Hi Paul,
To me, the term "cryopumping" is a confusing and misleading term that can
describe several things that are going on. We need more words to describe
the different meanings of cryopumping. Like CryoEvacuation, meaning the
evacuation by freezing the contents of an enclosed volume or space. The
R-Value of closed cell foam increase when the cells are CryoEvacuated, the
gas used to inflate the bubble or cell is frozen leaving a vacuum in the
remaining volume. If the contents of the bubble or cell are brought down to
a temperature where the contents are liquid (and gas), the cell could
actually be equivalent to a "heat pipe" and transfer heat faster
(boiling-condensation convection). Heat-pipes are thermal conductors worst
than if the cell only contained gas (conduction only, no convection) or
only contained solid (vacuum). I am unsure if the small cells can actually
work like a "heat pipe", but larger volumes would.
So, for a closed cell foam surrounding a Hydrogen tank, there are three
zones. The Dewar zone where the cells are CryoEvacuated, the Heat-Pipe zone
where the contents of the cell are liquid (and gas), and the insulation
zone (what most people think of as insulation) with low conduction of wall
and gas. Hydrogen, tank wall, Great R-Value, ?Worst R-Value?, Regular
R-Value, Air.
Like the Submarine, 5/8" thick steel is required for a large vacuum
chamber........The Glass Micro Balloons Uwe mentioned are micro-vacuum
chambers that can hold back the pressure at the bottom of the Mariana's
Trench. The glass micro balloons are used for flotation of deep sea
submarines.
So, how close can We get the truck with the hydrogen to the beach on the
4th?
https://www.google.com/maps/@28.4600264,-80.5269691,383m/data=!3m1!1e3
--
Craig Fink
WeBeGood@xxxxxxxxx
On Mon, Jun 17, 2019 at 5:59 PM Paul Mueller <paul.mueller.iii@xxxxxxxxx>
wrote:
Regarding the "hard ice" outer shell in a disposable insulation scheme, ICryogenic storage is preferred to keep volumes and pressure vessel masses
would worry that it would not be able to handle the "cryopumping"
(condensation of gas in the insulation layer resulting in near-vacuum,
great for reducing conductivity) and would buckle under the atmospheric
pressure load. For example, on the vacuum-jacketed ground storage tank at
Vandenberg (and similarly at KSC), the outer vessel had to be quite stout
(5/8" thick steel IIRC) to keep from collapsing. Not quite a submarine, but
the same idea.
One of the challenges for propellant production on Mars (using hydrogen
brought from Earth to react with atmospheric CO2 to produce methane and
oxygen propellants) was how to store the hydrogen on the Martian surface
during the months-long propellant production process.
within reason, but it was tough to find a suitable insulation. It appearedAn aerogel insulation would have the same problem as multilayer
that atmospheric CO2 would form a hard, dense "ice" instead of a fluffy
insulating frost, though it was hard to find actual test results at that
time (I looked at this more than 20 years ago so I may be hopelessly out of
date).
insulation--the need for a rigid, leakproof outer shell to allow the
insulation to cryopump down to near vacuum without sucking in the
atmosphere. The outer shell wouldn't need to be super structurally stable
to not buckle under weak Martian "air" pressure, but it would still be a
challenge to make it lightweight, Standoffs from the inner pressure vessel
would help, but they were also heat leak paths. In the end, spray-on foam
seemed like the best solution.
Sorry for the boring details--I did a fair amount of research on it back
in the day. Cryogenic hydrogen is definitely a challenge, yet I don't think
the design space has been fully explored for such things as lifting-body
airliners, etc. It might work well. IMHO, I don't think it's very
practical for student rockets but it could be helpful for students to learn
safe handling practices if there ever were a significant "hydrogen economy"
in the future. Right now I think you'd be hard pressed to find any
university administrator willing to deal with it (especially due to the
Hindenburg syndrome). The Hindenburg disaster really gave hydrogen a black
eye, when what really was to blame was the solid rocket propellant
(aluminum powder and nitrate dope) that coated its entire outer surface!
On Sun, Jun 16, 2019 at 3:16 PM Charlie Garcia <dragonrider.hhcc@xxxxxxxxx>
wrote:
I did some a brief survey of adhesives on cryogenic tank domes, and
actually had some success with RTV. The best performance was rendered by a
conductive epoxy, but your run of the mill green hysol worked pretty well.
Seconding Zotek though. What a wonderful insulator. Beats the crap out of
spray on foam in terms of mess and hassle.
On Sun, Jun 16, 2019 at 5:10 PM Ben Brockert <wikkit@xxxxxxxxx> wrote:
RTV will break right off any metal surface at LOX temperature. I did
that as an experiment at Armadillo, I think I was trying to see if I could
glue the downcomer fairing on to the tank, rather than welding on mounting
points.
There are now very good cryogenic epoxies on the market, and the cryogel
application instructions call out a specific mastic for bonding the
insulation to the surface.
On Sunday, June 16, 2019, Michael S. Kelly <mskellyrlv@xxxxxxxxxxxxx>
wrote:
In the ICBM world, any time we put anything on a solid motor that could
see the plume (or a carbon-carbon extension cone), we’d cover it with glass
microballoon-loaded RTV. IIRC, they used blue pigmented RTV, when I
thought white would have been better. In my personal experience, RTV will
hold up even when it gets over 700 F. It adheres quite well to either
metallic or composite surfaces. The density and thermal conductivity can
be reduced by increasing microballoon loading, up to a point.
Sent from Mail <https://go.microsoft.com/fwlink/?LinkId=550986> for
Windows 10
*From: *Uwe Klein <uwe@xxxxxxxxxxxxxxxxxxx>
*Sent: *Sunday, June 16, 2019 5:11 AM
*To: *arocket@xxxxxxxxxxxxx
*Subject: *[AR] Re: tank frost (was Re: LH2.... Density)
Am 16.06.2019 um 00:22 schrieb Craig Fink:
Maybe it's very appealing, I'm going to withhold judgement until I see
the video.
Anyone experimented with Airo Gel or (glas)microballoon+binder based
insulations?
Uwe
