High-temperature corrosion of coal-fired boiler parts such as water walls and superheated tubes poses a serious threat to the efficiency of the thermal power plant. To overcome this, numbers of corrosion control techniques are commonly employed. But, a dense and defectfree coating deposited by the thermal spray technique has shown promising result to combat hot corrosion. Although open or closed porosity in distinct thermal spray coatings can originate from distinct factors such as partial or totally un-molten particles, inadequate flow or fragmentation of the molten particle at impact, non-optimal spray angle and entrapped gas. But, this can still only be prevented by coating post-treatment. Hence, in this paper, authors have reviewed the performance of distinct coatings deposited by diverse thermal spray processes. Then, the effect of distinct process parameters and heat treatments on microstructure and mechanical properties of coatings is described. Finally, the best coatings are suggested to combat maximum hot corrosion of boiler tubes.
WC-12%Co, Cr 3 C 2 -25%NiCr, 80%Ni-20%Cr, 87%Al 2 O 3 -13%TiO 2 coatings were deposited by Air Plasma Spray (APS) technique on ASTM A36 steel. Erosion behaviour of sprayed coated samples were investigated at three different impact angles (45°, 60°and 90°). The mechanism of erosion was investigated on uncoated and coated samples. The rate of erosion of the substrate first increased with increasing angle of impact and then gradually decreased. But the erosion rate of the coated samples increased steadily. Substrate shows the higher metal removal whereas coating shows the higher erosion resistance. WC-12%Co coated samples performed well in erosion testing and offered best erosion resistance as compared to the substrate and all other coatings. Ductile fracture takes place on substrate material at higher impact angle. Overall, all the coated samples have shown less erosion propensity when compare to the bare one.
Amid all convective heat transfer augmentation methods employing single phase, jet impingement heat transfer delivers significantly higher coefficient of local heat transfer. The arrangement leading to nine jets in square array has been used to cool a plate maintained at constant heat flux. Numerical study has been carried out using RANS-based turbulence modeling in commercial CFD Fluent software. The turbulent models used for the study are three different “k-ε” models (STD, RNG, and realizable) and SST “k-ω” model. The numerical simulation output is equated with the experimental results to find out the most accurate turbulence model. The impact of variation of Reynolds number, inter-jet spacing, and separation distance has been considered for the geometry considered. These parameters affect the coefficient of heat transfer, temperature, and turbulent kinetic energy related to flow. The local “h” values have been noticed to decline with the rise in separation distance “H/D.” The SST “k-ω” model has been noticed to be in maximum agreement with the experimental results. The average value of heat transfer coefficient “h” reduces from 210 to 193 W/m2K with increase in “H/D” from 6 to 10 at “Re” = 9000 and S/D of 3. As per numerical results, inter-jet spacing “S/D” of 3 has been determined to be the most optimum value.
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