High Deposition Efficiency Research Articles

Characteristics of Coal Dust Deposition in Boiler Tail Gas Pipelines

Coal dust deposition in boiler tail gas pipelines can significantly affect boilers’ thermal and energy efficiency. This study investigates the deposition characteristics of coal dust particles in boiler tail gas tubes in variable cross-section tubes. Numerical simulations were performed using the Reynolds Stress Model and the Discrete Particle Model. User-defined functions coding is used to construct the particle deposition model in the particle deposition model. The study analyses the distribution of turbulent kinetic energy locations in the gradient tube, compares the distribution of particle deposition on its wall, and concludes that the deposition distribution of coal dust particles in the gradient tube is slightly different for different particle sizes. Smaller particles have a higher deposition efficiency in equal cross-section pipes than larger particles. Particle size also has a significant effect on pipe taper and expansion. The results of this study can provide theoretical guidance for optimising the design of boiler tail gas pipelines, improving energy efficiency, and reducing environmental pollution.

Characteristics of Coal Dust Deposition in Boiler Tail Gas Pipelines

Coal dust deposition in boiler tail gas pipelines can significantly affect boilers’ thermal and energy efficiency. This study investigates the deposition characteristics of coal dust particles in boiler tail gas tubes in variable cross-section tubes. Numerical simulations were performed using the Reynolds Stress Model and the Discrete Particle Model. User-defined functions coding is used to construct the particle deposition model in the particle deposition model. The study analyses the distribution of turbulent kinetic energy locations in the gradient tube, compares the distribution of particle deposition on its wall, and concludes that the deposition distribution of coal dust particles in the gradient tube is slightly different for different particle sizes. Smaller particles have a higher deposition efficiency in equal cross-section pipes than larger particles. Particle size also has a significant effect on pipe taper and expansion. The results of this study can provide theoretical guidance for optimising the design of boiler tail gas pipelines, improving energy efficiency, and reducing environmental pollution.

Numerical Simulation of Pyrethrin Aerosol Deposition

Highlights A steady state, laminar CFD model was developed to simulate the airflow inside an aerosol exposure chamber. The CFD model predicted the droplet tracks and deposition of various sizes of aerosol droplets. Larger aerosol droplets had higher deposition efficiency. A Higher flow rate, but still within the laminar flow regime, caused lower deposition efficiency for all droplet sizes. Abstract. Aerosol insecticides (e.g., pyrethrin) are widely used for the control of stored products insects inside food facilities. To optimize pyrethrin aerosol application, computational fluid dynamics (CFD) was used to predict airflow and aerosol transport inside a vertical flow aerosol exposure chamber operated under laminar flow conditions. A discrete phase model in ANSYS FLUENT 2021 R1 was developed, and simulations were conducted to track pyrethrin droplets of various diameters (0.1 to 20 µm) and determine their deposition onto Petri dishes located near the center of the chamber. The deposition efficiency of the different aerosol droplet sizes and the effect of two flow rates (5 × 10-4 m3 s-1 and 4 × 10-4 m3 s-1) on deposition efficiency were determined. The results showed that the predicted deposition of pyrethrin aerosol increased with increasing droplet size, largely due to inertial and gravitational effects. Deposition efficiencies decreased with the higher flow rate—with 0.1% to 96.6% predicted deposition efficiencies for the low flow rate and 0.1% to 93.8% for the high flow rate. Results of this study can be used to improve aerosol application methods for stored product insect control. Keywords: Aerosol deposition, Aerosol insecticide, Computational fluid dynamics, Confused flour beetle, Deposition efficiency, Discrete phase model, Numerical simulation, Particle tracking, Pyrethrins, Stored product insect.

Dual-droplet transition control for improving forming quality and composition homogenizing in dual-wire additive manufacturing of Ti2AlNb alloy

Dual-wire additive manufacturing (AM) couples traditional wire-based AM for part fabrication and the molten pool metallurgy for material-preparation with high deposition efficiency and material utilization. However, compared with traditional single-wire AM technology, it has a more complex and sensitive dual-droplet transition distance (TD), which not only affects the forming quality but also the metallurgical quality. Therefore, it is necessary and urgent to monitor and control its TD value online. In this study, we systematically investigated the sensing, controlling, and influential mechanism of the TD value in dual-wire AM technology, and Ti2AlNb was taken as the target alloy owing to its great application prospects in the aerospace field. Specifically, a deposition experiment with different initial TD value was conducted to study the effect on the morphology and composition distribution of the as-printed part. Based on the optimal distance, the related image extraction algorithms and closed-loop control methods are developed. The closed-loop controlled verification experiment on the slope and step substrate, as well as the multi-layer deposition test, were carried out and analyzed. The results indicate that the developed system can control the TD to the desired value with good robustness. In addition, the controlled deposited multi-layer part exhibited good morphology and composition homogenizing in the post-characterization experiment. This study is of great significance for the intelligent and industrial development of dual-wire AM technology.

Comparing electrochemical pitting behavior and passive films of Fe-Cr-B alloy coatings manufactured via high deposition rate and conventional laser directed energy deposition

This study conducted a comparative analysis of the microstructural features and electrochemical pitting performance of high deposition rate laser directed energy deposition (H-LDED) and conventional laser directed energy deposition (LDED) Fe-Cr-B alloy coatings. It aimed to reveal the impact of process-induced microstructural differences on pitting performance. The microstructure of both coatings consists of a Fe-rich matrix phase and (Fe, Cr)2B phase. In comparison to LDED coatings, H-LDED coatings offer advantages due to their rapid solidification, resulting in significantly finer microstructure, reduced microelement segregation, and significantly lower dilution rates. However, H-LDED coatings exhibit higher porosity (0.06 %) compared to LDED coatings (0.02 %). Under identical chemical composition conditions, the thickness, structure, and composition of the passive film in both coatings are similar, indicating that microstructural differences have minimal impact on passive film formation. In cases of consistent coating thickness, dilution rate emerges as the most significant factor influencing corrosion resistance, while porosity plays a prominent role under uniform coating chemical composition conditions. In summary, the advantages of H-LDED coatings encompass high deposition efficiency and low dilution rates, allowing for the production of thin coatings that meet service requirements.

Combing of picogram level DNA equivalent to genomic DNA present in single human cell by self propelled droplet motion over a stable gradient surface

DNA combing is a powerful technique for studying replication profile, fork-directionality and fork velocity. At present, there is requirement of a methodology to comb DNA present in a single human cell for studying replication dynamics at early embryonic stage. In our study, a surface having dual characteristics i.e., affinity towards negatively charged single DNA molecules and a hydrophobic gradient for self propelled droplet motion of combing solution was developed. The surface was made by coating of TCOS (trichloro-octylsilane) by vapor diffusion on APTES (Aminopropyl-triethoxysilane) coated glass slides. A gradient surface having high deposition efficiency (DE) was developed on which 5 picogram DNA equivalent to genomic DNA present in one single human cell can be combed. The gradient surface was thermostable in nature having the ability to sustain boiling temperature for two hours and sustain anisotropy in 70 % ethanol for 80 h. Applicability for multiple runs was enhanced such that the surface can be used for 13–14 times. Factors associated with gradient surface are unidirectional movement of combing solution droplet over the gradient surface for combing straight DNA molecules and a longer gradient surface of more than 1 cm such that long size DNA molecules can be combed. Ellipsometry and contact angle hysteresis confirmed the presence of hydrophobic gradient. XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier Transform Infrared Spectroscopy) confirmed the presence of characteristic affinity towards negatively charged DNA molecules on the gradient surface. Combing solution was optimized for increasing deposition efficiency and for increasing the applicability of gradient surface for multiple runs. High temperature of combing solution was found to increase Deposition Efficiency. Combing solution was also optimized for combing single DNA molecules over the gradient surface. Single DNA molecules were combed by reducing pH and lowering concentration of triton-X in the combing solution. Dye: bp ratio was optimized for high fluorescent intensity and low surface background.

Effect of process modes on microstructure and mechanical properties of CMT wire arc additive manufactured WE43 magnesium alloy

The traditional WE43 magnesium alloy (WE43-Mg) manufacturing process faces challenges in producing large and complex structures. The cold metal transfer wire arc additive manufacturing (CMT-WAAM) offers a promising solution due to its flexibility, high deposition efficiency and low heat put. However, energy transfer and mass transfer are highly coupled in the CMT additive manufacturing process. Under different working modes, the local thermal processes are quite different for the same transition metals, which can produce different microstructures and mechanical properties. Therefore, it is necessary to study the effect of working modes on microstructure and mechanical properties. This study successfully deposited single-pass multi-layer WE43-Mg components using four CMT processes: CMT, CMT-Pulse, CMT-Advance, and CMT-Pulse + Advance. The microstructure and mechanical properties of these deposited samples were compared. Results revealed equiaxed grains with uniform sizes in the top and middle regions, with fine-grain regions between layers in the four CMT modes. Compare the microstructure characterization results, the higher the line energy, the narrower the width of the remelted fine grain zone. Four CMT modes deposited components exhibited superior mechanical properties compared to as-cast WE43-Mg. The CMT pulse mode shows the best results due to its low porosity. The average yield strength is 149.0 MPa, tensile strength is 222.9 MPa, and elongation is 6.4 %.

The Potential of High-Velocity Air-Fuel Spraying (HVAF) to Manufacture Bond Coats for Thermal Barrier Coating Systems

Driven by the search for an optimum combination of particle velocity and process temperature to achieve dense hard metal coatings at high deposition efficiencies and powder feed rates, the high-velocity air-fuel spraying process (HVAF) was developed. In terms of achievable particle velocities and temperatures, this process can be classified between high-velocity oxy-fuel spraying (HVOF) and cold gas spraying (CGS). The particular advantages of HVAF regarding moderate process temperatures, high particle velocities as well as high productivity and efficiency suggest that the application of HVAF should be also investigated for the manufacture of MCrAlY (M = Co and/or Ni) bond coats (BCs) in thermal barrier coating (TBC) systems. In this work, corresponding HVAF spray parameters were developed based on detailed process analyses. Different diagnostics were carried out to characterize the working gas jet and the particles in flight. The coatings were investigated with respect to their microstructure, surface roughness and oxygen content. The spray process was assessed for its effectiveness. Process diagnostics as well as calculations of the gas flow in the jet and the particle acceleration and heating were applied to explain the governing mechanisms on the coating characteristics. The results show that HVAF is a promising alternative manufacturing process.

Oxidative potential and source apportionment of size-resolved particles from indoor environments: Dithiothreitol (DTT) consumption and ROS production

Oxidation potential (OP) is an emerging index to measure the toxicity of atmospheric particulate matter (PM), but little research data on indoor PM OP are available. This study focuses on the size-resolved particle OP and source apportionment of PM from indoor environments. Different-size PM samples were gathered from March 6, 2022, to April 18, 2022, from offices, canteens, dormitories, and laboratories using Anderson samplers. Particles from these indoor environments were separated into nine size fractions, and the chemical components (including transition metals, ions, and water-soluble organic carbon (WSOC)) were measured. The water-soluble OP (OPws) of the investigated PM was highest in the dormitory (61.02 nmol min−1 μg−1) and lowest in the canteen (25.58 nmol min−1 μg−1), varying by factors of up to 2.38. Additionally, the particulate Mn (r2 = 0.94), Fe (r2 = 0.93), and Zn (r2 = 0.92) concentrations were closely related to OPws. The OPws distribution in indoor PM samples featured a single peak from 0.7 to 3.2 μm. ROS (·OH) showed the same trend (1.1–3.2 μm) as PM OP, which shows that PM3.2 is the main contributor to adverse health effects among all size fractions of PM due to the strengthened oxidative ability of PM3.2 compared to PM > 3.2. The source apportionment results showed that secondary sources (52.3%), construction sources (28%), vehicle emissions (18.5%), and dust sources (1.2%) were the main sources of indoor PM OP. Multiple path particle dosimetry (MPPD) model tests evidenced that PM3.2 control the lung OPws and ROS (accounting for >71.49% and 68.07%, respectively) deposition because of the high deposition efficiency and metal concentration in the alveolar region. The experimental trend of OP was closely related to that of ROS. Overall, since OPws is directly associated with diverse health effects for PM OP, special attention to PM3.2 impact.

Optimization of Segmented Thermal Barrier Coatings (s-TBCs) for High-Temperature Applications

AbstractHot section components of stationary gas turbines, such as turbine blades and vanes, are coated with thermal barrier coatings (TBCs) to increase the component life. TBCs provide thermal insulation to the metallic components from hot gas in the gas turbines. The TBCs represent high-performance ceramics and are mainly composed of yttria-stabilized zirconia (YSZ) to fulfill the thermal insulation function. The microstructure of the TBCs should be porous to decrease heat conduction. Besides the porous TBCs, the subsequently developed vertically segmented thermal barrier coatings (s-TBCs) feature outstanding thermal durability. For the formation of this segmented coating microstructure, the YSZ should be deposited under high thermal tensile stress during the coating process. Therefore, substrates are heated just before the coating by plasma or in an oven in recent research. In this work, the development of process parameters for s-TBCs produced by atmospheric plasma spray (APS) without pre-heating is presented. Within the experiments, the relevant process parameters, such as plasma gases, powder feed rate, surface speed, and pathway strategy, have been optimized to achieve the segmented coating microstructure with high deposition efficiency by a conventional plasma torch. Furthermore, YSZ powders used in this study are characterized, and the effect of powder characteristics on the coating microstructure is investigated. The coating microstructure in this work aims to achieve the formation of a high number of vertical cracks with a combination of low internal residual stress and high adhesive tensile strength for the s-TBCs.

Directed energy deposition of SS 316L/SiC composites using coincident and coaxial wire-powder feeding

The wire-powder fed directed energy deposition (WP-DED) process enables the fabrication of metal matrix composites (MMCs) with a high deposition efficiency. Lateral wire-powder feeding as well as lateral wire and coaxial powder feeding are two existing methods for WP-DED of MMCs. However, the lateral filler injection limits the fabrication of three-dimensional parts with complex geometry. In this study, we applied the coaxial wire-powder fed DED (CWP-DED) to fabricate the SS 316L/SiC parts with different SiC weight fractions. The effects of SiC content on defects and microstructure of as-built parts were investigated. Three types of interior defects including pores, inclusions, and cracks were observed in as-built samples fabricated with high SiC content. With an increase in SiC content, the grains were refined by dissolved nano-scale SiC particles and more γ-(FeCrNi) phases transformed into α-(FeCrNi) phases. Tensile properties and the underlying strengthening mechanisms of as-built SS 316/SiC specimens were elucidated. This paper will guide the process development for CWP-DED of high-performance MMCs.

Systematic Approach to Optimize Technological and Economical Aspects of Atmospheric Plasma Sprayed Thermal Barrier Coatings

Plasma‐sprayed yttria‐stabilized zirconia coatings have been used in gas turbines for decades. They are applied for thermal insulation to increase operating temperature and hence efficiency and component's lifetime. To keep manufacturing costs low, especially deposition efficiency is important. However, increasing it is also related to a reduction in porosity, affecting the insulating properties of the layer. To find an optimal combination of efficiency and technological performance, a systematic study of the most affecting parameters of the atmospheric plasma spraying process is conducted, using response surface methodology. In detail, the influence of current, spraying distance, and hydrogen gas flow is investigated with respect to the deposition efficiency, porosity, microstructure, and mechanical properties of the coatings. Characterization is carried out by scanning electron microscopy, microindentation tests, and three‐point bending tests. The models generated based on these measured properties allow predictions of the system responses for any parameter variation in the investigated design space. In addition, a numerical model is developed for targeted optimization of the coating properties. This can be used to produce optimized coatings for load‐flexible gas turbines with high deposition efficiency, high porosity, and at the same time advantageous mechanical properties.

Effect of composition gradient design on microstructure and mechanical properties of dual-wire plasma arc additively manufactured 316L/IN625 functionally graded materials

Wire and arc additive manufacturing (WAAM) is a promising technology for the preparation of refractory metal functional gradient materials (FGMs) due to its high material utilization, high deposition efficiency and ability to create large-sized parts. In the present work, 316L/IN625 FGM with chemical composition gradients of 25 wt% and 100 wt% were fabricated using dual-wire plasma arc additive manufacturing (DW-PAAM) by changing the wire feeding speeds (WFSs) layer by layer. The phase evolution, microstructure, chemical composition and mechanical properties of the FGM were analyzed. The results demonstrated that the microstructure in all regions was predominantly the austenite phase, and no cracks or defects were observed. The microstructure of the 100 wt% 316L zone was composed of the austenite phase (face-centered cubic, FCC) and a small amount of ferrite phase (body-centered cubic, BCC), whereas mainly FCC structure was observed in the other chemical composition regions. There was a certain error between the actual composition gradient and the designed gradient. The microhardness transition of S1 was smoother and wider, while the tensile test results of S2 were better. In addition, the position of the tensile fracture was different for S1 and S2. In conclusion, the DW-PAAM process shows great potential for manufacturing FGM with desirable properties for various industrial applications. Further studies are warranted to optimize process parameters and develop new design strategies to enhance the performance of FGM in various industrial applications.

Research on transition layer microstructure and properties of Al–Cu/Al–Si gradient materials fabricated by cold metal transfer

As an important part of the additive manufacturing technology, wire arc additive manufacture (WAAM) is outstanding with high deposition efficiency, large size of deposited parts, short periodic time, and low costs. WAAM also shows potential in in-situ composite manufacturing and gradient material preparation. Given the potential in wire arc manufacturing of double-alloy gradient structured materials, the walls were deposited using alternating feeds (depositing a layer of A wire and then depositing a layer of B wire) of high-strength-low-plasticity ZL205 and low-strength-high-plasticity 4043 welding wire. In this process, the liquid phases of the two types of wire were efficiently mixed, which showed a regular distribution of molten pool track and avoided evident defects. Generally, through such gradient structure design, high-strength low-toughness materials and high-toughness low-strength materials can be effectively combined, which achieves the regulation of mechanical properties. Specifically, the overall structural and mechanical properties can be improved by adjusting the proportion of a certain component. As an extension from the wire arc printing technology, WAAM shows extremely high application potential and industrial values. Moreover, the addition of a dissimilar alloy can decrease the formation of columnar grains during additive manufacturing. Such compositional gradient can destroy the columnar extensive growth during the deposition in WAAM.

Improving the Interparticle Bonding and Ductility of Cold Sprayed Aluminum Alloys by Deformation Processing

Cold spray (CS) can produce thick coatings and free-standing bulk materials and is adaptable to additive manufacturing, including on-site repair. However, the structural applications of CS materials have been limited by the inherently incomplete interparticle metallurgical bonding in CS materials. In this work, an ultrasonic washing test (UWT) was used to semi-quantitatively assess the extent of interparticle bonding in CS Al6061 and CS Al2024 in relation to key CS parameters and post-CS deformation processing. Results indicate that spraying with a lighter gas or a softer powder promotes the interparticle bonding, although full metallurgical bonding is hardly achieved even by spraying at high deposition efficiencies. Sprayed particles remain in the deposit only because they acquire partial bonding that is sufficient to prevent them from bouncing off. Post-CS rolling and T6 heat treatment increase the interparticle bonding and hence ductility of CS Al alloys. Ultrasonic ironing (UI), a new post-CS deformation processing technique, also produces similar effects. The increased interparticle bonding by post-CS deformation processing arise from fragmentation of oxide layers inherited from powder particle surfaces and consequent metal-to-metal joining at the particle boundaries.

Wire and arc additive manufacturing of Fe-based shape memory alloys: Microstructure, mechanical and functional behavior

Shape memory alloys (SMA) are a class of smart materials with inherent shape memory and superelastic characteristics. Unlike other SMAs, iron-based SMAs (Fe-SMA) offer cost-effectiveness, weldability, and robust mechanical strength for the construction industry. Thus, applying these promising materials to advanced manufacturing processes is of considerable industrial and academic relevance. This study aims to present a pioneer application of a Fe–Mn–Si–Cr–Ni–V-C SMA to arc-based directed energy deposition additive manufacturing, namely wire and arc additive manufacturing (WAAM), examining the microstructure evolution and mechanical/functional response. The WAAM-fabricated Fe-SMAs presented negligible porosity and high deposition efficiency. Microstructure characterization encompassing electron microscopy and high energy synchrotron X-ray diffraction revealed that the as-deposited material is primarily composed by γ FCC phase with modest amounts of VC, ε and σ phases. Tensile and cyclic testing highlighted the Fe-SMA's excellent mechanical and functional response. Tensile testing revealed a yield strength and fracture stress of 472 and 821 MPa, respectively, with a fracture strain of 26%. After uniaxial tensile loading to fracture, the γ → ε phase transformation was clearly evidenced with post-mortem synchrotron X-ray diffraction analysis. The cyclic stability during 100 load/unloading cycles was also evaluated, showcasing the potential applicability of the fabricated material for structural applications.

High-Temperature Oxidation Behaviour of CrSi Coatings on 316 Austenitic Stainless Steel.

In this study, a closed-field unbalanced magnetron sputtering system, which is environmentally friendly and has high deposition efficiency, was used to deposit CrSi coatings on 316 austenitic stainless steel. This system utilised separate Cr and Si targets, and the appropriate content of Cr and Si of the coatings was adjusted by changing the currents applied to the targets. A series of CrSi coatings with different Si/Cr ratios were produced, and their oxidation behaviour at elevated temperatures was investigated. By analysing the weight gain, surface morphology and microstructure, composition and phase constituents, the oxidation behaviour at 600 °C, 700 °C and 800 °C was investigated and the optimized coating to protect the stainless steel has been identified. The outcome of the research indicated that a small amount of Si (between 4-7 at.%) in Cr coatings is effective in protecting the austenitic stainless steel against oxidation at high temperatures, while a high Si content (around 10 at.% or more) makes the coating more brittle and prone to cracking or delamination during oxidation at 800 °C.

Experimental optimization of physicochemical factors for spontaneous deposition of 210Po using newly designed deposition kit

A simple spontaneous deposition kit for 210Po determination using alpha spectrometry was newly designed, and polonium deposition characteristics under various physicochemical conditions were evaluated using it. The high-purity silver disc (99.99%) showed high deposition efficiencies of over 85.1% in the HCl concentration range of 0.01–6 M. Optimal physicochemical factors were determined to be a temperature of 90 °C, deposition time of 90 min, and the use of ascorbic acid as a reducing agent in an amount similar to that of the interfering element (Fe).

High-Performance Pure Aluminum Coatings on Stainless Steels by Cold Spray

Aluminum target material is an important target material and is widely used in preparations of semiconductor films, integrated circuits, display circuits, protective films, decorative films, etc. In this study, pure aluminum coatings were deposited on stainless steel substrates by cold-spray technology as part of an overall project to produce large-size pure aluminum sputtering target materials. The results show that pure aluminum coatings exhibit high adhesive strength (~98 MPa), high deposition efficiency (~95%), and low porosity (~0.3%) on stainless steel substrates. The bonding mechanisms of pure aluminum coatings on stainless steel are a combination of metallurgical and mechanical interlocking. The evolutions of microstructure and mechanical properties of pure aluminum coatings under different heat treatments were also studied. With the increase of heat treatment temperature, it is found that cold-sprayed aluminum coatings become more homogenous in microstructure, the microhardness is reduced, and the adhesive strength seems to be slightly reduced. Overall, this study demonstrates significant advantages of cold-spray technology in depositing high-performance pure aluminum coatings on stainless steels.

A Static Tin-Manganese Battery with 30000-Cycle Lifespan Based on Stabilized Mn3+/Mn2+ Redox Chemistry.

High-potential Mn3+/Mn2+ redox couple (>1.3 V vs SHE) in a static battery system is rarely reported due to the shuttle and disproportionation of Mn3+ in aqueous solutions. Herein, based on reversible stripping/plating of the Sn anode and stabilized Mn2+/Mn3+ redox couple in the cathode, an aqueous Sn-Mn full battery is established in acidic electrolytes. Sn anode exhibits high deposition efficiency, low polarization, and excellent stability in acidic electrolytes. With the help of H+ and a complexing agent, a reversible conversion between Mn2+ and Mn3+ ions takes place on the graphite surface. Pyrophosphate ligand is initially employed to form a protective layer through a complexation process with Sn4+ on the electrode surface, effectively preventing Mn3+ from disproportionation and hindering the uncontrollable diffusion of Mn3+ to electrolytes. Benefiting from the rational design, the full battery delivers satisfied electrochemical performance including a large capacity (0.45 mAh cm-2 at 5 mA cm-2), high discharge plateau voltage (>1.6 V), excellent rate capability (58% retention from 5 to 30 mA cm-2), and superior cycling stability (no decay after 30 000 cycles). The battery design strategy realizes a robustly stable Mn3+/Mn2+ redox reaction, which broadens research into ultrafast acidic battery systems.