Thermally Sprayed Coatings as Resistive Heating Systems for Wind Turbine Blades and Airfoils
Creators: Taghian Dehaghani, Shahed
Publisher: name: University of Alberta Library
Year: 2023

<p>Accumulation of ice on the surface of wind turbine blades and aircraft wings in cold environments causes serious issues such as decrease in performance and efficiency. Ice accretion alters the geometrical profile and aerodynamic performance of the surface and increases the weight of the original structure. Furthermore, in some cases, icing may cause casualties and produce other significant safety issues. These undesired and detrimental effects, necessitates further development of novel de-icing systems.<br>
In this doctoral research program, the main objective is to develop thermally sprayed coatings to serve as de-icing elements for wind turbine blades and aircraft wings. Thus far, this research has focused on studying the effect of reinforcing ceramic particles on the heating performance of Ni-based resistive heating coatings and their erosion resistance. Nickel-chromium-aluminum-yttrium (NiCrAlY) powder was chosen as the matrix and was mechanically blended with three different ceramic powders namely, alumina, titania, and tungsten carbide, to produce feedstock powders for fabrication of metal matrix composite (MMC) coatings. A number of Joule heating tests were conducted by creating voltage differences across the coatings to enable electron flow and measuring the surface temperature of the heating elements. The effect of electrical resistance and dielectric behavior of the ceramic particles on the performance of the heating elements was investigated. These tests were conducted in an air duct under free and forced convection. It was observed that the ramp-up rate and the steady-state temperature were considerably affected by the electrical properties of the MMC coatings. A two-dimensional transient heat conduction model is being developed in order to predict the temperature distribution during the heating process.<br>
The surface of these coating-based heating systems were exposed to surface degradation involving solid particle and water droplet impact erosion. For this reason, two types of erosion tests were conducted in order to study the effect of ceramic reinforcement on the wear resistance of the de-icing elements. For the water droplet impact experiments, samples were placed inside a high-speed wind tunnel with an approximate droplet impact speed of 60 m/s. Solid particle impact tests were performed using a low-pressure cold spraying unit for impingement of erodent particles. The data demonstrated considerably lower wear rate in NiCrAlY-WC-12Co and NiCrAlY-titania compared to other coatings. The results suggest that MMC coatings could be effectively used to increase the erosion resistance of coating-based heating systems.<br>
Real-time variation of the coatings electrical resistance and temperature during the material removal stage of the dry erosion experiments demonstrated the effect of ceramic reinforcement phase on overall functionality of the coatings. The heating elements were also subjected to a series of icing/de-icing tests in a closed-loop icing wind tunnel. MMC elements with higher electrical resistivity exhibited considerably better performance in terms of the required de-icing time and the total consumed energy.</p>