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CAFE Electric Aircraft Symposium Set For May 1



 
 
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  #21  
Old May 10th 15, 06:13 PM posted to rec.aviation.piloting
[email protected]
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Default CAFE Electric Aircraft Symposium Set For May 1

Dave Doe wrote:
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?


Air is 78% nitrogen.

Air is used as the oxidizer in an engine.

At high temperatures, i.e. inside an engine, the nitrogen combines
with the excess oxygen to produce NOx; mostly NO and NO2.

It does not matter what is actually "burning", it is the temperature
that causes the reaction and hydrogen has a very high flame temperature.

As hydrocarbons as a rule do not contain nitrogen, where do you think
the NOx emmisions come from?


--
Jim Pennino
  #24  
Old May 11th 15, 09:10 PM posted to rec.aviation.piloting
Larry Dighera
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Posts: 3,953
Default 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  
Old May 11th 15, 09:57 PM posted to rec.aviation.piloting
Skywise
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Posts: 140
Default 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  
Old May 14th 15, 06:49 PM posted to rec.aviation.piloting
Larry Dighera
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Posts: 3,953
Default 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.

  #27  
Old May 14th 15, 07:14 PM posted to rec.aviation.piloting
Vaughn
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Posts: 154
Default 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.
  #28  
Old May 17th 15, 06:31 PM posted to rec.aviation.piloting
Larry Dighera
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Posts: 3,953
Default 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.




  #29  
Old June 3rd 15, 07:14 PM posted to rec.aviation.piloting
Larry Dighera
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Posts: 3,953
Default 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  
Old June 3rd 15, 10:57 PM posted to rec.aviation.piloting
Skywise
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Posts: 140
Default 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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