant compared to heat/steam.

There may be a fair bit of hydrogen produced by the reaction of aluminium with water. The discharge is likely stripping the oxide off the foil, and probably also atomising some of the foil, leading to a large reaction surface.

[davekni]

"There may be a fair bit of hydrogen produced by the reaction of aluminium with water."

Yes, perhaps.  I'm a bit skeptical, unless significant amount of aluminum is atomizing.  Think of the reaction of dropping solid sodium into water.  Rapid, but not so much compared to the <millisecond of this discharge.

[Max]

I tend to agree with davekni. And it should be rather simple to find out who's right. Take copper electrodes and repeat the experiment, measuring the difference. Or, if you have a precision scale, you can measure the difference in weight of the electrodes before and after let's say 100 shots. If I'm not mistaken you should get about 15 Joules of energy from every milligram of Aluminium that reacts. However, this assumes no change in temperature, so the value may not be usable at all. Also, you should clean the electrodes to remove any residual Al(OH)3 that could have formed during the reaction.

Assuming you're using copper electrodes and no chemical reaction with the electrodes takes place, Twospoons is entirely right. The fact that some or even all of the water dissociates and recombines doesn't add any energy. The reason is that it takes exactly as much energy to dissociate the water than it takes to recombine. Anything else would violate the law of conservation of energy and allow you to create infinite amounts of energy (You could just continuously dissociate and recombine water to gain more and more energy).
You mention pressure, too. However, that pression doesn't magically form. Since you're not adding any mass to the system, any pressure change can only arise from two things: change in temperature and change of the state of aggregation (solid/liquid/gas). In other words, water does not vaporize because of an increased pressure. Rather the pressure increases because water has been vaporized in first place.
The other way around you would again create a perpetuum mobile. Take any sufficiently robust enclosure and fill it with let's say 1l water. now create a minuscule spark. Just enough to locally rise pressure and temperature such that some water vaporizes. If you were right, this would make the water around vaporize, too. And because this would rise the pressure further, the temperature would increase further, which would vaporize even more water. See where this is going? your minuscule spark would vaporize any amount of water. But it doesn't. You get a blip, and an overall increase of temperature that wouldn't even be measurable.

Same thing for your steam engine. You don't get any more energy out of the thing than you put into it. If you use reactive electrodes, that's additional energy you're going to put into it. However I'm assuming that's not what you want (otherwise you may start looking into explosives which are far better sources of "rapid" chemical energy than corroding aluminium electrodes). So I think it is safe to assume that you want to vaporize water with the electric energy only. And that leads without mercy or "escape" to the values quoted by Twospoons. 334J/g to get from 20°C to 100°C and an additional 2260J/g to get vapor. Add a couple tens to hundreds of Joules for losses to the environment, cables, etc. The law of conservation of energy is hard and doesn't know exceptions for hobby or free energy projects.
Rounding those values leads to 3kJ per 1 gram of water that you want to get from 20°C to fully vaporized. Sure, with only 1kJ you'd still get a decent bang and "steam". But that "steam" would be 2/3 atomized water (fine droplets of liquid water flying around), not vaporized water.


Kind regards,
Max

[plasma]

Thanks all
I added the diodes across the capacitor bank, more energy seems to go into the discharge, 200V, it drops to 1.2V Vfd.
I'm still looking at other salts, as I think they can add to the gas/vapour.
The 2-4kJ was expected, and within the 4-8kW Genny boundary.
The Al seems to work better in air, but apart from some wire feed system like a Mig welder, I'm not sure.
I think a salt that can lower resistance of the salt gap, will produce more I^2R heat in the water due to more current but less resistance.

[plasma]

Tested with thin Ali wire, it vaporized and sent a large spray of water.

Thinking of using ZnCl2 its highly dissolved and I think it will lower resistance, just worried about by produced.