Active Cooling Question

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KJ_Lesnick

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In order, which would make a better active coolant in terms of it's ability to take away heat from a surface... (like if you had a surface that was 1200 F, would these fuels have different abilities to absorb heat, or just a difference in the ability to absorb heat without combusting)

- JP-4,
- JP-5,
- JP-7,
- LCH4
- LH2


KJ Lesnick
 
KJ_Lesnick said:
In order, which would make a better active coolant in terms of it's ability to take away heat from a surface... (like if you had a surface that was 1200 F, would these fuels have different abilities to absorb heat, or just a difference in the ability to absorb heat without combusting)

- JP-4,
- JP-5,
- JP-7,
- LCH4
- LH2


KJ Lesnick
Click to expand...

Somewhere in a box I have a set of papers and articles that would very precisely answer that question. If I have some time this week I'll look for it.
Anyway, it's a tougher problem than just that. For the purposes of cooling an aircraft, you look at not only the heat capacity, but things like what the fuel breaks down into. If I remember correctly JP-4 isn't suitable for this kind of thing, as it breaks down into junk when you expose it to high heat for a while. Methyl cyclohexane (again, IIRC) on the other hand breaks down into hydrogen and toluene - it's close to ideal for this kind of application.
 
To simply absorb heat is a waste. You must do something with that heat to extract the energy from it. Cracking of JP fuels or LH2 triple point is my favorite, then methane. LH2 heated to gas form then expelled through proper injector design = very high ISP even without combustion. Cooling requirements can lead to rich mixture which can be utilized in base burn to reduce base drag.
 
airrocket,

To simply absorb heat is a waste. You must do something with that heat to extract the energy from it. Cracking of JP fuels or LH2 triple point is my favorite, then methane. LH2 heated to gas form then expelled through proper injector design = very high ISP even without combustion. Cooling requirements can lead to rich mixture which can be utilized in base burn to reduce base drag.
Click to expand...

First of all, the question was to determine the effects of active-cooling on reducing the temperature of the plane's skin thus allowing it to fly at a given mach number with a cooler skin or for the same skin temperature to fly faster.

Basically, figures more or less for a given skin temperature with a given type of fuel used

Still, regardless what exactly is a base-burn?


KJ Lesnick
 
KJ_Lesnick said:
airrocket,

To simply absorb heat is a waste. You must do something with that heat to extract the energy from it. Cracking of JP fuels or LH2 triple point is my favorite, then methane. LH2 heated to gas form then expelled through proper injector design = very high ISP even without combustion. Cooling requirements can lead to rich mixture which can be utilized in base burn to reduce base drag.
Click to expand...

First of all, the question was to determine the effects of active-cooling on reducing the temperature of the plane's skin thus allowing it to fly at a given mach number with a cooler skin or for the same skin temperature to fly faster.

Basically, figures more or less for a given skin temperature with a given type of fuel used

Still, regardless what exactly is a base-burn?


KJ Lesnick
Click to expand...

Until I get a chance to dig out those papers, this patent actually provides a good overview of the subject:
http://www.patentstorm.us/patents/5176814/description.html

And this is a good resource that expands on that quite a bit. May or may not be too technical for your needs, but all the numbers you could want should be here:
http://books.nap.edu/openbook.php?record_id=10980&page=122
 
Base burning .... similar to afterburner where injected fuel or rich unburnt fuel is shockwave compressed and burnt at the base (outside of the nozzle) of the vehicle. Pressure from this combustion counteracts base drag associated with angular blunt tail lifting bodies. Win Win greater ISP plus reduction of base drag. A fin with a diamond shaped airfoil can become an external scramjet at high mach numbers. LH2 is injected onto the wing surface where it is compressed and ignitied by the shockwaves. One uses a rocket to accelerate to M12 and external shockwave compression for sustained M12cruise...ram/scaramjet not required.
 

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