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NUCLEARSPACE MESSAGE BOARD (ACTIVE) -> SCIENCE & ENGINEERING -> Transpiration cooling offers protection for spaceplanes
Post Info TOPIC: Transpiration cooling offers protection for spaceplanes
10kBq Jaro


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Transpiration cooling offers protection for spaceplanes
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Very interesting research, with a variety of applications....


http://www.flightglobal.com/articles/2007/05/15/213860/transpiration-cooling-offers-protection-for-spaceplanes.html
15/05/07  
SOURCE:Flight International
Transpiration cooling offers protection for spaceplanes
By Rob Coppinger

Water's high vaporisation temperature makes it ideal for re-entry nosecone treatmentTranspiration cooling using water can provide thermal protection for the hot structures of hypersonic vehicles and spaceplanes, according to German researchers.

German aerospace centre DLR's Spaceliner design for a two-stage, 50-passenger suborbital vehicle for intercontinental flights was used for the research.

The rocket-powered vehicle would accelerate to 14,900mph (24,100km/h) at an altitude of less than 100km (60 miles), releasing its fly-back propellant-tank first stage and then continuing on a ballistic trajectory.

Even using a skipping re-entry trajectory to reduce the heat load, temperatures of up to 2,630ºC (4,760ºF) are expected on the wing leading edges of the second-stage vehicle, requiring new thermal protection technology.

Transpiration cooling was looked at for the nosecone, with water the fluid of choice as it has the highest heat of vaporisation of any liquid: 2,260kJ/kg at 1bar. In the experiments, 0.2g/s (0.42oz/min) of water was flowed into porous aluminium oxide/silica nosecones of up to 25mm (0.98in) radius, cooling a 25mm-radius cone from over 1,727ºC to below 227ºC. As the water flowed through the cone vaporisation encouraged capillary action to draw in more water.

"With Spaceliner you need 9t of water [for transpiration cooling]," said Martin Sippel, head of the Cologne-based DLR space launcher systems analysis group, at the final report event for the Key Technologies for Reusable Space Systems (Respace) virtual institute.

Respace also analysed gas transpiration cooling of ceramic-matrix composite (CMC) materials including carbon carbon and carbon silicon carbide and wound highly porous oxide, known as Whipox. Effective cooling was achieved with gaseous helium flow rates as low as those for water, 0.2g/s. However, questions remain over water compatibility with CMCs due to stresses from internal pressure build-up from vaporisation. Further work is required to examine wing leading-edge transpiration cooling. That research could continue under the German Research Foundation's proposed Transregio hypersonics project, involving Respace's German universities

The work will also examine rocket base-flow aerodynamics, TPS film cooling concepts and basic launcher technologies. A decision on Transregio is expected in July.



-- Edited by 10kBq Jaro at 00:41, 2007-05-15

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GoogleNaut


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Transpiration cooling is one of the most effective active cooling methods around. It is also used to aid in the cooling of the combustion chamber and throat of the Space Shuttle Main Engine--hundreds of thousands of tiny (almost microscopic) pores are used to allow a certain amount of liquid hydrogen to 'sweat' on the inside surface of the engine. This does two things: it creates a barrier which cuts down the radiant heat loading to the wall, and also carries away some of the heat that does make it to the surface. This reduces the thermal stresses on the inside of the engine which improves its life by reducing the tendency to crack.

NASA has done some research into piezoelectricly driven microatomization in which cooling can be enhanced further by breaking tiny streams of fluid into microscopic droplets. Interestingly enough--this technology has actually found applications in some inkjet printers rather than cooling rocket engines!



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