CAFE Electric Aircraft Symposium Set For May 1

On 5/3/2015 10:10 PM, Skywise wrote:
Although liquid hydrogen has nearly 3 times more energy per
unit weight, that does not take into account the mass of the
containment vessel. A liquid hydrogen tank is going to more
than 3 times as massive as a gasoline tank or fuel bladder,
thus resulting in a net loss of energy per unit weight of the
fuel plus it's container.

I'm not sure where you got that information from, but it's wrong.
Compressed hydrogen takes a heavy tank because of the pressure.

On the other hand, liquid hydrogen need not be under pressure, so it
does not need a massive tank. However, cryogenic fuels have their own
issues! What a cryogenic fuel tank needs that is different from other
liquid fuels is insulation. That insulation need not be heavy, but it
will take up valuable volume in your airframe. Also, cryogenic tanks
are always venting unless you have heavy, expensive power-hungry
refrigeration equipment aboard. So that means that your liquid
hydrogen-fueled airplane could be assumed to be sitting in a cloud of
flammable gaseous fuel whenever it is fueled and sitting on the ground.
No thanks!

Vaughn wrote in :

On 5/3/2015 10:10 PM, Skywise wrote:
Although liquid hydrogen has nearly 3 times more energy per
unit weight, that does not take into account the mass of the
containment vessel. A liquid hydrogen tank is going to more
than 3 times as massive as a gasoline tank or fuel bladder,
thus resulting in a net loss of energy per unit weight of the
fuel plus it's container.

I'm not sure where you got that information from, but it's wrong.

http://www.tinaja.com/glib/energfun.pdf

The numbers can be confirmed by other sources.

But I think you misread what I wrote.

Brian
--
http://www.earthwaves.org/forum/index.php - Earth Sciences discussion
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?

On Mon, 04 May 2015 08:33:26 -0400, Vaughn wrote:

On the other hand, liquid hydrogen need not be under pressure, so it
does not need a massive tank. However, cryogenic fuels have their own
issues! What a cryogenic fuel tank needs that is different from other
liquid fuels is insulation. That insulation need not be heavy, but it
will take up valuable volume in your airframe. Also, cryogenic tanks
are always venting unless you have heavy, expensive power-hungry
refrigeration equipment aboard. So that means that your liquid
hydrogen-fueled airplane could be assumed to be sitting in a cloud of
flammable gaseous fuel whenever it is fueled and sitting on the ground.
No thanks!

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.

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.

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'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? 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. If you don't vent
it... KABOOOM!

Remember Challenger? That's what happens when the tank breaches.

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.

Personally, I find the whole argument on hydrogen as a replacement
for gasoline a joke. It's basic physics. So unless the laws of
physics go out the window.... 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
--
http://www.earthwaves.org/forum/index.php - Earth Sciences discussion
http://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism
Sed quis custodiet ipsos Custodes?

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

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?

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

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?

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.

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