Abstract
Surface modification of the metal components involved in heat transfer is one of the passive methods used to enhance their heat transfer efficiency. Coatings with micro- or nano-scale features are widely employed to modify surfaces due to their enhanced surface area, which increases the number of boiling nucleation sites, leading to the generation of a higher number of bubbles. In geothermal power generation, due to the aggressive nature of the working fluid and chemistry of the geothermal brine, ceramic coatings are preferred. Along with having good compressive strength and hardness, ceramic coatings can protect the surface against corrosion, oxidation and wear. The coating deposition method has a specific impact on the coating microstructural characteristic as well as performance, which define its application. Among these, plasma-spraying has been widely used to deposit ceramic materials, due to its high jet enthalpy and the excellent corrosion and wear resistance of the obtained coatings. In this work, solution precursor plasma sprayed coatings of TiO2/Al2O3 composite were developed on carbon steel for boiling heat transfer applications in geothermal heat exchangers. The effect of plasma current and stand-off distance variation on the microstructural properties of coated samples were assessed. The morphology of the final coatings was compared using SEM/EDX. Further, the surface wetting property was analyzed through a drop sample analyzer and found that with spray parameters the water contact angle and diiodomethane contact angle fluctuate.
