To what pressure? What is the diffuser design, or what reference
should an interested student be designing from? Do you run the tank
empty of LOX? How long can it be pressurized? How much nitrogen is
used relative to an ideal analysis assuming no liquefaction or
dissolution?
On Thu, Apr 21, 2016 at 3:42 PM, Bruno Berger <mailinglists@xxxxxx> wrote:
We at SPL only pressurize with N2. He is ok for launch vehicles but
simply to expensive for everyday tests. As you and others said: A good
diffuser and pressurization just before firing and a quick release after
it. Never had an issue. But we only work with rel. small run tanks. If
you have to pressurize a big tank for several firings during a longer
time frame things may look different.
Also consider pressurization of the LOX with GOX. It's as cheap as N2
and you don't contaminate. And no, the problem with condensation isn't a
big problem as long as you don't use sub-cooled LOX (It's kind of an
equilibrium... The gas entering the tank might condense, but it also
forces the LOX to boil a bit because it's warmer). But then you need a
separate N2 supply for the LOX-purging.
Bruno
--
Bruno Berger
Swiss Propulsion Laboratory
E-Mail: bruno.berger@xxxxxx (HTML-Mails will be dropped!)
WWW: http://www.spl.ch
HAM: HB9RSU
Am 21.04.16 um 08:23 schrieb Jonas Bjarnø:
I can only corroborate what David says. I've done a number of LOX-based
systems with GN2 pressurization and its fully doable. Key is to get the
diffuser design right and only complete pressurization just prior to
firing. You basically want to make sure your diffuser reduces the
vertical velocity component of the incoming GN2, so as to minimze the
interaction with the LOX surface.
BR's
Jonas
2016-04-21 5:24 GMT+02:00 David Gregory <david.c.gregory@xxxxxxxxx
<mailto:david.c.gregory@xxxxxxxxx>>:
It seems we are in agreement on solubility, tho I can't tell from
your post. This is a clear area where the "new space way" is more
expensive and onerous than the "conventional aerospace way" that is
so reviled. As I said below, personal experience with no less than
five test stands, many many hundreds of tests, tens of millions of
dollars of propellant burned - only a handful pressurized lox with
helium.
On Apr 20, 2016, at 8:10 PM, Randall Clague <rclague@xxxxxxxxx
<mailto:rclague@xxxxxxxxx>> wrote:
Ben says, can't pressurize LOX with nitrogen, bad bad bad, but he
doesn't say why. Solubility is why. If you pressurize your LOX
with nitrogen, you may get a LOX froth when you try to fire the
engine. In the very early days, when you don't care about that,
nitrogen is fine. And boy howdy is it cheaper.
When Henry talks about fuel in the LOX system costing lots of
money, listen to him. He was the investigating officer for an
incident where that very thing happened. It didn't do a lot of
damage, but it set back the schedule by months.
-R
On Wed, Apr 20, 2016 at 11:22 AM, David Gregory
<david.c.gregory@xxxxxxxxx <mailto:david.c.gregory@xxxxxxxxx>> wrote:
The main issue to be avoided is the extraordinary solubility
of GN2 in liquid oxygen. I don't have my references handy
but it's something like 2:1 by mass (2 lbs of gn2 disolves in
1 lb of lox). It's not condensing, it dissolving like CO2 into
soda. Tanks usually have a diffuser to slow the pressurant
velocity and avoid stirring the tank. If the tank is stirred
by the incoming n2, it will just run away as the control
system tries to add ever more gas which simply disolves faster
due to more stirring.
For a flight system you have the added complexity of
mechanical agitation of the tank. But as others say, it has
been done.
> On Apr 20, 2016, at 5:28 AM, Ben Brockert <wikkit@xxxxxxxxx
<mailto:wikkit@xxxxxxxxx>> wrote:
>
> That is cool. Can you give more details on how to make it
work, now
> that you're free of the silence of the endless blue? Putting
a gas
> over a liquid that is significantly below the gas's boiling
point has
> given bad results in the straightforward attempts I've heard.
>
> On Wed, Apr 20, 2016 at 8:18 PM, David Gregory
> <david.c.gregory@xxxxxxxxx
<mailto:david.c.gregory@xxxxxxxxx>> wrote:
>> I've worked on five different test stands that used
nitrogen pressurization for LOx and only had an issue once.
You'll want to pay attention to to diffusion, but you don't
have to use helium.
>>
>>> On Apr 19, 2016, at 11:31 PM, Ben Brockert
<wikkit@xxxxxxxxx <mailto:wikkit@xxxxxxxxx>> wrote:
>>>
>>> Hi Kyle,
>>>
>>> Sounds like a fun project. Some thoughts:
>>>
>>> * If your cryo main valve has a normal pneumatic actuator,
it will
>>> typically have a maximum actuator inlet pressure of around
150psi.
>>> That would be an unusually low pressure to do all your
engine tests,
>>> so you may want to add another regulator for pneumatic
pressure. It
>>> shouldn't be very expensive.
>>>
>>> * The vent valves have their own symbol, neither manual or
electronic.
>>> What kind of valve are they? Vent absolutely must be
remote operated,
>>> and almost always should be normally open (so that if
power is lost to
>>> the stand the vents will open). The vent lines themselves
out of those
>>> valves need to point in directions that won't spray at people.
>>>
>>> * You have to use helium to pressurize LOX, it doesn't
matter how much
>>> it costs. You may find it's more cost effective over the
long run to
>>> have nitrogen for the fuel and helium for the LOX. It
means a little
>>> bit more plumbing but it reduces operating cost and
eliminates any
>>> possibility of cross contamination from the fuel side to
the LOX side.
>>>
>>> * The gauges shown by the engine should probably be
transducers.
>>>
>>> * It's a fairly minor thing, but the ball on the symbol
for a check
>>> valve indicates the inlet end. So two of yours are backwards.
>>>
>>> * The helium and possible nitrogen bottles have hand
valves on them,
>>> so the hand valve on your high pressure line probably
isn't necessary.
>>> High pressure regulators also often have filters on their
inlet
>>> already, so you may not have to put that filter in. If the
regulators
>>> don't have filters, they're a good idea though.
>>>
>>> * Basically every design document says to not relieve
pressure from a
>>> line by cracking open a fitting, but... I wouldn't bother
with the
>>> vent valve on the high pressure side. Unless the line
between the
>>> bottle and the regulator is particularly long, it's not
unreasonable
>>> to let that pressure off when unscrewing the CGA fitting
from the
>>> bottle. CGA fittings take a big wrench and have a lot of
straight
>>> threads, so there's little risk of it coming all the way
undone and
>>> whipping around.
>>>
>>> * I've used non-cryo rated valves for cryo vent before and
gotten away
>>> with it. Needs to have suitable materials (brass or
stainless body,
>>> PTFE seats and seals) and it may require experimentation,
but it can
>>> be done.
>>>
>>> * For remote LOX fill you hook the dewar up to a normally
closed cryo
>>> fill valve via a cryo hose (McMaster sells a -8 or -10
one), open the
>>> globe valve on the dewar, and run away. Operate the fill valve
>>> remotely until liquid shoots out the vent. (Have a dip
tube on the
>>> vent line inside the tank to ensure some ullage). For
remote fuel you
>>> could do a similar setup with an electric fuel pump. I
generally
>>> wouldn't bother with either, I prefer to have the LOX
dewar and fuel
>>> drum away from the test stand at test time.
>>>
>>> * For LOX system drying, the optimum is to not ever put
water in the
>>> system after it has been oxidizer cleaned and component
level and
>>> assembled. Do liquid nitrogen if you want to do a cold
flow before
>>> comitting to LOX, which is a good idea. If you must load
water in it,
>>> all ball valves have to be opened half way and blown
through with dry
>>> gas as you suggest. One option is to hook up a bottle of
nitrogen and
>>> slowly blow the entire bottle through the system. Another
is to get an
>>> oilless compressor, put a high quality water and oil
filter on its
>>> outlet, and blow clean air through. Any ball valves have
to be 45
>>> degrees open though, if full open any water trapped in the
cavity
>>> between ball and body will stay there. And operate the
ball valve a
>>> dozen or so times with gas flowing.
>>>
>>> * You're going to want purges to clear out the lines to
the engine
>>> before and after running. Typically they come from above
the tank
>>> press valve, through an orifice and a solenoid valve and a
check valve
>>> or two, and are injected on the downstream side of the
engine run
>>> valve.
>>>
>>> What's your plan for propellant tanks?
>>>
>>> An important next step is to make another P&ID that goes
all the way
>>> to component level, making sure that fitting types sizes
are correct
>>> on everything. Then from that you can create a realistic
BOM and
>>> figure out how much everything is going to cost.
>>>
>>> No mild steel parts anywhere in the LOX system, and if you
bolt the
>>> LOX tank or downstream parts to a steel structure they
need thermal
>>> isolation.
>>>
>>> Ben
>>>
>>>> On Wed, Apr 20, 2016 at 9:15 AM, Kyle Meeuwsen
<meeuwsen.engr@xxxxxxxxx <mailto:meeuwsen.engr@xxxxxxxxx>> wrote:
>>>> Hello All,
>>>>
>>>> This is my first post and I hope I am doing it correctly...
>>>>
>>>> I am with the Portland State Aerospace Society and we are
developing our
>>>> first liquid engine test stand. This is a LOX and Ethanol
system pressurized
>>>> by either Nitrogen or Helium depending on the quote back
from Praxair.
>>>>
>>>> Below is a link to the Test Stand PID on Imgur. I am
looking for either
>>>> approval or to discuss design concerns. Please note that
the valve below the
>>>> LOX tank is cryo rated with a pneumatic actuator that is
pressurized by two
>>>> solenoids which are fed from the LOX pressurant line.
>>>>
>>>> The senior design team before me also selected relief
valves and solenoids
>>>> for venting on the top of the LOX tank that are not cryo
rated. I have
>>>> concerns that heat transfer from the tank to the LOX
might freeze these
>>>> components that are attached to the top of the LOX tank.
I could attempt a
>>>> very shaky heat transfer analysis unless people know
right away that these
>>>> components will freeze very quickly.
>>>>
>>>> I am also still searching for filters and burst discs,
and a way to safely
>>>> fill the LOX and Ethanol tank from a great distance away.
>>>>
>>>> Also, any suggestions on how to purge the system of
moisture prior to
>>>> testing would be greatly appreciated. I have been told to
run hot pressurant
>>>> gas through the system for an extending period of time
but I am currently
>>>> not in possession of a heat exchanger or an ample amount
of pressurant gas.
>>>>
>>>> https://imgur.com/gallery/wVbtgUz
>
