The Experts below are selected from a list of 1524 Experts worldwide ranked by ideXlab platform
Liang Jiang - One of the best experts on this subject based on the ideXlab platform.
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Control of crystal orientation and continuous growth through inclination of Coaxial Nozzle in laser powder deposition of single-crystal superalloy
Journal of Materials Processing Technology, 2016Co-Authors: Zhaoyang Liu, Liang JiangAbstract:Abstract The effects of inclining angle of the Coaxial Nozzle in the longitudinal section of deposited bead on the molten pool geometry and the corresponding crystal growth in laser powder deposition of single-crystal superalloy are studied through the coupling of a numerical FLUENT program and a three-dimensional transient transport phenomena mathematical model. Systematical experiments with single-crystal nickel-based superalloy were conducted to verify the computational results. The results show that the inclination angle of the Coaxial Nozzle in the longitudinal section of deposited bead has a predominant effect on the molten pool geometry and the solidified microstructure. The inclination of Coaxial Nozzle reduces the height of the molten pool while increases the melting depth compared to the normal-direction deposition. The epitaxial grain growth in the deposited bead is enhanced when the Coaxial Nozzle inclines toward the laser scanning direction, while it is restrained as the Nozzle inclines toward the opposite direction. When the Coaxial Nozzle inclines to a +45°, the ratio of melting depth to the height of equiaxied stray grain on the top of the previous layer of deposited bead exceeds 1.0, which implies that the deposited layer can completely remelt the stray grains in the previous layer. The capacity of continuous-epitaxial grain growth can be therefore achieved through the Nozzle inclination effectively. This method can be used to optimize and control the processing parameters and broaden the processing window for a single-crystal turbine blade tip repair.
Zhaoyang Liu - One of the best experts on this subject based on the ideXlab platform.
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Control of crystal orientation and continuous growth through inclination of Coaxial Nozzle in laser powder deposition of single-crystal superalloy
Journal of Materials Processing Technology, 2016Co-Authors: Zhaoyang Liu, Liang JiangAbstract:Abstract The effects of inclining angle of the Coaxial Nozzle in the longitudinal section of deposited bead on the molten pool geometry and the corresponding crystal growth in laser powder deposition of single-crystal superalloy are studied through the coupling of a numerical FLUENT program and a three-dimensional transient transport phenomena mathematical model. Systematical experiments with single-crystal nickel-based superalloy were conducted to verify the computational results. The results show that the inclination angle of the Coaxial Nozzle in the longitudinal section of deposited bead has a predominant effect on the molten pool geometry and the solidified microstructure. The inclination of Coaxial Nozzle reduces the height of the molten pool while increases the melting depth compared to the normal-direction deposition. The epitaxial grain growth in the deposited bead is enhanced when the Coaxial Nozzle inclines toward the laser scanning direction, while it is restrained as the Nozzle inclines toward the opposite direction. When the Coaxial Nozzle inclines to a +45°, the ratio of melting depth to the height of equiaxied stray grain on the top of the previous layer of deposited bead exceeds 1.0, which implies that the deposited layer can completely remelt the stray grains in the previous layer. The capacity of continuous-epitaxial grain growth can be therefore achieved through the Nozzle inclination effectively. This method can be used to optimize and control the processing parameters and broaden the processing window for a single-crystal turbine blade tip repair.
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The effects of the inclination angle of Coaxial Nozzle on crystal growth and microstructure formation in laser powder deposition of single-crystal superalloy
International Congress on Applications of Lasers & Electro-Optics, 2014Co-Authors: Zhaoyang LiuAbstract:A three-dimensional mathematical model was developed to investigate the effects of inclination angle of the Coaxial Nozzle on crystal growth pattern and microstructure formation during laser powder deposition of single-crystal superalloy. Detailed experiments with SX nickel-based superalloy were conducted to verify the computational results. Results show that the inclination of the Coaxial Nozzle in the longitudinal section of deposited bead has a predominant effect on solidification conditions and corresponding microstructure formation in molten pool. The inclination of Coaxial Nozzle from normal direction of depositing surface delays the stray grain formation while increases the melting depth of substrate. When the inclination of Coaxial Nozzle toward laser scanning direction reaches 45°, the height ratio of melting depth to stray grain region exceeds 1.0, which enhances capability of the total remelting of stray grain. The simulation results and experimentally observed microstructure agree well. With the optimized processing parameters, the epitaxial columnar dendrite can grows continuously in multi-layer laser powder deposition of single-crystal superalloy. These findings have some important implications for SX LPD repair processing.A three-dimensional mathematical model was developed to investigate the effects of inclination angle of the Coaxial Nozzle on crystal growth pattern and microstructure formation during laser powder deposition of single-crystal superalloy. Detailed experiments with SX nickel-based superalloy were conducted to verify the computational results. Results show that the inclination of the Coaxial Nozzle in the longitudinal section of deposited bead has a predominant effect on solidification conditions and corresponding microstructure formation in molten pool. The inclination of Coaxial Nozzle from normal direction of depositing surface delays the stray grain formation while increases the melting depth of substrate. When the inclination of Coaxial Nozzle toward laser scanning direction reaches 45°, the height ratio of melting depth to stray grain region exceeds 1.0, which enhances capability of the total remelting of stray grain. The simulation results and experimentally observed microstructure agree well. With t...
Frank W Liou - One of the best experts on this subject based on the ideXlab platform.
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the investigation of gravity driven metal powder flow in Coaxial Nozzle for laser aided direct metal deposition process
Journal of Manufacturing Science and Engineering-transactions of The Asme, 2006Co-Authors: Todd E Sparks, Yogesh D. Thakar, Frank W LiouAbstract:The quality and efficiency of laser-aided direct metal deposition largely depends on the powder stream structure below the Nozzle. Numerical modeling of the powder concentration distribution is complex due to the complex phenomena involved in the two-phase turbulence flow. In this paper, the gravity-driven powder flow is studied along with powder properties, Nozzle geometries, and shielding gas settings. A 3-D numerical model is introduced to quantitatively predict the powder stream concentration variation in order to facilitate Coaxial Nozzle design optimizations. Effects of outer shielding gas directions, inner/outer shielding gas flow rate, powder passage directions, and opening width on the structure of the powder stream are systematically studied. An experimental setup is designed to quantitatively measure the particle concentration directly for this process. The numerical simulation results are compared with the experimental data using prototyped Coaxial Nozzles. The results are found to match and then validate the simulation. This study shows that the particle concentration mode is influenced significantly by Nozzle geometries and gas settings.
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Numerical simulation of metallic powder flow in a Coaxial Nozzle for the laser aided deposition process
Journal of Materials Processing Technology, 2005Co-Authors: Heng Pan, Frank W LiouAbstract:Abstract Laser aided deposition process offers the ability to make a metal component directly from CAD drawings. Analysis of metallic powder flow in the feeding system is of particular significance to researchers in order to optimize this technique. Powder flow simulation holds a critical role in understanding flow phenomenon so as to ensure proper design and sound functionality of the Coaxial Nozzle. Numerical study of metallic powder flow in the Coaxial Nozzle for laser aided deposition is, however, barely existent. This is partially because not all of gas-atomized powders and none of water-atomised powders can be considered spheres and an accurate and economic modeling approach in describing non-spherical powder dispersion behavior can rarely be seen. To quickly simulate realistic powder flow and also meet the practical requirement for design optimization of the Coaxial Nozzle, a stochastic model, which considers particle shape effects, is developed. The validity of the model is demonstrated through comparison with experiment. The application of the model to the evaluation of various Nozzle geometrical configurations is shown.
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Numerical and Experimental Analysis of the Powder Flow Streams in the Laser Aided Material Deposition Process
2004Co-Authors: Yogesh D. Thakar, Heng Pan, Frank W LiouAbstract:Axial powder stream concentration between the Nozzle end and the deposition point is an important process parameter in the laser aided material deposition process. The powder concentration is greatly influenced by the Nozzle geometry in use. This paper describes the numerical and experimental analysis of this important parameter in relation to the Coaxial Nozzle. The experiments are performed with the different Nozzle geometries to generate various flow patterns of the gravity fed powder in a cold stream. The results of the experimental analysis are compared with the numerical simulation and found justified. These results are used in concluding the significance of important Nozzle parameters for various powder concentration modes. Introduction Laser deposition process consists of feeding the metal powder into a hot spot called as melt pool to form a melted zone which solidifies into a bead. The Coaxial Nozzle is widely used for this metal deposition process [3, 9]. The metal powder is fed through the Nozzle in the melt pool in a Coaxial system instead of the external tubes as in the side Nozzle. Laser aided deposition quality largely depends on the powder stream structure below the Nozzle [7]. The variation of the powder stream concentration in axial direction affects the material delivery rate at the deposition point and the interaction of the laser beam radiation with the powder stream [4]. High efficiency of the powder deposition in a Coaxial system is an important subject for the study. The focusability of the stream structure is a key factor of the energy utilization and catchment efficiency of the Coaxial Nozzle [5]. It is found that most of the laser power reaches the substrate with some energy loss in the particles in laser deposition process [9]. This is sometimes caused by the shadow effect of one particle over another due to the absorption of the beam energy by the powder stream. The stream structure is mainly influenced by the powder flow settings and Nozzle arrangements [5]. It is also found that the powder catchment increases with increase in the powder flow velocity [9]. The process of deposition involves control of various parameters like powder type, powder flow velocity and gas velocities. Though these are actual process parameters, the initial powder flow is defined by the Nozzle geometry in use. Thus, optimizing the deposition Nozzle for such process is not an easy task and hence requires a lot of experimentation and numerical simulation. It is difficult to find the literature explaining about the effect of Nozzle geometry at the powder outlet area of the Coaxial Nozzle on the powder concentration mode. Though the above mentioned studies have been carried out, the detailed study needed to be done entailing the effect of the Nozzle geometry at the powder passage on the flow mode. The initial consideration should be given in generating various types of powder streams by using different Nozzle geometries at the powder outlet area. It is necessary to understand the proper powder flow behavior to determine the displacement of the powder between the Nozzle and deposition point. This will help in getting the value for the distance of maximum concentration point of the merging streams
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Analysis of the powder flow characteristics for the direct laser deposition process
International Congress on Applications of Lasers & Electro-Optics, 2004Co-Authors: Yogesh D. Thakar, Heng Pan, Frank W LiouAbstract:Direct laser deposition process is one of the advanced technologies in the current industrial and research scenario. In this process, metal and/or alloy powder is directly fed into the melt pool created by the laser to form the solid parts. The powder flow characteristics play an important role in the laser aided deposition. The melting of the powder depends mostly on the laser beam spot size and the powder flow from the Nozzle. The intention of this contribution is to study this basic parameter of the powder flow in detail with respect to the Coaxial deposition Nozzle. Different Nozzle dimensions are used to analyze the different flow patterns of the gravity fed powder in a cold stream. Rapid prototyping technique is used to make this analysis cost and time efficient. This analysis lays down the benchmark for the Coaxial Nozzle design used for the laser aided deposition process in a productive manner.Direct laser deposition process is one of the advanced technologies in the current industrial and research scenario. In this process, metal and/or alloy powder is directly fed into the melt pool created by the laser to form the solid parts. The powder flow characteristics play an important role in the laser aided deposition. The melting of the powder depends mostly on the laser beam spot size and the powder flow from the Nozzle. The intention of this contribution is to study this basic parameter of the powder flow in detail with respect to the Coaxial deposition Nozzle. Different Nozzle dimensions are used to analyze the different flow patterns of the gravity fed powder in a cold stream. Rapid prototyping technique is used to make this analysis cost and time efficient. This analysis lays down the benchmark for the Coaxial Nozzle design used for the laser aided deposition process in a productive manner.
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Numerical and Experimental Study of Shielding Gas Orientation Effects on Particle Stream Concentration Mode in Coaxial Laser Aided Material Deposition Process
Volume 1: 30th Design Automation Conference, 2004Co-Authors: Heng Pan, Yogesh D. Thakar, Frank W LiouAbstract:Laser aided deposition quality largely depends on the powder stream structure below the Nozzle. Modeling of the powder concentration distribution rarely relies on the numerical approach partially due to the complex phenomenon involved in the two-phase turbulence flow. In this paper, a numerical model is introduced to predict the particle-gas flow precisely and economically in order to meet the practical requirement for Coaxial Nozzle design optimizations. This model is able to quantitatively predict the powder stream concentration mode under different outer shielding gas directions and inner/outer gas velocity ratio. The numerical simulation results are compared with the experimental study using prototyped Coaxial Nozzles. The results are found to match. This study shows that the particle concentration mode is influenced significantly by the outer gas direction and gas flow settings.Copyright © 2004 by ASME
Jeffery Chi Chuen Lo - One of the best experts on this subject based on the ideXlab platform.
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Coaxial Nozzle-assisted 3D Printing with in-situ UV LED Curing for Microfluidic Connectors
2019 20th International Conference on Electronic Packaging Technology(ICEPT), 2019Co-Authors: Qianwen Xu, Jeffery Chi Chuen LoAbstract:Mechanical interface with external tubing is the technical barrier to microfluidic commercialization. This paper presents an alternative approach to fabricate microfluidic connectors based on Coaxial Nozzle-assisted 3D printing with in-situ UV LED curing. An assembled Coaxial Nozzle was designed to enable co-fluid extrusion. The inner fluid is water (as the sacrificial channel) and the outer fluid is the UV curable adhesive. With the assistance of UV LED fixed at the neighborhood, cured hollow cylindrical connectors can be vertically printed on the substrate with matching holes. In order to master the Coaxial printing process, UV curing kinematics were characterized by a rheometer to predict the cross-linking state while co-flow behaviors were investigated to enable successful printing without collapse. The hollow cylindrical connector with an inner diameter at the order of 100 microns demonstrated its feasibility for microfluidic application.
Nesreen Ghaddar - One of the best experts on this subject based on the ideXlab platform.
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Low-mixing Coaxial Nozzle for effective personalized ventilation:
Indoor and Built Environment, 2013Co-Authors: Alain Makhoul, Kamel Ghali, Nesreen GhaddarAbstract:The aim of this work was to study the performance of a novel Coaxial Nozzle for personalized ventilation that can be used as an add-on to ceiling diffuser. The Coaxial Nozzle minimizes air entrainment between the central fresh air stream and the room air. It allows effective delivery of clean air to the breathing zone while the recirculated conditioned air is supplied to the space by the associated ceiling diffuser. Detailed 3-D Computational Fluid Dynamics (CFD) simulations were performed and numerical results on velocity, temperature, and CO2 concentration fields agreed well with experimentally measured values. The effect of the jet flow rate, temperature, and inclination angle on air quality at the breathing zone of the occupant was then investigated. The proposed Coaxial personalized ventilation achieved high air quality in the breathing zone demonstrated by a personal exposure effectiveness of 32% at fresh airflow rate of 10 L s−1 per person. It contributed also to the attainment of temperature diffe...
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Thermal comfort and energy performance of a low-mixing ceiling-mounted personalized ventilator system
Building and Environment, 2013Co-Authors: Alain Makhoul, Kamel Ghali, Nesreen GhaddarAbstract:This paper studies the performance of an integrated ceiling diffuser and personalized ventilator Coaxial Nozzle system to localize the air conditioning and fresh air needs around the occupants. The Coaxial Nozzle minimizes air entrainment between the fresh air stream and the room air and allows effective delivery of clean air. A detailed 3D CFD model is coupled to a bioheat model to improve prediction of the microenvironment conditions around the human and the associated local and overall thermal comfort. Subjective assessments were carried out with 10 human participants who were given the chance to undergo three different experimental runs individually and cast their votes about thermal comfort. The 30 samples obtained experimentally were within ±20% of the predicted numerical values especially for the upper body parts. Extensive simulations were performed to assess the effect of Nozzle supply temperature and flow rate on the performance of the cooling system and on occupant comfort. The localized air conditioning system reduced the energy consumption by up to 34% when compared with conventional mixing systems providing the same level of thermal comfort.