How Does a Heat-Pipe Work

[KJ_Lesnick]

How exactly does a heat-pipe work and is it useful as an overall thermal protection system?

Kendra

 

[Simon666]

Wikipedia exists for these kind of questions.

http://en.wikipedia.org/wiki/Heat_pipe

 

[KJ_Lesnick]

I'm not sure if it said anything about being useful as a complete thermal protection system, or if it would only be useful as part of it.

KJ

 

[Simon666]

I'm not sure if it said anything about being useful as a complete thermal protection system, or if it would only be useful as part of it.

Just Google e.g. "heat pipe" and "leading edge" or "thermal protection" and you'll get things like this:

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790005730_1979005730.pdf

 

[KJ_Lesnick]

What I'm not getting is...
-A heat pipe works on convection; it carries heat from one area to another.
-How does that not heat up the insides of the plane? Since wouldn't carrying the heat from the skin, carry it into the plane? Or would it carry it to some other area on the skin that's not as hot and can take the extra heat?
-Does the pipe itself reflect away a lot of the heat with the substance in the pipe shuffling around the rest? If so, how does it keep the skin reasonably cool if significant heat is reflected -- some back to the skin?

Is this better/worse than various other thermal protection systems, especially types that reflect large amounts of heat away without absorbing much?


Kendra Lesnick

BTW: Has anyone heard of some kind of stuff called "Starlite" or "Firepaste"? Starlite was some kind of coating which allegedly was ceramic based and could allegedly take temperatures of 10,000 F to 20,000 F so I was told. I remember hearing of an experiment in which a hard-boiled egg was treated with this stuff then put under a (acetylene?) blow-torch. After they were done they cracked open the egg and the egg was unscathed. Firepaste is cruder and simpler and less capable but nonetheless is based on the same principle and works quite well. Since the stuff isn't exactly rigid or hard and capable of withstanding extreme stress... in combination with a fairly light heat-shield this stuff would be incredible.

 

[sferrin]

What I'm not getting is...
-A heat pipe works on convection; it carries heat from one area to another.
-How does that not heat up the insides of the plane?

Because you dump the heat into the fuel headed to the engines. There are limits to that however. One other use for that heat can be used to "crack" heavy hydrocarbon fuel into something "lighter" that lights off quicker for use in a scramjet. X-51 does this as I recall.

BTW: Has anyone heard of some kind of stuff called "Starlite" or "Firepaste"? Starlite was some kind of coating which allegedly was ceramic based and could allegedly take temperatures of 10,000 F to 20,000 F so I was told. I remember hearing of an experiment in which a hard-boiled egg was treated with this stuff then put under a (acetylene?) blow-torch. After they were done they cracked open the egg and the egg was unscathed. Firepaste is cruder and simpler and less capable but nonetheless is based on the same principle and works quite well. Since the stuff isn't exactly rigid or hard and capable of withstanding extreme stress... in combination with a fairly light heat-shield this stuff would be incredible.

If you feel like looking through a decade's worth of AvWeek there was an ad in the 80s advertising coatings that could survice "particle beams and temperatures up to 50,000 degrees". Whether it was BS, someone added an extra zero or what have you I don't know. I do find it extremely hard to believe as carbon vaporizes at around 7000F and I don't see how you could take element A & element B and combine them to get a compound/alloy that has a higher melting point than either. Any chemists/metallurgists feel free to correct me.

(edit: Actually, table salt would fall into that category. Hmmmm.)

 

[KJ_Lesnick]

Because you dump the heat into the fuel headed to the engines. There are limits to that however. One other use for that heat can be used to "crack" heavy hydrocarbon fuel into something "lighter" that lights off quicker for use in a scramjet. X-51 does this as I recall.

Oh, that's a "hot-structure", right?
They work, but I'm more fond of reflecting as much heat away from the vehicle as I can possibly get away with -- you wouldn't need as elaborate a cooling system.

I know of one fuel that works like what you described: Methylcyclohexane (MCH) -- get it real hot and it breaks down into Hydrogen and Toluene which gets burned up.

If you feel like looking through a decade's worth of AvWeek there was an ad in the 80s advertising coatings that could survice "particle beams and temperatures up to 50,000 degrees". Whether it was BS, someone added an extra zero or what have you I don't know. I do find it extremely hard to believe as carbon vaporizes at around 7000F and I don't see how you could take element A & element B and combine them to get a compound/alloy that has a higher melting point than either. Any chemists/metallurgists feel free to correct me.

(edit: Actually, table salt would fall into that category. Hmmmm.)

50,000 Farenheit? Yikes, I thought it was 20,000 Farenheit. Were they talking about one coating, or multiple types of coatings?

The only theory I've ever heard floating around that made any sense was that it somehow acted like a mirror to infrared light, and possibly a few other wavelengths reflecting damn near all of it away and absorbing virtually none.

What kind of particle beams were they talking about?


Kendra