[ RadSafe ] Liquid nitrogen as vehicle "fuel" (was: "Another recentarticle")

[Brennan, Mike (DOH)]

I agree that LN2 isn't going to compete with gas, or even LNG, as a
portable energy source.  The question is whether it can compete with
energy storage systems, should a society REALLY try to provide all its
electrical needs from intermittent sources, such as wind or solar.  In
that application, LN2 is not competing with gasoline, but with such
things as batteries, pumped water, hydrogen, and flywheels.  

Pumped water is one of the more efficient storage systems, is safe in
anything bet extreme events, and is as mature a technology as you get.
It is also difficult to site and not all portable.

Batteries are evolving, with improvements on almost a weekly basis.  I
expect ultimately the power densities will be very high (the will have
to be to power my laser rifle).  But they will probably take more and
more high tech materials, probably will continue to wear out, and will
be progressively more exciting in accidents that cause discharge, or
leakage or internal components.  I expect ultimately batteries will win
in most energy storage situations, particularly where volume is at a
premium.  

Hydrogen as a energy storage system is dangerous and difficult, and is
only in consideration due to misguided political thinking.

Flywheels are interesting, and have good energy storage characteristics,
particularly if made out of DU.  I've read science fiction stories where
there were flywheel powered cars, and I've always wanted to see one try
to take a high speed corner.

I am not saying LN2 is perfect, or even necessarily good enough.  I do
think it is interesting.  And the premise that if something was good
enough to be of value someone would have already thought of it before is
not supported by the continued existence of patent offices.    

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Ernesto
Faillace
Sent: Wednesday, June 06, 2012 11:33 AM
To: radsafe at health.phys.iit.edu
Subject: [ RadSafe ] Liquid nitrogen as vehicle "fuel" (was: "Another
recentarticle")

If liquid nitrogen were a practical alternative to battery storage
and/or
combustible fuels, you'd think someone would have thought of this a long
time ago...  If it sounds too good to be true, it probably is.

Here's one reason why:
*Energy density of liquid nitrogen*

*Any process that relies on a phase-change of a substance will have much
lower **energy densities*
<http://en.wikipedia.org/wiki/Energy_density>*than processes involving
a chemical reaction in a substance, which in turn
have lower energy densities than nuclear reactions*. Liquid nitrogen as
an
energy store has a low energy density. Liquid hydrocarbon fuels by
comparison have a high energy density. A high energy density makes the
logistics of transport and storage more convenient. Convenience is an
important factor in consumer acceptance. The convenient storage of
petroleum fuels combined with its low cost has led to an unrivaled
success.
In addition, a petroleum fuel is a primary energy
source<http://en.wikipedia.org/wiki/Primary_energy_source>,
not just an energy storage and transport medium.

The energy density - derived from nitrogen's isobaric heat of
vaporization
and specific heat in gaseous state - that can be realised from liquid
nitrogen at atmospheric pressure and zero degrees Celsius ambient
temperature is about 97 watt-hours per kilogram (W-hr/kg). This compares
with 100-250 W-hr/kg for a lithium-ion
battery<http://en.wikipedia.org/wiki/Lithium-ion_battery>and 3,000
W-hr/kg for a gasoline combustion
engine <http://en.wikipedia.org/wiki/Internal_combustion_engine> running
at
28% thermal efficiency, 30 times the density of liquid nitrogen used at
the
Carnot
efficiency.[2]<http://en.wikipedia.org/wiki/Liquid_nitrogen_vehicle#cite
_note-Knowlen-1>

For an isothermal expansion engine to have a range comparable to an
internal combustion engine, *a 350-litre (92 US gal) insulated onboard
storage vessel is
required.[2]<http://en.wikipedia.org/wiki/Liquid_nitrogen_vehicle#cite_n
ote-Knowlen-1>
* A practical volume, but a noticeable increase over the typical
50-litre
(13 US gal) gasoline tank. The addition of more complex power cycles
would
reduce this requirement and help enable frost free operation. However,
no
commercially practical instances of liquid nitrogen use for vehicle
propulsion exist.
http://en.wikipedia.org/wiki/Liquid_nitrogen_vehicle#Energy_density_of_l
iquid_nitrogen
Much more practical (at today's relatively low natural gas prices) would
be
to use methanol in existing or modified flex fuel vehicles (and this has
already been proven feasible).  About half the energy density of
gasoline,
but better engine performance (higher "octane"), methanol has comparable
costs of production and distribution (at today's relatively high
gasoline
costs), and no need to make substantial changes to motors, fuel tanks or
distribution networks.  It is usually blended at 85% methanol/15%
gasoline
(M85) to prevent cold-start or vapor-lock issues.

For more, see http://en.wikipedia.org/wiki/Methanol_fuel

-- 
Ernesto Faillace, CHP