Magnetohydrodynamics - Propelling Liquid Metal with Magnets!

Hello,

magnetohydrodynamics

, that's a long word for a very old principle, the same principle that drives basically all of our electric motors and operates our electric generators effectively. When a charged particle, such as an electron, moves, it becomes associated with an electromagnetic field and by convention we use what is called the right-hand rule which states that if the electron moves in the direction of the thumb of my hand right, the field is considered to move in the direction of the fingers of my right hand. For lefties, you're not excluded because the field doesn't actually rotate or move, it just has an associated chirality, an associated polarity, which by convention we consider this to be the standard orientation of the field and as long as we stick with that convention , okay, it's consistent if we take a wire like this which is basically an electron tube and we place it near another similar wire and we cross the space with another conductor following the right hand rule the field in this conductor wraps like this way the field in this conductor is wrapped this way in the field and this return conductor is wrapping itself this way, as a result all these fields oppose each other and like a current moves through here as the electrons move move around here, they all want to move away from each other and So these rods, these wires would want to expand with each other and this armature would want to move away from the conducting loop which is basically the principle behind an electric motor, if the armature can move freely and we put current Here, the armature would want to move along the rails, if the rails were round, like the tires of a bicycle and the armature were connected via an electrical power, the armature would move within the pattern of the wheel of the bicycle and would form a rotational torque, you produce a motor, the field mass generated by this small circuit is extremely weak and the force is the product of those very weak fields.

It is the field of this multiplied by the field of this and therefore the amount of current that would have to flow through this circuit to produce a significant force would have to be in the thousands. of amps practically that is difficult to achieve and that is why when you look at an electric motor you will see many turns of wire because if you actually put, say, a thousand little wires inside this open tube and ran an amplifier through each one, you would get the same electric field outside the tube as passing a thousand amperes through the tube, so an electric motor is recycling its electrons to produce the fields necessary to cause significant motion;

However, it would still require a lot of current to generate much significant force and these motors and generators are typically augmented by the use of a permanent magnet. A magnet is made up of crystals that have an extreme amount of polarity, there is a graveyard in the distribution of electrons as a result of the small particles, the small crystals, are extremely powerful

magnets

, but before they are formed into a magnetic block, The powder that will be centered on this is random, so there is no kind of net or macroscopic magnetic field outside the sample after they center it on a block.

They expose it to an extremely strong electromagnetic pulse that orients all the crystals in a unidirectional orientation so that the overall magnetic field of the magnet is not that different from the individual magnetic field of small particles and will remain permanently unless you heat the magnet further. its Curie temperature, which is where the crystals become mobile enough to disorient them or you expose it to a very strong countermagnetic field which can change the orientation of the crystals, but as long as you don't do those extreme things to The magnet is basically to always if you put a magnet in the same place as the little loop of wire that we produced, it is still a magnetic field and as a result the force on this armature is not the product of a weak magnetic field multiplied by a weak magnetic field. or two low numbers is the product of a large number and a small number, so this armature produces much more force if you have

magnets

located in the motor and that is why when you look at permanent magnet motors or generators, they use these magnets not because the wires are not producing a field, but to increase the field, this process can be reversed and if you imagine for a second that we have produced motion in this wire because we have the electrons inside it that we want to move at right angles. to this field and right angles to the current moving through it, if instead what we do is force the armature through a magnetic field, what happens is that the electrons inside the armature, because they move In this way, they produce a magnetic field. and that magnetic field interacts with the permanent magnetic field of the magnet, therefore those electrons want to move at right angles to the magnetic field of the magnet and with the direction of movement and therefore those electrons will be induced to flow along along the conductor, therefore we generate a current of electrons and that's how we form a generator so you can reverse it, it's just two different points of view for the same process, the important thing is that it doesn't have to be a wire and that's where magnetic hydrodynamics comes into play.

I have an n40 magnet of relatively modest strength and on each side I have two nickel electrodes. What I am going to do is fill this container with water, very pure distilled water is a very poor conductor and, in fact, very puristic waters are often characterized by their electrical resistance, they are deionized and the higher the electrical resistance , the purer the water, in fact, super pure water is actually corrosive because it lacks ions and we can address that in another video. but, however, we can improve the conductivity if we add regular sodium chloride to the water salt, table salt salts have a very low ionic bond strength and therefore in positive sodium and negative chlorides are Exposed to very polar water molecules, the water molecules will intercalate. and make the positive and negative ions separate from each other and flow into the medium that we put them in, so if I put it in there and let it shake a little bit, these ions can do the same thing that electrons do.

They are much more massive and there are far fewer of them, so ionized water like salt water or seawater conducts electricity, but not very well, so we need to use a fairly high voltage to make a significant current move. between these electrodes so that the salt is dissolving. Now I'm going to connect two cables from this power supply to the electrodes. If you have read the book Hunt for Red October, the Russians developed a submarine based on a propulsion system that used

magnetohydrodynamics

. It's kind of interesting because The process works and it should be saline enough now, once it stops flowing, what I'm going to do is put a little bit of dye between the electrodes so you can visualize a little better what's happening and there's a pair.

There are plenty of YouTube videos showing this, it's an interesting little phenomenon. Hopefully it's not flowing too fast right now, maybe a little while, okay, not much now, if I take the power supply and apply a voltage, what will happen? What happens is as the voltage increases, we start to generate a current that you'll see here and the current will cause the dye to flow now if I take my little Q-tip, my little toothpick and do it a little bit. Look, it's transmitting pretty well, uh, now if I turn the voltage up a little bit more, you can see the flow is pretty impressive, but if I was working for the Soviets during submarine development, I think I'd probably end up in Siberia.

If you were proposing to drive a boat with this, however, the force generated is proportional to the current which is currently about 0.3 amps and the magnetic field. So what happens if we get a slightly stronger magnet and a much stronger field? Now what I did was replace this device with a new one and in this case, instead of using a N 40 magnet, I am using a N 50 magnet 2. The number at the end represents the strength of the magnet. This is a lot. Also, with a stronger magnet you will notice that the width of the channel is only half, as a result the current flow is proportional to the contact area of ​​the

liquid

across the electrodes, but also proportional to the distance the current has. to flow, which makes it narrower.

It means that for a given voltage drop we're going to get more current here and as a consequence we're going to get much higher flows out of this thing, as I'll demonstrate, so when you start increasing the current here, the voltage You'll notice that you get quite a bit of flow. significant, so it may not end up in Siberia, but we are at three and a half amps when before we were only generating about 0.3 amps. Also, you will notice this foam that is forming. This is how they discovered or were able to locate the Russian submarine and this is the hydrolysis of water that occurs when a potential between the electrodes of 1.2 volts is exceeded, the electrical potential is actually dissociating the hydrogen and oxygen and those bubbles are released. foam from the hydrogen and oxygen that are released now, as I said before, a generator and an engine are basically two views of the same process, so this process can be reversed and we can use this process to generate electricity.

Let me show you that. Now what I have done is I have taken the same salt water and placed it on this little pin, what I am going to do is open the valve and we are going to flow the

liquid

and you We will see here the voltage that occurs when we start a flow of the liquid ionic through the magnetic field. As you can notice, it's not much, but it still shows that there is some potential and the reason the voltage is so low is simply because we have very little velocity here and we don't have a very large surface area on a very large magnet. weak, but this system generates 56 millivolts, to get real power from this we would have to flow the fluid much faster. and we would like the gap to be much smaller and the magnetic field, if possible, much stronger.

However, the conductivity of ionic liquids is so low that it would be difficult to get a huge amount of energy unless we could actually improve the conductivity and a better alternative is to move away from ionic liquids and go to something more

metal

-like and specifically to liquid

metal

, so we have a nice apparatus outside and I'll show you what happens when we do that, okay? What I need to do is repeat the demonstration now with a liquid metal and since I don't like working with mercury when I can and certainly not inside, I have decided to use a low melting point on a metal alloy that will conduct electricity but is substantially safer.

This alloy is called sera low 136 and is a kind of member of a family of so-called eutectic alloys. These are alloys of different metals that melt at a low temperature and that, when combined, the individual metals interfere with the crystallization of their neighbors and, therefore, the result that that combination melts at a much lower temperature than the individual metals it contains. Sera whoa 136 is a bit unusual in that it is one of the few metals that does not contain gallium or cadmium, so it tends to be substantially safer, being made from a combination of lead, bismuth, tin and indium.

What I did was I put some of this into this channel and we're going to demonstrate how this material typically behaves when it hardens. pewter and when liquid it looks like liquid solder and is frequently used by mold makers to make liquid metal solders. It can be used in a machining operation to fix very delicate components that would otherwise be very difficult to hold and then when you are done with the machining operation you can simply heat the part a little and take out the emerging part because it melts. at 136 degrees Fahrenheit. I'm out just to allow myself to use this heater to bring this great water bath guarantee up to above 136 degrees, but you can see on the temperature probe that right now it's at about one hundred and forty-two degrees and that's why this It's liquid, so now the material in the channel is in contact with two electrodes like we had before. on top of the magnet and I have it connected to a power source and when I apply the current, if I'm not sure that you'll be able to see all of this at the same time, you might want to go through the video a couple of times or we can repeat this depending on how we edit this, but as I turn up the voltage, the current will increase very quickly and you'll want to see what happens to the liquid in the channel as the current increases.

I'm going to start raising the voltage now here we see it move up and I turn it off and it goes back again don't turn it on again and you can see that the metal even though it is extremely dense is able to move. On the same hill where the ionic liquid was able to rise and the current that has been flowing there is about 15 or 16 amps, in fact, the ability to move metal with MHD types was finally starting to awaken. The use of pumps has been applied to coolnuclear reactors, it is very difficult to cool high temperature devices in which you do not want moving parts, you do not want pumps or pistons or anything that can be damaged by high temperatures and I do not want to include them in the fluid circuit, that is why it is used around the world for cooling purposes and when we get in I'll show you how we can use it for a kind of unusual application, okay, up to this point, to demonstrate some of the forces involved, I've relied on the powerful magnetic field of a magnet. permanent but because as I explained above there are forces that are generated by current if you get enough current you can actually produce very significant forces so what I've done is set up a little demo here using a power supply to charge a fairly large electrolytic capacitor.

This is a 4700 micro farad 450 volt capacitor and this capacitor goes. discharged or shorted through what is called a pancake thyristor or scr. These are quite unusual solid state switches that can handle extremely high voltages, thousands of volts, and they can handle tremendous currents, tens of thousands of amps, and the way they work is you effectively loading them. or allow current to flow through one side and then there is a small gate which is a switch and the way the gate works is that there is a small bias voltage that I create between the ground of the thyristor and the upper voltage that they produce the three. volts from the battery so effectively, by providing three volts above ground to the discharge end of the switch, the switch will open and allow all the voltage and all the current from the capacitor to discharge through this Loup that I have formed between these two closely. spaced conductive rods back to ground, what we're going to do is demonstrate this and show that noticeable forces can be generated if a sufficient amount of current is developed and we're going to start charging the capacitor, these are the DC studs.

Through this capacitor, while the power supply is charging, it will go to about 50 volts or so and then when I press this button, I will close the switch and allow current to pass through the two conductors. Notice the two parallel conductors, one, two, three. you will see that they separated, the connector at the end also felt a force, it wanted to move this way, but it is tied by the weight of the wires, the current output of this capacitor is proportional to the voltage, the current, the energy is proportional to the square of the voltage but the current is proportional to the voltage the forces between these rods however are proportional to the square of the current the field in one interacts with a field and the other so if I double the field here and I double the field here I get four times the force, so if I charge the capacitor up to, say, a hundred volts or twice that, I get four times the force between these two conductive rods, once we get this to about a hundred volts, we'll hit the switch. and you will see what the difference is: one, two, three substantially different.

These are the same forces that are used to operate a railgun and one of the interesting things is that the current that flows through here is quite substantial, it's in the order. of thousands of amps and I'm going to demonstrate exactly what that is with an oscilloscope. Okay, now I've set up the oscilloscope and what we're doing is measuring the voltage across the capacitor and when we turn on the circuit. show the voltage drop across the capacitor as it passes through the short circuit. One of the things about these capacitors is that they have a fairly high internal resistance, so it is actually the capacitor itself that limits the discharge rate, not these wires, this is significant as I'll explain it in just a second. , but what we'll do is increase this to about a hundred volts and when I trigger this to three, you'll see a trace of the voltage going through those two, one, two, three.

If you see in this scan, the voltage has dropped to about 30% of its initial point at these are 50 microsecond skill grids in proxy from about a hundred to 150 microseconds. Now, what that means is that almost all of the energy from the capacitor has been discharged in about a six-thousandth of a second and that's significant because the two ways we're going to continue with this information is that we're building a very yoke-style magnet. large to produce a much higher field than those you have seen in these small tests, they test devices to produce a much more powerful MHD pump, as well as a much more powerful MHD generator that will run on seawater, in addition, what we are going to To do is use some of this technology to build a railgun.

The principles of a railgun are very easy to understand. I mean, we just looked at that, but there are two very, very difficult problems that need to be solved with those devices. The first is that when a railgun fires the pressures. that you see here, which are microscopic and based on a few thousand amperes, are multiplied thousands of times and the forces that separate the rails when a railgun is fired are measured in thousands of kilograms, the sliding armor that goes between the two rails has to make almost perfect contact but it has almost no resistance and as you can imagine that would be extremely difficult to do because if you have too much resistance before any load has been produced such as the projectile or the armor that you are going to be the slide can be blocked and when it does, all the current will flow through it, it will weld into position, it will probably explode and if it has enough free space to pass through, what will happen is under the forces of the discharge.

The rails can separate microscopically, you will get an air gap, you will develop arcs and plasma and you will waste a lot of energy and potentially explode again, choose your armor, so one of the techniques we will use uses the same What I demonstrated with the liquid metal is We are going to use a liquid metal SAPO to help provide good contact with relatively low machining tolerances. The US military has released information that they were investigating so early. Russian researchers have published some papers and the comments are: This looks very promising, but could be a bit expensive.

I don't think that should be a limitation, at least if the process works, so we're going to try to make the second aspect of this that Look, if you watch some YouTube shows or YouTubers that try to build railguns, they will often take a large number of these capacitors, they will connect them in parallel and then use the armature itself as the switch that it provides. disk, as I demonstrated, this four thousand seven hundred microfarad capacitor that at about one hundred volts stores about 25 joules will discharge almost all of its energy in about 6,000 of a second if you imagine a railgun of let's say about half a meter long if the initial velocity of the projectile is close to zero and the final terminal velocity is what leaves the gun, the average velocity of the projectile is half, so if you travel half a meter in 6000th of a second, you are essentially traveling at a speed of about 3,000 meters per second on average and a maximum speed of 6,000 meters per second, which is a much higher orbital speed than any railgun shot, so the problem of discharging these capacitors directly through a short circuit is You end up using all of your energy from the start, usually welding your light to your projectile or blowing it up and not getting the energy out when you need it, what you need is to use what is called a pulse forming network which essentially gets all the energy of the capacitors that can, but not before, the projectile leaves the end of the weapon and a pulse is formed.

The network introduces inductances to slow down the pulse and adapt it to the duration of the flight time through the rails, also, almost all the youtubers who have done this, as I said, cutting these electrolytic capacitors through these rails and through their projectile, when they do, they create tremendous inductive fields as we have demonstrated here and those inductive fields as soon as the voltage drops across the capacitor will then feed back the capacitor in the opposite polarity and this type of feedback will continue until the capacitor reaches a certain voltage and then it will be fed back into the field and this type of voltage reversal up and down across the capacitor is called ring down and that ringing on a polarized capacitor is lethal so it is surprising that any of them survive more than one pulse, but it certainly wouldn't survive many and that's one of the reasons you want to use a thyristor or rectifier to protect the capacitors in the build process.

Railgun, so as we move forward with this project, we'll go in both directions, but you can get an idea of ​​some of the principles behind what we're doing and I'm looking forward to putting the magnet together and I'm looking forward to getting some real information out there. through leads, so we'll show you that as soon as those things mature a little bit more, but I want to thank you so much for watching. I would really appreciate it if you would. subscribe because it really helps us a lot in any case have a wonderful afternoon good night