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Thread: Electrogasdynamic generator

  1. #1 Electrogasdynamic generator 
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    Could somebody help me to calculate potential efficiency, power density and issues with the following device?:

    In a heat resistant and non-conducting tube two electrodes are placed, a cathode which emits electrons with help of both cold and hot emission, and an anode which collects electrons. Cathode is under high voltage and creates a cloud of electrons - a space charge. However anode is placed on sufficient distance from cathode that charge tunneling would not be able to happen under "no power" condition. In a combustion camber some fuel is burned and expanding gases move space charge from cathode to anode. Electrons are collected on anode and electric circuit is closed. In this way power is generated.

    I wish to know what would be likely the looses in different parts of a system and what would be possible efficiency. The system suppose to work as an open cycle. Could there be some air and corrosion resistant materials which could serve as an electron emitters and withstand open air and different gases for a long time with no corrosion? How dense could be a space charge cloud and which currents per certain tube diameter could it deliver? Would it require some liquid cooling? How is it possible to achieve uniform blowing of a space charge and prevent formation of gas leakages? Would it require some air compressor and heat recuperator? Would it work by Bryton cycle similar to gas turbine? How is it possible to obtain as colder exhaust as possible (to obtain more of useful work)? Etc.


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    Quote Originally Posted by Stanley514 View Post
    Could somebody help me to calculate potential efficiency, power density and issues with the following device?:

    In a heat resistant and non-conducting tube two electrodes are placed, a cathode which emits electrons with help of both cold and hot emission, and an anode which collects electrons. Cathode is under high voltage and creates a cloud of electrons - a space charge. However anode is placed on sufficient distance from cathode that charge tunneling would not be able to happen under "no power" condition. In a combustion camber some fuel is burned and expanding gases move space charge from cathode to anode. Electrons are collected on anode and electric circuit is closed. In this way power is generated.

    I wish to know what would be likely the looses in different parts of a system and what would be possible efficiency. The system suppose to work as an open cycle. Could there be some air and corrosion resistant materials which could serve as an electron emitters and withstand open air and different gases for a long time with no corrosion? How dense could be a space charge cloud and which currents per certain tube diameter could it deliver? Would it require some liquid cooling? How is it possible to achieve uniform blowing of a space charge and prevent formation of gas leakages? Would it require some air compressor and heat recuperator? Would it work by Bryton cycle similar to gas turbine? How is it possible to obtain as colder exhaust as possible (to obtain more of useful work)? Etc.
    Maybe I've not grasped the concept properly but something feels dodgy about it. What is meant by cathode and anode if there is no externally applied potential difference between the two? If there is, what purpose does the gas stream serve? And of there isn't, what makes one electrode the cathode and one the anode?


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    Maybe I've not grasped the concept properly but something feels dodgy about it. What is meant by cathode and anode if there is no externally applied potential difference between the two? If there is, what purpose does the gas stream serve? And of there isn't, what makes one electrode the cathode and one the anode?
    It seems you need to read my post more carefully. The device is used to convert heat to electricity directly. Did you ever heard about electrogasdynamic generators in general? There is different models of such and I advise you to start reading. For example:
    http://www.ecobuilding-club.net/down...EGD-Trigen.pdf

    In my model, as I already wrote, high voltage is supplied to cathode and makes it an electron emitter. If there is high voltage, apparently there should be a potential difference. A cathode could be made out of Tungsten wire covered by Barium Oxide and on top covered with extremely thing anti-oxidant covering. Gas stream serves purpose to perform work and generate power (current flow) in the device. There are similar devices such as electrostatic wind turbines (though they do not use hot air stream and there is no electron emitting electrode, only charged water). But some principle is similar. Bladeless wind turbine produces energy with no moving parts (Wired UK)
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    Quote Originally Posted by Stanley514 View Post
    Maybe I've not grasped the concept properly but something feels dodgy about it. What is meant by cathode and anode if there is no externally applied potential difference between the two? If there is, what purpose does the gas stream serve? And of there isn't, what makes one electrode the cathode and one the anode?
    It seems you need to read my post more carefully. The device is used to convert heat to electricity directly. Did you ever heard about electrogasdynamic generators in general? There is different models of such and I advise you to start reading. For example:
    http://www.ecobuilding-club.net/down...EGD-Trigen.pdf

    In my model, as I already wrote, high voltage is supplied to cathode and makes it an electron emitter. If there is high voltage, apparently there should be a potential difference. A cathode could be made out of Tungsten wire covered by Barium Oxide and on top covered with extremely thing anti-oxidant covering. Gas stream serves purpose to perform work and generate power (current flow) in the device. There are similar devices such as electrostatic wind turbines (though they do not use hot air stream and there is no electron emitting electrode, only charged water). But some principle is similar. Bladeless wind turbine produces energy with no moving parts (Wired UK)
    Rereading your post did not help me, but the reference you supplied certainly did - especially the diagram. Now I see the principle: the gas stream transports charged particles against the gradient of an electric field, thereby doing work and raising the collector to an even higher potential, the general principle being similar to that of a Van Der Graaf generator.

    Clearly you are deeply into this already, so I am not able to contribute much. I have one question, though. I notice, from the web references that I could trace on EGD, that there seems to have been a flurry of interest in this at the end of the 1960s and early 1970s (for example the New Scientist article from 1973, mentioning a BP pilot plant). But since then it looks as if everyone lost interest in it. Why do you think this was?
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    Now I see the principle: the gas stream transports charged particles against the gradient of an electric field, thereby doing work and raising the collector to an even higher potential, the general principle being similar to that of a Van Der Graaf generator.
    This is one of the principles, especially if you need to generate high voltages. If you need to generate high currents instead of high voltages this principle should be redesigned. For example, I'm not sure that particles should be transported against electric field.
    I have one question, though. I notice, from the web references that I could trace on EGD, that there seems to have been a flurry of interest in this at the end of the 1960s and early 1970s (for example the New Scientist article from 1973, mentioning a BP pilot plant). But since then it looks as if everyone lost interest in it. Why do you think this was?
    The similar thing happened to MHD generator. Why interest have waned? Probably not too many researchers believe that farther extensive researches will lead to immediate output worth of efforts. In the past many difficulties they experienced. But now as technologies gone much farther and there is need for a compact, high power, efficient electricity generator, why not to continue research?
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    Quote Originally Posted by Stanley514 View Post
    Now I see the principle: the gas stream transports charged particles against the gradient of an electric field, thereby doing work and raising the collector to an even higher potential, the general principle being similar to that of a Van Der Graaf generator.
    This is one of the principles, especially if you need to generate high voltages. If you need to generate high currents instead of high voltages this principle should be redesigned. For example, I'm not sure that particles should be transported against electric field.
    I have one question, though. I notice, from the web references that I could trace on EGD, that there seems to have been a flurry of interest in this at the end of the 1960s and early 1970s (for example the New Scientist article from 1973, mentioning a BP pilot plant). But since then it looks as if everyone lost interest in it. Why do you think this was?
    The similar thing happened to MHD generator. Why interest have waned? Probably not too many researchers believe that farther extensive researches will lead to immediate output worth of efforts. In the past many difficulties they experienced. But now as technologies gone much farther and there is need for a compact, high power, efficient electricity generator, why not to continue research?
    Well you must transport the gas against a field gradient or it isn't doing work, i.e. no energy is being transferred. But if you rebalance for high current rather than high voltage, then certainly you would want the gradient to be less and to compensate you would want to transport a greater mass of charged particles against this less steep gradient. In other words more amps and fewer volts.

    But I think if I were you I'd research a bit more into what went wrong last time, just to be sure there is nothing fundamental that prevents it being scaled up from a lab-scale curiosity to a commercial device.
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    Well you must transport the gas against a field gradient or it isn't doing work
    I think there could be different ways to do it. One way is to push particles of some charge against a field with
    the same charge. For example push electrons to collector with negative charge. Other way it to pull electrons
    from positive charge on cathode to the neutrally charged collector. Most of previous designs use charged aerosol
    particles and use corona discharge to charge them. Closed cycle is more common. Hence low power and efficiency.
    I'm interested to know if the is way to use cold emission of electrons to create dense electron cloud similar to what
    is used in vacuum diode.
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  9. #8  
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    Quote Originally Posted by Stanley514 View Post
    Well you must transport the gas against a field gradient or it isn't doing work
    I think there could be different ways to do it. One way is to push particles of some charge against a field with
    the same charge. For example push electrons to collector with negative charge. Other way it to pull electrons
    from positive charge on cathode to the neutrally charged collector. Most of previous designs use charged aerosol
    particles and use corona discharge to charge them. Closed cycle is more common. Hence low power and efficiency.
    I'm interested to know if the is way to use cold emission of electrons to create dense electron cloud similar to what
    is used in vacuum diode.
    I doubt it. You will not get a cloud of free electrons unless you have a vacuum, which of course you cannot have since you want to push them with a gas stream. If gases are present the electrons will charge the molecules of gas, making them ions. But iIt does not matter from your point of view, as they are charged particles being pushed "uphill" electrostatically and then discharged on contact with an electrode.
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    You will not get a cloud of free electrons unless you have a vacuum
    Why not?
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  11. #10  
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    Quote Originally Posted by Stanley514 View Post
    You will not get a cloud of free electrons unless you have a vacuum
    Why not?
    Because free electrons tend to be unstable in the presence of neutral atoms or molecules. In other words, they can usually move to a lower energy state by adding to the atom or molecule to produce an anion. So they do that.

    Can you think of any apparatus in which a cloud of free electrons exists, other than in a vacuum?
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    In other words, they can usually move to a lower energy state by adding to the atom or molecule to produce an anion.
    I do not think that majority of electrons will form anions, rather they will mechanically interact with molecules. But in either case I do not see how it makes problem to my device. Am I wrong? The largest problems that I see is to find a materials which would be able to serve as an electron emitters and in the same time to be very heat and corrosion resistant and how to prevent carbon depositions on electrodes. Also how to achieve a uniform charge movement and prevent energy leakages. Also to understand if liquid cooling of electrodes would be necessary.
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  13. #12  
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    Quote Originally Posted by Stanley514 View Post
    In other words, they can usually move to a lower energy state by adding to the atom or molecule to produce an anion.
    I do not think that majority of electrons will form anions, rather they will mechanically interact with molecules. But in either case I do not see how it makes problem to my device. Am I wrong? The largest problems that I see is to find a materials which would be able to serve as an electron emitters and in the same time to be very heat and corrosion resistant and how to prevent carbon depositions on electrodes. Also how to achieve a uniform charge movement and prevent energy leakages. Also to understand if liquid cooling of electrodes would be necessary.
    Yes as I said before I don't think it matters whether the charged particles are electrons or ions. The rest of your issues are engineering ones to do with the specifics of materials and the makeup and pressures and temperature of the exhaust gases. These are all features of a specific design, so are unanswerable in general, it seems to me. I suppose carbon electrodes would be one option.
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    I suppose carbon electrodes would be one option.
    I thought carbon easily burns on air. Could you give an example of any device with carbon electrodes which suppose to work in open air at extreme temperatures?
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  15. #14  
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    Quote Originally Posted by Stanley514 View Post
    I suppose carbon electrodes would be one option.
    I thought carbon easily burns on air. Could you give an example of any device with carbon electrodes which suppose to work in open air at extreme temperatures?
    But why the "extreme temperatures"? Surely all you want to do is let the expanding gas push the charged particles. For that, surely you just want any old gas flow, not a specially hot one?
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    But why the "extreme temperatures"? Surely all you want to do is let the expanding gas push the charged particles. For that, surely you just want any old gas flow, not a specially hot one?
    The device suppose to work on heat from burning hydrocarbons. Temperature of burning hydrocarbons could reach over 2.200 C. Also, the higher temperature of a hot heat sink, the higher efficiency. (Carnot theorem).
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  17. #16  
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    Quote Originally Posted by Stanley514 View Post
    But why the "extreme temperatures"? Surely all you want to do is let the expanding gas push the charged particles. For that, surely you just want any old gas flow, not a specially hot one?
    The device suppose to work on heat from burning hydrocarbons. Temperature of burning hydrocarbons could reach over 2.200 C. Also, the higher temperature of a hot heat sink, the higher efficiency. (Carnot theorem).
    Yes but you won't get higher efficiency unless the temperature difference between T1 and T2 is greater. You need to find a way to allow for your gas to expand so much that it cools a lot. I think you may find that difficult in this scenario, but it all depends on how much work your expanding gas can do against the the electrostatic gradient.
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    Yes but you won't get higher efficiency unless the temperature difference between T1 and T2 is greater. You need to find a way to allow for your gas to expand so much that it cools a lot. I think you may find that difficult in this scenario, but it all depends on how much work your expanding gas can do against the the electrostatic gradient.
    Why do you think it would be difficult or at least more difficult than in case with actual mechanical pistons like in ICE?
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  19. #18  
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    Quote Originally Posted by Stanley514 View Post
    Yes but you won't get higher efficiency unless the temperature difference between T1 and T2 is greater. You need to find a way to allow for your gas to expand so much that it cools a lot. I think you may find that difficult in this scenario, but it all depends on how much work your expanding gas can do against the the electrostatic gradient.
    Why do you think it would be difficult or at least more difficult than in case with actual mechanical pistons like in ICE?
    I'd like to see a design showing what back pressure you expect to get from the electric field gradient. A mechanical piston obviously exerts a big back pressure, being rigidly attached to a crankshaft. Maybe you can do the same thing with an electric field, but I have some difficulty visualising it.
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    I'd like to see a design showing what back pressure you expect to get from the electric field gradient. A mechanical piston obviously exerts a big back pressure, being rigidly attached to a crankshaft. Maybe you can do the same thing with an electric field, but I have some difficulty visualising it.
    Could you explain what do you mean as "back pressure" and why is it important? in Wikipedia back pressure mentioned as:
    Back pressure in automotive (four-stroke engine) exhaust

    Back pressure caused by the exhaust system (consisting of the exhaust manifold, catalytic converter, muffler and connecting pipes) of an automotive four-stroke engine has a negative effect on engine efficiency resulting in a decrease of power output that must be compensated by increasing fuel consumption.
    Back pressure - Wikipedia, the free encyclopedia
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  21. #20  
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    Quote Originally Posted by Stanley514 View Post
    I'd like to see a design showing what back pressure you expect to get from the electric field gradient. A mechanical piston obviously exerts a big back pressure, being rigidly attached to a crankshaft. Maybe you can do the same thing with an electric field, but I have some difficulty visualising it.
    Could you explain what do you mean as "back pressure" and why is it important? in Wikipedia back pressure mentioned as:
    Back pressure in automotive (four-stroke engine) exhaust

    Back pressure caused by the exhaust system (consisting of the exhaust manifold, catalytic converter, muffler and connecting pipes) of an automotive four-stroke engine has a negative effect on engine efficiency resulting in a decrease of power output that must be compensated by increasing fuel consumption.
    Back pressure - Wikipedia, the free encyclopedia
    Perhaps I'm not using the right words. What I have in mind is that the energy you get out of your stream of gas depends on what F x d work you make it do, in pushing the cloud of charged particles. If you can calculate the magnitude of the resistance, per unit area, of the electric field gradient and you know the distance you move the charged particles before they reach the anode and are neutralised, that will tell you the work done, and if you then have a rate of movement, you have a power output.

    I'm not an engineer but I think I would find it useful to do this calculation, as it would set some basic parameters for the design, e.g. how many volts/metre field gradient, what size pipe, what gas flow rate, and what pressure of gas you need to make it flow at a rate to give the desired power output. Once you know the pressure and flow rate, you can work out how much expansion the gas has to undergo and hence the temperature drop it will experience, which will start to give you an idea of working temperatures and so on.

    Or have you already done all this?
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    Or have you already done all this?
    Unfortunately, I cannot do it in details, I'm amateur, not an engineer. I thought that on this forum could be a person who is proficient in electrogasdynamics.

    Some previous EHD generator designs also mention "the electrical breakdown limit of the medium" as severe restriction. I wish to know does what it mean.
    https://archive.org/stream/analysiso...0gawa_djvu.txt
    Last edited by Stanley514; September 22nd, 2014 at 01:51 PM.
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  23. #22  
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    Quote Originally Posted by Stanley514 View Post
    Or have you already done all this?
    Unfortunately, I cannot do it in details, I'm amateur, not an engineer. I thought that on this forum could be a person who is proficient in electrogasdynamics.

    Some previous EHD generator designs also mention "the electrical breakdown limit of the medium" as severe restriction. I wish to know does what it mean.
    https://archive.org/stream/analysiso...0gawa_djvu.txt
    Not sure, but it could be the breakdown voltage, i.e. the potential difference between the electrodes at which arcing will occur.
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