Slurry Deposited Environmental and Thermal Barrier Coatings and Design of Microchannel Cooling System for Enhanced Efficiency of Gas Turbine Engine Application /

Abstract

In this era, energy technologies are suitable to meet the challenges of fuel depletion and global warming. Energy generation from natural resources such as coal, natural gas, and oil is an approach to fulfill the electricity demand. Depletion of non-renewable resources put an emphasis to increase the efficiency of thermal power plants. Gas turbine engine efficiency can only be increased after increasing the inlet gas temperature and reducing the cooling air flow. These attributes originated the need of thermal management for the combustor section in terms of material selection, protective coating and cooling or heat removal systems. Ni superalloy i.e. Monel 400 is the conventional material that exhibits good mechanical properties, is a potential candidate for the manufacture of gas turbine engine components e.g. turbine blade, vanes, etc. High-temperature oxidation and diffusion of deleterious elements reduced their applicability in power and aerospace industry. C/SiC composites are the materials of today engine world because of lightweight, high density, low CTE, and high thermal conductivity. Since C/SiC has poor oxidation resistance against high-temperature, a composite engine design will facilitate us to achieve higher efficiencies to meet the energy demands. The environmental and thermal barrier coating (ETBC) is the technique to combat thermal degradation risk to increase the endurance of materials against high thermal exposure. In this study, oxidation protective shield of Al2O3 was developed on Monel 400 superalloy and C/SiC composite via an easy and cost-effective slurry dip coating route instead of expensive thermal spray process. Slurry was prepared after employing solution method and deposited after using dip-coater. After deposition, coating was vacuum dried and sintered to consolidate the surface structure. In case of Monel 400 superalloy, Isothermal oxidation testing at 600⁰C, 800⁰C, and 1000⁰C for several hours was performed. Reduction in weight gain was observed. Analytical techniques such as XRD, SEM, EDS and image analysis were performed for analyzing the microstructure and microchemistry to analyze the thermal performance of coating. For Al2O3 coated C/SiC composite, reduction in porosity before and after sintering was analyzed by Image J software. SurfChar J analysis measured effective surface roughness Ra of about 7-16 μm with positive skewness and kurtosis. Coating with 8-15% surface porosity proved sustainable after performing dynamic thermal shock testing (DTS). During testing corresponding weight loss was measured. SEM based cross-sectional analysis depicts a well-established and adherent interface. Coating was remained intact vii without spallation or peeling. Slurry deposited Al2O3 protected the C/SiC composite from surface oxidation with weight loss in fraction. As part of exchange program at MIME (TEST lab), Oregon State University, research work was carried out on condensation across microchannels. For cooling of combustion section, an innovative microchannel cooling system at low mass fluxes 75-150kg/m²-s at saturation temperature of 40°C and 55°C for efficient heat transfer was studied. The study focused to analyze the transition of flow regimes and vapor quality at low mass fluxes. The experiments were performed at low mass fluxes 75-150kg/m²-s at saturation temperature of 40°C and 55°C. For all conditions, annular /annular wavy flow regimes observed, with no distinct intermittent flow. The experimental data was compared against the two-phase flow map of Taitel and Duckler which shows good agreement for condensation of R134a.