Li heat sink

(Henry Spencer) wrote in message ...

They don't have to meet -- the lithium will be enclosed in some other
metal anyway.

Probably thin metal, right? Trying to contain a friendly metal like
lithium in a thin, flight weight heat shield would be
an...interesting...challenge that would get worse with the number of
welds, expansion joints, and other complications in the lithium's
container.

I don't think there's the same experience handling molten lithium as
there is handling liquid sodium, let alone in containers that would
meet the requirements of a heat sink heat shield and survive hot
immersion in salt water with hot lithium on the other side.

But, then again, there's probably a simple alloy and heat shield
demonstrator that has already addressed those concerns and Mr. Spencer
is about to tell me about it.

Mike Miller, Materials Engineer

In article ,
Derek Lyons wrote:
(And a water touchdown would be *really fun*.)
Doesn't seem to have been a problem for Al Shepard or Gus Grissom.

...A Be heatshields thermal properties are quite
different than the Li/Be system proposed here, and the mechanical
details of the two systems are very different as well. I'd be
hesitant in claiming that safe operation of one system 'proves' the
safe operation of another, very different system.

However, saying it "would be" really fun implies that it is definitely
unsafe, which is not the same thing as merely having doubts. I never said
it was proven safe; I merely noted that the situation isn't *inherently*
unsafe, because heat-sink heatshields have done water touchdowns without
great problems in the past. It's challenging, but perhaps not unsolvable.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

In article ,
Keith Harwood wrote:
...It sounded to me like he was talking merely about a
heat-sink heatshield meeting water... which has been done.

I was thinking about accidents.

That's not what Derek said, however.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

In article ,
Mike Miller wrote:
They don't have to meet -- the lithium will be enclosed in some other
metal anyway.

Probably thin metal, right? Trying to contain a friendly metal like
lithium in a thin, flight weight heat shield would be
an...interesting...challenge...

Understand, I'm not saying it's necessarily easy, or even that it can be
done with acceptable reliability. I'm rebutting an assertion that the
situation is (essentially) inherently and inevitably disastrous. No, it
doesn't *have* to be. "Challenging" I will accept. :-)
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Gordon D. Pusch) writes:

Weren't they going to use some sort of salt?

Sorry, no, but thank you for playing. Any such solar-dynamic system
would necessarily need to use some type of radiative cooling.
A fixed chunk of material =CANNOT= serve as a "heat sink" indefinitely:
Eventually, it will heat up to the temperature of the boiler --- and at
that point, the heat engine stops producing any power. (T_hot == T_cold
implies _zero_ thermodynamic efficiency!)

It is perhaps possible that some solar dynamic designs might have included
a molten salt tank to _STORE_ heat for use during the portion of the orbit
where the solar dynamic plant was in the Earth's shadow --- but unless you're
willing to dump the working-fluid overboard, in space the only practical
"heat sink" is a large radiating fin.

They did, and that's what I was asking about.

Would that possibly be more environmentally benign if it needed to
be dumped overboard from an emergency landing?

The "salts" used in phase-change thermal storage are not your rock salt
or table salt. They are oddball substances such as "Glauber's salt"
(sodium sulphate decahydrate), or Calcium chloride hexahydrate,
or Zinc nitrate hexahydrate, or various metal oxides or hydroxides
dissolved in dilute acid. Various organic compounds have also been
proposed. However, none of these phase-change thermal storage materials
have anywhere near the specific heat capacity that you can get by simply
boiling water and venting it. And you really =DON'T= want to be _storing_
all that heat in the spacecraft, where it will simply cause problems later;
you want to be dumping that heat overboard !!!

Tell the people who started the thread, which is about finding better
heat-sink materials than beryllium.

Gordon D. Pusch wrote:
However, none of these phase-change thermal storage materials
have anywhere near the specific heat capacity that you can get by simply
boiling water and venting it. And you really =DON'T= want to be _storing_
all that heat in the spacecraft, where it will simply cause problems later;
you want to be dumping that heat overboard !!!

Actually, I did once sketch out a design which did keep it on board all
the way through the reentry interface. The point is that you don't
really want to have landing fuel *and* reentry coolant. It's actually
easier if your landing fuel IS your reentry coolant.

When you want to land you just open a valve through some nozzles and
phoooomf you land in a big cloud of steam and get to live today. Yhe
landing is 'sporty'; but atleast you don't have to light the engine, and
you'd know well before hand whether enough pressure is in the system for
you to survive- if not, a parachute is recommended as backup.

A slightly less scary approach would be to use a Roton style rotor, and
vent the steam through that.

-- Gordon D. Pusch

Henry Spencer wrote:
The basic answer is exactly what you see with the shuttle (which
has quite a bit of heat stored in its tiles at landing time):
one of the first things that happens after touchdown is that an
air-conditioning truck is hastily hooked up to the vehicle to
keep the interior cool.

How warm would it get if the air-conditioning truck is not available,
e.g. after an unscheduled emergency landing at an unusual location?
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.

In article ,
Keith F. Lynch wrote:
The basic answer is exactly what you see with the shuttle (which
has quite a bit of heat stored in its tiles at landing time):
one of the first things that happens after touchdown is that an
air-conditioning truck is hastily hooked up...

How warm would it get if the air-conditioning truck is not available,
e.g. after an unscheduled emergency landing at an unusual location?

My impression -- I have no specific data -- is that cabin and cargo bay
would both get unpleasantly hot, but not disastrously so. Enough to
perhaps ruin biological specimens, not enough to damage equipment, is
my understanding.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |