COMPUTATIONAL EVALUATION OF THERMAL BARRIER COATINGS

In the power plant industry, the turbine inlet temperature (TIT) plays a key role in the efficiency of the gas turbine and, therefore, the overall—in most cases combined—thermal power cycle efficiency. Gas turbine efficiency increases by increasing TIT. However, an increase of TIT would increase the turbine component temperature which can be critical (e.g., hot gas attack). Thermal barrier coatings (TBCs)—porous media coatings—can avoid this case and protect the surface of the turbine blade. This combination of TBC and film cooling produces a better cooling performance than conventional cooling processes. The effective thermal conductivity of this composite is highly important in the design and other thermal/structural assessments. In this article, the effective thermal conductivity of a simplified model of TBC is evaluated. This work details a numerical study on the steady-state thermal response of two-phase porous media in two dimensions using personal finite element analysis (FEA) code. Specifically, the system response quantity (SRQ) under investigation is the dimensionless effective thermal conductivity of the domain. A thermally conductive matrix domain is modeled with a thermally conductive circular pore arranged in a uniform packing configuration. Both the pore size and the pore thermal conductivity are varied over a range of values to investigate the relative effects on the SRQ. In this investigation, an emphasis is placed on using code and solution verification techniques to evaluate the obtained results. The method of manufactured solutions (MMS) was used to perform code verification for the study, showing the FEA code to be second-order accurate. Solution verification was performed using the grid convergence index (GCI) approach with the global deviation uncertainty estimator on a series of five systematically refined meshes for each porosity and thermal conductivity model configuration. A comparison of the SRQs across all domain configurations is made, including uncertainty derived through the GCI analysis.References: [1] Ibrahim, T. K. and Rahman, M. M., 2013, “Study on effective parameter of the triple-pressure reheat combined cycle performance,” Thermal Science, 17(2), pp. 497-508. [2] Nayak, J. and Mahto, D., 2014, “Effect of Gas Turbine Inlet Temperature on Combined Cycle Performance,” International Conference on Recent Innovations in Engineering & Technology. [3] Fathi, N., McDaniel, P., Forsberg, C., and de Oliveira, C., 2018, "Power Cycle Assessment of Nuclear Systems, Providing Energy Storage for Low Carbon Grids," Journal of Nuclear Engineering and Radiation Science, 4(2), 020911. [4] Fathi, Nima, Patrick McDaniel, Charles Forsberg, and Cassiano de Oliveira. "Nuclear Systems for a Low Carbon Electrical Grid." In 2016 24th International Conference on Nuclear Engineering, pp. V001T03A007-V001T03A007. American Society of Mechanical Engineers, 2016. [5] Hunter, I., Daleo, J., Wilson, J., and Ellison, K., 1999, “Analysis of Hot Section Failures on Gas Turbines in Process Plant Service,” Proceedings of the 28th Turbomachinery Symposium, 28, pp. 9-20. [6] Zohuri, Bahman, and Nima Fathi. "Thermal-Hydraulic Analysis of Nuclear Reactors." [7] Salehnasab, B., Poursaeidi, E., Mortazavi, S. A., and Farokhian, G. H, 2016, “Hot corrosion failure in the first stage nozzle of a gas turbine engine,” Engineering Failure Analysis, 60, pp. 316-325. [8] Rechard, Robert P., Teklu Hadgu, Yifeng Wang, Lawrence C. Sanchez, Patrick McDaniel, Corey Skinner, and Nima Fathi. Technical Feasibility of Direct Disposal of Electrorefiner Salt Waste. No. SAND2017-10554. Sandia National Lab.(SNLNM), Albuquerque, NM (United States), 2017. [9] Rechard, Rob P., Teklu Hadgu, Yifeng Wang, Larry C. Sanchez, Patrick McDaniel, Corey Skinner, Nima Fathi, Steven Frank, and Michael Patterson. "Feasibility of Direct Disposal of Salt Waste from Electochemical Processing of Spent Nuclear Fuel." arXiv preprint arXiv:1710.00855 (2017). [10] Lai, G. Y., 2007, High-Temperature Corrosion and Materials Applications, ASM International, Novelty, OH. [11] Rao, A. D, 2012, Combined Cycle Systems for Near-Zero Emission Power Generation, Woodhead Publishing Limited, Cambridge, UK.  [12] Ma, W., Li, X., Meng, X, Xue, Y, Bai, Y, Chen, W., and Dong, 2018, “Microstructure and Thermophysical Properties of SrZrO3 Thermal Barrier Coating Prepared by Solution Precursor Plasma Spray,” Journal of Thermal Spray Technology, 27(7), pp. 1056-1063. [13] McCay, M. H., Hsu, P.-f., Croy, D. E., Moreno, D., and Zhang, M., 2017, “The Fabrication, High Heat Flux Testing, and Failure Analysis of Thermal Barrier Coatings for Power Generation Gas Turbines,” Turbo Expo: Power for Land, Sea, and Air, 6():V006T24A008. [15] Irick, Kevin, and Nima Fathi. "Thermal Response of Open-Cell Porous Materials: A Numerical Study and Model Assessment." In ASME 2018 Verification and Validation Symposium, pp. V001T03A002-V001T03A002. American Society of Mechanical Engineers, 2018.