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CAFE Electric Aircraft Symposium Set For May 1



 
 
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  #11  
Old May 8th 15, 07:30 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 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
  #12  
Old May 8th 15, 10:28 PM posted to rec.aviation.piloting
Skywise
external usenet poster
 
Posts: 140
Default 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?
  #13  
Old May 9th 15, 07:25 PM posted to rec.aviation.piloting
Vaughn
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Posts: 154
Default 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.
  #14  
Old May 9th 15, 09:32 PM posted to rec.aviation.piloting
[email protected]
external usenet poster
 
Posts: 2,892
Default 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
  #17  
Old May 10th 15, 02:39 AM posted to rec.aviation.piloting
Skywise
external usenet poster
 
Posts: 140
Default 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?
  #19  
Old May 10th 15, 10:18 AM posted to rec.aviation.piloting
Skywise
external usenet poster
 
Posts: 140
Default 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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