The deposition characteristics of weld fume particles in an electrostatic precipitator were investigated by means of numerical simulations. In the calculations, the particle characteristics of the ...weld fume particles and the effect of ionic wind are considered. The effects of applied voltage, flow velocity, collecting plate spacing, particle concentration, electric field strength, and ionic wind on the collection efficiency of weld fume particles in the ESP are discussed. The velocity distribution of weld fume particles in the Electrostatic precipitator (ESP) was also investigated. The results show that the smaller the collection plate spacing, the higher the collection efficiency of particles. The particle concentration has a small effect on the collection efficiency of weld fume particles. The higher the applied voltage, the more obvious the difference of ESP on the collection efficiency of different particles.
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•The characteristics of welding fume particles was considered.•The influencing factors of collection efficiency were explored.•The movement of particles in ESP was investigated.
•The apparent contact angle is influenced by nano-bubbles at the bottom of the porous coating. As heat flux density increases, these nano-bubbles gradually form thickening vapor films.•This study ...proposes a CHF prediction model applicable to biphilic surfaces based on the two-dimensional distribution of Helmholtz instability at the interface.•This study presents a CHF prediction model tailored for biphilic surfaces based on the influence of Taylor instability on the formation location of mushroom bubbles and the impact of Helmholtz instability on the liquid layer beneath the bubbles.
This study demonstrated that combination hydrophilic copper and hydrophobic nano-silver surfaces simultaneously enhanced the critical heat flux (CHF) and heat transfer coefficient (HTC) in pool boiling heat transfer (BHT) with deionized water as the employed working fluid. To further investigate the influence of geometric factors on heat transfer, this study designed three patterns denoted as squares/stripes/networks, ranging from 50 μm to 3000 μm. The effects of pattern size d, spacing p, and pitch ratio p/d on heat transfer results were obtained. Based on bubble visualization, the study further analyzed the reasons for inflection points in the boiling curve and the mechanisms caused by porous hydrophobic coating. Finally, the study proposed a numerical model suitable for predicting CHF of biphilic surfaces based on Helmholtz instability and Taylor instability. The model began with vapor columns escaping toward far-field and the fluid supplied to the heating surface. Concrete model derivation and adjustments are categorized according to the relationship between pattern size and bubble detachment diameter. For surfaces where the bubble detachment diameter exceeds the pattern size, this study originated from the perspective of Helmholtz instability on the vapor column surface. The resulting model is anticipated to quantitatively solve for the former and modulate the wavelength of Taylor instability on biphilic surfaces. Regarding surfaces with bubble detachment diameters smaller than the pattern size, this research begins with the existence time of the micro-liquid layer. The derived model validates the predominant role of p/d in the CHF values on micron-scale biphilic surfaces.
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Erosion-corrosion resistance is a critical factor in the service life extension of metallic structural materials in front of complex flow and solid impingement. To improve the erosion-corrosion ...resistance, a CrN/Cr gradient coating was fabricated on carbon steel by the double glow plasma alloying technique. The CrN/Cr gradient coating mainly consists of the CrN phase and (Fe, Cr) metal phase. Debye rings from the X-ray pattern illustrated that the coating was under a compressive stress of 868 MPa. Residual stress and fine toughness of the gradient structure enhanced its adhesion strength, endowing it with the potential to accommodate strains caused by external forces. The potentiodynamic polarization test illustrated that the addition of solid particles and the increase in flow velocity severely weakened the protective ability. The mass loss rate results illustrated that the synergistic effect made the greatest contribution to the erosion-corrosion damage of the CrN/Cr gradient coating, while its proportion increased as the flow velocity increased. Compared to the substrate, the gradient structure of the coating facilitated interruption of the sharp interfaces, thereby reducing the deformation mismatch and enhancing the damage tolerance of the coating.
Abstract Ethylene plays a crucial role as an intermediate component in the cracking and combustion processes of large molecular alkane and olefins. In this article, the laminar flame speed of ...ethylene–air mixtures was measured using the heat flux method. The mechanism of ethylene was simplified by utilizing the error propagation directed relationship graph (DRGEP) and sensitivity analysis (SA), and the Arrhenius pre‐exponential factors for 20 selected reactions in the skeletal mechanism were optimized using the particle swarm optimization (PSO) algorithm. Finally, an ethylene optimization mechanism including 39 species and 85 reactions was obtained. The prediction results for flame speed, ignition delay time, and species concentration were compared with experimental data and other mechanisms, covering a wide range of temperatures (298–1725 K), pressures (1–22.8 atm), and equivalence ratios (0.5–2.0). The findings demonstrate that the optimization mechanism not only improves the prediction results of laminar flame speed in the rich combustion zone and low oxygen environment but also enhances the prediction accuracy of the ignition delay time at high pressure and in the lean combustion zone, as well as the prediction accuracy of C 2 H 4 and H 2 O radicals. In conclusion, the optimized mechanism exhibits higher accuracy and broader applicability.
Four kinds of (Sm1−xYbx)2(Zr0.7Ce0.3)2O7 (x = 0, 0.1, 0.2, 0.3) ceramics with different contents of Yb were prepared by the solid-phase reaction. Their thermochemical reaction behaviors with ...calcium-magnesium-alumina-silicate (CMAS) at 1300 °C were investigated. Among them, (Sm0.7Yb0.3)2(Zr0.7Ce0.3)2O7 has the best corrosion resistance to CMAS. The increase of Yb content can accelerate the formation rate of apatite, preventing the ceramic layer from erosion of CMAS and improving the strain tolerance of the ceramic. In addition, the CMAS wetting, corrosion process and failure mechanisms were discussed by high-temperature field wetting and transmission electron microscopy.
•The CMAS resistance of (Sm1-xYbx)2(Zr0.7Ce0.3)2O7 enhances with the growth of Yb2O3 doping.•(Sm0.7Yb0.3)2(Zr0.7Ce0.3)2O7 exhibits low wettability during in-situ high temperature wetting process.•The reaction between rare-earth zirconates and CMAS to form apatite is accelerated obviously after the doping of Yb with small ionic radius.
Welding fume is hazardous to the environment and human health and is purified using an electrostatic precipitator (ESP). Electrostatic precipitators are widely used in waste gas treatment processes ...in thermal power plants, cement plants and other factories. The use of electrostatic precipitators to treat welding fumes requires further research. Corona discharge occurs at the electrostatic precipitator, the primary condition for particle charging. The components and physical parameters of the treated particles should be considered in the numerical simulation. This paper investigates the effects of polygonal electrode form, deflection angle, and spacing on the electric field distribution and collection efficiency. The physical quantities in the vicinity of the electrodes vary greatly. Therefore, the focus is on the vicinity of the electrode, and curves describing the trend. It is shown that the maximum velocity did not vary monotonically with increasing the number of tips and that the highest collection efficiency is obtained with a triangle electrode. Furthermore, it is shown that the variation of interelectrode distance leads to variations in the inter-electrode shielding effect.
•Effect of corona electrode shape.•Welding fume particle composition.•The change is described by the curve.•Focus on the vicinity of corona electrodes.
A high entropy zirconate ceramic (Gd0.2Y0.2Er0.2Tm0.2Yb0.2)2Zr2O7 (HEZ) with fluorite structure has been synthesized by solid state reaction and high temperature sintering successfully. The ...investigation indicated that HEZ has ultra-low thermal conductivity (0.82 W × m−1 × K−1 at 1200 °C), similar thermal expansion coefficient (10.61 × 10−6 K−1 at 1300–1400 °C) with that of YSZ, excellent mechanical properties (hardness, elastic modulus, fracture toughness), and great CMAS corrosion resistance. Emphasis is given to discussing the CMAS wetting, corrosion process and failure mechanisms using high-temperature in-site wetting method and transmission electron microscopy (TEM). The results show that the HEZ exhibits better corrosion resistance than single rare earth zirconate Gd2Zr2O7 due to the coupling effect of anti-wettability, gradient diffusion rate and multicomponent apatite crystallization produced by doping rare earth ion (Gd3+, Y3+) close to Ca2+ radius and rare earth ion (Er3+, Tm3+, Yb3+) with small ion radii. In the comprehensive view, (Gd0.2Y0.2Er0.2Tm0.2Yb0.2)2Zr2O7 is a competitive candidate for high reliability TBC materials.
Al20Cr5Fe50Mn20Ti5 medium-entropy alloy (MEA) coatings with different preparation process parameters were successfully fabricated by laser cladding (LC) on Inconel 718 Ni-alloy substrate. Comparison ...of two coatings with optimal macroscopic morphology, and the phase, micro-structure and hardness were characterized using SEM, XRD, and EBSD. The thermal stability performance of the two MEA coatings was systematically analyzed by combining phase diagram calculation and experimental tests. Compared to the substrate, the frictional wear properties of the MEA coatings at 400 °C, 600 °C and 800 °C were systematically analyzed. The results show that Al20Cr5Fe50Mn20Ti5 MEA coatings with two different parameters formed a good metallurgical bond with the substrate, contained BCC, FCC and Ti-rich phases, and both had a good thermal stability at the range of room temperature to 1000 °C. The refinement of grain size and the enhancement of dislocation density improved Al20Cr5Fe50Mn20Ti5 MEA coatings wear properties. The generation of Ti-rich phase enhanced the wear performance, while excessive fusion of Ti elements into the coating caused oxidation at high temperatures to generate brittle phases, which reduced wear performance and led to coating failure. Through this study, new designed MEA system with low cost advantage can be applied in high temperature environment.
•A new low-cost Al20Cr5Fe50Mn20Ti5 MEAs coating was made and the effect of process parameters on the morphology was analyzed.•Combined with phase diagram calculations and molecular dynamics simulations, the properties of the coatings were described.•The wear behavior at high temperatures was tested, and the failure mechanism and strengthening mechanism were analyzed.
c-TiAlN/h-Cr2N multilayer thin films, with modulation period λ of 10 nm, 20 nm, and 30 nm and different Cr2N/ λ thickness ratios (25 %, 50 % and 75 %), were deposited on c-plane sapphire using ...reactive DC magnetron sputtering. All multilayers exhibited preferred orientation Cr2N(0001)/ TiAlN(111)x, regardless of the modulation period and thickness ratios. X-ray diffraction φ-scans revealed an influence of the Cr2N layer thickness on the overall orientation quality of the multilayer, where the thicker the Cr2N layer the higher orientation quality. Atomically resolved high-angle annular dark-field scanning transmission electron microscopy revealed well defined and homogeneous atom stacking in the Cr2N layers. In contrast, the cubic TiAlN layer was found to be composed of coherent cubic AlN-rich and TiN-rich regions. Additionally, the TiAlN layers were found with a higher density of grain boundaries compared to the Cr2N layers. Mechanical properties evaluation revealed that the film with a 20 nm period and 75 % Cr2N thickness ratio exhibited the highest hardness of 27.11 ± 0.72 GPa and an reduced elastic modulus of 349.1 ± 6.84 GPa. The hardness increased as the thickness of Cr2N increased, until reaching 10 nm, after which it remained at a high level (∼ 25 GPa).
•Heteroepitaxial growth of c-TiAlN/h-Cr2N multilayer films with smooth boundaries•Increase in hardness with the increase of Cr2N thickness•Improvement of the epitaxial quality with hexagonal Cr2N material in multilayer films with TiAlN
