Hello. There today we look at Magnetohydrodynamic Power Generation. So, that’s the topic for today’s class, well let’s look at some of the terms right at the title slide. So, we do have this term hydrodynamic. So, if you are a mechanical engineering background student or even otherwise you may have encountered this term, essentially it has got to do with the fluid flow with you know the movement of saying some mass in the presence of a fluid, relative movement of the mass with or some object, in the presence of moving fluid, and that is what we that study is then referred to as the hydrodynamic you know the study of that a combination of some movement of this liquid and this mass. So, that is hydrodynamics relative moment study of the relative moment of solid in some fluid flow. So, that’s what we are looking at hydrodynamic behaviour. Now we are additionally adding something here, magnetohydrodynamics. So, there is some fluid flow here. So, as you can imagine from this terminology there is some fluid flow here, there is some magnetic field here, and there is some relative motion. So, all these things are going to be there in the concept that we are going to discuss through this class. And it is associated with power generation. So, and that’s the relevance of this topic to our course. ah Now I will also point out that people have studied this, and there is still some work that goes on it; however, it is not still that commonplace, and there are competing technologies, there are issues with this technology etcetera. So, it is not something that and that’s the reason why most of us are unlikely to have heard about this. So, it is you know, for example, this is yeah. So, this is abbreviated as MHD, but chances are most of us have not really heard about it or you know heard about it as something significant you don’t really read too many articles about it, and in the general public parlance. Unlike say lithium-ion batteries or any other such technology which you are hearing about all the time. So, that’s something to keep in the background so, although we will look at this for a sort of a sake of completeness kind of activity, and it does have some relevance in the grand scheme of you know what impact it is making it may not be as significant as of it’s of today ok. (Refer Slide Time: 02:34) So, we will learn objectives for this class are to look at the operating principle of magnetohydrodynamic power generation, and we will also see that there are different modes in which it can be implemented. So, we will briefly look at those different modes in which this magnet magnetohydrodynamic power generation can be implemented and of course, in the context of this discussion we look at the challenges posed by this technology and try to get a sense of what is possible here ok. So, those are our learning objectives the operating principle the different modes, in which the magnetohydrodynamic operation happens, and what are the challenges supposed to wait. (Refer Slide Time: 03:13) So, if you see what do we normally do in terms of a large scale power generation plant. In a large scale power generation plant, you have some fuel and that fuel is burnt ok. So, it is burnt to release that energy, and so that energy then moves this way ok. So, some from fuel some energy is coming out that energy moves this way, and then it heads off towards some generator. So, maybe let’s say turbines that rotate, and that is connected to a generator, and then we get electricity right. So, our output is electricity; input is some fuel which is then burnt, then moves through this process and generates electricity. So, when you do this as we are aware since it’s like a heat engine kind of a process you have this thermal energy that is coming and you are converting that to electricity after discarding some amount of heat, the efficiency is given by 1 minus T 2 by T 1. So, we are sort of limited to this efficiency and therefore, it is in the scope of this efficiency that we pick up energy from the fuel. So, there is some energy in the fuel we pick up that energy. So, there is always interest to see if there is some little extra energy that we can squeeze out of the fuel over and above this you know this limitation. This limitation is there, but is there a way to work around it is there a way to do something before we reach this hit this limitation etcetera, and so that is something that we are interested in always looking at. (Refer Slide Time: 04:54) So, as I suggest said you know in a typical thermal power plant that’s our scheme of operation. So, we have some hot gas that is coming in, and that’s essentially sent towards the thermal plant, and in the thermal plant, we are generating electricity. So, that is the general scheme of operation that we have, and as I just mentioned this is our efficiency limit ok. So, that is basically what we are trying to do. So, as I said we intend to see if there is something extra we can do in this circumstance to get a little bit more energy out of this fuel, and any extra energy that we get out of the fuel essentially increases our overall efficiency, overall process efficiency relative to the energy that is available in the fuel is only going to go up if there is some way, we can squeeze out some more energy from this process right. (Refer Slide Time: 05:47) So, this is where we create this we utilize this magnetohydrodynamic generation process ok. So, this MHD process is utilized in this context it’s the magnetohydrodynamic energy generation process is used, in this context of utilizing the process flow that’s already happening in a thermal plant, and sort of introducing this into that process flow to see if you can extract some more energy out of that fuel. So, basically now what we do instead of going from the hot gas directly to the thermal plant which is the turbines essentially, and where you know you generate electricity, and then you get the electricity out of it, instead of doing that the hot gas first goes to this magnetohydrodynamic generator, and from there it goes to the thermal plant. So, this is the pathway it takes right. So, first to the MHD and then to the thermal plant so in fact, they call this as the topping cycle and sort of the bottoming cycle. So, at the top end of this cycle of you know the movement of this fuel, we pick up some energy that’s the MHD cycle, and then the thermal plant comes right after that and that’s the bottom half of this cycle. So, usually, the MHD is operated in this mode, in a combined cycle power plant ok. So, typically it’s not really operated separately of course, for study purposes you can operate it separately I mean that may be the best way for it to operate it even. But generally, you are looking at a combined cycle power plant, which is where we generate this energy. So, it is in this context that it is utilized ok. (Refer Slide Time: 07:23) So, to do this process to you know to operate this magnetohydrodynamic generator, we actually need to create a plasma ok. So, we need to create a plasma. So, what is plasma? Plasma is actually it is considered as the fourth state of matter ok. So, we are more familiar with solid liquid and gas. So, these are the 3 that we are more familiar with plasma is the fourth state of matter ok. So, it is basically you can think of it as an ionized form of gas it is gas, in an ionized form it is only in the form of ions that it is present, and it has it is own behaviour associated with it and it is actually the fourth state of matter. So, interestingly I mean the reason again; we don’t hear about it much we do not talk about plasma much, because for the most part on the on our planet we are not really dealing with plasma ok. So, you have to go to fairly high temperatures or fields high electric fields etcetera to create this plasma kind of a situation, normally in you know commonplace activities that we deal with for the most part on the planet; we don’t see plasma, for the most part, we are not really encountering it daily in any of the activities that we do typically we don’t see plasma. Interestingly though if you take the universe as a whole even, if you take the solar system and you take the universe as a whole, plasma is the most common form of matter ok. So, it’s the easily we are considered as the most common form of matter, it is there across the universe there is a lot of ionized material around the universe. So, for example in all the stars in the sun, the temperature is so high that the material stays in the ionized state. So, in the sun we have a plasma, and if you look at the mass of the sun, mass or volume of the sun, well over 99.5 per cent of the mass of the solar system is the sun right. So, 99 points whatever more than 99.5 maybe 99.9 per cent of the mass of the solar system is the sun rest of all it is all very small relatively speaking. So, if you look at it that way in terms of mass or volume even concerning just our solar system, if most of the sun has this plasma in it, clearly plasma is the most common form of matter in our solar system ok. So, that is unusual to most of us because we don’t see it on our daily basis, and so something that we do not see on earth that much is what is most common in the universe. So, across all stars wherever you know you associate matter with stars essentially and all that stars have plasma. So, that sense it’s a very common state of matter so actually, the solid-liquid gas that we are talking of is the most uncommon state of matter. So, actually, we should call plasma as the number 1 state of matter everything else should be less common so, but that’s a uniquely concerning our experience it is the other way round. So, it basically consists of ionized gas. So, that is what plasma is and, so if you want to create plasma. So, you need to get to high temperatures as I said you can put high fields etcetera to create plasma, but if you want to create plasma easily, you need to have elements in your stream which have low ionization energy ok. So, generally, I mean given the various options, if you are trying to create plasma, if you have a material that has low ionization energy you have atoms of a particular kind which have low ionization energy, then those atoms can be converted into plasma much more easily, than other atoms which have high ionization energy. So, where you have to put in a lot of energy to get those electrons off, and in that context caesium and potassium have relatively low ionization energy, if you look at the periodic table, and you look at all the elements, and see what all ionization they have caesium, and potassium have relatively low ionization energy, and the I mean there are some other elements in between which also have low ionization energy, but they may be rarer to find. So, these are relatively you know I mean in comparison to at least some of the other elements these are much more available and they are more easily ionizable. So, incidentally, we do have you know plasma is also of different kinds in different depends on you know; the when I say high temperature the temperature doesn’t even have to be uniform across the plasma, you can have a situation when you talk of plasma you are talking of ions and you are talking of electrons so ok. So, you have ions and electrons; so, once you create plasma where you have this ion separated from the electron and the electrons are moving around, the ions are moving around; they don’t necessarily have to have the same energy ok. So, you can have electrons having much higher energy, the ions having much lower energy you will have some average energy, but in general, you can have a situation where much more of the energy is being held by the electrons much less is being held by the ions and so on. So, in that case. So, you can have a somewhat cold plasma, you can have plasma that is a hot lot of different options are available here when you talk of plasma. So, we do have you know plasma related electronic devices that we utilize. So, some of these you know lamps which have some vapour in them, and then they are giving you the light they all have this ionized form of matter plasma. So, you do have some of the lighting systems that we use are based on plasma, some of the display systems that we use are based on plasma. So so the plasma is there in some of the devices that we are using, although we may not have consciously understood what exactly we are referring to when we are talking of a plasma ok. So so, it is available it is the fourth state of matter it is ionized gas, and if you are trying to ionize caesium or potassium it may be easier. So, you can get plasma out of it much more easily. So, what is that relevance of plasma concerning magnetic hydro hydrodynamic power generation ok? (Refer Slide Time: 13:17) So, what we are trying to do is essentially create a situation, where we have this fuel that is burnt, and so you get high-temperature high-temperature gas that has been generated. So, that’s the first part of our energy generation process, that we sent through some passageway and then eventually we arrive at this power turbines and generate power turbines etcetera. And we generate power. So, there’s another process that is there later on where we are generating power. Now there is you have the option that before this hot gas goes to the regular thermal plant cycle, where you have this turbine, and you are doing some various activities associated with that before you get there you can see if you can get some energy out of this hot gas, because it is already hot, and we spoke about plasma where basically you can ionize some material. So, we idea in tension in this or the principle behind this magnetohydrodynamic power generation is to take this hot gas and introduce into it the atoms such as potassium and caesium, these will then ionize okay so they will ionize, and then so now, in that gas stream why do they ionize the ionized? Because the gas is at high temperature ok. So, because the gas is at high temperature the electrons, and ions will separate. And so, you have an ionized gas and, so this ionized gas is now moving in a stream. If now you apply a magnetic field perpendicular to the direction of movement of this ionized gas, you can get the ions and electrons to deflect ok. So, that’s the basic principle you get the ions, and electrons to deflect; they deflect in different directions because of the charge that they have, and in that process, you generate a voltage that voltage you can tap ok. So, this process these individual steps that I put together here, this entire process is then referred to as the magneto of the hydrodynamic power regeneration process. So, you ionize a gas you get it to go through an area where there is a magnetic field, and because of that magnetic field the ions and the electrons move in different directions and you generate a potential difference. So, that’s the basic idea. So, the burnt high-temperature gas is there, and you have introduced say potassium or caesium, and then you have this magnetic field here. So, the magnetic field now is into the plane of the display that you see. So, and so then the electrons and ions so, you will have e minus and you will have ions, which are positively charged they will get deflected. So, you can get them deflected in different directions. So, you will have them deflecting, and you will have them deflecting like that. So, you will have some deflection occurring and in that process, you get a potential difference which you can capture. So, this is the energy that is available in the stream which we are now capturing differently. So, what have we done here? We have basically created a situation where the thermal energy that is available in the incoming stream has been used to do some ionization ok. So, some amount of thermal energy has been used for that ionization process. So, that created ions, now that ions and electronic ion pair that you had, you use that to generate a potential difference, and using that potential difference you generate electricity ok. So, you have picked up some electricity from. So, some electrical energy has come out of the thermal energy that was available in the gas stream using, an ionization step in the middle ok. So, you had thermal energy, and that gave from there itself directly you got electrical energy.
























So, from thermal energy, you went to electrical energy by simply including an ionization process in the middle ok. So, that’s the idea so that is in this process. So, that is why this process is explored and investigated. Because it gives you a pathway to pick up energy from because your original energy is only in thermal forms so, you have burnt fuel. So, you have fuel the energy is available in thermal energy form from that only you are trying to generate electricity. So, you could do that by doing all those turbine related activities all the heat exchange-related activities that occur with a normal power thermal power plant. And that is that would be another legitimate way in which you could generate your electricity, except that that would be subject to all those limitations of you know 1 minus T 2 by T 1 kind of a limitation efficiency. So, even before you do that, you add 1 ionization process in the middle, and in that process, you change the form of energy, from thermal energy to something that is now in the electric form and then you tap that energy. So, you get electrical energy; so, ions and electrons will get deflected in opposite directions generating voltage, we will come back to this in just a moment. (Refer Slide Time: 18:21) So, this is the basic idea. So, you get voltage potential difference, now you will get a potential difference here, and so you put an electrode here this is an electrode, and this is another electrode or a current collector ok. So, you put 2 electrodes, and you generate you it’s the system is already generated a potential the potential difference. So, then you can tap the electricity, and so you have a load resistor which is your external circuit and in that process you tapped electricity. So, this is the basic idea and as I said caesium and potassium can be added to the gas, the temperature should be high enough to ionize these right. So, it should be high enough to ionize this caesium and potassium, and this idea of adding caesium and potassium to it is referred to as seeding not to get rain you add seeds to the clouds right. So, cloud seeding that is different here, you are adding potassium and caesium as seeds to generate the ionization process to enable ionization process, because the ion is very easily. So, that is the basic idea. So, if you want to look at relative to what we saw a little while earlier. So, you have the hot gas coming in, but before the hot gas goes to the MHD if you just send it directly into a region and you call that you just put 2 electrodes and you send this hot gas in there that is not really going to help you in a big way. So, you have to do the seeding so caesium or potassium, and here you are going to have a magnetic field, and then you have the thermal power plant. So, you get some electricity out of this. So, you have some electricity generation out of this, and then you have further electricity generation out of this. So, you have you know you are generating electricity in a 2 step process as opposed to a single-step process, you have 2 steps of electricity generation that is happening here, and therefore, this is interesting I mean we are getting 1 additional amount of electricity over and above what you would have otherwise got and therefore, your overall efficiency is going up. Now, I must point out that if you look at this situation here that you know you have these electrons, and ions that are moving in the in response to the magnetic field that you have put, you must keep in mind and it is not as simple as it as it is shown in this figure, although in principle this is what is happening the electron is moving in 1 direction, the ions are moving in another direction, and then you have a potential difference. But there are a lot of other aspects that we have to keep in mind so for example, the mass so mass of ion right. So the mass of the ion. (Refer Slide Time: 21:33) So let me put it here, the mass of an ion is much much greater than the mass of the electron, the right mass of an ion is much much greater than the mass of the electron. So, therefore, given the same amount of magnetic field, and the fact that it is all coming in the plasma to together, the extent to which the ion will deflect it will be a lot less than the extent to which the electron will deflect. The electron will deflect much faster much more steeply than the ion. So, you may have the ions much more gradually deflecting whereas, you may have the electron deflecting much faster, relatively speaking right. So, you may have that kind of a situation the electron will deflect much faster, the ion may deflect much more slowly. So, you may even have some of the ions leaving this region without even reaching the electrodes. So, that’s a concept that you have to keep in mind. Also, we have to understand that as the electron begins to deflect, it is not sitting in vacuum right. So, it is an electron that is going along with a plasma that is moving right. So, when that happens you may have a velocity of the electron in different directions, and based on which direction it is in the magnetic field can impact it or may not impact it. So, to the extent that there is a component of the velocity perpendicular to the magnetic field, it will start doing this deflection the way we have shown it I have shown you. So, and as it deflects it doesn’t just deflect once and just go straight into the electrode, it will continue to deflect. So, in principle, it can actually get into a loop. So, it in principle this can start travelling in a loop, over and above that if there is a component of the velocity in the direction of the magnetic field ok. So, if it is already in the direction of the magnetic field, then it is not getting affected by the magnetic field, it will simply spiral along that direction ok. So, if there is a component of the magnetic field in that direction. So, a velocity electron velocity in that direction, because of the magnetic field also in that direction the deflection is happening like this due to the component of the velocity in this direction, but the component of the velocity in that direction simply pushes the electron further that way. So, it will spiral that way. So, it will just spiral that way and go both. So, you are having that is itself 1 no motion that is happening over, and above that, it is going to interact with the ions that are moving there, it is going to interact with the plasma that is moving there, some probability of interaction will be there. So, it is all statistical you have to see what the probability of interaction is and so on. So, it will have some interaction. So, the movement can be quite complicated it is not going to be quite simple it is going to be relatively complicated. Because there are many factors here which are impacting the movement of that electron over and above that if you generate a potential also right. So, you have you end up generating potential as we saw here. So, we have a potential difference. So, now over and above the magnetic field, you also have an electrostatic field right. So, because the so this means this potential has been generated due to let’s say the first set of electrons that underwent this process. So, the fresh and the next set of electrons that are arriving will see this potential already existing, against I mean which will impact the may which will also influence the way they move. So, now they are moving in the presence of a magnetic field, as well as an electrostatic field. So, several things are happening here, also, you will have a situation that if the electron is deflecting right, there is a relative to the plasma, there is some you know movement of the electron this way, and there is also a movement a relative velocity, if this deflection had not been there it would have moved further right. So, there is some relative movement this if this way also. So, there is a movement this way there is a movement vertically down, and there is a relative movement a horizontally as well relative to the plasma. So, what happens is if you actually want to step back and see there is electricity in both the direction perpendicular to this movement original movement of the electron and also in the direction against the direction of the movement of the electron. So, this is referred to as the Faraday effect Faraday based effect which is causing this movement perpendicular to the original direction of flow of electron. And this movement which is happening you know due to this curvature as it happens in the presence of the magnetic field, and as a result, it is moving actually slower than the plasma this is due to the Hall Effect ok, on the movement of the electron. So, you can sort of seeing that there can be a potential difference in the vertical direction, there can also be a potential difference in the horizontal direction, generating if you just look at this region if you look at this region and you go from left to right there can be a potential difference due to this Hall Effect, if you go from top to bottom you can have a potential difference due to the Faraday effect. So, it’s a fairly complex situation that we are dealing with when you are talking of this kind of a situation where you have a hot gas going, you added something to it created a plasma, and that plasma is now interacting with this magnetic field it is generating an electric field, and then both of them are present, and then subsequent you know atoms, and I mean atoms that come there which become ions, and the electrons have to deal with all of this or are interacting with all of this. So, it’s a fairly complex situation that we have here, but still, at the end of it we have a potential which is the potential that we tap, and then we get the load resistor to function. (Refer Slide Time: 27:04) So, if you actually see we can as I said you know the movement of the electrons and the ions will depend on charge as well as mass right on charge as well as mass. And that is why we had this you know movement this way, we had the movement that way, and then even here so, this is an electron that is an icon, and then here also we were looking at what is the extent of movement this way, what is the extent of movement in that direction and so on. So, all of that is happening in this generator at the same time. (Refer Slide Time: 27:34) So, to the extent that we tap the voltage, as I said you know there is a potential difference here. So, there is a potential difference between the top and the bottom of this unit. So, to the extent that we tap this potential difference between the top, and the bottom we refer to it as the Faraday generator ok. So, so in the context of a magnetohydrodynamic generator, you have multiple ways in which you can tap electricity, even from this you know this region this overall region which is the MHD generator, within this region after this it becomes a regular thermal power plant activity. So, and before this is also just the fuel burning. So, in this region you can tap electricity in more than one way; you can think of different configurations in which you can tap electricity, and then they and that you know usually accentuates 1 aspect of this process. And then we try to capture it in that form, and so for example, this manner in which we are we are capturing energy where we put 1 large electrode here, 1 single large electrode right. So, this is 1 way we would do it similarly on top you will also have another single large electrode, so you put a single large electrode on top and you put a single large electrode to the bottom, and then you know to connect the external circuit to it and then you get electricity. So, you connect the external circuit to it, and then you have a flow of electrons, and you generate your captured electricity you have generated electricity which you are capturing elsewhere. So, what are we done here one of the things that we have done when and the reason that is the reason why I am emphasizing this idea that we have put a single large electrode on that side as well as a single large one single large electrode this side. The point of emphasizing that is that as I mentioned you will also have the Hall Effect, the Hall Effect is also is related to the fact that this electron is moving in the presence of this magnetic field. And as a result, in general, it ends up having a relative motion with the plasma that was moving, originally it came with the same velocity as the plasma. Now because of the Hall Effect, it may actually be moving with the lower velocity for the plasma. And because it is curving away and so, then you have to look at how much no displacement it had in the direction of the plasma. So, you have a potential difference that is coming from the horizontal moment of the electron. So, when you put a single large electrode you are sort of smearing that out ok. So, once you put a single metallic surface they are a single large electrode you are smearing that out. So, you are essentially smearing out the Hall Effect so you are smearing out the whole effect. So, the difference in potential in the horizontal direction is being ignored, and it is you know is being converted to 1 flat electrode of a common potential, and from that you ar