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2022-11-29, 08:41:37
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Author Topic: Archimedes' screw applied to electricity  (Read 1503 times)
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@Fred

The principle of Hatsopoulos' patent is indeed very close to the Chinese Maxwell's demon in the way of using the magnetic field to promote the movement of electrons from the hot plate to the cold plate. But I wonder why this temperature difference since it should work as well with hot plates only. The extraction of electrons from a hot plate and then their deflection by the field seems to be the only condition necessary for operation.

Hi F6FLT,

Looking further, the concept of using magnetic fields to direct electrons from plate to plate seems to have been prior art even at the time of Hatsopoulo's patent, being used in a wide variety of so-called 'cross field devices'. For the most part the US patent office hasn't allowed devices in a single temperature bath because of the thermodynamic issues, so I'm guessing even if the inventor had thought of it, he wouldn't have put it in there. I've only seen two patents that convert heat at a single temperature, and each is somewhat 'in disguise'-- one using the diffusion current due to differential doping of semiconductors, and one as a quasi-Seebeck effect.

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I looked into the possibility of thermionic emission some time ago, I have a number of files on a back-up memory stick somewhere.  The "Nottingham Effect" comes to mind and also the little used "Inverse Nottingham Effect".  The scheme used magnetic fields to direct the cathode emissions away from the anode that supplied the electric field pulling the electrons away to another collecting electrode sitting behind the cathode and therefore not in the electric field.  If anyone is interested, I will dig out the data.

Smudge

Hi Smudge,

I think some people would be interested, including me. I am thinking of checking in a future project with a simple plasma in the air if it is possible to "sort" the charges thanks to a magnetic field and according to their energy. The Nottingham effect would seem to help.
Perhaps you could open a new thread on the subject?


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Hi F6FLT,

I'm not sure if you noticed, but I uploaded one of Smudge's papers just before you wrote to him.

I've ordered the parts for a test of 'stimulated drift current in a thermoelectric module at a single temperature.'

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@Freed

Thanks for the information, I had indeed missed the paper of Smudge, and to give us the result when you will have done the tests



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@Freed

Thanks for the information, I had indeed missed the paper of Smudge, and to give us the result when you will have done the tests

Hi F6FLT,

I've done some initial tests with a thermoelectric module with somewhat interesting results. I used the module whose datasheet is attached. My wife has a device for drying the air in the laundry area that consists of a heating element in a plastic box with holes in the top. The temperature measured with a digital cooking thermometer is a steady 54.4 C.
The bias circuit consisted of 4 AA batteries in series with a 10K resistor. Voltage was 6.65 V and the I was below 1 mA, the resolution of my Fluke meter.
After checking that the module worked in the normal fashion, I wanted to see if it would generate power at a single temperature. I put the module on top of the dryer hot side down but without a heat sink on the exposed cold side.  The upper side of the module was exposed to air, but this was warm air from the dryer, and the temperature between top and bottom of the module was less than a degree apart after 5 minutes.
After it had been in position for 5 minutes I took measurements. The V across the module was around 65 mV and the current through it was 15 mA giving a power output of .9 mW. The current didn't drop over time though the voltage did vary considerably, so this was an estimate of the average V. It's a pretty efficient module as these things go-- from the datasheet I estimate that it generates about 19 mW for every degree difference between cold and hot sides. So perhaps the small difference between the sides in my setup was enough for a small standard Seebeck output.
Application of the bias across the cell had inconsistent results. There was always some effect, but sometimes the I of the cell dropped, and sometimes it rose. There might be an effect essentially due to the speed of my manual switching of the voltage with a key type switch. In any case the bias V was very low, and results were within the margin of error. I'm going to get a power supply so I can bias with 60 V. 
The final result was the most interesting. I had two small disc shaped neodymium magnets and on a whim put them on top of the module while it had a stable output of around .9 mW. The output immediately shot up to 79 mV and 23 mA, or 1.7 mW! I thought perhaps this was due to the magnets being cold and providing a temporary temperature differential, and indeed the effect seemed to vary somewhat each time I did it. However, I left the magnets on the dryer surface for some time to reach equilibrium and they still had an immediate effect on both current and voltage.
Perhaps a Hall or Nernst effect? I have no idea..

Fred
 
   
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The final result was the most interesting. I had two small disc shaped neodymium magnets and on a whim put them on top of the module while it had a stable output of around .9 mW. The output immediately shot up to 79 mV and 23 mA, or 1.7 mW! I thought perhaps this was due to the magnets being cold and providing a temporary temperature differential, and indeed the effect seemed to vary somewhat each time I did it. However, I left the magnets on the dryer surface for some time to reach equilibrium and they still had an immediate effect on both current and voltage.
Perhaps a Hall or Nernst effect? I have no idea..

Fred

Hi Fred,

It is indeed very intriguing. We would need to know what materials are inside the thermoelectric generator. The effect of the magnet could be to optimise the operation by chance, by mechanical pressure on the magnetic products inside or by variation of their permeability. Otherwise it's more interesting. If you are sure that you have eliminated the effect of temperature perturbation when you position the magnet, then the effect could be due to the transverse deflection of the electrons by the Lorentz force, which would favour the dissymmetry between electrodes as if it were a temperature difference.
The results would have to be evaluated according to the direction of the magnetic field with respect to the plane of the component.



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Hi F6FLT,

Your comments are very useful going forward. I haven't had time today to do any more tests, but the very first one will be to stand the module on end on the hot surface, equalize the temperature, and then check the output again. If the output is only due to residual standard Seebeck effect then it should be much reduced since both sides have the same contact with heat. I expect this will be the case. Then apply the magnets as before but putting a small gap between them and the module to eliminate any mechanical effects. 
There's no information on the Marlow site about the composition of the module, but the vast majority of commercial modules are made of p- and n- doped Bismuth Telluride. BiTe is a high electron mobility Hall material. Establishing the Hall Coefficient Rh of the BiTe material is more difficult since it varies depending on the doping material and its concentration, and also declines greatly with temperature for some materials. Rather than get into a lot of detail about that, I'll do the suggested test as to orientation of the B field. In the test done already, the field is parallel to the flow of electrons and holes, so if there were a Hall effect it would indeed resemble a Lorentz force acting on them, causing them to corkscrew down through the ceramic blocks. This would tend to make their mean free paths longer and reduce efficiency, I think. Putting the magnets at right angles to electron and hole flow should establish whether the Hall effect is in play.

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Hi F6FLT,

So I was only able to do one test today. I stood the module on edge on my air dryer. Temp was still 54.4, very steady. After 20 minutes I checked V and I. V was a steady 4 mV, and current varied between 1-2 mA, giving at minimum an output of .4 mW.
This should be a good test of output at a single temperature since the ceramic bricks of n- and p- BiTe are oriented parallel to the surface of the heat source. Even with a heat differential between the edge touching the heater and the top edge, all n- and p- pairs at the same height experience the same temperature, so no current should flow through any pairs due to the Seebeck effect.
This would seem to indicate a small output from a single temperature thermal bath, as in the Graphene experiments.

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This would seem to indicate a small output from a single temperature thermal bath, as in the Graphene experiments.

Fred

We should be sure by lowering the temperature to room temperature instead of 54.4.
Even if the current was only 100µA, it would be significant. Is there still a current at room temperature?



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Hi F6FLT,

I got 0 V and 0 A for this test. However, my meter can only go down to 1 mA and 1 mV, so these lower outputs wouldn't be detected.
Now I'm trying the small magnets under these conditions, and without pressure or contact by the magnets. 

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Hi F6FLT,

Placing the stack of two small neo magnet discs on the surface of the module at RT (about 21 C), separated from it by a thin cloth, immediately caused the voltage to rise to 2-3 mV, with still no observable current. The V still seems to gradually be rising, so I'm going to leave the meter connected and come back after a while..

Fred
   
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Hi F6FLT,

It rose to 5 mV and then gradually declined to zero over about 20 minutes. Not sure what to make of that...

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@Fred

Difficult to draw conclusions. Maybe a certain temperature threshold is needed. It should be left for a long time in a hot container (60 c or more) and extremely well regulated, and see if a current stabilizes.


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Hi F6FLT,

Indeed difficult, especially with my primitive equipment. I'm jumping ahead too fast due to finding the magnetic effect. I need to read more about Nernst effect anyway. I'm going to drop it for now to focus on establishing some basic facts. I will wrap the module tightly in plastic and put it in a bowl of hot water in the sink, not touching the sides. Then after some time to give the module a chance to reach a uniform temperature, I'll take measurements of V, I and temperature of the bath. This will establish for sure whether there is a single temperature effect, and also possibly some sense of the magnitude relative to temperature.

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Hi F6FLT,

I did the test with the module wrapped in plastic and suspended in a water bath at 65 C. After some ten minutes in the water, there was only a persistent V of 1-2 mV and no current to the limits of my meter. It will take a more sensitive meter or a hotter bath to go further.

In the meantime I'll return to trying a bias voltage, which was my original objective.

Fred
   

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Note that since electrons move very slowly in a conductor, the rotation will have to be done very slowly too (linear speed of the order of mm/s), otherwise it is not sure that the electrons can follow the plate because they are subject to the resistance of the conductor.

I don't know if it can work. If it works, I don't know how much current we can reach. Finally I have no idea of practical application nor if it can be a way for energy. I have not seen the principle applied anywhere in a conductor. A similar idea is exploited in travelling wave tubes, but there it is in vacuum, not in a conductor. So it's just something I would like to test.
I already tried to apply the idea to dielectrics (it's on this forum), but it's impossible because the effect on positive charges cancels the one on negative charges. But in a conductor, it should work. Before I go into a practical realization, please tell me if you see any objections to the possibility of operation.
Everything seems to be simple here. The interaction of charge and field is always associated with work. If an electric charge moves against the forces of an electrostatic field, then this leads to an increase in the field potential. If, on the contrary, it leads to a decrease in the field potential. In this case, the movement of the charge due to the forces of the electrostatic field will lead to a decrease in the field potential. To maintain this potential at a constant level, an external high-voltage source that creates a field must do work (expend power).
In addition, they say, the electric field does not penetrate the conductor. its is not there.
What will push the electrons?
   
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In addition, they say, the electric field does not penetrate the conductor. its is not there.
What will push the electrons?

The question is legitimate, this is the point that makes me doubt the operation, I talked about it with the tidal effect.

Let's place ourselves in the case where the coil is fixed and the plate turns around it.
We must also see the coil as a plate with which the other real plate constitutes a capacitor.
As in any capacitor where the electrons accumulate on the opposite plates, the electrons of the coil will be attracted to the side of the plate, even when the plate is rotating. As a result, there will be a displacement of electrons relative to the coil, and therefore a current.
The defect is that the electrons attracted to the plate can come from either side, i.e. some turn clockwise to move towards the plate, and others counter-clockwise, cancelling out their effects. This is the tidal effect I fear, where the net movement of the electrons will not depend on the direction of rotation of the plate.

Only experiment can tell, but I have postponed testing because the thread on the gradient of the vector potential seems more promising.




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Hi F6FLT,

My initial concept before going off into magnetic effects, or single temperature operation, was to determine whether a bias voltage could improve the output of a thermoelectric module. I've established this pretty solidly now.

A 6.65 bias V was applied in series with a 1 Mohm resistor through a switch to the negative terminal of the module while it was on the air dryer.

There was a temperature difference of about 9 degrees between top and bottom of the module, so the Seebeck effect was in operation.

The current from the module averaged around 11 mA, but varied somewhat over time. I recorded the current and then closed the switch. Leaving aside one anomalous reading where the current rose by 7 mA, the current rose an average of 4 mA every time the bias was applied. The effect was consistent and repeatable.

The actual current from the bias was below what my meter could measure, but simple calculation shows that it could not have been more than .67 mA with the measured V and R of the bias. The effect was actually stronger with the 1 Mohm than with the 100 Kohm, showing that only the EMF was responsible for the effect.

I haven't done voltage/power measurements at this point. I just wanted to nail down the drift current effect. Next will be to see if the actual power output is increased.

I'm using a very small bias voltage, but soon will have a better power supply and can work at more practical levels.

Fred

 
   
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Hi F6FLT,

I'm getting my new power supply tomorrow. I've confirmed that I can increase the steady state power output of the thermoelectric module under the conditions already described from 146 mW to 197 mW by application of the 6.65 V bias through a 1 Mohm resistor. The power from the bias is calculated to be around 44 mW, so there is a gain of 6 mW through this process. Not much-- but using the bias in series is not ideal, nor is the bias or R value. When I get the PS I will be working with V up to 60 V, R up to 10 Mohm, with bias in parallel.

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Conventionally, to obtain a current in a conductor one creates an electric field along the conductor, for example by connecting it to a battery. Here the aim is to drive the electrons along a conductor, thus obtaining this current, by attracting or repelling them by an electric field external to the conductor. By separating the control circuit from the driven circuit, this would be equivalent to the principle of induction between coils, but with the advantage of being able to pass DC current.

The current impossibility of DC current induction seems to me to be the result of a missing link, not in the theory of electromagnetism, but in the practice we have of it. The spatial gradient of the potential vector, considered in another thread, also seeks this same result.

Electrons move very slowly in a conductor, in proportion to the intensity of the current. We should therefore drive them with the same slowness. Let's quantify it.

For the current/speed correspondence, we have to go through the current density J = I/S where I is the current and S the cross-section of the conductor, and the drift velocity of electrons is given by v = J/ρ where ρ is the charge density in the conductors, which depends on the nature of the conductors. For copper, ρ = 1.4 * 1010 C/m³.
Example: 20A in 2.5 mm² wire gives us a velocity of 0.6 mm/s. As an indication, I produce here the distance travelled by an electron during one period of an AC signal. At 50 Hz, this corresponds to an oscillation of 2µm amplitude. In TV at 500 MHz, we get to the nanometre level.
Note that the drift velocity is very low compared to the thermal agitation speeds which are of the order of 105  m/s.

If, to begin modestly, we are looking to obtain a current of only 1 mA, it is in our interest to use the thinnest possible conductor, so as to increase the current density and the speed. There is magnet wire with a diameter of 0.05 mm, which would give us a current density J=10-3 / (pi*(0.025*10-3 )²)=509296 A/m². The drift velocity of the electrons would be v = J/ρ = 0.036 mm/s.
But even so, if we use a coil with a diameter of 5 cm, we will need a field rotating around it at only 0.18 Hz or about 1/6th of a revolution/s. For a mechanical realisation, such a slow rotation will have to use a stepper motor, or gears, which is not easy. But for a field rotating from quadrature signals, it is perfectly within the reach of a signal generator.

If the field rotates too fast, the electrons will not follow because of the resistance of the conductor. The question now is to optimise the coupling of the external field to the free electrons in the conductor.


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Example: 20A in 2.5 mm² wire gives us a velocity of 0.6 mm/s. As an indication, I produce here the distance travelled by an electron during one period of an AC signal.
What if we took a superconductor. The diameter can be made small enough, and the current density and electron velocity large enough.
   
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What if we took a superconductor. The diameter can be made small enough, and the current density and electron velocity large enough.

The only problem is that I haven't seen any in the shops at a reasonable price :).


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