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CAFE Electric Aircraft Symposium Set For May 1
On Fri, 8 May 2015 01:39:59 +0000 (UTC), Skywise
wrote: Larry Dighera wrote in : I hadn't considered the explosive environment created by venting liquid hydrogen. How is that dealt with by suppliers, laboratories and users today? Perhaps the venting H2 could be captured and run through the fuel-cell and the resulting electric power stored in batteries for future use to preclude the explosive atmosphere forming. Just more equipment that can fail and adds weight and cost. I'm sure the airlines would like that. Or, would you like that on your car? I wasn't considering electric airliners yet; I was thinking more along the lines of GA-sized aircraft. I'm still curious how venting H2 is kept from producing an explosive atmosphere in laboratories and at the gas plants where it is produced. Surely the technology exists... I'm wondering if the heat produced by a fuel-cell could be used to change the liquid H2 into the gaseous phase, and if the resulting cooling of the fuel-cell will contribute to its efficiency. Why would you want to heat liquid H2? 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. The reason tanks vent is because it's boiling off. It's very difficult to insulate a tank to LH2 temperatures, so some of it boils off. It would be interesting to know just how difficult it is to insulate a LH2 vessel, so that the boil-off rate is reasonably slow. If you don't vent it... KABOOOM! Yeah. I recall the resounding POP that occurs when a burning splint is inserted into the inverted test tube containing the evolved H2 from electrolysis. It's a definite issue, as is the explosive atmosphere created by venting gasoline vapors. But, obviously methods have been successfully developed to deal with it. Remember Challenger? That's what happens when the tank breaches. My recollection was that the seals on the Solid Rocket Boosters on the sides of the big central O2-H2 tank had failed, and the hot SRB gases had breached the big tank. I wasn't aware of an H2 venting issue. Speaking of rockets, ever notice how they are constantly venting while on the pad? They close the valves just before lift-off. If the launch is delayed the valves are reopened to prevent too much pressure from building. After launch it's not a problem because the fuel is being consumed fast enough. Agreed. Ever notice the main rocket nozzles suddenly ice-up shortly after ignition? I believe that's a result of the cold liquid combustion gases being routed through tubing coiled around the rocket motors to keep them from melting and assist in atomizing the gases, so that they will react more readily. Just a guess. Personally, I find the whole argument on hydrogen as a replacement for gasoline a joke. The limited research I conducted years ago seemed to suggest that there wasn't much else that approached the energy density of gasoline/kerosene. So, while perhaps not ideal, hydrogen is a somewhat viable alternative to petroleum, that has the potential to provide efficiencies several times better than the ~30% efficiency obtained with internal combustion power plants. If you consider that only one third the fuel will be required to achieve the current performance, the numbers begin to make more sense. With 70% of the energy blowing out the exhaust as heat, internal combustion engine efficiency is comparable to an incandescent lamp that consumes ~90% of its energy usage to produce heat, and only ~10% to produce light. LEDs, on the other hand, can be 90% more efficient than tungsten filament lamps, and they last many times longer too. It's basic physics. So unless the laws of physics go out the window.... I understand what you are saying, and I agree; the solution isn't obvious, but it may be possible. Apparently a lot of large commercial entities seem to think so... Well, there are those who think science and basic physics are a conspiracy to keep the truth from being revealed... But I'm not assuming anyone here is in that camp. Yet. Brian Hey. Let's leave T. Cruz and Santorum out of this discussion. :-) -- Irrational acts are ultimately founded on irrational beliefs. -- Larry Dighera |
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CAFE Electric Aircraft Symposium Set For May 1
Larry Dighera wrote in
news I wasn't considering electric airliners yet; I was thinking more along the lines of GA-sized aircraft. I'm still curious how venting H2 is kept from producing an explosive atmosphere in laboratories and at the gas plants where it is produced. Surely the technology exists... It's burned off to prevent just such a situation. Why would you want to heat liquid H2? 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. It doesn't take much to heat it up. That's why the tanks vent. The reason tanks vent is because it's boiling off. It's very difficult to insulate a tank to LH2 temperatures, so some of it boils off. It would be interesting to know just how difficult it is to insulate a LH2 vessel, so that the boil-off rate is reasonably slow. I'm sure you could eliminated venting altogether with s sufficiently strong tank and MAINTAINED crygenic cooling. Remember Challenger? That's what happens when the tank breaches. My recollection was that the seals on the Solid Rocket Boosters on the sides of the big central O2-H2 tank had failed, and the hot SRB gases had breached the big tank. I wasn't aware of an H2 venting issue. My point was the size of the KABOOOM. Perhaps a better example.... Hindenburg. Ever notice the main rocket nozzles suddenly ice-up shortly after ignition? I believe that's a result of the cold liquid combustion gases being routed through tubing coiled around the rocket motors to keep them from melting and assist in atomizing the gases, so that they will react more readily. Just a guess. You're correct. http://www.nasa.gov/mission_pages/co...edia/cece.html https://www.youtube.com/watch?v=5QJNnTRRLOo Although not all rocket engines do this. With 70% of the energy blowing out the exhaust as heat, internal combustion engine efficiency is comparable to an incandescent lamp that consumes ~90% of its energy usage to produce heat, and only ~10% to produce light. LEDs, on the other hand, can be 90% more efficient than tungsten filament lamps, and they last many times longer too. Good analogy. But that is an example not of more efficient energy production, but more efficient energy consumption. Although both are needed in the grand scheme of things, IMO. What's to say we can't find a more efficient way to consume fossil fuels? Although it tends to sound conspiracy theory like, I think there is some merit to the notion that more fuel efficiency in cars is being held back for monetary reasons. It is a fact that vehicles have been designed that get far higher MPG than you typically find on the road. Why aren't they being sold? For example, I just found the following on a VW diesel hybrid capable of nearly 300 MPG. http://hereandnow.wbur.org/2014/09/1...uel-efficiency http://www.wired.com/2013/05/volkswagen-xl1-driven/ This leads to another point I learned myself while driving. People race from red light to red light. Not don't get me wrong. I like to drive fast just like anyone else. But what I learned to do is to not make it a drag race. I still go ten over on the streets, cruise 80-85mph on the freeway (I'm in LA). I just don't stomp on the gas pedal to get there. I did a comparison on this change in driving style. I increased my MPG by at least 10% just by changing the way I accelerate. Funny thing is, I often find myself pulling up to the same cars at the light... those racing off the line. It's basic physics. So unless the laws of physics go out the window.... I understand what you are saying, and I agree; the solution isn't obvious, but it may be possible. Apparently a lot of large commercial entities seem to think so... I guess I'm arguing against the public perception. There's a lot of bad info out there. I don't profess to be any kind of expert myself, but I know what I know, otherwise I shut up. So many people think it's a simple thing to just convert all our cars to some other form of energy and overnight we can change the world. Well, we can't. We've had a hundred years to develop IC engines. It may take another hundred years to replace them. What happens in the lab does not always translate to real-world practical application. Can an alternative be found? I'm sure of it. Well, there are those who think science and basic physics are a conspiracy to keep the truth from being revealed... But I'm not assuming anyone here is in that camp. Yet. Hey. Let's leave T. Cruz and Santorum out of this discussion. :-) Hey, the other side of the aisle isn't much smarter. Two sides of the same coin if you ask me. hehehe... well, there's a web forum that I visit regularly that is chock full of nutters. Needless to say my actual participation has been decreasing over time as I realize the futility of even existing in such an environment. The New Dark Ages are upon us. 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 5/8/2015 2:30 PM, Larry Dighera wrote:
Personally, I find the whole argument on hydrogen as a replacement for gasoline a joke. The limited research I conducted years ago seemed to suggest that there wasn't much else that approached the energy density of gasoline/kerosene. So, while perhaps not ideal, hydrogen is a somewhat viable alternative to petroleum, that has the potential to provide efficiencies several times better than the ~30% efficiency obtained with internal combustion power plants. If you consider that only one third the fuel will be required to achieve the current performance, the numbers begin to make more sense. With 70% of the energy blowing out the exhaust as heat, internal combustion engine efficiency is comparable to an incandescent lamp that consumes ~90% of its energy usage to produce heat, and only ~10% to produce light. LEDs, on the other hand, can be 90% more efficient than tungsten filament lamps, and they last many times longer too. Simply put, the problem with using hydrogen as a fuel is that we have no natural source of it in unattached gaseous form. So we have to MAKE hydrogen by reforming it from natural gas, or by some even more energy-hungry method such as electrolysis of water. So while hydrogen can be used as a fuel, it is not a SOURCE of energy such as natural gas or gasoline is. Hydrogen is only a CARRIER of energy (much like our electrical utilities are a carrier of energy, not a source of energy). In the process of converting "something" to hydrogen, you never have 100% efficiency, so on a whole-cycle macro scale the efficiency picture of hydrogen can look pretty dismal. Also, an article might extol the clean burning properties of hydrogen in an engine or fuel cell, while failing the mention the pollution produced by the manufacture of hydrogen. |
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CAFE Electric Aircraft Symposium Set For May 1
Vaughn wrote:
On 5/8/2015 2:30 PM, Larry Dighera wrote: Personally, I find the whole argument on hydrogen as a replacement for gasoline a joke. The limited research I conducted years ago seemed to suggest that there wasn't much else that approached the energy density of gasoline/kerosene. So, while perhaps not ideal, hydrogen is a somewhat viable alternative to petroleum, that has the potential to provide efficiencies several times better than the ~30% efficiency obtained with internal combustion power plants. If you consider that only one third the fuel will be required to achieve the current performance, the numbers begin to make more sense. With 70% of the energy blowing out the exhaust as heat, internal combustion engine efficiency is comparable to an incandescent lamp that consumes ~90% of its energy usage to produce heat, and only ~10% to produce light. LEDs, on the other hand, can be 90% more efficient than tungsten filament lamps, and they last many times longer too. Simply put, the problem with using hydrogen as a fuel is that we have no natural source of it in unattached gaseous form. So we have to MAKE hydrogen by reforming it from natural gas, or by some even more energy-hungry method such as electrolysis of water. So while hydrogen can be used as a fuel, it is not a SOURCE of energy such as natural gas or gasoline is. Hydrogen is only a CARRIER of energy (much like our electrical utilities are a carrier of energy, not a source of energy). In the process of converting "something" to hydrogen, you never have 100% efficiency, so on a whole-cycle macro scale the efficiency picture of hydrogen can look pretty dismal. Also, an article might extol the clean burning properties of hydrogen in an engine or fuel cell, while failing the mention the pollution produced by the manufacture of hydrogen. If you burn hydrogen in an engine, you get lots of NOX byproducts, i.e. smog, because air is mostly nitrogen and hydrogen has a very high flame temperature. Fuel cells do not have that problem as the temperatured involved are much lower. -- Jim Pennino |
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CAFE Electric Aircraft Symposium Set For May 1
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CAFE Electric Aircraft Symposium Set For May 1
wrote in :
Vaughn wrote: On 5/9/2015 4:32 PM, wrote: If you burn hydrogen in an engine, you get lots of NOX byproducts, i.e. smog, because air is mostly nitrogen and hydrogen has a very high flame temperature. Fuel cells do not have that problem as the temperatured involved are much lower. Yes, but my point was that you are still left with the problem of the pollution and greenhouse gas generated by the production of your "clean" hydrogen fuel. Besides, for at least the last 30 years, mass consumer fuel cells have been "just around the corner". Even if they suddenly became practical and economical, we would still be left with the huge problems involved in producing and distributing hydrogen. You can wave your arms and talk about fuel cells all day, but the problems with hydrogen won't go away. Hydrogen is not an energy source. To make hydrogen, you make pollution. And my point was if you BURN hydrogen, you make pollution. You are BOTH right. And a similar argument can be made for going all electric. How do you make electricity? Right now, most of it is made by BURNING hydrocarbons. Moving to electric powered vehicles only shifts the location of the burning from the vehicle to the electric power plant. The only way to make electric vehicles viable from a 'pollution elimination' point of view is to ALSO generate the electricity from some other method than burning hydrocarbons. As Vaughn pointed out, we have to find an alternate SOURCE of energy, not an alternate medium by which to store it. Hydrocarbons are a source of energy. We get more energy out of hydrocarbons than we put in to extract it. We don't have to make it. Although there is the argument about how much is left. The problem is finding a viable alternate source of energy to replace hydrocarbons. Ones that can produce energy on par with, and for future growth eventually exceed the scale of what we get out of hydrocarbons. And then there's the whole problem of upgrading the power grid to handle everyone plugging in their e-car's without the wires glowing. The alternative to that may well be distributed energy generation. Replacing hydrocarbons for transportation use is not a simple or singular problem. At the risk of sounding cliche, it will require a paradigm shift in the way energy is produced, distributed, and consumed, and it will have to be adopted by everyone to make it work. 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
In article , ,
says... Vaughn wrote: On 5/9/2015 4:32 PM, wrote: If you burn hydrogen in an engine, you get lots of NOX byproducts, i.e. smog, because air is mostly nitrogen and hydrogen has a very high flame temperature. Fuel cells do not have that problem as the temperatured involved are much lower. Yes, but my point was that you are still left with the problem of the pollution and greenhouse gas generated by the production of your "clean" hydrogen fuel. Besides, for at least the last 30 years, mass consumer fuel cells have been "just around the corner". Even if they suddenly became practical and economical, we would still be left with the huge problems involved in producing and distributing hydrogen. You can wave your arms and talk about fuel cells all day, but the problems with hydrogen won't go away. Hydrogen is not an energy source. To make hydrogen, you make pollution. And my point was if you BURN hydrogen, you make pollution. Water is pollution? I think you either need to get your chemistry right, or define "hydrogen" - or perhaps, what you are burning. Hydrocarbons? -- Duncan. |
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CAFE Electric Aircraft Symposium Set For May 1
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. 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
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