Title:
Thermogravimetric Analysis of Carbon Felt Insulation for Flexible Thermal Protection System Thermal Response Modeling
Thermogravimetric Analysis of Carbon Felt Insulation for Flexible Thermal Protection System Thermal Response Modeling
Author(s)
Rossman, Grant
Braun, Robert D.
Braun, Robert D.
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Abstract
A multi-layered, Flexible Thermal Protection System (FTPS) heatshield configuration layup has previously undergone ground-based testing in an arc-jet facility to simulate atmospheric entry heat exposure. An existing thermal response model has been developed at NASA to simulate heat transfer through an FTPS layup during an arc-jet experiment by predicting measured temperatures between layers. A carbon felt insulator, located in the middle of this FTPS layup, decomposes when exposed to high heating in an atmosphere that contains significant amounts of oxygen. The current module in the FTPS thermal response model that simulates insulator decomposition has not yet leveraged experimentally determined quantities. In an effort to achieve better temperature predictions in the thermal model, a Thermogravimetric Analysis (TGA) experimental campaign was performed on virgin samples of a carbon felt insulator to rigorously characterize decomposition by obtaining its activation energy. Experiments were performed in a zero-moisture air environment using Standard TGA and Modulated TGA methods with a TA Instruments Q5000IR apparatus to obtain estimates of activation energy. The mean activation energy for carbon felt was determined to be 131.56 kJ/mol and 121.16 kJ/mol for Standard and Modulated TGA methods, respectively. Limited TGA testing resources in the past have resulted in rough approximations FTPS insulator activation energy with little knowledge of uncertainty. This TGA experimental campaign also determined the corresponding activation energy uncertainty for carbon felt samples using a t-distribution. The activation energy standard deviation was determined to be 5.79 kJ/mol and 8.66 kJ/mol for Standard and Modulated TGA methods, respectively. The activation energy obtained from the Standard TGA method was inserted into the FTPS thermal response model to compare resulting temperature profile predictions with measured thermocouple temperature data recorded during ground-based arc-jet testing. Preliminary results show significant improvement in thermal response model temperature predictions using this experimentally-determined value for activation energy. This investigation shows promise for a newly developed decomposition module within the FTPS thermal response model based on rigorous experimentation and enables future probabilistic analysis to include activation energy as an uncertain parameter.
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2017-01
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