Catalysis and Oxidation of Copper Calorimeters – Are we Over-Testing Material Samples?
Start Date
1-3-2011 8:00 AM
End Date
3-3-2011 12:30 PM
Description
Arc-jet tests are the most important criteria for designing and accepting thermal protection systems (TPS). Their plasma plume is characterized by using a copper calorimeter measuring heat flux, which is inserted into the stream. The measured heat flux value is then converted to incident hot wall heat flux at which a thermal protection material is tested. The model assumptions used to convert the calorimeter reading to an equivalent hot wall heat flux are currently based on the assumption of full catalycity of copper during plasma exposure, meaning that the plasma chemical energy is fully converted to heat flux. Oxidation effects on the copper calorimeter and on the heat flux are not considered - despite the fact that it is expected of copper exposed to air plasma to change surface composition and morphology. Literature shows that different copper oxides form at different temperatures; each of them being characterized by a lower catalytic coefficient than that of pure copper. The value of the heat flux at which TPS are currently tested is thus higher than required, leading to over-dimensioning the TPS for a flight design. An effort is needed, which aims at providing a clear understanding of the oxidation effects on copper calorimeters exposed to various arc-jet test conditions and the direct impact oxidation has on the resulting catalytic coefficient. This would enable us to correct the models and thus test TPS under more accurate aero-thermal environment. This will ultimately lead to more realistic TPS weight budget for all EDL missions (in particular where high enthalpies are expected during entry such as into Earth and Mars), increasing mission payloads and moving into reach missions that currently, from a TPS perspective, seem impossible. The proposed poster will highlight unknown areas of error when using copper calorimeters for heat flux characterization. It will propose a path forward, and serve as a baseline for discussion and potential collaboration.
Catalysis and Oxidation of Copper Calorimeters – Are we Over-Testing Material Samples?
Arc-jet tests are the most important criteria for designing and accepting thermal protection systems (TPS). Their plasma plume is characterized by using a copper calorimeter measuring heat flux, which is inserted into the stream. The measured heat flux value is then converted to incident hot wall heat flux at which a thermal protection material is tested. The model assumptions used to convert the calorimeter reading to an equivalent hot wall heat flux are currently based on the assumption of full catalycity of copper during plasma exposure, meaning that the plasma chemical energy is fully converted to heat flux. Oxidation effects on the copper calorimeter and on the heat flux are not considered - despite the fact that it is expected of copper exposed to air plasma to change surface composition and morphology. Literature shows that different copper oxides form at different temperatures; each of them being characterized by a lower catalytic coefficient than that of pure copper. The value of the heat flux at which TPS are currently tested is thus higher than required, leading to over-dimensioning the TPS for a flight design. An effort is needed, which aims at providing a clear understanding of the oxidation effects on copper calorimeters exposed to various arc-jet test conditions and the direct impact oxidation has on the resulting catalytic coefficient. This would enable us to correct the models and thus test TPS under more accurate aero-thermal environment. This will ultimately lead to more realistic TPS weight budget for all EDL missions (in particular where high enthalpies are expected during entry such as into Earth and Mars), increasing mission payloads and moving into reach missions that currently, from a TPS perspective, seem impossible. The proposed poster will highlight unknown areas of error when using copper calorimeters for heat flux characterization. It will propose a path forward, and serve as a baseline for discussion and potential collaboration.