High Velocity Air Research Articles

A microwave discharge in high-velocity flows initiated by a half-wave antenna

A microwave discharge in high-velocity (150—250 m/s) air flows induced on a half-wave vibrator is studied. A cw magnetron microwave generator with a frequency of 2.45 GHz and an output power of up to 5 kW was used for initiation of the microwave discharge. The high-speed video imaging was used for studying the discharge structure, determining the diameter and length of the plasma channel as a function of flow velocity and pressure. Electron concentration and temperature, along with characteristic gas temperature, were determined based on the optical spectra. The possibility of using this microwave discharge for ignition of hydrocarbon–air mixtures in combustion chambers of ramjet engines is proved experimentally.

Erosion Wear Behavior of HVAF-Sprayed WC/Cr3C2-Based Cermet and Martensitic Stainless Steel Coatings on AlSi7Mg0.3 Alloy: A Comparative Study

The paper presents a comparative study of the erosion wear resistance of WC-10Co4Cr, Cr3C2-25NiCr and martensitic stainless steel (SS) coatings deposited onto an AlSi7Mg0.3 (Al) alloy substrate by high-velocity air‒fuel (HVAF) spraying. The influence of the abrasive type (quartz sand or granite gravel), erodent attack angle, thickness, and microhardness of the coatings on their and Al substrate’s wear resistance was comprehensively investigated under dry erosion conditions typical for fan blades. The HVAF-spraying process did not affect the Al substrate’s structure, except for when the near-surface layer was 20‒40 μm thick. This was attributed to the formation of a modified Al-Si eutectic with enhanced microhardness and strength in the near-substrate area. Mechanical characterization revealed significantly higher microhardness values for the cermet WC-10Co4Cr (~12 GPa) and Cr3C2-25NiCr (~9 GPa) coatings, while for the SS coating, the value was ~5.7 GPa. Erosion wear tests established that while Cr3C2-25NiCr and SS coatings were more sensitive to abrasive type, the WC-10Co4Cr coating exhibited significantly higher wear resistance, outperforming the alternatives by 2‒17 times under high abrasive intensity. These findings highlight the potential of HVAF-sprayed WC-10Co4Cr coatings for extending the service life of AlSi7Mg0.3-based fan blades exposed to erosion wear at normal temperatures.

Artificial intelligence as a tool for predicting the quality attributes of garlic (Allium sativum L.) slices during continuous infrared-assisted hot air drying.

Effective drying methods are a highly suitable solution for ensuring stable food supply chains, reducing postharvest agricultural losses, and preventing the spoilage of perishable fruits and vegetables. Moreover, machine learning techniques are innovative and dependable, especially in addressing food spoilage and optimizing drying processes. This study utilized a continuous infrared (IR) hot air dryer to dry garlic (Allium sativum L.) slices. The experiments were conducted at different levels of IR power, air velocities (V), and temperature (T). The relationships between the input process parameters (IR, T, and V) and response parameters, including effective moisture diffusivity (Deff), drying time, and physicochemical properties of the dried slices (rehydration ratio [RR], total color change, flavor strength, and allicin content in the garlic), were modeled using an artificial neural network (ANN). Our findings showed that the maximum Deff of 6.8×10-10m2/s and minimum drying time of 225min were achieved with an IR of 3000W/m2, an air velocity of 0.7m/s, and a temperature of 60°C. The total color change and RR values increased with IR and higher air temperature but declined with higher air velocity. Furthermore, the garlic's flavor strength and allicin content levels decreased as the IR and air temperature increased. The results demonstrated a significant influence of the independent parameters on the response parameters (p<0.01). Interestingly, the ANN predictions closely matched the test data sets, providing valuable insights for understanding and controlling the factors affecting drying behaviors.

An Assessment of Coating Thickness on the Microstructure and Mechanical Behavior of IN625 Coating on Ni-Based Superalloy Substrate Deposited by High Velocity Air Fuel Technique

An Assessment of Coating Thickness on the Microstructure and Mechanical Behavior of IN625 Coating on Ni-Based Superalloy Substrate Deposited by High Velocity Air Fuel Technique

Rapid aerodynamic characterization of surface heat exchangers for turbofan aeroengines through optical techniques and additive manufacturing

Surface heat exchangers that use the bypass flow as heat sink are becoming a widely used solution to alleviate the high thermal load of modern aeroengines. Experimental characterization of such heat exchangers in full-scale engine tests is extremely expensive and time-consuming, so carrying out experiments in scaled wind tunnels that can replicate their very challenging flow conditions is highly desirable. However, intrusive instrumentation can affect the actual aerodynamics of the component due to the reduced size of the section and the typical high air velocities of turbofan engines. For this reason, a methodology to characterize a surface heat exchanger designed to work in the turbofan bypass using optical techniques is presented in this work. Additionally, the possibility of replicating the experimental conditions using additively manufactured models of exchangers would allow rapid preliminary characterization of these components. In this investigation, different non-intrusive techniques such as PIV, LDA, Schlieren, or LDV have been applied to determine the heat exchanger aerodynamic performance and vibration response, and a detailed characterization of the flow field has been carried out. Data have been cross-validated using different measurement techniques. A 3D-printed model has also been built to compare with the aluminum heat exchanger, showing almost an identical behavior in terms of velocity distribution downstream of the heat exchanger and pressure drop induced by its fins, as well as corrected frequencies, confirming thus the suitability of additive manufacturing for the aerodynamic characterization of these devices in preliminary stages.

Improving thermal shock and oxidation resistance of Cr3C2/WC-NiCr cermet coating by embedding large NiCrAlY superalloy particles

Cr3C2/WC-based cermet coating is widely used on the surface of mechanical equipment to strengthen its wear and corrosion resistance. Improving the high-temperature performance of cermet coating is the key to its industrial application. In this study, a novel type of bimodal microstructure cermet coating with the design of functional sites was fabricated via high-velocity air fuel (HVAF) spray technology. The toughness NiCrAlY superalloy particles are introduced into the traditional Cr3C2/WC-NiCr cermet structure to construct the thermal stress release site, which significantly improved the thermal shock resistance and thermal oxidation properties of the coating. The addition of NiCrAlY superalloy particle reduces the porosity of Cr3C2/WC-NiCr coating to 0.29 % and creates high-quality interface bonding and surface passivation layer. The newly structured cermet coating exhibits outstanding high-temperature performance. In a 1000 °C oxidation environment, the new coating remained intact after 120 h of exposure, while the traditional Cr3C2/WC-NiCr cermet coating exfoliated completely after 48 h of exposure. Further, in the thermal shock condition at 1000 °C, the lifetime of the new coating is 50 times greater than that of the traditional cermet coating, displaying excellent ability to relieve thermal stress. Additionally, the new coating shows good wear resistance and stability during high-temperature thermal exposure. After thermal exposure for 24 h and 72 h, the wear rates of the coating are 5.28 and 5.83 × 10−5 mm3 N−1 m−1, respectively, which is slightly lower than that of the as-sprayed coating. This study provides guidance for the improvement of high temperature resistance of thermally sprayed Cr3C2/WC-based cermet coatings.

Preparation process, surface properties and mechanistic study of HVAF-sprayed CoCrFeNiMo0.2 high-entropy alloy coatings

The objective of this study is to develop infrared reflective coatings with excellent service performance in extreme environments, aimed at reducing system energy consumption and enhancing service life. In this work, CoCrFeNiMo0.2 high-entropy alloy (HEA) powder was deposited on the 316 L stainless steel (SS) substrate using High-Velocity Air Fuel (HVAF) thermal spray technology. The microstructure, mechanical properties, infrared reflectivity, and corrosion resistance of the coatings under different spraying parameters were investigated and compared with those of the substrate. Computational Fluid Dynamics (CFD) simulation was employed to analyze the influence of HVAF spraying parameters on flame characteristics and particle flight behavior, providing guidance for optimizing the spraying process and explaining underlying mechanisms. Results demonstrated that adjusting parameters such as propane and air pressure, spraying distance, and powder feed rate could produce dense coatings with <1 % porosity. The microhardness of the coatings was approximately 1.8 times that of the substrate, and the bonding strength between the coating and the substrate is increased to 39.4 MPa. Additionally, the near-infrared reflectivity of the coatings was significantly higher than that of the substrate, with an enhancement of 18.7 %. Coatings sprayed under different parameters exhibited superior passivation and pitting corrosion resistance compared to the substrate in 3.5 wt% NaCl and 1 mol/L HCl solutions. Optimization of spraying parameters further enhanced the protective capability of the passivation film and corrosion resistance. Consequently, CoCrFeNiMo0.2 HEA coatings prepared by HVAF spraying technology demonstrate excellent comprehensive performance, holding promising potential for industrial applications.

Cracking resistance behavior of HVAF-sprayed monolayer and hierarchical Fe-based amorphous coatings under bending stress

The bending strength and fracture toughness are two key indicators that determine the service performance of thermally sprayed Fe-based amorphous coatings (AMCs) in harsh environments. Unfortunately, due to the inherent heterogeneous porosity and limited thickness (typically <1 mm) of the coatings, obtaining these properties is constrained by traditional fracture analysis methods. To address this, a three-point bending combined with the digital image correlation (DIC) method, without prefabricating notch or removing substrate, was proposed in the current work, and the effect of hierarchical structures on the fracture performance of the coatings was successfully revealed. Excitingly, the results show that compared to monolayer coating, hierarchical structures comprising two layers with different porosities can realize the synergistic improvement in the fracture strength and fracture strain of the coatings by alleviating local stress concentration and inducing crack deflection. Further, a finite element method (FEM) was employed to gain insight into the intrinsic relationship between the coating microstructures and the crack evolution behavior. This work not only proposes a simple method for evaluating the fracture performance of Fe-based AMCs sprayed with high velocity air fuel (HVAF), but also presents an innovative idea for optimizing the coating's properties.

Structural optimization and battery temperature prediction of battery thermal management system based on machine learning

Lithium-ion batteries significantly extend the driving range for electric motorcycles. The battery thermal management system (BTMS) is critical for achieving optimal battery performance. Moreover, precise battery temperature prediction is essential for efficient thermal management. Therefore, a battery thermal management system integrating air and phase change material (PCM) cooling is proposed. Initially, the impact of PCM height, PCM thickness, and air velocity on battery temperature is analyzed. Subsequently, with cost minimization as the objective and ensuring that the maximum battery temperature remains below a threshold, the Black Kite Algorithm (BKA) is employed to optimize the BTMS structure. Finally, a BKA-Convolutional Neural Network (CNN)-Self Attention (SA) model is introduced for battery temperature prediction. The results indicate that increasing the thickness of the PCM and air velocity facilitates battery heat dissipation but with diminishing marginal effects. An increase in PCM height enhances battery cooling at low air velocities but becomes detrimental at high air velocities. The optimized PCM height is 35 mm, resulting in a cost of 0.073 USD for the BTMS per battery. Additionally, the BKA-CNN-SA model achieved a maximum error of 0.45 °C on the validation set and accurately predicted battery temperature changes before and after PCM melting.

Comparative study of modelling, drying kinetics and specific energy consumption of desiccated coconut during convective and infrared drying

White coconut shreds were dried in this study utilizing convective (CD) and infrared (IR) drying methods to produce desiccated coconuts. The drying duration, drying rate, effective moisture diffusivity, activation energy, and specific energy consumption of desiccated coconuts were examined and compared between convective and infrared drying. The experiments were carried out at three levels of air temperatures (50, 60 and 70°C) for convective drying and the same heating temperature was used for infrared drying. Air velocity of (1.5, 2.3 and 3.0 m/s) was supplied at every temperature for both drying methods. In order to determine the ideal model for desiccated coconuts, six mathematical models were fitted to both drying techniques with the Page model providing a better fit than other models in all drying parameter ranges. Experimental drying curves displayed only a falling drying rate period. The experimental findings demonstrated that drying temperature, air velocity, and drying techniques had a substantial impact on drying kinetics. The highest effective moisture diffusivity value of desiccated coconuts was 1.66×10-9 m 2 /s at 70°C and 3.0 m/s and 2.79×10-9 m 2 /s at 70°C and 1.5 m/s from convective and infrared drying, respectively. For convective and infrared drying, respectively, the specific energy consumption varied from 64.80 to 112.54 kWh/kg and 18.68 to 37.72 kWh/kg. The drying time between convective and infrared drying was inversely influenced by higher air velocity at the same temperature. Air velocity had a substantial effect during infrared drying whereby the activation energy of 9.42 kJ/mol was the lowest at 2.3 m/s. Infrared drying proved to have a better synergistic effect by providing a higher drying rate and effective moisture diffusivity with the shortest drying time when compared to convective drying.

Knapsack air assisted electrostatic sprayer for agricultural formulations

An experimental prototype of a backpack-type rechargeable battery-powered air-assisted electrostatic sprayer was designed and tested for performance while preserving techno-commercial competence and affordability for India's marginal and small farmer communities. The designed prototype electrostatic sprayer achieved good levels of charge induction on the spray particles at various electrode potentials (1 to 12 kV). At a charging electrode potential of 9 kV and a nozzle discharge rate of 2 mL s−1, electrostatically charged spray had a maximum charge to mass ratio (CMR) of 1.79 mC kg−1. The Electric Ducted Fan (EDF) used for high velocity air assistance was capable of transporting charged spray droplets onto distant targets such as orchard trees and field crops with a spray throw of up to 5 m. The high-pressure atomization method produced fine droplets within a Volume Median Diameter (VMD) range of 90 to 100 µm, resulting in better charge induction and wrap-around effect. As the prototype features fewer moving mechanical components, reduced total noise and vibrations, it promises operator comfort in the long run while requiring less system maintenance. Environmental contamination can be minimized as the large quantity of harmful chemicals be prevented from drifting into the soil and nearby waterbodies. The competitive performance and lower investment could encourage majority of the Indian famers to upgrade with the developed air assisted electrostatic spraying system contributing to agro-socio-economic welfare.

Experimental study on heat storage characteristics of an air-sand moving bed heat exchanger

The air-sand moving bed heat exchanger, designed for storing fluctuating medium-temperature gas waste heat, offers significant potential for energy conservation and carbon reduction in industrial settings. However, its operational characteristics are insufficiently explored. This study investigates the heat storage process involving direct contact and cross-flow of air and quartz sand within a rectangular heat exchanger chamber. Comprehensive analyses were conducted to explore flow resistance characteristics, temperature response, and heat storage performance. Results indicate that pressure drop increases with higher air velocity and temperature, and lower air pressure, particle diameter. The relative discrepancy between fitted pressure drops and experimental data is below 10%. The primary heat transfer zone exists during particle descent. As the air-particle mass flow ratio increases, the descent rate of this zone along the airflow direction slows. Additionally, higher air temperatures elevate the optimal air-particle mass flow ratio. With inlet temperatures for air and particles set at 350 °C and 30 °C respectively, and a mass flow ratio of 0.81, an exergy efficiency of 58.93% and a power density of 600.64 kW·m−3 are achieved. These findings offer crucial insights for air-sand moving bed heat exchangers for medium-temperature gas waste heat recovery.

Microstructure, multi-scale mechanical and tribological performance of HVAF sprayed AlCoCrFeNi high-entropy alloy coating

Thermal spray high-entropy alloy (HEA) coatings have demonstrated potential for improving the wear resistance of conventional materials used in extreme engineering environments. In the present work, an equiatomic AlCoCrFeNi HEA coating was manufactured using the high velocity air fuel (HVAF) process. The phase and microstructural transformations in gas-atomized (GA) powder during HVAF spraying were analyzed using SEM, EDS and EBSD techniques. The tribological properties of this HEA coating sliding against an Al2O3 ball at both room temperature (RT) and 600 °C were also evaluated. The GA powder was composed of Body Centred Cubic (BCC) + ordered BCC (B2) phases, which transformed to BCC + B2 + minor Face Centred Cubic (FCC) phases during the HVAF coating process, validating the thermodynamic phase prediction projected by the Scheil simulation for non-equilibrium processing conditions. The rapid solidification and high velocity impact-assisted deformation of GA powder resulted in significant grain refinement in the HVAF coating, which ultimately improved the mechanical properties at both micro and nanoscale levels. The wear resistance of the HEA coating at RT was severely impacted by the relatively brittle BCC/B2 phase structure, leading to susceptibility to abrasive wear and surface fatigue. The wear resistance at 600 °C was slightly lower at RT due to the formation of a brittle oxide layer on the worn surface, which induced surface fatigue and aggravated mass loss of the coating.

Effect of liquid properties on film behavior on the surface of an airfoil in a high-speed flow and subsequent atomization from the trailing edge

This study examines the behavior of ethanol or water films on the surface of a NACA 0012 airfoil placed in a high-speed air flow. New water film results complement previous measurements of time averaged ligament lengths and droplet sizes generated with the same airfoil. In addition, new data are obtained for ethanol. Air velocities up to 175 m/s are used with liquid flow rates between 1.4 cm2/s and 2.6 cm2/s. The liquid was introduced onto one side of the airfoil via 26 holes, each measuring 0.5 mm in diameter and spaced 1 mm apart. These holes are positioned 35 mm downstream from the leading edge and 65 mm upstream from the trailing edge. Film behavior on the vane is captured with front-lit high-speed video. The accumulation of liquid and breakup of ligaments are captured with backlit highspeed video. Phase Doppler interferometry is used to measure droplet size and simultaneous axial and pitch wise velocity 70 mm downstream of the trailing edge. Finally, laser diffraction is used to measure line averaged droplet sizes. The results indicate notable differences between ethanol and water films. The ethanol film spreads more extensively across the width of airfoil which is attributed due to its lower surface tension. The maximum ligament length for both liquids decrease with higher air velocity and increase with the liquid flow rate. A correlation for maximum ligament length is developed and captures the effect of liquid properties, flow rate, and air velocity. Furthermore, the variation in liquid volume flow rate did not impact droplet size. However, for a given air velocity, the Sauter Mean Diameter is found to depend on surface tension. On the dependency of droplet size on the Weber number, ethanol produced smaller droplet sizes at low values of Weber number. However, at relatively high Weber numbers, the droplet sizes for both water and ethanol were similar. This suggests that droplet size is influenced by factors besides surface tension at low Weber numbers but not at higher Weber numbers. In addition, the Nukiyama-Tanasawa model to fit the volume distribution curves is simplified by fixing p and q terms. Simplification makes the model easier to understand and implement.

Simultaneous PIV/LIF Measurements Of Velocity And Oxygen In An Advecting Air-Water Channel Flow

We investigate oxygen transfer across an air-water interface using an integrated Particle Image Velocimetry (PIV) and Laser-Induced Fluorescence (LIF) system. This setup allows for the simultaneous measurement of velocity and dissolved oxygen (DO) concentration fields, alongside the visualization of the air-water interface. The imaging process begins with zero DO concentration and continues until oxygen saturation in the water is achieved. Calibration of the oxygen LIF intensity field is performed using these images, benchmarked against measurements from an optical oxygen point probe, to ensure accurate conversion to a physically relevant unit. The air channel generates an air flow with a center-line mean velocity of 8.84 m/s, corresponding to a Taylor Reynolds number of 100. This high-velocity air flow results in the formation of wavy structures on the water interface creating situations similar to those found in nature (such as rivers and oceans). The wavy structures create reflections from the air-water interface; these reflections are mitigated during post-processing using a Wavelet-Fast Fourier Transform (W-FFT) method to remove high intensity noise. Additionally, the wind shear generated by the air flow induces high turbulence intensity and vortices near the air-water interface, significantly enhancing the dissolution of oxygen into the water. This turbulence and the associated vortical structures play a crucial role in the mixing process and the overall oxygen transfer efficiency. The study presents instantaneous dissolved oxygen structures overlapped with velocity structures in a flow with deformable interface, providing some insights into the oxygen transfer and mixing processes.

Optimizing airflow in spiral blast freezers

Spiral blast freezing is a common unit operation used in food processing facilities for rapidly freezing a variety of foodstuffs. The purpose of a blast freezer is to generate high velocity, low temperature air flow over food products being conveyed within refrigerated enclosures to accomplish the freezing process. However, air flow patterns observed within field operating blast freezers are often suboptimal, resulting in diminished system performance. This paper applies a Monte Carlo simulation technique to a food product freezing simulation in order to identify velocity profiles that optimize the freezing process. A one-dimensional food product model is used to evaluate the interplay between the time variation in the magnitude of the air velocity over food products conveyed through the freezing system and the resulting dwell time needed to achieve a target product core temperature at the blast freezer exit. Temporal heat transfer coefficients derived from field measurements made in a newly installed spiral blast freezer serve as a basis to calibrate the one-dimensional product model.The results of the Monte Carlo analysis show freezing system performance is improved when high and stable air velocities over the product are achieved early in the freezing process dwell time. Air flow patterns within a freezing system that result in high air velocity later in the freezing process dwell time are suboptimal. Field-measured data on a newly installed spiral blast freezer showed this suboptimal air flow pattern and the use of baffling within the spiral enables improved airflow leading to an estimated 10 % increase in production throughput.

Experimental and numerical studies of the processes of spraying coal-water slurries with pneumatic nozzle

The article presents the results of spraying tests of highly viscous coal-water slurries with a pneumatic nozzle and numerical studies of the structure of the gas-drop jet. An increase in the viscosity of coal-water slurries was ensured by introducing a third component into its composition – industrial waste (pyrogenetic liquid). The moderate effect of the slurry viscosity on the average droplet size of coal-water slurries in the jet is due to the high efficiency of the aerodynamic characteristics of the pneumatic nozzle. Introduction of pyrogenetic liquid in the amount of 20 % by weight into the composition of coal-water slurry significantly increases its viscosity. The value of the surface tension of such a slurry is more than doubled. The increase in the average droplet size was no more than 25 % when pyrogenetic liquid content in the composition of coal-water slurry was over 10 % by weight. The average droplet size of coal-water slurries varied in the range from 180 to 210 microns in the study area of gas droplet jet. The results of experimental and numerical studies have shown good convergence. High air velocities at short distances from the nozzle ensure high crushing efficiency of the jet of coal-water slurry. The breakdown of the boundary layer of the liquid from the periphery of the droplets of coal-water slurries and its subsequent destruction was observed at short distances from the nozzle. The values of the Weber number were 100<We<350. At considerable distances from the nozzle (more than 0.5 m), droplets of coal-water slurries were subjected to vibrational crushing (We<50).

Thermal shock resistance of WC–Cr3C2–Ni coatings deposited via high-velocity air fuel spraying

In this study, the high-velocity air fuel (HVAF) spraying technique was used to deposit WC–Cr3C2–Ni wear-resistant coatings on the surface of crystallization rollers to overcome the wear problem of the substrate of thin-strip continuous-casting crystallization rollers and thus improve their efficiency. The performance and durability of the WC–Cr3C2–Ni coatings on the surface of the roller body during the actual continuous casting process were investigated by performing thermal shock tests. It was found that the thermal shock resistance of the closed-curved surface coatings increased with their thickness. The coatings exhibited the best thermal shock resistance at a thickness of 300 μm, and the number of cycles they could withstand at 800 °C reached 15. The results of the high-temperature wear tests showed that the WC–Cr3C2–Ni coatings deposited on the surface of the crystallization roller via HVAF reduced the friction coefficient of the surface of the roller body (from 0.425 to 0.362), and greatly reduced the wear loss volume during the wear process (reduced by 83 %). The WC-Cr3C2-Ni coating showed excellent resistance to crack initiation and propagation during wear and can be stabilized in long-cycle production and protect the substrate of the crystallization roller effectively. This study provides a theoretical basis for the selection and preparation of surface coatings for thin-strip continuous-casting crystallization rollers.

Improving wear and corrosion resistance of HVAF sprayed 316L stainless steel coating by adding TiB2 ceramic particles and CeO2

316L stainless steel is used in a wide variety of corrosion-prone locations. However, its low hardness and poor tribological properties limit its application under heavy wear conditions. In this study, 316L Fe-based composite coatings co-doped with TB2 hard phases and rare-earth CeO2 exhibited excellent wear and corrosion resistance. Firstly, 316L-TiB2 cermet powder and (316L-TiB2)/CeO2 composite powder with high sphericity and density were prepared by high energy ball milling (HEBM), spraying drying granulation (SD), plasma spheroidization (PS) process. Then, 316L coatings, 316L-TiB2 and (316L-TiB2)/CeO2 cermet coatings were deposited by high velocity air fuel (HVAF) spraying. Finally, the effects of TiB2 and CeO2 additions on the microstructure, wear and corrosion behavior of the coatings were investigated. The results showed that TiB2 hard particles and CeO2 were uniformly distributed in the HVAF sprayed 316L-TiB2 and (316L-TiB2)/CeO2 coatings. The wear resistance of the coating prepared by 316L Fe-based composite powder with TiB2 and CeO2 is significantly improved. The hardness of the (316L-TiB2)/CeO2 composite coating was increased from 269 Hv0.3 to 826 Hv0.3 for the pure 316L coating, while the volumetric wear rate was only 3.6 % of that of the pure 316L coating (110 × 10−5 down to 4 × 10−5 mm3/N). Electrochemical tests show that the corrosion resistance of the coating decreases with the addition of TiB2 alone, but it can be improved by doping CeO2. The 316L Fe-based coating prepared by adding TiB2 and CeO2 can significantly improve the wear resistance of the coating, while the corrosion resistance decreases only slightly.

Analysis of OWC impulse turbine flow characteristics considering the blade tip clearance

Abstract Oscillating water column (OWC) ocean wave energy recovery device is a popular technology in current wave energy research, which possesses the advantages of a sturdy structure and low-maintenance requirements. The device recovers energy by unidirectional rotation in the reciprocating airflow generated by an impulse turbine. Its operational performance depends on the flow efficiency of the core component, the air turbine. In this paper, a prototype impulse turbine with blades tip clearance of 1 mm was considered, and the SST k-ω turbulence model is used to calculate the operating performance of the air turbine at different operating points. The calculation result shows that the efficiency of the turbine under the optimal operating conditions is about 51.41%. When the flow coefficient is less than 0.8, the primary focus of energy loss in the rotor occurs at the blade tip. The low flow rate leads to a high inlet angle causing fluid friction. In these small flow conditions, the pressure drop at the leaf top gap is cantered on the inlet, and the speed in the gap flow field is significantly reduced. When the flow coefficient is greater than 1.4, the concentration of energy loss in the rotor primarily occurs within the flow channel, where the high-velocity air causing a local high-speed zone.