Application of Transpiration Cooling for Hot Structures
Specific parts of re-entry vehicles are exposed to severe conditions. Thereby, the material’s capabilities can be exceeded by far and advanced cooling methods become necessary. Within the scope of this work, transpiration cooling was investigated in arc j
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Summary Specific parts of re-entry vehicles are exposed to severe conditions. Thereby, the material’s capabilities can be exceeded by far and advanced cooling methods become necessary. Within the scope of this work, transpiration cooling was investigated in arc jet heated plasma flows by means of flat plate models. Screening tests pointed out, that transpiration cooling at the conditions tested is working well. Extensive testing at more severe conditions was done using three porous sample materials: Standard C/C with coolant flows parallel and perpendicular to the material’s fibre layers and highly porous C/C. Coolant gases used were air, argon, helium and nitrogen. Minimal optimal coolant mass flows of 0.5 g/s Ar, 0.2 g/s He and 0.4 g/s N2 were determined resulting in sample under surface temperature reductions of 50-60%. Altogether, sample under surface temperature reductions of 64% for He, 65% for Ar, 67% for air and 70% for N2 were detected. These test series verified that transpiration cooling can be applied successfully for hot structures at application relevant re-entry conditions.
1 Introduction 1.1 Background For highly demanded parts of re-entry vehicles, high temperature usable materials like ceramic matrix composites (CMC’s) are being used. Such parts are in particular thermal protection system elements and hot structures like leading edges, flaps or components of propulsion systems. In most cases, the cooling of such hot structures relies on radiation cooling. However, in some situations the material’s capabilities can be exceeded, for instance by higher-energetic (interplanetary) re-entry conditions, smaller structure nose radii or higher ballistic coefficients. Therefore, e.g. ablative or advanced cooling techniques like active cooling systems become necessary. Thereby, reusability is a great advantage of active cooling systems in contrast to ablative ones. 1.2 Motivation Active cooling systems usually consist of internally, convective cooled structures like heat pipes. Additionally, it is possible to perform external active cooling systems; such systems could be for example transpired surfaces, which have not been applied successfully to reusable spacecraft yet. Basically, the principle of transpiration A. Gülhan (Ed.): RESPACE – Key Tech. for Reusable Space Sys., NNFM 98, pp. 82–103, 2008. © Springer-Verlag Berlin Heidelberg 2008 springerlink.com
Application of Transpiration Cooling for Hot Structures
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cooling consists of two heat mechanisms (see Fig. 1): Firstly, the porous structure is being cooled by convection of the coolant flow penetrating the porous media. Secondly, a thermal blocking coolant layer is built on the outer, hot surface of the porous structure, which tremendously reduces heat transfer to the outer surface. Hot gas flow
Hot gas flow
Boundary layer
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Porous sample
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Coolant
Coolant layer Porous sample Coolant
Convective coolant flow
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Fig. 1. Transpiration cooling mechanisms
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