Li heat sink

We know that beryllium heat sink heat shields can be fabricated and
expected to work, based on the mercury program. The fabrication
difficulties and weight pushed newer designs to ablatives, which make
sense for expendable vehicles, but heat sink designs still have an
appeal as a completely passive, completely reusable system for RLVs.

Why not use lithium as a heat sink? You would fabricate a shell from
a conventional nickel superalloy that retained good strength and
oxidation resistance up to 2200F or so, then fill it up with molten
lithium.

Lithium is almost twice as good a heat sink as Be: 3582 J/kg*K vs
1825 J/kg * K

You could probably push the maximum temperature up a couple hundred
degrees beyond what a solid Be shield would be good for if you wanted
to.

With the heat sink in a liquid form, you would get much better heat
transfer due to convection during high G deceleration.

Without having a big hunk of solid metal, you don't have heat shock or
thermal stress issues, which should make it reliably reusable for a
very long time.

Lithium is less than a quarter the cost of Be. Not a big deal for an
RLV, true.

A water transpiration cooling system that made a good boundary layer
would still be a good deal lighter, but there is definitely something
to be said for a completely passive system with no maintenance
requirements.

You might want to put a thin platinum plating on the inside of the
container to make absolutely sure it isn't going to react with
lithium. There is probably some other coating you should apply to the
outside to make it as non-catalytic to the disassociated ions as
possible. Can anyone comment on the appropriate materials for that?
A metallic bond would be preferable over a ceramic of any sort.

John Carmack
www.armadilloaerospace.com

John Carmack wrote:

Why not use lithium as a heat sink? You would fabricate a shell from
a conventional nickel superalloy that retained good strength and
oxidation resistance up to 2200F or so, then fill it up with molten
lithium.

Lithium hydride does even better.

I've sometimes thought that a good electric car would be one that
has an insulated container of hot LiH, which would be used to run
a heat engine. The energy storage density of LiH far exceeds that
of chemical batteries, even taking into account losses in the heat
engine.

Paul

In article ,
John Carmack wrote:
Why not use lithium as a heat sink? You would fabricate a shell from
a conventional nickel superalloy that retained good strength and
oxidation resistance up to 2200F or so, then fill it up with molten
lithium.

The Ely book says that a similar scheme using molten copper and an outer
shell of tantalum got some attention in early ICBM development, but
reliably containing the molten metal proved difficult and the idea was
abandoned. I imagine it would be even worse for liquid lithium, which is
highly corrosive to most other metals.

There are occasional hints that lithium is used as an expendable coolant
in some ICBM warheads. The Jan 1969 Journal of Spacecraft and Rockets has
a paper on cooling the inner surface of a nose cap with a liquid-lithium
spray.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(John Carmack) wrote:

A water transpiration cooling system that made a good boundary layer
would still be a good deal lighter, but there is definitely something
to be said for a completely passive system with no maintenance
requirements.

The big problem is; How do you keep the heat in the shield from
penetrating to your crew/payload compartment after re-entry? That's a
lot of BTU's, and they have to go somewhere.

D.
--
Touch-twice life. Eat. Drink. Laugh.

On Mon, 15 Mar 2004, John Carmack wrote:

Lithium is almost twice as good a heat sink as Be: 3582 J/kg*K vs
1825 J/kg * K

You could probably push the maximum temperature up a couple hundred
degrees beyond what a solid Be shield would be good for if you wanted
to.

With the heat sink in a liquid form, you would get much better heat
transfer due to convection during high G deceleration.

Ouch, upon lift off all liquid sinks to bottom of craft with much force,
leaving top of craft without heat sinking and busting bottom open

You might want to put a thin platinum plating on the inside of the
container to make absolutely sure it isn't going to react with
lithium.

resulting in lithium violently reacting with the atmosphere.
The appropiate day for lauch would be July 4. ;-)

(John Carmack) writes:

We know that beryllium heat sink heat shields can be fabricated and
expected to work, based on the mercury program. The fabrication
difficulties and weight pushed newer designs to ablatives, which make
sense for expendable vehicles, but heat sink designs still have an
appeal as a completely passive, completely reusable system for RLVs.

Why not use lithium as a heat sink? You would fabricate a shell from
a conventional nickel superalloy that retained good strength and
oxidation resistance up to 2200F or so, then fill it up with molten
lithium.

Lithium is almost twice as good a heat sink as Be: 3582 J/kg*K vs
1825 J/kg * K


Another potential advantage of lithium, it has an incredibly high
enthalpy of vaporization: 21,025 kJ/kg at normal boiling point,
compared to 2255 kJ/kg for water and not that far from graphite's
29,625 kJ/kg.

Depending on how you contain the molten lithium in its heat-sink
role, you could have the basis for a very effective ablator as
well. I'm particularly fond of thermal protection systems with
a backup mode, and this could be one.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *

William Elliot wrote:
On Mon, 15 Mar 2004, John Carmack wrote:

Lithium is almost twice as good a heat sink as Be: 3582 J/kg*K vs
1825 J/kg * K

You could probably push the maximum temperature up a couple hundred
degrees beyond what a solid Be shield would be good for if you wanted
to.

With the heat sink in a liquid form, you would get much better heat
transfer due to convection during high G deceleration.

Ouch, upon lift off all liquid sinks to bottom of craft with much force,
leaving top of craft without heat sinking and busting bottom open

Lithium is solid till 150C (?) so at lift-off, it'll be solid.

I'd be worried about it melting cleanly, you might need to preheat the
lithium to get it to work well.

You might want to put a thin platinum plating on the inside of the
container to make absolutely sure it isn't going to react with
lithium.

resulting in lithium violently reacting with the atmosphere.
The appropiate day for lauch would be July 4. ;-)

In article ,
Derek Lyons wrote:
The big problem is; How do you keep the heat in the shield from
penetrating to your crew/payload compartment after re-entry? That's a
lot of BTU's, and they have to go somewhere.

The whole point of a heatsink system, though, is that they don't have to
go anywhere in a hurry.

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. In the case
of John's vehicle, a plausible option is that the truck also starts
pumping cold deionized water through a set of built-in cooling passages at
the top of the vehicle heatshield, and venting the resulting steam.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

(Henry Spencer) wrote:

In article ,
Derek Lyons wrote:
The big problem is; How do you keep the heat in the shield from
penetrating to your crew/payload compartment after re-entry? That's a
lot of BTU's, and they have to go somewhere.

The whole point of a heatsink system, though, is that they don't have to
go anywhere in a hurry.

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.

Works for a land touchdown at a prepared site. Questionable for an
unprepared site. (And a water touchdown would be *really fun*.) Come
to think of it, so could touch down on a surface thats merely damp.

In the case of John's vehicle, a plausible option is that the truck also starts
pumping cold deionized water through a set of built-in cooling passages at
the top of the vehicle heatshield, and venting the resulting steam.

I shouldn't think it would need to be de-ionized, just distilled. It
would be an interesting design problem.

D.
--
Touch-twice life. Eat. Drink. Laugh.

In article , John
Carmack wrote:

Why not use lithium as a heat sink? You would fabricate a shell from
a conventional nickel superalloy that retained good strength and
oxidation resistance up to 2200F or so, then fill it up with molten
lithium.

And people will stop saying 'That John Carmack is crazy, he's using
peroxide in his rocket.'

--
David M. Palmer (formerly @clark.net, @ematic.com)