(126D) Oxidation Of Microvascular Carbon/Carbon Composites By Super-Critical Carbon Dioxide Flow

Concentrating solar power (CSP) systems are increasingly becoming a more significant part of the renewable energy grid in the United States. By concentrating sunlight into a single receiver, a working fluid is heated and usually sent to conventional steam turbines to produce electricity. The use of supercritical carbon dioxide (sCO2) Brayton-cycles have been identified as a replacement for conventional steam turbines in CSP systems, providing higher thermal to electricity efficiencies. With this in mind, the direct use of sCO2 as the heat transfer fluid in gas receivers has been proposed. Furthermore, conventional solar receivers are subjected to thermal stresses due to daily startup operations, and thus prone to fatigue failures. Therefore, the use of a novel Carbon/Carbon composite for a modular gas receiver is being investigated due to its lower coefficient of thermal expansion while maintaining high thermal conductivity and mechanical properties. The chemical reaction between sCO2 and the composite, though not significant at low temperatures, is enhanced at the high operating temperatures of the modules. Due to this effect, mass loss of the composite is a concern. In this presentation, a CFD analysis of sCO2 flow in a C/C composite micro-channel is performed with the reaction at the channel’s surface to model the surface recession rate of the channel’s walls. Using literature kinetic data for C/C composites at varying stages of production together with kinetic data from experiments for composites fabricated in-house, channel recession rates are obtained to propose a predictive model for the composite’s mass loss.