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#22
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CAFE Electric Aircraft Symposium Set For May 1
Dave Doe wrote:
In article , , Skywise says... Dave Doe wrote in : Water is pollution? I think you either need to get your chemistry right, or define "hydrogen" - or perhaps, what you are burning. Hydrocarbons? Burning hydrogen with pure oxygen produces only water vapor. For example, LH2 and O2 rocket engines such as the Shuttle's. Burning hydrogen with 'air' also produces other compounds, including nitrous oxides (smog, harmful to humans). 'Air' is not pure oxygen. Check your chemistry. Oh I have! Hence the question. I'm sure you've heard of Oxyhydrogen plants (as in Oxyacetalene plants). Those are not engines and an oxygen/hydrogen flame exposed to air produces NOx through the temperatures involved. It is purely an effect of heating air to a temperature sufficient for the reaction; the heat source is irrelevant. -- Jim Pennino |
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CAFE Electric Aircraft Symposium Set For May 1
wrote in :
It is purely an effect of heating air to a temperature sufficient for the reaction; the heat source is irrelevant. Good point. For example, in the following nuclear test footage, the red/brown cloud around the stem of the mushroom is nitrous oxides caused by the heat of the fireball. It's almost literally "burning the air". https://www.youtube.com/watch?v=-WsouJ4YzO4 Brian -- http://www.earthwaves.org/forum/index.php - Earth Sciences discussion http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Sed quis custodiet ipsos Custodes? |
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CAFE Electric Aircraft Symposium Set For May 1
On Fri, 8 May 2015 21:28:24 +0000 (UTC), Skywise
wrote: Larry Dighera wrote in news I was thinking it might be necessary to heat the LH2 so that it could keep up with the fuel demand of the fuel-cell producing the power to produce the motive thrust. Stop refridgerating it? LH2 is -423F/-253C. That brings up an interesting opportunity for an electric power plant: superconductivity. This liquid hydrogen fuel concept is beginning to become more interesting... http://en.wikipedia.org/wiki/Superconductivity |
#25
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CAFE Electric Aircraft Symposium Set For May 1
Larry Dighera wrote in
: On Fri, 8 May 2015 21:28:24 +0000 (UTC), Skywise wrote: Larry Dighera wrote in news I was thinking it might be necessary to heat the LH2 so that it could keep up with the fuel demand of the fuel-cell producing the power to produce the motive thrust. Stop refridgerating it? LH2 is -423F/-253C. That brings up an interesting opportunity for an electric power plant: superconductivity. This liquid hydrogen fuel concept is beginning to become more interesting... http://en.wikipedia.org/wiki/Superconductivity I really think you are completely missing the problem. It takes energy to do these things. It is not a source of energy. It takes energy to make the hydrogen because it doesn't exist in it's free state naturally on Earth. Currently, most hydrogen is produced from natural gas, with CO2 as a byproduct. It takes energy to compress it, or liquify it. It takes energy to refridgerate it to such low temperatures. and to keep it there. Where is all that energy going to come from? And you will never ever EVER get out of LH2 the amount of energy that went into producing it. It's a simple numbers game. Balance the books. You're in the red. On the other hand, if you do find an alternate SOURCE of energy, one that is so cheap and plentiful and does minimal or no harm to the environment, then maybe you can look at things like LH2 as a medium to store and use energy (after solving the CO2 problem), and all the losses in it's production won't matter because the actual SOURCE of energy is so cheap and plentiful you don't mind wasting a bit of it. Nuclear is the only source of producing mass quantities of energy that I know of, but it has it's own inherent risks and challenges, most of which I think are solvable except for the public relations side of it. But, it does not emit CO2 which is the major argument regarding fossil fuels. Fusion reactors have been a decade away for the past 5 decades. There aren't enough rivers to dam, and it harms ecosystems. Wind is intermittent and too little. And kills birds. Solar is viable, but only works during the day. It can be scaled to compensate along with appropriate electricity storage mechanisms to offset night and cloudy days. Perhaps Tesla's house battery is a step in this direction? However, solar cells are still too expensive to force people to switch. Folks can't see CO2. They can't feel .2 degrees Celcius. But they CAN see the numbers on their credit card bills. Which brings up another point. The energy problem is as much a human psychology problem as it is a technical problem. To put it bluntly, the vast majority of people don't give a F. Brian -- http://www.earthwaves.org/forum/index.php - Earth Sciences discussion http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Sed quis custodiet ipsos Custodes? |
#26
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CAFE Electric Aircraft Symposium Set For May 1
On Mon, 11 May 2015 20:57:57 +0000 (UTC), Skywise
wrote: Larry Dighera wrote in : On Fri, 8 May 2015 21:28:24 +0000 (UTC), Skywise wrote: Larry Dighera wrote in news I was thinking it might be necessary to heat the LH2 so that it could keep up with the fuel demand of the fuel-cell producing the power to produce the motive thrust. Stop refridgerating it? LH2 is -423F/-253C. That brings up an interesting opportunity for an electric power plant: superconductivity. This liquid hydrogen fuel concept is beginning to become more interesting... http://en.wikipedia.org/wiki/Superconductivity I really think you are completely missing the problem. It takes energy to do these things. It is not a source of energy. It takes energy to make the hydrogen because it doesn't exist in it's free state naturally on Earth. Currently, most hydrogen is produced from natural gas, with CO2 as a byproduct. It takes energy to compress it, or liquify it. It takes energy to refridgerate it to such low temperatures. and to keep it there. Photovoltaic powered electrolysis of H2O would be my choice to produce hydrogen. It might even power the compressor and condenser to liquefy it also. Other than the energy used to make the solar cells, there is no energy cost and no byproducts. Making this practical will take some ingenuity, but theoretically, I'd suppose it is possible. Where is all that energy going to come from? And you will never ever EVER get out of LH2 the amount of energy that went into producing it. With free solar power, that isn't much of an issue. It's a simple numbers game. Balance the books. You're in the red. On the other hand, if you do find an alternate SOURCE of energy, one that is so cheap and plentiful and does minimal or no harm to the environment, then maybe you can look at things like LH2 as a medium to store and use energy (after solving the CO2 problem), and all the losses in it's production won't matter because the actual SOURCE of energy is so cheap and plentiful you don't mind wasting a bit of it. Yep. Nuclear is the only source of producing mass quantities of energy that I know of, If energy production is decentralized, mass quantities aren't required. Think every home with rooftop photovoltaics. Of course, that won't do for airline operations, but 250 megawatt solar facilities are in operation in California and Nevada now: http://investor.firstsolar.com/releasedetail.cfm?ReleaseID=793411, and even the Air Force has a 14.2 megawatts installation: http://www.cnet.com/news/air-force-base-in-nevada-goes-solar-with-14-megawatt-array/#!. but it has it's own inherent risks and challenges, most of which I think are solvable except for the public relations side of it. But, it does not emit CO2 which is the major argument regarding fossil fuels. You believe the "inherent risks and challenges" are solvable, because they have been woefully underestimated as have the costs. The way I see the current state of nuclear is a lot like the oceans. When the sea is calm, things are fine. But the sea has the potential for ENORMOUS destruction, as born out recently in the Fukushima tsunami. Despite the sea wall, the sea managed to cause massive destruction beyond what engineers had estimated. And there's NOTHING to prevent an even larger tsunami from occurring in the future. The nuclear industry has voluntarily created a $12.6-billion insurance fund and enacted legislation limiting their liability to that amount. The Fukushima disaster is estimated at $500-billion. And after 29 years hundreds of square miles of Chernobyl is still uninhabitable. Nuclear plants are continually venting radio-active products into the environment during normal operation. And in the event of a containment breach, the spread of radioactivity can be alarming. Here's what happened as a result of the Chernobyl meltdown: Chernobyl disaster effects National and international spread of radioactive substances Four hundred times more radioactive material was released from Chernobyl than by the atomic bombing of Hiroshima. The disaster released 1/100 to 1/1000 of the total amount of radioactivity released by nuclear weapons testing during the 1950s and 1960s.[88] Approximately 100,000 km˛ of land was significantly contaminated with fallout, with the worst hit regions being in Belarus, Ukraine and Russia.[89] Slighter levels of contamination were detected over all of Europe except for the Iberian Peninsula.[16][90][91] The initial evidence that a major release of radioactive material was affecting other countries came not from Soviet sources, but from Sweden. On the morning of 28 April[92] workers at the Forsmark Nuclear Power Plant (approximately 1,100 km (680 mi) from the Chernobyl site) were found to have radioactive particles on their clothes.[93] So, from my point of view, nuclear fission power is far too dangerous for consideration as a "free" and "clean" power source. Just ask the residents who have to pay to saw up, and haul away the entire San Onofre power plant. And without a safe place to store the radioactive waste, it is just plane irresponsible. And the potential for catastrophe has been under estimated by several orders of magnitude, just like the potential of the sea. But the military wants it, and the war profiteers are happy to oblige.... Fusion reactors have been a decade away for the past 5 decades. How many years passed between the time Leonardo da Vinci conceived of the helicopter and it's production? There aren't enough rivers to dam, and it harms ecosystems. Wind is intermittent and too little. And kills birds. I recall living under the flight path of LAX in the '50s. You couldn't hold a conversation at dinner time for the din of arriving B-707s. Today, I reside very close to KSBA, and the airliners are significantly quieter than the GA piston aircraft. Progress takes time... Solar is viable, but only works during the day. It can be scaled to compensate along with appropriate electricity storage mechanisms to offset night and cloudy days. Perhaps Tesla's house battery is a step in this direction? However, solar cells are still too expensive to force people to switch. Responsible people are switching voluntarily; no need to force them. The price of solar panels is dropping all the time. Last I checked, it was possible to purchase solar panels on eBay for ~$1/watt. Folks can't see CO2. They can't feel .2 degrees Celcius. But they CAN see the numbers on their credit card bills. Which brings up another point. The energy problem is as much a human psychology problem as it is a technical problem. The way I see it, it's more a matter of entrenched wealthy businessman protecting their cash cows... To put it bluntly, the vast majority of people don't give a F. Brian Fortunately, that is changing ... So, the use of LH2 to generate electricity with a fuel-cell to drive an electrical motor that employs superconductivity seem a worthwhile course to investigate for powering future aircraft. Granted there are currently obstacles to achieving a viable system, but I don't believe physics precludes it; only the development of the technology stands in the way. |
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CAFE Electric Aircraft Symposium Set For May 1
On 5/14/2015 1:49 PM, Larry Dighera wrote:
It takes energy to make the hydrogen because it doesn't exist in it's free state naturally on Earth. Currently, most hydrogen is produced from natural gas, with CO2 as a byproduct. It takes energy to compress it, or liquify it. It takes energy to refridgerate it to such low temperatures. and to keep it there. Photovoltaic powered electrolysis of H2O would be my choice to produce hydrogen. It might even power the compressor and condenser to liquefy it also. Other than the energy used to make the solar cells, there is no energy cost and no byproducts. Making this practical will take some ingenuity, but theoretically, I'd suppose it is possible. Sorry, but there is no free energy, and there is no totally clean energy, not even solar. At present, there isn't enough solar energy to go around. There isn't likely to EVER be enough solar energy to go around, that's also true of wind and hydro power. More importantly, if we divert solar energy from the grid to make hydrogen, then we must make up the difference from somewhere else, which means burning more fuel. So there is no advantage to diverting "clean" energy towards something like producing hydrogen, whilst we are burning coal (or whatever) to make grid power. Energy is energy! Wasting energy is always a dirty thing to do, even if it's solar. And the hydrogen energy cycle is inherently wasteful. |
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CAFE Electric Aircraft Symposium Set For May 1
On Thu, 14 May 2015 14:14:43 -0400, Vaughn wrote:
On 5/14/2015 1:49 PM, Larry Dighera wrote: It takes energy to make the hydrogen because it doesn't exist in it's free state naturally on Earth. Currently, most hydrogen is produced from natural gas, with CO2 as a byproduct. It takes energy to compress it, or liquify it. It takes energy to refridgerate it to such low temperatures. and to keep it there. Photovoltaic powered electrolysis of H2O would be my choice to produce hydrogen. It might even power the compressor and condenser to liquefy it also. Other than the energy used to make the solar cells, there is no energy cost and no byproducts. Making this practical will take some ingenuity, but theoretically, I'd suppose it is possible. Sorry, but there is no free energy, Agreed. I don't think that is at issue here. and there is no totally clean energy, not even solar. Aside from the waste products associated with the production of solar cells, I'm not aware of any polluting products emitted by photovoltaic electricity generation. At present, there isn't enough solar energy to go around. Mmmm... When it isn't cloudy, there's about 1KW per square meter. It would seem, that if you've got the land area, there's more than enough solar energy "to go around", at lease here in southern California. What makes you say that? Are you saying, that there currently hasn't been enough solar energy generating stations built to supply the entire nation/world? There isn't likely to EVER be enough solar energy to go around, Are you able to cite a credible source that supports that assertion? What leads you to believe that? that's also true of wind and hydro power. Are you intimating that petroleum based electric generation is the sole technology that is able to supply the world's needs? Again, are you able to cite a credible source that supports your an opinion? More importantly, if we divert solar energy from the grid to make hydrogen, then we must make up the difference from somewhere else, which means burning more fuel. So there is no advantage to diverting "clean" energy towards something like producing hydrogen, whilst we are burning coal (or whatever) to make grid power. I wasn't suggesting that grid electricity be used to electrolyze H2O. I was thinking that solar cells on the roof of a home might be employed electrolyze water to produce H2 and O2 that would be stored, and used to produce electricity at a later date. Energy is energy! Wasting energy is always a dirty thing to do, even if it's solar. So, you're saying, that when the Sun is shining on bear earth, we are doing a "dirty thing" by not capturing the solar energy? Or am I missing your point? And the hydrogen energy cycle is inherently wasteful. It is true that electrolysis of H2O is not too efficient yet. Until recently fuel-cell technology hasn't been too efficient either (about 30%). but when I visited the 2014 Consumer Electronics Show in Las Vegas, an automotive engineer assured me that they had increased fuel-cell efficiency to 60%, so presumably the art is making strides toward increasing efficiency. And, if/when H2 power becomes more mainstream, I would expect the resulting increase in R&D funding to continue that trend. How efficient is distilling petroleum into gasoline/kerosene? How efficient are internal combustion engines piston and turbine? I appreciate your interest in the subject, but I'm at a loss to understand your points. And without any supporting research studies or hard data, I'm unable to put much credence in your unsupported assertions. Please tell me more about what you KNOW about this subject. |
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CAFE Electric Aircraft Symposium Set For May 1
Hello Brian, You seem to have firm grasp of the physics involved. Are you able to suggest how efficient an electric power system powered by LH2 would have to be to offset the power density difference from gasoline/kerosene? Larry On Mon, 4 May 2015 22:27:45 +0000 (UTC), Skywise wrote: Larry Dighera wrote in : I'll agree that a liquid H2 tank will likely be more massive than today's gasoline tanks, but couldn't liquid H2 be stored in a Styrofoam containing vessel? The problem is either temperature or pressure, or both. Liquid H2 is cryogenic. It doesn't exert pressure any more than water does in a tank. But it has to be kept at -423F or -253C. Styorofoam would just take up space. If the idea is to avoid the crygenic temperatures, you then need to fight the pressure. If I did my math right, and read the phase diagram for hydrogen right, then liquid H2 at room temperature has a pressure of about 2.5 million atmospheres. There's no tank in the world that can hold that back. Pressurized hydrogen at room temperature is just compressed gaseous hydrogen. So a vehicle with that is like carrying around a bunch of scuba tanks, which IIRC are only 3000-4000 psi or about 200 to 270 atmospheres pressure, and look at how heavy those are!! I have heard about efforts to store hydrogen in metallic foams but don't know the state of that work. The problem is, the energy is in the hydrogen atoms. The more atoms you have, the more energy you have. So if you want a lot of energy, you have to cram a bunch of hydrogen atoms together in a small space. Now here's the killer. The properties of hydrocarbon molecules is such that gasoline has a higher density of hydrogen atoms than even liquid hydrogen!!! There's more hydrogen atoms per unit volume. That's why gasoline has a 3x higher energy/density value than liquid hydrogen. There are simply more hydrogen atoms and therefore more energy. Aren't the relative efficiencies of electrical propulsion vs internal combustion powerplants being overlooked here? My thought on electrical propulsion is, how is the electricity produced in the first place? One rule of reality is that every time you convert one form of energy to another, there are losses, eventually ending up as heat. Basic Laws of Thermodynamics stuff. Internal combustion (or turbine) engines burn the fuel and directly convert it to mechanical work. That's bascially only one stage of conversion to have any conversion losses. Or, burn the fuel to drive a generator (loss 1), which generates electricity (loss 2), which is then stored in a battery (loss 3), which then is drawn from the battery (loss 4) to power an electic motor (loss 5). All those conversion losses add up. That's why gasoline is so hard to beat. Doesn't matter if you like fossil fuels or hate it, it's a simple fact that right now and in the forseable future, it's the most efficient energy storage mechanism around. The only alternative I see is to use elctricity from batteries but generate the electricity by some other means than fossil fuels. After all, isn't the whole point of this? to stop burning oil and polluting the atmosphere? Burning the fossil fuels to generate electricity to run cars and busses and planes only changes the location of where it's burned. All these people driving their electric cars feeling smug about themselves are not realizing that the electricity is most likely coming from a coal fired generating plant. And due to conversion losses, there's a good chance they are actually increasing their "carbon footprint" than decreasing it. Brian |
#30
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CAFE Electric Aircraft Symposium Set For May 1
Larry Dighera wrote in
: Hello Brian, You seem to have firm grasp of the physics involved. Are you able to suggest how efficient an electric power system powered by LH2 would have to be to offset the power density difference from gasoline/kerosene? A quick disclaimer.... I don't have any degrees in this stuff or work with it. I just happen to be very interested in the sciences in general and have taught myself a few things over the years. Having said that, I try very hard to check my facts and figures before I say anything. I have an allergy to foot-in-mouth disease. On to your question.... Per numbers in http://www.tinaja.com/glib/energfun.pdf Liquid H2 has an energy density of 2600 Watt-hours/liter. Gasoline is 9000 Watt-hours/liter. [I used energy density per volume rather than per mass because that's the limiting factor in any vehicle, the volume of the 'gas tank'] If we make an assumption for discussion's sake that an LH2 powered system were 100% efficient, then the gasoline system would only need to be 2600/9000 = 29% efficient to reach parity with LH2. But note that nothing is ever 100% efficient. There are _always_ conversion losses. It's a matter of how much. Per: http://en.wikipedia.org/wiki/Interna...rgy_efficiency Engine efficiency is limited by thermodynamic laws. "Most steel engines have a thermodynamic limit of 37%." Further, "most engines retain an average efficiency of about 18%-20%." Right away we see it's at least potentially possible for gasoline to still beat out 100% efficient LH2. But let's go on the low side and assume a gasoline engine is 18% efficient. Then we need to figure out the efficiency required of an LH2 system to beat gasoline: 9000 * 18% = 1620 1620 / 2600 = 62% Therefore an LH2 system would have to be 62% efficient overall to beat a typical gasoline engine. Per the same Wikipedia article, "Electric motors are better still, at around 85%-90% efficiency or more, but they rely on an external power source (often another heat engine at a power plant subject to similar thermodynamic efficiency limits)." OK. So an electric motor _by itself_ is more than efficient, but as stated it has to get it's electricity from somewhere else. We are assuming an LH2 powered source. Let's go with the high side of 90% on the electric motor. So we have to now figure out what efficiency is required in converting LH2 to electrity so a 90% efficient electric motor produces 1620 Wh/l of LH2... 1620/.90/2600 = 69% Now that leaves us with finding out how efficiently LH2 can be converted to electricity. Per: http://energy.gov/eere/fuelcells/fuel-cells "Fuel cells can operate at higher efficiencies than combustion engines, and can convert the chemical energy in the fuel to electrical energy with efficiencies of up to 60%." So we may be coming up a bit short. However, all my pondering here is surely a gross oversimplification. And it's possible I goofed on my math or went astray with my logic. And I imagine different sources will give different numbers. But I hope it gives you some idea. There are surely other factors that need to be taken into account. Some may make things work out better, others may make things worse. Brian -- http://www.earthwaves.org/forum/index.php - Earth Sciences discussion http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Sed quis custodiet ipsos Custodes? |
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