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Sample records for hvof particle velocity

  1. Effect of Spray Particle Velocity on Cavitation Erosion Resistance Characteristics of HVOF and HVAF Processed 86WC-10Co4Cr Hydro Turbine Coatings

    Science.gov (United States)

    Kumar, R. K.; Kamaraj, M.; Seetharamu, S.; Pramod, T.; Sampathkumaran, P.

    2016-08-01

    The hydro plants utilizing silt-laden water for power generation suffer from severe metal wastage due to particle-induced erosion and cavitation. High-velocity oxy-fuel process (HVOF)-based coatings is widely applied to improve the erosion life. The process parameters such as particle velocity, size, powder feed rate, temperature, affect their mechanical properties. The high-velocity air fuel (HVAF) technology, with higher particle velocities and lower spray temperatures, gives dense and substantially nonoxidized coating. In the present study, the cavitation resistance of 86WC-10Co4Cr-type HVOF coating processed at 680 m/s spray particle velocity was compared with HVAF coatings made at 895, 960, and 1010 m/s. The properties such as porosity, hardness, indentation toughness, and cavitation resistance were investigated. The surface damage morphology has been analyzed in SEM. The cohesion between different layers has been examined qualitatively through scratch depth measurements across the cross section. The HVAF coatings have shown a lower porosity, higher hardness, and superior cavitation resistance. Delamination, extensive cracking of the matrix interface, and detachment of the WC grains were observed in HVOF coating. The rate of metal loss is low in HVAF coatings implying that process parameters play a vital role in achieving improved cavitation resistance.

  2. Dynamic analysis of particle temperature in HVOF spray

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Based on "Gas Dynamics", "Thermodynamics", "Fluid Dynamics of Multiphase Systems" and other theories, dynamic analyses of the particle temperature in a HVOF spray have been accomplished. The relationship between the temperature of the particle and the heated time has been proposed in this paper. Meanwhile, the influences of the temperature of the hot gas of a HVOF gun and the particle size on the temperature of a particle for depositing have been discussed in detail. It is evident that the velocity of a particle heated in the hot gas of a HVOF gun is very high, and the maximum theoretic temperature of a particle heated is mostly equivalent to the temperature of the hot gas.

  3. A Comprehensive Review on Fluid Dynamics and Transport of Suspension/Liquid Droplets and Particles in High-Velocity Oxygen-Fuel (HVOF Thermal Spray

    Directory of Open Access Journals (Sweden)

    Mehdi Jadidi

    2015-10-01

    Full Text Available In thermal spraying processes, molten, semi-molten, or solid particles, which are sufficiently fast in a stream of gas, are deposited on a substrate. These particles can plastically deform while impacting on the substrate, which results in the formation of well-adhered and dense coatings. Clearly, particles in flight conditions, such as velocity, trajectory, temperature, and melting state, have enormous influence on the coating properties and should be well understood to control and improve the coating quality. The focus of this study is on the high velocity oxygen fuel (HVOF spraying and high velocity suspension flame spraying (HVSFS techniques, which are widely used in academia and industry to generate different types of coatings. Extensive numerical and experimental studies were carried out and are still in progress to estimate the particle in-flight behavior in thermal spray processes. In this review paper, the fundamental phenomena involved in the mentioned thermal spray techniques, such as shock diamonds, combustion, primary atomization, secondary atomization, etc., are discussed comprehensively. In addition, the basic aspects and emerging trends in simulation of thermal spray processes are reviewed. The numerical approaches such as Eulerian-Lagrangian and volume of fluid along with their advantages and disadvantages are explained in detail. Furthermore, this article provides a detailed review on simulation studies published to date.

  4. Production of Babbitt Coatings by High Velocity Oxygen Fuel (HVOF) Spraying

    Science.gov (United States)

    Nascimento, A. R. C.; Ettouil, F. B.; Moreau, C.; Savoie, S.; Schulz, R.

    2017-08-01

    This work presents HVOF as an alternative means to produce dense Babbitt coatings by thermal spray. A radial injection setup and low fuel flow rates were used to minimize heat transfer to the low melting point alloy. In-flight particle diagnostic systems were used to correlate spray parameters with the changes in particle velocity and thermal radiation intensity. The use of particles with larger diameters resulted in higher deposition efficiencies. It was shown that HVOF Babbitt coatings combine a dense structure and a fine distribution of intermetallic phases when compared to more traditional babbitting techniques.

  5. Effect of particle impact on residual stress development in HVOF sprayed coatings

    Science.gov (United States)

    Bansal, P.; Shipway, P. H.; Leen, S. B.

    2006-12-01

    The application of thick high-velocity oxyfuel (HVOF) coatings on metallic parts has been widely accepted as a solution to improve their wear properties. The adherence of these coatings to the substrate is strongly influenced by the residual stresses generated during the coating deposition process. In an HVOF spraying process, due to the relatively low processing temperature, significant peening stresses are generated during impact of molten and semimolten particles on the substrate. At present, finite-element (FE) models of residual stress generation for the HVOF process are not available due to the increased complexities in modeling the stresses generated due to the particle impact. In this work, an explicit FE analysis is carried out to study the effect of molten particle impingement using deposition of an HVOF sprayed copper coating on a copper substrate as an example system. The results from the analysis are subsequently used in a thermomechanical FE model to allow the development of the residual stresses in these coatings to be modeled.

  6. DYNAMIC ANALYSIS OF PARTICLE FLYING VELOCITY IN HIGH VELOCITY OXYGEN FUEL SPRAY

    Institute of Scientific and Technical Information of China (English)

    Wang Zhiping; Dong Zujue; Huo Shubin

    2000-01-01

    Based on gas dynamics,thermodynamics,fluid dynamics of multiphase systems and other theories,the dynamic analyses of the particle flying velocity in a high velocity oxygen fuel spray (HVOF) is accomplished.The relationships between the flying velocity of a particle and the flying time or flying length,particle size,hot gas velocity,and pressure or density of the gas are proposed.Meanwhile,the influences of the velocity and mass rate of flow of the flame gas of a HVOF gun,and particle size on the particle flying velocity are discussed in detail.The dynamic pressure concept is introduced to express the flow capacity of hot gas of a HVOF gun,and the relationship between the dynamic pressure of a HVOF gun and the velocity of a particle for depositing is presented.

  7. Effects of particle density on depositing properties of WC-1 7 Co by HVOF process

    Institute of Scientific and Technical Information of China (English)

    丁坤英; 王立君

    2014-01-01

    The in-flight and deposition properties ofthree types ofWC-1 7 Co powder with different particle densities during a high-velocity oxygen fuel (HVOF)thermal spray process were investigated.Three types ofpowder exhibited similar velocity upon impact on the substrate surface.The powder with the lower particle density exhibited a higher temperature upon impingement process,resulting in the generation ofa higher flattening ratio.Thus,the coating derived from the powder with the lower particle density possessed superior micro-hardness,porosity and surface roughness.However,the coating with the lowest particle density showed the poorest fracture toughness because ofthe generation ofthe largest amount ofamorphous phase.

  8. Influences of gas flow rates on melting of particles of HVOF sprayed CoCrW coating and coating properties

    Institute of Scientific and Technical Information of China (English)

    YANG Zhongyuan

    2004-01-01

    This paper discussed influences of flow rates of O2, C3H8, and compressed air on the melting degree of particles during HVOF (high velocity oxy-fuel) sprayed CoCrW coating. The O2 flow rate has the maximal effect on the melting of particles, the C3H8 flow rate has the second, and the compressed air flow rate has the minimal effect. The bond strength of the HVOF sprayed CoCrW coating is over 54 MPa. The porosity ratio of the HVOF sprayed CoCrW coating after optimization of gas flow rates is less than 2%. The average microhardness of the coating is up to HV0.1 545. The oxidation amount per unit area of the HVOF sprayed CoCrW coating increases with the holding time increasing at 800°C. In the same way,the oxidation amount of the coating increases as the temperature increases. Particularly, the oxidation of the coating drastically increases over 850°C.

  9. Manufacturing and Properties of High-Velocity Oxygen Fuel (HVOF)-Sprayed FeVCrC Coatings

    Science.gov (United States)

    Sassatelli, Paolo; Bolelli, Giovanni; Lusvarghi, Luca; Manfredini, Tiziano; Rigon, Rinaldo

    2016-10-01

    This paper studies the microstructure, sliding wear behavior and corrosion resistance of high-velocity oxygen fuel (HVOF)-sprayed FeVCrC-based coatings. Various process parameters were tested to evaluate their effects on the coating properties, which were also compared to those of HVOF-sprayed NiCrBSi and Stellite-6 coatings. The Fe alloy coatings are composed of flattened splats, originating from molten droplets and consisting of a super-saturated solid solution, together with rounded particles, coming from partially unmolten material and containing V- and Fe-based carbide precipitates. All process parameters, apart from "extreme" settings with excess comburent in the flame, produce dense coatings, indicating that the feedstock powder is quite easily processable by HVOF. These coatings, with a microhardness of 650-750 HV0.3, exhibit wear rates of ≈2 × 10-6 mm3/(Nm) in ball-on-disk tests against sintered Al2O3 spheres. They perform far better than the reference coatings, and better than other Fe- and Ni-based alloy coatings tested in previous research. On the other hand, the corrosion resistance of the coating material (tested by electrochemical polarization in 0.1 M HCl solution) is quite low. Even in the absence of interconnected porosity, this results in extensive, selective damage to the Fe-based matrix. This coating material is therefore unadvisable for severely corrosive environments.

  10. HVOF Spraying of Fe-Based MMC Coatings with In Situ Formation of Hard Particles by Hot Isostatic Pressing

    Science.gov (United States)

    Röttger, A.; Weber, S. L.; Theisen, W.; Rajasekaran, B.; Vaßen, R.

    2012-03-01

    Thick (2-3 mm) Fe-base coatings with admixed ferrotitanium (Fe30Ti70) were applied to austenitic steel by a high-velocity oxy-fuel process (HVOF). Hot-isostatic pressing (HIP) was carried out to the decrease porosity and to increase the material strength, wear resistance, and adhesive bond strength of the deposited coating to the substrate material. SEM and XRD investigations confirmed the formation of hard titanium carbide (TiC) particles during HIP treatment as a result of strong carbon diffusion out of the metal matrix and into the Fe30Ti70 particles. The mechanical and wear properties of the densified coatings were investigated by means of shear tests, hardness measurements, and abrasive wear tests. A comparison of the coatings in the as-sprayed and the HIPed state showed a large increase in the wear resistance due to in situ TiC formation.

  11. Physicochemical Characteristics of Dust Particles in HVOF Spraying and Occupational Hazards: Case Study in a Chinese Company

    Science.gov (United States)

    Huang, Haihong; Li, Haijun; Li, Xinyu

    2016-06-01

    Dust particles generated in thermal spray process can cause serious health problems to the workers. Dust particles generated in high velocity oxy-fuel (HVOF) spraying WC-Co coatings were characterized in terms of mass concentrations, particle size distribution, micro morphologies, and composition. Results show that the highest instantaneous exposure concentration of dust particles in the investigated thermal spray workshop is 140 mg/m3 and the time-weighted average concentration is 34.2 mg/m3, which are approximately 8 and 4 times higher than the occupational exposure limits in China, respectively. The large dust particles above 10 μm in size present a unique morphology of polygonal or irregular block of crushed powder, and smaller dust particles mainly exist in the form of irregular or flocculent agglomerates. Some heavy metals, such as chromium, cobalt, and nickel, are also found in the air of the workshop and their concentrations are higher than the limits. Potential occupational hazards of the dust particles in the thermal spray process are further analyzed based on their characteristics and the workers' exposure to the nanoparticles is assessed using a control banding tool.

  12. Application of High-Velocity Oxygen-Fuel (HVOF Spraying to the Fabrication of Yb-Silicate Environmental Barrier Coatings

    Directory of Open Access Journals (Sweden)

    Emine Bakan

    2017-04-01

    Full Text Available From the literature, it is known that due to their glass formation tendency, it is not possible to deposit fully-crystalline silicate coatings when the conventional atmospheric plasma spraying (APS process is employed. In APS, rapid quenching of the sprayed material on the substrate facilitates the amorphous deposit formation, which shrinks when exposed to heat and forms pores and/or cracks. This paper explores the feasibility of using a high-velocity oxygen-fuel (HVOF process for the cost-effective fabrication of dense, stoichiometric, and crystalline Yb2Si2O7 environmental barrier coatings. We report our findings on the HVOF process optimization and its resultant influence on the microstructure development and crystallinity of the Yb2Si2O7 coatings. The results reveal that partially crystalline, dense, and vertical crack-free EBCs can be produced by the HVOF technique. However, the furnace thermal cycling results revealed that the bonding of the Yb2Si2O7 layer to the Silicon bond coat needs to be improved.

  13. The Effects of Particle Size on the Surface Properties of an HVOF Coating of WC-Co

    Energy Technology Data Exchange (ETDEWEB)

    Cho, Tong Yul; Yoon, Jae Hong; Yoon, Sang Hwan; Joo, Yun Kon [Changwon National University, Changwon (Korea, Republic of); Choi, Won Ho; Son, Young Bok [Xinix Metallizing Co., Ltd, Gyungnam (Korea, Republic of)

    2017-04-15

    The effects of particle size on the surface properties of HVOF spray coating were studied to improve of the durability of metal components. Micro and nano sized WC-12Co powders were coated on the surface of Inconel718, and the effects of particle size on surface properties were studied. Surface hardness was reduced when the particle sizes of the powder were decreased, because the larger specific surface area of the smaller particles caused greater heat absorption and decomposition of the hard WC to less hard W{sub 2}C and graphite. Porosity was increased by decreasing the particle size, because the larger specific surface area of the smaller particles caused a greater decomposition of WC to W{sub 2}C and free carbon. The free carbon formed carbon oxide gases which created the porous surface. The friction coefficient was reduced by decreasing the particle size because the larger specific surface area of the smaller particles produced more free carbon free Co and Co oxide which acted as solid lubricants. The friction coefficient increased when the surface temperature was increased from 25 to 500 ℃, due to local cold welding. To improve the durability of metal mechanical components, WC-Co coating with the proper particle size is recommended.

  14. Tribo-Mechanical Properties of HVOF Deposited Fe3Al Coatings Reinforced with TiB2 Particles for Wear-Resistant Applications

    Directory of Open Access Journals (Sweden)

    Mahdi Amiriyan

    2016-02-01

    Full Text Available This study reveals the effect of TiB2 particles on the mechanical and tribological properties of Fe3Al-TiB2 composite coatings against an alumina counterpart. The feedstock was produced by milling Fe3Al and TiB2 powders in a high energy ball mill. The high-velocity oxy-fuel (HVOF technique was used to deposit the feedstock powder on a steel substrate. The effect of TiB2 addition on mechanical properties and dry sliding wear rates of the coatings at sliding speeds ranging from 0.04 to 0.8 m·s−1 and loads of 3, 5 and 7 N was studied. Coatings made from unreinforced Fe3Al exhibited a relatively high wear rate. The Vickers hardness, elastic modulus and wear resistance of the coatings increased with increasing TiB2 content in the Fe3Al matrix. The wear mechanisms strongly depended on the sliding speed and the presence of TiB2 particles but were less dependent on the applied load.

  15. Properties of Plasma and HVOF Sprayed Coatings

    Directory of Open Access Journals (Sweden)

    Wojciech Żórawski

    2012-11-01

    Full Text Available The work compares the properties of plasma and HVOF thermally sprayed coatings obtained by blending the NiCrBSi and Fe2O3 powders. The deposition was performed by means of the Plancer PN-120 and the Diamond Jet guns for plasma spraying and HVOF spraying respectively. The SEM (EDS method was employed to study the microstructure of the produced coatings. Although the blended powders differ in particle size, shape, and distribution, it is possible to obtain composite coatings with an NiCrBSi matrix containing iron oxides. Except for a different microstructure, plasma and HVOF coatings have a different phase composition, which was examined using the Bruker D-8 Advance diffractometer. Studies of the coatings wear and scuffing resistance showed that an optimal content of Fe2O3 is about 26 % for plasma sprayed coatings and 22.5 % for HVOF deposited coatings.

  16. Numerical Simulation on Supersonic Flow in High-Velocity Oxy-Fuel Thermal Spray Gun

    Institute of Scientific and Technical Information of China (English)

    Hiroshi KATANODA; Hideki YAMAMOTO; Kazuyasu MATSUO

    2006-01-01

    This paper analyzes the behaviour of coating particles as well as the gas flow both inside and outside of the High-Velocity Oxy-Fuel (HVOF) thermal spray gun by using a quasi-one-dimensional analysis and a numerical simulation. The HVOF gun in the present analysis is an axially symmetric convergent-divergent nozzle with the design Mach number of 2.0. From the present analysis, the distributions of velocity and temperature of the coating particles flying inside and outside of the HVOF gun are predicted. The velocity and temperature of the coating particles at the exit of the gun calculated by the present method agree well with the previous experimental results. Therefore, the present method of calculation is considered to be useful for predicting the HVOF gas and particle flows.

  17. Evaluation of HVOF coatings

    Directory of Open Access Journals (Sweden)

    Mariana Landová

    2016-07-01

    Full Text Available Attention in this paper is devoted to the evaluation of wear coatings deposited using HVOF technology (high velocity oxy-fuel. There were evaluated three types of coatings based on WC-Co (next only 1343, WC-Co-Cr (next only 1350 and Cr3C2-25NiCr (next only 1375. There was assessed adherence of coatings, micro hardness, porosity and the tribological properties of erosive, abrasive, adhesive and wear resistance of coatings in terms of cyclic thermal load. Thanks to wide variety of suitable materials and their combinations, the area of utilization thermally sprayed coatings is very broad. It is possible to deposit coatings of various materials from pure metals to special alloys. The best results in the evaluated properties were achieved at the coating with the label 1375.

  18. Computational analysis of a three-dimensional High-Velocity Oxygen-Fuel (HVOF) Thermal Spray torch

    Energy Technology Data Exchange (ETDEWEB)

    Hassan, B.; Lopez, A.R.; Oberkampf, W.L.

    1995-07-01

    An analysis of a High-Velocity Oxygen-Fuel Thermal Spray torch is presented using computational fluid dynamics (CFD). Three-dimensional CFD results are presented for a curved aircap used for coating interior surfaces such as engine cylinder bores. The device analyzed is similar to the Metco Diamond Jet Rotating Wire torch, but wire feed is not simulated. To the authors` knowledge, these are the first published 3-D results of a thermal spray device. The feed gases are injected through an axisymmetric nozzle into the curved aircap. Argon is injected through the center of the nozzle. Pre-mixed propylene and oxygen are introduced from an annulus in the nozzle, while cooling air is injected between the nozzle and the interior wall of the aircap. The combustion process is modeled assuming instantaneous chemistry. A standard, two-equation, K-{var_epsilon} turbulence model is employed for the turbulent flow field. An implicit, iterative, finite volume numerical technique is used to solve the coupled conservation of mass, momentum, and energy equations for the gas in a sequential manner. Flow fields inside and outside the aircap are presented and discussed.

  19. Transport velocities of coal and sand particles

    Energy Technology Data Exchange (ETDEWEB)

    Adanez, J. (Inst. de Carboquimica, Zaragoza (Spain)); Diego, L.F. de (Inst. de Carboquimica, Zaragoza (Spain)); Gayan, P. (Inst. de Carboquimica, Zaragoza (Spain))

    1993-10-01

    Transport velocities of narrow cut sizes of coarse particles of sand and coal were determined at room temperature and atmospheric pressure. These velocities were obtained by four different methods previously utilized by other authors with fine particles. The four methods tested gave good predictions of the transport velocities. The method based on the measurement of the time required for all the solids to leave the bed without feeding in any fresh solid is specially interesting because of its rapidity and simplicity. The determined transport velocities were strongly dependent on the solid particle size and density. The experimental values were fitted to an equation which fitted both the experimental results obtained in this work and other published results obtained with fine particles. (orig.)

  20. Characterization and High-Temperature Erosion Behaviour of HVOF Thermal Spray Cermet Coatings

    Science.gov (United States)

    Kumar, Pardeep; Sidhu, Buta Singh

    2016-01-01

    High-velocity oxygen fuel (HVOF) thermal spray, carbide-cermet-based coatings are usually employed in high-temperature erosive and erosive-corrosive environments. Extensive literature is available on high-temperature erosion performance of HVOF coatings under moderate to low particle flux and velocities for application in boiler tubes. This research work presents the characterization and high-temperature erosion behaviour of Cr3C2-25NiCr and WC-10Co-4Cr HVOF-sprayed coatings. Coatings were formulated on the substrate steel of type AISI 304, commonly used for the fabrication of pulverized coal burner nozzles (PCBN). Erosion testing was carried out in high-temperature air-jet erosion tester after simulating the conditions akin to that prevailing in PCBN in the boiler furnace. The coatings were tested for erosion behaviour at different angles and temperatures by freezing other test parameters. Brittle erosion behaviour was depicted in erosion testing, and the coatings couldn't restrain the erodent attacks to protect the substrate. High particle velocity and high particle flux were attributed to be the reasons of extensive erosive weight loss of the coatings. The surface morphology of the eroded specimens was analysed from back-scattered electron images to depict the probable mechanism of material removal. The coatings were characterized with optical microscopy, SEM-EDS analysis, XRD analysis, micro-hardness testing, porosity measurements, surface roughness testing and bond strength testing. The work was undertaken to investigate the performance of the selected coatings in highly erosive environment, so as to envisage their application in PCBNs for protection against material degradation. The coatings could only sustain in oblique impact erosion at room temperature and depleted fully under all other conditions.

  1. A novel two dimensional particle velocity sensor

    NARCIS (Netherlands)

    Pjetri, Olti; Wiegerink, Remco J.; Lammerink, Theo S.; Krijnen, Gijs J.

    2013-01-01

    In this paper we present a two wire, two-dimensional particle velocity sensor. The miniature sensor of size 1.0x2.5x0.525 mm, consisting of only two crossed wires, shows excellent directional sensitivity in both directions, thus requiring no directivity calibration, and is relatively easy to fabrica

  2. Tomographic Particle Localization and Velocity Measurement

    Science.gov (United States)

    Kirner, S.; Forster, G.; Schein, J.

    2015-01-01

    Wire arc spraying is one of the most common and elementary thermal spray processes. Due to its easy handling, high deposition rate, and relative low process costs, it is a frequently used coating technology for the production of wear and corrosion resistant coatings. In order to produce reliable and reproducible coatings, it is necessary to be able to control the coating process. This can be achieved by analyzing the parameters of the particles deposited. Essential for the coating quality are, for example, the velocity, the size, and the temperature of the particles. In this work, an innovative diagnostic for particle velocity and location determination is presented. By the use of several synchronized CMOS-Cameras positioned around the particle jet, a series of images from different directions is simultaneously taken. The images contain the information that is necessary to calculate the 3D-location-vector of the particles and finally with the help of the exposure time the trajectory can be determined. In this work, the experimental setup of the tomographic diagnostic is presented, the mathematical method of the reconstruction is explained, and first measured velocity distributions are shown.

  3. Electrophoresis of particles with Navier velocity slip.

    Science.gov (United States)

    Park, Hung Mok

    2013-03-01

    In the present investigation, it is found that the electrophoretic mobility of hydrophobic particles is affected not only by the zeta potential but also by the velocity slip at the particle surface. From a physicochemical viewpoint, zeta potential represents the surface charge properties and the slip coefficient indicates the hydrophobicity of the particle surface. Thus, it is necessary to separate the contribution of zeta potential from that of slip coefficient to the particle mobility, since zeta potential can be changed by varying the bulk ionic concentration while the slip coefficient can be modified by adjusting surfactant concentration. In the present investigation, a method is devised that allows a simultaneous estimation of zeta potential and slip coefficient of micro and nanoparticles using measurements of electrophoretic mobility at various bulk ionic concentrations. Employing a nonlinear curve-fitting technique and an analytic solution of electrophoresis for a particle with velocity slip, the present technique predicts both zeta potential and slip coefficient simultaneously with reasonable accuracy using the measured values of electrophoretic mobility at various bulk ionic concentrations.

  4. Investigation on Interface Structure and Wear-resistant Properties of HVOF Sprayed Carbides Coating onto Copper Substrate

    Institute of Scientific and Technical Information of China (English)

    HOU Li-feng; ZHANG Heng-jin; WEI Ying-hui; YAN Kai; HU Lan-qing; XU Bing-she

    2004-01-01

    In this paper, we deposited carbides on copper substrate by High velocity oxy-fuel (HVOF) spraying. The structure of the coating and microstructure of the substrate-coating interface have been investigated by means of scanning electron microscope (SEM) and transmission electron microscopy (TEM). We observed the worn surface of the coating and investigated the wear mechanism. The results show that the microstructure of the interface between HVOF sprayed coating and substrate which consists of the amorphous layers, nanocrystalls in the coating and dislocation cells in copper substrate,etc. is complex. The amorphous layers are formed from heated adhesion after rapidly cooling, while the nanocrystalls come from the fragmentation of half-molten carbides. At the same time we found that the wear-resistant properties of the WC-Co coating is better than that of Cr3C2-NiCr coating at room temperature. The early wear-resistance of the HVOF sprayed coating is poor because of the roughness of its surface or bad bond of hard composite particles. The high velocity of molten droplets is propitious to fill up the interspaces between carbides, so as to make the coating more compact and reduce its porosities, thus the wear-resistance of carbides coatings is improved.

  5. Investigation on Interface Structure and Wear-resistant Properties of HVOF Sprayed Carbides Coating onto Copper Substrate

    Institute of Scientific and Technical Information of China (English)

    HOULi-feng; ZHANGHeng-jin; WEIYing-hui; YANKai; HULan-qing; XUBing-she

    2004-01-01

    In this paper, we deposited carbides on copper substrate by High velocity oxy-fuel (HVOF) spraying. The structure of the coating and microstructure of the substrate-coating interface have been investigated by means of scanning electron microscope (SEM) and transmission electron microscopy (TEM). We observed the worn surface of the coating and investigated the wear mechanism. The results show that the microstructure of the interface between HVOF sprayed coating and substrate which consists of the amorphous layers, nanocrystalls in the coating and dislocation cells in copper substrate, etc. is complex. The amorphous layers are formed from heated adhesion after rapidly cooling, while the nanocrystalls come from the fragmentation of half-molten carbides. At the same time we found that the wear-resistant properties of the WC-Co coating is better than that of Cr3C2-NiCr coating at room temperature. The early wear-resistance of the HVOF sprayed coating is poor because of the roughness of its surface or bad bond of hard composite particles. The high velocity of molten droplets is propitious to fill up the interspaces between carbides, so as to make the coating more compact and reduce its porosities, thus the wear-resistance of carbides coatings is improved.

  6. Behavior of HVOF WC-10Co4Cr Coatings with Different Carbide Size in Fine and Coarse Particle Abrasion

    Science.gov (United States)

    Ghabchi, Arash; Varis, Tommi; Turunen, Erja; Suhonen, Tomi; Liu, Xuwen; Hannula, S.-P.

    2010-01-01

    A modified ASTM G 65 rubber wheel test was employed in wet and dry conditions using 220 nm titania particles and 368 μm sand particles, respectively. Both tests were conducted on WC-CoCr coatings produced with two powders with different carbide grain sizes (conventional and sub-micron) to address the effect of carbide size and abrasive medium characteristics on the wear performance. The same spot before and after the wet abrasion wear testing was analyzed in detail using SEM to visualize wear mechanisms. It was shown that the wear mechanism depends on the relative size of the carbide and abrasive particles. Wear mechanisms in dry sand abrasion were studied by analyzing the single scratches formed by individual abrasive particles. Interaction of surface open porosity with moving abrasive particles causes formation of single scratches. By tailoring the carbide size, the wear performance can be improved.

  7. Development and application of DZ9000E portable HVOF system

    Institute of Scientific and Technical Information of China (English)

    Wang Ruijun; Tian Hehong; Lü Yufen; Zhang Tianjian

    2008-01-01

    A new type of DZ9OOOE Oxygen Gaseous HVOF system (GHVOF) is developed which can reduce the cost of coatings and increase the in-situ removability to adapt various working conditions. The whole system is economical, which enables the system to meet the requirement of spraying medium or low cost High Velocity Oxy-Fuel (HVOF) coatings for medium and small job shops. The deposited cermets coatings by the DZ9OOOE system have good performance with average microhardness Hvo.2 of more than 1 000 and the bond strength between coating and substrate of greater than 50 Mpa.

  8. A Study of Cr3C2-Based HVOF- and HVAF-Sprayed Coatings: Microstructure and Carbide Retention

    Science.gov (United States)

    Matikainen, V.; Bolelli, G.; Koivuluoto, H.; Honkanen, M.; Vippola, M.; Lusvarghi, L.; Vuoristo, P.

    2017-08-01

    The research on high-velocity air-fuel (HVAF)-sprayed Cr3C2-based materials has mostly focused on conventional Cr3C2-25NiCr composition. In this paper, two alternative compositions (Cr3C2-50NiCrMoNb and Cr3C2-37WC-18NiCoCrFe) were sprayed with high-velocity oxy-fuel (HVOF) and HVAF spray processes to evaluate the material behavior during spraying and to provide characterization of the microstructures and mechanical properties of the coatings. For comparison, coatings from the Cr3C2-25NiCr composition were sprayed with both processes. Spray diagnostics were carried out to obtain average particle velocity and temperature for each material and process combinations. The measured average in-flight particle data were 1800 °C and 700 m/s for HVOF process, and 1450 °C and 900 m/s for HVAF process. Characterization of the coating microstructures was carried out by scanning electron microscopy and X-ray diffraction. In addition, the carbon content of the feedstock powders and sprayed coatings was measured with carbon analyzer. The results show that carbide rebounding or selective deposition of particles with higher metal matrix content is the dominating reason for carbide loss during HVAF spraying, while carbide dissolution is an additional source for the HVOF spraying. Higher particle velocities and controlled temperature measured for the HVAF process produced dense coatings with improved toughness and more homogenous coating structure.

  9. High Power Diode Laser-Treated HP-HVOF and Twin Wire Arc-Sprayed Coatings for Fossil Fuel Power Plants

    Science.gov (United States)

    Mann, B. S.

    2013-08-01

    This article deals with high power diode laser (HPDL) surface modification of twin wire arc-sprayed (TWAS) and high pressure high velocity oxy-fuel (HP-HVOF) coatings to combat solid particle erosion occurring in fossil fuel power plants. To overcome solid particle impact wear above 673 K, Cr3C2-NiCr-, Cr3C2-CoNiCrAlY-, and WC-CrC-Ni-based HVOF coatings are used. WC-CoCr-based HVOF coatings are generally used below 673 K. Twin wire arc (TWA) spraying of Tafa 140 MXC and SHS 7170 cored wires is used for a wide range of applications for a temperature up to 1073 K. Laser surface modification of high chromium stainless steels for steam valve components and LPST blades is carried out regularly. TWA spraying using SHS 7170 cored wire, HP-HVOF coating using WC-CoCr powder, Ti6Al4V alloy, and high chromium stainless steels (X20Cr13, AISI 410, X10CrNiMoV1222, 13Cr4Ni, 17Cr4Ni) were selected in the present study. Using robotically controlled parameters, HPDL surface treatments of TWAS-coated high strength X10CrNiMoV1222 stainless steel and HP-HVOF-coated AISI 410 stainless steel samples were carried out and these were compared with HPDL-treated high chromium stainless steels and titanium alloy for high energy particle impact wear (HEPIW) resistance. The HPDL surface treatment of the coatings has improved the HEPIW resistance manifold. The improvement in HPDL-treated stainless steels and titanium alloys is marginal and it is not comparable with that of HPDL-treated coatings. These coatings were also compared with "as-sprayed" coatings for fracture toughness, microhardness, microstructure, and phase analyses. The HEPIW resistance has a strong relationship with the product of fracture toughness and microhardness of the HPDL-treated HP-HVOF and TWAS SHS 7170 coatings. This development opens up a possibility of using HPDL surface treatments in specialized areas where the problem of HEPIW is very severe. The HEPIW resistance of HPDL-treated high chromium stainless steels and

  10. Design Optimization of Liquid Fueled High Velocity Oxy- Fuel Thermal Spraying Technique for Durable Coating for Fossil Power Systems

    Energy Technology Data Exchange (ETDEWEB)

    Choudhuri, Ahsan [Univ. of Texas, El Paso, TX (United States); Love, Norman [Univ. of Texas, El Paso, TX (United States)

    2016-11-04

    High-velocity oxy–fuel (HVOF) thermal spraying was developed in 1930 and has been commercially available for twenty-five years. HVOF thermal spraying has several benefits over the more conventional plasma spray technique including a faster deposition rate which leads to quicker turn-around, with more durable coatings and higher bond strength, hardness and wear resistance due to a homogeneous distribution of the sprayed particles. HVOF thermal spraying is frequently used in engineering to deposit cermets, metallic alloys, composites and polymers, to enhance product life and performance. HVOF thermal spraying system is a highly promising technique for applying durable coatings on structural materials for corrosive and high temperature environments in advanced ultra-supercritical coal- fired (AUSC) boilers, steam turbines and gas turbines. HVOF thermal spraying is the preferred method for producing coatings with low porosity and high adhesion. HVOF thermal spray process has been shown to be one of the most efficient techniques to deposit high performance coatings at moderate cost. Variables affecting the deposit formation and coating properties include hardware characteristics such as nozzle geometry and spraying distance and process parameters such as equivalence ratio, gas flow density, and powder feedstock. In the spray process, the powder particles experience very high speeds combined with fast heating to the powder material melting point or above. This high temperature causes evaporation of the powder, dissolution, and phase transformations. Due to the complex nature of the HVOF technique, the control and optimization of the process is difficult. In general, good coating quality with suitable properties and required performance for specific applications is the goal in producing thermal spray coatings. In order to reach this goal, a deeper understanding of the spray process as a whole is needed. Although many researchers studied commercial HVOF thermal spray

  11. Microstructural Characteristics and Tribological Behavior of HVOF-Sprayed Novel Fe-Based Alloy Coatings

    Directory of Open Access Journals (Sweden)

    Andrea Milanti

    2014-01-01

    Full Text Available Thermally-sprayed Fe-based coatings have shown their potential for use in wear applications due to their good tribological properties. In addition, these kinds of coatings have other advantages, e.g., cost efficiency and positive environmental aspects. In this study, the microstructural details and tribological performances of Fe-based coatings (Fe-Cr-Ni-B-C and Fe-Cr-Ni-B-Mo-C manufactured by High Velocity Oxygen Fuel (HVOF thermal spray process are evaluated. Traditional Ni-based (Ni-Cr-Fe-Si-B-C and hard-metal (WC-CoCr coatings were chosen as references. Microstructural investigation (field-emission scanning electron microscope FESEM and X-Ray diffractometry XRD reveals a high density and low oxide content for HVOF Fe-based coatings. Particle melting and rapid solidification resulted in a metastable austenitic phase with precipitates of mixed carbides and borides of chromium and iron which lead to remarkably high nanohardness. Tribological performances were evaluated by means of the ball on-disk dry sliding wear test, the rubber-wheel dry particle abrasion test, and the cavitation erosion wear test. A higher wear resistance validates Fe-based coatings as a future alternative to the more expensive and less environmentally friendly Ni-based alloys.

  12. Experimental investigation of particle velocity distributions in windblown sand movement

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    With the PDPA(Phase Doppler Particle Analyzer) measurement technology,the probability distributions of particle impact and lift-off velocities on bed surface and the particle velocity distributions at different heights are detected in a wind tunnel. The results show that the probability distribution of impact and lift-off velocities of sand grains can be expressed by a log-normal function,and that of impact and lift-off angles complies with an exponential function. The mean impact angle is between 28° and 39°,and the mean lift-off angle ranges from 30° to 44°. The mean lift-off velocity is 0.81-0.9 times the mean impact velocity. The proportion of backward-impacting particles is 0.05-0.11,and that of backward-entrained particles ranges from 0.04 to 0.13. The probability distribution of particle horizontal velocity at 4 mm height is positive skew,the horizontal velocity of particles at 20 mm height varies widely,and the variation of the particle horizontal velocity at 80 mm height is less than that at 20 mm height. The probability distribution of particle vertical velocity at different heights can be described as a normal function.

  13. Wear and impact resistance of HVOF sprayedceramic matrix composites coating

    Science.gov (United States)

    Prawara, B.; Martides, E.; Priyono, B.; Ardy, H.; Rikardo, N.

    2016-02-01

    Ceramic coating has the mechanical properties of high hardness and it is well known for application on wear resistance, but on the other hand the resistance to impact load is low. Therefore its use is limited to applications that have no impact loading. The aim of this research was to obtain ceramic-metallic composite coating which has improved impact resistance compared to conventional ceramic coating. The high impact resistance of ceramic-metallic composite coating is obtained from dispersed metallic alloy phase in ceramic matrix. Ceramic Matrix Composites (CMC) powder with chrome carbide (Cr3C2) base and ceramic-metal NiAl-Al2O3 with various particle sizes as reinforced particle was deposited on mild steel substrate with High Velocity Oxygen Fuel (HVOF) thermal spray coating. Repeated impact test showed that reinforced metallic phase size influenced impact resistance of CMC coating. The ability of CMC coating to absorb impact energy has improved eight times and ten times compared with original Cr3C2 and hard chrome plating respectively. On the other hand the high temperature corrosion resistance of CMC coating showed up to 31 cycles of heating at 800°C and water quenching cooling.

  14. Relationships Between Process Parameters, Microstructure, and Adhesion Strength of HVOF Sprayed IN718 Coatings

    Science.gov (United States)

    Lyphout, Christophe; Nylén, Per; Östergren, Lars

    2011-01-01

    Fundamental understanding of relationships between process parameters, particle in-flight characteristics, and adhesion strength of HVOF sprayed coatings is important to achieve the high coating adhesion that is needed in aeronautic repair applications. In this study, statistical Design of Experiments (DoE) was used to identify the most important process parameters that influence adhesion strength of IN718 coatings sprayed on IN718 substrates. Special attention was given to the parameters combustion ratio, total gas mass flow, stand-off distance and external cooling, since these parameters were assumed to have a significant influence on particle temperature and velocity. Relationships between these parameters and coating microstructure were evaluated to fundamentally understand the relationships between process parameters and adhesion strength.

  15. Corrosion behavior of NiCrBSi coatings deposited by HVOF spraying

    Institute of Scientific and Technical Information of China (English)

    赵卫民; 王勇; 吴开源; 薛锦

    2003-01-01

    The corrosion resistance of NiCrBSi coating deposited on steel substrate by HVOF was examined using electrochemical tests and immersion tests so as to offer an experimental basis to expand a promising applied field of HVOF in aqueous medium, comparing with those of coatings deposited by oxyacetylene flame spraying and flame cladding. The results show that the general corrosion rate of HVOF sprayed coatings is quite bigger than that of clad coatings, but it is less sensitive to local corrosion. There is less and smaller porosity in the coatings deposited by HVOF than that in flame sprayed coatings. The effects of porosity on the corrosion current density was indistinctive, but the existence of large amount of defects in the coatings damaged the cohesion of the coatings, causing the metallic particles drop off from the coatings under the influence of corrosive medium. Improving the quality and reducing the porosity of coatings is the key to get the coatings with high corrosion resistance.

  16. Theoretical Particle Limiting Velocity From The Bicubic Equation: Neutrino Example

    CERN Document Server

    Soln, Josip

    2014-01-01

    There has been a lot of interest in measuring the velocities of massive elementary particles, particularly the neutrinos. Some neutrino experi- ments at first observed superluminal neutrinos, thus violating the velocity of light c as a limiting velocity. But, after eliminating some mistakes, such as, for the OPERA experiments plugging the cable correctly and calibrat- ing the clock correctly, the measured neutrino velocity complied with c. Pursuing the theoretical side of particle limiting velocities, here directly from the special relativistic kinematics, in which all physical quantities are in the overall mathematical consistency with each other, one treats formally the velocity of light c as yet to be deduced particle limiting ve- locity, and derives the bicubic equation for the particle limiting velocity in the arbitrary reference frame.

  17. HVOF sprayed WC-CoCr coatings on aluminum: tensile and tribological properties

    Science.gov (United States)

    Koutsomichalis, A.; Vardavoulias, M.; Vaxevanidis, N.

    2017-02-01

    This paper provides a comprehensive assessment of the tensile and sliding wear behaviour of WC-10Co4Cr agglomerated and sintered powder deposited on aluminum by Hyper Velocity Oxy-Fuel (HVOF) process. Microstructural analysis (SEM) identified grains of tungsten carbide (WC) in the metal matrix of the cobalt-chromium (Co-Cr). A transformation of the WC in the W2C phase was observed and decomposition of WC in the metal matrix. The HVOF WC-Co-Cr coating was found to decrease tensile strength of the aluminum substrate. Transverse cracks were observed to initiate on the coating surface, increasing rapidly with the increase in tensile strain and stopped on the coating-substrate interface causing decohesion. Tribological properties were examined using the pin-on-disk method under various loads. The friction coefficient rose abruptly at the start-up phase and stabilized at almost the same sliding distance independently of the applied load. Both the friction coefficient and the wear volume were found to increase with increasing applied load. Study of the wear mechanisms revealed surface micro-cracking and fragmentation of flattened coating layers with subsequent gradual pull out of the carbide particles.

  18. Result of search for low velocity exotic particles

    Institute of Scientific and Technical Information of China (English)

    MA Xin-Hua; DING Lin-Kai; GUO Ya-Nan; HE Zuo-Xiu; HUO An-Xiang; JING Cai-Liu; KUANG Hao-Huai; MA Yu-Qian; QING Cheng-Rui; SHEN Chang-Quan; YU Zhong-Qiang; ZHANG Chao; ZHU Qing-Qi

    2009-01-01

    The L3+C experiment, taking advantage of the L3 muon magnetic spectrometer, measured the spatial tracks of charged cosmic ray particles to obtain rigidity as well as velocity. One possible low velocity exotic particle is observed. The existing uncertainties are discussed, and the flux upper limit of the low velocity exotic particles from this observation is deduced based on the assumption of a null observation. The result is 6.2×10-10 cm-2.s-1.sr-1 at 90% confidence level in the velocity range from 0.04c to 0.5c.

  19. Analytical Equation for Estimating Terminal Velocities of Spheroidal Particles

    Energy Technology Data Exchange (ETDEWEB)

    Marshall, Douglas W.

    2007-06-01

    An analytical method for estimating the terminal velocities of spheroidal particles in a fluid medium has been derived form a graphical approach proposed by Haider and Levenspiel. Using an analytical equation enables the researcher to calculate the terminal velocities without resorting to graphical interpolations, thereby reducing errors and enabling terminal velocities to be estimated in automated calculations.

  20. Characteristics of MCrAlY coatings sprayed by high velocity oxygen-fuel spraying system

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Y.; Saitoh, M.; Tamura, M.

    2000-01-01

    High velocity oxygen-fuel (HVOF) spraying system in open air has been established for producing the coatings that are extremely clean and dense. It is thought that the HVOF sprayed MCrAlY (M is Fe, Ni and/or Co) coatings can be applied to provide resistance against oxidation and corrosion to the hot parts of gas turbines. Also, it is well known that the thicker coating can be sprayed in comparison with any other thermal spraying systems due to improved residual stresses. However, thermal and mechanical properties of HVOF coatings have not been clarified. Especially, the characteristics of residual stress, that are the most important property from the view point of production technique, have not been made clear. In this paper, the mechanical properties of HVOF sprayed MCrAlY coatings were measured in both the case of as-sprayed and heat-treated coatings in comparison with a vacuum plasma sprayed MCrAlY coatings. It was confirmed that the mechanical properties of HVOF sprayed MCrAlY coatings could be improved by a diffusion heat treatment to equate the vacuum plasma sprayed MCrAlY coatings. Also, the residual stress characteristics were analyzed using a deflection measurement technique and a X-ray technique. The residual stress of HVOF coating was reduced by the shot-peening effect comparable to that of a plasma spray system in open air. This phenomena could be explained by the reason that the HVOF sprayed MCrAlY coating was built up by poorly melted particles.

  1. Particle Velocity Fluctuations in Steady State Sedimentation: Stratification Controlled Correlations

    CERN Document Server

    Segrè, P N

    2007-01-01

    The structure and dynamics of steady state sedimentation of semi-concentrated ($\\phi=0.10$) monodisperse spheres are studied in liquid fluidized beds. Laser turbidity and particle imaging methods are used to measure the particle velocity fluctuations and the steady state concentration profiles. Using a wide range of particle and system sizes, we find that the measured gradients $\

  2. Near-wall velocity measurements by Particle-Shadow-Tracking

    CERN Document Server

    Lancien, Pierre; Métivier, François; 10.1007/s00348-007-0260-z

    2009-01-01

    We report a new method to measure the velocity of a fluid in the vicinity of a wall. The method, that we call Particle-Shadow Tracking (PST), simply consists in seeding the fluid with a small number of fine tracer particles of density close to that of the fluid. The position of each particle and of its shadow on the wall are then tracked simultaneously, allowing one to accurately determine the distance separating tracers from the wall and therefore to extract the velocity field. We present an application of the method to the determination of the velocity profile inside a laminar density current flowing along an inclined plane.

  3. Properties of Cr3C2-NiCr Cermet Coating Sprayed by High Power Plasma and HVOF Processes

    OpenAIRE

    Otsubo, Fumitaka; Era, Hidenori; Kishitake, K; Uchida, T.

    2000-01-01

    The structure, hardness and shear adhesion strength have beeninvestigated in Cr3C2-NiCr cermet coatings sprayed onto a mild steelsubstrate by 200 kW high power plasma spraying (HPS) and high velocityoxy-fuel (HVOF) processes. Amorphous and supersaturated nickel phasesform in both as-sprayed coatings. The hardness of the HVOF coating ishigher than that of the HPS coating because the HVOF coating containsmore non-melted Cr3C2 carbide particles. On heat-treating at 873 K, theamorphous phase deco...

  4. Correlation Between Particle Velocities and Conditions of Abrasive Waterjet Formation

    Science.gov (United States)

    Chen, Wei-Long

    1990-01-01

    The velocities of water and abrasive particles in abrasive waterjet(AWJ) were measured by the use of Laser Transit Anemometer(LTA). A setup for the velocity measurement was constructed and a statistical technique was used to improve the accuracy of the velocity determination. A comparison of the magnitude of velocities determined by LTA, Piezoelectric Force Transducer and Schlieren Photograph clearly indicates the feasibility of the use of LTA. The velocities of water and particles were measured for different diameters of water and slurry nozzles, abrasive mass flow rates and particle sizes. The performed experiments enabled us to evaluate the effects of conditions of jet formation on the particles velocities. An empirical equation for the prediction of particles velocities was constructed by the use of obtained results. The coefficient of correlation between experimental and computed results is equal to 0.93. The acquired information can be used to select the operational parameters in AWJ cutting. The obtained results also provide information on the acceleration mechanism of entrained particles, which may be used to improve the design of slurry nozzle.

  5. HIGH VELOCITY THERMAL GUN FOR SURFACE PREPARATION AND TREATMENT

    Directory of Open Access Journals (Sweden)

    I.A. Gorlach

    2012-01-01

    Full Text Available Many surface preparation and treatment processes utilise compressed air to propel particles against surfaces in order to clean and treat them. The effectiveness of the processes depends on the velocity of the particles, which in turn depends on the pressure of the compressed air. This paper describes a thermal gun built on the principles of High Velocity Air Fuel (HVAF and High Velocity Oxy Fuel (HVOF processes. The designed apparatus can be used for abrasive blasting, coating of surfaces, cutting of rocks, removing rubber from mining equipment, cleaning of contaminations etc.

  6. Increasing of horizontal velocity of particles leaving a belt conveyor

    Directory of Open Access Journals (Sweden)

    Tavares Abraão

    2017-01-01

    Full Text Available We investigate the transport of granular materials by a conveyor belt via numerical simulations. We report an unusual increasing of particles horizontal velocity when they leave the belt and initiate free-fall. Using Discrete Elements Method, the mechanism underlying this phenomenon were investigated, and a study on how particle and system properties influences this effect were conducted.

  7. Identifying the optimal HVOF spray parameters to attain minimum porosity and maximum hardness in iron based amorphous metallic coatings

    Directory of Open Access Journals (Sweden)

    S. Vignesh

    2017-04-01

    Full Text Available Flow based Erosion – corrosion problems are very common in fluid handling equipments such as propellers, impellers, pumps in warships, submarine. Though there are many coating materials available to combat erosion–corrosion damage in the above components, iron based amorphous coatings are considered to be more effective to combat erosion–corrosion problems. High velocity oxy-fuel (HVOF spray process is considered to be a better process to coat the iron based amorphous powders. In this investigation, iron based amorphous metallic coating was developed on 316 stainless steel substrate using HVOF spray technique. Empirical relationships were developed to predict the porosity and micro hardness of iron based amorphous coating incorporating HVOF spray parameters such as oxygen flow rate, fuel flow rate, powder feed rate, carrier gas flow rate, and spray distance. Response surface methodology (RSM was used to identify the optimal HVOF spray parameters to attain coating with minimum porosity and maximum hardness.

  8. Glassy dynamics of Brownian particles with velocity-dependent friction

    Science.gov (United States)

    Yazdi, Anoosheh; Sperl, Matthias

    2016-09-01

    We consider a two-dimensional model system of Brownian particles in which slow particles are accelerated while fast particles are damped. The motion of the individual particles is described by a Langevin equation with Rayleigh-Helmholtz velocity-dependent friction. In the case of noninteracting particles, the time evolution equations lead to a non-Gaussian velocity distribution. The velocity-dependent friction allows negative values of the friction or energy intakes by slow particles, which we consider active motion, and also causes breaking of the fluctuation dissipation relation. Defining the effective temperature proportional to the second moment of velocity, it is shown that for a constant effective temperature the higher the noise strength, the lower the number of active particles in the system. Using the Mori-Zwanzig formalism and the mode-coupling approximation, the equations of motion for the density autocorrelation function are derived. The equations are solved using the equilibrium structure factors. The integration-through-transients approach is used to derive a relation between the structure factor in the stationary state considering the interacting forces, and the conventional equilibrium static structure factor.

  9. Particle In-Flight Velocity and Dispersion Measurements at Increasing Particle Feed Rates in Cold Spray

    Science.gov (United States)

    Meyer, M.; Yin, S.; Lupoi, R.

    2017-01-01

    Cold spray (CS) is attracting interest of research and industry due to its rapid, solid-state particle deposition process and respective advantages over conventional deposition technologies. The acceleration of the particles is critical to the efficiency of CS, and previous investigations rarely consider the particle feed rate. However, because higher particle loadings are typically used in the process, the effect of this cannot be assumed negligible. This study therefore investigates the particle velocities in the supersonic jet of an advanced CS system at low- and high pressure levels and varying particle feed rates using particle image velocimetry. The particle dispersion and velocity evolution along the jet axis were investigated for several feedstock materials. It was found that the average particle velocity noticeably decreases with increasing particulate loading in all cases. The velocity distribution and particle dispersion were also observed to be influenced by the feed rate. Effects are driven by both mass loading and volume fraction, depending on the feedstock's particle velocity parameter. Increased particle feed rates hence affect the magnitude and distribution of impact velocity and consequently the efficiency of CS. In particular, numerical models neglecting this interconnection are required to be further improved, based on these experimental studies.

  10. Magnetophoretic velocities of superparamagnetic particles, agglomerates and complexes

    Energy Technology Data Exchange (ETDEWEB)

    Wise, Naomi, E-mail: naomi.wise@eng.ox.ac.uk [Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kindom (United Kingdom); Grob, Tim [Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kindom (United Kingdom); Morten, Karl [Nuffield Department of Obstetrics and Gynaecology, University of Oxford, The Women Centre, John Radcliffe Hospital, Headley Way, Headington, Oxford OX3 9DU (United Kingdom); Thompson, Ian; Sheard, Steve [Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kindom (United Kingdom)

    2015-06-15

    A study into the magnetically induced mobility of four types of superparamagnetic particles (SMPs) was conducted using a video camera, an inverted light microscope and ImageJ tracking software. The objective is to improve the understanding of how SMP-capture assays perform by measuring mobilities of SMPs, when aggregated together or attached to non-magnetic beads (NMB). The magnetically induced velocities of self-assembled SMP chains were measured and found to meet the proposed models. A study into the zeta potential of the SMPs was completed to determine a scenario for maximal electrostatic interactions and efficient capture of the SMPs to a target. SMPs were bound to biotinylated NMBs, representing attachment to a disease biomarker. The drift velocity of SMP chains and SMP–NMB complexes in a gradient magnetic field was compared. It is expected that the observable changes to the magnetophoretic mobility of SMPs attached to a disease biomarker will lead to new biosensor technology. - Highlights: • Analysis of the magnetically induced drift velocity of superparamagnetic particles. • Zeta potential of superparamagnetic particles and non-magnetic particles found. • Drift velocity of single particles, chains and complexes determined experimentally. • Magnetic drift velocities of chains and complexes predicted by simple models.

  11. Settling velocity of marine microplastic particles: laboratory tests

    Science.gov (United States)

    Isachenko, Igor; Khatmullina, Lilia; Chubarenko, Irina; Stepanova, Natalia

    2016-04-01

    An assessment of the settling velocity of different classes of microplastic particles (microplastic particles is usually outside the Stokes range (Re 105). Even for such transitional regime, the settling velocity of the particles that could be treated as more or less smooth spheres can be predicted with high accuracy by relationships available in publications. This is not the case for the non-spherical particles like fibres or flakes. There are quite a large number of quasi-theoretical or semi-empirical approaches that take into account the shape and roughness of the particles, usually in the applications to transport of natural sediments. Some engineering formulas for the settling velocity are also developed which have simpler structure along with high degree of accuracy on the set of experimental data. For marine microplastic particles, the absence of relationship between the settling velocity and the properties of the particle requires testing on the samples of marine microplastics. Besides small fragments of rigid plastic (granules, microbeads), there are also fibres and thin plastic sheets (flakes) with some degree of flexibility. The applicability of available formulae to thin and/or flexible plastic particles again requires verification by experiments. The set of laboratory experiments on settling of microplastic particles of various shapes and excess densities in homogeneous water is reported. The particles were collected in water column, bottom sediments and on the beaches of the South-Eastern Baltic. The experiments demonstrate not just different regimes of motion but different manner of the sinking of spheres, flakes and fibres. The very definition of the "settling velocity" has a specific meaning for every kind of a particle shape. The results of test measurements are compared with predictions by several published semi-empirical formulae. We conclude that there are several new questions to discuss in this regard: (i) proper definition of the meaning of

  12. Effect of flame conditions on abrasive wear performance of HVOF sprayed nanostructured WC-12Co coatings

    Institute of Scientific and Technical Information of China (English)

    WANG Yu-yue; LI Chang-jiu; MA Jian; YANG Guan-jun

    2004-01-01

    Nanostructured WC-12Co coatings were deposited by high velocity oxy-fuel (HVOF) spraying with an agglomerated powder. The effect of flame conditions on the microstructure of the nanostructured coatings was investigated. The wear properties of the coatings were characterized using a dry rubber-wheel wear test. The results show that the nanostructured WC-Co coatings consist of WC, W2C, W and an amorphous binder phase. The microstructure of the coating is significantly influenced by the ratio of oxygen flow to fuel flow. Under the lower ratio of oxygen/fuel flow, the nanostructured coating presents a relative dense microstructure and severe decarburization of WC phase occurs during spraying. With increasing ratio of oxygen/fuel flow, the bonding of WC particles in the coating becomes loose resulting from the original structure of feedstock and the decarburization of WC becomes less owing to limited heating to the powder. Both the decarburization of WC particles in spraying and the bonding among WC particles in the coatings affect the wear performance. The examination of the worn surfaces of the nanostructured coatings reveals that the dominant wear mechanisms would be spalling from the interface of WCCo splats when spray particles undergo a limited melting. While the melting state of the spray particles is improved,the dominant wear mechanisms become the plastic deformation and plowing of the matrix and spalling of WC particles from the matrix.

  13. Effect of heat treatment on the wear and corrosion behaviors of a gray cast iron coated with a COLMONOY 88 alloy deposited by high velocity oxygen fuel (HVOF thermal spray

    Directory of Open Access Journals (Sweden)

    A. Öz

    2013-07-01

    Full Text Available The present work has been conducted in order to determine the influence of heat treatment on the wear and corrosion behaviours of a gray cast iron substrate coated with a Ni base coating deposited by HVOF thermal spray. The wear resistance of the coatings was obtained using a reciprocating wear tester by rubbing a 10 mm diameter steel ball on the coatings at normal atmospheric conditions. Corrosion tests were performed using potentiodynamic polarization measurements in a 3,5 % NaCl solution. It was observed that the corrosion and wear resistance of the coatings increased along with the reduction of porosity and roughness by the heat treatment.

  14. Particle position and velocity measurement in dusty plasmas using particle tracking velocimetry

    Science.gov (United States)

    Feng, Yan; Goree, J.; Haralson, Zach; Wong, Chun-Shang; Kananovich, A.; Li, Wei

    2016-06-01

    > Methods of imaging and image analysis are presented for dusty plasma experiments. Micron-sized polymer spheres, electrically suspended in a partially ionized gas, are illuminated by a sheet of laser light and imaged by video cameras. Image analysis methods yield particle positions and velocities of individual particles in each video image. Methods to minimize errors in the particle positions and velocities, which are now commonly used in the dusty plasma community, are described.

  15. Effect of injecting inert particles on coking prohibition and particle velocity uniformization in downer reactors

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, J.Y.; Zhu, Y.; Tian, Y.J.; Xie, K.C. [Fuzhou University, Fuzhou (China). Inst. of Chemical Engineering & Technology

    2007-02-15

    The coking observation and particle flow behaviour in both thermal plasma and cold plexiglas downers were investigated in a binary particle system formed by injecting coarse inert particles (carrying coke away and scouring wall) and fine coal powders into the downer reactor. The results demonstrate that this scheme is a rational selection to prevent coking on downer walls and improve particle velocity distribution along the radial direction. When injected coarse particles mixed with fine powders in downers, the fluctuation of local particle velocity in the radial direction becomes smaller and two peaks in the radial distribution of local particle velocity occur due to the improved dispersing character and flow structure, which are beneficial to the thermo-plasma coal cracking reaction and coking prevention.

  16. Low-velocity collisions of a many-particle-system

    Science.gov (United States)

    Weidling, René; Blum, Jurgen; Güttler, Carsten

    To understand the formation of planetesimals, it is important to study collisions between dust aggregates. As shown in the collision model by Güttler et al. (2010, Astronomy & Astrophysics, in press), the results of dust-aggregate collisions vary according to size, velocity and porosity of the particles. While many experiments were performed for velocities above ˜0.1 m/s, it is very difficult to achieve lower velocities. In our drop tower-experiment, an ensemble of dust-particles undergoes inelastic collisions and by this dynamically 'cools' down so that velocities below 1 cm/s can be reached. In order to achieve even lower velocities than in the drop tower, the experiment will be part of MEDEA-payload onboard a suborbital flight of Blue Origin, providing about 180 seconds of reduced gravity. During this time we will not only be able to observe many more collisions, but allow the many-particle system to show collective effects like clustering, which have so far never been studied in dust aggregation experiments.

  17. Particle Velocity Measurement for Spherical Wave in Solid

    Institute of Scientific and Technical Information of China (English)

    ZHENG Xue-feng; WANG Zhan-jiang; LIN Jun-de; SHEN Jun-yi

    2006-01-01

    An experimental technique for research on spherical divergent wave propagation in a solid has been developed,in which the source of generating spherical wave is a center initiating explosive charge designed in a mini-spherical shape with yield equivalent to 0.125 g and 0. 486 g TNT and a set of circular electromagnetic particle velocity gages is used to record the particle velocity histories. By using the circular electromagnetic particle velocity gages, the signal outputs not only are unattenuated due to the geometrical divergence, but also represent the average of the measured dynamic states of the medium over a circle on the wavefront. The distinctive features of this technique are very useful for the study of spherical divergent wave propagation in a solid, especially in an inhomogeneous solid, and the corresponding material dynamics.Many experimental measurements were conducted in polymethylmethacrylate (PMMA) and granite by means of the technique, and the reproducibility of tests was shown to be good. The measurement technique of the circular electromagnetic particle velocity gages is also suitable to the case of cylindrical wave.

  18. A simple formula for predicting settling velocity of sediment particles

    Directory of Open Access Journals (Sweden)

    Song Zhiyao

    2008-03-01

    Full Text Available Based on the general relationship described by Cheng between the drag coefficient and the Reynolds number of a particle, a new relationship between the Reynolds number and a dimensionless particle parameter is proposed. Using a trial-and-error procedure to minimize errors, the coefficients were determined and a formula was developed for predicting the settling velocity of natural sediment particles. This formula has higher prediction accuracy than other published formulas and it is applicable to all Reynolds numbers less than 2×105.

  19. A generalized transport-velocity formulation for smoothed particle hydrodynamics

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Chi; Hu, Xiangyu Y., E-mail: xiangyu.hu@tum.de; Adams, Nikolaus A.

    2017-05-15

    The standard smoothed particle hydrodynamics (SPH) method suffers from tensile instability. In fluid-dynamics simulations this instability leads to particle clumping and void regions when negative pressure occurs. In solid-dynamics simulations, it results in unphysical structure fragmentation. In this work the transport-velocity formulation of Adami et al. (2013) is generalized for providing a solution of this long-standing problem. Other than imposing a global background pressure, a variable background pressure is used to modify the particle transport velocity and eliminate the tensile instability completely. Furthermore, such a modification is localized by defining a shortened smoothing length. The generalized formulation is suitable for fluid and solid materials with and without free surfaces. The results of extensive numerical tests on both fluid and solid dynamics problems indicate that the new method provides a unified approach for multi-physics SPH simulations.

  20. Laser Surface Treatment of Stellite 6 Coating Deposited by HVOF on 316L Alloy

    Science.gov (United States)

    Shoja-Razavi, Reza

    2016-07-01

    This research aimed to study the effects of laser glazing treatment on microstructure, hardness, and oxidation behavior of Stellite 6 coating deposited by high velocity oxygen fuel (HVOF) spraying. The as-sprayed Stellite 6 coating (ST-HVOF) was subjected to single-pass and multiple-pass laser treatments to achieve the optimum glazing parameters. Microstructural characterizations were performed by x-ray diffractometry and field emission scanning electron microscopy equipped with energy-dispersive spectroscopy. Two-step optimization showed that laser treatment at the power of 200 W with a scan rate of 4 mm/s causes a surface layer with a thickness of 208 ± 32 µm to be remelted, while the underlying layers retain the original ST-HVOF coating structure. The obtained sample (ST-Glazing) exhibited a highly dense and uniform structure with an extremely low porosity of ~0.3%, much lower than that of ST-HVOF coating (2.3%). The average microhardness of ST-Glazing was measured to be 519 Hv0.3 indicating a 17% decrease compared to ST-HVOF (625 Hv0.3) due to the residual stress relief and dendrite coarsening from submicron size to ~3.4 µm after laser treatment. The lowest oxidation mass gain was obtained for ST-Glazing by 2 mg/cm2 after 8 cycles at 900 °C indicating 52 and 84% improvement in oxidation resistance in comparison to ST-HVOF and bare 316L steel substrates, respectively.

  1. Characterization of Fe-Cr-B based coatings produced by HVOF and PTA processes

    Science.gov (United States)

    Kim, Hyung-Jun; Grossi, Stephanie; Kweon, Young-Gak

    1999-02-01

    Two Fe-Cr-B based gas atomized powders, Armacor M and 16, were thermally sprayed on a low carbon steel substrate, using the HVOF (High Velocity Oxygen Fuel) process. Armacor M was also weld-surfaced with the PTA (Plasma Transferred Arc) process. The resultant deposits were subsequently characterized, using X-ray diffraction, scanning electron microscopy, and microhardness measurement. The effects of heat treatment were also studied for HVOF-sprayed coatings. The wear performance of the coatings was investigated by two-body abrasive wear tests. The results of microstructural analysis of as-sprayed deposits revealed oxide and boride phases such as Fe3O4 and Cr1.65F0.35B0.96 in an α matrix for the HVOF-sprayed Armacor 16 coating, and only the boride phases (Cr1.65F0.35B0.96 and Cr2B) in an α matrix for the HVOFsprayed Armacor M coating. PTA weld-surfaced Armacor M coating contains needle-type long precipitates of Cr2B) and Cr1.65F0.35B0.96, in the α matrix. The hardness of the HVOF-sprayed Armacor 16 coating after heat treatment was substantially less than that of the as-sprayed coating due to the phase transformation from α to γ phase. Heat treatments of the HVOF-sprayed Armacor M coating did not produce changes in phase and its hardness decreased as compared to that of the as-sprayed coating. While HVOF-sprayed and PTA weld-surfaced Armacor M coatings have the same hardness, the latter shows better abrasive wear resistance because of the size and orientation of its boride phases. The broadening of the XRD patterns and the increase in hardness after wear testing suggest that the transformation from the crystalline to the amorphous structure occurred on the uppermost layer during wear testing.

  2. HVOF coatings for steam oxidation protection

    Energy Technology Data Exchange (ETDEWEB)

    Agueero, A.; Muelas, R.; Gonzalez, V. [Instituto Nacional de Tecnica Aeroespacial (INTA), Area de Materiales Metalicos, Madrid (Spain)

    2008-05-15

    In the context of the European project 'Coatings for Supercritical Steam Cycles' (SUPERCOAT), the use of steam oxidation resistant coatings on currently available ferritic materials with high creep strength but poor oxidation resistance was investigated in order to allow increase in the operating temperature of steam power plants from 550 to 650 C. Among the explored coating techniques for this application, chosen on the basis of being potentially appropriate for coating steam turbine components, High Velocity Oxy Fuel (HVOF) thermal spray has resulted in one of the most successful techniques. Different alloyed materials such as FeCrAl, NiCrSiFeB, FeAl, NiCr and FeCr have been deposited, optimized and tested under flowing steam at 650 C. Characterization of as deposited and tested samples by metallography, SEM-EDS and XRD was carried out. Some of these coatings form protective pure chromium or aluminium oxides exhibiting excellent behaviour for at least 15 000 h of exposure, whereas others form less stable complex mixed oxides which nevertheless grow at considerably slower rates than the oxides formed on uncoated P92 (9 wt%Cr ferritic steel). (Abstract Copyright [2008], Wiley Periodicals, Inc.)

  3. Special relativity with an arbitrary limiting velocity of particle

    CERN Document Server

    Parvan, A S

    2012-01-01

    It is shown that a generalized special theory of relativity (GSTR) with an arbitrary limiting velocity of particle different or equal to the speed of light in vacuum can be constructed from the canonical equation of the 4-dimensional hyperboloid of revolution. In particular, when the limiting velocity equals the speed of light, the special theory of relativity (STR), which corresponds to the equation of the equilateral hyperboloid of revolution, is recovered. The (generalized) Lorentz transformations were obtained. It was established that the rest mass of a space-like particle is real. Our results strongly suggest that the muon neutrino in the OPERA experiment is most likely a time-like or a light-like superluminal particle, whose limiting velocity may exceed the speed of light in vacuum, rather than a superluminal space-like particle (tachyon) with a speed limit equal to speed of light for which the rest mass $mc^{2}=117.1^{+11.0}_{-10.5}$ MeV.

  4. Particle velocity non-uniformity and steady-wave propagation

    Science.gov (United States)

    Meshcheryakov, Yu. I.

    2017-03-01

    A constitutive equation grounded in dislocation dynamics is shown to be incapable of describing the propagation of shock fronts in solids. Shock wave experiments and theoretical investigations motivate an additional collective mechanism of stress relaxation that should be incorporated into the model through the standard deviation of the particle velocity, which is found to be proportional to the strain rate. In this case, the governing equation system results in a second-order differential equation of square non-linearity. Solution to this equation and calculations for D16 aluminum alloy show a more precise coincidence of the theoretical and experimental velocity profiles.

  5. Turbulence-Induced Relative Velocity of Dust Particles I: Identical Particles

    CERN Document Server

    Pan, Liubin

    2013-01-01

    We study the relative velocity of inertial particles suspended in turbulent flows and discuss implications for dust particle collisions in protoplanetay disks. We simulate a weakly compressible turbulent flow at 512^3 and evolve 14 species of particles with different friction timescales, tau_p. The Stoke number, St, of the smallest particles is ~0.1, where St is the ratio of tau_p to the Kolmorgorov timescale, while the largest particles have tau_p =54T_L, where T_L is the flow Lagrangian correlation timescale. We find that the model by Pan & Padoan (PP10) gives satisfactory predictions for the rms relative velocity between identical particles. The model shows that the relative velocity of two same-size particles is determined by the particle memory of the flow velocity difference along their trajectories, and thus depends on the particle pair separation backward in time. We compute the collision kernel accounting for the effect of turbulent clustering. The kernel per unit cross section shows an abrupt ri...

  6. Sound field separation with sound pressure and particle velocity measurements

    DEFF Research Database (Denmark)

    Fernandez Grande, Efren; Jacobsen, Finn; Leclère, Quentin

    2012-01-01

    separation techniques make it possible to distinguish between outgoing and incoming waves from the two sides, and thus NAH can be applied. In this paper, a separation method based on the measurement of the particle velocity in two layers and another method based on the measurement of the pressure...... and the velocity in a single layer are proposed. The two methods use an equivalent source formulation with separate transfer matrices for the outgoing and incoming waves, so that the sound from the two sides of the array can be modeled independently. A weighting scheme is proposed to account for the distance...... pressure-velocity method, although it requires an additional measurement surface. On the whole, the separation methods can be useful when the disturbance of the incoming field is significant. Otherwise the direct reconstruction is more accurate and straightforward. © 2012 Acoustical Society of America....

  7. Fluorescence-Doped Particles for Simultaneous Temperature and Velocity Imaging

    Science.gov (United States)

    Danehy, Paul M.; Tiemsin, Pacita I.; Wohl, Chrostopher J.; Verkamp, Max; Lowe, T.; Maisto, P.; Byun, G.; Simpson, R.

    2012-01-01

    Polystyrene latex microspheres (PSLs) have been used for particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) measurements for several decades. With advances in laser technologies, instrumentation, and data processing, the capability to collect more information about fluid flow beyond velocity is possible using new seed materials. To provide additional measurement capability, PSLs were synthesized with temperature-sensitive fluorescent dyes incorporated within the particle. These multifunctional PSLs would have the greatest impact if they could be used in large scale facilities with minimal modification to the facilities or the existing instrumentation. Consequently, several potential dyes were identified that were amenable to existing laser systems currently utilized in wind tunnels at NASA Langley Research Center as well as other wind and fluid (water) tunnels. PSLs incorporated with Rhodamine B, dichlorofluorescein (DCF, also known as fluorescein 548 or fluorescein 27) and other dyes were synthesized and characterized for morphology and spectral properties. The resulting particles were demonstrated to exhibit fluorescent emission, which would enable determination of both fluid velocity and temperature. They also would allow near-wall velocity measurements whereas laser scatter from surfaces currently prevents near-wall measurements using undoped seed materials. Preliminary results in a wind tunnel facility located at Virginia Polytechnic Institute and State University (Virginia Tech) have verified fluorescent signal detection and temperature sensitivity of fluorophore-doped PSLs.

  8. About the velocity operator for spinning particles in quantum mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Salesi, Giovanni [Universita Statale di Catania (Italy). Dipt. di Fisica]|[Istituto Nazionale di Fisica Nucleare, Catania (Italy); Recami, Erasmo; Rodrigues Junior, Waldyr A. [Universidade Estadual de Campinas, SP (Brazil). Dept. de Matematica Aplicada

    1995-12-01

    Starting from the formal expressions of the hydrodynamical (or local) quantities employed in the applications of Clifford Algebras to quantum mechanics, we introduce - in terms of the ordinary tensorial framework - a new definition for the field of a generic quantity. By translating from Clifford into sensor algebra, we also propose a new (non-relativistic) velocity operator for a spin 1/2 particle. This operator is the sum of the ordinary part p/m describing the mean motion (the motion of the center-of-mass), and of a second part associated with the so-called Zitterbewegung, which is the spin internal motion observed in the center-of-mass frame. This spin component of the velocity operator is non-zero not only in the Pauli theoretical framework in presence of external magnetic fields and spin precession, but also in the Schroedinger case, when the wave-function is a spin eigenstate. In the latter case, one gets a decomposition of the velocity field for the Madelueng fluid into two distinct parts: which constitutes the non-relativistic analogue of the Gordon decomposition for the Dirac current. We find furthermore that the Zitterbewegung motion involves a velocity field which is solenoidal, and that the local angular velocity is parallel to the spin vector. In presence of a non-constant spin vector (Pauli case) we have, besides the component normal to spin present even in the Schroedinger theory, also a component of the local velocity which is parallel to the rotor of the spin vector. (author). 19 refs.

  9. Residual stresses in high-velocity oxy-fuel metallic coatings

    Science.gov (United States)

    Totemeier, T. C.; Wright, R. N.; Swank, W. D.

    2004-06-01

    X-ray based residual stress measurements were made on type 316 stainless steel and Fe3Al coatings that were high-velocity oxy-fuel (HVOF) sprayed onto low-carbon and stainless steel substrates. Nominal coating thicknesses varied from 250 to 1500 µm. The effect of HVOF spray particle velocity on residual stress and deposition efficiency was assessed by preparing coatings at three different torch chamber pressures. The effect of substrate thickness on residual stress was determined by spraying coatings onto thick (6.4 mm) and thin (1.4 mm) substrates. Residual stresses were compressive for both coating materials and increased in magnitude with spray velocity. For coatings applied to thick substrates, near-surface residual stresses were essentially constant with increasing coating thickness. Differences in thermal expansion coefficient between low-carbon and stainless steels led to a 180 MPa difference in residual stress for Fe3Al coatings. Deposition efficiency for both materials is maximized at an intermediate (˜600 m/s) velocity. Considerations for X-ray measurement of residual stresses in HVOF coatings are also presented.

  10. Formation Mechanisms, Structure, and Properties of HVOF-Sprayed WC-CoCr Coatings: An Approach Toward Process Maps

    Science.gov (United States)

    Varis, T.; Suhonen, T.; Ghabchi, A.; Valarezo, A.; Sampath, S.; Liu, X.; Hannula, S.-P.

    2014-08-01

    Our study focuses on understanding the damage tolerance and performance reliability of WC-CoCr coatings. In this paper, the formation of HVOF-sprayed tungsten carbide-based cermet coatings is studied through an integrated strategy: First-order process maps are created by using online-diagnostics to assess particle states in relation to process conditions. Coating properties such as hardness, wear resistance, elastic modulus, residual stress, and fracture toughness are discussed with a goal to establish a linkage between properties and particle characteristics via second-order process maps. A strong influence of particle state on the mechanical properties, wear resistance, and residual stress stage of the coating was observed. Within the used processing window (particle temperature ranged from 1687 to 1831 °C and particle velocity from 577 to 621 m/s), the coating hardness varied from 1021 to 1507 HV and modulus from 257 to 322 GPa. The variation in coating mechanical state is suggested to relate to the microstructural changes arising from carbide dissolution, which affects the properties of the matrix and, on the other hand, cohesive properties of the lamella. The complete tracking of the coating particle state and its linking to mechanical properties and residual stresses enables coating design with desired properties.

  11. Velocity operator and velocity field for spinning particles in (non-relativistic) quantum mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Recami, E. [Bergamo Univ. (Italy). Facolta` di Ingegneria]|[INFN, Milan (Italy)]|[Campinas State Univ., SP (Brazil). Dept. of Applied Math.; Salesi, G. [Catania Univ. (Italy). Dip. di Fisica

    1995-06-01

    Starting from the formal expressions of the hydrodynamical (or local) quantities employed in the applications of Clifford Algebras to quantum mechanics, the paper introduces - in terms of the ordinary tensorial framework - a new definition for the field of a generic quantity. By translating from Clifford into tensor algebra, a new (non-relativistic) velocity operator for a spin 1/2 particle is also proposed. This operator is the sum of the ordinary part p/m describing the mean motion (the motion of the center-of-mass), and of a second part associated with the so-called Zitterbewegung, which is the spin internal motion observed in the center-of- mass frame. This spin component of the velocity operator is non-zero not only in the Pauli theoretical framework, i.e. in presence of external magnetic fields and spin precession, but also in the Schroedinger case, when the wave-function is a spin eigenstate. In the latter case, one gets a decomposition of the velocity field for the Madelueng fluid into two distinct parts: which the constitutes the non-relativistic analogue of the Gordon decomposition for the Dirac current.

  12. Particle fluctuation velocity in gas-fluidized beds

    Science.gov (United States)

    Cody, George

    1998-11-01

    The stability of the uniform state of a gas-fluidized bed was first discussed by Wilhelm and Kwauk in 1948, modeled by Jackson in 1963, and summarized in empirical rules by Geldart in 1973. Particles (Geldart-A) below a critical diameter fluidize before bubbling, and those above that diameter (Geldart-B) bubble at fluidization - why? The critical stability parameter is the mean-squared particle fluctuation velocity, or granular temperature, T*. It was first measured for monodispersed glass spheres by acoustic shot-noise excitation of the wall (Cody et al., 1996), and by diffusing-wave optical spectroscopy at the wall (Menon and Durian, 1997). For Geldart-B spheres the data agree, and both agree with a recent statistical model for T* based on random particle impact (Buyevich and Kapbasov, 1998). T* of Cody et al. jumps by tenfold at the Geldart-B/A transition, sufficient to make these Geldart-A spheres stable in the Jackson theory. It is proposed that the absence of this jump in the Menon and Durian data reflects the significant difference in bed geometry and circulation in the two experiments, and the dominant effect of random shear fluctuations on T* for sphere diameters in the Geldart-A regime (Cody, Kapbasov, Buyevich, Symp. B-1, Annual Meeting. AIChE 11/15-20/98).

  13. Combined slurry and cavitation erosion resistance of HVOF spray coated SS 410 steel

    Science.gov (United States)

    Amarendra, H. J.; Prathap, M. S.; Karthik, S.; Abhishek, A. M.; Madhu surya, K. C.; Gujjar gowda, S.; Anilkumar, T.

    2016-09-01

    The hydro turbine materials surface is degraded due to the slurry erosion and cavitation. The solid particles carried by water impacting the material results in slurry erosion. The damage occurred due to slurry erosion is the concern, when considered individually. The erosion damage is observed to be severe when slurry erosion and cavitation are combined. The hydro turbine material, martensitic stainless (SS 410) is surface modified with 80Ni-Cr by High Velocity Oxy Fuel spray process. The coated material subjected to post thermal treatment at a temperature of 950 ° C, soaked at 1 h, 2 h and 3 h are subjected to combined slurry and cavitation erosion test. The cavitation is created by using Cavitation Inducers. The tests are conducted by using silica sand as the erodent with three different sizes of 150, 200 and 300 μm. The results are compared with the as-received specimen. The results confirmed the effect of heat treatment on the end results, as the coated thermal treated specimens showed better erosion resistance against the as-received specimen. The eroded specimens are characterized by Scanning Electron Microscope. The thermal treated HVOF coated specimens shown the better erosion resistance.

  14. Particle size effect on velocity of gold particle embedded laser driven plastic targets

    Science.gov (United States)

    Dhareshwar, L. J.; Chaurasia, S.; Manmohan, K.; Badziak, J.; Wolowski, J.; Kasperczuk, A.; Pisarczyk, T.; Ryc, L.; Rosinski, M.; Parys, P.; Pisarczyk, P.; Ullschmidt, J.; Krousky, E.; Masek, K.

    2013-11-01

    A scheme to enhance the target foil velocity has been investigated for a direct drive inertial fusion target. Polymer PVA (polyvinyl alcohol or (C2H4O)n) target foils of thickness 15-20 μm were used in plain form and also embedded with gold in the nano-particle (Au-np) or micro-particle (Au-mp) form. Nano-particles were of 20-50 nm and micro-particles of 2-3 μm in size. 17% higher target velocity was measured for foils embedded with nano-particle gold (Au-np) as compared to targets embedded with micro-particles gold (Au-mp). The weight of gold in both cases was in the range 40-55% of the full target weight (atomic percentage of about 22%). Experiments were performed with the single beam of the Prague Asterix Laser System (PALS) at 0.43 μm wavelength (3ω of the fundamental wavelength), 120 Joule energy and 300 psec pulse duration. Laser intensity on the target was about 1015 W/cm2. A simple model has been proposed to explain the experimental results.

  15. Particle size effect on velocity of gold particle embedded laser driven plastic targets

    Directory of Open Access Journals (Sweden)

    Dhareshwar L.J.

    2013-11-01

    Full Text Available A scheme to enhance the target foil velocity has been investigated for a direct drive inertial fusion target. Polymer PVA (polyvinyl alcohol or (C2H4On target foils of thickness 15–20 μm were used in plain form and also embedded with gold in the nano-particle (Au-np or micro-particle (Au-mp form. Nano-particles were of 20–50 nm and micro-particles of 2–3 μm in size. 17% higher target velocity was measured for foils embedded with nano-particle gold (Au-np as compared to targets embedded with micro-particles gold (Au-mp. The weight of gold in both cases was in the range 40–55% of the full target weight (atomic percentage of about 22%. Experiments were performed with the single beam of the Prague Asterix Laser System (PALS at 0.43 μm wavelength (3ω of the fundamental wavelength, 120 Joule energy and 300 psec pulse duration. Laser intensity on the target was about 1015 W/cm2. A simple model has been proposed to explain the experimental results.

  16. Optimization and Characterization of High Velocity Oxy-fuel Sprayed Coatings: Techniques, Materials, and Applications

    Directory of Open Access Journals (Sweden)

    Maria Oksa

    2011-09-01

    Full Text Available In this work High Velocity Oxy-fuel (HVOF thermal spray techniques, spraying process optimization, and characterization of coatings are reviewed. Different variants of the technology are described and the main differences in spray conditions in terms of particle kinetics and thermal energy are rationalized. Methods and tools for controlling the spray process are presented as well as their use in optimizing the coating process. It will be shown how the differences from the starting powder to the final coating formation affect the coating microstructure and performance. Typical properties of HVOF sprayed coatings and coating performance is described. Also development of testing methods used for the evaluation of coating properties and current status of standardization is presented. Short discussion of typical applications is done.

  17. Effect of Heat Treatment on Wear Resistance of Nickel Aluminide Coatings Deposited by HVOF and PTA

    Science.gov (United States)

    Benegra, M.; Santana, A. L. B.; Maranho, O.; Pintaude, G.

    2015-08-01

    This study aims to compare the wear resistance of nickel aluminide coatings deposited using plasma transferred arc (PTA) and high-velocity oxygen fuel (HVOF) processes. Wear resistance was measured in rubber wheel abrasion tests. In both deposition processes, the same raw material (nickel aluminide powder) was atomized and deposited on a 316L steel plate substrate. After deposition, specimens were subjected to thermal cycling, aiming solubilization and precipitation. Coatings deposited using PTA developed different microstructures as a result of the incorporation of substrate elements. However, despite the presence of these microstructures, they performed better than coatings processed using HVOF before the heat treatment. After thermal cycling, the superficial hardness after the wear tests for both processes was similar, resulting in similar mass losses.

  18. Corrosive wear behaviours of HVOF-sprayed NiCr coatings on stainless steel substrates

    Energy Technology Data Exchange (ETDEWEB)

    Ak, N.F.; Celik, E.; Cetinel, H.; Tekmen, C. [Dokuz Eyluel Univ., Dept. of Metallurgy and Materials Engineering, Bornova, Izmir (Turkey); Soykan, H.S. [Kocaeli Univ., Dept. of Metallurgy and Materials Engineering, Izmit-Kocaeli (Turkey)

    2004-07-01

    The High Velocity Oxy-Fuel (HVOF) thermal spraying process can be used to produce dense hard coatings onto metallic surfaces with a good bond between the coating and substrate. These coatings have been applied in many different industries to provide wear, erosion and corrosion protection. In this study, the NiCr coatings were deposited on the stainless steel substrates by HVOF technique. Microstructural characterization of the coatings was examined by using optical microscope. Corrosive wear behaviour of these coatings was evaluated through a pin-on-plate configuration, the wear tests were carried out at ambient temperature in 1% H{sub 2}SO{sub 4} solutions. It has been found that NiCr coating is more resistance against to wear in acid condition rather than air condition. (orig.)

  19. Characterization of WC-10Ni HVOF Coating for Carbon Steel Blade

    Science.gov (United States)

    Ahmad, N. A.; Kamdi, Z.; Mohamad, Z.; Omar, A. S.; Latif, N. Abdul; Tobi, A. L. Mohd

    2017-01-01

    High Velocity Oxy-Fuel, HVOF is a depositing methods of a material layer over a base metal or substrate with characteristics of high flame velocity and moderate temperature. Where, tungsten carbide, WC cermet HVOF coatings is widely used to protect machine components from wear and corrosion. The main purpose of this present paper is to characterize the WC-10Ni coating deposited by HVOF thermal spray onto a carbon steel blade. The morphology and chemical composition of the coating were characterized by Scanning Electron Microstructure (SEM), electron dispersive spectrometer (EDS), and X-ray diffraction (XRD). The hardness test was carried out by using Vickers micro-hardness tester with loads of 490.3 mN (HV0.05). From XRD results, no sharp nickel peak was identified and has been replaced by a hump which indicate the amorphous Ni. The major crystalline phases were compounds WC, W2C and metallic phase of W. The WC-10Ni coating shows high hardness with low porosity distribution.

  20. Mechanical and Tribological Properties of HVOF-Sprayed (Cr3C2-NiCr+Ni) Composite Coating on Ductile Cast Iron

    Science.gov (United States)

    Ksiazek, Marzanna; Boron, Lukasz; Radecka, Marta; Richert, Maria; Tchorz, Adam

    2016-08-01

    The aim of the investigations was to compare the microstructure, mechanical, and wear properties of Cr3C2-NiCr+Ni and Cr3C2-NiCr coatings deposited by HVOF technique (the high-velocity oxygen fuel spray process) on ductile cast iron. The effect of nickel particles added to the chromium carbide coating on mechanical and wear behavior in the system of Cr 3 C 2 -NiCr+Ni/ductile cast iron was analyzed in order to improve the lifetime of coated materials. The structure with particular emphasis of characteristic of the interface in the system of composite coating (Cr 3 C 2 -NiCr+Ni)/ductile cast iron was studied using the optical, scanning, and transmission electron microscopes, as well as the analysis of chemical and phase composition in microareas. Experimental results show that HVOF-sprayed Cr3C2-NiCr+Ni composite coating exhibits low porosity, high hardness, dense structure with large, partially molten Ni particles and very fine Cr3C2 and Cr7C3 particles embedded in NiCr alloy matrix, coming to the size of nanocrystalline. The results were discussed in reference to examination of bending strength considering cracking and delamination in the system of composite coating (Cr 3 C 2 -NiCr+Ni)/ductile cast iron as well as hardness and wear resistance of the coating. The composite structure of the coating provides the relatively good plasticity of the coating, which in turn has a positive effect on the adhesion of coating to the substrate and cohesion of the composite coating (Cr3C2-NiCr+Ni) in wear conditions.

  1. Effect of particle volume fraction on the settling velocity of volcanic ash particles: insights from joint experimental and numerical simulations

    Science.gov (United States)

    Del Bello, Elisabetta; Taddeucci, Jacopo; de’ Michieli Vitturi, Mattia; Scarlato, Piergiorgio; Andronico, Daniele; Scollo, Simona; Kueppers, Ulrich; Ricci, Tullio

    2017-01-01

    Most of the current ash transport and dispersion models neglect particle-fluid (two-way) and particle-fluid plus particle-particle (four-way) reciprocal interactions during particle fallout from volcanic plumes. These interactions, a function of particle concentration in the plume, could play an important role, explaining, for example, discrepancies between observed and modelled ash deposits. Aiming at a more accurate prediction of volcanic ash dispersal and sedimentation, the settling of ash particles at particle volume fractions (ϕp) ranging 10‑7-10‑3 was performed in laboratory experiments and reproduced by numerical simulations that take into account first the two-way and then the four-way coupling. Results show that the velocity of particles settling together can exceed the velocity of particles settling individually by up to 4 times for ϕp ~ 10‑3. Comparisons between experimental and simulation results reveal that, during the sedimentation process, the settling velocity is largely enhanced by particle-fluid interactions but partly hindered by particle-particle interactions with increasing ϕp. Combining the experimental and numerical results, we provide an empirical model allowing correction of the settling velocity of particles of any size, density, and shape, as a function of ϕp. These corrections will impact volcanic plume modelling results as well as remote sensing retrieval techniques for plume parameters.

  2. Effect of particle volume fraction on the settling velocity of volcanic ash particles: insights from joint experimental and numerical simulations

    Science.gov (United States)

    Del Bello, Elisabetta; Taddeucci, Jacopo; de’ Michieli Vitturi, Mattia; Scarlato, Piergiorgio; Andronico, Daniele; Scollo, Simona; Kueppers, Ulrich; Ricci, Tullio

    2017-01-01

    Most of the current ash transport and dispersion models neglect particle-fluid (two-way) and particle-fluid plus particle-particle (four-way) reciprocal interactions during particle fallout from volcanic plumes. These interactions, a function of particle concentration in the plume, could play an important role, explaining, for example, discrepancies between observed and modelled ash deposits. Aiming at a more accurate prediction of volcanic ash dispersal and sedimentation, the settling of ash particles at particle volume fractions (ϕp) ranging 10−7-10−3 was performed in laboratory experiments and reproduced by numerical simulations that take into account first the two-way and then the four-way coupling. Results show that the velocity of particles settling together can exceed the velocity of particles settling individually by up to 4 times for ϕp ~ 10−3. Comparisons between experimental and simulation results reveal that, during the sedimentation process, the settling velocity is largely enhanced by particle-fluid interactions but partly hindered by particle-particle interactions with increasing ϕp. Combining the experimental and numerical results, we provide an empirical model allowing correction of the settling velocity of particles of any size, density, and shape, as a function of ϕp. These corrections will impact volcanic plume modelling results as well as remote sensing retrieval techniques for plume parameters. PMID:28045056

  3. Investigation on in-flight particle velocity in supersonic plasma spraying

    Institute of Scientific and Technical Information of China (English)

    Li Changqing; Ma Shining; Ye Xionglin

    2005-01-01

    In-flight particle velocity and flux distribution were measured using CCD thermal spray monitor system during supersonic plasma spray processing with nano-structured Al203-TiO2 feed stocks. According to the results of particle flux measurement, the largest radian of the divergent particle stream is about 0. 2. Within the measuring range, top speed of inflight particles reached 800 m/s. Particle acceleration was accomplished within 4 cm down stream of the nozzle. Average particle velocity ( about 450 m/s) exceeded local sound speed (340 m/s) even at a mean standoff distance of 17 cm. With increasing mean standoff distance, average velocity of in-flight particle decreased according to a parabolic rule approximately.Image diagnosis showed that the result of in-flight particle velocity measurement is credible.

  4. Influence of Bond Coat on HVOF-Sprayed Gradient Cermet Coating on Copper Alloy

    Science.gov (United States)

    Ke, Peng; Cai, Fei; Chen, Wanglin; Wang, Shuoyu; Ni, Zhenhang; Hu, Xiaohong; Li, Mingxi; Zhu, Guanghong; Zhang, Shihong

    2017-06-01

    Coatings are required on mold copper plates to prolong their service life through enhanced hardness, wear resistance, and oxidation resistance. In the present study, NiCr-30 wt.%Cr3C2 ceramic-metallic (cermet) layers were deposited by high velocity oxy-fuel (HVOF) spraying on different designed bond layers, including electroplated Ni, HVOF-sprayed NiCr, and double-decker Ni-NiCr. Annealing was also conducted on the gradient coating (GC) with NiCr bond layer to improve the wear resistance and adhesion strength. Coating microstructure was investigated by scanning electron microscopy and x-ray diffraction analysis. Mechanical properties including microhardness, wear resistance, and adhesion strength of the different coatings were evaluated systematically. The results show that the types of metallic bond layer and annealing process had a significant impact on the mechanical properties of the GCs. The GCs with electroplated Ni bond layer exhibited the highest adhesion strength (about 70 MPa). However, the GC with HVOF-sprayed NiCr bond layer exhibited better wear resistance. The wear resistance and adhesion strength of the coating with NiCr metallic bond layer were enhanced after annealing.

  5. Zero-velocity magnetophoretic method for the determination of particle magnetic susceptibility.

    Science.gov (United States)

    Watarai, Hitoshi; Duc, Hoang Trong Tien; Lan, Tran Thi Ngoc; Zhang, Tianyi; Tsukahara, Satoshi

    2014-01-01

    A simple zero-velocity method to determine the particle magnetic susceptibility by measuring the magnetophoretic velocity was proposed. The principle is that the magnetophoretic velocity of a particle in a liquid medium must be zero when the magnetic susceptibilities of the medium and the particle are equal, or the gravity force and the magnetophoretic force are balanced. By changing the medium magnetic susceptibility and measuring the magnetophoretic velocity of a particle, the particle magnetic susceptibility was determined from the medium magnetic susceptibility under the zero-velocity condition. The feasibility of the method was demonstrated for polystyrene particles using a Dy(III) solution in the horizontal migration mode and different organic solvents in the vertical migration mode.

  6. Effects of solid inertial particles on the velocity and temperature statistics of wall bounded turbulent flow

    DEFF Research Database (Denmark)

    Nakhaei, Mohammadhadi; Lessani, B.

    2016-01-01

    The effect of solid inertial particles on the velocity and temperature statistics of a non-isothermal turbulentchannel flow is studied using direct numerical simulation. The particles inertia is varied by changingthe particles diameter. The density of particles is kept constant. A two-way coupled...

  7. Scales of influence on the settling velocities of synthetic, industrial and natural particles in grid turbulence

    CERN Document Server

    Jacobs, Corrine; Jendrassak, Marek; Limpasuvan, Varavut; Gurka, Roi; Hackett, Erin E

    2015-01-01

    The settling velocities of natural, synthetic, and industrial particles were measured in a grid turbulence facility using optical measurement techniques. Particle Image Velocimetry and 2D Particle Tracking were used to measure the instantaneous velocities of the flow and the particles' trajectories simultaneously. We find that for particles examined in this study (Rep = 0.4 - 123), settling velocity is either enhanced or unchanged relative to stagnant flow for the range of investigated turbulence conditions. The smallest particles scaled best with a Kolmogorov-based Stokes number indicating the dissipative scales influence their dynamics. In contrast, the mid-sized particles scaled better with a Stokes number based on the integral time scale. The largest particles were largely unaffected by the flow conditions. Using Proper Orthogonal Decomposition (POD), the flow pattern scales are compared to particle trajectory curvature to complement results obtained through dimensional analysis using Stokes numbers. The ...

  8. Biofilm effects on size gradation, drag coefficient and settling velocity of sediment particles

    Institute of Scientific and Technical Information of China (English)

    Qian-qian SHANG; Hong-wei FANG; Hui-ming ZHAO; Guo-jian HE; Zheng-hui CUI

    2014-01-01

    Sediment particles are often colonized by biofilm in a natural aquatic ecological system, especially in eutrophic water body. A series of laboratory experiments on particle size gradation, drag coefficient and settling velocity were conducted after natural sediment was colonized by biofilm for 5, 10, 15 and 20 days. Particle image acquisition, particle tracking techniques of Particle Image Velocimetry and Particle Tracking Velocimetry were utilized to analyze the changes of these properties. The experimental results indicate that the size gradation, the drag force exerted on bio-particles, and the settling velocity of bio-particles underwent significant change due to the growth of biofilm onto the sediment surface. The study proposes a characteristic particle size formula and a bio-particle settling velocity formula based on the regression of experiment results, that the settling velocity is only 50% to 60%as the single particle which has the same diameter and density. However, biofilm growth causes large particle which the settling velocities are approximately 10 times larger than that of primary particles. These results may be specifically used in the low energy reservoir or lake environment.

  9. Two-dimensional acoustic particle velocity sensors based on a crossing wires topology

    NARCIS (Netherlands)

    Pjetri, O.

    2016-01-01

    This thesis describes the design and realization of two-dimensional acoustic particle velocity sensors based on thermal convection. The sensors are of the order of 1 mm×1 mm and consist of two crossing wires with each wire sensing the acoustic particle velocity in the direction parallel to it. Their

  10. Lorentz Invariance and Brownian Motion of Test Particles with Constant Classical Velocity in Electromagnetic Vacuum

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jia-Lin; YU Hong-Wei

    2005-01-01

    @@ We show that the velocity and position dispersions of a test particle with a nonzero constant classical velocity undergoing Brownian motion caused by electromagnetic vacuum fluctuations in a space with plane boundaries can be obtained from those of the static case by Lorentz transformation. We explicitly derive the Lorentz transformations relating the dispersions of the two cases and then apply them to the case of the Brownian motion of a test particle with a constant classical velocity parallel to the boundary between two conducting planes. Our results show that the influence of a nonzero initial velocity is negligible for nonrelativistic test particles.

  11. A new heat propagation velocity prevails over Brownian particle velocities in determining the thermal conductivities of nanofluids

    Directory of Open Access Journals (Sweden)

    Chon Chan

    2011-01-01

    Full Text Available Abstract An alternative insight is presented concerning heat propagation velocity scales in predicting the effective thermal conductivities of nanofluids. The widely applied Brownian particle velocities in published literature are often found too slow to describe the relatively higher nanofluid conductivities. In contrast, the present model proposes a faster heat transfer velocity at the same order as the speed of sound, rooted in a modified kinetic principle. In addition, this model accounts for both nanoparticle heat dissipation as well as coagulation effects. This novel model of effective thermal conductivities of nanofluids agrees well with an extended range of experimental data.

  12. Effect of particle volume fraction on the settling velocity of volcanic ash particles: implications for ash dispersion models

    Science.gov (United States)

    Del Bello, E.; Taddeucci, J.; De'Michieli Vitturi, M.; Scarlato, P.; Andronico, D.; Scollo, S.; Kueppers, U.

    2015-12-01

    We present the first report of experimental measurements of the enhanced settling velocity of volcanic particles as function of particle volume fraction. In order to investigate the differences in the aerodynamic behavior of ash particles when settling individually or in mass, we performed systematic large-scale ash settling experiments using natural basaltic and phonolitic ash. By releasing ash particles at different, controlled volumetric flow rates, in an unconstrained open space and at minimal air movement, we measured their terminal velocity, size, and particle volume fraction with a high-speed camera at 2000 fps. Enhanced settling velocities of individual particles increase with increasing particle volume fraction. This suggests that particle clustering during fallout may be one reason explaining larger than theoretical depletion rates of fine particles from volcanic ash clouds. We provide a quantitative empirical model that allows to calculate, from a given particle size and density, the enhanced velocity resulting from a given particle volume fraction. The proposed model has the potential to serve as a simple tool for the prediction of the terminal velocity of ash of an hypothetical distribution of ash of known particle size and volume fraction. This is of particular importance for advection-diffusion transport model of ash where generally a one-way coupling is adopted, considering only the flow effects on particles. To better quantify the importance of the enhanced settling velocity in ash dispersal, we finally introduced the new formulation in a Lagrangian model calculating for realistic eruptive conditions the resulting ash concentration in the atmosphere and on the ground.

  13. Application of TiC reinforced Fe-based coatings by means of High Velocity Air Fuel Spraying

    Science.gov (United States)

    Bobzin, K.; Öte, M.; Knoch, M. A.; Liao, X.; Sommer, J.

    2017-03-01

    In the field of hydraulic applications, different development trends can cause problems for coatings currently used as wear and corrosion protection for piston rods. Aqueous hydraulic fluids and rising raw material prices necessitate the search for alternatives to conventional coatings like galvanic hard chrome or High Velocity Oxygen Fuel (HVOF)-sprayed WC/Co coatings. In a previous study, Fe/TiC coatings sprayed by a HVOF-process, were identified to be promising coating systems for wear and corrosion protection in hydraulic systems. In this feasibility study, the novel High Velocity Air Fuel (HVAF)-process, a modification of the HVOF-process, is investigated using the same feedstock material, which means the powder is not optimized for the HVAF-process. The asserted benefits of the HVAF-process are higher particle velocities and lower process temperatures, which can result in a lower porosity and oxidation of the coating. Further benefits of the HVAF process are claimed to be lower process costs and higher deposition rates. In this study, the focus is set on to the applicability of Fe/TiC coatings by HVAF in general. The Fe/TiC HVAF coating could be produced, successfully. The HVAF- and HVOF-coatings, produced with the same powder, were investigated using micro-hardness, porosity, wear and corrosion tests. A similar wear coefficient and micro-hardness for both processes could be achieved. Furthermore the propane/hydrogen proportion of the HVAF process and its influence on the coating thickness and the porosity was investigated.

  14. Study of Influence of Experimental Technique on Measured Particle Velocity Distributions in Fluidized Bed

    Science.gov (United States)

    Gopalan, Balaji; Shaffer, Frank

    2013-11-01

    Fluid flows that are loaded with high concentration of solid particles are common in oil and chemical processing industries. However, the opaque nature of the flow fields and the complex nature of the flow have hampered the experimental and computational study of these processes. This has led to the development of a number of customized experimental techniques for high concentration particle flows for evaluation and improvement of CFD models. This includes techniques that track few individual particles, measures average particle velocity over a small sample volume and those over a large sample volume. In this work novel high speed PIV (HsPIV), with individual particle tracking, was utilized to measure velocities of individual particles in gas-particle flow fields at the walls circulating and bubbling fluidized bed. The HsPIV measurement technique has the ability to simultaneously recognize and track thousands of individual particles in flows of high particle concentration. To determine the effect of the size of the sample volume on particle velocity measurements, the PDF of Lagrangian particle velocity was compared with the PDF of Eulerian for different domain sizes over a range of flow conditions. The results will show that measured particle velocity distribution can vary from technique to technique and this bias has to be accounted in comparison with CFD simulations.

  15. Statistics of particle pair relative velocity in the homogeneous shear flow

    Science.gov (United States)

    Gualtieri, P.; Picano, F.; Sardina, G.; Casciola, C. M.

    2012-02-01

    Small scale clustering of inertial particles and relative velocity of particle pairs have been fully characterized for statistically steady homogeneous isotropic flows. Depending on the particle Stokes relaxation time, the spatial distribution of the disperse phase results in a multi-scale manifold characterized by local particle concentration and voids and, because of finite inertia, the two nearby particles have high probability to exhibit large relative velocities. Both effects might explain the speed-up of particle collision rate in turbulent flows. Recently it has been shown that the large scale geometry of the flow plays a crucial role in organizing small scale particle clusters. For instance, a mean shear preferentially orients particle patterns. In this case, depending on the Stokes time, anisotropic clustering may occur even in the inertial range of scales where the turbulent fluctuations which drive the particles have already recovered isotropy. Here we consider the statistics of particle pair relative velocity in the homogeneous shear flow, the prototypical flow which manifests anisotropic clustering at small scales. We show that the mean shear, by imprinting anisotropy on the large scale velocity fluctuations, dramatically affects the particle relative velocity distribution even in the range of small scales where the anisotropic mechanisms of turbulent kinetic energy production are sub-dominant with respect to the inertial energy transfer which drives the carrier fluid velocity towards isotropy. We find that the particles’ populations which manifest strong anisotropy in their relative velocities are the same which exhibit small scale clustering. In contrast to any Kolmogorov-like picture of turbulent transport these phenomena may persist even below the smallest dissipative scales where the residual level of anisotropy may eventually blow-up. The observed anisotropy of particle relative velocity and spatial configuration is suggested to influence the

  16. Flow Scales of Influence on the Settling Velocities of Particles with Varying Characteristics

    Science.gov (United States)

    Jacobs, Corrine N.; Merchant, Wilmot; Jendrassak, Marek; Limpasuvan, Varavut; Gurka, Roi; Hackett, Erin E.

    2016-01-01

    The settling velocities of natural, synthetic, and industrial particles were measured in a grid turbulence facility using optical measurement techniques. Particle image velocimetry and 2D particle tracking were used to measure the instantaneous velocities of the flow and the particles’ trajectories simultaneously. We find that for particles examined in this study (Rep = 0.4–123), settling velocity is either enhanced or unchanged relative to stagnant flow for the range of investigated turbulence conditions. The smallest particles’ normalized settling velocities exhibited the most consistent trends when plotted versus the Kolmogorov-based Stokes numbers suggesting that the dissipative scales influence their dynamics. In contrast, the mid-sized particles were better characterized with a Stokes number based on the integral time scale. The largest particles were largely unaffected by the flow conditions. Using proper orthogonal decomposition (POD), the flow pattern scales are compared to particle trajectory curvature to complement results obtained through dimensional analysis using Stokes numbers. The smallest particles are found to have trajectories with curvatures of similar scale as the small flow scales (higher POD modes) whilst mid-sized particle trajectories had curvatures that were similar to the larger flow patterns (lower POD modes). The curvature trajectories of the largest particles did not correspond to any particular flow pattern scale suggesting that their trajectories were more random. These results provide experimental evidence of the “fast tracking” theory of settling velocity enhancement in turbulence and demonstrate that particles align themselves with flow scales in proportion to their size. PMID:27513958

  17. Velocity fluctuations and population distribution in clusters of settling particles at low Reynolds number

    CERN Document Server

    Boschan, A; Annichini, M; Gauthier, G

    2016-01-01

    A study on the spatial organization and velocity fluctuations of non Brownian spherical particles settling at low Reynolds number in a vertical Hele-Shaw cell is reported. The particle volume fraction ranged from 0.005 to 0.05, while the distance between cell plates ranged from 5 to 15 times the particle radius. Particle tracking revealed that particles were not uniformly distributed in space but assembled in transient settling clusters. The population distribution of these clusters followed an exponential law. The measured velocity fluctuations are in agreement with that predicted theoretically for spherical clusters, from the balance between the apparent weight and the drag force. This result suggests that particle clustering, more than a spatial distribution of particles derived from random and independent events, is at the origin of the velocity fluctuations.

  18. Near-field acoustic holography with sound pressure and particle velocity measurements

    DEFF Research Database (Denmark)

    Fernandez Grande, Efren

    of particle velocity measurements and combined pressure-velocity measurements in NAH, the relation between the near-field and the far-field radiation from sound sources via the supersonic acoustic intensity, and finally, the reconstruction of sound fields using rigid spherical microphone arrays. Measurement...... of the particle velocity has notable potential in NAH, and furthermore, combined measurement of sound pressure and particle velocity opens a new range of possibilities that are examined in this study. On this basis, sound field separation methods have been studied, and a new measurement principle based on double...... layer measurements of the particle velocity has been proposed. Also, the relation between near-field and far-field radiation from sound sources has been examined using the concept of the supersonic intensity. The calculation of this quantity has been extended to other holographic methods, and studied...

  19. Inertialess Velocity Change and a Two Particle Model of the Photon

    OpenAIRE

    David L. Spencer

    2017-01-01

    Building on the idea presented earlier that the gravitational fields outside of basic particles are those particles’ inertia and that acceleration results only from inertial field imbalances, inertialess velocity changes may result when motivation for motion arises from within basic particles. A two particle model of the photon shows how this might work

  20. On the velocity of ghost particles and the bias errors in Tomographic-PIV

    NARCIS (Netherlands)

    Elsinga, G.E.; Westerweel, J.; Scarano, F.; Novara, M.

    2010-01-01

    The paper discusses bias errors introduced in Tomographic-PIV velocity measurements by the coherent motion of ghost particles under some circumstances. It occurs when a ghost particle is formed from the same set of actual particles in both reconstructed volumes used in the cross-correlation analysis

  1. Particle descending velocity near the wall of a rolling circulating fluidized bed

    Science.gov (United States)

    Zhao, Tong; Takei, Masahiro; Murata, Hiroyuki; Liu, Kai

    2014-04-01

    As part of the study to develop compact and efficient marine exhaust gas treatment system with circulating fluidized bed (CFB), effects of the swing motion of a ship on gas-solid flow in the CFB was investigated. The heat transfer efficiency of the CFB is closely related with the particle flow near the wall of riser. As a trial to evaluate the particle flow near the wall of riser quantitatively, descending velocity of particles at upright and swing condition was measured by a particle image velocimetry (PIV) system. Particle motion near the wall of riser was recorded through an observation window by a high speed camera. The recorded images were processed to evaluate the local descending velocity of particles under different swing amplitude and period. As results, the swing motion affects the down-flow of particles, namely, descending particle flow along the wall of riser. The time-averaged descending velocity near the wall of riser is remarkably decreased by the motion. Effect of the swing period on the particle descending velocity is really small. But as the swing amplitude increases, the descending velocity of particle decreased significantly.

  2. Iron-Based Amorphous Coatings Produced by HVOF Thermal Spray Processing-Coating Structure and Properties

    Energy Technology Data Exchange (ETDEWEB)

    Beardsley, M B

    2008-03-26

    The feasibility to coat large SNF/HLW containers with a structurally amorphous material (SAM) was demonstrated on sub-scale models fabricated from Type 316L stainless steel. The sub-scale model were coated with SAM 1651 material using kerosene high velocity oxygen fuel (HVOF) torch to thicknesses ranging from 1 mm to 2 mm. The process parameters such as standoff distance, oxygen flow, and kerosene flow, were optimized in order to improve the corrosion properties of the coatings. Testing in an electrochemical cell and long-term exposure to a salt spray environment were used to guide the selection of process parameters.

  3. Turbulence-Induced Relative Velocity of Dust Particles II: The Bidisperse Case

    CERN Document Server

    Pan, Liubin; Scalo, John

    2014-01-01

    We investigate the relative velocity of inertial particles induced by turbulent motions, extending our earlier work on equal-size particles to the bidisperse case for different particles of arbitrary sizes. The model of Pan & Padoan (PP10) shows that the relative velocity between different particles has two contributions, named the generalized shear and acceleration terms, respectively. The generalized shear term represents the particles' memory of the spatial flow velocity difference across the particle distance at given times in the past, while the acceleration term is associated with the temporal flow velocity difference on individual particle trajectories. The latter vanishes for equal-size particles. Using a simulation, we compute the root-mean-square (rms) relative velocity, ^1/2, as a function of the particle friction times, tau_p1 and tau_p2, and show that the prediction of the PP10 model is in satisfactory agreement with the data, confirming the validity of its physical picture. For a given tau_p...

  4. Scaling laws of impact induced shock pressure and particle velocity in planetary mantle

    Science.gov (United States)

    Monteux, J.; Arkani-Hamed, J.

    2016-01-01

    While major impacting bodies during accretion of a Mars type planet have very low velocities (propagation and, hence, the derived scaling laws are poorly known for these low velocity impacts. Here, we use iSALE-2D hydrocode simulations to calculate shock pressure and particle velocity in a Mars type body for impact velocities ranging from 4 to 10 km/s. Large impactors of 100-400 km in diameter, comparable to those impacted on Mars and created giant impact basins, are examined. To better represent the power law distribution of shock pressure and particle velocity as functions of distance from the impact site at the surface, we propose three distinct regions in the mantle: a near field regime, which extends to 1-3 times the projectile radius into the target, where the peak shock pressure and particle velocity decay very slowly with increasing distance, a mid field region, which extends to ∼4.5 times the impactor radius, where the pressure and particle velocity decay exponentially but moderately, and a more distant far field region where the pressure and particle velocity decay strongly with distance. These scaling laws are useful to determine impact heating of a growing proto-planet by numerous accreting bodies.

  5. Relationships between spray parameters, microstructures and ultrasonic cavitation erosion behavior of HVOF sprayed Fe-based amorphous/nanocrystalline coatings.

    Science.gov (United States)

    Qiao, Lei; Wu, Yuping; Hong, Sheng; Zhang, Jianfeng; Shi, Wei; Zheng, Yugui

    2017-11-01

    Fe-based amorphous/nanocrystalline coatings were prepared on the AISI 321 steel substrate by the high-velocity oxygen-fuel (HVOF) thermal spraying technology. The effect of selected parameters (oxygen flow, kerosene flow and spray distance) on the cavitation erosion resistance (denoted as Rc) of the coating were investigated by using the Taguchi method. Statistical tools such as design of experiments (DOE), signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were used to meet the expected objective. It was concluded that the kerosene flow had greater influence on the Rc of the coating and followed by the spray distance and the oxygen flow, respectively. The optimum spray parameters (OSP) were 963L/min for the oxygen flow, 28L/h for the kerosene flow, and 330mm for the spray distance. The Rc of the coating increased with the increase of hardness or the decrease of porosity, and the hardness had a greater influence on Rc than the porosity. The Fe-based coating deposited under the OSP exhibited the best cavitation erosion resistance in distilled water. The cracks initiated at the edge of the pores and the interfaces between the un-melted or half-melted particles, and finally leaded to the delamination of the coating. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Calculation of a velocity distribution from particle trajectory end-points.

    Science.gov (United States)

    Rasmussen, Lowell A.

    1983-01-01

    The longitudinal component of the velocity of a particle at or near a glacier surface is considered, its position as a function of time being termed its trajectory. Functional relationships are derived for obtaining the trajectory from the spatial distribution of velocity and for obtaining the velocity distribution from the trajectory. It is established that the trajectory end-points impose only an integral condition on the velocity distribution and that no individual point on the velocity distribution can be determined if only the end-points are known.-from Author

  7. Lyapunov exponents for particles advected in compressible random velocity fields at small and large Kubo numbers

    CERN Document Server

    Gustavsson, K

    2013-01-01

    We calculate the Lyapunov exponents describing spatial clustering of particles advected in one- and two-dimensional random velocity fields at finite Kubo number Ku (a dimensionless parameter characterising the correlation time of the velocity field). In one dimension we obtain accurate results up to Ku ~ 1 by resummation of a perturbation expansion in Ku. At large Kubo numbers we compute the Lyapunov exponent by taking into account the fact that the particles follow the minima of the potential function corresponding to the velocity field. In two dimensions we compute the first four non-vanishing terms in the small-Ku expansion of the Lyapunov exponents. For large Kubo numbers we estimate the Lyapunov exponents by assuming that the particles sample stagnation points of the velocity field with det A > 0 and Tr A < 0 where A is the matrix of flow-velocity gradients.

  8. Lagrangian velocity and acceleration correlations of large inertial particles in a closed turbulent flow

    CERN Document Server

    Machicoane, Nathanaël

    2015-01-01

    We investigate the response of large inertial particle to turbulent fluctuations in a inhomogeneous and anisotropic flow. We conduct a Lagrangian study using particles both heavier and lighter than the surrounding fluid, and whose diameters are comparable to the flow integral scale. Both velocity and acceleration correlation functions are analyzed to compute the Lagrangian integral time and the acceleration time scale of such particles. The knowledge of how size and density affect these time scales is crucial in understanding partical dynamics and may permit stochastic process modelization using two-time models (for instance Saw-ford's). As particles are tracked over long times in the quasi totality of a closed flow, the mean flow influences their behaviour and also biases the velocity time statistics, in particular the velocity correlation functions. By using a method that allows for the computation of turbulent velocity trajectories, we can obtain unbiased Lagrangian integral time. This is particularly usef...

  9. Formulation of the Settling Velocity of Small Particles Initially Situated inside an Inclined Vortex

    Directory of Open Access Journals (Sweden)

    Urbano Sánchez

    2016-01-01

    Full Text Available Both the estimation of the time that small heavy particles remain inside a 3D vortex and the estimation of the average settling velocity of those particles are some important features in many practical situations. Previous works focused on the case of a horizontal 2D vortex. In this paper, we simulate the dynamics of heavy particles initially situated inside a three-dimensional vortex obtaining a formula for their average settling velocity. In a previous paper we obtained the trajectories of the particles and a formula that provides the time that they need to escape, Te⁎. This work simulates and analyses the escape process, and its main result is the obtaining, from numerical simulation, of a theoretical formulation of the average settling velocity Vz⁎ and its relationship with the elapsed time. We prove that the permanence time is of the order of dp⁎-10 (with dp⁎ particle diameter and that the average settling velocity is of the order of Te⁎-1/5 for sufficiently small particles. Some applications of the settling velocity formula developed in this work would be the design of mixture devices, the design of particle separation devices, and the prediction of the settling of pollutant particles, seeds, and pollen.

  10. Recording of particles velocity spectrum at the shock impact on different viscosity interface of liquids

    Directory of Open Access Journals (Sweden)

    Fedorov A.V.

    2015-01-01

    Full Text Available The results of experiments concerning the study of cavitational mechanism of liquid failure in a wide range of shock loading are presented in this paper. Free surface velocity of liquids and velocity spectrum of particles and jets were recorded using PDV method [1], their size was also determined. The value of spall strength of distilled water was defined.

  11. Measuring the Variations of the Apparent Settling Velocity for Fine Particles

    DEFF Research Database (Denmark)

    Larsen, Torben

    2000-01-01

    This note establishes the fact that the settling velocity for fine flocculent particles in flowing aquatic systems vary considerably and the settling velocity should therefore be understood as a variable which varies temporally and spatially in the flow field. In the mathematical formulation...

  12. A Raman anemometer for component-selective velocity measurements of particles in a flow

    NARCIS (Netherlands)

    Florisson, O.; Mul, de F.F.M.; Winter, de H.G.

    1981-01-01

    An anemometer for the measurement of the velocity of particles of different components in a flow, separate and apart from that of the flow itself, is described. As a component-selective mechanism Raman scattering is used. The velocity is measured by relating the autocorrelated scattering signal to t

  13. Influence of Processing Parameters on Residual Stress of High Velocity Oxy-Fuel Thermally Sprayed WC-Co-Cr Coating

    Science.gov (United States)

    Gui, M.; Eybel, R.; Asselin, B.; Radhakrishnan, S.; Cerps, J.

    2012-10-01

    Residual stress in high velocity oxy-fuel (HVOF) thermally sprayed WC-10Co-4Cr coating was studied based on design of experiment (DOE) with five factors of oxygen flow, fuel gas hydrogen flow, powder feed rate, stand-off distance, and surface speed of substrate. In each DOE run, the velocity and temperature of in-flight particle in flame, and substrate temperature were measured. Almen-type N strips were coated, and their deflections after coating were used for evaluation of residual stress level in the coating. The residual stress in the coating obtained in all DOE runs is compressive. In the present case of HVOF thermally sprayed coating, the residual stress is determined by three types of stress: peening, quenching, and cooling stress generated during spraying or post spraying. The contribution of each type stress to the final compressive residual stress in the coating depends on material properties of coating and substrate, velocity and temperature of in-flight particle, and substrate temperature. It is found that stand-off distance is the most important factor to affect the final residual stress in the coating, following by two-factor interaction of oxygen flow and hydrogen flow. At low level of stand-off distance, higher velocity of in-flight particle in flame and higher substrate temperature post spraying generate more peening stress and cooling stress, resulting in higher compressive residual stress in the coating.

  14. A high velocity impact experiment of micro-scale ice particles using laser-driven system

    Science.gov (United States)

    Yu, Hyeonju; Kim, Jungwook; Yoh, Jack J.

    2014-11-01

    A jet engine for high speed air breathing propulsion is subject to continuous wear as a result of impacts of micro-scale ice particles during a flight in the atmosphere. The inlet duct and compressor blades are exposed to on-coming frozen moisture particles that may result in the surface damage and significantly shorten the designed lifetime of the aircraft. Under such prolonged high-speed impact loading, the performance parameters such as flight instability and power loss of a jet engine can be significantly degraded. In this work, a laser-driven system was designed to accelerate micro-scale ice particles to the velocity up to Mach 2 using a Q-switched Nd:YAG laser beam at 100-600 mJ with 1064 nm wavelength and 9 ns pulse duration. The high speed images (Phantom v711) and double exposure shadowgraphs were used to calculate the average velocity of ice particles and their deceleration. Velocity Interferometer System for Any Reflector measurements were also utilized for the analysis of free surface velocity of a metal foil in order to understand the interfacial dynamics between the impacting particles and accepting metal target. The velocity of our ice particles is sufficiently fast for studying the effect of moisture particle collision on an air-breathing duct of high speed aircraft, and thus the results can provide insight into how minute space debris or micrometeorites cause damage to the orbiting spacecraft at large.

  15. A zero-gravity instrument to study low velocity collisions of fragile particles at low temperatures

    NARCIS (Netherlands)

    Salter, D. M.; Heisselmann, D.; Chaparro, G.; van der Wolk, G.; Reissaus, P.; Borst, A. G.; Dawson, R. W.; de Kuyper, E.; Drinkwater, G.; Gebauer, K.; Hutcheon, M.; Linnartz, H.; Molster, F. J.; Stoll, B.; van der Tuijn, P. C.; Fraser, H. J.; Blum, J.

    2009-01-01

    We discuss the design, operation, and performance of a vacuum setup constructed for use in zero (or reduced) gravity conditions to initiate collisions of fragile millimeter-sized particles at low velocity and temperature. Such particles are typically found in many astronomical settings and in region

  16. On the advantage of a divergence-free velocity interpolation for particle-in

    Science.gov (United States)

    Wang, Hongliang; Agrusta, Roberto; van Hunen, Jeroen

    2015-04-01

    The Particle-in-cell (PIC) method is found to be the most flexible and robust method to model the geodynamic problems with chemical heterogeneity. The initial equally distributed particles, however, can disperse and cluster due to the inaccuracy of the particle velocity interpolation. Our models with analytical solution show this problem is independent of the choice of numerical stokes solver. Instead, it is caused by the fact that the different components of the velocity field are interpolated independently without considering the divergence of the velocity.By introducing a conservative velocity interpolation (divergence free for incompressible flow), our model results demonstrate that the dispersion and clustering of the particles are significantly reduced both in steady state flow problems and time-dependent flow problems. The new interpolation is able to maintain a more steady number of particles in any computation cell, without the need for very high particle densities or re-seeding during the calculation.Our results show that this method improves the particle distribution when used in common geodynamic settings with sharp viscosity such as subduction dynamics and lithosphere dynamics, both in 2D and 3D. Thus, the potential application of this improved particle displacement method and its extension in compressible flow is very promising.

  17. Simultaneous PIV and PTV measurements of wind and sand particle velocities

    Science.gov (United States)

    Zhang, Wei; Wang, Yuan; Lee, Sang Joon

    2008-08-01

    Wind-blown sand is a typical example of two-phase particle-laden flows. Owing to lack of simultaneous measured data of the wind and wind-blown sand, interactions between them have not yet been fully understood. In this study, natural sand of 100-125 μm taken from Taklimakan Desert was tested at the freestream wind speed of 8.3 m/s in an atmospheric boundary layer wind tunnel. The captured flow images containing both saltating sand and small wind tracer particles, were separated by using a digital phase mask technique. The 2-D PIV (particle imaging velocimetry) and PTV (particle tracking velocimetry) techniques were employed to extract simultaneously the wind velocity field and the velocity field of dispersed sand particles, respectively. Comparison of the mean streamwise wind velocity profile and the turbulence statistics with and without sand transportation reveal a significant influence of sand movement on the wind field, especially in the dense saltating sand layer ( y/ δ < 0.1). The ensemble-averaged streamwise velocity profile of sand particles was also evaluated to investigate the velocity lag between the sand and the wind. This study would be helpful in improving the understanding of interactions between the wind and the wind-blown sand.

  18. Particle fluxes in the deep Eastern Mediterranean basins: the role of ocean vertical velocities

    Directory of Open Access Journals (Sweden)

    L. Patara

    2008-08-01

    Full Text Available This paper analyzes the relationship between deep sedimentary fluxes and ocean current vertical velocities in an offshore area of the Ionian Sea, the deepest basin of the Eastern Mediterranean Sea. Sediment trap data are collected at 500 m and 2800 m depth in two successive moorings covering the period September 1999–May 2001. A tight coupling is observed between the upper and deep traps and the estimated particle sinking rates are higher than 200 m day−1. The current vertical velocity field is computed from a high resolution Ocean General Circulation Model simulation and from the wind stress curl. Current vertical velocities are larger and more variable than Ekman vertical velocities, yet the general patterns are alike. Current vertical velocities are generally smaller than 1 m day−1: we therefore exclude a direct effect of downward velocities in determining high sedimentation rates. However, we find that upward velocities in the subsurface layers of the water column are positively correlated with deep particle fluxes. We thus hypothesize that upwelling would produce an increase in upper ocean nutrient levels – thus stimulating primary production and grazing – a few weeks before an enhanced vertical flux is found in the sediment traps. By analyzing the delayed effects of ocean vertical velocities on deep particle fluxes we envisage a spectrum of particle sinking speeds ranging from about 100 m day−1 to more than 200 m day−1. High particle sedimentation rates may be attained by means of rapidly sinking fecal pellets produced by gelatinous macro-zooplankton. Other sedimentation mechanisms, such as dust deposition, are also considered in explaining large pulses of deep particle fluxes. The fast sinking rates estimated in this study might be an evidence of the efficiency of the biological pump in sequestering organic carbon from the surface layers of the deep Eastern Mediterranean basins.

  19. Micro-particle image velocimetry for velocity profile measurements of micro blood flows.

    Science.gov (United States)

    Pitts, Katie L; Fenech, Marianne

    2013-04-25

    Micro-particle image velocimetry (μPIV) is used to visualize paired images of micro particles seeded in blood flows. The images are cross-correlated to give an accurate velocity profile. A protocol is presented for μPIV measurements of blood flows in microchannels. At the scale of the microcirculation, blood cannot be considered a homogeneous fluid, as it is a suspension of flexible particles suspended in plasma, a Newtonian fluid. Shear rate, maximum velocity, velocity profile shape, and flow rate can be derived from these measurements. Several key parameters such as focal depth, particle concentration, and system compliance, are presented in order to ensure accurate, useful data along with examples and representative results for various hematocrits and flow conditions.

  20. The equilibrium velocity of spherical particles in rectangular microfluidic channels for size measurement.

    Science.gov (United States)

    Sommer, Christian; Quint, Stephan; Spang, Peter; Walther, Thomas; Bassler, Michael

    2014-07-01

    According to the Segré-Silberberg effect, spherical particles migrate to a lateral equilibrium position in parabolic flow profiles. Here, for the first time, the corresponding equilibrium velocity is studied experimentally for micro particles in channels with rectangular cross section. Micro channels are fabricated in PMMA substrate based on a hot embossing process. To measure individual particle velocities at very high precision, the technique of spatially modulated emission is applied. It is found that the equilibrium velocity is size-dependent and the method offers a new way to measure particle size in microfluidic systems. The method is of particular interest for microfluidic flow cytometry as it delivers an alternative to the scatter signal for cell size determination.

  1. Tribología de recubrimientos Cermet/NiCrBSi depositados mediante HVOF

    Directory of Open Access Journals (Sweden)

    Guilemany, J. M.

    2004-04-01

    Full Text Available This work consists on a deep tribological study of the WX system composed by a mechanical blend in different compositions of NiCrBSi and WC-12Co powders: 20% NiCrBSi (W2, 40% NiCrBSi (W4 y 60% NiCrBSi (W6. The coatings have been obtained by high velocity oxy-fuel process (HVOF. The measurements made by Ball-On-Disk test are: the friction coefficient is lower than 0.5 and the exchanged energy between the counterparts is under 10 KJ. To quantify the friction wear rate, the volume loss and the track depth, Scanning White Light Interferometry and SEM have been used. The track depth is proportional to the amount of NiCrBSi. A higher percentage of WC-12Co increases the friction wear resistance and decreases the abrasion wear rate (Rubber Wheel test. In all the coatings studied, no diffusion processes are found between the mixed phases, the adhesion between the coatings and the substrate is excellent, the porosity level is below 2% and an increase of microhardness of the coating due to a strengthening of the matrix produced by impacts of solid particles, takes place.

    El trabajo consta de un completo estudio tribológico del sistema WX que consiste en la mezcla mecánica de WC-12Co y NiCrBSi en diferentes proporciones: 20% NiCrBSi (W2, 40% NiCrBSi (W4 y 60% NiCrBSi (W6. Los recubrimientos se han obtenido por proyección térmica de alta velocidad (HVOF. Para todos los sistemas, el coeficiente de fricción es menor que 0.5 y la energía intercambiada entre el par friccionante y el recubrimiento es inferior a 10 KJ. Para cuantificar el desgaste por fricción se han utilizado la profundidad de la huella y el volumen perdido durante el ensayo, obtenidos mediante Interferometría de Barrido de Luz Blanca (SLWI y SEM. La profundidad de la huella sigue una evolución directamente proporcional al contenido en NiCrBSi. Un mayor contenido en WC-12Co aumenta la resistencia al desgaste por fricción y disminuye la velocidad de desgaste por abrasión (ensayo

  2. Study of the HVOF Ni-Based Coatings' Corrosion Resistance Applied on Municipal Solid-Waste Incinerators

    Science.gov (United States)

    Guilemany, J. M.; Torrell, M.; Miguel, J. R.

    2008-06-01

    Oxidation of exchanger steel tubes causes important problems in Municipal Solid-Waste Incinerator (MSWI) plants. The present paper shows a possible solution for this problem through High-Velocity Oxygen Fuel (HVOF) thermal spray coatings. A comparative study was carried out between powder and wire Ni-based thermal spray coatings (with the same composition). These optimized coatings were compared based on their microstructure, wear properties (ASTM G99-90, ASTM G65-91), and erosion-corrosion (E-C) resistance. An E-C test designed in the Thermal Spray Centre was performed to reproduce the mechanisms that take place in a boiler. Studying the results of this test, the wire HVT Inconel coating sprayed by propylene appears to be the best alternative. A commercial bulk material with a composition similar to Ni-based coatings was tested to find the products of the oxidation reactions. The protective mechanisms of these materials were assessed after studying the results obtained for HVOF coatings and the bulk material where the presence of nickel and chromium oxides as a corrosion product can be seen. Kinetic evolution of the Ni-based coatings can be studied by thermogravimetric analysis. The protection that Inconel coatings give to the tube through the difference of the gain mass can be seen. Ni-based HVOF coatings by both spray conditions are a promising alternative to MSWI protection against chlorine environments, and their structures have a very important role.

  3. High-temperature corrosion and wear properties of HVOF coatings of cobalt-based (CoCr) surfacing alloys

    Energy Technology Data Exchange (ETDEWEB)

    Raghu, D.; Lee, D.A.; Singh, P.M.

    1999-07-01

    High Velocity Oxy-Fuel (HVOF) thermal spraying is extensively used in industry to produce high-density, low porosity functional coatings to resist severe wear and corrosion. Increasingly there is a need to provide high-quality coatings that resist both wear and corrosion at high temperatures at the same time. Very few engineering data exist on such coatings. In this paper, a study of HVOF coatings of Co-Cr-Mo alloys, that relies on Laves phases or on carbides for wear and corrosion resistance is reported. The paper covers the basic metallurgy of the alloys, their design and microstructure. The oxidation and sulfidation resistances of the coatings are evaluated at 600 C. The high-temperature hardness and the room-temperature abrasion resistance, hardness and bond strengths are compared to assess their utility in high-temperature corrosion and wear-resistant applications. The test results indicate that these alloys are strong candidate materials for providing protection in the form of HVOF coatings, in high-temperature wear and corrosion environments.

  4. Simultaneous measurement of particle velocity and size based on gray difference and autocorrelation

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The gray of two images of a same particle taken by a digital camera with different exposure times is different too. Based on the gray difference of particle images in a double-exposed photo and autocorrelation processing of digital images,this paper proposes a method for measuring particle velocities and sizes simultaneously. This paper also introduces the theoretical foundation of this method,the process of particle imaging and image processing,and the simultaneous measurement of velocity and size of a low speed flow field with 35 μm and 75 μm standard particles. The graphical measurement results can really reflect the flow characteristics of the flow field. In addition,although the measured velocity and size histograms of these two kinds of standard particles are slightly wider than the theoretical ones,they are all still similar to the normal distribution,and the peak velocities and diameters of the histograms are consistent with the default values. Therefore,this measurement method is capable of providing moderate measurement accuracy,and it can be further developed for high-speed flow field measurements.

  5. Analysis of sand particles' lift-off and incident velocities in wind-blown sand flux

    Institute of Scientific and Technical Information of China (English)

    Tian-Li Bo; Xiao-Jing Zheng; Shao-Zhen Duan; Yi-Rui Liang

    2013-01-01

    In the research of windblown sand movement,the lift-off and incident velocities of saltating sand particles play a significant role in bridging the spatial and temporal scales from single sand particle's motion to windblown sand flux.In this paper,we achieved wind tunnel measurements of the movement of sand particles near sand bed through improving the wind tunnel experimental scheme of paticle image velocimetry (PIV) and data processing method.And then the influence of observation height on the probability distributions of lift-off and incident velocities of sand particles was analyzed.The results demonstrate that the observation height has no obvious influence on the distribution pattern of the lift-off and incident velocities of sand particles,i.e.,the probability distribution of horizontal and vertical velocities of lift-off and incident sand particles follow a Gaussian distribution and a negative exponential distribution,respectively.However,it influences the center of the Gaussian distribution,the decay constant and the amplitude of the negative exponential distribution.

  6. High-Temperature Erosion of HVOF Sprayed Cr3C2-NiCr Coating and Mild Steel for Boiler Tubes

    Science.gov (United States)

    Yang, Guan-Jun; Li, Chang-Jiu; Zhang, Shi-Jun; Li, Cheng-Xin

    2008-12-01

    The comparison of the high-temperature erosion behavior of a High-velocity oxyfuel (HVOF) sprayed Cr3C2-NiCr coating with mild steel for circulating fluidized bed boiler tubes was investigated. Results showed that the erosion rate of the mild steel at 800 °C was four times that at 300 °C at an erosion angle of 30°. However, the erosion rate of the HVOF sprayed Cr3C2-NiCr coating was not influenced by the temperature in the range of 300-800 °C. It was found that the erosion resistance of HVOF sprayed Cr3C2-NiCr coating was more than three times higher than that of the mild steel at 700-800 °C. In addition to the ploughing on the coating surface, the cracking along splat interfaces in the coating was clearly observed on the cross-sectional microstructure. The results indicate that the erosion performance of the HVOF sprayed Cr3C2-NiCr coating is controlled by the cohesion between splats and can be further enhanced by improving splat cohesion.

  7. About scaling properties of relative velocity between heavy particles in turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Lanotte, A S [ISAC-CNR, and INFN, Sez. Lecce, 73100 Lecce (Italy); Bee, J [Universite de Nice-Sophia Antipolis, CNRS- OCA, Laboratoire Cassiopee, 06300 Nice (France); Biferale, L [Department of Physics and INFN, University of Rome Tor Vergata, 00133 Rome (Italy); Cencini, M [INFM-CNR, SMC Department of Physics, University of Rome La Sapienza, and ISC-CNR, 00185 Roma (Italy); Toschi, F, E-mail: a.lanotte@isac.cnr.it [Department of Physics Technische Universiteit Eindhoven, 5600 MB Eindhoven (Netherlands)

    2011-12-22

    We present results obtained from high-resolution direct numerical simulations (DNS) of incompressible, statistically homogeneous and isotropic turbulence, up to a Taylor scale based Reynolds number Re{sub {lambda}} {approx_equal} 200 and with millions of heavy particles with different inertia. In our set-up, particles are assumed to be spherical and rigid, they simply move by viscous forces, such as the Stokes drag. The velocity statistics is found to be extremely intermittent, with an almost bi-fractal behavior. Here, we consider also a new data analysis for the stationary distribution of rescaled longitudinal velocity difference and further assess the intermittent character of the heavy particles velocities, characterized by the presence of quasi-algebraic tails.

  8. Measuring the translational and rotational velocity of particles in helical motion using structured light

    CERN Document Server

    Rosales-Guzmán, Carmelo; Belmonte, Aniceto; Torres, Juan P

    2014-01-01

    We measure the rotational and translational velocity components of particles moving in helical motion using the frequency shift they induced to the structured light beam illuminating them. Under Laguerre-Gaussian mode illumination, a particle with a helical motion reflects light that acquires an additional frequency shift proportional to the angular velocity of rotation in the transverse plane, on top of the usual frequency shift due to the longitudinal motion. We determined both the translational and rotational velocities of the particles by switching between two modes: by illuminating with a Gaussian beam, we can isolate the longitudinal frequency shift; and by using a Laguerre-Gaussian mode, the frequency shift due to the rotation can be determined. Our technique can be used to characterize the motility of microorganisms with a full three-dimensional movement.

  9. Particle image velocimetry measurements of 2-dimensional velocity field around twisted tape

    Energy Technology Data Exchange (ETDEWEB)

    Song, Min Seop; Park, So Hyun; Kim, Eung Soo, E-mail: kes7741@snu.ac.kr

    2016-11-01

    Highlights: • Measurements of the flow field in a pipe with twisted tape were conducted by particle image velocimetry (PIV). • A novel matching index of refraction technique utilizing 3D printing and oil mixture was adopted to make the test section transparent. • Undistorted particle images were clearly captured in the presence of twisted tape. • 2D flow field in the pipe with twisted tape revealed the characteristic two-peak velocity profile. - Abstract: Twisted tape is a passive component used to enhance heat exchange in various devices. It induces swirl flow that increases the mixing of fluid. Thus, ITER selected the twisted tape as one of the candidates for turbulence promoting in the divertor cooling. Previous study was mainly focused on the thermohydraulic performance of the twisted tape. As detailed data on the velocity field around the twisted tape was insufficient, flow visualization study was performed to provide fundamental data on velocity field. To visualize the flow in a complex structure, novel matching index of refraction technique was used with 3-D printing and mixture of anise and mineral oil. This technique enables the camera to capture undistorted particle image for velocity field measurement. Velocity fields at Reynolds number 1370–9591 for 3 different measurement plane were obtained through particle image velocimetry. The 2-dimensional averaged velocity field data were obtained from 177 pair of instantaneous velocity fields. It reveals the characteristic two-peak flow motion in axial direction. In addition, the normalized velocity profiles were converged with increase of Reynolds numbers. Finally, the uncertainty of the result data was analyzed.

  10. The measurement of abrasive particles velocities in the process of abrasive water jet generation

    Science.gov (United States)

    Zeleňák, Michal; Foldyna, Josef; Říha, Zdeněk

    2014-08-01

    An optimization of the design of the abrasive cutting head using the numerical simulation requires gathering as much information about processes occurring in the cutting head as possible. Detailed knowledge of velocities of abrasive particles in the process of abrasive water jet generation is vital for the verification of the numerical model. A method of measurement of abrasive particles at the exit of focusing tube using the FPIV technique was proposed and preliminary tests are described in the paper. Results of analysis of measured velocity fields are presented in the paper.

  11. Variables Affecting Smooth Particle Hydrodynamics Simulation of High-Velocity Flyer Plate Impact Experiments

    Energy Technology Data Exchange (ETDEWEB)

    Somasundaram, Deepak S [UNLV; Trabia, Mohamed [UNLV; O' Toole, Brendan [UNLV; Hixson, Robert S [NSTec

    2014-01-23

    This paper describes our work to characterize the variables affecting the smoothed particle hydrodynamics (SPH) method in the LS-DYNA package for simulating high-velocity flyer plate impact experiments. LS-DYNA simulations are compared with one-dimensional experimental data of an oxygen-free high-conductivity (OFHC) copper flyer plate impacting another plate of the same material. The comparison is made by measuring the velocity of a point on the back surface of the impact plate using the velocity interferometer system for any reflector (VISAR) technique.

  12. Effect of temperature on electrophoresis velocity of sol particles in water

    Institute of Scientific and Technical Information of China (English)

    鲍治宇; 顾大明

    2002-01-01

    Viscosity of water is affected by temperature and electrophoresis velocity is related to the viscosity of colloid. However, there hasn' t been any direct description about the relation between electrophoresis velocity of colloid and temperature. Based on a large number of tests, the relation between electrophoresis velocity and temperature is established as [ v = A + B( T-T°) ]. Meanwhile the ratio of the electric charge (q) of sol particles to their radium (r) is a constant is obtained. The results of above were testified in both experiment and theory.

  13. Microstructural characteristics and mechanical properties of HVOF sprayed NiCrAl coating on superalloys

    Energy Technology Data Exchange (ETDEWEB)

    Mahesh, R.A. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee 247667 (India); Jayaganthan, R. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee 247667 (India)], E-mail: rjayafmt@iitr.ernet.in; Prakash, S. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee 247667 (India)

    2009-01-22

    High velocity oxy-fuel (HVOF) process sprayed NiCrAl coatings on superalloys were characterized by various techniques such as optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive spectroscopic analysis (SEM/EDS) to render an insight into their microstrucural features and assess its suitability for high temperature corrosion resistance applications. The as sprayed coatings were found to be dense with splat like layered morphology. The XRD analysis of the coating showed the presence of Ni (fcc) as a prominent phase with Cr and Al as minor phases. The porosity of the coatings was calculated from its optical micrographs and found to be less than 1.7%. The measured hardness and average bond strength of the coatings were found to be in the range of 278-351 Hv and 59 MPa, respectively. The observed microstructral characteristics, higher bond strength, and hardness of HVOF sprayed NiCrAl coating show that it may act as an effective barrier to provide high temperature protection to the superalloys.

  14. Particle fluxes in the deep Eastern Mediterranean basins: the role of ocean vertical velocities

    Directory of Open Access Journals (Sweden)

    L. Patara

    2009-03-01

    Full Text Available This paper analyzes the relationship between deep sedimentary fluxes and ocean current vertical velocities in an offshore area of the Ionian Sea, the deepest basin of the Eastern Mediterranean Sea. Sediment trap data are collected at 500 m and 2800 m depth in two successive moorings covering the period September 1999–May 2001. A tight coupling is observed between the upper and deep traps and the estimated particle sinking rates are more than 200 m day−1. The current vertical velocity field is computed from a 1/16°×1/16° Ocean General Circulation Model simulation and from the wind stress curl. Current vertical velocities are larger and more variable than Ekman vertical velocities, yet the general patterns are alike. Current vertical velocities are generally smaller than 1 m day−1: we therefore exclude a direct effect of downward velocities in determining high sedimentation rates. However we find that upward velocities in the subsurface layers of the water column are positively correlated with deep particle fluxes. We thus hypothesize that upwelling would produce an increase in upper ocean nutrient levels – thus stimulating primary production and grazing – a few weeks before an enhanced vertical flux is found in the sediment traps. High particle sedimentation rates may be attained by means of rapidly sinking fecal pellets produced by gelatinous macro-zooplankton. Other sedimentation mechanisms, such as dust deposition, are also considered in explaining large pulses of deep particle fluxes. The fast sinking rates estimated in this study might be an evidence of the efficiency of the biological pump in sequestering organic carbon from the surface layers of the deep Eastern Mediterranean basins.

  15. Particle Paths of Lagrangian Velocity Distribution Simulating the Spiral Arms of Galaxy M51

    Institute of Scientific and Technical Information of China (English)

    Tzu-Fang Chen; Georgios H. Vatistas; Sui Lin

    2008-01-01

    Galaxies are huge families of stars held together by their own gravities. The system M51 is a spiral galaxy. It possesses billions of stars. The range of the spiral arms extends hundred thousand light years. The present study is in an attempt in using the particle paths of the Lagrangian flow field to simulate the spiral arms of Galaxy M51.The Lagrangian flow field is introduced. The initial locations of fluid particles in the space between two concentric cylinders are first specified. Then a linear velocity distribution of the fluid particles is used with different angle rotations of the particles to obtain the particle paths in the Lagrangian diagram. For simulating the spiral arms of Galaxy M51, the Lagrangian M51 diagram is developed. The particle paths of the Lagrangian M51 diagram agree quite well with the spiral arms of Galaxy M51.

  16. Luminescent two-color tracer particles for simultaneous velocity and temperature measurements in microfluidics

    Science.gov (United States)

    Massing, J.; Kaden, D.; Kähler, C. J.; Cierpka, C.

    2016-11-01

    The simultaneous and non-intrusive measurement of temperature and velocity fields in flows is of great scientific and technological interest. To sample the velocity and temperature, tracer particle based approaches have been developed, where the velocity is measured using PIV or PTV and the temperature is obtained from the intensity (LIF, thermographic phosphors) or frequency (TLC) of the light emitted or reflected by the tracer particles. In this article, a measurement technique is introduced, that relates the luminescent intensity ratio of individual dual-color luminescent tracer particles to temperature. Different processing algorithms are tested on synthetic particle images and compared with respect to their accuracy in estimating the intensity ratio. Furthermore, polymer particles which are doped with the temperature sensitive dye europium (III) thenoyltrifluoroacetonate (EuTTA) and the nearly temperature insensitive reference dye perylene are characterized as valid tracers. The results show a reduction of the temperature measurement uncertainty of almost 40% (95% confidence interval) compared to previously reported luminescent particle based measurement techniques for microfluidics.

  17. Turbulence-Induced Relative Velocity of Dust Particles III: The Probability Distribution

    CERN Document Server

    Pan, Liubin; Scalo, John

    2014-01-01

    Motivated by its important role in the collisional growth of dust particles in protoplanetary disks, we investigate the probability distribution function (PDF) of the relative velocity of inertial particles suspended in turbulent flows. Using the simulation from our previous work, we compute the relative velocity PDF as a function of the friction timescales, tau_p1 and tau_p2, of two particles of arbitrary sizes. The friction time of particles included in the simulation ranges from 0.1 tau_eta to 54T_L, with tau_eta and T_L the Kolmogorov time and the Lagrangian correlation time of the flow, respectively. The relative velocity PDF is generically non-Gaussian, exhibiting fat tails. For a fixed value of tau_p1, the PDF is the fattest for equal-size particles (tau_p2~tau_p1), and becomes thinner at both tau_p2tau_p1. Defining f as the friction time ratio of the smaller particle to the larger one, we find that, at a given f in 1/2>T_L). These features are successfully explained by the Pan & Padoan model. Usin...

  18. Shock Initiation of New and Aged PBX 9501 Measured with Embedded Electromagnetic Particle Velocity Gauges

    Energy Technology Data Exchange (ETDEWEB)

    L. G. Hill; R. L. Gustavsen; R. R. Alcon; S. A. Sheffield

    1999-09-01

    We have used an embedded electromagnetic particle velocity gauge technique to measure the shock initiation behavior in PBX 9501 explosive. Up to twelve separate particle velocity wave profile measurements have been made at different depths in a single experiment. These detail the growth from an input shock to a detonation. In addition, another gauge element called a ''shock tracker'' has been used to monitor the progress of the shock front as a function of time and position as it moves through the explosive sample. This provides data similar to that obtained in a traditional explosively driven wedge test and is used to determine the position and time that the wave attains detonation. Run distance-to-detonation vs. input pressure (Pop-plot) data and particle velocity wave profile data have been obtained on new PBX 9501 pressed to densities of 1.826, 1.830, and 1.837 g/cm{sup 3}. In addition, the same measurements were performed on aged material recovered from dismantled W76 and W78 weapons. The input pressure range covered was 3.0 to 5.2 GPa. All results to date show shock sensitivity to be a function only of the initial density and not of age. PBX 9501 shock initiates the same after 17 years in stockpile as it does on the day it is pressed. Particle velocity wave profiles show mixed heterogeneous initiation (growth in the front) and homogeneous initiation (growth behind the front).

  19. Imaginary particle tracking accelerometry based on time-resolved velocity fields

    Science.gov (United States)

    Wang, Zhongyi; Gao, Qi; Pan, Chong; Feng, Lihao; Wang, Jinjun

    2017-09-01

    An accurate calculation of material acceleration is important for particle image velocimetry-based pressure reconstruction. Therefore, an imaginary particle tracking accelerometry (IPTA) approach based on time-resolved velocity fields is described in this paper for a better determination of acceleration. Multi-velocity fields and a least squares polynomial fitting of the velocity along imaginary particle trajectories are introduced to improve the acceleration accuracy. The process of imaginary particle tracking is operated iteratively until a convergence condition is satisfied. Then the Lagrangian acceleration (or the material acceleration in the Eulerian coordinates) is acquired by the first-order time derivation of the fitting polynomial. In addition, the sensitivity of the IPTA approach to different levels of noise and parameters that affect its performance is investigated. A criterion is proposed to determine these parameters when using IPTA to calculate the acceleration. Performance of the IPTA method is compared with other velocity-based accelerometry methods, including both Eulerian and Lagrangian methods. Assessments are conducted in a synthetic solid body rotation flow, a synthetic flow of a vortex ring, and an experimental jet flow. The results show that IPTA is a robust method for experimental acceleration determination that can both improve the accuracy of acceleration and provide better physical characteristics of the flow field.

  20. Relaxation Time of the Particle Beam with an Anisotropic Velocity Distribution

    Directory of Open Access Journals (Sweden)

    V.P. Vechirka

    2012-11-01

    Full Text Available The computer experiment for study of the relaxation time of the beam particles with an anisotropic velocity distribution is performed by the molecular dynamics. Obtained results agree with the characteristic times of thermal relaxation in plasma for the electronic coolers in modern storage rings.

  1. Study on the physical basis of pressure and particle velocity combine processing

    Institute of Scientific and Technical Information of China (English)

    HUI Junying; LIU Hong; YU Huabing; FAN Minyi; LIANG Guolong

    2001-01-01

    Some basic studies of pressure and particle velocity combine processing such as correlation between them, average acoustic intensity processing, rotating and sharpening of directivity are described. Preliminary results based on theoretical analysis and lake trail will lay a foundation for further research.

  2. An integrated 3D sound intensity sensor using four-wire particle velocity sensors: II. Modelling

    NARCIS (Netherlands)

    Honschoten, van J.W.; Yntema, D.R.; Wiegerink, R.J.

    2010-01-01

    The sensitivity of a micromachined acoustic sensor consisting of four hot-wire particle velocity sensors is analysed theoretically and experimentally. The device and its fabrication have been presented in part 1 of this paper (Yntema et al 2010 J. Micromech. Microeng. 20 015042). A relatively straig

  3. Kinetic theory of binary particles with unequal mean velocities and non-equipartition energies

    Science.gov (United States)

    Chen, Yanpei; Mei, Yifeng; Wang, Wei

    2017-03-01

    The hydrodynamic conservation equations and constitutive relations for a binary granular mixture composed of smooth, nearly elastic spheres with non-equipartition energies and different mean velocities are derived. This research is aimed to build three-dimensional kinetic theory to characterize the behaviors of two species of particles suffering different forces. The standard Enskog method is employed assuming a Maxwell velocity distribution for each species of particles. The collision components of the stress tensor and the other parameters are calculated from the zeroth- and first-order approximation. Our results demonstrate that three factors, namely the differences between two granular masses, temperatures and mean velocities all play important roles in the stress-strain relation of the binary mixture, indicating that the assumption of energy equipartition and the same mean velocity may not be acceptable. The collision frequency and the solid viscosity increase monotonously with each granular temperature. The zeroth-order approximation to the energy dissipation varies greatly with the mean velocities of both species of spheres, reaching its peak value at the maximum of their relative velocity.

  4. Particle Size, Number Density, And Velocity Measurements In A 2800 K Combustion System

    Science.gov (United States)

    Farmer, W. M.; Schwartz, F. A.; Stallings, E. S.; Belz, R. A.

    1983-10-01

    Particle size and velocity measurements have been obtained in a low-speed (6 to 10 m/s), 2800 K combustor 30 cm in diameter. The measurements were obtained using a particle-sizing interferometer coupled to a 0.5 m spectrometer for background light rejection from radiant particles. Results obtained for the combustion of powdered coke clearly indicate the capabilities of this type of instrument to estimate combustor efficiency as a function of temperature. Comparison of the optically sampled measurements with other sampling techniques shows reasonable agreement.

  5. Measurement of velocity profiles of nanofluids in laminar channel flow using Particle Image Velocimetry

    Energy Technology Data Exchange (ETDEWEB)

    Nayak, Arun K.; Kulkarni, Parimal P.; Singh, R.K.; Verma, Pumendra [Bhabha Atomic Research Centre (BARC), Mumbai (India). Reactor Engineering Div.; Gandhi, Mayur [University Institute of Chemical Technology, Mumbai (India). Dept. of Chemical Engineering

    2014-06-15

    The objective of the paper is to measure the velocity profiles of water based nanofluids for flow through channels in order to understand whether the nanofluids behave Newtonian. For this purpose, experiments were carried for flow through a rectangular channel in laminar regime. Four different nanofluids were used, i.e. Al{sub 2}O{sub 3}, CuO, TiO{sub 2} and SiO{sub 2} with base fluid as water. Experiments were conducted at low concentration of these particles. The velocity profiles were measured using Particle Image Velocimetry. The results indicate that the velocity profiles are similar for all the fluids indicating the flows to be Newtonian. (orig.)

  6. Comparison of the terminal fall velocity, surface roughness and erosion threshold for volcanic particles.

    Science.gov (United States)

    Douillet, G. A.; Seybold, L.; Rasmussen, K. R.; Kueppers, U.,; Lo Castro, D.; Dingwell, D. B.

    2012-04-01

    Pyroclasts are particles emitted during explosive volcanic eruptions. They exhibit highly variable porosities, shapes, and densities. As such, their behaviors differ from the wind-blown and fluvial sand usually studied in clastic sedimentology. In order to better constrain the specificities of pyroclastic material, and gain insights into the flow and depositional processes within dilute pyroclastic density currents, the terminal fall velocity was experimentally measured in air and compared to surface roughness and saltation threshold data obtained from wind tunnel experiments as well as with shape parameters. Two types of particles were investigated (scoriaceous material and pumices), as well as different grain sizes (0.125-4mm for scoria and 0.125-16mm for pumices in half phi fractions). The terminal fall velocity corresponds to the velocity for which the drag exerted by air on a particle counteracts its weight, so that acceleration becomes null and the velocity constant. In order to measure the terminal fall velocity, particles were dropped in a closed and large vertical tube (to avoid any perturbation by air movement present in the lab) and the velocity derived from high speed video recorded near the bottom of the tube. By repeating the experiments from different heights, the velocity was seen to increase with increasing drop-height, until reaching a constant value, taken as the terminal fall velocity. The surface roughness is a value that defines how rough a bed of particles is seen by a wind. The saltation threshold corresponds to the near-bed shear-stress necessary for particles to leave the surface and begin to bounce on the bed. Both are derived from wind profiles experimentally measured in a wind tunnel in Aarhus (Denmark; see abstract 2128). Shape parameters were measured with a Camsizer (from Retsch) in Catania (Italy) and the sphericity, symmetry, aspect ratio, and convexity derived. Since the surface roughness, saltation threshold, and terminal fall

  7. Influences of interfacial damage on the effective wave velocity in composites with reinforced particles

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The scattering of elastic waves by a spherical particle with imperfect interface and the multiple scattering by many spherical particles with imperfect interface are studied in this paper. First,the scattering of elastic waves by a spherical particle with imperfect interface,i.e. spring interface model,is studied. Then,the multiple scattering by random distributed particles with interfacial damage in a composite material is investigated. The equations to evaluate velocity and attenuation of effective waves defined by statistic averaging are given. Furthermore,based on the established relation between the effective velocity and interfacial constants,a method to evaluate the interfacial damage nondestructively from the ultrasonic measure data is proposed. The numerical simulation is performed for the Sic-Al composites. The effective velocity is computed to show the influences of interface damage. By using the genetic algorithm,the interfacial damage is evaluated from the synthetic experimental data with various levels of error. The numerical results show the feasibility of the method proposed to approximately evaluate the interfacial damage in a composite material with reinforced particles based on ultrasonic data.

  8. Direct multi-scale reconstruction of velocity fields from measurements of particle tracks

    CERN Document Server

    Kelley, Douglas H

    2010-01-01

    We present a method for reconstructing two-dimensional velocity fields at specified length scales using observational data from tracer particles in a flow, without the need for interpolation or smoothing. The algorithm, adapted from techniques proposed for oceanography, involves a least-squares projection of the measurements onto a set of two-dimensional, incompressible basis modes with known length scales. Those modes are constructed from components of the velocity potential function, which accounts for inflow and outflow at the open boundaries of the measurement region; and components of the streamfunction, which accounts for the remainder of the flow. All calculations are evaluated at particle locations, without interpolation onto an arbitrary grid. Since the modes have a well-defined length scales, scale-local flow properties are available directly. The technique eliminates outlier particles automatically and reduces the apparent compressibility of the data. Moreover the technique can be used to produce s...

  9. High Velocity Impact Interaction of Metal Particles with Porous Heterogeneous Materials with an Inorganic Matrix

    Science.gov (United States)

    Glazunov, A. A.; Ishchenko, A. N.; Afanasyeva, S. A.; Belov, N. N.; Burkin, V. V.; Rogaev, K. S.; Tabachenko, A. N.; Khabibulin, M. V.; Yugov, N. T.

    2016-03-01

    A computational-experimental investigation of stress-strain state and fracture of a porous heterogeneous material with an inorganic matrix, used as a thermal barrier coating of flying vehicles, under conditions of a high-velocity impact by a spherical steel projectile imitating a meteorite particle is discussed. Ballistic tests are performed at the velocities about 2.5 km/s. Numerical modeling of the high-velocity impact is described within the framework of a porous elastoplastic model including fracture and different phase states of the materials. The calculations are performed using the Euler and Lagrange numerical techniques for the velocities up to 10 km/s in a complete-space problem statement.

  10. The terminal velocity of volcanic particles with shape obtained from 3D X-ray microtomography

    Science.gov (United States)

    Dioguardi, Fabio; Mele, Daniela; Dellino, Pierfrancesco; Dürig, Tobias

    2017-01-01

    New experiments of falling volcanic particles were performed in order to define terminal velocity models applicable in a wide range of Reynolds number Re. Experiments were carried out with fluids of various viscosities and with particles that cover a wide range of size, density and shape. Particle shape, which strongly influences fluid drag, was measured in 3D by High-resolution X-ray microtomography, by which sphericity Φ3D and fractal dimension D3D were obtained. They are easier to measure and less operator dependent than the 2D shape parameters used in previous papers. Drag laws that make use of the new 3D parameters were obtained by fitting particle data to the experiments, and single-equation terminal velocity models were derived. They work well both at high and low Re (3 × 10- 2 < Re < 104), while earlier formulations made use of different equations at different ranges of Re. The new drag laws are well suited for the modelling of particle transportation both in the eruptive column, where coarse and fine particles are present, and also in the distal part of the umbrella region, where fine ash is involved in the large-scale domains of atmospheric circulation. A table of the typical values of Φ3D and D3D of particles from known plinian, subplinian and ash plume eruptions is presented. Graphs of terminal velocity as a function of grain size are finally proposed as tools to help volcanologists and atmosphere scientists to model particle transportation of explosive eruptions.

  11. Low-velocity pneumatic conveying in horizontal pipe for coarse particles and fine powders

    Institute of Scientific and Technical Information of China (English)

    Yuji Tomita; Vijay Kumar Agarwal; Hiroyuki Asou; Katsuya Funatsu

    2008-01-01

    First,the characteristics of low-velocity conveying of particles having different hardness are experimentally investigated in a horizontal pipeline in terms of flow pattern and pressure drop to show that the slug flow can be classified into two types depending on the settling of particles along the pipeline,and the period is small for slug flow without the settled layer,which is called solitary slug flow.The pressure drop for soft particles is shown to be larger than that for hard particles.Then,experimental results are presented on horizontal fluidized-bed conveying of fine powders to show that air release from the top surface of the conveying channel is an important factor for high mass flow rate of particles.

  12. High Dynamic Velocity Range Particle Image Velocimetry Using Multiple Pulse Separation Imaging

    Directory of Open Access Journals (Sweden)

    Tadhg S. O’Donovan

    2010-12-01

    Full Text Available The dynamic velocity range of particle image velocimetry (PIV is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS technique (i records series of double-frame exposures with different pulse separations, (ii processes the fields using conventional multi-grid algorithms, and (iii yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods.

  13. Dry deposition velocity of total suspended particles and meteorological influence in four locations in Guangzhou, China

    Institute of Scientific and Technical Information of China (English)

    Leifu Chen; Shaolin Peng; Jingang Liu; Qianqian Hou

    2012-01-01

    Dry deposition velocity of total suspended particles (TSP) is an effective parameter that describes the speed of atmospheric particulate matter deposit to the natural surface.It is also an important indicator to the capacity of atmosphere self-depuration.However,the spatial and temporal variations in dry deposition velocity of TSP at different urban landscapes and the relationship between dry deposition velocity and the meteorological parameters are subject to large uncertainties.We concurrently investigated this relationship at four different landscapes of Guangzhou,from October to December of 2009.The result of the average dry deposition velocity is (1.49 ±0.77),(1.44 ± 0.77),(1.13 ± 0.53) and (1.82 ± 0.82) cm/sec for urban commercial landscape,urban forest landscape,urban residential landscape and country landscape,respectively.This spatial variation can be explained by the difference of both particle size composition of TSP and meteorological parameters of sampling sites.Dry deposition velocity of TSP has a positive correlation with wind speed,and a negative correlation with temperature and relative humidity.Wind speed is the strongest factor that affects the magnitude of TSP dry deposition velocity,and the temperature is another considerable strong meteorological factor.We also find out that the relative humidity brings less impact,especially during the dry season.It is thus implied that the current global warming and urban heat island effect may lead to correlative changes in TSP dry deposition velocity,especially in the urban areas.

  14. Noise reduction in acoustic measurements with a particle velocity sensor by means of a cross-correlation technique

    NARCIS (Netherlands)

    Honschoten, van J.W.; Druyvesteyn, W.F.; Kuipers, H.; Raangs, R.; Krijnen, G.J.M.

    2004-01-01

    In this paper a method is presented to reduce the noise level of a particle velocity sensor, a thermal two-wire sensor sensitive to acoustic particle velocities, which yields a reduction of the noise of 30 dB. The method is based on utilisation of cross- instead of auto-correlation spectra of two of

  15. Structure and Surface Characterization of Nanostructured Tio2 Coatings Deposited Via HVOF Thermal Spray Processes

    Directory of Open Access Journals (Sweden)

    Maryamossadat Bozorgtabar

    2015-01-01

    Full Text Available Titanium dioxide coatings were deposited by high velocity oxy-fuel spraying (HVOF with the use of agglomerated P25/20 nano-powder and different spraying parameters (e.g. fuel/flow ratio to determine their influence on the microstructure, crystalline structure and surface feature of the coatings. The microstructure of as-sprayed TiO2 coatings was characterized by scanning electron microscope (SEM, transmission electron microscope (TEM and X-ray diffraction (XRD. Surface features were investigated by Fourier transform infrared (FT-IR and X-ray photoelectron spectroscopy (XPS. The results showed that the fuel and oxygen flow ratio have an important influence on the microstructure, anatase content, surface chemical state and surface feature of the TiO2 coatings

  16. Modification of Bonding Strength Test of WC HVOF Thermal Spray Coating on Rocket Nozzle

    Directory of Open Access Journals (Sweden)

    Bondan Sofyan

    2010-10-01

    Full Text Available One way to reduce structural weight of RX-100 rocket is by modifying the nozzle material and processing. Nozzle is the main target in weight reduction due to the fact that it contributes 30 % to the total weight of the structur. An alternative for this is by substitution of massive graphite, which is currently used as thermal protector in the nozzle, with thin layer of HVOF (High Velocity Oxy-Fuel thermal spray layer. This paper presents the characterization of nozzle base material as well as the modification of bonding strength test, by designing additional jig to facilitate testing processes while maintaining level of test accuracy. The results showed that the material used for  RX-100 rocket nozzle is confirmed to be S45C steel. Modification of the bonding strength test was conducted by utilizing chains, which improve test flexibility and maintains level of accuracy of the test.

  17. Laser Treatment of HVOF Coating: Modeling and Measurement of Residual Stress in Coating

    Science.gov (United States)

    Arif, A. F. M.; Yilbas, B. S.

    2008-10-01

    High-velocity oxy-fuel (HVOF) coating of diamalloy 1005 (similar to Inconel 625 alloy) onto the Ti-6Al-4V alloy is considered and laser-controlled melting of the coating is examined. The residual stress developed after the laser treatment process is modeled using the finite element method (FEM). The experiment is conducted to melt the coating using a laser beam. The residual stress measurement in the coating after the laser treatment process is realized using the XRD technique. The morphological and metallurgical changes in the coating are examined using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the residual stress reduces at the coating-base material interface and the residual stress predicted agrees with the XRD measurements. A compact and crack-free coating is resulted after the laser treatment process.

  18. Flow rate of particles through apertures obtained from self-similar density and velocity profiles

    OpenAIRE

    2012-01-01

    ‘‘Beverloo’s law’’ is considered as the standard expression to estimate the flow rate of particles through apertures. This relation was obtained by simple dimensional analysis and includes empirical parameters whose physical meaning is poorly justified. In this Letter, we study the density and velocity profiles in the flow of particles through an aperture. We find that, for the whole range of apertures studied, both profiles are self-similar. Hence, by means of the functionality obtained for the...

  19. Particle velocity based universal algorithm for numerical simulation of hydraulic fractures

    CERN Document Server

    Wrobel, Michal

    2014-01-01

    In the paper, we propose a new effective mathematical formulation and resulting universal numerical algorithm capable of tackling various HF models in the framework of a unified approach. The presented numerical scheme is not limited to any particular elasticity model or crack propagation regime. Its basic assumptions are: i) proper choice of independent and dependent variables (with the direct utilization of a new one - the reduced particle velocity), ii) tracing the fracture front by use of the speed equation which can be integrated in a closed form and sets an explicit relation between the crack propagation speed and the coefficients in the asymptotic expansion of the crack opening, iii) proper regularization techniques, iv) improved temporal approximation, v) modular algorithm architecture. The application of the new dependent variable, the reduced particle velocity, instead of the usual fluid flow rate, facilitates the computation of the crack propagation speed from the local relation based on the speed ...

  20. Charged particle velocity map image reconstruction with one-dimensional projections of spherical functions

    Energy Technology Data Exchange (ETDEWEB)

    Gerber, Thomas; Liu Yuzhu; Knopp, Gregor; Hemberger, Patrick; Bodi, Andras; Radi, Peter; Sych, Yaroslav [Molecular Dynamics Group, Paul Scherrer Institut, 5232 Villigen (Switzerland)

    2013-03-15

    Velocity map imaging (VMI) is used in mass spectrometry and in angle resolved photo-electron spectroscopy to determine the lateral momentum distributions of charged particles accelerated towards a detector. VM-images are composed of projected Newton spheres with a common centre. The 2D images are usually evaluated by a decomposition into base vectors each representing the 2D projection of a set of particles starting from a centre with a specific velocity distribution. We propose to evaluate 1D projections of VM-images in terms of 1D projections of spherical functions, instead. The proposed evaluation algorithm shows that all distribution information can be retrieved from an adequately chosen set of 1D projections, alleviating the numerical effort for the interpretation of VM-images considerably. The obtained results produce directly the coefficients of the involved spherical functions, making the reconstruction of sliced Newton spheres obsolete.

  1. Estimation of pressure-particle velocity impedance measurement uncertainty using the Monte Carlo method.

    Science.gov (United States)

    Brandão, Eric; Flesch, Rodolfo C C; Lenzi, Arcanjo; Flesch, Carlos A

    2011-07-01

    The pressure-particle velocity (PU) impedance measurement technique is an experimental method used to measure the surface impedance and the absorption coefficient of acoustic samples in situ or under free-field conditions. In this paper, the measurement uncertainty of the the absorption coefficient determined using the PU technique is explored applying the Monte Carlo method. It is shown that because of the uncertainty, it is particularly difficult to measure samples with low absorption and that difficulties associated with the localization of the acoustic centers of the sound source and the PU sensor affect the quality of the measurement roughly to the same extent as the errors in the transfer function between pressure and particle velocity do.

  2. Rainbow Particle Imaging Velocimetry for Dense 3D Fluid Velocity Imaging

    KAUST Repository

    Xiong, Jinhui

    2017-04-11

    Despite significant recent progress, dense, time-resolved imaging of complex, non-stationary 3D flow velocities remains an elusive goal. In this work we tackle this problem by extending an established 2D method, Particle Imaging Velocimetry, to three dimensions by encoding depth into color. The encoding is achieved by illuminating the flow volume with a continuum of light planes (a “rainbow”), such that each depth corresponds to a specific wavelength of light. A diffractive component in the camera optics ensures that all planes are in focus simultaneously. For reconstruction, we derive an image formation model for recovering stationary 3D particle positions. 3D velocity estimation is achieved with a variant of 3D optical flow that accounts for both physical constraints as well as the rainbow image formation model. We evaluate our method with both simulations and an experimental prototype setup.

  3. Spatial coherences of the sound pressure and the particle velocity in underwater ambient noise

    Institute of Scientific and Technical Information of China (English)

    YAN Jin; LUO Xianzhi; HOU Chaohuan

    2007-01-01

    The spatial coherences were investigated between the sound pressure and the three orthogonal components of the particle velocity in underwater ambient noise. Based on the ray theory, integral expression was derived for the spatial coherence matrix of the sound pressure and the particle velocity in a stratified ocean with dipole noise sources homogenously distributed on the surface. The integrand includes a multiplying factor of the vertical directivity of the noise intensity, and the layered ocean environment affects the spatial coherences via this directivity factor. For a shallow water environment and a semi-infinite homogenous medium, the coherence calculation results were given. It was showed that the sound speed profile and the sea bottom could not be neglected in determining the spatial coherences of the ambient noise vector field.

  4. Two-phase velocity measurements around cylinders using particle image velocimetry

    Energy Technology Data Exchange (ETDEWEB)

    Hassan, Y.A.; Philip, O.G.; Schmidl, W.D. [Texas A& M Univ., College Station, TX (United States)] [and others

    1995-09-01

    The particle Image Velocimetry flow measurement technique was used to study both single-phase flow and two-phase flow across a cylindrical rod inserted in a channel. First, a flow consisting of only a single-phase fluid was studied. The experiment consisted of running a laminar flow over four rods inserted in a channel. The water flow rate was 126 cm{sup 3}/s. Then a two-phase flow was studied. A mixture of water and small air bubbles was used. The water flow rate was 378 cm{sup 3}/s and the air flow rate was approximately 30 cm{sup 3}/s. The data are analyzed to obtain the velocity fields for both experiments. After interpretation of the velocity data, forces acting on a bubble entrained by the vortex were calculated successfully. The lift and drag coefficients were calculated using the velocity measurements and the force data.

  5. A combined signal processing approach against coherent interference with pressure and particle velocity

    Institute of Scientific and Technical Information of China (English)

    HUI Junying; LI Chunxu; LIANG Guolong; LIU Hong

    2001-01-01

    Comparing with traditional underwater acoustic system which only utilizes pressure information, combine sensor system processes pressure together with particle velocity information of sound field. More information certainly brings nicer processing result. By using spatial directional information collected by combine sensor, the Coherent Interference Energy Suppress (CIES) technology, which can effectively suppress coherent interference and detect linear spectrum signal and wide-band continuous-spectrum signal as well, is presented. Current research has shown favorite result, and further research is going on.

  6. Spherical Harmonic Analysis of Particle Velocity Distribution Function: Comparison of Moments and Anisotropies using Cluster Data

    Science.gov (United States)

    Gurgiolo, Chris; Vinas, Adolfo F.

    2009-01-01

    This paper presents a spherical harmonic analysis of the plasma velocity distribution function using high-angular, energy, and time resolution Cluster data obtained from the PEACE spectrometer instrument to demonstrate how this analysis models the particle distribution function and its moments and anisotropies. The results show that spherical harmonic analysis produced a robust physical representation model of the velocity distribution function, resolving the main features of the measured distributions. From the spherical harmonic analysis, a minimum set of nine spectral coefficients was obtained from which the moment (up to the heat flux), anisotropy, and asymmetry calculations of the velocity distribution function were obtained. The spherical harmonic method provides a potentially effective "compression" technique that can be easily carried out onboard a spacecraft to determine the moments and anisotropies of the particle velocity distribution function for any species. These calculations were implemented using three different approaches, namely, the standard traditional integration, the spherical harmonic (SPH) spectral coefficients integration, and the singular value decomposition (SVD) on the spherical harmonic methods. A comparison among the various methods shows that both SPH and SVD approaches provide remarkable agreement with the standard moment integration method.

  7. Particle velocity and sediment transport at the limit of deposition in sewers.

    Science.gov (United States)

    Ota, J J; Perrusquía, G S

    2013-01-01

    This paper focuses on the sediment particle while it is transported at the limit of deposition in storm sewers, i.e. as bed load at the limit of concentration that leads to sediment deposition. Although many empirical sediment transport equations are known in the literature, there is only limited knowledge concerning particle velocity. Sediment particle and sphere velocity measurements were carried out in two pipe channels and these results led to the development of a semi-theoretical equation for sediment transport at the limit of deposition in sewers. Even in the transport process without deposition, sediment movement is slower than water velocity and depends on the angle of repose of sediment with a diameter d on the roughness k of the pipe channel. Instead of classical dimensionless bed shear stress ψ, a modified dimensionless bed shear stress ψ (d/k)(2/3) was suggested, based on the angle of repose and this parameter was proved to be significant for quantifying the transport capacity. The main purpose of this article is to emphasize the importance of careful observation of experiments. Not only number of tests, but physical understanding are essential for better empirical equations.

  8. Comparative High-Temperature Corrosion Behavior of Ni-20Cr Coatings on T22 Boiler Steel Produced by HVOF, D-Gun, and Cold Spraying

    Science.gov (United States)

    Kaushal, Gagandeep; Bala, Niraj; Kaur, Narinder; Singh, Harpreet; Prakash, Satya

    2014-01-01

    To protect materials from surface degradations such as wear, corrosion, and thermal flux, a wide variety of materials can be deposited on the materials by several spraying processes. This paper examines and compares the microstructure and high-temperature corrosion of Ni-20Cr coatings deposited on T22 boiler steel by high velocity oxy-fuel (HVOF), detonation gun spray, and cold spraying techniques. The coatings' microstructural features were characterized by means of XRD and FE-SEM/EDS analyses. Based upon the results of mass gain, XRD, and FE-SEM/EDS analyses it may be concluded that the Ni-20Cr coating sprayed by all the three techniques was effective in reducing the corrosion rate of the steel. Among the three coatings, D-gun spray coating proved to be better than HVOF-spray and cold-spray coatings.

  9. Flow Rate of Particles through Apertures Obtained from Self-Similar Density and Velocity Profiles

    Science.gov (United States)

    Janda, Alvaro; Zuriguel, Iker; Maza, Diego

    2012-06-01

    “Beverloo’s law” is considered as the standard expression to estimate the flow rate of particles through apertures. This relation was obtained by simple dimensional analysis and includes empirical parameters whose physical meaning is poorly justified. In this Letter, we study the density and velocity profiles in the flow of particles through an aperture. We find that, for the whole range of apertures studied, both profiles are self-similar. Hence, by means of the functionality obtained for them the mass flow rate is calculated. The comparison of this expression with the Beverloo’s one reveals some differences which are crucial to understanding the mechanism that governs the flow of particles through orifices.

  10. Velocity autocorrelation functions of particles and clusters in liquids. A possible criterion for correlation length of incipient glass formation

    Science.gov (United States)

    Variyar, Jayasankar E.; Kivelson, Daniel; Lynden-Bell, R. M.

    1992-12-01

    We have carried out molecular-dynamics simulations over a range of densities in two and three dimensions for particles that interact through soft repulsive potentials. We have also carried out calculations of the corresponding systems in which all particles except a tagged particle and its neighbors within a certain distance are frozen. Velocity autocorrelation functions for a single particle, for clusters containing the particle, and for the velocity of the particle relative to an embedding cluster were obtained. The single-particle velocity autocorrelation function can be resolved into correlation functions describing the local rattling in a cage or a cluster, the motion of the cluster itself, and a small cross-correlation term; the function for the single particle is sensitive to the structure of the fluid over a much shorter time scale than are those of clusters, and the shape of the single-particle velocity autocorrelation function comes primarily from rattling motion within a cage. We show that the velocity autocorrelation functions of clusters are probably better probes than that for the single particle for investigating incipient glass formation since they can be used to establish a correlation length which increases when a liquid is cooled. The dynamics of clusters at a given state point depend upon their sizes, and the nature of their motions changes qualitatively from ``rattling'' for small to ``diffusional'' for large clusters, the ``critical'' size at which the change occurs increasing with decreasing temperature. A simple model for this cluster behavior is presented.

  11. Measurement and simulation of the two-phase velocity correlation in sudden-expansion gas-particle flows

    Institute of Scientific and Technical Information of China (English)

    Li-Xing Zhou; Yang Liu; Yi Xu

    2011-01-01

    In this paper the present authors measured the gas-particle two-phase velocity correlation in sudden expansion gas-particle flows with a phase Doppler particle anemometer(PDPA) and simulated the system behavior by using both a Reynolds-averaged Navier-Stokes(RANS)model and a large-eddy simulation(LES). The results of the measurements yield the axial and radial time-averaged velocities as well as the fluctuation velocities of gas and three particle-size groups(30μm,50μm,and 95μm) and the gasparticle velocity correlation for 30μm and 50μm particles.From the measurements,theoretical analysis,and simulation,it is found that the two-phase velocity correlation of sudden-expansion flows,like that of jet flows,is less than the gas and particle Reynolds stresses. What distinguishes the two-phase velocity correlations of sudden-expansion flow from those of jet and channel flows is the absence of a clear relationship between the two-phase velocity correlation and particle size in sudden-expansion flows. The measurements,theoretical analysis,and numerical simulation all lead to the above-stated conclusions. Quantitatively,the results of the LES are better than those of the RANS model.

  12. A Comparative Study on Ni-Based Coatings Prepared by HVAF, HVOF, and APS Methods for Corrosion Protection Applications

    Science.gov (United States)

    Sadeghimeresht, E.; Markocsan, N.; Nylén, P.

    2016-12-01

    Selection of the thermal spray process is the most important step toward a proper coating solution for a given application as important coating characteristics such as adhesion and microstructure are highly dependent on it. In the present work, a process-microstructure-properties-performance correlation study was performed in order to figure out the main characteristics and corrosion performance of the coatings produced by different thermal spray techniques such as high-velocity air fuel (HVAF), high-velocity oxy fuel (HVOF), and atmospheric plasma spraying (APS). Previously optimized HVOF and APS process parameters were used to deposit Ni, NiCr, and NiAl coatings and compare with HVAF-sprayed coatings with randomly selected process parameters. As the HVAF process presented the best coating characteristics and corrosion behavior, few process parameters such as feed rate and standoff distance (SoD) were investigated to systematically optimize the HVAF coatings in terms of low porosity and high corrosion resistance. The Ni and NiAl coatings with lower porosity and better corrosion behavior were obtained at an average SoD of 300 mm and feed rate of 150 g/min. The NiCr coating sprayed at a SoD of 250 mm and feed rate of 75 g/min showed the highest corrosion resistance among all investigated samples.

  13. Fireside Corrosion Behavior of HVOF and Plasma-Sprayed Coatings in Advanced Coal/Biomass Co-Fired Power Plants

    Science.gov (United States)

    Hussain, T.; Dudziak, T.; Simms, N. J.; Nicholls, J. R.

    2013-06-01

    This article presents a systematic evaluation of coatings for advanced fossil fuel plants and addresses fireside corrosion in coal/biomass-derived flue gases. A selection of four candidate coatings: alloy 625, NiCr, FeCrAl and NiCrAlY were deposited onto superheaters/reheaters alloy (T91) using high-velocity oxy-fuel (HVOF) and plasma spraying. A series of laboratory-based fireside corrosion exposures were carried out on these coated samples in furnaces under controlled atmosphere for 1000 h at 650 °C. The tests were carried out using the "deposit-recoat" test method to simulate the environment that was anticipated from air-firing 20 wt.% cereal co-product mixed with a UK coal. The exposures were carried out using a deposit containing Na2SO4, K2SO4, and Fe2O3 to produce alkali-iron tri-sulfates, which had been identified as the principal cause of fireside corrosion on superheaters/reheaters in pulverized coal-fired power plants. The exposed samples were examined in an ESEM with EDX analysis to characterize the damage. Pre- and post-exposure dimensional metrologies were used to quantify the metal damage in terms of metal loss distributions. The thermally sprayed coatings suffered significant corrosion attack from a combination of aggressive combustion gases and deposit mixtures. In this study, all the four plasma-sprayed coatings studied performed better than the HVOF-sprayed coatings because of a lower level of porosity. NiCr was found to be the best performing coating material with a median metal loss of ~87 μm (HVOF sprayed) and ~13 μm (plasma sprayed). In general, the median metal damage for coatings had the following ranking (in the descending order: most to the least damage): NiCrAlY > alloy 625 > FeCrAl > NiCr.

  14. Performance characterization of metallic substrates coated by HVOF WC–Co

    Energy Technology Data Exchange (ETDEWEB)

    Venter, Andrew M., E-mail: andrew.venter@necsa.co.za [Research and Development Division, Necsa Limited, Pretoria (South Africa); School of Chemical and Metallurgical Engineering, University of the Witwatersrand (South Africa); DST/NRF Centre of Excellence in Strong Materials, University of the Witwatersrand (South Africa); Oladijo, O. Philip [School of Chemical and Metallurgical Engineering, University of the Witwatersrand (South Africa); DST/NRF Centre of Excellence in Strong Materials, University of the Witwatersrand (South Africa); Luzin, Vladimir [ANSTO (Australian Nuclear Science and Technology Organisation), Lucas Height (Australia); Cornish, Lesley A.; Sacks, Natasha [School of Chemical and Metallurgical Engineering, University of the Witwatersrand (South Africa); DST/NRF Centre of Excellence in Strong Materials, University of the Witwatersrand (South Africa)

    2013-12-31

    Integral to the performance of high-velocity oxygen-fuel (HVOF) coatings is the thermo-mechanical interaction associated with the thermal misfit, or differences in thermal expansion coefficients (CTEs), between coating and substrate. This investigation reports results on the microstructures, chemical phase content, coating–substrate misfit residual stress, and wear resistance. For this purpose a systematic characterization of WC–Co sprayed coatings on a number of substrates covering a range of CTE values were pursued for both the as-coated and heat-treated conditions. The neutron diffraction technique in conjunction with sub-millimeter sized gauge volumes enabled depth-resolved studies of the stress in the coatings and substrates by paying special attention to the determination of the stress contribution attributed by the final spray process. In the as-coated condition the stress values in the coatings were compressive for CTEs larger than that of WC–Co and tensile for CTE lower than WC–Co. Wear resistance increased for increased compressive stress and macrohardness. In the heat-treated condition, this trend became enhanced due to increased compressive stress in the coatings. - Highlights: • Four different substrate systems coated with HVOF WC-Co has been investigated. • Each substrate set encompassed the grit-blast surface and as-coated conditions, as well as their heat-treated counterparts. • Microstructural, macrohardness, wear performance and depth-resolved residual stress characterised. • Successful application of neutron strain scanning to investigating the combined systems, coatings and substrates. • Link observed between macrohardness, residual stress and wear performance.

  15. Comparative investigation on HVOF sprayed carbide-based coatings

    Science.gov (United States)

    Xie, Mingxiang; Zhang, Shihong; Li, Mingxi

    2013-05-01

    In this work, WC-17Co, WC-10Co-4Cr, WC-12Co and Cr3C2-25NiCr coatings were deposited on stainless steel using WOKAStar-640 HVOF spraying system. Three WC-based coatings were studied and compared with a chromium carbide-based coating. The microstructure, porosity, micro-hardness, indentation fracture toughness and adhesion strength of the coatings were investigated. The wear test was done by using silica grits as abrasive medium using a load of 20 N. The result shows that HVOF sprayed carbide-based coating possesses low porosity, high micro-hardness and high adhesion strength. Three WC-based coatings have higher micro-hardness and indentation fracture toughness compared to the Cr3C2-25NiCr coating. HVOF sprayed carbide coating has good wear resistance under 500 °C. The decarburization of WC-based coating has great effect on coating wear resistance. In addition, WC-17Co coating has best wear resistance.

  16. HVOF and HVAF Coatings of Agglomerated Tungsten Carbide-Cobalt Powders for Water Droplet Erosion Application

    Science.gov (United States)

    Tarasi, F.; Mahdipoor, M. S.; Dolatabadi, A.; Medraj, M.; Moreau, C.

    2016-12-01

    Water droplet erosion (WDE) is a phenomenon caused by impingement of water droplets of several hundred microns to a few millimeters diameter at velocities of hundreds of meters per second on the edges and surfaces of the parts used in such services. The solution to this problem is sought especially for the moving compressor blades in gas turbines and those operating at the low-pressure end of steam turbines. Thermal-sprayed tungsten carbide-based coatings have been the focus of many studies and are industrially accepted for a multitude of wear and erosion resistance applications. In the present work, the microstructure, phase analysis and mechanical properties (micro-hardness and fracture toughness) of WC-Co coatings are studied in relation with their influence on the WDE resistance of such coatings. The coatings are deposited by high-velocity oxygen fuel (HVOF) and high-velocity air fuel (HVAF) processes. The agglomerated tungsten carbide-cobalt powders were in either sintered or non-sintered conditions. The WDE tests were performed using 0.4 mm water droplets at 300 m/s impact velocity. The study shows promising results for this cermet as WDE-resistant coating when the coating can reach its optimum quality using the right thermal spray process and parameters.

  17. Shear velocity and wall position determination from particle image velocimetry data with seed centroid correction

    Science.gov (United States)

    Harris, Jeff; Lance, Blake; Skifton, Richard; Smith, Barton

    2015-11-01

    Two methods of computing the wall shear velocity from high-resolution particle image velocimetry (PIV) measurements are compared with and without a correction that accounts for seed gradient near the wall. It is crucial to know the wall position when computing the wall shear stress, but this can be difficult due to laser scatter on a wall. Furthermore, PIV is well known to be biased near walls due to seeding gradients. We compensate for these effects by replacing the cross-stream location of each vector with a value based on the centroid of the seeding in each interrogation region. The shear velocity and wall position resulting from methods outlined in the literature are presented. The boundary layer cases presented are influenced by buoyancy and the efficacy of these methods for convective flow will be discussed.

  18. Particle velocity measurements with macroscopic fluorescence imaging in lymph tissue mimicking microfluidic phantoms

    Science.gov (United States)

    Hennessy, Ricky; Koo, Chiwan; Ton, Phuc; Han, Arum; Righetti, Raffaella; Maitland, Kristen C.

    2011-03-01

    Ultrasound poroelastography can quantify structural and mechanical properties of tissues such as stiffness, compressibility, and fluid flow rate. This novel ultrasound technique is being explored to detect tissue changes associated with lymphatic disease. We have constructed a macroscopic fluorescence imaging system to validate ultrasonic fluid flow measurements and to provide high resolution imaging of microfluidic phantoms. The optical imaging system is composed of a white light source, excitation and emission filters, and a camera with a zoom lens. The field of view can be adjusted from 100 mm x 75 mm to 10 mm x 7.5 mm. The microfluidic device is made of polydimethylsiloxane (PDMS) and has 9 channels, each 40 μm deep with widths ranging from 30 μm to 200 μm. A syringe pump was used to propel water containing 15 μm diameter fluorescent microspheres through the microchannels, with flow rates ranging from 0.5 μl/min to 10 μl/min. Video was captured at a rate of 25 frames/sec. The velocity of the microspheres in the microchannels was calculated using an algorithm that tracked the movement of the fluorescent microspheres. The imaging system was able to measure particle velocities ranging from 0.2 mm/sec to 10 mm/sec. The range of flow velocities of interest in lymph vessels is between 1 mm/sec to 10 mm/sec; therefore our imaging system is sufficient to measure particle velocity in phantoms modeling lymphatic flow.

  19. The settling velocity of mineral, biomineral, and biological particles and aggregates in water

    Science.gov (United States)

    Maggi, Federico

    2013-04-01

    A new equation was developed to relate the size and settling velocity of particulate matter commonly recurring in aqueous ecosystems. This equation explicitly balanced the gravitational, buoyancy, viscous, and inertial forces as in Rubey () but was amended to describe in one instance both individual particles and granular aggregates with an internal fractal architecture. This approach allowed for an algebraic solution of the settling velocity, thus overcoming earlier approaches that required iterative numerical solutions. The equation was tested with mineral, biomineral, and biological suspended particles and granular aggregates from 52 existing experimental data sets, and resulted in average correlation coefficients R between 71% and 93.9%, and normilized residuals between 14.3% and 24.8% over Reynolds numbers ranging within 10-7 and 102. Accuracy of these results was generally better than for the Stokes' law, the Stokes' law modified with the Schiller-Naumann drag coefficient, and Rubey's equation. Estimated parameters ranged within observed ones, thus suggesting that the equation was robust. An analysis of the drag showed that inertial force was negligible only for biological cells (isolated cysts), whereas it contributed by not less than 5% to the drag on large mineral particles and up to 20% for biomineral and biological aggregates. Finally, a correlation was found between the organic matter content and fractal properties of granular aggregates, which were described by empirical equations proposed here for the first time. The hypothesis that the settling velocity is a function of linear and nonlinear drag, and is ultimately determined by physical characteristics as much as biological composition and internal aggregate geometry, is supported here by quantitative analyses.

  20. Simulation of Embedded Electromagnetic Particle Velocity Gauge Package Response in Gas-Gun Experiments

    Science.gov (United States)

    Finn, Katherine; Whitworth, Nick; Handley, Caroline

    2009-06-01

    In recent years, a comprehensive suite of gas-gun particle velocity gauge experiments have been conducted by Gustavsen et al. A detailed analysis of this data has led to advances in the understanding of the shock to detonation transition in polymer bonded explosives, and hydrocode simulations of the experiments are often used to calibrate reactive-burn models. In these simulations, the gauges are often modeled using Lagrangian marker particles, with no physical representation. In contrast, the experimental gauge package, as developed by Vorthman et al. in the early 1980s, consists of etched aluminium sandwiched between two sheets of FEP Teflon, using an urethane-based glue. The resulting gauge package is approximately 60 micrometres thick and is positioned between two wedge-shaped pieces of explosive at an angle of 30 degrees, to form a right-circular cylinder. This paper investigates whether there is a need to include an accurate representation of the gauge package within future hydrocode simulations.

  1. Improvement of Surface Properties of Inconel718 by HVOF Coating with WC-Metal Powder and by Laser Heat Treatment of the Coating

    Directory of Open Access Journals (Sweden)

    Hui Gon Chun

    2015-01-01

    Full Text Available High-velocity oxygen-fuel (HVOF thermal spray coating with WC-metal powder was carried out by using optimal coating process on an Inconel718 surface for improvement of the surface properties, friction, wear, and corrosion resistance. Binder metals such as Cr and Ni were completely melted and WC was decomposed partially to W2C and graphite during the high temperature (up to 3500°C thermal spraying. The melted metals were bonded with WC and other carbides and were formed as WC-metal coating. The graphite and excessively sprayed oxygen formed carbon oxide gases, and these gases formed porous coating by evolution of the gases. The surface properties were improved by HVOF coating and were improved further by CO2 laser heat treatment (LH. Wear resistance of In718 surface was improved by coating and LH at 25°C and an elevated temperature of 450°C, resulting in reduction of wear trace traces, and was further improved by LH of the coating in reducing wear depth. Corrosion resistance due to coating in sea water was improved by LH. HVOF coating of WC-metal powder on a metal surface and a LH of the coating were highly recommended for the improvement of In718 surface properties, the friction behavior, and wear resistance.

  2. Random Motion of a Charged Test Particle with a Classical Constant Velocity in Vacuum in a Cylindrical Spacetime

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jia-Lin; YU Hong-Wei

    2005-01-01

    @@ We examine the random motion of a charged test particle with a nonzero classical velocity driven by quantum electromagnetic vacuum fluctuations in a cylindrical spacetime and calculate both the velocity and position dispersions of the test particle. It is found that the dispersions display different behaviour in different directions.These differences can be understood as a result of the topology of the configuration and initial physical conditions.

  3. A note on the stochastic nature of particle cohesive force and implications to threshold friction velocity for aerodynamic dust entrainment

    Science.gov (United States)

    There is considerable interest to determine the threshold for aeolian dust emission on Earth and Mars. Existing schemes for threshold friction velocity are all deterministic in nature, but observations show that in the dust particle size range the threshold friction velocity scatters strongly due t...

  4. Berry Phase, Lorentz Covariance, and Anomalous Velocity for Dirac and Weyl Particles

    CERN Document Server

    Stone, Michael; Zhou, Tianci

    2014-01-01

    We consider the relation between spin and the Berry-phase contribution to the anomalous velocity of massive and massless Dirac particles. We extend the Berry connection that depends only on the spatial components of the particle momentum to one that depends on the the space and time components in a covariant manner. We show that this covariant Berry connection captures the Thomas-precession part of the Bargmann-Michel-Telegdi spin evolution, and contrast it with the traditional (unitary, but not naturally covariant) Berry connection that describes spin-orbit coupling. We then consider how the covariant connection enters the classical relativistic dynamics of spinning particles due to Mathisson, Papapetrou and Dixon. We discuss the problems that arise with Lorentz covariance in the massless case, and trace them mathematically to a failure of the Wigner-translation part of the massless-particle little group to be an exact gauge symmetry in the presence of interactions, and physically to the fact that the measur...

  5. Evaluation of Thermocyclic Oxidation Behavior of HVOF-Sprayed NiCrFeSiB Coatings on Boiler Tube Steels

    Science.gov (United States)

    Ramesh, M. R.; Prakash, S.; Nath, S. K.; Sapra, Pawan Kumar; Krishnamurthy, N.

    2011-09-01

    High velocity oxy-fuel (HVOF) spray process has grown into a well-accepted industrial technology for obtaining coatings resistant to significant surface degradation processes. In the present study, HVOF process was used to deposit Ni-based hardfacing NiCrFeSiB alloy powder on kinds of boiler tube steels designated as SA210 grade-A1, SA213-T11, and SA213-T22. The microstructures and several properties of the as-sprayed coatings have been investigated. Thermocyclic oxidation studies were performed in static air at 900 °C. NiCrFeSiB-coated steels showed slow oxidation kinetics and considerably lower weight gains than that of uncoated steels. The superior performance of NiCrFeSiB coatings can be attributed to continuous and protective thin oxide scale of amorphous SiO2 and Cr2O3 formed on the surface of the oxidized coatings. The combined technique of x-ray diffraction, scanning electron microscopy, energy dispersive x-ray analysis, and electron probe microanalysis are used to characterize reaction products of the oxidized surfaces.

  6. Effect of HVOF Processing Parameters on the Properties of NiCoCrAlY Coatings by Design of Experiments

    Science.gov (United States)

    Ruiz-Luna, H.; Lozano-Mandujano, D.; Alvarado-Orozco, J. M.; Valarezo, A.; Poblano-Salas, C. A.; Trápaga-Martínez, L. G.; Espinoza-Beltrán, F. J.; Muñoz-Saldaña, J.

    2014-08-01

    The effect of three principal, independent, high-velocity oxygen fuel (HVOF)-processing parameters on the properties of NiCoCrAlY coatings deposited using commercial powders is reported here. The design of experiments (DoE) technique at a two-level factorial and a central composite rotatable design was used to analyze and optimize the HVOF spraying process. The deposition parameters investigated were (1) fuel flow, (2) oxygen flow, and (3) stand-off distance. The effect of these processing variables was evaluated using selected responses, including porosity and oxide content, residual stresses, and deposition efficiency. Coatings with low porosity as well as with low residual stress were obtained using high fuel-rich conditions at a stand-off distance between 250 and 300 mm. At shorter and longer stand-off distances, respectively, either excessive flattening of splats or un-molten condition occurred, resulting in high levels of porosity and residual stress. The response surface, the empirical relationships among the variables, and the response parameters allowed the selection of optimum deposition parameters and the improvement of coating properties.

  7. High temperature wear performance of HVOF-sprayed Cr3C2-WC-NiCoCrMo and Cr3C2-NiCr hardmetal coatings

    Science.gov (United States)

    Zhou, Wuxi; Zhou, Kesong; Li, Yuxi; Deng, Chunming; Zeng, Keli

    2017-09-01

    A novel Cr3C2-WC-NiCoCrMo and commercial Cr3C2-NiCr thermal spray-grade powders with particle size of -45 + 15 μm were prepared by an agglomeration and sintering process. Cr3C2-WC-NiCoCrMo and Cr3C2-NiCr coatings were deposited by high velocity oxygen fuel (HVOF) spraying. The fundamental properties of both coatings were evaluated and friction wear test against Al2O3 counterbodies of both coatings at high temperatures (450 °C, 550 °C, 650 °C) were carried out ball-on-disk high temperature tribometer. All specimens were characterized by optical microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) and 3D non-contact surface mapping profiler. The results have shown that the Cr3C2-WC-NiCoCrMo coating exhibited lower porosity, higher micro-hardness compared to the Cr3C2-NiCr coating. The Cr3C2-WC-NiCoCrMo coating also exhibited better wear resistance and higher friction coefficient compared to the Cr3C2-NiCr coating when sliding against the Al2O3 counterpart. Wear rates of both coatings increased with raising temperature. Both coatings experienced abrasive wear; hard phase particles (WC and Cr3C2) with different sizes, distributed in the matrix phase, will effectively improve the resistance against wear at high temperatures.

  8. TOPICAL REVIEW Warm spraying—a novel coating process based on high-velocity impact of solid particles

    Directory of Open Access Journals (Sweden)

    Seiji Kuroda et al

    2008-01-01

    Full Text Available In recent years, coating processes based on the impact of high-velocity solid particles such as cold spraying and aerosol deposition have been developed and attracting much industrial attention. A novel coating process called 'warm spraying' has been developed, in which coatings are formed by the high-velocity impact of solid powder particles heated to appropriate temperatures below the melting point of the powder material. The advantages of such process are as follows: (1 the critical velocity needed to form a coating can be significantly lowered by heating, (2 the degradation of feedstock powder such as oxidation can be significantly controlled compared with conventional thermal spraying where powder is molten, and (3 various coating structures can be realized from porous to dense ones by controlling the temperature and velocity of the particles. The principles and characteristics of this new process are discussed in light of other existing spray processes such as high-velocity oxy-fuel spraying and cold spraying. The gas dynamics of particle heating and acceleration by the spraying apparatus as well as the high-velocity impact phenomena of powder particles are discussed in detail. Several examples of depositing heat sensitive materials such as titanium, metallic glass, WC–Co cermet and polymers are described with potential industrial applications.

  9. Brownian Motion of a Test Particle with a Normal Classical Velocity in Spacetime with a Plane Boundary

    Institute of Scientific and Technical Information of China (English)

    FU Xiang-Yun; YU Hong-Wei

    2007-01-01

    We study the random motion of a charged test particle with a normal classical constant velocity in a spacetime with a perfectly reflecting plane boundary and calculate both the velocity and position dispersions of the test particle. Our results show that the dispersions in the normal direction are weakened while those in the parallel directions are strengthened as compared to the classical static case when the test particle classically moves away from the boundary.However, if the classical motion reverses its direction, then the dispersions in the normal direction are reinforced while those in the parallel directions get weakened.

  10. Ultrasonic device for real-time sewage velocity and suspended particles concentration measurements.

    Science.gov (United States)

    Abda, F; Azbaid, A; Ensminger, D; Fischer, S; François, P; Schmitt, P; Pallarès, A

    2009-01-01

    In the frame of a technological research and innovation network in water and environment technologies (RITEAU, Réseau de Recherche et d'Innovation Technologique Eau et Environnement), our research group, in collaboration with industrial partners and other research institutions, has been in charge of the development of a suitable flowmeter: an ultrasonic device measuring simultaneously the water flow and the concentration of size classes of suspended particles. Working on the pulsed ultrasound principle, our multi-frequency device (1 to 14 MHz) allows flow velocity and water height measurement and estimation of suspended solids concentration. Velocity measurements rely on the coherent Doppler principle. A self developed frequency estimator, so called Spectral Identification method, was used and compared to the classical Pulse-Pair method. Several measurements campaigns on one wastewater collector of the French city of Strasbourg gave very satisfactory results and showed smaller standard deviation values for the Doppler frequency extracted by the Spectral Identification method. A specific algorithm was also developed for the water height measurements. It relies on the water surface acoustic impedance rupture and its peak localisation and behaviour in the collected backscattering data. This algorithm was positively tested on long time measurements on the same wastewater collector. A large part of the article is devoted to the measurements of the suspended solids concentrations. Our data analysis consists in the adaptation of the well described acoustic behaviour of sand to the behaviour of wastewater particles. Both acoustic attenuation and acoustic backscattering data over multiple frequencies are analyzed for the extrapolation of size classes and respective concentrations. Under dry weather conditions, the massic backscattering coefficient and the overall size distribution showed similar evolution whatever the measurement site was and were suggesting a global

  11. Gas dispersion and immobile gas volume in solid and porous particle biofilter materials at low air flow velocities.

    Science.gov (United States)

    Sharma, Prabhakar; Poulsen, Tjalfe G

    2010-07-01

    Gas-phase dispersion in granular biofilter materials with a wide range of particle sizes was investigated using atmospheric air and nitrogen as tracer gases. Two types of materials were used: (1) light extended clay aggregates (LECA), consisting of highly porous particles, and (2) gravel, consisting of solid particles. LECA is a commercial material that is used for insulation, as a soil conditioner, and as a carrier material in biofilters for air cleaning. These two materials were selected to have approximately the same particle shape. Column gas transport experiments were conducted for both materials using different mean particle diameters, different particle size ranges, and different gas flow velocities. Measured breakthrough curves were modeled using the advection-dispersion equation modified for mass transfer between mobile and immobile gas phases. The results showed that gas dispersivity increased with increasing mean particle diameter for LECA but was independent of mean particle diameter for gravel. Gas dispersivity also increased with increasing particle size range for both media. Dispersivities in LECA were generally higher than for gravel. The mobile gas content in both materials increased with increasing gas flow velocity but it did not show any strong dependency on mean particle diameter or particle size range. The relative fraction of mobile gas compared with total porosity was highest for gravel and lowest for LECA likely because of its high internal porosity.

  12. Simulations of Embedded Electromagnetic Particle Velocity Gauge Package Response in Gas-Gun Experiments

    Science.gov (United States)

    Finn, K. L.; James, H. R.; Whitworth, N. J.; Handley, C. A.

    2009-12-01

    In recent years a comprehensive suite of gas-gun particle velocity gauge experiments have been conducted at Los Alamos National Laboratory. Detailed analysis of this data has led to advances in the understanding of the shock to detonation transition in polymer bonded explosives hydrocode simulations of the experiments are frequently used to calibrate reactive-burn models. In these simulations the gauges are modelled using Lagrangian markers with no physical representation of the gauge package. In contrast the experimental gauge package consists of etched aluminium sandwiched between two sheets of FEP Teflon using an urethane-based glue. The gauge package is approximately 60 μm thick is positioned between two wedge-shaped pieces of explosive at an angle of 30 degrees to form a right circular cylinder. This paper investigates with one-dimensional calculations whether there is a need to include an accurate representation of the gauge package within future hydrocode simulations.

  13. Bayesian Reconstruction of the Velocity Distribution of Weakly Interacting Massive Particles from Direct Dark Matter Detection Data

    CERN Document Server

    Shan, Chung-Lin

    2014-01-01

    In this paper, we extended our earlier work on the reconstruction of the (time-averaged) one-dimensional velocity distribution of Galactic Weakly Interacting Massive Particles (WIMPs) and introduce the Bayesian fitting procedure to the theoretically predicted velocity distribution functions. In this reconstruction process, the (rough) velocity distribution reconstructed by using raw data from direct Dark Matter detection experiments directly, i.e. measured recoil energies, with one or more different target materials, has been used as "reconstructed-input" information. By assuming a fitting velocity distribution function and scanning the parameter space based on the Bayesian analysis, the astronomical characteristic parameters, e.g. the Solar and Earth's orbital velocities, will be pinned down as the output results. Our Monte-Carlo simulations show that this Bayesian scanning procedure could reconstruct the true (input) WIMP velocity distribution function pretty precisely with negligible systematic deviations ...

  14. Numerical study of turbulent diffusion. [Gaussian diffusion, velocity fields, small eddies, two-particle dispersion

    Energy Technology Data Exchange (ETDEWEB)

    McCoy, M.G.

    1975-11-01

    The problem of the numerical simulation of turbulent diffusion is studied. The two-dimensional velocity fields are assumed to be incompressible, homogeneous and stationary, and they are represented as stochastic processes. A technique is offered which creates velocity fields accurately representing the input statistics once a two point correlation function or an energy spectrum is given. Various complicated energy spectra may be represented utilizing this model. The program is then used to extract information concerning Gaussian diffusion processes. Various theories of other workers are tested including Taylor's classical representation of dispersion for times long compared with the Lagrangian correlation time. Also, a study is made of the relation between the Lagrangian and the Eulerian correlation function and a hypothesis is advanced and successfully tested. Questions concerning the relation between small eddies and the energy spectrum are considered. A criterion is advanced and successfully tested to decide whether small scale flow can be detected within the large eddies for any given spectrum. A method is developed to determine whether this small scale motion is in any sense periodic. Finally, the relation between two particle dispersion and the energy spectrum is studied anew and various theories are tested. (auth)

  15. Characterization of High-Velocity Single Particle Impacts on Plasma-Sprayed Ceramic Coatings

    Science.gov (United States)

    Kiilakoski, Jarkko; Lindroos, Matti; Apostol, Marian; Koivuluoto, Heli; Kuokkala, Veli-Tapani; Vuoristo, Petri

    2016-08-01

    High-velocity impact wear can have a significant effect on the lifetime of thermally sprayed coatings in multiple applications, e.g., in the process and paper industries. Plasma-sprayed oxide coatings, such as Cr2O3- and TiO2-based coatings, are often used in these industries in wear and corrosion applications. An experimental impact study was performed on thermally sprayed ceramic coatings using the High-Velocity Particle Impactor (HVPI) at oblique angles to investigate the damage, failure, and deformation of the coated structures. The impact site was characterized by profilometry, optical microscopy, and scanning electron microscopy (SEM). Furthermore, the connection between the microstructural details and impact behavior was studied in order to reveal the damage and failure characteristics at a more comprehensive level. Differences in the fracture behavior were found between the thermally sprayed Cr2O3 and TiO2 coatings, and a concept of critical impact energy is presented here. The superior cohesion of the TiO2 coating inhibited interlamellar cracking while the Cr2O3 coating suffered greater damage at high impact energies. The HVPI experiment has proven to be able to produce valuable information about the deformation behavior of coatings under high strain rates and could be utilized further in the development of wear-resistant coatings.

  16. Correlation of Fracture Mode Transition of Ceramic Particle with Critical Velocity for Successful Deposition in Vacuum Kinetic Spraying Process

    Science.gov (United States)

    Park, Hyungkwon; Kim, Jinyoung; Lee, Sung Bo; Lee, Changhee

    2016-12-01

    Vacuum kinetic spraying (VKS) is a promising room-temperature process to fabricate dense ceramic films. However, unfortunately, the deposition mechanism is still not clearly understood. In this respect, the critical conditions for successful deposition were investigated. Based on simulation and microstructural analysis, it was found that as the particle velocity increased, fracture mode transition from tensile fracture to shear fracture occurred and particle did not bounce off anymore above a certain velocity. Simultaneously, particle underwent shock-induced plasticity and dynamic fragmentation. The plasticity assisted to prevent the fragments from rebounding by spending the excessive kinetic energy and fragmentation is essential for fragment bonding and film growth considering that the deposition rate increased as the fraction of fragmentation increased. Accordingly, plasticity and fragmentation take a crucial role for particle deposition. In this respect, the velocity that fracture mode transition occurs is newly defined as critical velocity. Consequently, for successful deposition, the particle should at least exceed the critical velocity and thus it is very crucial for film fabrication in VKS process at room temperature.

  17. Effect of particle volume fraction on the settling velocity of volcanic ash particles: insights from joint experimental and numerical simulations

    OpenAIRE

    Del Bello, Elisabetta; Taddeucci, Jacopo; de’ Michieli Vitturi, Mattia; Scarlato, Piergiorgio; Andronico, Daniele; Scollo, Simona; Kueppers, Ulrich; Ricci, Tullio

    2017-01-01

    Most of the current ash transport and dispersion models neglect particle-fluid (two-way) and particle-fluid plus particle-particle (four-way) reciprocal interactions during particle fallout from volcanic plumes. These interactions, a function of particle concentration in the plume, could play an important role, explaining, for example, discrepancies between observed and modelled ash deposits. Aiming at a more accurate prediction of volcanic ash dispersal and sedimentation, the settling of ash...

  18. Feasibility studies for light scattering experiments to determine the velocity relaxation of small particles in a fluid

    Science.gov (United States)

    Acquista, C.; Narducci, L. M.

    1980-01-01

    An approach for measuring the non-Markoffian component in the relaxation mechanism of a Brownian particle is proposed which combines desirable features of both the shock wave experiment and conventional light scattering experiments. It is suggested that the radiation pressure generated by a C.W. laser be used to guide an individual spherical particle to terminal velocity. At an appropriate time, the beam intensity is suddenly lowered to a value at which the radiation pressure is negligible, and the ensuing velocity relaxation is measured directly.

  19. Accounting for the role of turbulent flow on particle dislodgement via a coupled quadrant analysis of velocity and pressure sequences

    Science.gov (United States)

    Shih, WuRong; Diplas, Panayiotis; Celik, Ahmet Ozan; Dancey, Clinton

    2017-03-01

    Recent studies have demonstrated the importance of duration, in addition to magnitude, of energetic turbulent events on particle dislodgement under threshold of motion conditions. It is therefore proposed here that the use of turbulence sequences, instead of single instantaneous extreme events, is more appropriate for characterizing the role of fluctuating velocities and associated hydrodynamic forces on particle mobility. The validity of the proposed method is examined through the detailed analysis of directly measured velocity and pressure data sets. In an effort to relate the results of the conventional velocity quadrant analysis with the instantaneous pressure measurements, the concept of pressure quadrant analysis is introduced. The coupled sequences of the synchronous velocity and pressure quadrant events allow for a more complete description of the local turbulent flow characteristics, including the prevalent coherent structures, and more clear interpretation of their role on particle mobility. It is concluded here that large-scale sweep structures are capable of generating excessive and persistent force fluctuations which are predominantly responsible for the dynamic process of particle dislodgement. This result supports the impulse criterion as the proper way of accounting for the cumulative effect of coherent structures on particle movement.

  20. Simultaneous measurements of the flow velocities in a microchannel by wide/evanescent field illuminations with particle/single molecules.

    Science.gov (United States)

    Gai, Hongwei; Li, Ying; Silber-Li, Zhanhua; Ma, Yinfa; Lin, Bingcheng

    2005-04-01

    A laser-induced fluorescence imaging method was developed to simultaneously measure flow velocities in the middle and near wall of a channel with particles or single molecules, by selectively switching from the wide field excitation mode to the evanescent wave excitation mode. Fluorescent microbeads with a diameter of 175 nm were used to calibrate the system, and the collisions of microbeads with channel walls were directly observed. The 175 nm microbeads velocities in the main flow and at 275 nm from the bottom of the channel were measured. The measured velocities of particles or single molecules in two positions in a microchannel were consistent with the calculated value based on Poiseuille flow theory when the diameter of a microbead was considered. The errors caused by Brownian diffusion in our measurement were negligible compared to the flow velocity. Single lambda DNA molecules were then used as a flowing tracer to measure the velocities. The velocity can be obtained at a distance of 309.0 +/- 82.6 nm away from bottom surface of the channel. The technique may be potentially useful for studying molecular transportation both in the center and at the bottom of the channel, and interactions between molecules and microchannel surfaces. It is especially important that the technique can be permitted to measure both velocities in the same experiment to eliminate possible experimental inconsistencies.

  1. Improvements on Particle Tracking Velocimetry: model-free calibration and noiseless measurement of second order statistics of the velocity field

    CERN Document Server

    Machicoane, Nathanael; Bourgoin, Mickael; Aliseda, Alberto; Volk, Romain

    2016-01-01

    This article describes two independent developments aimed at improving the Particle Tracking Method for measurements of flow or particle velocities. First, a stereoscopic multicamera calibration method that does not require any optical model is described and evaluated. We show that this new calibration method gives better results than the most commonly-used technique, based on the Tsai camera/optics model. Additionally, the methods uses a simple interpolant to compute the transformation matrix and it is trivial to apply for any experimental fluid dynamics visualization set up. The second contribution proposes a solution to remove noise from Eulerian measurements of velocity statistics obtained from Particle Tracking velocimetry, without the need of filtering and/or windowing. The novel method presented here is based on recomputing particle displacement measurements from two consecutive frames for multiple different time-step values between frames. We show the successful application of this new technique to re...

  2. Developments and difficulties in predicting the relative velocities of inertial particles at the small-scales of turbulence

    CERN Document Server

    Bragg, Andrew D

    2016-01-01

    In this paper, we use our recently developed theory for the backward-in-time (BIT) relative dispersion of inertial particles in turbulence (Bragg \\emph{et al.}, Phys. Fluids 28, 013305, 2016) to develop the theoretical model by Pan \\& Padoan (J. Fluid Mech. 661 73, 2010) for inertial particle relative velocities in isotropic turbulence. We focus on the most difficult regime to model, the dissipation range, and find that the modified Pan \\& Padoan model (that uses the BIT dispersion theory) can lead to significantly improved predictions for the relative velocities, when compared with Direct Numerical Simulation (DNS) data. However, when the particle separation distance, $r$, is less than the Kolmogorov length scale, $\\eta$, the modified model overpredicts the DNS data. We explain how these overpredictions arise from two assumptions in the BIT dispersion theory, that are in general not satisfied when the final separation of the BIT dispersing particles is $<\\eta$. We then demonstrate the failure of b...

  3. Investigation of the Corrosion Behaviors of HVOF-Sprayed Carbide Cernet Coatings in Molten Al-Zn-Si Alloy Bath

    Institute of Scientific and Technical Information of China (English)

    JIANG Zhen-hua; TAN Xing-hai; ZHANG Yue-gang; SUN Jia-shu

    2004-01-01

    In continuous hot-dip galvanization process the corrosion and chemical stability of the sink roll in the galvanizing bath are important problem which effects on the quality and productivity. In order to protect the sink roll the carbide cermet and/or ceramic coatings were deposited on the surface of the sink roll. The WC-, Cr3 C2-cermet coatings were deposited by high velocity oxygen fuel (HVOF) spray, respectively. The coating samples were immersed in molten Zn-alloy containing 50 wt % aluminum at 833 K for 24 hr and 144 hr, respectively. The inter-diffusion and inter-reaction of Zn, Al and elements in coating and corrosion behaviors of these coatings were investigated by XRD, SEM and EPMA etc. The corrosion mechanisms of the carbide cermet coatings and ceramic coatings in molten High Al-Zn-alloy were approached.

  4. Wear resistance of WC/Co HVOF-coatings and galvanic Cr coatings modified by diamond nanoparticles

    Science.gov (United States)

    Kandeva, M.; Grozdanova, T.; Karastoyanov, D.; Assenova, E.

    2017-02-01

    The efforts in the recent 20 years are related to search of ecological solutions in the tribotechnologies for the replacement of galvanic Cr coatings in the contact systems operating under extreme conditions: abrasion, erosion, cavitation, corrosion, shock and vibration loads. One of the solutions is in the composite coatings deposited by high velocity gas-flame process (HVOF). The present paper presents comparative study results for mechanical and tribological characteristics of galvanic Cr coatings without nanoparticles, galvanic Cr coatings modified by diamond nanoparticles NDDS of various concentration 0.6; 10; 15 и 20% obtained under three technological regimes, and composite WC-12Co coating. Comparative results about hardness, wear, wear resistance and friction coefficient are obtained for galvanic Cr-NDDS and WC-12Co coatings operating at equal friction conditions of dry friction on abrasive surface. The WC-12Co coating shows 5.4 to 7 times higher wear resistance compared to the galvanic Cr-NDDS coatings.

  5. Evaluation of hot corrosion behaviour of HVOF sprayed NiCrAl coating on superalloys at 900 deg. C

    Energy Technology Data Exchange (ETDEWEB)

    Mahesh, R.A. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, IIT Roorkee Campus, Roorkee 247667, Uttarakhand (India); Jayaganthan, R. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, IIT Roorkee Campus, Roorkee 247667, Uttarakhand (India)], E-mail: rjayafmt@iitr.ernet.in; Prakash, S. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, IIT Roorkee Campus, Roorkee 247667, Uttarakhand (India)

    2008-10-15

    In the present investigation, NiCrAl coating was deposited on Ni- and Fe-based superalloy substrates by using high velocity oxy-fuel (HVOF) process to study the hot corrosion behaviour in molten salt (Na{sub 2}SO{sub 4}-60% V{sub 2}O{sub 5}) environment at 900 deg. C under cyclic conditions. The mass gain measurements were performed after each cycle to establish the kinetics of corrosion using thermogravimetric technique. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopic analysis (SEM/EDS) and X-ray mapping techniques were used to analyse the corrosion products. The bare superalloys experienced higher weight gain. The NiCrAl-coated Superni 750 alloy (SN 750) provided a better protection among the coated superalloys investigated. The formation of oxides and spinels of nickel, chromium and aluminum may be contributing better resistance to hot corrosion.

  6. Electrochemical Study of Ni20Cr Coatings Applied by HVOF Process in ZnCl2-KCl at High Temperatures

    Science.gov (United States)

    Porcayo-Calderón, J.; Sotelo-Mazón, O.; Casales-Diaz, M.; Ascencio-Gutierrez, J. A.; Salinas-Bravo, V. M.; Martinez-Gomez, L.

    2014-01-01

    Corrosion behavior of Ni20Cr coatings deposited by HVOF (high velocity oxygen-fuel) process was evaluated in ZnCl2-KCl (1 : 1 mole ratio) molten salts. Electrochemical techniques employed were potentiodynamic polarization curves, open circuit potential, and linear polarization resistance (LPR) measurements. Experimental conditions included static air and temperatures of 350, 400, and 450°C. 304-type SS was evaluated in the same conditions as the Ni20Cr coatings and it was used as a reference material to assess the coatings corrosion resistance. Coatings were evaluated as-deposited and with a grinded surface finished condition. Results showed that Ni20Cr coatings have a better corrosion performance than 304-type SS. Analysis showed that Ni content of the coatings improved its corrosion resistance, and the low corrosion resistance of 304 stainless steel was attributed to the low stability of Fe and Cr and their oxides in the corrosive media used. PMID:25210645

  7. Oxidation behavior of HVOF-sprayed nanostructured and CeO2-modified WC-12Co coatings

    Science.gov (United States)

    Xi, Naiyuan; Hang, Zongqiu; Liu, Yan; Chen, Hui; Zhang, Mingyue; Gao, Wei

    2017-07-01

    Two types of WC-12Co coatings with different modifications were deposited on steel substrates using high velocity oxygen fuel (HVOF) spraying. The coated samples were oxidized at 550∘C and 650∘C in ambient atmosphere. Oxidation mass gain was measured by electronic balance. Phase composition and microstructure evolution of both coatings after oxidation were conducted by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Microhardness testing was performed before and after oxidation testing. The results showed that at 550∘C and 650∘C, the rare-earth modified WC-12Co coating has lower oxidation rates compared with the nanostructured WC-12Co coating. This might be due to the rare-earth modification coating reducing the porosity and oxygen diffusion in the coatings, therefore delaying the crack formation and propagation.

  8. Wear behaviors of HVOF sprayed WC-12Co coatings by laser remelting under lubricated condition

    Science.gov (United States)

    Dejun, Kong; Tianyuan, Sheng

    2017-03-01

    A HVOF (high velocity oxygen fuel) sprayed WC-12Co coating was remelted with a CO2 laser. The surface-interface morphologies and phases were analyzed by means of SEM (scanning electron microscopy), and XRD (X-ray diffraction), respectively. The friction and wear behaviors of WC-12Co coating under the dry and lubricated conditions were investigated with a wear test. The morphologies and distributions of chemical elements on worn scar were analyzed with a SEM, and its configured EDS (energy diffusive spectrometer), respectively, and the effects of lubricated condition on COFs (coefficient of friction) and wear performance were also discussed. The results show that the adhesion between the coating and the substrate is stronger after laser remetling (LR), in which mechanical bonding, accompanying with metallurgical bonding, was found. At the load of 80 N, the average COF under the dry and lubricated friction conditions is 0.069, and 0.052, respectively, the latter lowers by 23.3% than the former, and the wear rate under the lubricated condition decreases by 302.3% than that under the dry condition. The wear mechanism under the dry and lubrication conditions is primarily composed of abrasive wear, cracking, and fatigue failure.

  9. Self-sharpening-effect of nickel-diamond coatings sprayed by HVOF

    Science.gov (United States)

    Tillmann, W.; Brinkhoff, A.; Schaak, C.; Zajaczkowski, J.

    2017-03-01

    The durability of stone working and drilling tools is an increasingly significant requirement in industrial applications. These tools are mainly produced by brazing diamond metal matrix composites inserts to the tool body. These inserts are produced by sintering diamonds and metal powder (e.g. nickel). If the wear is too high, the diamonds will break out of the metal matrix and other diamonds will be uncovered. This effect is called self-sharpening. But diamonds are difficult to handle because of their thermal sensitivity. Due to their high thermal influence, manufacturing costs, and complicate route of manufacturing (first sintering, then brazing), there is a great need for alternative production methods for such tools. One alternative to produce wear-resistant and self-sharpening coatings are thermal spray processes as examined in this paper. An advantage of thermal spray processes is their smaller thermal influence on the diamond, due to the short dwelling time in the flame. To reduce the thermal influence during spraying, nickel coated diamonds were used in the HVOF-process (high velocity oxygen fuel process). The wear resistance was subsequently investigated by means of a standardized ball-on-disc test. Furthermore, a SEM (scanning electron microscope) was used to gain information about the wear-mechanism and the self-sharpening effect of the coating.

  10. In vitro characterization of hydroxyapatite layers deposited by APS and HVOF thermal spraying methods

    Directory of Open Access Journals (Sweden)

    Radu Alexandru Roşu

    2012-03-01

    Full Text Available Titanium alloys are successfully used in medicine as implants due to their high mechanical properties and good biocompatibility. To improve implant osseointegration of titanium alloys, they are covered with hydroxyapatite because of its bioactive properties. Coating the implants with hydroxyapatite by thermal spraying, due to the temperatures developed during the deposition process, the structure can be degraded, leading to formation of secondary phases, such as TCP, TT CP, CaO. The paper presents the experimental results of hydroxyapatite layers deposition by two thermal spraying methods: Atmospheric Plasma Spraying (APS and High Velocity Oxy-Fuel (HVOF. The microstructure of the deposited layers is characterized by X-ray diffraction analysis and electronic microscopy. The bioactivity of the hydroxyapatite layers was investigated in Simulated Body Fluid (SBF by immersing the covered samples deposited by the two thermal spraying methods. In both cases the coatings did not present defects as cracks or microcracks. X-ray diffraction performed on hydroxyapatite deposited layers shows that the structure was strongly influenced by plasma jet temperature, the structure consisting mainly of TCP (Ca3PO42. The samples deposited by HVO F after immersing in SBF lead to formation of biological hydroxyapatite, certifying the good bioactivity of the coatings.

  11. Corrosion Behavior of HVOF-Sprayed Fe-Based Alloy Coating in Various Solutions

    Science.gov (United States)

    Qiao, Lei; Wu, Yuping; Hong, Sheng; Qin, Yujiao; Shi, Wei; Li, Gaiye

    2017-08-01

    A Fe-based amorphous/nanocrystalline coating was prepared by the high-velocity oxygen fuel (HVOF) spraying process. The coating was characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy. The corrosion resistances of the Fe-based coating and a reference electroplated hard chromium (EHC) coating were evaluated in a 3.5% NaCl solution, a 1 mol/L HCl solution and a 1 mol/L NaOH solution using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). All of the results indicated that the corrosion resistance of the Fe-based coating was superior to the resistance of the EHC coating in both the 3.5% NaCl solution and the 1 mol/L HCl solution due to the dense structure and fewer defects of the Fe-based coating. However, the corrosion resistance of the Fe-based coating was inferior to corrosion resistance of the EHC coating in the 1 mol/L NaOH solution. This could be ascribed to the drastic passivation of the EHC coating in an alkaline environment.

  12. Corrosion behavior of HVOF sprayed hard face coatings in alkaline-sulfide solution

    Science.gov (United States)

    Li, Shenhou; Guo, Zhixing; Xiong, Ji; Lei, Yong; Li, Yuxi; Tang, Jun; Liu, Junbo; Ye, Junliu

    2017-09-01

    The paper focuses on the corrosion behavior of high velocity oxygen fuel (HVOF) sprayed WC-17Co, WC-10Co-4Cr, Cr3C2-25NiCr coatings in alkaline-sulfide solution (S2-, 0.2 ml/L, pH = 10). Eighteen days of immersion test is carried out and corrosion rate analysis shows that the Cr3C2-NiCr coating of low porosity exhibits the best corrosion resistance. In alkaline-sulfide solutions, porosity, passive film and microgalvanic between hard phase and binder phase have significant effect on the corrosion behavior of coatings. The corrosion mainly occurs in binder phase from SEM, though WO3, WS2, Cr2S3 are detected in XPS. In WC-17Co coating, the binder phase Co transforms to Co oxides and serious corrosion can be observed in binder phase. WC-10Co-4Cr coatings suffer localized corrosion since galvanic corrosion occurs between locations with different solubilities of W in Co binder. Cr3C2-25NiCr coating shows slight corrosion with the formation of NiS/Ni2O3/Cr2O3from the binder and Cr2S3 from the hard phase. The results are verified by the polarization curves, which show the longest passive region and lowest Icorrosion of Cr3C2-25NiCr coating.

  13. Efecto del tratamiento térmico posterior sobre la resistencia al desgaste por deslizamiento de un recubrimiento base níquel depositado por HVOF

    Directory of Open Access Journals (Sweden)

    Cadenas, P.

    2007-02-01

    Full Text Available In the present research, a nickel base coating was deposited on an AISI 1020 substrate by using high velocity oxy-fuel technique (HVOF. The coating was subsequently post heat -treated by means of an oxyacetylene flame. For the conditions evaluated in the present study, it was found that the CTT coating has 1,15 better wear resistance for the smaller level of the applied load and nearly 50 times for the highest level of the applied load when compared to the STT coatings. These results have been attributed to a better distribution of the hard phases, better cohesion between particles and an increase in hardness, as consequence of the post heat treatment process. A severe wear regime was found for all the samples since the wear rates presented values which were higher than 1·10-5 mm3/m. For the CTT coatings, the wear mechanism was mainly due to the adhesion and oxidation phenomena, meanwhile for the steel counterpart mechanisms such oxidation, grooving and three body abrasion were observed.

    En el presente trabajo, se depositó un recubrimiento base níquel sobre un acero AISI 1020 por la técnica de termorrociado de alta velocidad que utiliza oxígeno como combustible (High Velocity Oxygen Fuel - HVOF y, posteriormente, fue tratado térmicamente mediante llama oxiacetilénica. Para las condiciones evaluadas en este estudio, se encontró que el recubrimiento CTT tiene desde 1,15 veces más resistencia al desgaste, para el menor nivel de carga aplicada y mayor velocidad de deslizamiento y, hasta 50 veces más resistencia al desgaste para el mayor nivel carga aplicada y mayor velocidad de deslizamiento, comparado con el recubrimiento STT. Estos resultados se atribuyeron a una mejor distribución de las fases endurecedoras, una mejor cohesión entre partículas y un aumento en la microdureza del recubrimiento, como consecuencia del tratamiento térmico posterior. El régimen de desgaste presente en todas las muestras fue severo, ya que las

  14. Experimental analysis of sand particles' lift-off and incident velocities in wind-blown sand flux

    Institute of Scientific and Technical Information of China (English)

    Li Xie; Zhibao Dong; Xiaojing Zheng

    2005-01-01

    The probability distributions of sand particles' lift-off and incident velocities in a wind-blown sand flux play very important roles in the simulation of the wind-blown sand movement. In this paper, the vertical and the horizontal speeds of sand particles located at 1.0 mm above a sand-bed in a wind-blown sand flux are observed with the aid of Phase Doppler Anemometry (PDA) in a wind tunnel. Based on the experimental data, the probability distributions of not only the vertical lift-off speed but also the lift-off velocity as well as its horizontal component and the incident velocity as well as its vertical and horizontal components can be obtained by the equal distance histogram method. It is found, according to the results of the χ2-test for these probability distributions, that the probability density functions (pdf's) of the sand particles' lift-off and incident velocities as well as their vertical components are described by the Gamma density function with different peak values and shapes and the downwind incident and lift-off horizontal speeds, respectively, can be described by the lognormal and the Gamma density functions. These pdf's depend on not only the sand particle diameter but also the wind speed.

  15. Calibration of a micromachined particle velocity microphone in a standing wave tube using a LDA photon-correlation technique

    NARCIS (Netherlands)

    Raangs, R.; Schlicke, Ted; Barham, Richard

    2005-01-01

    In this paper, a new method of calibrating an acoustic particle velocity sensor using laser Doppler anemometry (LDA) is discussed. The results were compared and were in good agreement with the results obtained by conventional methods, where the sensitivity of the microflown is obtained with the use

  16. The Contradiction Between the Measurement Theory of Quantum Mechanics and the Theory that the Velocity of Any Particle Can Not be Larger than the Velocity of Light

    Science.gov (United States)

    Shen, Y.; Shen, Z. J.; Shen, G. T.; Yang, B. C.

    1996-01-01

    By the measurement theory of quantum mechanics and the method of Fourier transform,we proved that the wave function psi(x,y,z,t)= (8/((2(pi)(2L(exp (1/2)))(exp 3))(Phi(L,t,x)Phi(L,t,y)Phi(L,t,z)). According to the theory that the velocity of any particle can not be larger than the velocity of light and the Born interpretation, when absolute value of delta greater than (ct+ L),Phi(L,t,delta) = 0. But according to the calculation, we proved that for some delta, even if absolute value of delta is greater than (ct+L), Phi(L,t,delta) is not equal to 0.

  17. A Laboratory Modeling of the Velocity Field in the Convective Boundary Layer with the Particle Image Velocimetry Technique

    Institute of Scientific and Technical Information of China (English)

    李萍阳; 蒋维楣; 孙鉴泞; 袁仁民

    2003-01-01

    Based on the research of the convective boundary layer (CBL) temperature field in a convective tank, this paper studies the characteristics of the CBL velocity field in the convective tank. Aluminium powder (400 orders) is used as a tracer particle in the application of the particle image velocimetry (PIV)technique. The experiment demonstrates: the velocity distribution in the mixed layer clearly possesses the characteristics of CBL thermals; the velocity distribution in the top zone of the mixed layer shows entrainment layer characteristics; the vertical distribution of turbulent characteristic variables is reasonable,which is similar to field observations and other tank results; the error analysis demonstrates the validity of aluminium powder, which implies the reliability of the results.

  18. Low-velocity collisions of particles with a dry or wet wall

    Science.gov (United States)

    Kantak, Advait A.; Galvin, Janine E.; Wildemuth, Douglas J.; Davis, Robert H.

    2005-03-01

    Plastic and metal spheres were impacted at low velocities in the range 0.02-0.30 m/s with a quartz plate that was dry or covered with a thin oil layer. Collisions were performed with a specially designed device in the low-gravity environment provided by a KC-135 aircraft. A pendulum-based experimental set-up was also used to perform low-velocity collisions under normal gravity. The dry restitution coefficient (ratio of the rebound velocity and impact velocity) is found to decrease weakly with increasing approach velocity, as is the general case with materials exhibiting inelastic deformation. The wet restitution coefficient is zero below a critical velocity and then increases with the impact velocity before evening out to form a plateau. A simple model for the wet restitution coefficient, ewet=edry(1-Stc/St), was found to adequately predict the restitution coefficient, as has been reported in earlier studies at higher impact velocities, where edry is the dry restitution coefficient, St is the Stokes number and Stc is the critical Stokes number below which no rebound occurs. Surface asperities are seen to cause more scatter in the data at low velocities than at high velocities. The data from pendulum experiments coincide with those collected in low gravity, thereby affirming their applicability for performing low-velocity collisions.

  19. A Hot Spots Ignition Probability Model for Low-Velocity Impacted Explosive Particles Based on the Particle Size and Distribution

    Directory of Open Access Journals (Sweden)

    Hong-fu Guo

    2017-01-01

    Full Text Available Particle size and distribution play an important role in ignition. The size and distribution of the cyclotetramethylene tetranitramine (HMX particles were investigated by Laser Particle Size Analyzer Malvern MS2000 before experiment and calculation. The mean size of particles is 161 μm. Minimum and maximum sizes are 80 μm and 263 μm, respectively. The distribution function is like a quadratic function. Based on the distribution of micron scale explosive particles, a microscopic model is established to describe the process of ignition of HMX particles under drop weight. Both temperature of contact zones and ignition probability of powder explosive can be predicted. The calculated results show that the temperature of the contact zones between the particles and the drop weight surface increases faster and higher than that of the contact zones between two neighboring particles. For HMX particles, with all other conditions being kept constant, if the drop height is less than 0.1 m, ignition probability will be close to 0. When the drop heights are 0.2 m and 0.3 m, the ignition probability is 0.27 and 0.64, respectively, whereas when the drop height is more than 0.4 m, ignition probability will be close to 0.82. In comparison with experimental results, the two curves are reasonably close to each other, which indicates our model has a certain degree of rationality.

  20. Characterization of shape and terminal velocity of tephra particles erupted during the 2002 eruption of Etna volcano, Italy

    Science.gov (United States)

    Coltelli, M.; Miraglia, L.; Scollo, S.

    2008-09-01

    In this paper, we present a complete morphological characterization of the ash particles erupted on 18 December 2002 from Etna volcano, Italy. The work is based on the acquisition and processing of bidimensional digital images carried out by scanning electron microscopy (SEM) to obtain shape parameters by image analysis. We measure aspect ratio (AR), form factor (FF), compactness (CC), and rectangularity (RT) of 2065 ash particles with size between 0.026 and 1.122 mm. We evaluate the variation of these parameters as a function of the grain-size. Ash particles with a diameter of 0.250 mm are subelongate. We find that, on average, particles with a diameter of 0.50 mm are angular. Using this morphological analysis and an empirical relation between the drag coefficient ( C D) and Reynolds number ( R e) of Wilson and Huang (Earth Planet Sci Lett 44:311-324, 1979), we calculate the terminal settling velocities ( V WH). The comparisons between these velocities and those calculated with the formula of Kunii and Levenspiel ( Fluidization engineering. Wiley, New York, pp 97, 1969) ( V KL), which considers ash particles as spheres, show that V KL are in average 1.28 greater than V WH. Hence, we quantify the systematic error on the spatial distribution of the mass computed around the volcano carried out by tephra dispersal models when the particles are assumed to be spherical.

  1. Erosion behaviour of WC–10Co–4Cr coating on 23-8-N nitronic steel by HVOF thermal spraying

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Avnish, E-mail: avnishmnit@gmail.com [Department of Metallurgical and Materials Engineering, Malaviya National Institute of Technology, Jaipur, Rajasthan 302017 (India); Sharma, Ashok, E-mail: ashok.mnit12@gmail.com [Department of Metallurgical and Materials Engineering, Malaviya National Institute of Technology, Jaipur, Rajasthan 302017 (India); Goel, S.K., E-mail: skgoel@splsteel.com [Star Wire India Ltd., Ballabgarh, Haryana 121404 (India)

    2016-05-01

    Highlights: • WC–10Co–4Cr powder was HVOF sprayed on cast and solution treated 23-8-N nitronic steel. • Coated solution treated 23-8-N steel shows homogeneous microstructure, less decarburization and high fracture toughness as compared to coated cast steel. • Erosion behaviour of both coated steels was evaluated at two different impact angles. • Coated solution treated 23-8-N nitronic steel exhibits higher erosion resistance as compared to coated cast steel. • Key erosion resistance factors: homogeneous and well-bonded structure, high fracture toughness, optimum substrate properties. - Abstract: WC–10Co–4Cr coating was deposited by high-velocity oxy-fuel (HVOF) process on cast and solution treated (1220 °C/150 min) 23-8-N nitronic steel substrates. Solution treated substrate has shown higher toughness, ductility and impact energy with a marginal reduction in hardness as compared to cast substrate. This influence the coating deposition efficiency and erosion behaviour. Erosion resistance of coatings was evaluated by air jet erosion tester on two different impact angles (30° and 90°). Phases, microstructure and eroded surface of the coating were characterised by X-ray diffraction (XRD) analysis and field-emission scanning electron microscopy (FESEM) respectively. It is observed that coating on solution treated substrate was superior to cast substrate. The reason being that coating has dense and well-bonded structure with low porosity, less decarburization and inter-splat oxidation. Higher erosion resistance of coated solution treated 23-8-N nitronic steel was attributed to combination of high fracture toughness and hardness of coating including optimum mechanical properties of the substrate. FESEM analysis reveals that erosion response of WC–10Co–4Cr coating also dependent on the relative size of the impact crater with respect to the WC grain size. Coating is removed by combined mode of ductile and brittle erosion.

  2. Probability distributions of bed load particle velocities, accelerations, hop distances, and travel times informed by Jaynes's principle of maximum entropy

    Science.gov (United States)

    Furbish, David J.; Schmeeckle, Mark; Schumer, Rina; Fathel, Siobhan L.

    2016-01-01

    We describe the most likely forms of the probability distributions of bed load particle velocities, accelerations, hop distances, and travel times, in a manner that formally appeals to inferential statistics while honoring mechanical and kinematic constraints imposed by equilibrium transport conditions. The analysis is based on E. Jaynes's elaboration of the implications of the similarity between the Gibbs entropy in statistical mechanics and the Shannon entropy in information theory. By maximizing the information entropy of a distribution subject to known constraints on its moments, our choice of the form of the distribution is unbiased. The analysis suggests that particle velocities and travel times are exponentially distributed and that particle accelerations follow a Laplace distribution with zero mean. Particle hop distances, viewed alone, ought to be distributed exponentially. However, the covariance between hop distances and travel times precludes this result. Instead, the covariance structure suggests that hop distances follow a Weibull distribution. These distributions are consistent with high-resolution measurements obtained from high-speed imaging of bed load particle motions. The analysis brings us closer to choosing distributions based on our mechanical insight.

  3. Particle Filter Based Fault-tolerant ROV Navigation using Hydro-acoustic Position and Doppler Velocity Measurements

    DEFF Research Database (Denmark)

    Zhao, Bo; Blanke, Mogens; Skjetne, Roger

    2012-01-01

    This paper presents a fault tolerant navigation system for a remotely operated vehicle (ROV). The navigation system uses hydro-acoustic position reference (HPR) and Doppler velocity log (DVL) measurements to achieve an integrated navigation. The fault tolerant functionality is based on a modied...... particle lter. This particle lter is able to run in an asynchronous manner to accommodate the measurement drop out problem, and it overcomes the measurement outliers by switching observation models. Simulations with experimental data show that this fault tolerant navigation system can accurately estimate...

  4. Stereoscopy of dust density waves under microgravity: Velocity distributions and phase-resolved single-particle analysis

    Energy Technology Data Exchange (ETDEWEB)

    Himpel, Michael, E-mail: himpel@physik.uni-greifswald.de; Killer, Carsten; Melzer, André [Institute of Physics, Ernst-Moritz-Arndt-University, 17489 Greifswald (Germany); Bockwoldt, Tim; Piel, Alexander [IEAP, Christian-Albrechts-Universität Kiel, D-24098 Kiel (Germany); Ole Menzel, Kristoffer [ABB Switzerland Ltd, Corporate Research Center, 5405 Dättwil (Switzerland)

    2014-03-15

    Experiments on dust-density waves have been performed in dusty plasmas under the microgravity conditions of parabolic flights. Three-dimensional measurements of a dust density wave on a single particle level are presented. The dust particles have been tracked for many oscillation periods. A Hilbert analysis is applied to obtain trajectory parameters such as oscillation amplitude and three-dimensional velocity amplitude. While the transverse motion is found to be thermal, the velocity distribution in wave propagation direction can be explained by harmonic oscillations with added Gaussian (thermal) noise. Additionally, it is shown that the wave properties can be reconstructed by means of a pseudo-stroboscopic approach. Finally, the energy dissipation mechanism from the kinetic oscillation energy to thermal motion is discussed and presented using phase-resolved analysis.

  5. The functional TiO2-biodegradable plastic composite material produced by HVOF spraying process.

    Science.gov (United States)

    Bang, Hee-Seon; Bang, Han-Sur; Lee, Yoon-Ki

    2007-11-01

    Photocatalytic TiO2 coatings on bio-degradable plastic(polybutylene succinate: PBS) were prepared by HVOF spraying using three kinds of agglomerated powders (P200: 200 nm, P30: 30 nm, P7: 7 nm). The microstructures of the coatings were characterized with SEM and XRD analysis, and the photocatalytic efficiency of the coatings was evaluated by photo degradation of gaseous acetaldehyde. For both the HVOF sprayed P200 and P30 coatings, high anatase ratio of 100% was achieved, regardless of the fuel gas pressure. On the other hand, for the HVOF sprayed P7 coating, the anatase ratio decreased from 100% to 49.1% with increasing fuel gas pressure. This decrease may be attributed to the much higher susceptibility to heat of the 7 nm agglomerated powders than the 30 nm and 200 nm agglomerated powders. In terms of the photocatalytic efficiency, HVOF sprayed P200 and P30 coatings seemed to outperform the P7 coatings because of their higher anatase ratios. However, the HVOF sprayed P7 coatings did not show photocatalytic activity possibly because of the extremely small reaction surface area to the photo-catalytic activity and low anatase ratio. Therefore, the present study found that functional PBS plastic with photocatalytic performance could be produced by spraying of ceramics such as TiO2.

  6. Localization of massless Dirac particles via spatial modulations of the Fermi velocity

    Science.gov (United States)

    Downing, C. A.; Portnoi, M. E.

    2017-08-01

    The electrons found in Dirac materials are notorious for being difficult to manipulate due to the Klein phenomenon and absence of backscattering. Here we investigate how spatial modulations of the Fermi velocity in two-dimensional Dirac materials can give rise to localization effects, with either full (zero-dimensional) confinement or partial (one-dimensional) confinement possible depending on the geometry of the velocity modulation. We present several exactly solvable models illustrating the nature of the bound states which arise, revealing how the gradient of the Fermi velocity is crucial for determining fundamental properties of the bound states such as the zero-point energy. We discuss the implications for guiding electronic waves in few-mode waveguides formed by Fermi velocity modulation.

  7. Analytical Ultracentrifugation of Inorganic Colloids; Sedimentation Velocity of Interacting and Non-Interacting Particles

    NARCIS (Netherlands)

    Planken, K.L.|info:eu-repo/dai/nl/304841099

    2008-01-01

    Several case studies of the sedimentation velocity of non-interacting, attractive and repulsive colloids are discussed. After a brief introduction that highlights historical facts, basic analytical ultracentrifugation theory, some instrument issues and experiments are reviewed. The existence of disc

  8. Partitioning of particle velocities in gas-solid turbulent flows into a continuous field and a spatially uncorrelated random distribution: theoretical formalism and numerical study

    Science.gov (United States)

    Février, Pierre; Simonin, Olivier; Squires, Kyle D.

    2005-06-01

    The velocity distribution of dilute suspensions of heavy particles in gas-solid turbulent flows is investigated. A statistical approach - the mesoscopic Eulerian formalism (MEF) - is developed in which an average conditioned on a realization of the turbulent carrier flow is introduced and enables a decomposition of the instantaneous particle velocity into two contributions. The first is a contribution from an underlying continuous turbulent velocity field shared by all the particles - the mesoscopic Eulerian particle velocity field (MEPVF) - that accounts for all particle-particle and fluid-particle two-point correlations. The second contribution corresponds to a distribution - the quasi-Brownian velocity distribution (QBVD) - that represents a random velocity component satisfying the molecular chaos assumption that is not spatially correlated and identified with each particle of the system. The MEF is used to investigate properties of statistically stationary particle-laden isotropic turbulence. The carrier flow is computed using direct numerical simulation (DNS) or large-eddy simulation (LES) with discrete particle tracking employed for the dispersed phase. Particle material densities are much larger than that of the fluid and the force of the fluid on the particle is assumed to reduce to the drag contribution. Computations are performed in the dilute regime for which the influences of inter-particle collisions and fluid-turbulence modulation are neglected. The simulations show that increases in particle inertia increase the contribution of the quasi-Brownian component to the particle velocity. The particle velocity field is correlated at larger length scales than the fluid, with the integral length scales of the MEPVF also increasing with particle inertia. Consistent with the previous work of Abrahamson (1975), the MEF shows that in the limiting case of large inertia, particle motion becomes stochastically equivalent to a Brownian motion with a random spatial

  9. Velocity Distribution of Slurry in Horizontal Pipe When Solid Particles Sliding

    Institute of Scientific and Technical Information of China (English)

    ZhangShilin; XuZhenliang; Shaolongtan

    2004-01-01

    Based on the laws of momentum conservation and impulse in accelerating process, the distribution on speed of ununiform slurry flow in a horizontal pipe was studied. According to the momentum change of solid particles and conveying liquid of slurry flow during accelerating, and some effect factors, the relationship between the speed of solid particles and the speed of conveying liquid was obtained.When dealing with the friction between sliding solid particles and pipe, it is pivotal to reasonably distribute component of friction to each solid particle. The friction coefficient between solid particles was obtained by forces analysis and theoretic calculation, and can be used to calculate the friction force on every solid particle. The effect of friction on speed of ever), solid particle was investigated through the impulse law. The result is more accurate than that by using uniform friction on solid particles. It is completely new method to use above theory to get solid particles speed distribution, conveying liquid speed distribution and slurry speed distribution.

  10. Increased Lifetime for Biomass and Waste to Energy Power Plant Boilers with HVOF Coatings: High Temperature Corrosion Testing Under Chlorine-Containing Molten Salt

    Science.gov (United States)

    Oksa, Maria; Tuurna, Satu; Varis, Tommi

    2013-06-01

    Heat exchanger surfaces of waste to energy and biomass power plant boilers experience often severe corrosion due to very aggressive components in the used fuels. High velocity oxy-fuel (HVOF) coatings offer excellent protection for boiler tubes against high temperature corrosion due to their high density and good adherence to the substrate material. Several thermal spray coatings with high chromium content were sprayed with HVOF technique. Their mechanical properties and high temperature corrosion resistance were tested and analyzed. The coating materials included NiCr, IN625, Ni-21Cr-10W-9Mo-4Cu, and iron-based partly amorphous alloy SHS9172 (Fe-25Cr-15W-12Nb-6Mo). High temperature corrosion testing was performed in NaCl-KCl-Na2SO4 salt with controlled H2O atmosphere at 575 and 625 °C. The corrosion test results of the coatings were compared to corrosion resistance of tube materials (X20, Alloy 263 and Sanicro 25).

  11. The Wear Behavior of HVOF Sprayed Near-Nanostructured WC-17%Ni(80/20)Cr Coatings in Dry and Slurry Wear Conditions

    Science.gov (United States)

    Ben Mahmud, Tarek A.; Atieh, Anas M.; Khan, Tahir I.

    2017-07-01

    The ability to deposit nanostructured feedstock by using high-velocity oxygen-fuel (HVOF) spray offers potential improvements in coating hardness, wear resistance and toughness for applications in the oil sands industry. In this study, the wear behavior of a near-nanostructured coating was compared under dry and slurry abrasive wear test using an uncoated AISI-1018 low-carbon steel substrate as a reference. The coating microstructures were analyzed in the as-sprayed, dry and slurry test conditions using scanning electron microscopy, x-ray diffraction and microhardness measurements. Wear behavior of the steel and coating surfaces were assessed using a pin-on-plate wear test under various loads. The results showed that a coating could be successfully deposited using the HVOF spraying technique and with retention of the near-nanosized WC dispersion within the coating structure. The wear rate under dry test conditions was greater for the steel and coating compared to tests performed under slurry conditions. Examination of the wear tracks revealed that the wear mechanism was different for the two test conditions. Wear in the dry test condition resulted from 2-body abrasion, while 3-body abrasion dominated wear in slurry conditions. The latter showed lower wear rates due to a lubricating effect of the oil.

  12. Investigations on the Behavior of HVOF and Cold Sprayed Ni-20Cr Coating on T22 Boiler Steel in Actual Boiler Environment

    Science.gov (United States)

    Bala, Niraj; Singh, Harpreet; Prakash, Satya; Karthikeyan, J.

    2012-01-01

    High temperature corrosion accompanied by erosion is a severe problem, which may result in premature failure of the boiler tubes. One countermeasure to overcome this problem is the use of thermal spray protective coatings. In the current investigation high velocity oxy-fuel (HVOF) and cold spray processes have been used to deposit commercial Ni-20Cr powder on T22 boiler steel. To evaluate the performance of the coatings in actual conditions the bare as well as the coated steels were subjected to cyclic exposures, in the superheater zone of a coal fired boiler for 15 cycles. The weight change and thickness loss data were used to establish kinetics of the erosion-corrosion. X-ray diffraction, surface and cross-sectional field emission scanning electron microscope/energy dispersive spectroscopy (FE-SEM/EDS) and x-ray mapping techniques were used to analyse the as-sprayed and corroded specimens. The HVOF sprayed coating performed better than its cold sprayed counterpart in actual boiler environment.

  13. Mechanical property changes in HVOF sprayed nano-structured WC-17wt.%Ni(80/20)Cr coating with varying substrate roughness

    Science.gov (United States)

    Ben Mahmud, Tarek A.; Saha, Gobinda C.; Khan, Tahir I.

    2014-06-01

    Thermally sprayed coatings developed by use of high velocity oxy-fuel (HVOF) process are known for their superior wear characteristics. In many industrial applications, new parts as well as repaired and refurbished parts coated with WC-Co microstructured coatings have shown enhanced erosion-corrosion and abrasive resistant properties when compared with other surface modification technologies such as chrome replacement, fusion welding, and cladding. This research has been further directed towards the development of HVOF technique to deposit dense nanostructured ceramic-metallic composites. The mechanism of plastic deformation, which determines the strength and ductility of materials, in nanostructured materials are different, thereby leading to novel mechanical properties. Various parameters can influence these properties, but the substrate surface preparation by grit blasting before thermal spraying is one critical parameter. The grit blasting process generates a surface roughness, which ensures mechanical anchoring between the coating and the substrate surface. In this work, the sliding wear behavior and microhardness of WC-17wt.%Ni(80/20)Cr cermet coatings deposited onto carbon steel substrates are examined as a function of three different surface roughness values under different loads. The results show that as-prepared surface with different blasting profiles have a direct influence on the surface roughness and wear performance of the coatings. The sliding wear resistance of the coatings increased as the substrate surface roughness increased. The wear depth decreased with increasing surface roughness.

  14. The effect of spraying parameters on micro-structural properties of WC-12%Co coating deposited on copper substrate by HVOF process

    Energy Technology Data Exchange (ETDEWEB)

    Sathwara, Nishit, E-mail: nishit-25@live.in [Fusion Rector Material Development & Characterization Division, Institute for Plasma Research, GIDC Electronics Estate, Sec-25, Gandhinagar-382016 (India); Metallurgical & Materials Engineering Department, Indus University, Ahmedabad-382115 (India); Jariwala, C., E-mail: chetanjari@yahoo.com; Chauhan, N.; Raole, P. M. [Fusion Rector Material Development & Characterization Division, Institute for Plasma Research, GIDC Electronics Estate, Sec-25, Gandhinagar-382016 (India); Basa, D. K. [Metallurgical & Materials Engineering Department, Indus University, Ahmedabad-382115 (India)

    2015-08-28

    High Velocity Oxy-Fuel (HVOF) thermal sprayed coatingmade from Tungsten Carbide (WC) isconsidered as one of the most durable materials as wear resistance for industrial applications at room temperature. WC coating offers high wear resistance due to its high hardness and tough matrix imparts. The coating properties strongly depend on thermal spray processing parameters, surface preparation and surface finish. In this investigation, the effect of variousHVOF process parameters was studied on WC coating properties. The WC-12%Co coating was produced on Copper substrate. Prior to coating, theCopper substrate surface was prepared by grit blasting. WC-12%Co coatings were deposited on Coppersubstrates with varying process parameters such as Oxygen gas pressure, Air pressure, and spraying distance. Microstructure of coating was examined using Scanning Electron Microscope (SEM) and characterization of phasespresentin the coating was examined by X-Ray Diffraction (XRD). Microhardness of all coatingswas measured by VickerMicrohardness tester. At low Oxygen Pressure(10.00 bar), high Air pressure (7bar) and short nozzle to substrate distance of 170mm, best coating adhesion and porosity less structure isachieved on Coppersubstrate.

  15. 超音速氧焰喷涂HA/BG涂层的制备及表征%Research on Properties of HA/BG Coatings Prepared by HVOF Spraying

    Institute of Scientific and Technical Information of China (English)

    鲍益富; 翁杰; 冯波; 段可

    2009-01-01

    Hydroxyapatite (HA) coatings with bioactive glass (BG) was prepared on Ti6A14V matrix by high velocity oxygen-fuel spray. The phase morphology and bioactivity of the coatings were studied. The X-ray diffraction shows that the coatings are mainly crystalline HA and exhibit no thermal decomposition byproducts. The addition of BG does not affect the coating phases. The SEM observation shows that the HA particles are partially melted, with melting fraction of 13%, and spherical BG particles are incorporated on the HA coating. The BG content of the surface coating is lower than that in input powder. After soaking in simulated body fluid for 7 days, only the coating with 20% BG forms a bone-like apatite, which indicates that the addition of BG increases the bioactivity of the coating.%利用超音速氧焰喷涂(HVOF)在Ti6A14V基体上制备了羟基磷灰石(HA)/生物玻璃(BG)涂层,考察了涂层的相组成、表面形貌及生物活性.XRD显示:涂层的结晶相为HA,未检测到HA分解产物,添加生物玻璃不影响涂层的相组成;SEM结果表明:HA颗粒熔化较少,计算熔化比例为13%,BG颗粒以球形方式镶嵌在涂层表面,含量小于粉末中的比例:涂层浸泡在模拟体液中7天后发现:添加20%BG的涂层表面有类骨类磷灰石涂层生成,说明添加BG可以提高涂层的生物活性.

  16. Entropy production by active particles: Coupling of odd and even functions of velocity

    CERN Document Server

    Chaudhuri, Debasish

    2016-01-01

    Non-equilibrium stochastic dynamics of several active Brownian systems are modeled in terms of non-linear velocity dependent force. In general, this force may consist of both even and odd functions of velocity. We derive the expression for total entropy production in such systems using Fokker-Planck equation. The result is consistent with the expression for stochastic entropy production in the reservoir, that we obtain from probabilities of time-forward and time-reversed trajectories, leading to fluctuation theorems. Numerical simulation is used to find probability distribution of entropy production, which shows good agreement with the detailed fluctuation theorem.

  17. Quantization of a particle with a force quadratic in the velocity

    Energy Technology Data Exchange (ETDEWEB)

    Sa Borges, J.; Epele, L.N.; Fanchiotti, H.; Garcia Canal, C.A.; Sima-tildeo, F.R.A.

    1988-09-15

    The quantization of a system subject to a force quadratic in the velocity and position dependence is carried out in the phase-space path-integral framework. The resulting Hamiltonian coincides with that obtained by using the Weyl-ordering canonical prescription.

  18. Stream ambient noise, spectrum and propagation of sounds in the goby Padogobius martensii: sound pressure and particle velocity.

    Science.gov (United States)

    Lugli, Marco; Fine, Michael L

    2007-11-01

    The most sensitive hearing and peak frequencies of courtship calls of the stream goby, Padogobius martensii, fall within a quiet window at around 100 Hz in the ambient noise spectrum. Acoustic pressure was previously measured although Padogobius likely responds to particle motion. In this study a combination pressure (p) and particle velocity (u) detector was utilized to describe ambient noise of the habitat, the characteristics of the goby's sounds and their attenuation with distance. The ambient noise (AN) spectrum is generally similar for p and u (including the quiet window at noisy locations), although the energy distribution of u spectrum is shifted up by 50-100 Hz. The energy distribution of the goby's sounds is similar for p and u spectra of the Tonal sound, whereas the pulse-train sound exhibits larger p-u differences. Transmission loss was high for sound p and u: energy decays 6-10 dB10 cm, and sound pu ratio does not change with distance from the source in the nearfield. The measurement of particle velocity of stream AN and P. martensii sounds indicates that this species is well adapted to communicate acoustically in a complex noisy shallow-water environment.

  19. Holographic And Microscopic Study Of Morphology And Velocity Distribution Of Solidifying Particles In Rapidly Stirred Melts

    Science.gov (United States)

    Smeulders, R. J.; Mischgofsky, F. H.; Frankena, H. J...

    1983-12-01

    A technique is described to observe shape development and particle displacements of fast moving solidifying particles during stir casting. The optical set-up consists of a Ruby la-ser (generating pulse pairs), a frequency doubled Nd3+:YAG laser (generating single pulses at a 10 Hz repetition rate), a model device of an actual metal stir casting apparatus filled with a transparent organic alloy and three different recording systems. Double exposure holograms and microphotographs are used to analyse the three- and two-dimensional particle displacements, respectively. Simultaneously recorded videotapes, microphotographs and holograms provide the opportunity to study the shape development at a repetition rate of 10 Hz over periods of 103 seconds in an imaging volume of 3 x 2 x 2 mm3. We found that a NPA-water alloy nucleates initially as equiaxed dendritic particles. After a period of stirring, the dendrite tips become more rounded. Finally the particles obtain the shape of a bunch of grapes. This final state is in good agreement with the morphology of stir casted metal alloys. Further we found that the flow behaviour at the start of the experiment can be decisive for the solidification process. We observed Taylor vortices and measured particle displacements, that occur in the direction of rotation and also along the axis of rotation (although there was no flow pressure excerted in that direction) and in the radial direction, too.

  20. Effects of Reynolds Number and Stokes Number on Particle-pair Relative Velocity in Isotropic Turbulence: An Experimental Study

    Science.gov (United States)

    Dou, Zhongwang; Bragg, Andrew; Hammond, Adam; Liang, Zach; Collins, Lance; Meng, Hui

    2016-11-01

    Effects of Reynolds number (Rλ) and Stokes number (St) on particle-pair relative velocity (RV) were studied using four-frame particle tracking in an enclosed turbulence chamber. Two tests were performed: varying Rλ between 246 and 357 at six St values, and varying St between 0.02 and 4.63 at five Rλ values. By comparing experimental and DNS results of mean inward particle-pair RV, , we observed excellent agreement for all test conditions across a large range of particle separation distance (r) ; however at r values were higher than simulation. At fixed St , was found to be independent of Rλ in the observable St , r, and Rλ ranges. At fixed Rλ, increased with St at small r and decreased with St at large r. We further compared and variance of RV, , between experiments, DNS and theoretical predictions by Pan and Padoan (2010). At 0 theory-predicted and matched with DNS and experiment in the range of r = 1 - 60 η . As St increased, theoretical predictions were lower than experiment and DNS results. The potential causes of these trends are explored. Additionally, we discuss the observed electrostatic charge effect on particle relative motion in isotropic turbulence and our plans of studying this effect using an integrated experimental, numerical and theoretical approach. This work was supported by NSF CBET-0967407 and CBET-0967349.

  1. A Microfluidic Device with an Integrated Waveguide Beam Splitter for Velocity Measurements of Flowing Particles by Fourier Transformation

    DEFF Research Database (Denmark)

    Mogensen, Klaus Bo; Kwok, Y.C.; Eijkel, J.C.T.

    2003-01-01

    A microfabricated capillary electrophoresis device for velocity measurements of flowing particles is presented. It consists of a 1 x 128 planar waveguide beam splitter monolithically integrated with an electrically insulated fluidic channel network for fluorescence excitation at multiple points...... optics. The integrated planar waveguide beam splitter was, furthermore, permanently connected to the light source by a glued-on optical fiber, to achieve a robust and alignment-free operation of the system. The velocity was measured using a Fourier transformation with a Shah function, since the response...... of the fight array was designed to approximate a square profile. Deviations from this response were observed as a result of the multimode nature of the integrated waveguides....

  2. Measurement of burning velocity for bare strand casted with a frozen mixture of nano/micro-aluminum particles and water

    Energy Technology Data Exchange (ETDEWEB)

    Jun, Jin Yong; Lee, Byeong Jun; Song, Dong Joo [Yeungnam University, Gyeongsan (Korea, Republic of)

    2016-05-15

    Combustion characteristics of a mixture of nano- and micron-sized aluminum powder in ice were experimentally studied. Round barshaped bare strand was casted with a frozen mixture of aluminum and water and then electrically ignited in the air or argon environment. Propagating flame was recorded using a camcorder with an optical filter. Burning rate, defined as the slope in the graph of average flame position movement versus time, was also evaluated. The burning velocity peaked at equivalence ratio of 0.8. Flame propagation velocity increased with a pressure exponent of 0.61 for = 0.8 and pressure range of 0.1-0.8 MPa. For nano/micro-mixture at = 0.8, flame propagation was not feasible if the mass fraction of micron-sized particles in fuel is higher than 0.5.

  3. Particle-in-Cell simulation of two-dimensional electron velocity shear driven instability in relativistic domain

    CERN Document Server

    Shukla, Chandrasekhar; Patel, Kartik

    2016-01-01

    We carry out Particle-in-Cell (PIC) simulations to study the instabilities associated with a 2-D sheared electron flow configuration against a neutralizing background of ions. Both weak and strong relativistic flow velocities are considered. In the weakly relativistic case, we observe the development of electromagnetic Kelvin Helmholtz instability with similar characteristics as that predicted by the electron Magnetohydrodynamic (EMHD) model. On other hand, in strong relativistic case the compressibility effects of electron fluid dominate and introduce upper hybrid electrostatic oscillations transverse to the flow which are very distinct from EMHD fluid behaviour. In the nonlinear regime, both weak and strong relativistic cases lead to turbulence with broad power law spectrum.

  4. Meaningful use of peak particle velocities at excavation surfaces for the optimisation of the rockburst criteria for tunnels and stopes.

    CSIR Research Space (South Africa)

    Milev, AM

    2002-03-01

    Full Text Available Final Project Report The meaningful use of peak particle velocities at excavation surfaces for the optimisation of the rockburst criteria for tunnels and stopes A.M. Milev, S.M. Spottiswoode, B.R. Noble, L.M. Linzer, M. van Zyl, A. Daehnke & E... and Ventersdorp Contact Reef sites were carried out. A total number of 41 sites were monitored: • TauTona gold mine: a total number of 15 139 seismic events with a maximum PPV of 3 m/s was recorded during 2 437 site days; • Kloof gold mine: a total number of 6...

  5. An Electromagnetic Gauge Technique for Measuring Shocked Particle Velocity in Electrically Conductive Samples

    Science.gov (United States)

    Cheng, David; Yoshinaka, Akio

    2014-11-01

    Electromagnetic velocity (EMV) gauges are a class of film gauges which permit the direct in-situ measurement of shocked material flow velocity. The active sensing element, typically a metallic foil, requires exposure to a known external magnetic field in order to produce motional electromotive force (emf). Due to signal distortion caused by mutual inductance between sample and EMV gauge, this technique is typically limited to shock waves in non-conductive materials. In conductive samples, motional emf generated in the EMV gauge has to be extracted from the measured signal which results from the combined effects of both motional emf and voltage changes from induced currents. An electromagnetic technique is presented which analytically models the dynamics of induced current between a copper disk moving as a rigid body with constant 1D translational velocity toward an EMV gauge, where both disk and gauge are exposed to a uniform external static magnetic field. The disk is modelled as a magnetic dipole loop where its Foucault current is evaluated from the characteristics of the fields, whereas the EMV gauge is modelled as a circuit loop immersed in the field of the magnetic dipole loop, the intensity of which is calculated as a function of space and, implicitly, time. Equations of mutual induction are derived and the current induced in the EMV gauge loop is solved, allowing discrimination of the motional emf. Numerical analysis is provided for the step response of the induced EMV gauge current with respect to the Foucault current in the moving copper sample.

  6. Dynamical properties for the problem of a particle in an electric field of wave packet: Low velocity and relativistic approach

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Diego F.M., E-mail: diegofregolente@gmail.com [Institute for Multiscale Simulations, Friedrich-Alexander Universität, D-91052, Erlangen (Germany); Leonel, Edson D., E-mail: edleonel@rc.unesp.br [Departamento de Estatística, Matemática Aplicada e Computação, UNESP, Univ. Estadual Paulista, Av. 24A, 1515, Bela Vista, 13506-900, Rio Claro, SP (Brazil); Departamento de Física, UNESP, Univ. Estadual Paulista, Av. 24A, 1515, 13506-900, Rio Claro, SP (Brazil)

    2012-11-01

    We study some dynamical properties for the problem of a charged particle in an electric field considering both the low velocity and relativistic cases. The dynamics for both approaches is described in terms of a two-dimensional and nonlinear mapping. The structure of the phase spaces is mixed and we introduce a hole in the chaotic sea to let the particles to escape. By changing the size of the hole we show that the survival probability decays exponentially for both cases. Additionally, we show for the relativistic dynamics, that the introduction of dissipation changes the mixed phase space and attractors appear. We study the parameter space by using the Lyapunov exponent and the average energy over the orbit and show that the system has a very rich structure with infinite family of self-similar shrimp shaped embedded in a chaotic region.

  7. Fluidization velocity assessment of commercially available sulfur particles for use in autotrophic denitrification biofilters

    Science.gov (United States)

    There has been no evaluation of sulfur-based autotrophic denitrification using fluidized biofilters in a recirculating aquaculture system to mitigate nitrate-nitrogen loads. The objectives of this work were to quantify the particle size distribution, specific surface area, and fluidization velocitie...

  8. Effect of Plasma Nitriding and Nitrocarburizing on HVOF-Sprayed Stainless Steel Coatings

    Science.gov (United States)

    Park, Gayoung; Bae, Gyuyeol; Moon, Kyungil; Lee, Changhee

    2013-12-01

    In this work, the effects of plasma nitriding (PN) and nitrocarburizing on HVOF-sprayed stainless steel nitride layers were investigated. 316 (austenitic), 17-4PH (precipitation hardening), and 410 (martensitic) stainless steels were plasma-nitrided and nitrocarburized using a N2 + H2 gas mixture and the gas mixture containing C2H2, respectively, at 550 °C. The results showed that the PN and nitrocarburizing produced a relatively thick nitrided layer consisting of a compound layer and an adjacent nitrogen diffusion layer depending on the crystal structures of the HVOF-sprayed stainless steel coatings. Also, the diffusion depth of nitrogen increased when a small amount of C2H2 (plasma nitrocarburizing process) was added. The PN and nitrocarburizing resulted in not only an increase of the surface hardness, but also improvement of the load bearing capacity of the HVOF-sprayed stainless steel coatings because of the formation of CrN, Fe3N, and Fe4N phases. Also, the plasma-nitrocarburized HVOF-sprayed 410 stainless steel had a superior surface microhardness and load bearing capacity due to the formation of Cr23C6 on the surface.

  9. Observation of the Near-seabed Velocity and Particles Resuspension During Nonlinear Internal Solitary Wave Events near the Dongsha Plateau at the Northern South China Sea

    Science.gov (United States)

    2015-09-30

    1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Observation of the Near-seabed Velocity and Particles...likely form the continuous sediment waves on the seafloor [Ma et al., 2008 and Reeder et al., 2011]. To our knowledge, there are no direct observations ...of near-bottom velocity and sediment resuspension during ISW events. The main objectives are to measure the near bottom velocities and observe the

  10. Deposition and properties of high-velocity-oxygen-fuel and plasma-sprayed Mo-Mo2C composite coatings

    Science.gov (United States)

    Prchlik, L.; Gutleber, J.; Sampath, S.

    2001-12-01

    Molybdenum thermal-spray coatings, dispersion strengthened by molybdenum oxides and molybdenum carbides, play an important role in industrial tribological applications. Traditionally, they have been prepared by plasma and wire flame spraying. High porosity and lower cohesion strength limit their application in situations where both galling and abrasion wear is involved. In this study, high-velocity-oxygen-fuel (HVOF) deposition of molybdenum and molybdenum carbide coatings was attempted. Deposition was achieved for all powders used. Composition, microstructure, mechanical, and wear properties of the HVOF synthesized coatings were evaluated and compared with plasma-sprayed counterparts. The HVOF coatings possessed a very good abrasion resistance, whereas plasma deposits performed better in dry sliding tests. Measurements showed a close relationship between the coating surface hardness and its abrasion resistance. Results also suggested correlation between molybdenum carbide distribution in the molybdenum matrix and the sliding friction response of Mo-Mo2C coatings.

  11. Wall effects on the terminal velocity of spherical particles in Newtonian and non-Newtonian fluids

    Directory of Open Access Journals (Sweden)

    ATAÍDE C. H.

    1999-01-01

    Full Text Available The objective of this work is to study the effect of confining walls on the free settling of spherical particles along the axes of five vertical cylindrical tubes in Newtonian and non-Newtonian liquids. Experimental results were predominantly obtained in the particle flow region between the Stokes and the Newton regimes (intermediate region and displayed Reynolds numbers in the ranges 0.7

  12. Influence of powder particle injection velocity on the microstructure of Al-12Si/SiCp coatings produced by laser cladding

    NARCIS (Netherlands)

    Anandkumar, R.; Almeida, A.; Vilar, R.; Ocelik, V.; De Hosson, J. Th M.

    2009-01-01

    The influence of powder particle injection velocity on the microstructure of coatings consisting of an Al-Si matrix reinforced with SiC particles prepared by laser cladding from mixtures of powders of Al-12 wt.% Si alloy and SiC was investigated both experimentally and by modeling. At low injection

  13. Mathematical modeling of velocity and number density profiles of particles across the flame propagation through a micro-iron dust cloud.

    Science.gov (United States)

    Bidabadi, Mehdi; Haghiri, Ali; Rahbari, Alireza

    2010-04-15

    In this study, an attempt has been made to analytically investigate the concentration and velocity profiles of particles across flame propagation through a micro-iron dust cloud. In the first step, Lagrangian particle equation of motion during upward flame propagation in a vertical duct is employed and then forces acting upon the particle, such as thermophoretic force (resulted from the temperature gradient), gravitation and buoyancy are introduced; and consequently, the velocity profile as a function of the distance from the leading edge of the combustion zone is extracted. In the resumption, a control volume above the leading edge of the combustion zone is considered and the change in the particle number density in this control volume is obtained via the balance of particle mass fluxes passing through it. This study explains that the particle concentration at the leading edge of the combustion zone is more than the particle agglomeration in a distance far from the flame front. This increase in the particle aggregation above the combustion zone has a remarkable effect on the lower flammability limits of combustible particle cloud. It is worth noticing that the velocity and particle concentration profiles show a reasonable compatibility with the experimental data.

  14. Differential Velocity between Solar Wind Protons and Alpha Particles in Pressure Balance Structures

    Science.gov (United States)

    Yamauchi, Yohei; Suess, Steven T.; Steinberg, John T.; Sakurai, Takashi

    2004-01-01

    Pressure balance structures (PBSs) are a common high-plasma beta feature in high-latitude, high-speed solar wind. They have been proposed as remnants of coronal plumes. If true, they should reflect the observation that plumes are rooted in unipolar magnetic flux concentrations in the photosphere and are heated as oppositely directed flux is advected into and reconnects with the flux concentration. A minimum variance analysis (MVA) of magnetic discontinuities in PBSs showed there is a larger proportion of tangential discontinuities than in the surrounding high-speed wind, supporting the hypothesis that plasmoids or extended current sheets are formed during reconnection at the base of plumes. To further evaluate the character of magnetic field discontinuities in PBSs, differential streaming between alpha particles and protons is analyzed here for the same sample of PBSs used in the MVA. Alpha particles in high-speed wind generally have a higher radial flow speed than protons. However, if the magnetic field is folded back on itself, as in a large-amplitude Alfven wave, alpha particles will locally have a radial flow speed less than protons. This characteristic is used here to distinguish between folded back magnetic fields (which would contain rotational discontinuities) and tangential discontinuities using Ulysses high-latitude, high-speed solar wind data. The analysis indicates that almost all reversals in the radial magnetic field in PBSs are folded back field lines. This is found to also be true outside PBSs, supporting existing results for typical high-speed, high-latitude wind. There remains a small number of cases that appear not to be folds in the magnetic field and which may be flux tubes with both ends rooted in the Sun. The distinct difference in MVA results inside and outside PBSs remains unexplained.

  15. Estimation of particle velocity in moving beds based on a flow model for bulk solids. Ryudo model ni motozuita idoso no ryushi sokudo no suisan

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, H. (Muroran Inst. of Tech., Hokkaido (Japan)); Honda, Y. (Snow Brand Milk Products Co. Ltd., Sapporo (Japan))

    1992-11-10

    Based on a particle flow model (stress-shear strain velocity relational expression) which takes account of the bulk volume expansion effect during shearing deformation of particles, a new estimation method for particle velocity distribution and stress distribution is proposed. The method is applied to a crossflow moving bed and to a moving bed for comparison with the experimental values to examine its validity. The method is further extended to predict the velocity profile and stress profile of moving beds in a vertical tube (countercurrent and concurrent) accompanying gas flow. It is indicated that the bulk volume expansion effect differs according to dimensions. The velocity distribution and the stress distribution of flows in a vertical tube are greatly influenced by the nature of the flow, i.e. whether it is a counterflow or a concurrent flow, and the frictional force of solids on a wall surface increases markedly in a concurrent flow, which induces considerable lag of particle velocity. The parameter which is contained in the model and indicates the bulk volume expansion effect is a function of the particle velocity, and it is almost unaffected by the flow rate of gas moving. 7 refs., 10 figs.

  16. Evaluation of hot corrosion behaviour of HVOF sprayed Ni-5Al and NiCrAl coatings in coal fired boiler environment

    Energy Technology Data Exchange (ETDEWEB)

    Mahesh, R.A.; Jayaganthan, R.; Prakash, S. [VA Tech EWF Pvt Ltd., Prithla (India)

    2010-08-15

    Hot corrosion was recognised as a serious problem in connection with the degradation of fireside boiler tubes in coal fired steam generating plants. It is one of the most deleterious forms of surface degradation which can lead to the loss of mechanical strength and catastrophic failure of structural and engineering components. In the present investigation, an attempt has been made to evaluate the hot corrosion behaviour of high velocity oxyfuel (HVOF) sprayed Ni-5Al and NiCrAl coatings on iron based superalloy in an actual coal fired boiler environment. The coated specimens were hung in the low temperature superheater zone (about 700{sup o}C) of a coal fired boiler. The studies were carried out for 10 cycles each cycle consisting of exposing the coated specimens for 100 h followed by 1 h cooling to ambient conditions. NiCrAl coated specimen provided better resistance to hot corrosion than Ni-5Al coated specimen in the given environment.

  17. Electrochemical Corrosion of HVOF-Sprayed NiCoCrAlY Coatings in CO2-Saturated Brine

    Science.gov (United States)

    Ruiz-Luna, H.; Porcayo-Calderon, J.; Alvarado-Orozco, J. M.; García-Herrera, J. E.; Martinez-Gomez, L.; Trápaga-Martínez, L. G.; Muñoz-Saldaña, J.

    2016-10-01

    The effect of pre-oxidation treatment and surface preparation of optimized NiCoCrAlY coatings deposited by high-velocity oxygen fuel (HVOF) spraying and exposed to a low-temperature corrosive environment is reported herein. Coatings with two surface finish conditions (as-sprayed and ground) were heat treated under two different oxygen partial pressures (air and argon). The electrochemical corrosion behavior was evaluated in CO2-saturated brine via potentiodynamic polarization, polarization resistance, and electrochemical impedance measurements. The results show that the grinding process and pre-oxidation treatment in argon enhanced growth and formation of α-Al2O3 scale. The potentiodynamic polarization results show that both pre-oxidation and surface treatment had a positive influence on the corrosion resistance of the coating. The reduction of the porosity and the formation of a dense, uniform, and adherent oxide scale through pre-oxidation treatment led to an increase of the corrosion resistance due to a decrease in active sites and blocking of diffusion of reactive species into the coating. However, according to the results, complete transformation from metastable alumina phases to α-Al2O3 in addition to formation and growth of dense α-Al2O3 is required to ensure full protection of the coating and base material over long periods.

  18. Electrochemical Study of Ni20Cr Coatings Applied by HVOF Process in ZnCl2-KCl at High Temperatures

    Directory of Open Access Journals (Sweden)

    J. Porcayo-Calderón

    2014-01-01

    Full Text Available Corrosion behavior of Ni20Cr coatings deposited by HVOF (high velocity oxygen-fuel process was evaluated in ZnCl2-KCl (1 : 1 mole ratio molten salts. Electrochemical techniques employed were potentiodynamic polarization curves, open circuit potential, and linear polarization resistance (LPR measurements. Experimental conditions included static air and temperatures of 350, 400, and 450°C. 304-type SS was evaluated in the same conditions as the Ni20Cr coatings and it was used as a reference material to assess the coatings corrosion resistance. Coatings were evaluated as-deposited and with a grinded surface finished condition. Results showed that Ni20Cr coatings have a better corrosion performance than 304-type SS. Analysis showed that Ni content of the coatings improved its corrosion resistance, and the low corrosion resistance of 304 stainless steel was attributed to the low stability of Fe and Cr and their oxides in the corrosive media used.

  19. MnCo{sub 2}O{sub 4} spinel chromium barrier coatings for SOFC interconnect by HVOF

    Energy Technology Data Exchange (ETDEWEB)

    Lagerbom, J.; Varis, T.; Pihlatie, M.; Himanen, O.; Saarinen, V.; Kiviaho, J.; Turunen, E. [VTT Technical Research Centre of Finland, Espoo (Finland); Puranen, J. [Tampere Univ. of Technology (Finland). Inst. of Materials Science

    2010-07-01

    Chromia released from steel parts used for interconnect plates by evaporation and condensation can quickly degrade the cell (cathode) performance in solid oxide fuel cell SOFC. Coatings on top of the IC plate can work as a chromium evaporation barrier. The coating material should have good electrical conductivity, high temperature stability and nearly the same coefficient of thermal expansion as the cell materials. One candidate for the coating material is MnCo{sub 2}O{sub 4} spinel because of its suitable properties. High velocity oxy fuel (HVOF) spraying was used for the coating application on Crofer 22 APU steel samples. Using commercial and self made spray dried powders together with an HV2000 spray gun it was possible to successfully manufacture, well adhering, dense and reasonably uniform coatings. The samples were tested in oxidation exposure tests in air followed by post analysis in SEM. Powders and coatings microstructures are presented here, both before and after exposure. It was found out that together with spraying parameters the powder characteristics used influence clearly to the coating quality. Especially as very thin coatings was aimed with dense structure fine powders was found to be essential. (orig.)

  20. Comparative of the Tribological Performance of Hydraulic Cylinders Coated by the Process of Thermal Spray HVOF and Hard Chrome Plating

    Directory of Open Access Journals (Sweden)

    R.M. Castro

    2014-03-01

    Full Text Available Due to the necessity of obtaining a surface that is resistant to wear and oxidation, hydraulic cylinders are typically coated with hard chrome through the process of electroplating process. However, this type of coating shows an increase of the area to support sealing elements, which interferes directly in the lubrication of the rod, causing damage to the seal components and bringing oil leakage. Another disadvantage in using the electroplated hard chromium process is the presence of high level hexavalent chromium Cr+6 which is not only carcinogenic, but also extremely contaminating to the environment. Currently, the alternative process of high-speed thermal spraying (HVOF - High Velocity Oxy-Fuel, uses composite materials (metal-ceramic possessing low wear rates. Research has shown that some mechanical properties are changed positively with the thermal spray process in industrial applications. It is evident that a coating based on WC has upper characteristics as: wear resistance, low friction coefficient, with respect to hard chrome coatings. These characteristics were analyzed by optical microscopy, roughness measurements and wear test.

  1. Erosion behaviour of WC-10Co-4Cr coating on 23-8-N nitronic steel by HVOF thermal spraying

    Science.gov (United States)

    kumar, Avnish; Sharma, Ashok; Goel, S. K.

    2016-05-01

    WC-10Co-4Cr coating was deposited by high-velocity oxy-fuel (HVOF) process on cast and solution treated (1220 °C/150 min) 23-8-N nitronic steel substrates. Solution treated substrate has shown higher toughness, ductility and impact energy with a marginal reduction in hardness as compared to cast substrate. This influence the coating deposition efficiency and erosion behaviour. Erosion resistance of coatings was evaluated by air jet erosion tester on two different impact angles (30° and 90°). Phases, microstructure and eroded surface of the coating were characterised by X-ray diffraction (XRD) analysis and field-emission scanning electron microscopy (FESEM) respectively. It is observed that coating on solution treated substrate was superior to cast substrate. The reason being that coating has dense and well-bonded structure with low porosity, less decarburization and inter-splat oxidation. Higher erosion resistance of coated solution treated 23-8-N nitronic steel was attributed to combination of high fracture toughness and hardness of coating including optimum mechanical properties of the substrate. FESEM analysis reveals that erosion response of WC-10Co-4Cr coating also dependent on the relative size of the impact crater with respect to the WC grain size. Coating is removed by combined mode of ductile and brittle erosion.

  2. Electrochemical Corrosion of HVOF-Sprayed NiCoCrAlY Coatings in CO2-Saturated Brine

    Science.gov (United States)

    Ruiz-Luna, H.; Porcayo-Calderon, J.; Alvarado-Orozco, J. M.; García-Herrera, J. E.; Martinez-Gomez, L.; Trápaga-Martínez, L. G.; Muñoz-Saldaña, J.

    2016-08-01

    The effect of pre-oxidation treatment and surface preparation of optimized NiCoCrAlY coatings deposited by high-velocity oxygen fuel (HVOF) spraying and exposed to a low-temperature corrosive environment is reported herein. Coatings with two surface finish conditions (as-sprayed and ground) were heat treated under two different oxygen partial pressures (air and argon). The electrochemical corrosion behavior was evaluated in CO2-saturated brine via potentiodynamic polarization, polarization resistance, and electrochemical impedance measurements. The results show that the grinding process and pre-oxidation treatment in argon enhanced growth and formation of α-Al2O3 scale. The potentiodynamic polarization results show that both pre-oxidation and surface treatment had a positive influence on the corrosion resistance of the coating. The reduction of the porosity and the formation of a dense, uniform, and adherent oxide scale through pre-oxidation treatment led to an increase of the corrosion resistance due to a decrease in active sites and blocking of diffusion of reactive species into the coating. However, according to the results, complete transformation from metastable alumina phases to α-Al2O3 in addition to formation and growth of dense α-Al2O3 is required to ensure full protection of the coating and base material over long periods.

  3. Particle-in-cell simulation of two-dimensional electron velocity shear driven instability in relativistic domain

    Science.gov (United States)

    Shukla, Chandrasekhar; Das, Amita; Patel, Kartik

    2016-08-01

    We carry out particle-in-cell simulations to study the instabilities associated with a 2-D sheared electron flow configuration against a neutralizing background of ions. Both weak and strong relativistic flow velocities are considered. In the weakly relativistic case, we observe the development of electromagnetic Kelvin-Helmholtz instability with similar characteristics as that predicted by the electron Magnetohydrodynamic (EMHD) model. On the contrary, in a strong relativistic case, the compressibility effects of electron fluid dominate and introduce upper hybrid electrostatic oscillations transverse to the flow which are very distinct from EMHD fluid behavior. In the nonlinear regime, both weak and strong relativistic cases lead to turbulence with broad power law spectrum.

  4. Effects of variations in electron thermal velocity on the whistler anisotropy instability: Particle-in-cell simulations

    Science.gov (United States)

    Hughes, R. Scott; Wang, Joseph; Decyk, Viktor K.; Gary, S. Peter

    2016-04-01

    This paper investigates how the physics of the whistler anisotropy instability (WAI) is affected by variations in the electron thermal velocity vte, referred to here in terms of the ratio v̂ t e=vt e/c , where c is the speed of light. The WAI is driven by the electron condition RT>1 , where RT=Te ⊥/Te ∥ is the temperature anisotropy ratio and ⊥/∥ signify directions perpendicular/parallel to the background magnetic field B0 . While a typical value of v̂ t e in the solar wind is ˜0.005 , electromagnetic (EM) particle-in-cell (PIC) simulations often use a value near 0.1 in order to maximize the computational time step. In this study, a two-dimensional (2D) Darwin particle-in-cell (DPIC) code, MDPIC2, is used. The time step in the DPIC model is not affected by the choice of v̂ t e , making DPIC suited for this study. A series of simulations are carried out under the condition that the electron βe is held fixed, while v̂ t e is varied over the range 0.1 ≥v̂ t e≥0.025 . The results show that, with βe held fixed, the linear dispersion properties and the nonlinear saturation amplitude and pitch angle scattering rates associated with the WAI are insensitive to the value of v̂ t e . A supplementary investigation is conducted which characterizes how the WAI model is affected at various values of v̂ t e by noise associated with the limited number of particles in a typical PIC simulation. It is found that the evolution of the WAI is more strongly influenced by electrostatic noise as v̂ t e is decreased. The electrostatic noise level is inversely proportional to the number of particles per computational cell ( Nc ); this implies that the number of particles required to remove nonphysical effects from the PIC simulation increases as v̂ t e decreases. It is concluded that PIC simulations of this instability which use an artificially large value of v̂ t e accurately reproduce the response of a cooler plasma as long as a realistic value of βe is used

  5. Proton velocity ring-driven instabilities in the inner magnetosphere: Linear theory and particle-in-cell simulations

    Science.gov (United States)

    Min, Kyungguk; Liu, Kaijun

    2016-01-01

    Linear dispersion theory and electromagnetic particle-in-cell (PIC) simulations are used to investigate linear growth and nonlinear saturation of the proton velocity ring-driven instabilities, namely, ion Bernstein instability and Alfvén-cyclotron instability, which lead to fast magnetosonic waves and electromagnetic ion cyclotron waves in the inner magnetosphere, respectively. The proton velocity distribution is assumed to consist of 10% of a ring distribution and 90% of a low-temperature Maxwellian background. Here two cases with ring speeds vr/vA=1 and 2 (vA is the Alfvén speed) are examined in detail. For the two cases, linear theory predicts that the maximum growth rate γm of the Bernstein instability is 0.16Ωp and 0.19Ωp, respectively, and γm of the Alfvén-cyclotron instability is 0.045Ωp and 0.15Ωp, respectively, where Ωp is the proton cyclotron frequency. Two-dimensional PIC simulations are carried out for the two cases to examine the instability development and the corresponding evolution of the particle distributions. Initially, Bernstein waves develop and saturate with strong electrostatic fluctuations. Subsequently, electromagnetic Alfvén-cyclotron waves grow and saturate. Despite their smaller growth rate, the saturation levels of the Alfvén-cyclotron waves for both cases are larger than those of the Bernstein waves. Resonant interactions with the Bernstein waves lead to scattering of ring protons predominantly along the perpendicular velocity component (toward both decreasing and, at a lesser extent, increasing speeds) without substantial change of either the parallel temperature or the temperature anisotropy. Consequently, the Alfvén-cyclotron instability can still grow. Furthermore, the free energy resulting from the pitch angle scattering by the Alfvén-cyclotron waves is larger than the free energy resulting from the perpendicular energy scattering, thereby leading to the larger saturation level of the Alfvén-cyclotron waves.

  6. Oxidation behavior of HVOF-sprayed MCrAlY-Coatings; Oxidationsverhalten von HVOF-gespritzten MCrAlY-Schichten

    Energy Technology Data Exchange (ETDEWEB)

    Marginean, G.; Brandl, W. [Fachhochschule Gelsenkirchen (Germany); Frunzaverde, D. [Eftimie Murgu Univ., Resita (Romania)

    2007-03-15

    The influence of two spraying parameters (kerosene flow rate and pressure of the combusting chamber) on the high temperature oxidation behavior of HVOF-sprayed MCrAlY-coatings was studied on CoNiCrAlY-coatings containing 15wt.% aluminum. After thermal spraying, different test-specimens were heat treated for structure improvement (homogenization, reducing of the porosity and internal stresses as well as for new phase precipitation) and afterwards oxidized at 950 C for 3000 minutes in synthetic air. In order to point out the effects of the different spraying parameters on the oxidation behavior of the coatings, the thermo gravimetrical analysis (TG) was used. The morphology and structure of the coatings were characterized before and after oxidation experiments by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed indubitable, that an increase of the kerosene flow rate and of the pressure in the combusting chamber during the spraying process leads to a better oxidation behavior of the MCrAlY-coatings. (Abstract Copyright [2007], Wiley Periodicals, Inc.) [German] Der Einfluss zweier Spritzparameter (Kerosindurchfluss und Brennkammerdruck) auf das Hochtemperaturoxidationsverhalten von HVOF - gespritzten MCrAlY - Schichten wurde anhand von CoNiCrAlY - Schichten mit 15 Gew.-% Aluminium untersucht. Verschiedene Testproben wurden nach dem thermischen Spritzen zur Verbesserung des Aufbaus (Homogenisierung, Verminderung der Porositaet und der inneren Spannungen, Ausscheidung neuer Phasen) waermebehandelt und anschliessend bei 950 C fuer 3000 Minuten in synthetischer Luft oxidiert. Um den Einfluss der unterschiedlichen Spritzparameter auf das Oxidationsverhalten der Schichten zu erfassen wurde die thermogravimetrische Analyse (TG) eingesetzt. Zusaetzlich wurde vor und nach der Oxidation der Aufbau der Schichten mit Hilfe der Rasterelektronenmikroskopie (REM) und Roentgendiffraktometrie (XRD) untersucht. Die Ergebnisse zeigten eindeutig, dass

  7. Modelizacion de la formación de recubrimientos de WC-Co por proyección HVOF sobre sustratos de cobre

    Directory of Open Access Journals (Sweden)

    Sobolev, V. V.

    1997-10-01

    Full Text Available Present paper deals with the mathematical simulation of the heat transfer between a WC-Co coating and a copper substrate during HVOF spraying. This modelling includes the investigation of temperature variation, coating solidification, melting and subsequent solidification in the substrate interfacial region and specific features of the substrate-coating thermal interaction. The results obtained are used for modelling of the development of the coating structure and adhesion during HVOF spraying of the WC-Co powder on a copper substrate. Two types of substrate were considered: smooth (polished and rough. Variations of solidification times, solidification velocity, thermal gradient and cooling velocity in the coating and substrate interfacial region are studied. Development of the amorphous and crystalline structures in the coating and of the crystalline structure in the substrate interfacial region is discussed. Behaviour of the crystal size and intercrystalline distance with respect to the thermal spray parameters and morphology of the substrate surface is analyzed. Optimal conditions for the formation of fine and dense crystalline structure are determined. Structural changes in the solid state of the substrate occurring because of heating and rapid cooling are considered. Mechanical and thermal mechanisms of development of the substrate-coating adhesion are discussed. Results obtained agree well with experimental data.

    En el presente trabajo se ha investigado la simulación matemática de la transferencia de calor entre un recubrimiento de WC-Co y un sustrato de cobre durante la proyección HVOF. Este modelo incluye el estudio de la variación de termperatura, solidificación del recubrimiento, la fusión y posterior solidificación en la región interfacial del sustrato, y caracerísticas especiales de la interacción térmica sustrato- recubrimiento. Los resultados obtenidos han sido utilizados en la modelización del desarrollo de la

  8. Numerical investigation of liver radioembolization via computational particle-hemodynamics: The role of the microcatheter distal direction and microsphere injection point and velocity.

    Science.gov (United States)

    Aramburu, Jorge; Antón, Raúl; Rivas, Alejandro; Ramos, Juan Carlos; Sangro, Bruno; Bilbao, José Ignacio

    2016-11-07

    Liver radioembolization is a treatment option for patients with primary and secondary liver cancer. The procedure consists of injecting radiation-emitting microspheres via an intra-arterially placed microcatheter, enabling the deposition of the microspheres in the tumoral bed. The microcatheter location and the particle injection rate are determined during a pretreatment work-up. The purpose of this study was to numerically study the effects of the injection characteristics during the first stage of microsphere travel through the bloodstream in a patient-specific hepatic artery (i.e., the near-tip particle-hemodynamics and the segment-to-segment particle distribution). Specifically, the influence of the distal direction of an end-hole microcatheter and particle injection point and velocity were analyzed. Results showed that the procedure targeted the right lobe when injecting from two of the three injection points under study and the remaining injection point primarily targeted the left lobe. Changes in microcatheter direction and injection velocity resulted in an absolute difference in exiting particle percentage for a given liver segment of up to 20% and 30%, respectively. It can be concluded that even though microcatheter placement is presumably reproduced in the treatment session relative to the pretreatment angiography, the treatment may result in undesired segment-to-segment particle distribution and therefore undesired treatment outcomes due to modifications of any of the parameters studied, i.e., microcatheter direction and particle injection point and velocity.

  9. An Integrated Instrumentation System for Velocity, Concentration and Mass Flow Rate Measurement of Solid Particles Based on Electrostatic and Capacitance Sensors.

    Science.gov (United States)

    Li, Jian; Kong, Ming; Xu, Chuanlong; Wang, Shimin; Fan, Ying

    2015-12-10

    The online and continuous measurement of velocity, concentration and mass flow rate of pneumatically conveyed solid particles for the high-efficiency utilization of energy and raw materials has become increasingly significant. In this paper, an integrated instrumentation system for the velocity, concentration and mass flow rate measurement of dense phase pneumatically conveyed solid particles based on electrostatic and capacitance sensorsis developed. The electrostatic sensors are used for particle mean velocity measurement in combination with the cross-correlation technique, while the capacitance sensor with helical surface-plate electrodes, which has relatively homogeneous sensitivity distribution, is employed for the measurement of particle concentration and its capacitance is measured by an electrostatic-immune AC-based circuit. The solid mass flow rate can be further calculated from the measured velocity and concentration. The developed instrumentation system for velocity and concentration measurement is verified and calibrated on a pulley rig and through static experiments, respectively. Finally the system is evaluated with glass beads on a gravity-fed rig. The experimental results demonstrate that the system is capable of the accurate solid mass flow rate measurement, and the relative error is within -3%-8% for glass bead mass flow rates ranging from 0.13 kg/s to 0.9 kg/s.

  10. An Integrated Instrumentation System for Velocity, Concentration and Mass Flow Rate Measurement of Solid Particles Based on Electrostatic and Capacitance Sensors

    Directory of Open Access Journals (Sweden)

    Jian Li

    2015-12-01

    Full Text Available The online and continuous measurement of velocity, concentration and mass flow rate of pneumatically conveyed solid particles for the high-efficiency utilization of energy and raw materials has become increasingly significant. In this paper, an integrated instrumentation system for the velocity, concentration and mass flow rate measurement of dense phase pneumatically conveyed solid particles based on electrostatic and capacitance sensorsis developed. The electrostatic sensors are used for particle mean velocity measurement in combination with the cross-correlation technique, while the capacitance sensor with helical surface-plate electrodes, which has relatively homogeneous sensitivity distribution, is employed for the measurement of particle concentration and its capacitance is measured by an electrostatic-immune AC-based circuit. The solid mass flow rate can be further calculated from the measured velocity and concentration. The developed instrumentation system for velocity and concentration measurement is verified and calibrated on a pulley rig and through static experiments, respectively. Finally the system is evaluated with glass beads on a gravity-fed rig. The experimental results demonstrate that the system is capable of the accurate solid mass flow rate measurement, and the relative error is within −3%–8% for glass bead mass flow rates ranging from 0.13 kg/s to 0.9 kg/s.

  11. High-Temperature Exposure Studies of HVOF-Sprayed Cr3C2-25(NiCr)/(WC-Co) Coating

    Science.gov (United States)

    Singh, Harpreet; Kaur, Manpreet; Prakash, Satya

    2016-08-01

    In this research, development of Cr3C2-25(NiCr) + 25%(WC-Co) composite coating was done and investigated. Cr3C2-25(NiCr) + 25%(WC-Co) composite powder [designated as HP2 powder] was prepared by mechanical mixing of [75Cr3C2-25(NiCr)] and [88WC-12Co] powders in the ratio of 75:25 by weight. The blended powders were used as feedstock to deposit composite coating on ASTM SA213-T22 substrate using High Velocity Oxy-Fuel (HVOF) spray process. High-temperature oxidation/corrosion behavior of the bare and coated boiler steels was investigated at 700 °C for 50 cycles in air, as well as, in Na2SO4-82%Fe2(SO4)3 molten salt environment in the laboratory. Erosion-corrosion behavior was investigated in the actual boiler environment at 700 ± 10 °C under cyclic conditions for 1500 h. The weight-change technique was used to establish the kinetics of oxidation/corrosion/erosion-corrosion. X-ray diffraction, field emission-scanning electron microscopy/energy-dispersive spectroscopy (FE-SEM/EDS), and EDS elemental mapping techniques were used to analyze the exposed samples. The uncoated boiler steel suffered from a catastrophic degradation in the form of intense spalling of the scale in all the environments. The oxidation/corrosion/erosion-corrosion resistance of the HVOF-sprayed HP2 coating was found to be better in comparison with standalone Cr3C2-25(NiCr) coating. A simultaneous formation of protective phases might have contributed the best properties to the coating.

  12. Effect of injection velocity and particle concentration on transport of nanoscale zero-valent iron and hydraulic conductivity in saturated porous media.

    Science.gov (United States)

    Strutz, Tessa J; Hornbruch, Götz; Dahmke, Andreas; Köber, Ralf

    2016-08-01

    Successful groundwater remediation by injecting nanoscale zero-valent iron (NZVI) particles requires efficient particle transportation and distribution in the subsurface. This study focused on the influence of injection velocity and particle concentration on the spatial NZVI particle distribution, the deposition processes and on quantifying the induced decrease in hydraulic conductivity (K) as a result of particle retention by lab tests and numerical simulations. Horizontal column tests of 2m length were performed with initial Darcy injection velocities (q0) of 0.5, 1.5, and 4.1m/h and elemental iron input concentrations (Fe(0)in) of 0.6, 10, and 17g/L. Concentrations of Fe(0) in the sand were determined by magnetic susceptibility scans, which provide detailed Fe(0) distribution profiles along the column. NZVI particles were transported farther at higher injection velocity and higher input concentrations. K decreased by one order of magnitude during injection in all experiments, with a stronger decrease after reaching Fe(0) concentrations of about 14-18g/kg(sand). To simulate the observed nanoparticle transport behavior the existing finite-element code OGS has been successfully extended and parameterized for the investigated experiments using blocking, ripening, and straining as governing deposition processes. Considering parameter relationships deduced from single simulations for each experiment (e.g. deposition rate constants as a function of flow velocity) one mean parameter set has been generated reproducing the observations in an adequate way for most cases of the investigated realistic injection conditions. An assessment of the deposition processes related to clogging effects showed that the percentage of retention due to straining and ripening increased during experimental run time resulting in an ongoing reduction of K. Clogging is mainly evoked by straining which dominates particle deposition at higher flow velocities, while blocking and ripening play a

  13. 感应重熔超音速火焰喷涂铁基涂层的耐蚀性%Corrosion resistance of induction remelted Fe-based coatings prepared by HVOF spraying

    Institute of Scientific and Technical Information of China (English)

    叶富明; 周洪宇; 胡舸

    2016-01-01

    Induction remelting high velocity oxy-fuel (HVOF) sprayed Fe-based coatings were conducted by using ultrasonic frequency induction device.X-ray diffraction (XRD),scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS) analysis,microhardness test,polarization curve and electrochemical impedance spectroscopy technique were used to examine the microstructure,microhardness and corrosion resistance of the coatings.The results show that the porosity is reduced from 5.74% to 0.43% after the induction remelting.The phases of γ-Fe,(Cr,Fe)2 B and γ-Fe/(Cr,Fe)2B eutectics are identified in the induction remelted HVOF sprayed Fe-based coatings.Electrochemical test results in simulated sea water show that the polarization curve exhibits an activepassivation charicteristic.The corrosion current density of the induction-remelted coating is lower than that of the HVOF sprayed Fe-based coating due to the reduction of porosity and oxide inclusion content in the remelted coatings,by which the penetration of chloride ions through the pores to form inner galvanic couple is impeded.Electrochemical impedance spectroscopy results show capacitive reactance arc of the induction remelted HVOF sprayed Fe-based coating is larger than that of the HVOF sprayed Fe-based coating,the corrosion resistance increases by 2.74 times.%采用超音频感应熔覆技术获得高质量具有冶金结合的感应重熔超音速火焰喷涂(HVOF)铁基涂层.借助XRD、SEN/EDS、显微硬度计、极化曲线和交流阻抗手段综合分析涂层微观形貌、物相组成、显微硬度分布以及耐蚀性能.研究结果表明,感应重熔处理后涂层孔隙率从5.74%大幅降低至0.43%,感应重熔HVOF铁基涂层由γ-Fe、硼化物(Cr,Fe)2B以及少量的共晶体γ-Fe/(Cr,Fe)2B组成.在模拟海水溶液电化学测试结果显示,感应重熔HVOF铁基涂层极化曲线呈现典型活化-钝化特征,感应重熔涂层自腐蚀电流密度比HVOF铁基涂层明显

  14. Particle-in-cell simulations of velocity scattering of an anisotropic electron beam by electrostatic and electromagnetic instabilities

    Science.gov (United States)

    Fu, X. R.; Cowee, M. M.; Liu, K.; Peter Gary, S.; Winske, D.

    2014-04-01

    The velocity space scattering of an anisotropic electron beam (T⊥b/T∥b>1) flowing along a background magnetic field B0 through a cold plasma is investigated using both linear theory and 2D particle-in-cell simulations. Here, ⊥ and ∥ represent the directions perpendicular and parallel to B0, respectively. In this scenario, we find that two primary instabilities contribute to the scattering in electron pitch angle: an electrostatic electron beam instability and a predominantly parallel-propagating electromagnetic whistler anisotropy instability. Our results show that at relative beam densities nb/ne≤0.05 and beam temperature anisotropies Tb ⊥/Tb ∥≤25, the electrostatic beam instability grows much faster than the whistler instabilities for a reasonably fast hot beam. The enhanced fluctuating fields from the beam instability scatter the beam electrons, slowing their average speed and increasing their parallel temperature, thereby increasing their pitch angles. In an inhomogeneous magnetic field, such as the geomagnetic field, this could result in beam electrons scattered out of the loss cone. After saturation of the electrostatic instability, the parallel-propagating whistler anisotropy instability shows appreciable growth, provided that the beam density and late-time anisotropy are sufficiently large. Although the whistler anisotropy instability acts to pitch-angle scatter the electrons, reducing perpendicular energy in favor of parallel energy, these changes are weak compared to the pitch-angle increases resulting from the deceleration of the beam due to the electrostatic instability.

  15. The influence of particle size, fluidization velocity and fuel type on ash-induced agglomeration in biomass combustion

    Directory of Open Access Journals (Sweden)

    Bernhard eGatternig

    2014-11-01

    Full Text Available Agglomeration of the bed material is one of the main obstacles for biomass utilization in fluidized bed combustors. Especially high-potential fuels such as fast growing energy crops or biogeneous residues are affected, due to their high content of alkaline metals. Despite ongoing research efforts, the knowledge base on what fuels are affected is still limited. This paper describes the design and installation of two lab-scale reactors for the experimental determination of agglomeration temperatures. The reactor concept and measurement method were developed under consideration of experiences from existing test rigs published in literature. Preliminary tests confirmed a reproducibility of ±5°C for both new reactors.The results of an extended measurement campaign (156 test runs of 25 fuel species at a wide range of the operational parameters bed particle size, gas velocity, bed ash accumulation, based on design of experiment criteria, showed high agglomeration tendencies for residues (e.g., dried distillery grains, corn cobs while woody energy crops (e.g., willow, alder exhibited very stable combustion behavior. The operating parameters influenced the agglomeration behavior to a lesser degree than different ash compositions of fuel species tested. An interpolation within the design of experiment factor space allowed for a subsequent comparison of our results with experiments reported in literature. Good agreement was reached for fuels of comparable ash composition considering the interpolation errors of ±32°C on average.

  16. Kinetic effects on the Kelvin-Helmholtz instability in ion-to-magnetohydrodynamic scale transverse velocity shear layers: Particle simulations.

    Science.gov (United States)

    Nakamura, T K M; Hasegawa, H; Shinohara, I

    2010-04-01

    Ion-to-magnetohydrodynamic scale physics of the transverse velocity shear layer and associated Kelvin-Helmholtz instability (KHI) in a homogeneous, collisionless plasma are investigated by means of full particle simulations. The shear layer is broadened to reach a kinetic equilibrium when its initial thickness is close to the gyrodiameter of ions crossing the layer, namely, of ion-kinetic scale. The broadened thickness is larger in B⋅Ω0 case, where Ω is the vorticity at the layer. This is because the convective electric field, which points out of (into) the layer for B⋅Ω0), extends (reduces) the gyrodiameters. Since the kinetic equilibrium is established before the KHI onset, the KHI growth rate depends on the broadened thickness. In the saturation phase of the KHI, the ion vortex flow is strengthened (weakened) for B⋅Ω0), due to ion centrifugal drift along the rotational plasma flow. In ion inertial scale vortices, this drift effect is crucial in altering the ion vortex size. These results indicate that the KHI at Mercury-like ion-scale magnetospheric boundaries could show clear dawn-dusk asymmetries in both its linear and nonlinear growth.

  17. Research on the improvement of nuclear safety - Development of a technique for simultaneous measurement of particle size and velocity for direct containment heating accident analysis

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Sang Yong; Song, Si Hong; Koh, Kwang Woong; Kim, Joo Yeon; Kim, Jong Moon; Choi, Chul Jin [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of)

    1995-08-01

    The main objective is to develop a high performance software routine to process the output signals from the phase/Doppler device for simultaneous measurement of drop sizes and two-dimensional velocities of spray drops/particles. The present work has been carried out as an extension work of the first year`s research, where the principles and the limitation of this measuring technique have been thoroughly reviewed. In order to verify the performance and reliability of this software for simultaneous measurement of sizes and velocities of spray drops with two-dimensional motions, the results were compared with those from commercial signal processor DSA by Aerometrics, and concluded to be satisfactory. The routine developed throughout this project is applicable not only to the DCH model experiments but also to the measurements of sizes and velocities of drops/particles in combustors, dryers, humidifiers, and in various two-phase equipments. 20 refs., 5 tabs., 21 figs. (author)

  18. Spraying of Super Fine Powders With HVOF and Axial Plasma Thermal Spray Systems

    Institute of Scientific and Technical Information of China (English)

    Alan Burgess; G(o)tz Matth(a)us

    2004-01-01

    The use of fine powders in thermal spray can lead to many advantages. These advantages include denser coatings, coatings with increased wear resistance, coatings with smoother surface finish, coatings that can be applied to internal surfaces, less expensive coatings. The use of fine powders also has an disadvantage that th ey can have poor flow characteristics. The paper will discuss a feeder that is able to feed fine powders to overcome this difficulty and the coating equipment, both axial plasma and HVOF systems, used to deposit these materials to produce smooth dense coatings.

  19. A Flow Model for the Settling Velocities of Non Spherical Particles in Creeping Motion. Part III. Slender Bodies, the Stream Functions, the Flow and the Momentum Equation

    Directory of Open Access Journals (Sweden)

    Yuri Mendez

    2015-01-01

    Full Text Available This paper follows previous work regarding the settling velocity of non spherical particles in creeping motion. In this paper, we summarize the flow model, present solutions for the slender plate and the cylinder (Stoke’s paradox, demonstrate the application for euhedral pseudo hexagonal plates (KGa-1 and show the match to the experimental data. In addition, we derive the stream function for the sphere, the slender cylinder and the plate, develop the relationships to compute the flow about a settling particle, back calculate the momentum equation and examine the result

  20. DECELERATION OF ELECTRON VE LOCITY BASED ON THE WAVE- PARTICLE DUALITY LEADS TO RE LATIVE TIME ACCELERATION: HYPOTHESIS OF INCREASED BIOPHYSICAL REACTION VELOCITY

    Directory of Open Access Journals (Sweden)

    Horst Koch

    2013-03-01

    Full Text Available The high speed of biological processes such as photosynthesis, enzymatic reactions or neuronal activity cannot completely be explained on the basis of classic physical approaches. Different quantum biology effects such as tunnelling have been postulated. We hypothetically admit that deceleration of electron velocity based on light-particle duality of electrons leads to time acceleration. Deceleration from the status of light towards a status of a particle may therefore speed up biochemical or biophysical reactions in the atomic or molecular dimension. Electrophysiological and biological phenomena are discussed on the basis of the hypothesis

  1. Accelerator experiments with soft protons and hyper-velocity dust particles: application to ongoing projects of future X-ray missions

    DEFF Research Database (Denmark)

    Perinati, E.; Diebold, S.; Kendziorra, E.;

    2012-01-01

    We report on our activities, currently in progress, aimed at performing accelerator experiments with soft protons and hyper-velocity dust particles. They include tests of different types of X-ray detectors and related components (such as filters) and measurements of scattering of soft protons...... and hyper-velocity dust particles off X-ray mirror shells. These activities have been identified as a goal in the context of a number of ongoing space projects in order to assess the risk posed by environmental radiation and dust and qualify the adopted instrumentation with respect to possible damage...... or performance degradation. In this paper we focus on tests for the Silicon Drift Detectors (SDDs) used aboard the LOFT space mission. We use the Van de Graaff accelerators at the University of T\\"ubingen and at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg, for soft proton and hyper...

  2. Detection of number of sources and DOA stimation based on the combined information processing of pressure and particle velocity using acoustic vector sensor array

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    In order to solve the problem of DOA (direction of arrival) estimation of underwater remote targets, a novel subspace-decomposition method based on the cross covariance matrix of the pressure and the particle velocity of acoustic vector sensor arrays (AVSA) was proposed.Whereafter, using spatio-temporal virtual tapped-delay-line, a new eigenvector-based criteria of detection of number of sources and of subspace partition is also presented. The theoretical analysis shows that the new source detection and direction finding method is different from existing AVSA based DOA estimation methods using particle velocity information of acoustic vector sensor (AVS) as an independent array element. It is entirely based on the combined information processing of pressure and particle velocity, has better estimation performance than existing methods in isotropic noise field. Computer simulations with data from lake trials demonstrate, the proposed method is effective and obviously outperforms existing methods in resolution and accuracy in the case of low signal-to-noise ratio (SNR).

  3. Resistance of Cavitation Erosion of HVOF Sprayed WC-Co( Cr) Coating in NaCl Solution%超音速火焰喷涂WC-Co(Cr)涂层在NaCl溶液中抗空蚀性能研究

    Institute of Scientific and Technical Information of China (English)

    丁彰雄; 石琎; 丁翔; 胡一鸣; 廖星文; 邓帮华

    2016-01-01

    Two micro-structured WC-10Co4Cr cermet coatings and a nano-structured WC-12Co cermet coating are deposited by high velocity Oxy-fuel spray ( HVOF) , and the morphologies and structures of the coatings are analyzed by SEM .The coatings'porosity , fracture toughness and microhardness are measured .The CorrTest electrochemical testing system is used to analyze the electrochemical corrosion properties of the coatings .Resistance of coatings to cavitation erosion is studied by ultrasonic vibration cavitation equipment in 3.5wt%NaCl solution and the cavitation mechanisms are explored .It is shown that the nano-structured WC-12Co coating deposited by high velocity oxygen liquid fuel spray has lowest porosity and the densest microstructure , and frac-ture toughness is significantly higher than that of micron-structured WC-10Co4Cr coatings.Although the micron-structured WC-10Co4Cr cermet coating deposited by high velocity fuel oxygen liquid spray has coarser particles than the nano -structured, it ex-hibits the most excellent corrosion and cavitation erosion resistance .The cavitation rate is approximately one quarter that of the nano-structured WC-12Co cermet coating in 3.5wt%NaCl solution.%采用超音速火焰喷涂(HVOF)工艺制备2种微米结构WC-10Co4Cr及1种纳米结构WC-12Co金属陶瓷复合涂层;采用SEM分析涂层的组织结构;测量了涂层的显微硬度、孔隙率及开裂韧性;采用CorrT-est电化学测试系统分析涂层的电化学腐蚀性能;采用超声振动空蚀装置研究涂层在质量分数为3.5% NaCl溶液中的抗空蚀性能,探讨涂层的空蚀机理. 结果表明:使用液体燃料HVOF工艺喷涂的纳米WC-12Co涂层组织结构最细小,孔隙率最低,显微硬度和开裂韧性明显高于液体燃料和气体燃料HVOF工艺喷涂的微米WC-10Co4Cr涂层;采用液体燃料HVOF工艺喷涂的微米结构WC-10Co4Cr涂层在质量分数为3.5%NaCl溶液中显示了最优异的抗腐蚀和抗空蚀

  4. Hot Corrosion Behavior of HVOF Sprayed Coatings on ASTM SA213-T11 Steel

    Science.gov (United States)

    Sidhu, H. S.; Sidhu, B. S.; Prakash, S.

    2007-09-01

    Cr3C2-NiCr, NiCr, WC-Co and Stellite-6 alloy coatings were sprayed on ASTM SA213-T11 steel using the HVOF process. Liquid petroleum gas was used as the fuel gas. Hot corrosion studies were conducted on the uncoated as well as HVOF sprayed specimens after exposure to molten salt at 900 °C under cyclic conditions. The thermo-gravimetric technique was used to establish the kinetics of corrosion. XRD, SEM/EDAX and EPMA techniques were used to analyze the corrosion products. All these overlay coatings showed a better resistance to hot corrosion as compared to that of uncoated steel. NiCr Coating was found to be most protective followed by the Cr3C2-NiCr coating. WC-Co coating was least effective to protect the substrate steel. It is concluded that the formation of Cr2O3, NiO, NiCr2O4, and CoO in the coatings may contribute to the development of a better hot-corrosion resistance. The uncoated steel suffered corrosion in the form of intense spalling and peeling of the scale, which may be due to the formation of unprotective Fe2O3 oxide scale.

  5. Mechanical Properties and Corrosion Resistance of HVOF Sprayed Coatings Using Nanostructured Carbide Powders

    Directory of Open Access Journals (Sweden)

    Żórawski W.

    2016-12-01

    Full Text Available Nanostructured and composite WC-12Co coatings were prepared by means of the supersonic spray process (HVOF. The microstructure and composition of WC-12Co nanostructured powder were analyzed by scanning electron microscope (SEM and transmission electron microscope (TEM. Investigations revealed nano grains of WC with the size in the range of 50-500 nm. The nanostructured sprayed coating was analysed by SEM and phase composition was investigated by X-ray diffractometer (XRD. A denser coating structure with higher hardness was observed compared to conventional coating with a small amount of W2C, WC1−x, W and some amorphous phase. Young’s modulus and hardness were determined by depth sensing indentation in HVOF sprayed WC-12Co nanostructured coatings. Results were compared to conventional coatings and the relevance of the nanostructure was analyzed. An indentation size effect was observed on the polished surface and cross-section of both coatings. Data provided by indentation tests at maximum load allow to estimate hardness and elastic modulus. Enhanced nanomechanical properties of conventional coating in comparison to nanostructured one were observed. Nanostructured coatings WC-12Co (N revealed significantly better corrosion resistance.

  6. Aerodynamic Study on Supersonic Flows in High-Velocity Oxy-Fuel Thermal Spray Process

    Institute of Scientific and Technical Information of China (English)

    Hiroshi KATANODA; Takeshi MATSUOKA; Seiji KURODA; Jin KAWAKITA; Hirotaka FUKANUMA; Kazuyasu MATSUO

    2005-01-01

    @@ To clarify the characteristics of gas flow in high velocity oxy-fuel (HVOF) thermal spray gun, aerodynamic research is performed using a special gun. The gun has rectangular cross-sectional area and sidewalls of optical glass to visualize the internal flow. The gun consists of a supersonic nozzle with the design Mach number of 2.0 followed by a straight passage called barrel. Compressed dry air up to 0.78 MPa is used as a process gas instead of combustion gas which is used in a commercial HVOF gun. The high-speed gas flows with shock waves in the gun and jets are visualized by schlieren technique. Complicated internal and external flow-fields containing various types of shock wave as well as expansion wave are visualized.

  7. Simultaneous three-dimensional temperature and velocity field measurements using astigmatic imaging of non-encapsulated thermo-liquid crystal (TLC) particles.

    Science.gov (United States)

    Segura, Rodrigo; Rossi, Massimiliano; Cierpka, Christian; Kähler, Christian J

    2015-02-07

    A combination of cutting edge developments is presented to characterize three-dimensional (3D) temperature and velocity fields in microscopic flows. An emulsion of non-encapsulated thermo-liquid crystal (TLC) micro spheres, with a narrow size distribution is used to track the flow's motion and temperature distribution. A state-of-the-art light engine, which combines the spectrum of six light pipes, provides a balanced illumination which allows for strong and detectable color patterns across the TLC's temperature response range. Lastly, the ability of the TLC material to reflect select wavelength bands with an unchanging and independent circular polarization chirality is exploited by a filter that blocks background noise, while exclusively transmitting the color signal of the TLC particles. This approach takes advantage of the peculiar physical properties of TLCs to allow the estimation of individual TLC particle's 3D position, for the first time, using Astigmatism Particle Tracking Velocimetry (APTV).

  8. Modelizacion de la formación de recubrimientos de WC-Co por proyección HVOF sobre sustratos de cobre

    OpenAIRE

    Sobolev, V. V.; Guilemany, J. M.; J.A. Calero

    1997-01-01

    Present paper deals with the mathematical simulation of the heat transfer between a WC-Co coating and a copper substrate during HVOF spraying. This modelling includes the investigation of temperature variation, coating solidification, melting and subsequent solidification in the substrate interfacial region and specific features of the substrate-coating thermal interaction. The results obtained are used for modelling of the development of the coating structure and adhesion during HVOF sprayin...

  9. Accelerator experiments with soft protons and hyper-velocity dust particles: application to ongoing projects of future X-ray missions

    CERN Document Server

    Perinati, E; Kendziorra, E; Santangelo, A; Tenzer, C; Jochum, J; Bugiel, S; Srama, R; Del Monte, E; Feroci, M; Rubini, A; Rachevski, A; Zampa, G; Zampa, N; Rashevskaya, I; Vacchi, A; Azzarello, P; Bozzo, E; Herder, J -W den; Zane, S; Brandt, S; Hernanz, M; Leutenegger, M A; Kelley, R L; Kilbourne, C A; Meidinger, N; Strüder, L; Cordier, B; Götz, D; Fraser, G W; Osborne, J P; Dennerl, K; Freyberg, M; Friedrich, P

    2012-01-01

    We report on our activities, currently in progress, aimed at performing accelerator experiments with soft protons and hyper-velocity dust particles. They include tests of different types of X-ray detectors and related components (such as filters) and measurements of scattering of soft protons and hyper-velocity dust particles off X-ray mirror shells. These activities have been identified as a goal in the context of a number of ongoing space projects in order to assess the risk posed by environmental radiation and dust and qualify the adopted instrumentation with respect to possible damage or performance degradation. In this paper we focus on tests for the Silicon Drift Detectors (SDDs) used aboard the LOFT space mission. We use the Van de Graaff accelerators at the University of T\\"ubingen and at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg, for soft proton and hyper-velocity dust tests respectively. We present the experimental set-up adopted to perform the tests, status of the activities...

  10. Kinetic freeze-out temperature and flow velocity extracted from transverse momentum spectra of final-state light flavor particles produced in collisions at RHIC and LHC

    Energy Technology Data Exchange (ETDEWEB)

    Wei, Hua-Rong; Liu, Fu-Hu [Shanxi University, Institute of Theoretical Physics, Shanxi (China); Lacey, Roy A. [Stony Brook University, Departments of Chemistry and Physics, Stony Brook, NY (United States)

    2016-04-15

    The transverse momentum spectra of final-state light flavor particles produced in proton-proton (p-p), copper-copper (Cu-Cu), gold-gold (Au-Au), lead-lead (Pb-Pb), and proton-lead (p -Pb) collisions for different centralities at relativistic heavy ion collider (RHIC) and large hadron collider (LHC) energies are studied in the framework of a multisource thermal model. The experimental data measured by the STAR, CMS, and ALICE Collaborations are consistent with the results calculated by the multi-component Erlang distribution and Tsallis Statistics. The effective temperature and real temperature (kinetic freeze-out temperature) of the interacting system at the stage of kinetic freeze-out, the mean transverse flow velocity and mean flow velocity of particles, and the relationships between them are extracted. The dependences of effective temperature and mean (transverse) momentum on rest mass, moving mass, centrality, and center-of-mass energy, and the dependences of kinetic freeze-out temperature and mean (transverse) flow velocity on centrality, center-of-mass energy, and system size are obtained. (orig.)

  11. Special relativity as classical kinematics of a particle with the upper bound on its speed. Part II. The general Lorentz transforrmation and the generalized velocity composition theorem

    CERN Document Server

    Granik, Alex

    2014-01-01

    The kinematics of a particle with the upper bound on the particle's speed (a modification of classical kinematics where such a restriction is absent) has been developed in [arXiv:1204.5740]. It was based solely on classical mechanics without employing any concepts , associated with the time dilatation or/and length contraction. It yielded the 1-D Lorentz transformation (LT), free of inconsistencies (inherent in the canonical derivation and interpretations of the LT). Here we apply the same approach to derive the LT for the 3-dimensional motion of a particle and the attendant law of velocity composition. As a result, the infinite set of four-parameter transformations is obtained. The requirement of linearity of these transformations selects out of this set the two-parameter subset . The values of the remaining two parameters ,dictated by physics of the motion, is explicitly determined , yielding the canonical form of the 3-dimensional LT. The generalized law of velocity composition and the attendant invariant ...

  12. Modification of Plasma-sprayed TiO2 Coatings Characteristics via Controlling the In-flight Temperature and Velocity of the Powder Particles

    Science.gov (United States)

    Cizek, Jan; Dlouhy, Ivo; Siska, Filip; Khor, Khiam Aik

    2014-12-01

    The study presents a comprehensive research on the plasma spray fabrication of TiO2 coatings with microstructural properties adjustable via controlling the respective in-flight properties of the feedstock particles. The in-flight properties can be, in return, governed by tuning the plasma system spray parameters. By determining and linking the two interrelationships, a connection between the important coating characteristics (composition, microstructure, surface and mechanical properties) to the plasma system settings was established. It was shown that by changing the values of six parameters representing the flexibility of the plasma system, the temperatures and velocities of the particles within the jet can be altered from 2125 to 2830 K and 137 to 201 m s-1, respectively. The values of the in-flight temperature critically influenced the efficiency of the coating build-up (values ranging from 8 to 84 μm per 1 torch pass) and the content of anatase phase in the fabricated coatings (0-5.8%), while the in-flight velocity of the TiO2 particles was found to be connected to the porosity of the coatings (ranging from 14.4 to 26.2%) and the adhesion strength at the coating-substrate interface (2.6 × difference).

  13. Note: development of a compact x-ray particle image velocimetry for measuring opaque flows. II. Three-dimensional velocity field reconstruction.

    Science.gov (United States)

    Jung, Sung Yong; Lee, Sang Joon

    2012-04-01

    An x-ray particle image velocimetry (PIV) system using a cone-beam type x-ray was developed. The field of view and the spatial resolution are 36 × 24.05 mm(2) and 20 μm, respectively. The three-dimensional velocity field was reconstructed by adopting the least squares minimum residue and simultaneous multiplicative algebraic reconstruction techniques. According to a simulation study with synthetic images, the reconstructions were acceptable with 7 projections and 50 iterations. The reconstructed and supplied flow rates differed by only about 6.49% in experimental verification. The x-ray tomographic PIV system would be useful for 3D velocity field information of opaque flows.

  14. Non-perturbative renormalization group calculation of the quasi-particle velocity and the dielectric function of graphene

    Science.gov (United States)

    Sharma, Anand; Bauer, Carsten; Rueckriegel, Andreas; Kopietz, Peter

    We use a nonperturbative functional renormalization group approach to calculate the renormalized quasiparticle velocity v (k) and the static dielectric function ɛ (k) of suspended graphene as function of an external momentum k. We fit our numerical result for v (k) to v (k) /vF = A + Bln (Λ0 / k) , where vF is the bare Fermi velocity, Λ0 is an ultraviolet cutoff, and A = 1 . 37 , B = 0 . 51 for the physically relevant value (e2 /vF = 2 . 2) of the coupling constant. In stark contrast to calculations based on the static random-phase approximation, we find that ɛ (k) approaches unity for k --> 0 . Our result for v (k) agrees very well with a recent measurement by Elias etal. [Nat. Phys. 7, 701 (2011)]. With in the same approximation, we also explore an alternative scheme in order to understand the true nature of the low energy (momentum) behavior in graphene.

  15. On the variations of acoustic absorption peak with particle velocity in micro-perforated panels at high level of excitation.

    Science.gov (United States)

    Tayong, Rostand; Dupont, Thomas; Leclaire, Philippe

    2010-05-01

    The acoustic behavior of micro-perforated panels (MPP) is studied theoretically and experimentally at high level of pressure excitation. A model based on Forchheimer's regime of flow velocity in the perforations is proposed. This model is valid at relatively high Reynolds numbers and low Mach numbers. The experimental method consists in measuring the acoustical pressure at three different positions in an impedance tube, the two measurement positions usually considered in an impedance tube and one measurement in the vicinity of the rear surface of the MPP. The impedance tube is equipped with a pressure driver instead of the usual loudspeaker and capable of delivering a high sound pressure level up to 160 dB. MPP specimens made out of steel, dural and polypropylene were tested. Measurements using random noise or sinusoidal excitation in a frequency range between 200 and 1600 Hz were carried out on MPPs backed by air cavities. It was observed that the maximum of absorption can be a positive or a negative function of the flow velocity in the perforations. This suggests the existence of a maximum of absorption as a function of flow velocity. This behavior was predicted by the model and confirmed experimentally.

  16. Particle deposition in a realistic geometry of the human conducting airways: Effects of inlet velocity profile, inhalation flowrate and electrostatic charge.

    Science.gov (United States)

    Koullapis, P G; Kassinos, S C; Bivolarova, M P; Melikov, A K

    2016-07-26

    Understanding the multitude of factors that control pulmonary deposition is important in assessing the therapeutic or toxic effects of inhaled particles. The use of increasingly sophisticated in silico models has improved our overall understanding, but model realism remains elusive. In this work, we use Large Eddy Simulations (LES) to investigate the deposition of inhaled aerosol particles with diameters of dp=0.1,0.5,1,2.5,5 and 10μm (particle density of 1200kg/m(3)). We use a reconstructed geometry of the human airways obtained via computed tomography and assess the effects of inlet flow conditions, particle size, electrostatic charge, and flowrate. While most computer simulations assume a uniform velocity at the mouth inlet, we found that using a more realistic inlet profile based on Laser Doppler Anemometry measurements resulted in enhanced deposition, mostly on the tongue. Nevertheless, flow field differences due to the inlet conditions are largely smoothed out just a short distance downstream of the mouth inlet as a result of the complex geometry. Increasing the inhalation flowrate from sedentary to activity conditions left the mean flowfield structures largely unaffected. Nevertheless, at the higher flowrates turbulent intensities persisted further downstream in the main bronchi. For dp>2.5μm, the overall Deposition Fractions (DF) increased with flowrate due to greater inertial impaction in the oropharynx. Below dp=1.0μm, the DF was largely independent of particle size; it also increased with flowrate, but remained significantly lower. Electrostatic charge increased the overall DF of smaller particles by as much as sevenfold, with most of the increase located in the mouth-throat. Moreover, significant enhancement in deposition was found in the left and right lung sub-regions of our reconstructed geometry. Although there was a relatively small impact of inhalation flowrate on the deposition of charged particles for sizes dp<2.5μm, impaction prevailed over

  17. Particle-in-cell Simulations of Waves in a Plasma Described by Kappa Velocity Distribution as Observed in the Saturńs Magnetosphere

    Science.gov (United States)

    Alves, M. V.; Barbosa, M. V. G.; Simoes, F. J. L., Jr.

    2016-12-01

    Observations have shown that several regions in space plasmas exhibit non-Maxwellian distributions with high energy superthermal tails. Kappa velocity distribution functions can describe many of these regions and have been used since the 60's. They suit well to represent superthermal tails in solar wind as well as to obtain plasma parameters of plasma within planetary magnetospheres. A set of initial velocities following kappa distribution functions is used in KEMPO1 particle simulation code to analyze the normal modes of wave propagation. Initial conditions are determined using observed characteristics for Saturńs magnetosphere. Two electron species with different temperatures and densities and ions as a third species are used. Each electron population is described by a different kappa index. Particular attention is given to perpendicular propagation, Bernstein modes, and parallel propagation, Langmuir and electron-acoustic modes. The dispersion relation for the Bernstein modes is strongly influenced by the shape of the velocity distribution and consequently by the value of kappa index. Simulation results are compared with numerical solutions of the dispersion relation obtained in the literature and they are in good agreement.

  18. Particle Paths of Lagrangian Velocity Distribution Simulating Yin-Yang Balance in Ancient Tai-Chi Diagram

    Institute of Scientific and Technical Information of China (English)

    Sui Lin; Tzu-Fang Chen

    2007-01-01

    The particle paths of the Lagrangian flow field simulate very well the interface curve of the Yin-Yang balance in the ancient Tai-Chi diagram. There are four forms called the "four states" in the Tai-Chi diagram. Of the four states, under Yang are the Major Yang and the Minor Yin, and under Yin are the Major Yin and the Minor Yang. The present study provides the proper positions of the four states in the ancient Tai-Chi diagram. The Fu Xi's Eight Trigrams Chart located along the ancient Tai-Chi diagram is also developed in the present study. The interface curve of Yin-Yang in the ancient Tai-Chi diagram has never been described mathematically. It can now be formulated by the equations describing the particle paths in the Lagrangian flow field.

  19. Study of multifragmentation: contribution of reduced velocity correlations between particles and fragments; Etude de la multifragmentation: apport des correlations en vitesse reduite entre particules et fragments

    Energy Technology Data Exchange (ETDEWEB)

    Le Fevre, A. [Paris-7 Univ., 75 (France)

    1997-05-14

    This work is focused on the study of fragment and light particle production mechanisms in the multifragmentation process of hot nuclei, which are formed in the central collisions of Xe+Sn at 50 MeV/u. The experiment has been performed with the INDRA multidetector. The central collision events, selected via the flow angle variable, exhibit the presence of a heavy (Z=90) and highly excited (E{sup *}=12.5 MeV/u) isotropic emission source. The comparison of the data with a statistical multifragmentation model (MMMC) and a dynamical model (BNV) makes us conclude that the multifragmentation can only be explained in the frame of a relatively cold process, around 6 MeV/u of thermal excitation energy, preceded by a primary emission stage of the expanding source, during which nearly one third of the excitation energy is dissipated. In addition, it appears that the fragment energy spectra are not explained by a purely thermal process, and that one has to put forward an expansion collective motion, of 2 MeV/u of energy, following the compression of the compound system. In order to precise the existence of a two-step particle emission (primary and secondary), we have developed and applied an original method of reduced velocity correlations between particles and fragments. It has allowed us to underline two distinct origins for the particle production: one corresponding to secondary emissions, coming from the fragments, and the other one, associated with emissions which occur prior to the fragment production. At last, it has allowed us, also to bring out a hierarchy in the emission time in the decay process, with respect to the particle type. (author) 90 refs.

  20. 下行床反应器中惰性颗粒射入对结焦抑止和颗粒速度均匀化的影响%Effect of Injecting Inert Particles on Coking Prohibition and Particle Velocity Uniformization in Downer Reactors

    Institute of Scientific and Technical Information of China (English)

    张济宇; 祝媛; 田亚峻; 谢克昌

    2007-01-01

    The coking observation and particle flow behaviour in both thermal plasma and cold plexiglas downers were investigated in a binary particle system formed by injecting coarse inert particles (carrying coke away and scouring wall) and fine coal powders into the downer reactor. The results demonstrate that this scheme is a rational selection to prevent coking on downer walls and improve particle velocity distribution along the radial direction.When injected coarse particles mixed with fine powders in downers, the fluctuation of local particle velocity in the radial direction becomes smaller and two peaks in the radial distribution of local particle velocity occur due to the improved dispersing character and flow structure, which are beneficial to the thermo-plasma coal cracking reaction and coking prevention.

  1. Parametric study of an HVOF process for the deposition of nanostructured WC-Co coatings

    Science.gov (United States)

    Bartuli, Cecilia; Valente, Teodoro; Cipri, Fabio; Bemporad, Edoardo; Tului, Mario

    2005-06-01

    Nanocrystalline WC-Co coatings were deposited by high velocity oxyfuel from commercial nanostructured composite powders. Processing parameters were optimized for maximal retention of the nanocrystalline size and for minimal decarburation of the ceramic reinforcement. Thermochemical and gas-dynamical properties of gas and particle flows within the combustion flame were identified in various operating conditions by computational fluid-dynamics (CFD) simulation. Significant improvements of the mechanical properties of the coatings were obtained: a decrease of the friction coefficient was measured for the nanostructured coatings, together with an increase of microhardness and fracture toughness.

  2. Microstructure and Wear Behavior of FeCoCrNiMo0.2 High Entropy Coatings Prepared by Air Plasma Spray and the High Velocity Oxy-Fuel Spray Processes

    Directory of Open Access Journals (Sweden)

    Tianchen Li

    2017-09-01

    Full Text Available In the present research, the spherical FeCoCrNiMo0.2 high entropy alloy (HEA powders with a single FCC solid solution structure were prepared by gas atomization. Subsequently, the FeCoCrNiMo0.2 coatings with a different content of oxide inclusions were prepared by air plasma spraying (APS and high-velocity oxy-fuel spraying (HVOF, respectively. The microstructure, phase composition, mechanical properties, and tribological behaviors of these HEA coatings were investigated. The results showed that both HEA coatings showed a typical lamellar structure with low porosity. Besides the primary FCC phase, a mixture of Fe2O3, Fe3O4, and AB2O4 (A = Fe, Co, Ni, and B = Fe, Cr was identified as the oxide inclusions. The oxide content of the APS coating and HVOF coating was calculated to be 47.0% and 12.7%, respectively. The wear resistance of the APS coating was approximately one order of magnitude higher than that of the HVOF coating. It was mainly attributed to the self-lubricated effect caused by the oxide films. The mass loss of the APS coating was mainly ascribed to the breakaway of the oxide film, while the main wear mechanism of the HVOF coating was the abrasive wear.

  3. Study of plasma meniscus and beam halo in negative ion sources using three dimension in real space and three dimension in velocity space particle in cell model

    Energy Technology Data Exchange (ETDEWEB)

    Nishioka, S., E-mail: nishioka@ppl.appi.keio.ac.jp; Goto, I.; Hatayama, A. [Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan); Miyamoto, K. [School of Natural and Living Sciences Education, Naruto University of Education, 748 Nakashima, Takashima, Naruto-cho, Naruto-shi, Tokushima 772-8502 (Japan); Okuda, S.; Fukano, A. [Toshiba, 33 Isogo-chou, Isogo-ku, Yokohama-shi, Kanagawa 235-001 (Japan)

    2014-02-15

    Our previous study by two dimension in real space and three dimension in velocity space-particle in cell model shows that the curvature of the plasma meniscus causes the beam halo in the negative ion sources. The negative ions extracted from the periphery of the meniscus are over-focused in the extractor due to the electrostatic lens effect, and consequently become the beam halo. The purpose of this study is to verify this mechanism with the full 3D model. It is shown that the above mechanism is essentially unchanged even in the 3D model, while the fraction of the beam halo is significantly reduced to 6%. This value reasonably agrees with the experimental result.

  4. Intelligent-based multi-robot path planning inspired by improved classical Q-learning and improved particle swarm optimization with perturbed velocity

    Directory of Open Access Journals (Sweden)

    P.K. Das

    2016-03-01

    Full Text Available Classical Q-learning takes huge computation to calculate the Q-value for all possible actions in a particular state and takes large space to store its Q-value for all actions, as a result of which its convergence rate is slow. This paper proposed a new methodology to determine the optimize trajectory of the path for multi-robots in clutter environment using hybridization of improving classical Q-learning based on four fundamental principles with improved particle swarm optimization (IPSO by modifying parameters and differentially perturbed velocity (DV algorithm for improving the convergence. The algorithms are used to minimize path length and arrival time of all the robots to their respective destination in the environment and reducing the turning angle of each robot to reduce the energy consumption of each robot. In this proposed scheme, the improve classical Q-learning stores the Q-value of the best action of the state and thus save the storage space, which is used to decide the Pbest and gbest of the improved PSO in each iteration, and the velocity of the IPSO is adjusted by the vector differential operator inherited from differential evolution (DE. The validation of the algorithm is studied in simulated and Khepera-II robot.

  5. 波粒二象性理论与波速问题探讨%Discussion on the Particle-Wave Duality and the Wave Velocity Problem

    Institute of Scientific and Technical Information of China (English)

    黄志洵

    2014-01-01

    of the velocity definition,we have v→=▽S/m[ m is the particle’ s mass and ψ=Aexp( jS/ћ) ] . This method builds the relation of velocity and wave function,but it is not the necessary and useful concept of wave’ s speed. The velocity of light in vacuum is a common basic constant of physics,however QM also need this parameter obviously,i. e. the new wave mechanics is on need of this physical quantity. The process and result of people’ s practice show that,scientist has intended to bring forth in the measure-ment of c with very high accuracy does stand out,if he used the scalar equation c=fλ. Modern physics maintain that the wave velocities ( phase velocityvp、group velocity vg ) are scalars,not vectors.The wave has its special scientific features;the regular pattern is different from the Classical Mechan-ics ( CM) . It needs supports of the QM,but it is not identical with the serious QM. Now,it has not only a theory that can explain the wave problems perfectly,so it is support by the classical physics and quantum physics. The quantization process of EM fields explains the particle-wave duality mathematically. Post quanti-zation,from the EM fields we obtained the photons. But scientist still is puzzled by a difficult question:“what is photon”. As the common knowledge,the matter waves of photon still a paradox in physics. In ad-dition,the electronic probability waves corresponding the Schrödinger equation,but people says the pho-tonic probability waves have not that wave equation. In other words, the physical meanings of matter wave’ s phase velocity are not clear,and why the phase velocity of de Broglie waves is faster-than-light, many explanations will be needed. Many instances similar to these examples make the particle- wave duality still the magic ghost in modern physics. Finally,the study on negative wave velocity( NWV) in recent years has a great deal of ex-perience on wave sciences,and bring the new chance on theoretical thinking.

  6. Analysis of Terminal Velocity and VHF Backscatter of Precipitation Particles Using Chung-Li VHF Radar Combined with Ground-Based Disdrometer

    Directory of Open Access Journals (Sweden)

    Ching-Lun Su and Yen-Hsyang Chu

    2007-01-01

    Full Text Available The backscatter from precipitation particles observed by the vertically pointed antenna beam of the Chung-Li VHF radar and the drop size distributions measured by a ground-based disdrometer co-located at the radar site are analyzed and studied in this article. We find that the disdrometermeasured drop size distribution can be well approximated to a Gamma distribution. On the basis of this property and a power law approximation to the fallspeed-diameter relation VD = ADB, we derive the theoretical relation between terminal velocity VD and range-corrected VHF backscatter P of the precipitation particles. We find that the VD - P relation follows a power law in the form of VD = _ where _ _ both the functions of the precipitation parameters. Chu et al. (1999 first found that the relation between _ _ be empirically approximated to an exponential form of _ _ where _ a function of B and _ a factor associated with precipitation. In this article, under the assumptions of the Gamma distribution of the drop size distribution and the power-law relation between VD and D, we theoretically show that the analytical relation between _ _ follows an exponential form of _ _ where _ a function of the drop size distribution. The experimental results obtained by the Chung-Li VHF radar combined with the ground-based disdrometer measurements validate the exponential approximation to the _ _ The uses of the _ _ for the investigations of the rainfall rate and properties of drop size distribution are presented and discussed.

  7. Particle Velocity in the Three-phase Flow of Solid-liquid-gas in a Flotation Cell%浮选槽中固-液-气三相流中颗粒的速度

    Institute of Scientific and Technical Information of China (English)

    曾克文; 薛玉兰; 余永富

    2001-01-01

    采用PDA激光流速测试技术,在固-液-气三相体系中对浮选槽中固体颗粒进行了流速测定,获得了固体颗粒的速度分布,为矿粒与气泡粘附过程和脱附过程机理的研究提供可靠数据。%PDA laser flow velocity testing technique was used to measure the flow velocity of solid particles in the solid-liquid-gas three-phase system in a flotation cell and obtained the velocity distribution of solid particles so as to provide reliable data for the study on adsorption and deadsoption mechanism of particles onto and off from bubbles.

  8. Comparative characteristic and erosion behavior of NiCr coatings deposited by various high-velocity oxyfuel spray processes

    Science.gov (United States)

    Sidhu, Hazoor Singh; Sidhu, Buta Singh; Prakash, S.

    2006-12-01

    The purpose of this study is to analyze and compare the mechanical properties and microstructure details at the interface of high-velocity oxyfuel (HVOF)-sprayed NiCr-coated boiler tube steels, namely ASTM-SA-210 grade A1, ASTM-SA213-T-11, and ASTM-SA213-T-22. Coatings were developed by two different techniques, and in these techniques liquefied petroleum gas was used as the fuel gas. First, the coatings were characterized by metallographic, scanning electron microscopy/energy-dispersive x-ray analysis, x-ray diffraction, surface roughness, and microhardness, and then were subjected to erosion testing. An attempt has been made to describe the transformations taking place during thermal spraying. It is concluded that the HVOF wire spraying process offers a technically viable and cost-effective alternative to HVOF powder spraying process for applications in an energy generation power plant with a point view of life enhancement and to minimize the tube failures because it gives a coating having better resistance to erosion.

  9. High Temperature Oxidation Behavior of HVOF-sprayed Coatings for Use in Thixoextrusion Processes

    Science.gov (United States)

    Picas, J. A.; Punset, M.; Menargues, S.; Campillo, M.; Baile, M. T.; Forn, A.

    2011-05-01

    The dies used for the thixoextrusion of steels have to be capable of withstanding complex thermal and mechanical loads, while giving a sufficient wear resistance against abrasion and adhesion at very high temperatures. In order to improve the wear resistance and reduce the heating of the extrusion die it can be protected with a hard cermet coating. The purpose of this work is to study the high-temperature performance of CrC-CoNiCrAlY coating and explore the potential application of this coating to improve dies used in thixoextrusion processes. A two-layer 75CrC-25CoNiCrAlY coating with a CoNiCrAlY bond-coating was fabricated by the HVOF thermal spray process on a steel substrate. Coatings were heat-treated at a range of temperatures between 900 °C and 1100 °C. The microstructural characterization of the coatings before and after heat treatment was conducted by scanning electron microscopy (SEM) and an X-ray diffractometer (XRD). The mechanical properties of coatings were determined as a function of the temperature of heat treatment. The bond coat effect on the thermal shock resistance of CrC-CoNiCrAlY coating was analyzed.

  10. WIND TUNNEL EXPERIMENT OF SAND VELOCITY IN NATURE AEOLIAN SAND TRANSPORT USING PARTICLE IMAGE VELOCIMETRY%天然混合沙运动速度特征的风洞PIV实验

    Institute of Scientific and Technical Information of China (English)

    佟鼎; 黄宁

    2011-01-01

    Sand velocity in aeolian sand transport is measured using the PIV system(Particle Imaging Velocimetry) in a wind tunnel.The velocity probability distribution of ascending and descending particles,as well the influences of sand ripple on the sand particle motion are analyzed.The results show that velocity distributions of take-off particles and particles during sand movement accord with logarithm normal distribution.The mean incident velocity of sand particles is 1.005-1.4 times higher than take-off ones with different wind speed.It is found that sand ripples play an important role on the sand particles motion,which is a key factor that can not be neglected.%采用PIV(Particle Image Velocimetry)系统测量了天然混合沙风沙两相流中沙粒的速度分布特征,得到了沙粒入射以及起跳的速度分布情况,并且分析了沙波纹对风沙运动的影响。结果表明:沙粒运动过程中的速度分布与沙粒起跳速度的分布可以应用对数正态分布来表明;当有沙波纹存在时,沙粒总体速度分布与平坦沙床面差别很大,是不可忽略的重要因素;平坦沙床面沙粒平均入射速度是起跳平均速度的1.005倍~1.4倍,具体关系可以应用线性函数来拟合。

  11. The Microflown particle velocity sensor

    DEFF Research Database (Denmark)

    Jacobsen, Finn; de Bree, Hans-Elias

    2008-01-01

    The Handbook of Signal Processing in Acoustics will compile the techniques and applications of signal processing as they are used in the many varied areas of Acoustics. The Handbook will emphasize the interdisciplinary nature of signal processing in acoustics. Each Section of the Handbook will pr...

  12. Experimental research of the influence of particle size and fluidization velocity on zeolite drying in a two-component fluidized bed

    Directory of Open Access Journals (Sweden)

    Janevski Jelena N.

    2016-01-01

    Full Text Available This paper presents the results of the kinetics research into the drying of fine grained material in a two-component fluidized bed. A review of theoretical and experimental investigations of aerodynamics of the fluidized bed is given, with a special insight into two-component fluidized beds, as well as the basics of heat and material transfer through a fluidized bed. Apart from the theoretical basis of convective drying of wet materials in a stagnant fluidized bed, the paper also emphasizes different approaches to fine grained material drying kinetics. Based on the experimental investigations, where zealots used as a representative of fine grained material and polyethylene as a representative of inert material (another component, an analysis of the influence of working parameters on drying in a two-component fluidized bed is performed. It is established that, apart from the influence of the considered parameters, such as fluidization velocity, diameter of fine grained material particles and drying agent temperature, on the drying curve, the participation of inert material can considerably increase the intensity of heat and material transfer in the fluidized bed. A comparison of the experimental drying curves of fine grained material in the two-component fluidized bed with the results from the studies by other authors shows satisfactory agreement.

  13. Comparing study of high temperature erosion of HVOF sprayed Cr{sub 3}C{sub 2}-NiCr coating and mild steel for boiler tube

    Energy Technology Data Exchange (ETDEWEB)

    Yang, G.; Zhang, S.; Wang, Y.; Li, C.; Li, C. [Xi' an Jiaotong Univ., Xi' an (China)

    2008-07-01

    The significant erosion of the boiler tube at high temperature becomes an important problem for the safe operation of circulating fluidized bed boiler. This paper investigated the erosion behavior of the HVOF sprayed Cr{sub 3}C{sub 2}-NiCr coating at high temperature comparing with the typical mild steel for boiler tube. Results showed that the erosion rate of the mild steel increased with the increase of temperature. The erosion rate of the mild steel at 800 C was 4 times that at 300 C at an erosion angle of 30 . However, the erosion rate of the HVOF sprayed Cr{sub 3}C{sub 2}-NiCr coating was not influenced by the temperature in the range of 300 to 800 C. It is found that the erosion resistance of HVOF sprayed Cr{sub 3}C{sub 2}-NiCr coating was more than 3 time higher than that of the mild steel at 700 to 800 C. In addition to the ploughing on the surface of the worn coating, the cracking along splats interfaces in the coating was clearly observed on the cross-sectional microstructure of the coating. The results indicate that the erosion performance of the HVOF sprayed Cr{sub 3}C{sub 2}-NiCr coating is controlled by the cohesion between splats in the coating and can be further enhanced by improving splat cohesion. (orig.)

  14. Influence of HVOF coating on the HCF of 300M low alloy steel

    Institute of Scientific and Technical Information of China (English)

    DENG; Chun-ming; LIU; Min; ZHOU; Ke-song; SONG; Jin-bing; WU; Chao-qun; KUANG; Min

    2005-01-01

    The ultimate methods for solving the contamination of Cr6+ is to replace the Cr electroplating with other techniques, thermal spray provides one of the best choices among those alternative techniques. The influence of coatings upon the fatigue performance of substrate, however,should be labeled as an important factor at some high level applications. The effects of both coatings manufactured by HVOF and Cr electroplating respectively on the fatigue performance of substrate are investigated in this article. These results show that the fatigue limit strength at P= 50 %of thermal spray coating is 750 MPa in comparing with fatigue limit 726 MPa for substrate, and the fatigue life increase 25%- 150% when comparing with fatigue life of substrate at different stress levels. The fatigue life increases in the stress scope of 750-850 MPa even the area of thermal spray coating is subtracted. Cr eleetroplating coating reduces the fatigue life by 70%- 95% and the fatigue limit is only 600 MPa. Fracture analysis reveals that the main fracture is initiated at the subsurface, which is 0.2-0.5 mm away from substrate surface. The analysis also observes that the crack in the Cr electroplating propagates through the interface and finally into the substrate which hastens the formation of crack origin and the extension of crack in the substrate, however, the crack in the thermal spray coating deflects at the interface, spreads along the interface, as a result,the crack forming in the coatings has no negative influence on the main crack initiator and crack extension in the substrate.

  15. Evaluation of the CR{sub 3}C{sub 2}(NICR) coating deposited on S4400 with the HVOF process for PEM fuel flow plates; Evaluacion del recubrimiento CR{sub 3}C{sub 2}(NICR) depositado sobre S4400 por el proceso HVOF para placas de flujo de celdas de combustible PEM

    Energy Technology Data Exchange (ETDEWEB)

    Rendon Belmonte, M.; Perez Quiroz, J.T. [Instituto Mexicano del Transporte, Queretaro, Queretaro (Mexico)]. E-mail: marielarb17@hotmail.com; Porcayo Calderon, J. [Instituto de Investigaciones Electricas, Cuernavaca, Morelos (Mexico); Orozco, G. [Centro de Investigacion y Desarrollo Tecnologico en Electroquimica S. C., Queretaro, Queretaro (Mexico)

    2009-09-15

    This research studied the behavior of Cr{sub 3}C{sub 2}(NiCr) coating deposited on S4400 with the HVOF (High Velocity Oxygen-Fuel) thermal projection process. Coating was applied after the surface of the plate was prepared with ceramic granulated metal burst according to norm NACE No. 1/ SSPC-SP 5 and cleaned with acetone. The electrolyte used was an H{sub 2}SO{sub 4} 0,5 M + 2 ppm F{sup -} solution at ambient temperature. Mercury sulfate (Hg{sub 2}SO{sub 4}) electrode was used as the reference electrode and the counter electrode used was a graphite bar. To study the electrochemical behavior, polarization curves were generated with a sweep speed of 0.15 mV/s, according to norms ASTM G5 and ASTM G59. Before testing, the Ecorr was measured with a high impedance multimeter (10{sup 6}). The morphological aspect of the coating evaluated was analyzed with SEM (sweep electron microscopy). Based on the obtained icorr values of 1.7*10{sup -4} mA/cm{sup 2} for a period of 576 hours, we can state that this coating meets the criteria for resistance to corrosion required by the DOE (U.S. Department of Energy) for consideration of its use in PEM fuel cell flow plates. [Spanish] En esta investigacion se estudio el comportamiento del recubrimiento Cr{sub 3}C{sub 2}(NiCr), depositado sobre S4400 mediante el proceso de proyeccion termica HVOF (High Velocity Oxygen-Fuel). Previo a la aplicacion del recubrimiento, la placa fue preparada superficialmente mediante rafaga de granalla ceramica de acuerdo con la norma NACE No. 1/ SSPC-SP 5, limpiada con acetona y en esta condicion se procedio a la aplicacion del recubrimiento. El electrolito empleado fue una solucion de H{sub 2}SO{sub 4} 0,5 M + 2 ppm F{sup -} a temperatura ambiente, como electrodo de referencia se empleo un electrodo de sulfato mercuroso (Hg{sub 2}SO{sub 4}) y como contraelectrodo una barra de grafito. Para estudiar el comportamiento electroquimico se realizaron curvas de polarizacion con una velocidad de barrido de 0

  16. Energy velocity and group velocity

    Institute of Scientific and Technical Information of China (English)

    陈宇

    1995-01-01

    A new Lagrangian method for studying the relationship between the energy velocity and the group velocity is described. It is proved that under the usual quasistatic electric field, the energy velocity is identical to the group velocity for acoustic waves in anisotropic piezoelectric (or non-piezoelectric) media.

  17. 爆炸和超音速火焰喷涂MCrAlYX涂层的显微结构、力学性能及抗氧化特性%Microstructure, mechanical and oxidation characteristics of detonation gun and HVOF sprayed MCrAlYX coatings

    Institute of Scientific and Technical Information of China (English)

    高俊国; 汤智慧; 王长亮; 郭孟秋; 崔永静

    2015-01-01

    对爆炸(D-gun)和超音速火焰喷涂(HVOF)MCrAlYX涂层的显微结构、力学性能和抗氧化性能进行研究。结果表明,D-gun涂层呈现片层显微结构,而HVOF涂层呈现均匀结构。同时,在爆炸喷涂过程中发生了元素重新分布以及新相的形成。此外,D-gun涂层的孔隙率明显低于HVOF涂层的。在力学性能方面,2种涂层的显微硬度在同一水平(均在HV 910左右),但由于D-gun涂层的片层显微结构及不同相组成,其纤维硬度的标准偏差明显高于HVOF涂层的。由于涂层颗粒及片层之间存在大量的残余压应力,所以,D-gun涂层的弯曲结合强度明显高于HVOF涂层的。高温氧化实验结果表明,D-gun制备的MCrAlYX涂层的抗氧化性能更优异,因为D-gun涂层更致密,使其表面能够尽早地形成连续致密的氧化保护层,从而进一步抑制氧化并控制氧化膜的厚度较小。%Microstructure, mechanical property and oxidation resistance of MCrAlYX coatings prepared by detonation gun (D-gun) and HVOF spraying were investigated. Lamellar microstructure and uniform microstructure formed in D-gun sprayed MCrAlYX coating and HVOF sprayed coating, respectively. Element redistribution and formation of new phase took place during the detonation process. Besides, the porosity of D-gun sprayed coating was much lower than that of HVOF sprayed coating. On the mechanical property, the micro-hardnesses of the two coatings were in the same level (~HV 910). However, D-gun sprayed MCrAlYX coating exhibited larger standard deviation of microhardness due to its lamellar microstructure, and exhibited better bend bonding strength owing to the existence of residual compressive stress between the layers and particles. Meanwhile, due to the much more compact microstructure, D-gun sprayed MCrAlYX coating showed superior oxidation resistance to the HVOF sprayed coating. The continuous dense protective layer can form earlier in D

  18. Characterisations of HVOF sprayed NiCrBSi coatings on Ni- and Fe-based superalloys and evaluation of cyclic oxidation behaviour of some Ni-based superalloys in molten salt environment

    Energy Technology Data Exchange (ETDEWEB)

    Sidhu, T.S. [Metallurgical and Materials Engineering Department, Indian Institute of Technology Roorkee, Roorkee-247667 (India)]. E-mail: tssidhu@rediffmail.com; Prakash, S. [Metallurgical and Materials Engineering Department, Indian Institute of Technology Roorkee, Roorkee-247667 (India); Agrawal, R.D. [Metallurgical and Materials Engineering Department, Indian Institute of Technology Roorkee, Roorkee-247667 (India)

    2006-09-25

    Microstructure plays a predominant role in determining material behaviour. Increasing microstructure uniformity has long been considered a fruitful means of improving thermal, chemical and mechanical properties of the materials. High velocity oxy-fuel (HVOF) is one of the emerging technologies among the thermal spraying techniques, for producing uniform and dense coatings, having high hardness and good adhesion values. In this study, HVOF technique was used to deposit NiCrBSi coatings, approximately 250-300 {mu}m thick, on the Ni- and Fe-based superalloys for hot corrosion applications. The coatings were characterised in relation to coating thickness, porosity, microhardness and microstructure. The hot corrosion behaviour of the coatings deposited on nickel-based superalloys after exposure to molten salt (Na{sub 2}SO{sub 4}-60% V{sub 2}O{sub 5}) at 900 deg. C under cyclic conditions was also studied. The techniques used in the present investigation include X-ray diffraction, optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX) and electron probe microanalysis (EPMA). The thermogravimetric technique was used to establish kinetics of corrosion. The structure of the as sprayed NiCrBSi coating mainly consisted of {gamma}-nickel solid solution containing small fraction of Cr{sub 7}C{sub 3} and Ni{sub 3}B phases. Very weak peaks of NiCr{sub 2}O{sub 4} spinel oxides were also formed during spraying of the coatings. Some porosity (less than 1.4%) and inclusions were observed in the structure of the coatings. Coating microhardness values were found to be in the range of 750-930 Hv (Vickers Hardness) on different substrates. The NiCrBSi coating was found to be very effective in decreasing the corrosion rate in the given molten salt environment at 900 deg. C. The hot corrosion resistance imparted by NiCrBSi coatings may be attributed to the formation of oxides of silicon, chromium, nickel and spinels of nickel and chromium.

  19. Resistance of cavitation erosion of multimodal WC-12Co coatings sprayed by HVOF%超音速火焰喷涂制备多峰WC-12Co涂层的抗汽蚀性能

    Institute of Scientific and Technical Information of China (English)

    丁彰雄; 陈伟; 王群

    2011-01-01

    Conventional,submicron and multimodal WC-12Co cermet coatings were deposited by high velocity oxy-fuel (HVOF).The microhardness and microstructure of the coatings were compared,and the resistance of the coatings to cavitation erosion was studied by ultrasonic vibration cavitation equipment.Cavitation pits and craters were observed by SEM and cavitation mechanisms were explored.The results show that the microstructures of submicron and multimodal WC-12Co coatings prepared by HVOF are dense with little porosity,and their microhardness values are obviously higher than that of the conventional WC-12Co coating.The average microhardness of multimodal WC-12Co coating reaches nearly HV1500,whieh is much higher than that of the conventional one.As well,it is found that the multimodal WC-12Co coating exhibits the best cavitation erosion resistance among the three coatings,the erosion rate is approximately 40% that of the conventional coating,and the cavitation erosion resistance of multimodal WC-12Co coating is enhanced by above 150% in comparison with the conventional coating.%采用超音速火焰喷涂技术制备常规、亚微米及多峰3种WC- 12Co金属陶瓷涂层,比较分析涂层的显微硬度及显微组织.采用超声振动汽蚀装置研究3种涂层的抗汽蚀性能,并采用扫描电镜观察涂层表面的汽蚀坑,探讨不同涂层的汽蚀机理.研究表明:采用超音速火焰喷涂制备的亚微米及多峰WC- 12Co涂层结构致密、孔隙率低,其显微硬度明显高于常规的WC- 12Co涂层.多峰WC- 12Co涂层的平均显微硬度接近HV 1500,远高于常规的WC- 12Co涂层.在3种涂层中,多峰WC- 12Co涂层表现出最优良的抗汽蚀性能,涂层的汽蚀率大约为常规涂层的40%;与常规涂层相比,多峰WC-12Co涂层的抗汽蚀性能提高150%以上.

  20. Settling Velocity of Single Particle Sediment Measured By High-speed Video%基于高速摄像的单颗粒泥沙沉速试验

    Institute of Scientific and Technical Information of China (English)

    宋佳苑; 孙志林

    2016-01-01

    Settling velocity is an important issue in the mechanics of sediment transport. A new measurement method for settling velocity was proposed. Utilizing the precise timing of a high-speed video camera, settling velocities of a single particle was measured by the record of the settling process. The analysis of the data predicted when the particle size is small, the measured settling velocity is bigger than the one calculated by the formulas. Besides, the smaller the particle size is, the more obviously of the phenomenon reveals. Effective resistance of the sediment particle is related to the geometric mean of stagnant resistance and turbulent resistance. Single particle sedimentation formula was derived in the transition zone, and determined the coefficients based on experimental data. The calculated results matched the data of the experiment well.%沉速是泥沙运动研究的关键课题。利用高速摄像仪的高精度计时能力,记录单颗粒泥沙在水体中的下沉过程,测得沉降速度。从结果分析,当颗粒粒径较小时,实测的沉速比常用沉速公式计算值偏大,且粒径越小这一现象越明显。认为泥沙颗粒受到的有效阻力与滞流阻力和紊流阻力的几何平均正相关,推导出单颗粒在过渡区的沉降公式,并根据实验数据确定其系数。经验证,计算公式与试验结果符合度良好。

  1. Mechanical Properties and Fracture Mechanism of WC-10Co4Cr Coating Sprayed by High Velocity Oxygen Fuel%超音速火焰喷涂 WC-10Co4Cr 涂层的力学性能及断裂机理

    Institute of Scientific and Technical Information of China (English)

    周夏凉; 陈小明; 吴燕明; 伏利; 王莉容; 马红海

    2015-01-01

    WC-10Co4Cr coating was prepared on the substrate of stainless steel by high velocity oxygen fuel (HVOF)spraying.The micro-hardness and bond strength of the coating were investigated;phase composition, section and surface morphology was studied;and the fracture mode and mechanism were analyzed as well.The results show that the average micro-hardness of the WC-10Co4Cr coating reached to 1 147.6 HV and the bond strength was 70 MPa.The tensile fracture was with typical characteristics of brittle fracture and there was no significant plastic deformation.The fracture cracks were formed under the external stress due to the pores and microcracks among particles in the coating.These cracks propagated along the interface between particle and particle and were accompanied by deflections of crack paths,then caused the fracture of the coating.%采用超音速火焰喷涂技术(HVOF)在不锈钢基体上制备了 WC-10Co4Cr 涂层,测试了涂层的显微硬度和结合强度,研究了涂层的物相组成和横截面、断裂面的形貌,分析了涂层的断裂方式和断裂机理.结果表明:WC-10Co4Cr 涂层的平均显微硬度达1147.6 HV,结合强度为70 MPa;涂层的拉伸断裂为典型的脆性断裂,没有明显的塑性变形过程;涂层中颗粒间的孔隙和微裂纹在外应力的作用下形成裂纹,裂纹沿颗粒与颗粒间的界面扩展并伴随扩展方向的偏转,最终导致涂层的断裂.

  2. HVOF- and HVAF-Sprayed Cr3C2-NiCr Coatings Deposited from Feedstock Powders of Spherical Morphology: Microstructure Formation and High-Stress Abrasive Wear Resistance Up to 800 °C

    Science.gov (United States)

    Janka, L.; Norpoth, J.; Trache, R.; Thiele, S.; Berger, L.-M.

    2017-08-01

    Chromium carbide-based coatings are commonly applied to protect surfaces against wear at high temperatures. This work discusses the influence of feedstock powder and spray torch selection on the microstructure and high-stress abrasion resistance of thermally sprayed Cr3C2-NiCr coatings. Four commercial feedstock powders with spherical morphology and different microstructures were deposited by different high-velocity spray processes, namely third-generation gas- and liquid-fueled HVOF torches and by the latest generation HVAF torch. The microstructures of the coatings were studied in the as-sprayed state and after various heat treatments. The high-stress abrasion resistance of as-sprayed and heat-treated coatings was tested at room temperature and at 800 °C. The study reveals that the selection of the spray torch mainly affects the room temperature abrasion resistance of the as-sprayed coatings, which is due to differences in the embrittlement of the binder phase generated by carbide dissolution. At elevated temperatures, precipitation and growth of secondary carbides yields a fast equalization of the various coatings microstructures and wear properties.

  3. Engineered Three-Dimensional Electrodes by HVOF Process for Hydrogen Production

    Science.gov (United States)

    Aghasibeig, Maniya; Moreau, Christian; Dolatabadi, Ali; Wuthrich, Rolf

    2016-12-01

    High velocity oxy-fuel process was used to prepare nickel electrode coatings for hydrogen production by alkaline water electrolysis. To further increase the active surface area of the electrodes, pyramidal fin arrays with two different sizes were deposited on the top surface of the electrodes using mesh screen masks. The surface microstructure, topology and roughness of the coatings were studied using scanning electron microscope, optical microscopy and confocal laser scanning microscopy. Steady-state polarization curves were used to evaluate the electrocatalytic activity of the electrodes. The performance of the electrodes coated using mesh outperformed the electrode deposited without using mesh. In addition, the electrode that was coated using the coarse mesh was characterized with the highest activity with the exchange current density and overpotential values of 9.3 × 10-3 A/cm2 and -306 mV, respectively. Formation of different roughness levels due to the combination of normal and off-normal impact of the coating particles on the surface of the fins was identified as the main factor for the increased activity of this electrode toward the hydrogen evolution reaction.

  4. Forward-scattering particle image velocimetry (FSPIV): application of Mie and imaging theory to measure 3D velocities in microscopic flows using partially coherent illumination and high-aperture opt

    Science.gov (United States)

    Ovryn, Ben; Khaydarov, John D.

    1997-04-01

    We have combined Mie scattering theory and image theory to predict the forward scattering of light from spherical particles in a seeded fluid using high numerical aperture collection optics. Using this method, it is possible to determine all three components of a fluid's velocity by measuring the scattering from homogeneous spherical particles without moving the optics. The transverse velocity component is determined by following the centroid of the scattering pattern (with respect to time), while the component along the optical axis is determined by comparing the experimental data with numerical computations. We have verified our theoretical model and computer code by measuring the scattering from polystyrene particles illuminated with partially coherent, Koehler illumination in a transmitted light microscope. The three-dimensional scattering data is in quite good agreement with our model. To further verify our approach, we have measured the three- dimensional (parabolic) profile of a parallel flow of a low viscosity, seeded fluid in a straight channel (6 mm by 48 mm by 0.315 mm). The channel was placed on the stage of a conventional microscope equipped with a long working distance microscope objective, with the narrow dimension along the optical axis (OA). Instead of directly imaging the seed particles, the forward scattered light is recorded from the spherical, polystyrene seed particles (7 micrometer diameter).

  5. Interacción térmica recubrimiento-sustrato en la proyección a alta velocidad (HVOF de partículas (polvo de WC-Co

    Directory of Open Access Journals (Sweden)

    Sobolev, V. V.

    1995-06-01

    Full Text Available The mathematical simulation of the thermal interaction between a 34CrMo4 (UNS-G41350 steel substrate and a coating formed by the droplets of WC-12 % Co powder particles during HVOF spraying is undertaken. Analysis of the heat transfer processes permitted the investigation of the temperature evolution, coating solidification, substrate fusion and solidification, particular features of the thermal interactions between the substrate and the coating as well as between the successive coating layers. The analysis has also permitted to estimate the optimal conditions of the substrate and the coating structure formation. The obtained results were used in subsequent articles to predict the structure parameters, which agree with the experimental data.

    Se utiliza la simulación matemática para establecer la interacción térmica entre un substrato y un recubrimiento obtenido mediante proyección térmica de alta velocidad, HVOF. El substrato es un acero 34CrMo4(UNS-G41350 y el recubrimiento está formado por la solidificación de gotas semifundidas de partículas de polvo de WC-12 % Co. El análisis del proceso de transferencia de calor permite la investigación de la evolución de la temperatura, la solidificación del recubrimiento, la fusión y posterior solidificación del substrato, las características peculiares de la interacción térmica entre el substrato y la primera capa de recubrimiento, así como con las diferentes capas sucesivas, y la estimación de las condiciones óptimas para la formación de la estructura del substrato y del recubrimiento. Los resultados obtenidos se han utilizado en posteriores artículos para predecir parámetros estructurales que están, por su parte, en concordancia con los datos experimentales.

  6. Effect of binder on abrasive wear resistance of tungsten carbide coating prepared by HVOF spraying%粘结剂对超音速火焰喷涂碳化钨涂层磨粒磨损性能的影响

    Institute of Scientific and Technical Information of China (English)

    梁文军; 张宏; 沈承金; 马瑞勇

    2012-01-01

    WC-lONi and WC-12Co coatings were deposited on 35 steel substrate by HVOF (high velocity oxygen fuel) spraying process. The effects of Ni and Co as binders on microhardness, friction coefficient, and abrasive wear resistance of WC coating were studied. The surface morphologies of the coating before and after wearing were analyzed by scanning electron microscopy (SEM) and the mechanism of abrasive wear was discussed. The results indicated that both WC coatings prepared by HVOF have high microhardness, and show little difference in friction coefficient when they rub against SiC sandpaper under dry friction condition. Both coatings have good anti-abrasive wear performance at low load, while at high load the WC-12Co coating has obviously better wear resistance than the WC-lONi coating. Their main abrasive wear form is uniform abrasion wear and the abrasive wear mechanismis mainly micro-cutting and micro-peeling. The surface damage of the WC-12Co coating after wearing is lighter and has better comprehensive performance as compared with the WC-lONi coating.%采用超音速火焰喷涂(HVOF)工艺在35钢基体上制备了WC- 10Ni涂层和WC- 12Co涂层,研究了镍、钴这两种粘结剂对WC涂层的显微硬度、摩擦系数和抗磨粒磨损性能的影响,采用扫描电子显微镜观察涂层磨损前后的表面形貌,探讨了WC涂层的磨粒磨损机理.结果表明,以HVOF方法制备的2种WC涂层均有较高的显微硬度,WC- 10Ni涂层和WC- 12Co涂层与SiC砂纸摩擦副之间的干摩擦系数相差不大.2种涂层在低载荷下均有较好的抗磨粒磨损性能,但在较高载荷下WC- 12Co涂层的抗磨性明显优于WC-10Ni涂层.2种涂层的磨粒磨损形式主要为均匀磨耗磨损,磨损机理以微切削和微剥落为主.WC-12Co涂层的磨损表面损伤较轻微,综合性能优于WC- 10Ni涂层.

  7. Microstructure and Properties of Cu Coating Fabricated onto Diamond-Cu Substrate by Low-Temperature HVOF Process

    Science.gov (United States)

    Liu, Min; Yang, Kun; Deng, Chun-ming; Deng, Chang-guang; Zhou, Ke-song

    2016-12-01

    Diamond-Cu composites have been considered to be the next generation of electronic packing materials. One of the key stumbles for such an application is the joining problem between diamond-Cu composites and other materials due to the poor wettability of the diamond particles in the composites. In order to overcome this hurdle, pure Cu powder was thermally sprayed onto diamond-Cu substrate by low-temperature high-velocity oxygen fuel spraying process. Microstructure and some fundamental properties of the coating obtained were systematically investigated, and morphologies of the single splat deposited on the diamond-Cu substrate were also observed. The splats obtained have good adhesion with the substrate as fine particles flattened sufficiently, while the coarse particles were significantly deformed. The coating was quite dense with porosity lower than 1%, oxygen content under 0.5% and thermal conductivity about 266 Wm-1 K-1 and still remained on the diamond-Cu substrate after 50 thermal shock cycles between 300 °C and water bath at room temperature. Meanwhile, the solderability of the coating was significantly improved. Therefore, Cu coating deposited on diamond-Cu substrate by low-temperature high-velocity oxygen fuel spraying process can be beneficial in electronic industry assisting with soldering and improved wettability for joining of other materials.

  8. Superluminal Recession Velocities

    CERN Document Server

    Davis, T M; Davis, Tamara M.; Lineweaver, Charles H.

    2000-01-01

    Hubble's Law, v=HD (recession velocity is proportional to distance), is a theoretical result derived from the Friedmann-Robertson-Walker metric. v=HD applies at least as far as the particle horizon and in principle for all distances. Thus, galaxies with distances greater than D=c/H are receding from us with velocities greater than the speed of light and superluminal recession is a fundamental part of the general relativistic description of the expanding universe. This apparent contradiction of special relativity (SR) is often mistakenly remedied by converting redshift to velocity using SR. Here we show that galaxies with recession velocities faster than the speed of light are observable and that in all viable cosmological models, galaxies above a redshift of three are receding superluminally.

  9. Minimal information in velocity space

    CERN Document Server

    Evrard, Guillaume

    1995-01-01

    Jaynes' transformation group principle is used to derive the objective prior for the velocity of a non-zero rest-mass particle. In the case of classical mechanics, invariance under the classical law of addition of velocities, leads to an improper constant prior over the unbounded velocity space of classical mechanics. The application of the relativistic law of addition of velocities leads to a less simple prior. It can however be rewritten as a uniform volumetric distribution if the relativistic velocity space is given a non-trivial metric.

  10. Light charged particle and neutron velocity spectra in coincidence with projectile fragments in the reaction sup 4 sup 0 Ar(44 A MeV)+ sup 2 sup 7 Al

    CERN Document Server

    Lanzanò, G; Geraci, M; Pagano, A; Aiello, S; Cunsolo, A; Fonte, R; Foti, A; Sperduto, M L; Volant, C; Charvet, J L; Dayras, R; Legrain, R

    2001-01-01

    We present a three source analysis of velocity spectra of light charged particles (LCP) and neutrons emitted in the reaction sup 4 sup 0 Ar+ sup 2 sup 7 Al at 44 A MeV. The light particle (LP) velocity spectra are studied as a function of the detection angle (1.5 deg. velocity and the intensity of each source are extracted as a function of the PLF charge. While the temperature parameters for PLF and target-like fragments (TLF) are very similar and show a dependence on the PLF charge, the temperature parameter for the intermediate source is approximately 15 MeV, independent of the PLF charge. Comparison with temperature values extracted from double isotopic ratios, shows an agreement only between the temperature values extracted from formula involving sup 3 He, sup 4 He, d, t ratios and the PLF proton temperature parameter. The characteristics of the PLF sources are derived. Present ...

  11. Characterization of High-Velocity Solution Precursor Flame-Sprayed Manganese Cobalt Oxide Spinel Coatings for Metallic SOFC Interconnectors

    Science.gov (United States)

    Puranen, Jouni; Laakso, Jarmo; Kylmälahti, Mikko; Vuoristo, Petri

    2013-06-01

    A modified high-velocity oxy-fuel spray (HVOF) thermal spray torch equipped with liquid feeding hardware was used to spray manganese-cobalt solutions on ferritic stainless steel grade Crofer 22 APU substrates. The HVOF torch was modified in such a way that the solution could be fed axially into the combustion chamber through 250- and 300-μm-diameter liquid injector nozzles. The solution used in this study was prepared by diluting nitrates of manganese and cobalt, i.e., Mn(NO3)2·4H2O and Co(NO3)2·6H2O, respectively, in deionized water. The as-sprayed coatings were characterized by X-ray diffraction and field-emission scanning electron microscopy operating in secondary electron mode. Chemical analyses were performed on an energy dispersive spectrometer. Coatings with remarkable density could be prepared by the novel high-velocity solution precursor flame spray (HVSPFS) process. Due to finely sized droplet formation in the HVSPFS process and the use of as delivered Crofer 22 APU substrate material having very low substrate roughness ( R a < 0.5 μm), thin and homogeneous coatings, with thicknesses lower than 10 μm could be prepared. The coatings were found to have a crystalline structure equivalent to MnCo2O4 spinel with addition of Co-oxide phases. Crystallographic structure was restored back to single-phase spinel structure by heat treatment.

  12. Particle deposition in a realistic geometry of the human conducting airways: Effects of inlet velocity profile, inhalation flowrate and electrostatic charge

    DEFF Research Database (Denmark)

    Koullapis, P. G.; Kassinos, S. C.; Bivolarova, Mariya Petrova

    2016-01-01

    Understanding the multitude of factors that control pulmonary deposition is important in assessing the therapeutic or toxic effects of inhaled particles. The use of increasingly sophisticated in silico models has improved our overall understanding, but model realism remains elusive. In this work......, we use Large Eddy Simulations (LES) to investigate the deposition of inhaled aerosol particles with diameters of dp=0.1,0.5,1,2.5,5dp=0.1,0.5,1,2.5,5 and 10μm (particle density of 1200 kg/m3). We use a reconstructed geometry of the human airways obtained via computed tomography and assess the effects....... Nevertheless, flow field differences due to the inlet conditions are largely smoothed out just a short distance downstream of the mouth inlet as a result of the complex geometry. Increasing the inhalation flowrate from sedentary to activity conditions left the mean flowfield structures largely unaffected...

  13. Role of HVOF-spray NiCr coatings to control high temperature oxidation of some boiler steels

    Energy Technology Data Exchange (ETDEWEB)

    Kaushal, G. [RIMT-Institute of Engineering and Technology, Mandi Gobind Garh (India); Singh, H. [BBSB Engineering College, Fatehgarh Sahib (India); Prakash, S. [Indian Inst. of Technology, Roorkee (India)

    2008-07-01

    A study was carried out to determine the role of HVOF-spray Ni-20Cr coatings to enhance high temperature oxidation resistance of T22 and 347H boiler steels. Ni-20Cr coatings were deposited on the boiler steels. Subsequently high temperature oxidation behavior of these coatings was investigated by laboratory tests at an elevated temperature of 900 C under cyclic conditions.These coatings were also subjected to a boiler environment at an elevated temperature of 700 C under cyclic conditions to ascertain their erosion-corrosion behaviour. Thermogravimetric data was taken after each cycle to formulate the oxidation, as well as, erosion-corrosion kinetics. The specimens were also physically examined after each cycle to notice any macrographic physical changes, spallation tendency of their oxide scales etc. The exposed specimens were examined using scanning electron microscopy and Energy Dispersive Spectroscopy (SEM/EDS) analysis. It was observed that oxidation rate was subsequently low in the coated substrates as compare to uncoated steels. It was observed that Ni-20Cr coating on 347H boiler substrate showed the maximum oxidation resistance. Moreover, both the steels showed better resistance to erosion-corrosion in actual boiler conditions after the application of Ni-20Cr coating. (orig.)

  14. Comportamiento tribológico de los recubrimientos nanocristalinos de CrC-NiCr obtenidos por proyección térmica HVOF

    Directory of Open Access Journals (Sweden)

    Igartua, A.

    2004-04-01

    Full Text Available One of the most important uses of HVOF thermal plasma spray coatings is for wear resistance. In this work, the characteristics of nanocristalline CCr-NiCr coating and their effect on the mechanical properties and tribological behaviour of the material have been investigated. The objective of this study is the replacement of hazardous hard chromium plating technology used today in industry for an efficient and clean HVOF technology, using micro and nanocristalline CCr-NiCr coatings. Commercially available CCr-NiCr powder was mechanically treated, in order to obtain nano powders. Later the HVOF thermal spray process was used to produce conventional and nanocrystalline CCr-NiCr coatings. The ultra-microindentation technique was applied to evaluate the grain size effect in the hardness and the elasto-plastic properties of the coating. Difference in roughness has been determined by profilometry. The coating microstructures were characterised by SEM and optical microscopy and the porosity percentage was determined by Image Analysis technique. In order to evaluate the friction and wear properties of different substrate materials a reciprocating sliding motion has been used. CrC-NiCr standard coatings shows better tribological properties than WC-CoCr coatings.

    Una de las características más importantes de los recubrimientos de proyección térmica HVOF es su resistencia al desgaste. En este proyecto, se han investigado las características del recubrimiento nanocristalinos de CrC-NiCr y su efecto en las propiedades mecánicas y tribológicas del material. De acuerdo con los ensayos realizados, los recubrimientos nanocristalinos CrC-NiCr proporcionan una rugosidad un 66% menor, que los recubrimientos estándar, lo que produce una importante mejora en las propiedades de fricción (reducción coeficiente de fricción del 38% y desgaste (reducción del desgaste del 84%.

  15. ANÁLISIS DE LA FUNCIÓN DE CORRECCIÓN DE LA VELOCIDAD DE SEDIMENTACIÓN PARA MICRO PARTÍCULAS ANALYSIS OF THE CORRECTION FUNCTION FOR MICRO-PARTICLE SEDIMENTATION VELOCITY

    Directory of Open Access Journals (Sweden)

    Gonzalo Salinas-Salas

    2007-12-01

    Full Text Available La velocidad de sedimentación de las partículas presentes en una suspensión sufre una caída monótona en función de la concentración volumétrica de éstas, por efecto de las fuerzas hidrodinámicas y electroquímicas que se presentan en una suspensión. El valor efectivo que alcanza la velocidad de sedimentación puede evaluarse a partir de la velocidad de sedimentación teórica de una partícula única, multiplicada por la denominada función de corrección de velocidad o función obstáculo, la que considera tanto el régimen de escurrimiento como la concentración volumétrica de partículas. Los valores determinados para esta función por Richardson y Zaki en 1954 [14] son los más utilizados actualmente, donde el valor propuesto para el caso de regímenes de escurrimiento del fluido por sobre las partículas, cuyos números de Reynolds sean menores a 0,25, se establece un valor único de 4,65, independientemente del tamaño de las partículas. El presente artículo muestra los resultados alcanzados a partir de un trabajo experimental desarrollado con micro partículas calibradas de óxido de silicio (SiO2, que indica que el valor del exponente de la función de corrección depende inversamente del tamaño, para el caso de partículas de orden micrométrico, lo que daría lugar a un nuevo valor para el exponente.The sedimentation velocity of micro-particles in suspension decreases with increasing concentration due to hydrodynamic and electrostatic forces. This velocity can be estimated on the basis of the theoretical velocity of a single particle, multiplied by a correction factor which depends on the flow regime as well as the volumetric concentration of the particles. The most commonly used values are those determined by Richardson and Zaki in 1954 [14]. For flow regimes characterized by a Reynolds' number less than 0,25, a constant value of 4,65 is used which does not depend on the particle size. The present article presents

  16. Desirability-Based Multi-Criteria Optimization of HVOF Spray Experiments to Manufacture Fine Structured Wear-Resistant 75Cr3C2-25(NiCr20) Coatings

    Science.gov (United States)

    Tillmann, W.; Vogli, E.; Baumann, I.; Kopp, G.; Weihs, C.

    2010-01-01

    Thermal spraying of fine feedstock powders allow the deposition of cermet coatings with significantly improved characteristics and is currently of great interest in science and industry. However, due to the high surface to volume ratio and the low specific weight, fine particles are not only difficult to spray but also show a poor flowability in the feeding process. In order to process fine powders reliably and to preserve the fine structure of the feedstock material in the final coating morphology, the use of novel thermal spray equipment as well as a thorough selection and optimization of the process parameters are fundamentally required. In this study, HVOF spray experiments have been conducted to manufacture fine structured, wear-resistant cermet coatings using fine 75Cr3C2-25(Ni20Cr) powders (-8 + 2 μm). Statistical design of experiments (DOE) has been utilized to identify the most relevant process parameters with their linear, quadratic and interaction effects using Plackett-Burman, Fractional-Factorial and Central Composite designs to model the deposition efficiency of the process and the majorly important coating properties: roughness, hardness and porosity. The concept of desirability functions and the desirability index have been applied to combine these response variables in order to find a process parameter combination that yields either optimum results for all responses, or at least the best possible compromise. Verification experiments in the so found optimum obtained very satisfying or even excellent results. The coatings featured an average microhardness of 1004 HV 0.1, a roughness Ra = 1.9 μm and a porosity of 1.7%. In addition, a high deposition efficiency of 71% could be obtained.

  17. Microstructure Characterization of WCCo-Mo Based Coatings Produced Using High Velocity Oxygen Fuel

    Directory of Open Access Journals (Sweden)

    Serkan Islak

    2015-12-01

    Full Text Available The present study has been carried out in order to investigate the microstructural properties of WCCo-Mo composite coatings deposited onto a SAE 4140 steel substrate by high velocity oxygen fuel (HVOF thermal spray. For this purpose, the Mo quantity added to the WCCo was changed as 10, 20, 30 and 40 wt. % percents. The coatings are compared in terms of their phase composition, microstructure and hardness. Phase compound and microstructure of coating layers were examined using X-ray diffractometer (XRD and scanning electron microscope (SEM. XRD results showed that WCCo-Mo composite coatings were mainly composed of WC, W2C, Co3W3C, Mo2C, MoO2, Mo and Co phases. The average hardness of the coatings increased with increasing Mo content.

  18. Comportamiento Tribológico y Microestructural en Recubrimientos Aplicados por GTAW y HVOF (Proceso Térmico de Espreado y Usado en Recuperación de Aceros Grado Herramienta AISI/SAE D2

    Directory of Open Access Journals (Sweden)

    Carlos Alberto Guevara Chávez

    Full Text Available Resumen Las aleaciones de Fe-Cr-Mo se utilizan en recubrimientos para proteger componentes que están sometidos a condiciones de desgaste y corrosión. La alta velocidad de deposición del metalizado térmico (HVOF (High Velocity Oxi-Fuel aplicado en aleaciones de acero grado herramienta para trabajo en frío con la aplicación de sustratos Fe-Cr-Mo ha mostrado buenos resultados en los campos de proyección. El HOVF es un método atractivo para aplicar revestimientos y recuperar diámetros que fueron desgastados durante el proceso de operación. Nuevas superficies y materiales pueden ser provistos sin la distorsión causada por los procesos convencionales de soldadura. Para aquellos materiales que son susceptibles a agrietarse gracias a la formación de fases fuera de equilibrio duras con composiciones con altos contenidos de carbono y de cromo, debido a las condiciones del proceso que combinan una temperatura de la flama relativamente baja y con un tiempo de baja exposición. La microestructura las características del recubrimiento son determinadas por las propiedades físicas y químicas de las partículas impregnadas en el sustrato que a su vez dependen de una gran cantidad de parámetros como el diseño de pistola, la relación de oxígeno / combustible, método de inyección, tamaño de partícula y forma, entre otros La presente investigación estudia la influencia de los parámetros de procesamiento sobre las propiedades mecánicas y microestructurales del recubrimiento Diamalloy 1008 (aleación en mezcla de Fe-Cr-Mo revestimiento aplicado con Oxí-combustible de alta velocidad (HVOF y cinco diferentes tipos de electrodos aplicados por soldadura, TIG (GTAW en un acero grado herramienta para trabajo en frio. El objetivo de estos recubrimientos se utiliza habitualmente como una protección contra la corrosión y el desgaste, pero también tienen la capacidad de recuperar las zonas dañadas como es el caso de los dados de estampado de la

  19. Kriging Interpolating Cosmic Velocity Field

    CERN Document Server

    Yu, Yu; Jing, Yipeng; Zhang, Pengjie

    2015-01-01

    [abridge] Volume-weighted statistics of large scale peculiar velocity is preferred by peculiar velocity cosmology, since it is free of uncertainties of galaxy density bias entangled in mass-weighted statistics. However, measuring the volume-weighted velocity statistics from galaxy (halo/simulation particle) velocity data is challenging. For the first time, we apply the Kriging interpolation to obtain the volume-weighted velocity field. Kriging is a minimum variance estimator. It predicts the most likely velocity for each place based on the velocity at other places. We test the performance of Kriging quantified by the E-mode velocity power spectrum from simulations. Dependences on the variogram prior used in Kriging, the number $n_k$ of the nearby particles to interpolate and the density $n_P$ of the observed sample are investigated. (1) We find that Kriging induces $1\\%$ and $3\\%$ systematics at $k\\sim 0.1h{\\rm Mpc}^{-1}$ when $n_P\\sim 6\\times 10^{-2} ({\\rm Mpc}/h)^{-3}$ and $n_P\\sim 6\\times 10^{-3} ({\\rm Mpc...

  20. 新型二维发散波电磁粒子速度计的设计与应用%Design and Application of a Novel Two-dimension Electromagnetic Particle Velocity Gauge under Divergent Wave

    Institute of Scientific and Technical Information of China (English)

    吴祖堂; 李进; 王占江; 张景森; 黄晓飞

    2011-01-01

    发散波作用下粒子速度的二维电磁测试关键技术包括恒定强磁场、动态载荷与磁场同步、交叉干扰项信号消除等.研究并设计了米级尺度的Helmholtz线圈,对Helmholtz线圈施加脉冲电流,获得了持续时间8.26~30.62 ms的恒定磁场平台,峰值波动误差为0.1%~1.0%.设计了新型二维发散波电磁粒子速度计,采用“对称双S型”布局感应线圈,消除干扰项,获取有效的微弱信号.有机玻璃样品中粒子速度的一维和二维电磁测试对比实验结果表明:粒子速度首峰值随爆心距的变化关系、信号时间特性符合物理规律.为有分界面、沟槽或节理的非均匀分层介质中发散波传播规律研究提供了有效的测试手段.%The key techniques of the electromagnetic test of two-dimension particle velocity under divergent waves included the pulse magnetic field with invariable platform, the synchronization between dynamic load and magnetic field and the elimination of the interference signal of down-lead in the two-dimension magnetic field. The characteristic of a Helmholtz coil with a diameter of up to 1.5 meter in the action of pulse current was analyzed and a magnetic field with a platform duration from 8.26 ms to 30.62 ms with a fluctuation from 0. 1% to 1% was gained. A novel two-dimension electromagnetic particle velocity gauge was designed by adopting the symmetrical dual-S type induce coil to eliminate the interference and obtain valid weak signal. The performance was verified through the contrast experiment of electromagnetic measurement of one-dimension and two-dimension particle velocity in PMMA. The time domain characteristic of particle velocity signal and the relation between the first peak value and the scale distance accorded with physics law. It is a more efficient means for the propagation research of divergent wave in inhomogeneous mediums even with interfaces, grooves and joints.

  1. Measurement of the velocity of a quantum object: A role of phase and group velocities

    Science.gov (United States)

    Lapinski, Mikaila; Rostovtsev, Yuri V.

    2017-08-01

    We consider the motion of a quantum particle in a free space. Introducing an explicit measurement procedure for velocity, we demonstrate that the measured velocity is related to the group and phase velocities of the corresponding matter waves. We show that for long distances the measured velocity coincides with the matter wave group velocity. We discuss the possibilities to demonstrate these effects for the optical pulses in coherently driven media or for radiation propagating in waveguides.

  2. HVOF on the Surface Strengthen Treatment to the flow Parts of Hydraulic Turbine

    Institute of Scientific and Technical Information of China (English)

    AI You-zhong; LU Jin-yu; TU Yang-wen; LI Cui-lin

    2004-01-01

    China has the most outstanding and serious problem of silt abrasion on hydraulic turbine, especially in the power station on mainstream of Yellow River and the upriver anabranch of Yangtze River. For many years, in order to find the destruction rules of silt to hydraulic turbine, and study how to slow down the destruction speed of sandiness stream to surface on flow parts of hydraulic turbine, various kinds of new technology, new material, new craftwork have been verified in lab and on spot. It is proved that using high velocity oxygen fuel to strengthen the surface on flow parts of hydraulic turbine can effectively prolong the service life of hydroelectric generating set.

  3. 基于声压—质点速度声强探头的材料吸声系数的测量%Measurements of the absorption coefficients with a combined particle velocity-pressure sound intensity probe

    Institute of Scientific and Technical Information of China (English)

    李凌志; 程攻; 刘英杰; 卢炳武

    2012-01-01

    通过由一个声压换能器和一个质点速度换能器所构成的传感器(p-u声强探头)同时测量材料表面附近的声压和质点振动速度,可直接得到其声学阻抗,进而得到材料的反射因子、吸声系数.本文利用一个p-u探头声强测量系统,在半消声室内测量了三聚氰胺泡沫的吸声系数,分析了声源高度和入射角度、材料样本尺寸和厚度对吸声系数测量的影响,并和阻抗管中测量得到的法向吸声系数进行了对比.最后分析了声阻抗率的幅值和相位误差对吸声系数的影响,推导了它们的误差传递公式.%Using a combined particle velocity-pressure sensor (p-u sound intensity probe), the acoustic impedance of an absorbing materials, and consequently its reflection factor and absorption coefficient, can be determined by simultaneous measurements of sound pressure and particle velocity at a position near the surface of the materials. Using a p-u intensity probe system in a semi-anechoic room, we measured the acoustic impedance of melamine, and analyzed how the source height, incidence angle, the size and thickness of the materials sample affect the measurement, and compared to the normal impedance measured using a standing wave tube. We also analyzed how the amplitude and phase error of the acoustic impedance affect the absorption coefficient, and derived an error propagation formula.

  4. Modification of the ultrasound induced activity by the presence of an electrode in a sono-reactor working at two low frequencies (20 and 40 kHz). Part II: Mapping flow velocities by particle image velocimetry (PIV).

    Science.gov (United States)

    Mandroyan, A; Doche, M L; Hihn, J Y; Viennet, R; Bailly, Y; Simonin, L

    2009-01-01

    Sonoelectrochemical experiments differ from sonochemical ones by the introduction of electrodes in the sonicated reaction vessel. The aim of the study is to characterize the changes in the ultrasonic activity induced by the presence of an electrode located in front of the transducer. The scope of our investigations concerns two low frequency vibration modes: 20 and 40 kHz. For this purpose, two laser visualization techniques have been used. The first part of the study, described in a previous paper (Part I), deals with the laser tomography technique which provides an accurate picture of the reactor active zones, related to numerous cavitation events. The second part of the paper (Part II) will describe the particle image velocimetry (PIV) technique used to measure the velocity vector field in the fluid portion between the horn and the electrode. As for the previous study, two parameters were studied: the electrical power supplied to the transducer and the electrode/transducer distance. The velocity vector fields show a main flow in the reactor axis. This flow seems to correspond to the conical cavitation bubbles structure which is observed on the laser tomography pictures. When an electrode is introduced into the reactor, two additional symmetric transversal flows can be quantified on both sides of the electrode.

  5. Minimum Length - Maximum Velocity

    CERN Document Server

    Panes, Boris

    2011-01-01

    We study a framework where the hypothesis of a minimum length in space-time is complemented with the notion of reference frame invariance. It turns out natural to interpret the action of the obtained reference frame transformations in the context of doubly special relativity. As a consequence of this formalism we find interesting connections between the minimum length properties and the modified velocity-energy relation for ultra-relativistic particles. For example we can predict the ratio between the minimum lengths in space and time using the results from OPERA about superluminal neutrinos.

  6. Experimental study on influence of particle roughness on shear wave velocity of sand%砂土颗粒粗糙度对剪切波速影响的试验研究

    Institute of Scientific and Technical Information of China (English)

    刘瑜; 夏唐代

    2011-01-01

    6 sand samples are made by use of Fujian standard sand, Hangzhou sand and man-made quartz sand, respectively, with each sample composed of the single sand particle in diameter.The average particle roughness of every sample and the shear wave velocities (Vs) of each sample in different porosities are obtained by electron microscope and bender element testing equipment.The analytic results indicate that Vs is greatly influenced by the particle roughness, and the magnitude of Vs decreases with the increase of the particle roughness.The roughness coefficient is introduced to deduce the formula of Vs by means of the researches on micro fabrics and constitutive relations of granular materials, elastic contact of rough particles, etc.Moreover, the results drawn from the present method are compared with the measured data, and the calculating method of the roughness coefficient for low sands is obtained.In addition, the relationship between the roughness coefficient and the stress is discussed.%将福建标准砂、杭州黄砂和人工石英砂制备成6个砂样,每个砂样只由一种粒径的砂颗粒组成,从每个砂样中选取一定数量的颗粒进行电镜扫描并分析砂样的颗粒平均粗糙度,用弯曲元测试仪测试各砂样在不同孔隙比下的剪切波速(Vs).对比分析说明颗粒粗糙度对Vs的影响显著,Vs随着颗粒粗糙度的增大而减小.引入粗糙度修正系数,在散粒体介质细观组构与本构关系、弹性粗糙颗粒接触等研究的基础上推导了砂土Vs计算公式.将计算结果与试验实测值进行对比,得到了浅层砂土的粗糙度修正系数的计算方法,讨论了粗糙度修正系数随应力大小的变化趋势.

  7. Velocity dependant splash behaviour

    Science.gov (United States)

    Hamlett, C. A. E.; Shirtcliffe, N. J.; McHale, G.; Ahn, S.; Doerr, S. H.; Bryant, R.; Newton, M. I.

    2012-04-01

    Extreme soil water repellency can occur in nature via condensation of volatile organic compounds released during wildfires and can lead to increased erosion rate. Such extreme water repellent soil can be classified as superhydrophobic and shares similar chemical and topographical features to specifically designed superhydrophobic surfaces. Previous studies using high speed videography to investigate single droplet impact behaviour on artificial superhydrophobic have revealed three distinct modes of splash behaviour (rebound, pinned and fragmentation) which are dependent on the impact velocity of the droplet. In our studies, using high-speed videography, we show that such splash behaviour can be replicated on fixed 'model' water repellent soils (hydrophobic glass beads/particles). We show that the type of splash behaviour is dependent on both the size and chemical nature of the fixed particles. The particle shape also influences the splash behaviour as shown by drop impact experiments on fixed sand samples. We have also studied soil samples, as collected from the field, which shows that the type of droplet splash behaviour can lead to enhanced soil particle transport.

  8. The Dry Sliding Wear Behavior of HVOF-Sprayed WC: Metal Composite Coatings

    Science.gov (United States)

    Ward, Liam P.; Pilkington, Antony

    2014-09-01

    WC-based cermet coatings containing various metallic binders such as Ni, Co, and Cr are known for their superior tribological properties, particularly abrasion resistance and enhanced surface hardness. Consequently, these systems are considered as replacements for traditional hard chrome coatings in critical aircraft components such as landing gear. The purpose of this investigation was to conduct a comparative study on the dry sliding wear behavior of three WC-based cermet coatings (WC-12Ni, WC-20Cr2C3-7Ni, and WC-10Co-4Cr), when deposited on carbon steel substrates. Ball on disk wear tests were performed on the coatings using a CSEM Tribometer (pin-on-disk) with a 6-mm ruby ball at 20 N applied load, 0.2 m/s sliding velocity, and sliding distances up to 2000 m. Analysis of both the coating wear track and worn ruby ball was performed using optical microscopy and an Alphastep-250 profilometer. The results of the study revealed both wear of the ruby ball and coated disks allowed for a comparison of both the ball wear and coating wear for the systems considered. Generally, the use of Co and Cr as a binder significantly improved the sliding wear resistance of the coating compared to Ni and/or Cr2C3.

  9. Corrosion Testing of Ni Alloy HVOF Coatings in High Temperature Environments for Biomass Applications

    Science.gov (United States)

    Paul, S.; Harvey, M. D. F.

    2013-03-01

    This paper reports the corrosion behavior of Ni alloy coatings deposited by high velocity oxyfuel spraying, and representative boiler substrate alloys in simulated high temperature biomass combustion conditions. Four commercially available oxidation resistant Ni alloy coating materials were selected: NiCrBSiFe, alloy 718, alloy 625, and alloy C-276. These were sprayed onto P91 substrates using a JP5000 spray system. The corrosion performance of the coatings varied when tested at ~525, 625, and 725 °C in K2SO4-KCl mixture and gaseous HCl-H2O-O2 containing environments. Alloy 625, NiCrBSiFe, and alloy 718 coatings performed better than alloy C-276 coating at 725 °C, which had very little corrosion resistance resulting in degradation similar to uncoated P91. Alloy 625 coatings provided good protection from corrosion at 725 °C, with the performance being comparable to wrought alloy 625, with significantly less attack of the substrate than uncoated P91. Alloy 625 performs best of these coating materials, with an overall ranking at 725 °C as follows: alloy 625 > NiCrBSiFe > alloy 718 ≫ alloy C-276. Although alloy C-276 coatings performed poorly in the corrosion test environment at 725 °C, at lower temperatures (i.e., below the eutectic temperature of the salt mixture) it outperformed the other coating types studied.

  10. Effect of Load on Friction-Wear Behavior of HVOF-Sprayed WC-12Co Coatings

    Science.gov (United States)

    Yifu, Jin; Weicheng, Kong; Tianyuan, Sheng; Ruihong, Zhang; Dejun, Kong

    2017-07-01

    A WC-12Co coating was sprayed on AISI H13 hot work mold steel using a high-velocity oxygen fuel. The morphologies, phase compositions, and distributions of chemical elements of the obtained coatings were analyzed using a field emission scanning electron microscope, x-ray diffraction, and energy-dispersive spectroscope (EDS), respectively. The friction-wear behaviors under different loads were investigated using a reciprocating wear tester; the morphologies and distributions of the chemical elements of worn tracks were analyzed using a SEM and its configured EDS, respectively. The results show the reunited grains of WC are held together by the Co binder; the primary phases of the coating are WC, Co, and a small amount of W2C and W, owing to the oxidation and decarburization of WC. Inter-diffusion of Fe and W between the coating and the substrate is shown, which indicates a good coating adhesion. The values of the average coefficient of friction under the loads of 40, 80, and 120 N are 0.29, 0.31, and 0.49, respectively. The WC grains are pulled out of the coating during the sliding wear test, but the coating maintains its integrity, suggesting that the coating is intact and continuously protects the substrate from wearing.

  11. Effect of Shot Peening on Tribological Behaviors of Molybdenum-Thermal Spray Coating using HVOF Method

    Directory of Open Access Journals (Sweden)

    H. Mohassel

    2017-03-01

    Full Text Available We have investigated the influence of post-shot peening on Mo-coating as compared to substrate steel 16MnCr5 (according to ZFN-413 A. Shot peening of carburized steel discs with and without Mo-coating was performed by using Shot size S230, Almen intensity 0.42 mm ’A’ and exposure time 96 sec. Tribological properties were analyzed, using pin-on-disc tribometer apparatus, under dry sliding conditions at different specific applied loads, sliding velocities and distance. Typical standardized methods were used for studying of surface integrity parameters (micro-hardness, topography and surface roughness. Surface morphology of the Mo-coating specimens with and without Shot Peening before and after wear was evaluated by Scanning Electron Microscopy. The results showed that shot peening after Mo-coating has considerable effect on improving wear resistance and because of having low friction coefficient has showed better wear behavior and tribologi cal properties over that of the un-peened Mo-coating.

  12. Fuzzy Logic Particle Tracking

    Science.gov (United States)

    2005-01-01

    A new all-electronic Particle Image Velocimetry technique that can efficiently map high speed gas flows has been developed in-house at the NASA Lewis Research Center. Particle Image Velocimetry is an optical technique for measuring the instantaneous two component velocity field across a planar region of a seeded flow field. A pulsed laser light sheet is used to illuminate the seed particles entrained in the flow field at two instances in time. One or more charged coupled device (CCD) cameras can be used to record the instantaneous positions of particles. Using the time between light sheet pulses and determining either the individual particle displacements or the average displacement of particles over a small subregion of the recorded image enables the calculation of the fluid velocity. Fuzzy logic minimizes the required operator intervention in identifying particles and computing velocity. Using two cameras that have the same view of the illumination plane yields two single exposure image frames. Two competing techniques that yield unambiguous velocity vector direction information have been widely used for reducing the single-exposure, multiple image frame data: (1) cross-correlation and (2) particle tracking. Correlation techniques yield averaged velocity estimates over subregions of the flow, whereas particle tracking techniques give individual particle velocity estimates. For the correlation technique, the correlation peak corresponding to the average displacement of particles across the subregion must be identified. Noise on the images and particle dropout result in misidentification of the true correlation peak. The subsequent velocity vector maps contain spurious vectors where the displacement peaks have been improperly identified. Typically these spurious vectors are replaced by a weighted average of the neighboring vectors, thereby decreasing the independence of the measurements. In this work, fuzzy logic techniques are used to determine the true

  13. Microstructure and Properties of HVOF-Sprayed NiCrAlY Coatings Modified by Rare Earth

    Science.gov (United States)

    Chen, S. F.; Liu, S. Y.; Wang, Y.; Sun, X. G.; Zou, Z. W.; Li, X. W.; Wang, C. H.

    2014-06-01

    Rare earth (RE)-modified NiCrAlY powders were prepared by ultrasonic gas atomization and deposited on stainless steel substrate by high-velocity oxygen fuel spraying. The effects of the RE on the microstructure, properties, and thermal shock resistance of the NiCrAlY coatings were investigated. The results showed that the NiCrAlY powders were refined and distributed uniformly after adding RE, while the number of unmelted particles in the coatings was reduced. Moreover, the RE-modified coatings showed improved microhardness and distribution uniformity. The microhardness of the coating reached a maximum after adding 0.9 wt.% RE, being 34.4 % higher than that of coatings without RE. The adhesive strength increased and reached a maximum after adding 0.6 wt.% RE, being 18.8 % higher than that of coatings without RE. Excessive RE decreased the adhesive strength. The thermal cycle life of NiCrAlY coatings increased drastically with RE addition. The coating with 0.9 wt.% RE showed optimum thermal shock resistance, being 21.2 % higher than that of coatings without RE.

  14. Group Settling Velocity of Non-Cohesive Sediment Mixtures

    Institute of Scientific and Technical Information of China (English)

    WU Hualin; SHEN Huanting; ZHU Jianrong; ZHANG Xiaofeng

    2000-01-01

    Settling velocity is a fundamental parameter in sediment transport dynamics. For uniform par-ticles, there are abundant formulas for calculation of their settling velocities. But in natural fields, sediment consists of non-uniform particles. The interaction among particles is complex and should not be neglected. In this paper, based on the analysis of settling mechanism of non-cohesive and non-uniform particles, a theoretical model to describe settling mechanism is proposed. Besides suspension concentration andupward turbulent flow caused by other particles, collision among particles is another main factor influencing settling velocity. By introducing the collision theory, equations of fall velocity before collision, collision probability, and fall velocity after collision are established. Finally, a formula used to calculate the settling velocity of non-cohesive particles with wide grain gradation is presented, which agrees well with the experimental data.

  15. Kriging interpolating cosmic velocity field

    Science.gov (United States)

    Yu, Yu; Zhang, Jun; Jing, Yipeng; Zhang, Pengjie

    2015-10-01

    Volume-weighted statistics of large-scale peculiar velocity is preferred by peculiar velocity cosmology, since it is free of the uncertainties of galaxy density bias entangled in observed number density-weighted statistics. However, measuring the volume-weighted velocity statistics from galaxy (halo/simulation particle) velocity data is challenging. Therefore, the exploration of velocity assignment methods with well-controlled sampling artifacts is of great importance. For the first time, we apply the Kriging interpolation to obtain the volume-weighted velocity field. Kriging is a minimum variance estimator. It predicts the most likely velocity for each place based on the velocity at other places. We test the performance of Kriging quantified by the E-mode velocity power spectrum from simulations. Dependences on the variogram prior used in Kriging, the number nk of the nearby particles to interpolate, and the density nP of the observed sample are investigated. First, we find that Kriging induces 1% and 3% systematics at k ˜0.1 h Mpc-1 when nP˜6 ×1 0-2(h-1 Mpc )-3 and nP˜6 ×1 0-3(h-1 Mpc )-3 , respectively. The deviation increases for decreasing nP and increasing k . When nP≲6 ×1 0-4(h-1 Mpc )-3 , a smoothing effect dominates small scales, causing significant underestimation of the velocity power spectrum. Second, increasing nk helps to recover small-scale power. However, for nP≲6 ×1 0-4(h-1 Mpc )-3 cases, the recovery is limited. Finally, Kriging is more sensitive to the variogram prior for a lower sample density. The most straightforward application of Kriging on the cosmic velocity field does not show obvious advantages over the nearest-particle method [Y. Zheng, P. Zhang, Y. Jing, W. Lin, and J. Pan, Phys. Rev. D 88, 103510 (2013)] and could not be directly applied to cosmology so far. However, whether potential improvements may be achieved by more delicate versions of Kriging is worth further investigation.

  16. High-Temperature Behavior of a High-Velocity Oxy-Fuel Sprayed Cr3C2-NiCr Coating

    Science.gov (United States)

    Kaur, Manpreet; Singh, Harpreet; Prakash, Satya

    2012-08-01

    High-velocity oxy-fuel (HVOF) sprayed coatings have the potential to enhance the high-temperature oxidation, corrosion, and erosion-corrosion resistance of boiler steels. In the current work, 75 pct chromium carbide-25 pct (nickel-20 pct chromium) [Cr3C2-NiCr] coating was deposited on ASTM SA213-T22 boiler steel using the HVOF thermal spray process. High-temperature oxidation, hot corrosion, and erosion-corrosion behavior of the coated and bare steel was evaluated in the air, molten salt [Na2SO4-82 pct Fe2(SO4)3], and actual boiler environments under cyclic conditions. Weight-change measurements were taken at the end of each cycle. Efforts were made to formulate the kinetics of the oxidation, corrosion, and erosion-corrosion. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM)/energy dispersive spectroscopy (EDS) techniques were used to analyze the oxidation products. The coating was found to be intact and spallation free in all the environments of the study in general, whereas the bare steel suffered extensive spallation and a relatively higher rate of degradation. The coating was found to be useful to enhance the high-temperature resistance of the steel in all the three environments in this study.

  17. Extension of the Child-Langmuir law to a beam of particles having an initial velocity; Extension de la loi de Child-Langmuir a un faisceau de particules anime d'une vitesse dirigee

    Energy Technology Data Exchange (ETDEWEB)

    Geller, R. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1965-07-01

    A DC ion current of 50 mA/cm{sup 2} has been obtained with approximately 100 volts extraction from the plasma created by the CIRCE device, and a still stronger electron current was obtained with a still lower extraction. These results are an order of magnitude higher than the ordinary characteristics. In the neutral plasma beam produced in the CIRCE device, the ions have mainly longitudinal energy whereas the electron energy is transverse. This situation makes the charge separation easier. In the present paper one tries to explain partially the result on a basis of current increase due to the initial velocity of the particles. (author) [French] On a verifie qu'il etait possible d'extraire, en regime continu, du plasma fourni par la machine CIRCE des courants de protons d'environ 50 mA/cm{sup 2} avec des tensions d'extraction d'environ 100 volts et des courants d'electrons d'une intensite encore plus forte avec quelques volts d'extraction. Ces resultats sont d'un ordre de grandeur superieur aux performances des sources classiques. Dans le faisceau neutre produit par CIRCE les ions sont doues d'une energie essentiellement longitudinale alors que l'energie des electrons est surtout transverse. Cette situation est favorable a une separation. Dans le present rapport nous essayons de donner une explication du mecanisme physique d'une partie du phenomene: celle concernant l'accroissement du courant de protons, du a leur vitesse dirigee. (auteur)

  18. Video measurements of fluid velocities and water levels in breaking waves

    CSIR Research Space (South Africa)

    Govender, K

    2002-01-01

    Full Text Available The cost-effective measurement of the velocity flow fields in breaking water waves, using particle and correlation image velocimetry, is described. The fluid velocities are estimated by tracking the motion of neutrally buoyant particles and aeration...

  19. Accurate particle speed prediction by improved particle speed measurement and 3-dimensional particle size and shape characterization technique

    DEFF Research Database (Denmark)

    Cernuschi, Federico; Rothleitner, Christian; Clausen, Sønnik

    2017-01-01

    Accurate particle mass and velocity measurement is needed for interpreting test results in erosion tests of materials and coatings. The impact and damage of a surface is influenced by the kinetic energy of a particle, i.e. particle mass and velocity. Particle mass is usually determined with optic...

  20. The Velocity Distribution of Isolated Radio Pulsars

    CERN Document Server

    Arzoumanian, Z; Cordes, J M

    2002-01-01

    (Abridged) We infer the velocity distribution of radio pulsars by modelling their birth, evolution, and detection in large-scale 0.4 GHz pulsar surveys, and by comparing model distributions of measurable pulsar properties with survey data using a likelihood function. We test models that characterize a population's birth rate, luminosity, shutoff of radio emission, birth locations, and birth velocities. We infer that the radio beam luminosity (i) is comparable to the energy flux of relativistic particles in models for spin-driven magnetospheres, signifying that radio emission losses reach nearly 100% for the oldest pulsars; and (ii) scales approximately as sqrt(Edot) which, in magnetosphere models, is proportional to the voltage drop available for acceleration of particles. We find that a two-component velocity distribution with characteristic velocities of 90 km/s and 500 km/s is greatly preferred to any one-component distribution. We explore some consequences of the preferred birth velocity distribution: (i)...

  1. Effect of Pressure on Minimum Fluidization Velocity

    Institute of Scientific and Technical Information of China (English)

    Zhu Zhiping; Na Yongjie; Lu Qinggang

    2007-01-01

    Minimum fluidization velocity of quartz sand and glass bead under different pressures of 0.5, 1.0, 1.5 and 2.0 Mpa were investigated. The minimum fluidization velocity decreases with the increasing of pressure. The influence of pressure to the minimum fluidization velocities is stronger for larger particles than for smaller ones.Based on the test results and Ergun equation, an experience equation of minimum fluidization velocity is proposed and the calculation results are comparable to other researchers' results.

  2. Velocity anticipation in the optimal velocity model

    Institute of Scientific and Technical Information of China (English)

    DONG Li-yun; WENG Xu-dan; LI Qing-ding

    2009-01-01

    In this paper,the velocity anticipation in the optimal velocity model (OVM) is investigated.The driver adjusts the velocity of his vehicle by the desired headway,which depends on both instantaneous headway and relative velocity.The effect of relative velocity is measured by a sensitivity function.A specific form of the sensitivity function is supposed and the involved parameters are determined by the both numerical simulation and empirical data.It is shown that inclusion of velocity anticipation enhances the stability of traffic flow.Numerical simulations show a good agreement with empirical data.This model provides a better description of real traffic,including the acceleration process from standing states and the deceleration process approaching a stopped car.

  3. Development of wear resistant nanostructured duplex coatings by high velocity oxy-fuel process for use in oil sands industry.

    Science.gov (United States)

    Saha, Gobinda C; Khan, Tahir I; Glenesk, Larry B

    2009-07-01

    Oil sands deposits in Northern Alberta, Canada represent a wealth of resources attracting huge capital investment and significant research focus in recent years. As of 2005, crude oil production from the current oil sands operators accounted for 50% of Canada's domestic production. Alberta's oil sands deposits contain approximately 1.7 trillion barrels of bitumen, of which over 175 billion are recoverable with current technology, and 315 billion barrels are ultimately recoverable with technological advances. A major problem of operating machinery and equipment in the oil sands is the unpredictable failure from operating in this highly aggressive environment. One of the significant causes of that problem is premature material wear. An approach to minimize this wear is the use of protective coatings and, in particular, a cermet thin coating. A high level of coating homogeneity is critical for components such as bucketwheels, draglines, conveyors, shovels, heavyhauler trucks etc. that are subjected to severe degradation through abrasive wear. The identification, development and application of optimum wear solutions for these components pose an ongoing challenge. Nanostructured cermet coatings have shown the best results of achieving the degree of homogeneity required for these applications. In this study, WC-17Co cermet powder with nanocrystalline WC core encapsulated with 'duplex' Co layer was used to obtain a nanostructured coating. To apply this coating, high velocity oxy-fuel (HVOF) thermal spraying technique was used, as it is known for producing wear-resistant coatings superior to those obtained from plasma-based techniques. Mechanical, sliding wear and microstructural behavior of the coating was compared with those of the microstructured coating obtained from spraying WC-10Co-4Cr cermet powder by HVOF technique. Results from the nanostructured coating, among others, showed an average of 25% increase in microhardness, 30% increase in sliding wear resistance and

  4. Microstructure and high temperature cyclic oxidation in atmospheres with variable oxygen contents of plasma and HVOF NiCrBSiFe sprayed coatings; Microestructura y oxidacion ciclica en atmosferas con contenidos de oxigeno variables de un recubrimiento NiCrBSiFe proyectado termicamente por plasma y HVOF

    Energy Technology Data Exchange (ETDEWEB)

    Higuera-Hidalgo, V.; Belzunce-Varela, F. J.; Riba-Lopez, J.

    2006-07-01

    The influence of thermal spraying procedure (plasma and HVOF) on the microstructure, high temperature oxidation resistance and adherence of NiCrSiFe coatings has been examined. Two different series of oxidation tests have been carried out in air (21% oxygen) at 800 and 1,000 degree centigree (1,073 y 1,273 K) and in a simulated gas turbine environment (10% oxygen) representative of a combined-cycle power generation plant, at the same temperatures. Coating microstructure, porosity, oxide content and microhardness are highly dependent on the spraying procedure and coating hardness also significantly decreases after long maintenance at high temperature (1,000 degree centigree). Finally, the oxidation weight gain and the adherence of NiCrBSiFe coatings are also dependent on the morphology of the coating but, nevertheless, the oxidation behaviour of these coatings was very good as protective chromium and silicon oxides were always formed. (Author) 14 refs.

  5. Performance of high-velocity oxy-fuel-sprayed chromium carbide-nickel chromium coating in an actual boiler environment of a thermal power plant

    Energy Technology Data Exchange (ETDEWEB)

    Sidhu, T.S.; Prakash, S.; Agrawal, R.D. [Industrial Technology Institute, Roorkee (India)

    2007-09-15

    The present study aims to evaluate the performance of a high-velocity oxy-fuel (HVOF)-sprayed Cr{sub 3}C{sub 2}-NiCr (chromium carbide-nickel chromium) coating on a nickel-based super-alloy in an actual industrial environment of a coal-fired boiler, with the objective to protect the boiler super-heater and reheater tubes from hot corrosion. The tests were performed in the platen super heater zone of a coal-fired boiler for 1,000 h at 900 degrees C under cyclic conditions. The Cr{sub 3}C{sub 2}-NiCr coating imparted the necessary protection to the nickel-based super alloy in the given environment. The dense and flat splat structure of the coating, and the formation of oxides of chromium and nickel and their spinels, might have protected the substrate super alloy from the inward permeation of corrosive species.

  6. Apparatus for measuring particle properties

    Science.gov (United States)

    Rader, D.J.; Castaneda, J.N.; Grasser, T.W.; Brockmann, J.E.

    1998-08-11

    An apparatus is described for determining particle properties from detected light scattered by the particles. The apparatus uses a light beam with novel intensity characteristics to discriminate between particles that pass through the beam and those that pass through an edge of the beam. The apparatus can also discriminate between light scattered by one particle and light scattered by multiple particles. The particle`s size can be determined from the intensity of the light scattered. The particle`s velocity can be determined from the elapsed time between various intensities of the light scattered. 11 figs.

  7. Velocity Fluctuations in Electrostatically Driven Granular Media

    OpenAIRE

    Aranson, I. S.; Olafsen, J. S.

    2001-01-01

    We study experimentally the particle velocity fluctuations in an electrostatically driven dilute granular gas. The experimentally obtained velocity distribution functions have strong deviations from Maxwellian form in a wide range of parameters. We have found that the tails of the distribution functions are consistent with a stretched exponential law with typical exponents of the order 3/2. Molecular dynamic simulations shows qualitative agreement with experimental data. Our results suggest t...

  8. 非凝聚态粒子对超流临界速度实验值的影响%Effects of uncompensated particles on the experimental values of superfluity's critical velocity

    Institute of Scientific and Technical Information of China (English)

    罗运文

    2012-01-01

    超流关键的物理量就是临界速度,MIT(麻省理工学院)实验组用激光来同扫描凝聚体的方法测出BEC超流体的临界速度,但是与理论值相比小得多.考虑到非凝聚态粒子的影响,发现MIT组测得的实验值并不是临界速度,而是玻色气体获得能量的最小速度,实际临界速度比测得的速度要大.通过修正玻色气体获得能量的速率公式从而得出临界速度与实验测量数据的关系,并发现修正后的临界速度的实验值符合理论值.%The key physical quantity is the critical velocity of superfluity. The MIT group tested the critical velocity of condensate by moving a laser beam through the condensate at different velocities, but its data was much small than the data of theory. In this research, the effect made by the noncondensates was considered, and it was found that the data made by experiments was not the real critical velocity, but the velocity of Bose gas got energy. The real critical velocity was bigger than the experimental data. The relation between critical velocity and experimental data by modifying the formula of energy transfer rate has been found, and it has shown that the modified experimental data agree well with the theory date.

  9. High-velocity clouds

    NARCIS (Netherlands)

    Wakker, BP; vanWoerden, H

    1997-01-01

    High-velocity clouds (HVCs) consist of neutral hydrogen (HI) at velocities incompatible with a simple model of differential galactic rotation; in practice one uses \\v(LSR)\\ greater than or equal to 90 km/s to define HVCs. This review describes the main features of the sky and velocity distributions,

  10. Transverse Spectral Velocity Estimation

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt

    2014-01-01

    A transverse oscillation (TO)-based method for calculating the velocity spectrum for fully transverse flow is described. Current methods yield the mean velocity at one position, whereas the new method reveals the transverse velocity spectrum as a function of time at one spatial location. A convex...

  11. Peculiar velocities in dynamic spacetimes

    CERN Document Server

    Bini, Donato

    2014-01-01

    We investigate the asymptotic behavior of peculiar velocities in certain physically significant time-dependent gravitational fields. Previous studies of the motion of free test particles have focused on the \\emph{collapse scenario}, according to which a double-jet pattern with Lorentz factor $\\gamma \\to \\infty$ develops asymptotically along the direction of complete gravitational collapse. In the present work, we identify a second \\emph{wave scenario}, in which a single-jet pattern with Lorentz factor $\\gamma \\to \\infty$ develops asymptotically along the direction of wave propagation. The possibility of a connection between the two scenarios for the formation of cosmic jets is critically examined.

  12. Minimum length-maximum velocity

    Science.gov (United States)

    Panes, Boris

    2012-03-01

    We study a framework where the hypothesis of a minimum length in space-time is complemented with the notion of reference frame invariance. It turns out natural to interpret the action of the obtained reference frame transformations in the context of doubly special relativity. As a consequence of this formalism we find interesting connections between the minimum length properties and the modified velocity-energy relation for ultra-relativistic particles. For example, we can predict the ratio between the minimum lengths in space and time using the results from OPERA on superluminal neutrinos.

  13. Analysis of particle kinematics in spheronization via particle image velocimetry.

    Science.gov (United States)

    Koester, Martin; Thommes, Markus

    2013-02-01

    Spheronization is a wide spread technique in pellet production for many pharmaceutical applications. Pellets produced by spheronization are characterized by a particularly spherical shape and narrow size distribution. The particle kinematic during spheronization is currently not well-understood. Therefore, particle image velocimetry (PIV) was implemented in the spheronization process to visualize the particle movement and to identify flow patterns, in order to explain the influence of various process parameters. The spheronization process of a common formulation was recorded with a high-speed camera, and the images were processed using particle image velocimetry software. A crosscorrelation approach was chosen to determine the particle velocity at the surface of the pellet bulk. Formulation and process parameters were varied systematically, and their influence on the particle velocity was investigated. The particle stream shows a torus-like shape with a twisted rope-like motion. It is remarkable that the overall particle velocity is approximately 10-fold lower than the tip speed of the friction plate. The velocity of the particle stream can be correlated to the water content of the pellets and the load of the spheronizer, while the rotation speed was not relevant. In conclusion, PIV was successfully applied to the spheronization process, and new insights into the particle velocity were obtained.

  14. The effects of different nano particles of Al2O3 and Ag on the MHD nano fluid flow and heat transfer in a microchannel including slip velocity and temperature jump

    Science.gov (United States)

    Karimipour, Arash; D'Orazio, Annunziata; Shadloo, Mostafa Safdari

    2017-02-01

    The forced convection of nanofluid flow in a long microchannel is studied numerically according to the finite volume approach and by using a developed computer code. Microchannel domain is under the influence of a magnetic field with uniform strength. The hot inlet nanofluid is cooled by the heat exchange with the cold microchannel walls. Different types of nanoparticles such as Al2O3 and Ag are examined while the base fluid is considered as water. Reynolds number are chosen as Re=10 and Re=100. Slip velocity and temperature jump boundary conditions are simulated along the microchannel walls at different values of slip coefficient for different amounts of Hartmann number. The investigation of magnetic field effect on slip velocity and temperature jump of nanofluid is presented for the first time. The results are shown as streamlines and isotherms; moreover the profiles of slip velocity and temperature jump are drawn. It is observed that more slip coefficient corresponds to less Nusselt number and more slip velocity especially at larger Hartmann number. It is recommended to use Al2O3-water nanofluid instead of Ag-water to increase the heat transfer rate from the microchannel walls at low values of Re. However at larger amounts of Re, the nanofluid composed of nanoparticles with higher thermal conductivity works better.

  15. Velocity selective optical pumping

    OpenAIRE

    Aminoff, C. G.; Pinard, M.

    1982-01-01

    We consider optical pumping with a quasi monochromatic tunable light beam, in the low intensity limit where a rate equation regime is obtained The velocity selective optical pumping (V.S.O.P.) introduces a correlation between atomic velocity and internal variables in the ground (or metastable) state. The aim of this article is to evaluate these atomic observables (orientation, alignment, population) as a function of velocity, using a phenomenological description of the relaxation effect of co...

  16. Robot based deposition of WC-Co HVOF coatings on HSS cutting tools as a substitution for solid cemented carbide cutting tools

    Science.gov (United States)

    Tillmann, W.; Schaak, C.; Biermann, D.; Aßmuth, R.; Goeke, S.

    2017-03-01

    Cemented carbide (hard metal) cutting tools are the first choice to machine hard materials or to conduct high performance cutting processes. Main advantages of cemented carbide cutting tools are their high wear resistance (hardness) and good high temperature strength. In contrast, cemented carbide cutting tools are characterized by a low toughness and generate higher production costs, especially due to limited resources. Usually, cemented carbide cutting tools are produced by means of powder metallurgical processes. Compared to conventional manufacturing routes, these processes are more expensive and only a limited number of geometries can be realized. Furthermore, post-processing and preparing the cutting edges in order to achieve high performance tools is often required. In the present paper, an alternative method to substitute solid cemented carbide cutting tools is presented. Cutting tools made of conventional high speed steels (HSS) were coated with thick WC-Co (88/12) layers by means of thermal spraying (HVOF). The challenge is to obtain a dense, homogenous, and near-net-shape coating on the flanks and the cutting edge. For this purpose, different coating strategies were realized using an industrial robot. The coating properties were subsequently investigated. After this initial step, the surfaces of the cutting tools were ground and selected cutting edges were prepared by means of wet abrasive jet machining to achieve a smooth and round micro shape. Machining tests were conducted with these coated, ground and prepared cutting tools. The occurring wear phenomena were analyzed and compared to conventional HSS cutting tools. Overall, the results of the experiments proved that the coating withstands mechanical stresses during machining. In the conducted experiments, the coated cutting tools showed less wear than conventional HSS cutting tools. With respect to the initial wear resistance, additional benefits can be obtained by preparing the cutting edge by means

  17. Comparative study of Cr{sub 3}C{sub 2}-NiCr coatings obtained by HVOF and hard chromium coatings

    Energy Technology Data Exchange (ETDEWEB)

    Guilemany, J.M. [CPT Thermal Spray Centre, Materials Engineering, Dept. Ciencia de Materiales e Ingenieria Metalurgica, Universidad de Barcelona, C/Marti i Franques 1, CP 08028 Barcelona (Spain)]. E-mail: cpt-cmem@ub.edu; Espallargas, N. [CPT Thermal Spray Centre, Materials Engineering, Dept. Ciencia de Materiales e Ingenieria Metalurgica, Universidad de Barcelona, C/Marti i Franques 1, CP 08028 Barcelona (Spain); Suegama, P.H. [CPT Thermal Spray Centre, Materials Engineering, Dept. Ciencia de Materiales e Ingenieria Metalurgica, Universidad de Barcelona, C/Marti i Franques 1, CP 08028 Barcelona (Spain); Dep. Fisico-Quimica, Instituto de Quimica, Universidade Estadual Paulista, UNESP, CP 355, 14801-970 Araraquara, SP (Brazil); Benedetti, A.V. [CPT Thermal Spray Centre, Materials Engineering, Dept. Ciencia de Materiales e Ingenieria Metalurgica, Universidad de Barcelona, C/Marti i Franques 1, CP 08028 Barcelona (Spain) and Dep. Fisico-Quimica, Instituto de Quimica, Universidade Estadual Paulista, UNESP, CP 355, 14801-970 Araraquara, SP (Brazil)]. E-mail: benedeti@iq.unesp.br

    2006-10-15

    In the present work the corrosion resistance of micro-cracked hard chromium and Cr{sub 3}C{sub 2}-NiCr (HVOF) coatings applied on a steel substrate have been compared using open-circuit potential (E {sub OC}) measurements, electrochemical impedance spectroscopy (EIS) and polarization curves. The coatings surfaces and cross-section were characterized before and after corrosion tests using optical microscopy (OM) and scanning electron microscopy (SEM). After 18 h of immersion, the open-circuit potential values were around -0.50 and -0.25 V/(Ag vertical bar AgCl vertical bar KCl{sub sat}) for hard chromium and Cr{sub 3}C{sub 2}-NiCr, respectively. The surface analysis done after 12 h of immersion showed iron on the hard chromium surface inside/near surface cracks, while iron was not detected on the Cr{sub 3}C{sub 2}-NiCr surface even after 18 h. For longer immersion time hard chromium was more degraded than thermal sprayed coating. For hard chromium coating a total resistance values between 50 and 80 k{omega} cm{sup 2} were measured and two well-defined time constants were observed, without significant change with the immersion time. For Cr{sub 3}C{sub 2}-NiCr coating the total impedance diminished from around 750 to 25 k{omega} cm{sup 2} as the immersion time increased from 17 up to 132 h and two overlapped time constants were also observed. Polarization curves recorded after 18 h of immersion showed a lower current and higher corrosion potential for Cr{sub 3}C{sub 2}-NiCr coating than other samples studied.

  18. Microstructure Evolution and Its Effect on the Wear Performance of HVOF-Sprayed Conventional WC-Co Coating

    Science.gov (United States)

    Fu, Dingfa; Xiong, Haoqi; Wang, Qun

    2016-10-01

    In this work, a conventional tungsten carbide 12% cobalt (WC-12Co) coating was deposited by using a liquid fuel JP-8000 high velocity oxyfuel spray system. The properties of the coating namely phase content, microstructure, hardness, porosity, and fracture toughness were examined. The microstructure evolution and its influence on the abrasive wear behavior of the coatings were evaluated in detail by in-situ scanning electron microscopy and a comprehensive model for decarburization of WC has been established using x-ray diffraction and transmission electron microscopy analyses.

  19. High velocity collisions of nanoparticles

    Science.gov (United States)

    Johnson, Donald F.; Mattson, William D.

    2017-01-01

    Nanoparticles (NPs) are a unique class of material with highly functionalizable surfaces and exciting applications. With a large surface-to-volume ratio and potentially high surface tension, shocked nanoparticles might display unique materials behavior. Using density functional theory, we have simulated high-velocity NP collisions under a variety of conditions. NPs composed of diamond-C, cubic-BN, and diamond-Si were considered with particle sizes up to 3.5 nm diameter. Additional simulations involved NPs that were destabilized by incorporating internal strain. The initial spherical NP structures were carved out of bulk crystals while the NPs with internal strain were constructed as a dense core (compressive strain) encompassed by a thin shell (tensile strain). Both on-axis and off-axis collisions were simulated at 10 km/s relative velocity. The amount of internal strain was artificially increased by creating a dense inner core with bond lengths compressed up to 8%. Collision dynamics, shock propagation, and fragmentation will be analyzed, but the simulation are ongoing and results are not finalized. The effect of material properties, internal strain, and collision velocity will be discussed.

  20. Estimation of vector velocity

    DEFF Research Database (Denmark)

    2000-01-01

    Using a pulsed ultrasound field, the two-dimensional velocity vector can be determined with the invention. The method uses a transversally modulated ultrasound field for probing the moving medium under investigation. A modified autocorrelation approach is used in the velocity estimation. The new...

  1. Estimation of vector velocity

    DEFF Research Database (Denmark)

    2000-01-01

    Using a pulsed ultrasound field, the two-dimensional velocity vector can be determined with the invention. The method uses a transversally modulated ultrasound field for probing the moving medium under investigation. A modified autocorrelation approach is used in the velocity estimation. The new...

  2. Velocity distributions in dilute granular systems.

    Science.gov (United States)

    van Zon, J S; MacKintosh, F C

    2005-11-01

    We investigate the idea that velocity distributions in granular gases are determined mainly by eta, the coefficient of restitution and q, which measures the relative importance of heating (or energy input) to collisions. To this end, we study by numerical simulation the properties of inelastic gases as functions of eta, concentration phi, and particle number N with various heating mechanisms. For a wide range of parameters, we find Gaussian velocity distributions for uniform heating and non-Gaussian velocity distributions for boundary heating. Comparison between these results and velocity distributions obtained by other heating mechanisms and for a simple model of a granular gas without spatial degrees of freedom, shows that uniform and boundary heating can be understood as different limits of q, with q>1 and q < or approximately 1 respectively. We review the literature for evidence of the role of q in the recent experiments.

  3. Velocity moments of dark matter haloes

    CERN Document Server

    Wojtak, R; Gottlöber, S; Mamon, G A; Wojtak, Radoslaw; Lokas, Ewa L.; Gottloeber, Stefan; Mamon, Gary A.

    2006-01-01

    Using cosmological N-body simulations we study the line-of-sight velocity distribution of dark matter haloes focusing on the lowest-order even moments, dispersion and kurtosis, and their application to estimate the mass profiles of cosmological structures. For each of the ten massive haloes selected from the simulation box we determine the virial mass, concentration and the anisotropy parameter. In order to emulate observations from each halo we choose randomly 300 particles and project their velocities and positions along the line of sight and on the surface of the sky, respectively. After removing interlopers we calculate the profiles of the line-of-sight velocity moments and fit them with the solutions of the Jeans equations. The estimates of virial mass, concentration parameter and velocity anisotropy obtained in this way are in good agreement with the values found from the full 3D analysis.

  4. Continuous Time Random Walks for the Evolution of Lagrangian Velocities

    CERN Document Server

    Dentz, Marco; Comolli, Alessandro; Borgne, Tanguy Le; Lester, Daniel R

    2016-01-01

    We develop a continuous time random walk (CTRW) approach for the evolution of Lagrangian velocities in steady heterogeneous flows based on a stochastic relaxation process for the streamwise particle velocities. This approach describes persistence of velocities over a characteristic spatial scale, unlike classical random walk methods, which model persistence over a characteristic time scale. We first establish the relation between Eulerian and Lagrangian velocities for both equidistant and isochrone sampling along streamlines, under transient and stationary conditions. Based on this, we develop a space continuous CTRW approach for the spatial and temporal dynamics of Lagrangian velocities. While classical CTRW formulations have non-stationary Lagrangian velocity statistics, the proposed approach quantifies the evolution of the Lagrangian velocity statistics under both stationary and non-stationary conditions. We provide explicit expressions for the Lagrangian velocity statistics, and determine the behaviors of...

  5. Rotational diffusion of particles in turbulence

    CERN Document Server

    Meyer, Colin R

    2013-01-01

    Through laboratory measurements, we compare the rotation of spherical and ellipsoidal particles in homogeneous, isotropic turbulence. We find that the particles' angular velocity statistics are well described by an Ornstein-Uhlenbeck (OU) process. This theoretical model predicts that the Lagrangian autocovariance of particles' angular velocity will decay exponentially. We measure the autocovariance using stereoscopic particle image velocimetry (SPIV) applied to particles whose size is within the inertial subrange of the ambient turbulence. The SPIV resolves the motion of points interior to the particles, from which we calculate the solid body rotation of the particles. This provides us with the angular velocity time series for individual particles. Through ensemble statistics, we determine the autocovariance of angular velocity and confirm that it matches the form predicted by an OU process. We can further use the autocovariance curve to quantify the turbulent rotational diffusivity.

  6. Simultaneous temperature and velocity Lagrangian measurements in turbulent thermal convection

    CERN Document Server

    Liot, O; Zonta, F; Chibbaro, S; Coudarchet, T; Gasteuil, Y; Pinton, J -F; Salort, J; Chillà, F

    2015-01-01

    We report joint Lagrangian velocity and temperature measurements in turbulent thermal convection. Measurements are performed using an improved version (extended autonomy) of the neutrally-buoyant instrumented particle that was used by to performed experiments in a parallelepipedic Rayleigh-Benard cell. The temperature signal is obtained from a RFtransmitter. Simultaneously, we determine particle's position and velocity with one camera, which grants access to the Lagrangian heat flux. Due to the extended autonomy of the present particle, we obtain well converged temperature and velocity statistics, as well as pseudo-eulerian maps of velocity and heat flux. Present experimental results have also been compared with the results obtained by a corresponding campaign of Direct Numerical Simulations and Lagrangian Tracking of massless tracers. The comparison between experimental and numerical results show the accuracy and reliability of our experimental measurements. Finally, the analysis of lagrangian velocity and t...

  7. Attempt to measure the temperature, pressure and particle velocity of pyrocastic surge with penetrator-type gauge. ; Airdropping experiment at Unzen volcano. Penetrator hoshiki ni yoru kasai surge no ondo, atsuryoku, ryushi sokudo sokutei no kokoromi. ; Unzendake ni okeru toka jikken

    Energy Technology Data Exchange (ETDEWEB)

    Taniguchi, H. (Science Education Institute of Osaka Prefecture, Osaka (Japan)); Kamata, K.; Sange, K. (Kobe University, Kobe (Japan). Faculty of Science); Nakada, S. (Kyushu University, Fukuoka (Japan). Faculty of Science); Kamata, H. (Geological Survey of Japan, Osaka Office, Osaka (Japan))

    1992-08-01

    This paper describes development of a penetrator intended of measuring temperatures, pressures, and particle velocities of air blasts and pyroclastic surges occurring in volcanos, and its airdropping experiment. This device forms a spear with a total length of 150 cm to 160 cm disposed with wings at the tail, and a stopper to prevent the spear from penetrating into ground deeper than 60 cm. The device for measuring temperatures suspends metal pieces of 16 kinds in total including such metals as lead and tin, and such alloys as eutectic solders and type lead to enable measuring a temperature range from 100[degree]C to 810[degree]C . The device for measuring pressures consists of a square pipe with a length little shorter than one meter, twisted to 22.5[degree] at three locations, each of the 16 faces made from the twisting being attached with two blast meters (using lead and copper foils, serving also as particle velocity meters). Twelve prototype devices have been dropped (not having been recovered yet) on five points of the east side slope of Mt. Unzen using a helicopter. 5 refs., 3 figs.

  8. Momentum particle swarm optimizer

    Institute of Scientific and Technical Information of China (English)

    Liu Yu; Qin Zheng; Wang Xianghua; He Xingshi

    2005-01-01

    The previous particle swarm optimizers lack direct mechanism to prevent particles beyond predefined search space, which results in invalid solutions in some special cases. A momentum factor is introduced into the original particle swarm optimizer to resolve this problem. Furthermore, in order to accelerate convergence, a new strategy about updating velocities is given. The resulting approach is mromentum-PSO which guarantees that particles are never beyond predefined search space without checking boundary in every iteration. In addition, linearly decreasing wight PSO (LDW-PSO) equipped with a boundary checking strategy is also discussed, which is denoted as LDWBC-PSO. LDW-PSO, LDWBC-PSO and momentum-PSO are compared in optimization on five test functions. The experimental results show that in some special cases LDW-PSO finds invalid solutions and LDWBC-PSO has poor performance, while momentum-PSO not only exhibits good performance but also reduces computational cost for updating velocities.

  9. Significance of relative velocity in drag force or drag power estimation for a tethered float

    Digital Repository Service at National Institute of Oceanography (India)

    Vethamony, P.; Sastry, J.S.

    There is difference in opinion regarding the use of relative velocity instead of particle velocity alone in the estimation of drag force or power. In the present study, a tethered spherical float which undergoes oscillatory motion in regular waves...

  10. Particle Pollution

    Science.gov (United States)

    ... Your Health Particle Pollution Public Health Issues Particle Pollution Recommend on Facebook Tweet Share Compartir Particle pollution ... see them in the air. Where does particle pollution come from? Particle pollution can come from two ...

  11. Extreme Velocity Wind Sensor

    Science.gov (United States)

    Perotti, Jose; Voska, Ned (Technical Monitor)

    2002-01-01

    This presentation provides an overview of the development of new hurricane wind sensor (Extreme Velocity Wind Sensor) for the Kennedy Space Center (KSC) which is designed to withstand winds of up to three hundred miles an hour. The proposed Extreme Velocity Wind Sensor contains no moveable components that would be exposed to extreme wind conditions. Topics covered include: need for new hurricane wind sensor, conceptual design, software applications, computational fluid dynamic simulations of design concept, preliminary performance tests, and project status.

  12. Hot Corrosion Studies of HVOF-Sprayed Coating on T-91 Boiler Tube Steel at Different Operating Temperatures

    Science.gov (United States)

    Bhatia, Rakesh; Singh, Hazoor; Sidhu, Buta Singh

    2013-11-01

    The aim of the present work is to investigate the usefulness of high velocity oxy fuel-sprayed 75% Cr3C2-25% (Ni-20Cr) coating to control hot corrosion of T-91 boiler tube steel at different operating temperatures viz 550, 700, and 850 °C. The deposited coatings on the substrates exhibit nearly uniform, adherent and dense microstructure with porosity less than 2%. Thermogravimetry technique is used to study the high temperature hot corrosion behavior of uncoated and coated samples. The corrosion products of the coating on the substrate are analyzed by using XRD, SEM, and FE-SEM/EDAX to reveal their microstructural and compositional features for the corrosion mechanisms. It is found that the coated specimens have shown minimum weight gain at all the operating temperatures when compared with uncoated T-91 samples. Hence, coating is effective in decreasing the corrosion rate in the given molten salt environment. Oxides and spinels of nickel-chromium may be the reason for successful resistance against hot corrosion.

  13. HVOF Thermal Spray TiC/TiB2 Coatings for AUSC Boiler/Turbine Components for Enhanced Corrosion Protection

    Energy Technology Data Exchange (ETDEWEB)

    Mondal, Kanchan [Southern Illinois Univ., Carbondale, IL (United States). Dept. of Mechanical Engineering and Energy Processes; Koc, Rasit [Southern Illinois Univ., Carbondale, IL (United States). Dept. of Mechanical Engineering and Energy Processes; Fan, Chinbay [Gas Technology Inst., Des Plaines, IL (United States)

    2016-12-07

    The high temperatures of operations still pose significant risk of degradation and fatigue from oxidizing, corroding and eroding environment. In addition to unused O2, water from combustion and SOx from the coal sulfur oxidation that result in highly corrosive environment, acid gases such as HCl and other sulfur compounds may also be present. These adverse effects are further accelerated due to the elevated temperatures. In addition, ash particulates and unburnt carbon and pyritic sulfur can cause erosion of the surface and thus loss of material. Unburnt carbon and pyritic sulfur may also cause localized reduction sites. Thus, fireside corrosion protection and steam oxidation protection alternatives to currently used Ni-Cr overlays need to be identified and evaluated. Titanium carbide (TiC) is a suitable alternative on account of the material features such as the high hardness, the high melting point, the high strength and the low density for the substitution or to be used in conjunction with NiCr for enhancing the fireside corrosion and erosion of the materials. Another alternative is the use of titanium boride as a coating for chemical stability required for long-term service and high erosion resistance over the state-of-the-art, high fracture toughness (K1C ~12 MPam1/2) and excellent corrosion resistance (kp~1.9X10-11 g2/cm4/s at 800°C in air). The overarching aim of the research endeavor was to synthesize oxidation, corrosion and wear resistant TiC and TiB2 coating powders, apply thermal spray coating on existing boiler materials and characterize the coated substrates for corrosion resistance for applications at high temperatures (500 -750 °C) and high pressures (~350 bars) using the HVOF process and to demonstrate the feasibility of these coating to be used in AUSC boilers and turbines.

  14. Fine velocity structures collisional dissipation in plasmas

    Science.gov (United States)

    Pezzi, Oreste; Valentini, Francesco; Veltri, Pierluigi

    2016-04-01

    In a weakly collisional plasma, such as the solar wind, collisions are usually considered far too weak to produce any significant effect on the plasma dynamics [1]. However, the estimation of collisionality is often based on the restrictive assumption that the particle velocity distribution function (VDF) shape is close to Maxwellian [2]. On the other hand, in situ spacecraft measurements in the solar wind [3], as well as kinetic numerical experiments [4], indicate that marked non-Maxwellian features develop in the three-dimensional VDFs, (temperature anisotropies, generation of particle beams, ring-like modulations etc.) as a result of the kinetic turbulent cascade of energy towards short spatial scales. Therefore, since collisional effects are proportional to the velocity gradients of the VDF, the collisionless hypothesis may fail locally in velocity space. Here, the existence of several characteristic times during the collisional relaxation of fine velocity structures is investigated by means of Eulerian numerical simulations of a spatially homogeneous force-free weakly collisional plasma. The effect of smoothing out velocity gradients on the evolution of global quantities, such as temperature and entropy, is discussed, suggesting that plasma collisionality can increase locally due to the velocity space deformation of the particle velocity distribution. In particular, by means of Eulerian simulations of collisional relaxation of a spatially homogeneous force-free plasma, in which collisions among particles of the same species are modeled through the complete Landau operator, we show that the system entropy growth occurs over several time scales, inversely proportional to the steepness of the velocity gradients in the VDF. We report clear evidences that fine velocity structures are dissipated by collisions in a time much shorter than global non-Maxwellian features, like, for example, temperature anisotropies. Moreover we indicate that, if small-scale structures

  15. Viscosity of particle laden films

    Science.gov (United States)

    Timounay, Yousra; Rouyer, Florence

    2017-06-01

    We perform retraction experiments on soap films where large particles bridge the two interfaces. Local velocities are measured by PIV during the unstationnary regime. The velocity variation in time and space can be described by a continuous fluid model from which effective viscosity (shear and dilatational) of particulate films is measured. The 2D effective viscosity of particulate films η2D increases with particle surface fraction ϕ: at low ϕ, it tends to the interfacial dilatational viscosity of the liquid/air interfaces and it diverges at the critical particle surface fraction ϕc ≃ 0.84. Experimental data agree with classical viscosity laws of hard spheres suspensions adapted to the 2D geometry, assuming viscous dissipation resulting from the squeeze of the liquid/air interfaces between the particles. Finally, we show that the observed viscous dissipation in particulate films has to be considered to describe the edge velocity during a retraction experiment at large particle coverage.

  16. Transport of active ellipsoidal particles in ratchet potentials

    Energy Technology Data Exchange (ETDEWEB)

    Ai, Bao-Quan, E-mail: aibq@scnu.edu.cn; Wu, Jian-Chun [Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China)

    2014-03-07

    Rectified transport of active ellipsoidal particles is numerically investigated in a two-dimensional asymmetric potential. The out-of-equilibrium condition for the active particle is an intrinsic property, which can break thermodynamical equilibrium and induce the directed transport. It is found that the perfect sphere particle can facilitate the rectification, while the needlelike particle destroys the directed transport. There exist optimized values of the parameters (the self-propelled velocity, the torque acting on the body) at which the average velocity takes its maximal value. For the ellipsoidal particle with not large asymmetric parameter, the average velocity decreases with increasing the rotational diffusion rate, while for the needlelike particle (very large asymmetric parameter), the average velocity is a peaked function of the rotational diffusion rate. By introducing a finite load, particles with different shapes (or different self-propelled velocities) will move to the opposite directions, which is able to separate particles of different shapes (or different self-propelled velocities)

  17. Influence of powder and spray parameters on erosion and corrosion properties of HVOF sprayed WC-Co-Cr coatings

    Energy Technology Data Exchange (ETDEWEB)

    Berget, John

    1998-07-01

    Thermal spraying is a generic term including various processes used to deposit coatings on surfaces. The coating material is in the form of powder or a wire and is melted or softened by means of a heat source. A gas stream accelerates the material towards a prepared surface and deposits it there to form the coating. Examples of components being maintained by application of thermal spray coatings are gate valves and ball valves for the offshore industry and turbine blades in power generations installations. Recent investigation has shown that the commonly used coating material WC-Co is not corrosion resistant. But it can be improved by the addition of Cr. The main objective of this thesis is to study the influence of spray process control variables and powder characteristics on the erosion and erosion-corrosion properties of the coatings. Spray process variables investigated include energy input, powder feed rate and spray distance. Powder characteristics studied are average size of the WC particles, relative proportions of Co and Cr in the metal phase and powder grain size distribution.

  18. Velocity Segregation and Systematic Biases In Velocity Dispersion Estimates with the SPT-GMOS Spectroscopic Survey

    Science.gov (United States)

    Bayliss, Matthew. B.; Zengo, Kyle; Ruel, Jonathan; Benson, Bradford A.; Bleem, Lindsey E.; Bocquet, Sebastian; Bulbul, Esra; Brodwin, Mark; Capasso, Raffaella; Chiu, I.-non; McDonald, Michael; Rapetti, David; Saro, Alex; Stalder, Brian; Stark, Antony A.; Strazzullo, Veronica; Stubbs, Christopher W.; Zenteno, Alfredo

    2017-03-01

    The velocity distribution of galaxies in clusters is not universal; rather, galaxies are segregated according to their spectral type and relative luminosity. We examine the velocity distributions of different populations of galaxies within 89 Sunyaev Zel’dovich (SZ) selected galaxy clusters spanning 0.28population. We find good agreement with simulations regarding the shape of the relationship between the measured velocity dispersion and the fraction of passive versus star-forming galaxies used to measure it, but we find a small offset between this relationship as measured in data and simulations, which suggests that our dispersions are systematically low by as much as 3% relative to simulations. We argue that this offset could be interpreted as a measurement of the effective velocity bias that describes the ratio of our observed velocity dispersions and the intrinsic velocity dispersion of dark matter particles in a published simulation result. Measuring velocity bias in this way suggests that large spectroscopic surveys can improve dispersion-based mass-observable scaling relations for cosmology even in the face of velocity biases, by quantifying and ultimately calibrating them out.

  19. 粒径和流速对大肠杆菌在饱和多孔介质中迁移的影响%Effects of particle size and pore water velocity on transport of Escherichia coli in saturated porous media

    Institute of Scientific and Technical Information of China (English)

    姚舜译; 袁雪梅; 杨新瑶; 邓仕槐

    2016-01-01

    采用室内柱迁移实验,研究了在不同离子强度下多孔介质粒径和孔隙水流速对大肠杆菌在饱和石英砂柱中沉积与释放行为的影响。结果表明,介质粒径和孔隙水流速均能影响大肠杆菌在石英砂中的迁移过程。介质粒径的减小可增强大肠杆菌在多孔介质中的筛滤效应,增加其沉积率和滞留率,减小水化学扰动引起的释放效应;流速的降低有利于提高大肠杆菌的沉积率和滞留率。离子强度的高低可改变粒径和流速对大肠杆菌迁移影响的大小,在较高离子强度条件下,减小介质粒径和孔隙水流速对提高大肠杆菌的沉积率和滞留率的作用增强。由于自然环境的复杂性,今后的研究应注重真实地下水环境中多因素对大肠杆菌迁移行为的复合影响,以便更加准确地掌握大肠杆菌在多孔介质中迁移的规律。%The transport of pathogenic microbes in porous media is critical to groundwater quality. This study investigated the combined ef-fects of particle size and pore water velocity on the deposition and release behavior of Escherichia coli(E. coli)in saturated quartz sands at different ionic strengths. Results showed that both particle size and pore water velocity affected the transport of E. coli in porous media. De-creasing particle size increased straining effect, deposition and thus retention rates of E. coli. Moreover, the enhanced straining effect result-ed in lower releases of E. coli from the smaller particles. Reducing pore water velocity tended to increase deposition and retention rates of E. coli. At greater ionic strength, decreases in both particle size and pore water velocity further enhanced deposition and retention rates of E. coli. These results would improve our understanding of releases and transport of biocolloids under transient ionic strength.

  20. Velocities in Solar Pores

    Science.gov (United States)

    Balasubramaniam, K. S.; Keil, S. L.; Smaldone, L. A.

    1996-05-01

    We investigate the three dimensional structure of solar pores and their surroundings using high spatial and spectral resolution data. We present evidence that surface velocities decrease around pores with a corresponding increase in the line-of-sight (LOS) velocities. LOS velocities in pores increase with the strength of the magnetic field. Surface velocities show convergence toward a weak downflow which appear to trace boundaries resembling meso-granular and super granular flows. The observed magnetic fields in the pores appear near these boundaries. We analyze the vertical velocity structure in pores and show that they generally have downflows decreasing exponentially with height, with a scale height of about 90 km. Evidence is also presented for the expanding nature of flux tubes. Finally we describe a phenomenological model for pores. This work was supported by AFOSR Task 2311G3. LAS was partially supported by the Progetto Nazionale Astrofisica e Fisica Cosmica of MURST and Scambi Internazionali of the Universita degli Studi di Napoli Frederico II. National Solar Observatory, NOAO, is operated for the National Science Foundation by AURA, Inc.

  1. Analysis on Velocity Characteristics of Cavitation Flow Around Hydrofoil

    Institute of Scientific and Technical Information of China (English)

    LI Xiang-bin; LIU Shu-yan; WANG Guo-yu; ZHANG Bo; ZHANG Min-di

    2010-01-01

    The time-averaged velocity distributions in flows around a hydronautics hydrofoil were measured by using a digit-al particle image velocimeter (DPIV) system. The results show that the velocity distribution in the whole flow field depends on the development of cavitation structures with the decreasing of cavitation number. The high-fluctuation region with lower velocity relates to the cavitation area. The lowest velocity distribution in the cavity core becomes more uniform, and its in-fluence becomes smaller gradually as moving to downstream. The main-stream velocity distribution is even, then fluctuate and even at last. In the supercavitation stage, the fluid velocity in the cavitation region, corresponding to the front of the hydrofoil's suction surface, has a distribution close to the main stream, while the fluid velocity in other cavitation area is lower.

  2. Velocity Segregation and Systematic Biases In Velocity Dispersion Estimates With the SPT-GMOS Spectroscopic Survey

    Energy Technology Data Exchange (ETDEWEB)

    Bayliss, Matthew.B. [MIT, MKI; Zengo, Kyle [Colby Coll.; Ruel, Jonathan [Harvard U., Phys. Dept.; Benson, Bradford A. [Fermilab; Bleem, Lindsey E. [Argonne; Bocquet, Sebastian [Argonne; Bulbul, Esra [MIT, MKI; Brodwin, Mark [Missouri U., Kansas City; Capasso, Raffaella [Munich, Tech. U., Universe; Chiu, I-non [Taiwan, Natl. Tsing Hua U.; McDonald, Michael [MIT, MKI; Rapetti, David [NASA, Ames; Saro, Alex [Munich, Tech. U., Universe; Stalder, Brian [Inst. Astron., Honolulu; Stark, Antony A. [Harvard-Smithsonian Ctr. Astrophys.; Strazzullo, Veronica [Munich, Tech. U., Universe; Stubbs, Christopher W. [Harvard-Smithsonian Ctr. Astrophys.; Zenteno, Alfredo [Cerro-Tololo InterAmerican Obs.

    2016-12-08

    The velocity distribution of galaxies in clusters is not universal; rather, galaxies are segregated according to their spectral type and relative luminosity. We examine the velocity distributions of different populations of galaxies within 89 Sunyaev Zel'dovich (SZ) selected galaxy clusters spanning $ 0.28 < z < 1.08$. Our sample is primarily draw from the SPT-GMOS spectroscopic survey, supplemented by additional published spectroscopy, resulting in a final spectroscopic sample of 4148 galaxy spectra---2868 cluster members. The velocity dispersion of star-forming cluster galaxies is $17\\pm4$% greater than that of passive cluster galaxies, and the velocity dispersion of bright ($m < m^{*}-0.5$) cluster galaxies is $11\\pm4$% lower than the velocity dispersion of our total member population. We find good agreement with simulations regarding the shape of the relationship between the measured velocity dispersion and the fraction of passive vs. star-forming galaxies used to measure it, but we find a small offset between this relationship as measured in data and simulations in which suggests that our dispersions are systematically low by as much as 3\\% relative to simulations. We argue that this offset could be interpreted as a measurement of the effective velocity bias that describes the ratio of our observed velocity dispersions and the intrinsic velocity dispersion of dark matter particles in a published simulation result. Measuring velocity bias in this way suggests that large spectroscopic surveys can improve dispersion-based mass-observable scaling relations for cosmology even in the face of velocity biases, by quantifying and ultimately calibrating them out.

  3. Quantitative velocity modulation spectroscopy

    Science.gov (United States)

    Hodges, James N.; McCall, Benjamin J.

    2016-05-01

    Velocity Modulation Spectroscopy (VMS) is arguably the most important development in the 20th century for spectroscopic study of molecular ions. For decades, interpretation of VMS lineshapes has presented challenges due to the intrinsic covariance of fit parameters including velocity modulation amplitude, linewidth, and intensity. This limitation has stifled the growth of this technique into the quantitative realm. In this work, we show that subtle changes in the lineshape can be used to help address this complexity. This allows for determination of the linewidth, intensity relative to other transitions, velocity modulation amplitude, and electric field strength in the positive column of a glow discharge. Additionally, we explain the large homogeneous component of the linewidth that has been previously described. Using this component, the ion mobility can be determined.

  4. Experimental Studies of the Effect of Wall Roughness on Particle Behavior in Gas-Particle Flows

    Institute of Scientific and Technical Information of China (English)

    周力行; 张夏

    2004-01-01

    The effect of wall roughness on particle behavior in two-phase flows in a horizontal backward-facing step is studied using a phase-Doppler particle anemometer. The results show that the wall roughness widens the particle velocity probability density distribution, enhances the redistribution of particle velocity into different directions,reduces the particle longitudinal mean velocity and increases the longitudinal and transverse fluctuation velocities and Reynolds shear stress. The effect of roughness on particle motion in the recirculation zone is weaker than that in the fully developed flow region. The effect of roughness for small particles is restricted only in the near-wall region, while that for large particle diffuses to the whole flow field.

  5. Avaliação de tensões residuais pelo método de difração de raios-X em revestimentos de inconel 625 obtidos por HVOF

    OpenAIRE

    Mariana Sgambaro de Lorenzi

    2015-01-01

    A aspersão térmica por chama hipersônica tem se destacado pelo método rápido e eficiente para aplicação de revestimentos com grandes vantagens como: tempo, custo e qualidade. Os revestimentos de Inconel 625 apresentam uma série de aplicações industriais principalmente nos segmentos industriais: químico e petroquímico. Neste contexto, o presente trabalho tem por objetivo avaliar as tensões residuais em revestimentos de Inconel 625 obtidos por aspersão térmica de chama hipersônica (HVOF) atravé...

  6. The Prescribed Velocity Method

    DEFF Research Database (Denmark)

    Nielsen, Peter Vilhelm

    The- velocity level in a room ventilated by jet ventilation is strongly influenced by the supply conditions. The momentum flow in the supply jets controls the air movement in the room and, therefore, it is very important that the inlet conditions and the numerical method can generate a satisfactory...... description of this momentum flow. The Prescribed Velocity Method is a practical method for the description of an Air Terminal Device which will save grid points close to the opening and ensure the right level of the momentum flow....

  7. Cirrus Crystal Terminal Velocities.

    Science.gov (United States)

    Heymsfield, Andrew J.; Iaquinta, Jean

    2000-04-01

    Cirrus crystal terminal velocities are of primary importance in determining the rate of transport of condensate from upper- to middle-tropospheric levels and profoundly influence the earth's radiation balance through their effect on the rate of buildup or decay of cirrus clouds. In this study, laboratory and field-based cirrus crystal drag coefficient data, as well as analytical descriptions of cirrus crystal shapes, are used to derive more physically based expressions for the velocities of cirrus crystals than have been available in the past.Polycrystals-often bullet rosettes-are shown to be the dominant crystal types in synoptically generated cirrus, with columns present in varying but relatively large percentages, depending on the cloud. The two critical parameters needed to calculate terminal velocity are the drag coefficient and the ratio of mass to cross-sectional area normal to their fall direction. Using measurements and calculations, it is shown that drag coefficients from theory and laboratory studies are applicable to crystals of the types found in cirrus. The ratio of the mass to area, which is shown to be relatively independent of the number of bullets in the rosette, is derived from an analytic model that represents bullet rosettes containing one to eight bullets in 19 primary geometric configurations. The ratio is also derived for columns. Using this information, a general set of equations is developed to calculate the terminal velocities and masses in terms of the aspect ratio (width divided by length), ice density, and rosette maximum dimension. Simple expressions for terminal velocity and mass as a function of bullet rosette maximum dimension are developed by incorporating new information on bullet aspect ratios.The general terminal velocity and mass relations are then applied to a case from the First International Satellite Cloud Climatology Project (ISCCP) Research Experiment (FIRE) 2, when size spectra from a balloon-borne ice crystal

  8. Critical Landau velocity in helium nanodroplets.

    Science.gov (United States)

    Brauer, Nils B; Smolarek, Szymon; Loginov, Evgeniy; Mateo, David; Hernando, Alberto; Pi, Marti; Barranco, Manuel; Buma, Wybren J; Drabbels, Marcel

    2013-10-11

    The best-known property of superfluid helium is the vanishing viscosity that objects experience while moving through the liquid with speeds below the so-called critical Landau velocity. This critical velocity is generally considered a macroscopic property as it is related to the collective excitations of the helium atoms in the liquid. In the present work we determine to what extent this concept can still be applied to nanometer-scale, finite size helium systems. To this end, atoms and molecules embedded in helium nanodroplets of various sizes are accelerated out of the droplets by means of optical excitation, and the speed distributions of the ejected particles are determined. The measurements reveal the existence of a critical velocity in these systems, even for nanodroplets consisting of only a thousand helium atoms. Accompanying theoretical simulations based on a time-dependent density functional description of the helium confirm and further elucidate this experimental finding.

  9. Discrete particle simulation of the homogeneous fluidization of Geldart A particles

    OpenAIRE

    Ye, M.; Hoef, van der, M.A.; J.A.M. Kuipers

    2004-01-01

    The homogeneous fluidization of Geldart A particles has been studied with a 2D soft-sphere discrete particle model. We find that the homogeneous fluidization regime represents a quasi-equilibrium state where the force balance exists at the macroscopic-level, but not at the level of individual particles. The velocity fluctuation of particles is an exponential function of the squared superficial gas velocity in the homogeneous fluidization regime, not a linear function as found by Cody et al.

  10. Lagrangian multi-particle statistics

    DEFF Research Database (Denmark)

    Lüthi, Beat; Berg, Jacob; Ott, Søren

    2007-01-01

    Combined measurements of the Lagrangian evolution of particle constellations and the coarse-grained velocity derivative tensor. partial derivative(u) over tilde (i) /partial derivative x(j) are presented. The data are obtained from three-dimensional particle tracking measurements in a quasi isotr...

  11. Saltation and suspension of wind-blown particle movement

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Several factors that affect the trajectories of sand particles in a wind-blown sand flux are analyzed by considering the stochastic movement of sand particles transported within turbulent flow in the atmospheric boundary layer. The results show that there are remarkably different trajectories for particles with the same diameter, the same vertical liftoff velocity from sand bed and the same friction ve-locity of wind because of the presence of turbulence flow. The vertical fluctuating velocity of sand particles can be regarded as a reflection of the transport mode, which is related to not only the diameters and liftoff velocity of sand particles but also the shear stress velocity of wind. The critical liftoff velocity and the fraction of each transport mode are calculated for the given particle diameter and friction ve-locity of wind. A comparison of the predicted fraction and the statistical fraction with and without the wind-sand couple effect is made.

  12. Calculations of the cosmic ray modulation in interplanetary space taking into account the possible dependence of the transport travel for the scattering of the particles and of the velocity of the solar winds on the angles they make with the helioequator plane: The case of isotropic diffusion

    Science.gov (United States)

    Dorman, L. I.; Kobilinski, Z.

    1975-01-01

    The modulation of galactic cosmic rays is studied by the magnetic heterogeneities stream on the assumption that the diffusion coefficient is reduced whereas the solar wind velocity is increased with the growth of the angle between the sun's rotation axis and the direction of solar plasma motion. The stationary plane problem of isotropic diffusion is solved as it applies to two cases: (1) with due account of particle retardation by the antiphermium mechanism; and (2) without an account of the above mechanism. This problem is solved by the grid method in the polar coordinate system. The results of the calculations are followed by a discussion of the method of solution and of the errors.

  13. Note: A helical velocity selector for continuous molecular beams.

    Science.gov (United States)

    Szewc, Carola; Collier, James D; Ulbricht, Hendrik

    2010-10-01

    We report on a modern realization of the classic helical velocity selector for gas phase particle beams. The device operates stably under high vacuum conditions at rotational frequencies limited only by commercial dc motor capabilities. Tuning the rotational frequency allows selective scanning over a broad velocity band. The width of the selected velocity distributions at full-width-half-maximum is as narrow as a few percent of the selected mean velocity and independent of the rotational speed of the selector. The selector generates low vibrational noise amplitudes comparable to mechanically damped state-of-the-art turbo-molecular pumps and is therefore compatible with vibration sensitive experiments like molecule interferometry.

  14. Modeling Terminal Velocity

    Science.gov (United States)

    Brand, Neal; Quintanilla, John A.

    2013-01-01

    Using a simultaneously falling softball as a stopwatch, the terminal velocity of a whiffle ball can be obtained to surprisingly high accuracy with only common household equipment. This classroom activity engages students in an apparently daunting task that nevertheless is tractable, using a simple model and mathematical techniques at their…

  15. Influence of high velocity oxy-fuel parameters on properties of nanostructured TiO2 coatings

    Indian Academy of Sciences (India)

    Maryamossadat Bozorgtabar; Mehdi Salehi; Mohammadreza Rahimipour; Mohammadreza Jafarpour

    2010-12-01

    A liquid fuel high velocity oxy-fuel (HVOF) thermal spray process has been used to deposit TiO2 nanostructured coatings utilizing a commercially available nanopowder as the feedstock. The coatings were characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. Photocatalytic activity was evaluated as a rate constant of decomposition reaction of methylene blue (MB) determined from the changes of relative concentration of MB with UV irradiation time. The results indicate that the sprayed TiO2 coatings were composed of both TiO2 phases viz. anatase and rutile, with different phase contents and crystallite sizes. A high anatase content of 80% by volume was achieved at 0.00015, fuel-to-oxygen ratio with nanostructure coating by grain size smaller than feedstock powder. Photocatalytic activity evaluation results indicated that all the TiO2 coatings are effective to degradation MB under UV radiation and their activities differ in different spray conditions. It is found that fuel flow rate strongly influenced on phase transformation of anatase to rutile and by optimizing the rate which can promote structural transformation and grain coarsening in coating and improving photocatalytic activity.

  16. Oxidation behavior of Fe40Al-xWC composite coatings obtained by high-velocity oxygen fuel thermal spray

    Institute of Scientific and Technical Information of China (English)

    XIANG Jun-huai; ZHU Xing-he; CHEN Gang; DUAN Zhi; LIN Yan; LIU Ying

    2009-01-01

    The Fe40Al-xWC (x=0,10,12,15) coatings with dense structure were successfully deposited by high-velocity oxygen fuel (HVOF) spraying of a mixture of Fe,Al and WC powders.The objective of the present work is to provide insight into the oxidation behavior of the as-deposited coatings at 650 ℃ under 0.1 Mpa flowing pure O_2.The present results show differences in the oxidation behavior of Fe40Al coating and Fe40Al-xWC composite coatings.The irregular Fe_2O_3 layer is seen on the top surface of the composite coatings.Fe40Al coating and Fe40Al-15WC composite coating both suffer a catastrophic corrosion due to the formation of a porous structure during 24 h of oxidation.However,Fe40Al-10WC and Fe40Al-12WC composite coatings show a good oxidation resistance behavior due to their dense structure.

  17. Hot corrosion resistance of high-velocity oxyfuel sprayed coatings on a nickel-base superalloy in molten salt environment

    Science.gov (United States)

    Sidhu, T. S.; Prakash, S.; Agrawal, R. D.

    2006-09-01

    No alloy is immune to hot corrosion attack indefinitely. Coatings can extend the lives of substrate materials used at higher temperatures in corrosive environments by forming protective oxides layers that are reasonably effective for long-term applications. This article is concerned with studying the performance of high-velocity oxyfuel (HVOF) sprayed NiCrBSi, Cr3C2-NiCr, Ni-20Cr, and Stellite-6 coatings on a nickel-base superalloy at 900 °C in the molten salt (Na2SO4-60% V2O5) environment under cyclic oxidation conditions. The thermogravimetric technique was used to establish kinetics of corrosion. Optical microscope, x-ray diffraction, scanning electron microscopy/electron dispersive analysis by x-ray (SEM/EDAX), and electron probe microanalysis (EPMA) techniques were used to characterize the as-sprayed coatings and corrosion products. The bare superalloy suffered somewhat accelerated corrosion in the given environmental conditions. whereas hot corrosion resistance of all the coated superalloys was found to be better. Among the coating studied, Ni-20Cr coated superalloy imparted maximum hot corrosion resistance, whereas Stellite-6 coated indicated minimum resistance. The hot corrosion resistance of all the coatings may be attributed to the formation of oxides and spinels of nickel, chromium, or cobalt.

  18. Rotational Diffusion of Particles in Turbulence

    Science.gov (United States)

    Variano, Evan; Meyer, Colin; Byron, Margaret

    2011-11-01

    We experimentally compare the rotation of spherical and ellipsoidal particles in homogeneous, isotropic turbulence. We find that the particle orientation is well described by a Gaussian diffusion process. This theoretical model would predict that the Lagrangian autocorrelation function for angular velocity is a negative exponential. We measure this Lagrangian autocorrelation function using stereoscopic particle image velocimetry (SPIV) applied to particles whose size is within the inertial subrange of the ambient turbulence. The SPIV resolves 3 velocity components in a nearly 2-dimensional planar volume, which we use as inputs for a nonlinear optimization to quantify the solid body rotation of the particles. This provides us the angular velocity timeseries for individual particles. Through ensemble statistics, we determine the Lagrangian autocorrelation function of angular velocity, from which we can quantify the turbulent rotational diffusivity and its behavior between the extremes of short-term non-Fickian transport and long-term Fickian diffusion.

  19. An Extended Particle Swarm Optimizer

    Institute of Scientific and Technical Information of China (English)

    XU Jun-jie; XIN Zhan-hong

    2005-01-01

    An Extended Particle Swarm Optimizer (EPSO) is proposed in this paper. In this new algorithm, not only the local but also the global best position will impact the particle's velocity updating process. EPSO is an integration of Local Best paradigm (LBEST) and Global Best paradigm (GBEST) and it significantly enhances the performance of the conventional particle swarm optimizers. The experiment results have proved that EPSO deserves to be investigated.

  20. Thermophoresis of charged colloidal particles.

    Science.gov (United States)

    Fayolle, Sébastien; Bickel, Thomas; Würger, Alois

    2008-04-01

    Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients. The results are discussed in view of previous work and available experimental data.

  1. Thermophoresis of charged colloidal particles

    OpenAIRE

    Fayolle, Sébastien; Bickel, Thomas; Würger, Alois

    2008-01-01

    International audience; Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients. The results are discussed in view of previous work and available experimental data.

  2. Performance of high-velocity oxyfuel-sprayed coatings on an Fe-based superalloy in Na2SO4-60%V2O5 environment at 900 °C part II: Hot corrosion behavior of the coatings

    Science.gov (United States)

    Sidhu, T. S.; Prakash, S.; Agrawal, R. D.

    2006-02-01

    NiCrBSi, Cr3C2-NiCr, Ni-20Cr, and Stellite-6 coatings were deposited on an Fe-based superalloy by the high-velocity oxyfuel (HVOF) thermal spray process. The hot corrosion behavior of the coatings in an aggressive environment of Na2SO4-60%V2O5 at 900 °C under cyclic conditions was studied. The thermogravimetric technique was used to establish the kinetics of corrosion. X-ray diffraction, scanning electron microscopy/energy-dispersive x-ray and electron probe microanalysis techniques were used to analyze the corrosion products. Hot corrosion resistances of all the coatings were found to be better than the uncoated superalloy. The Ni-20Cr coating was found to be the most protective, followed by Cr3C2-NiCr coatings. The Ni-20Cr coating had reduced the mass gain by 90% of that gained by the uncoated superalloy. The hot corrosion resistance shown by the Cr3C2-NiCr coating was slightly better compared with the NiCrBSi coating; however, both of the coatings performed better than the Stellite-6 coating. The Stellite-6 coating was the least effective among the coatings studied, but it was still successful in decreasing the mass gain to about one fourth compared with the uncoated superalloy. The formation of oxides and spinels of nickel, chromium, or cobalt may be contributing to the development of hot corrosion resistance in the coatings. This article focuses on the hot corrosion behavior of HVOF coatings. The characterization of these coatings has been presented in part I included in this issue.

  3. Wave propagation and group velocity

    CERN Document Server

    Brillouin, Léon

    1960-01-01

    Wave Propagation and Group Velocity contains papers on group velocity which were published during the First World War and are missing in many libraries. It introduces three different definitions of velocities: the group velocity of Lord Rayleigh, the signal velocity of Sommerfeld, and the velocity of energy transfer, which yields the rate of energy flow through a continuous wave and is strongly related to the characteristic impedance. These three velocities are identical for nonabsorbing media, but they differ considerably in an absorption band. Some examples are discussed in the last chapter

  4. Fall velocity of multi-shaped clasts

    Science.gov (United States)

    Le Roux, Jacobus P.

    2014-12-01

    Accurate settling velocity predictions of differently shaped micro- or macroclasts are required in many branches of science and engineering. Here, a single, dimensionally correct equation is presented that yields a significant improvement on previous settling formulas for a wide range of clast shapes. For smooth or irregular clasts with known axial dimensions, a partially polynomial equation based on the logarithmic values of dimensionless sizes and settling velocities is presented, in which the values of only one coefficient and one exponent need to be adapted for different shapes, irrespective of the Reynolds number. For irregular, natural clasts with unknown axial dimensions, a polynomial equation of the same form is applied, but with different coefficients. Comparison of the predicted and measured settling velocities of 8 different shape classes as well as natural grains with unknown axial dimensions in liquids, representing a total of 390 experimental data points, shows a mean percentage error of - 0.83% and a combined R2 value of 0.998. The settling data of 169 differently shaped particles of pumice, glass and feldspar falling in air were also analyzed, which demonstrates that the proposed equation is also valid for these conditions. Two additional shape classes were identified in the latter data set, although the resultant equations are less accurate than for liquids. An Excel spreadsheet is provided to facilitate the calculation of fall velocities for grains settling individually and in groups, or alternatively to determine the equivalent sieve size from the settling velocity, which can be used to calibrate settling tubes.

  5. Limitations of estimating turbulent convection velocities from PIV

    CERN Document Server

    de Kat, Roeland; Dawson, James R; Ganapathisubramani, Bharathram

    2013-01-01

    This paper deals with determination of turbulent convection velocities from particle image velocimetry (PIV). Turbulent convection velocities are of interest because they can be used to map temporal information into space. Convection velocity can be defined in several different ways. One approach is to use the phase-spectrum of two signals with a time-separation. Obtaining convection velocity per wavenumber involves determining a spatial spectrum. PIV data is limited in spatial resolution and sample length. The influence of truncation of both spatial resolution and frequency resolution is investigated, as well as the influences of spatial filtering and measurement noise. These issues are investigated by using a synthetic data set obtained by creating velocity-time data with an imposed spectrum. Results from the validation show that, when applying a Hamming window before determining the phase spectrum, there is a usable range of wavenumbers for which convection velocities can be determined. Simulation of flow ...

  6. Radial Velocities with PARAS

    Science.gov (United States)

    Roy, Arpita; Mahadevan, S.; Chakraborty, A.; Pathan, F. M.; Anandarao, B. G.

    2010-01-01

    The Physical Research Laboratory Advanced Radial-velocity All-sky Search (PARAS) is an efficient fiber-fed cross-dispersed high-resolution echelle spectrograph that will see first light in early 2010. This instrument is being built at the Physical Research laboratory (PRL) and will be attached to the 1.2m telescope at Gurushikhar Observatory at Mt. Abu, India. PARAS has a single-shot wavelength coverage of 370nm to 850nm at a spectral resolution of R 70000 and will be housed in a vacuum chamber (at 1x10-2 mbar pressure) in a highly temperature controlled environment. This renders the spectrograph extremely suitable for exoplanet searches with high velocity precision using the simultaneous Thorium-Argon wavelength calibration method. We are in the process of developing an automated data analysis pipeline for echelle data reduction and precise radial velocity extraction based on the REDUCE package of Piskunov & Valenti (2002), which is especially careful in dealing with CCD defects, extraneous noise, and cosmic ray spikes. Here we discuss the current status of the PARAS project and details and tests of the data analysis procedure, as well as results from ongoing PARAS commissioning activities.

  7. The effect of post-treatment of a high-velocity oxy-fuel Ni-Cr-Mo-Si-B coating part 2: Erosion-corrosion behavior

    Science.gov (United States)

    Shrestha, S.; Hodgkiess, T.; Neville, A.

    2001-12-01

    In this paper, a study of the erosion-corrosion characteristics of a Ni-Cr-Mo-Si-B coating applied by the high-velocity oxy-fuel (HVOF) process on to an austenitic stainless steel (UNS S31603) substrate are reported. The coatings were studied in the as-sprayed condition, after vacuum sealing with polymer impregnation and after vacuum furnace fusion. The erosion-corrosion characteristics were assessed in an impinging liquid jet of 3.5% NaCl solution at 18 °C at a velocity of 17 m/s at normal incidence in two conditions: (1) free from added solids and (2) containing 800 ppm silica sand. The methodology employed electrochemical control and monitoring to facilitate the identification of the separate and interrelated erosion and corrosion contributions to the erosion-corrosion process. The rates of erosion-corrosion damage were drastically accelerated in the presence of the suspended solids. The application of cathodic protection significantly reduced the deterioration process. The study showed the effect of sealing with polymer impregnation did not significantly alter the erosion-corrosion behavior of the sprayed coating. However, there was a significant improvement in erosion-corrosion durability afforded by the postfusion process. The mechanisms by which the improved performance of vacuum-fused coatings is achieved are discussed.

  8. On the modification of particle dispersion in isotropic turbulence by free rotation of particle

    Science.gov (United States)

    Park, Yongnam; Lee, Changhoon

    2008-11-01

    Effect of a particle's spin is investigated numerically by considering the effect of lift occurring due to difference of rotations of a particle and of fluid such as the Saffman lift and Magnus force. These lift forces have been neglected in many previous works on particle-laden turbulence. The trajectory of particles can be changed by the lift forces, resulting in significant modification of the stochastic characteristics of heavy particles. Probability density functions and autocorrelations are examined of velocity, acceleration of solid particle and acceleration of fluid at the position of solid particle. Changes in velocity statistics are negligible but statistics related with acceleration are a little bit changed by particle's rotation. When a laden particle encounters with coherent structures during the motion, the particle's rotation might significantly affects the motion due to intermittently large fluid acceleration near coherent structures. The result can be used for development of stochastic model for particle dispersion. Detailed physical interpretation will be presented in the meeting.

  9. Gravity-driven clustering of inertial particles in turbulence.

    Science.gov (United States)

    Park, Yongnam; Lee, Changhoon

    2014-06-01

    We report a different kind of particle clustering caused purely by gravity, discovered in our simulation of particle-laden turbulence. Clustering in a vertical strip pattern forms when strong gravity acts on heavy particles. This phenomenon is explained by the skewness of the flow velocity gradient in the gravitational direction experienced by particles, which causes horizontal convergence of particles.

  10. Suspension flow: do particles act as mixers?

    CERN Document Server

    Boschan, A; Gauthier, G

    2015-01-01

    Recently, Roht et al. [J. Contam. Hydrol. 145, 10-16 (2013)] observed that the presence of suspended non-Brownian macroscopic particles decreased the dispersivity of a passive solute, for a pressure-driven flow in a narrow parallel-plates channel at low Reynolds number. This result contradicts the idea that the streamline distortion caused by the random diffusive motion of the particles increases the dispersion and mixing of the solute. Therefore, to estimate the influence of this motion on the dispersivity of the solute, and investigate the origin of the reported decrease, we experimentally studied the probability density functions (pdf) of the particle velocities, and spatio-temporal correlations, in the same experimental configuration. We observed that, as the mean suspension velocity exceeds a critical value, the pdf of the streamwise velocities of the particles markedly changes from a symmetric distribution to an asymmetric one strongly skewed to high velocities and with a peak of most probable velocity ...

  11. Experimental analysis of turbulence effect in settling velocity of suspended sediments

    Directory of Open Access Journals (Sweden)

    H. Salinas–Tapia

    2008-01-01

    Full Text Available Settling velocities of sediment particles for different size ranges were measured in this work using PIV with the help of discriminatory filters. An experimental channel 10x15 cm cross section was used in order to obtain two set of turbulent characteristics corresponding with two different flow rates. The purpose was to analyze the effect of turbulence on the solids settling velocity. The technique allowed us to measure the individual settling velocity of the particles and the flow velocity field of the fluid. Capture and image analysis was performed with digital cameras (CCD using the software Sharp–provision PIV and the statistical cross correlation technique. Results showed that settling velocity of particles is affected by turbulence which enhances the fluid drag coefficient. Physical explanation of this phenomenon is related with the magnitude of the vertical fluctuating velocity of the fluid. However, more research is needed in order to define settling velocity formulas that takes into account this effect

  12. Transverse velocity shifts in protostellar jets: rotation or velocity asymmetries?

    CERN Document Server

    De Colle, Fabio; Riera, Angels

    2016-01-01

    Observations of several protostellar jets show systematic differences in radial velocity transverse to the jet propagation direction, which have been interpreted as evidence of rotation in the jets. In this paper we discuss the origin of these velocity shifts, and show that they could be originated by rotation in the flow, or by side to side asymmetries in the shock velocity, which could be due to asymmetries in the jet ejection velocity/density or in the ambient medium. For typical poloidal jet velocities (~ 100-200 km/s), an asymmetry >~ 10% can produce velocity shifts comparable to those observed. We also present three dimensional numerical simulations of rotating, precessing and asymmetric jets, and show that, even though for a given jet there is a clear degeneracy between these effects, a statistical analysis of jets with different inclination angles can help to distinguish between the alternative origins of transverse velocity shifts. Our analysis indicate that side to side velocities asymmetries could ...

  13. Errors in particle tracking velocimetry with high-speed cameras

    CERN Document Server

    Feng, Yan; Liu, Bin

    2011-01-01

    Velocity errors in particle tracking velocimetry (PTV) are studied. When using high-speed video cameras, the velocity error may increase at a high camera frame rate. This increase in velocity error is due to particle-position uncertainty, which is one of two sources of velocity errors studied here. The other source of error is particle acceleration, which has the opposite trend of diminishing at higher frame rates. Both kinds of errors can propagate into quantities calculated from velocity, such as the kinetic temperature of particles or correlation functions. As demonstrated in a dusty plasma experiment, the kinetic temperature of particles has no unique value when measured using PTV, but depends on the sampling time interval or frame rate. It is also shown that an artifact appears in an autocorrelation function computed from particle positions and velocities, and it becomes more severe when a small sampling-time interval is used. Schemes to reduce these errors are demonstrated.

  14. Dark Matter Velocity Spectroscopy.

    Science.gov (United States)

    Speckhard, Eric G; Ng, Kenny C Y; Beacom, John F; Laha, Ranjan

    2016-01-22

    Dark matter decays or annihilations that produce linelike spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will have the precision needed. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.

  15. Dark Matter Velocity Spectroscopy

    CERN Document Server

    Speckhard, Eric G; Beacom, John F; Laha, Ranjan

    2016-01-01

    Dark matter decays or annihilations that produce line-like spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming and proposed experiments will make significant improvements. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.

  16. An active particle in a complex fluid

    CERN Document Server

    Datt, Charu; Hatzikiriakos, Savvas; Elfring, Gwynn J

    2016-01-01

    In this work, we study active particles with prescribed surface velocities in non-Newtonian fluids. We employ the reciprocal theorem to derive a general form of the propulsion velocity of a single active particle (or swimmer) in a weakly non-Newtonian background flow in the absence of inertia. Using this formulation, we obtain the velocity of an active spherical particle with an arbitrary axisymmetric slip-velocity in an otherwise quiescent second-order fluid. Finally, we determine how the motion of a diffusiophoretic Janus particle is affected by complex fluid rheology, namely viscoelasticity and shear-thinning. We find that a Janus particle may go faster or slower in a viscoelastic fluid, but is always slower in a shear-thinning fluid as compared to a Newtonian fluid.

  17. A Typical Path Model of Tracheobronchial Clearance of Inhaled Particles in Rats

    Science.gov (United States)

    2002-01-01

    A mathematical description of particle clearance from the ciliated conducting airways (tracheobronchial region) of the lungs in rats was developed...particle transport velocities for given generations of airways were estimated from reported tracheal transport velocities. Using typical rat airway geometry...and estimated particle transport velocities solutions of sets of rate equations for transport from each generation of airways were summed to estimate

  18. Movement of heavy particles in tornadoes

    Science.gov (United States)

    Ingel, L. Kh.

    2017-07-01

    The horizontal movement of inertial particles in the intensive vortices, where the centrifugal force can be substantially higher than the gravity, is studied analytically. A similar problem was studied earlier for small (Stokes) particles at low Reynolds number, which allow one to be limited to the linear resistance law. It is shown that the previous results to a great extent can be extrapolated to the case of considerably heavier particles (e.g., water droplets with a diameter up to 1 mm at Reynolds numbers up to 103). The nonlinear nature of the resistance, i.e., its dependence on the particle velocity relative to the medium, should be taken into account for such particles. Some general laws are established for particle dynamics. In particular, their tangential velocity is close to the velocity of the medium, while the radial velocity is substantially lower (it is close on the order of magnitude to the geometric mean of the particle tangential velocity and the difference between the latter and the tangential velocity of the medium). The limits of applicability of the results are found, i.e., the restrictions to the size and mass/density of particles.

  19. Superluminal Velocities in the Synchronized Space-Time

    Directory of Open Access Journals (Sweden)

    Medvedev S. Yu.

    2014-07-01

    Full Text Available Within the framework of the non-gravitational generalization of the special relativity, a problem of possible superluminal motion of particles and signals is considered. It has been proven that for the particles with non-zero mass the existence of anisotropic light barrier with the shape dependent on the reference frame velocity results from the Tangherlini transformations. The maximal possible excess of neutrino velocity over the absolute velocity of light related to the Earth (using th e clock with instantaneous synchronization has been estimated. The illusoriness of t he acausality problem has been illustrated and conclusion is made on the lack of the upper limit of velocities of signals of informational nature.

  20. Critical superfluid velocity in a trapped dipolar gas.

    Science.gov (United States)

    Wilson, Ryan M; Ronen, Shai; Bohn, John L

    2010-03-01

    We investigate the superfluid properties of a dipolar Bose-Einstein condensate (BEC) in a fully three-dimensional trap. Specifically, we estimate a superfluid critical velocity for this system by applying the Landau criterion to its discrete quasiparticle spectrum. We test this critical velocity by direct numerical simulation of condensate depletion as a blue-detuned laser moves through the condensate. In both cases, the presence of the roton in the spectrum serves to lower the critical velocity beyond a critical particle number. Since the shape of the dispersion, and hence the roton minimum, is tunable as a function of particle number, we thereby propose an experiment that can simultaneously measure the Landau critical velocity of a dipolar BEC and demonstrate the presence of the roton in this system.

  1. Hard-sphere interactions in velocity-jump models

    Science.gov (United States)

    Franz, Benjamin; Taylor-King, Jake P.; Yates, Christian; Erban, Radek

    2016-07-01

    Group-level behavior of particles undergoing a velocity-jump process with hard-sphere interactions is investigated. We derive N -particle transport equations that include the possibility of collisions between particles and apply different approximation techniques to get expressions for the dependence of the collective diffusion coefficient on the number of particles and their diameter. The derived approximations are compared with numerical results obtained from individual-based simulations. The theoretical results compare well with Monte Carlo simulations providing the excluded-volume fraction is small.

  2. Hard-sphere interactions in velocity jump models

    CERN Document Server

    Franz, Benjamin; Yates, Christian; Erban, Radek

    2014-01-01

    Group-level behaviour of particles undergoing a velocity jump process with hard-sphere interactions is investigated. We derive $N$-particle transport equations that include the possibility of collisions between particles and apply different approximation techniques to get expressions for the dependence of the collective diffusion coefficient on the number of particles and their diameter. The derived approximations are compared with numerical results obtained from individual-based simulations. The theoretical results compare well with Monte Carlo simulations providing the excluded volume fraction is small.

  3. Anomalous particle pinch in Tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Miskane, F.; Garbet, X. [Association Euratom-CEA/Cadarache, Dept. de Recherches sur la Fusion Controlee, DRFC, 13 - Saint-Paul-lez-Durance (France); Dezairi, A.; Saifaoui, D. [Faculte des Sciences Ain Chok, Casablanca (Morocco)

    2000-06-01

    The diffusion coefficient in phase space usually varies with the particle energy. A consequence is the dependence of the fluid particle flux on the temperature gradient. If the diffusion coefficient in phase space decreases with the energy in the bulk of the thermal distribution function, the particle thermodiffusion coefficient which links the particle flux to the temperature gradient is negative. This is a possible explanation for the inward particle pinch that is observed in tokamaks. A quasilinear theory shows that such a thermodiffusion is generic for a tokamak electrostatic turbulence at low frequency. This effect adds to the particle flux associated with the radial gradient of magnetic field. This behavior is illustrated with a perturbed electric potential, for which the trajectories of charged particle guiding centers are calculated. The diffusion coefficient of particles is computed and compared to the quasilinear theory, which predicts a divergence at low velocity. It is shown that at low velocity, the actual diffusion coefficient increases, but remains lower than the quasilinear value. Nevertheless, this differential diffusion between cold and fast particles leads to an inward flux of particles. (author)

  4. Modified constriction particle swarm optimization algorithm

    Institute of Scientific and Technical Information of China (English)

    Zhe Zhang; Limin Jia; Yong Qin

    2015-01-01

    To deal with the demerits of constriction particle swarm optimization (CPSO), such as relapsing into local optima, slow convergence velocity, a modified CPSO algorithm is proposed by improving the velocity update formula of CPSO. The random ve-locity operator from local optima to global optima is added into the velocity update formula of CPSO to accelerate the convergence speed of the particles to the global optima and reduce the likeli-hood of being trapped into local optima. Final y the convergence of the algorithm is verified by calculation examples.

  5. A probability density function of liftoff velocities in mixed-size wind sand flux

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    With the discrete element method(DEM) ,employing the diameter distribution of natural sands sampled from the Tengger Desert,a mixed-size sand bed was produced and the particle-bed collision was simulated in the mixed-size wind sand movement. In the simulation,the shear wind velocity,particle diameter,incident velocity and incident angle of the impact sand particle were given the same values as the experimental results. After the particle-bed collision,we collected all the initial velocities of rising sand particles,including the liftoff angular velocities,liftoff linear velocities and their horizontal and vertical components. By the statistical analysis on the velocity sample for each velocity component,its probability density functions were obtained,and they are the functions of the shear wind velocity. The liftoff velocities and their horizontal and vertical components are distributed as an exponential density function,while the angular velocities are distributed as a normal density function.

  6. Indirect determination of the turbulent velocity profile origin

    OpenAIRE

    Lukerchenko, N.; Vlasák, P. (Pavel)

    2012-01-01

    The vertical co-ordinate of the logarithmic turbulent velocity profile origin yo is an important characteristic of turbulent flow in conduit with rough walls. Because length and height of saltation depend strongly on the position of the velocity profile origin, it can be determined by comparison of experimental values of particle saltation and their numerical simulation. The parameter y0 can be expressed as function of saltation length or height, or the boundary Reynolds number, and it was sh...

  7. Dense velocity reconstruction from tomographic PTV with material derivatives

    Science.gov (United States)

    Schneiders, Jan F. G.; Scarano, Fulvio

    2016-09-01

    A method is proposed to reconstruct the instantaneous velocity field from time-resolved volumetric particle tracking velocimetry (PTV, e.g., 3D-PTV, tomographic PTV and Shake-the-Box), employing both the instantaneous velocity and the velocity material derivative of the sparse tracer particles. The constraint to the measured temporal derivative of the PTV particle tracks improves the consistency of the reconstructed velocity field. The method is christened as pouring time into space, as it leverages temporal information to increase the spatial resolution of volumetric PTV measurements. This approach becomes relevant in cases where the spatial resolution is limited by the seeding concentration. The method solves an optimization problem to find the vorticity and velocity fields that minimize a cost function, which includes next to instantaneous velocity, also the velocity material derivative. The velocity and its material derivative are related through the vorticity transport equation, and the cost function is minimized using the limited-memory Broyden-Fletcher-Goldfarb-Shanno (L-BFGS) algorithm. The procedure is assessed numerically with a simulated PTV experiment in a turbulent boundary layer from a direct numerical simulation (DNS). The experimental validation considers a tomographic particle image velocimetry (PIV) experiment in a similar turbulent boundary layer and the additional case of a jet flow. The proposed technique (`vortex-in-cell plus', VIC+) is compared to tomographic PIV analysis (3D iterative cross-correlation), PTV interpolation methods (linear and adaptive Gaussian windowing) and to vortex-in-cell (VIC) interpolation without the material derivative. A visible increase in resolved details in the turbulent structures is obtained with the VIC+ approach, both in numerical simulations and experiments. This results in a more accurate determination of the turbulent stresses distribution in turbulent boundary layer investigations. Data from a jet

  8. Analysis of particle-wall interactions during particle free fall.

    Science.gov (United States)

    Chein, Reiyu; Liao, Wenyuan

    2005-08-01

    In this study, the vertical motion of a particle in a quiescent fluid falling toward a horizontal plane wall is analyzed, based on simplified models. Using the distance between the particle and wall as a parameter, the effects of various forces acting on the particle and the particle motion are examined. Without the colloidal and Brownian forces being included, the velocity of small particles is found to be approximately equal to the inverse of the drag force correction function used in this study as the particle approaches the near-wall region. Colloidal force is added to the particle equation of motion as the particle moves a distance comparable to its size. It is found that the particle might become suspended above or deposited onto the wall, depending on the Hamaker constant, the surface potentials of the particle and wall, and the thickness of the electrical double layer (EDL). For strong EDL repulsive force and weaker van der Waals (VDW) attractive force, the particle will become suspended above the wall at a distance at which the particle velocity is zero. This location is referred to as the equilibrium distance. The equilibrium distance is found to increase with increased in EDL thickness when a repulsive force barrier appears in the colloidal force interaction. For the weak EDL repulsive force and strong VDW attractive force case, the particle can become deposited onto the wall without the Brownian motion effect. The Brownian jump length was found to be very small. Many Brownian jumps would be required in a direction toward the wall for a suspended particle to become deposited.

  9. Kinematic determination of Electron-Hole velocities

    Science.gov (United States)

    Hutchinson, Ian H.; Zhou, C.

    2016-10-01

    Coherent self-sustaining BGK potential structures, like the electron holes that often form during nonlinear electrostatic instabilities and are frequently observed in space plasmas, have ``kinematic'' momentum conservation properties that determine their velocity. The electron and ion momentum, both internal and external to the hole, must be included. Momentum changes arise from hole acceleration and from hole depth growth, by energization processes we call jetting; and these must balance any additional external forces on the particles. Comprehensive analytic expressions for the contributions have been calculated for holes of arbitrary localized potential form. Using these, we can deduce velocity changes in various interesting situations such as the self-acceleration of electron holes during formation, the circumstances under which holes accelerate at the rate of the electrons in a background electric field, the influence of the ion stream pushing and pulling holes to higher or lower speeds, and the trapping of hole velocity between the velocity of two ion streams. The predictions are in excellent quantitative agreement with targeted PIC simulations. The kinematic theory thus explains why isolated holes behave the way they do. Partially supported by NSF/DOE Basic Plasma Grant DE-SC0010491.

  10. Velocity centroids as tracers of the turbulent velocity statistics

    CERN Document Server

    Lazarian, A E A

    2004-01-01

    We use the results of magnetohydrodynamic (MHD) simulations to emulate spectroscopic observations, and produce maps of variations of velocity centroids to study their scaling properties. We compare them with those of the underlying velocity field, and analytic predictions presented in a previous paper (Lazarian & Esquivel 2003). We tested, with success, a criteria for recovering velocity statistics from velocity centroids derived in our previous work. That is, if >> (where S is a 2D map of ``unnormalized'', v velocity, and I integrated intensity map -column density-), then the structure function of the centroids is dominated by the structure function of velocity. We show that it is possible to extract the velocity statistics using centroids for subsonic and mildly supersonic turbulence (e.g. Mach numbers ~2.5). While, towards higher Mach numbers other effects could affect significantly the statistics of centroids.

  11. Statistics of Velocity from Spectral Data Modified Velocity Centroids

    CERN Document Server

    Lazarian, A

    2003-01-01

    We address the problem of studying interstellar (ISM) turbulence using spectral line data. We construct a measure that we term modified velocity centroids (MVCs) and derive an analytical solution that relates the 2D spectra of the modified centroids with the underlying 3D velocity spectrum. We test our results using synthetic maps constructed with data obtained through simulations of compressible MHD turbulence. We prove that the MVCs are able to restore the underlying spectrum of turbulent velocity. We show that the modified velocity centroids (MVCs) are complementary to the the Velocity Channel Analysis (VCA) technique that we introduced earlier. Employed together they make determining of the velocity spectral index more reliable. At the same time we show that MVCs allow to determine velocity spectra when the underlying statistics is not a power law and/or the turbulence is subsonic.

  12. Entropic Ratchet transport of interacting active Brownian particles

    Energy Technology Data Exchange (ETDEWEB)

    Ai, Bao-Quan, E-mail: aibq@hotmail.com [Laboratory of Quantum Engineering and Quantum Materials, School of Physics and Telecommunication Engineering, South China Normal University, 510006 Guangzhou (China); He, Ya-Feng [College of Physics Science and Technology, Hebei University, 071002 Baoding (China); Zhong, Wei-Rong, E-mail: wrzhong@jnu.edu.cn [Department of Physics and Siyuan Laboratory, College of Science and Engineering, Jinan University, 510632 Guangzhou (China)

    2014-11-21

    Directed transport of interacting active (self-propelled) Brownian particles is numerically investigated in confined geometries (entropic barriers). The self-propelled velocity can break thermodynamical equilibrium and induce the directed transport. It is found that the interaction between active particles can greatly affect the ratchet transport. For attractive particles, on increasing the interaction strength, the average velocity first decreases to its minima, then increases, and finally decreases to zero. For repulsive particles, when the interaction is very weak, there exists a critical interaction at which the average velocity is minimal, nearly tends to zero, however, for the strong interaction, the average velocity is independent of the interaction.

  13. The Light Velocity Casimir Effect Does the Velocity of Light Increase when Propagating Between the Casimir Plates?

    CERN Document Server

    Ostoma, T; Ostoma, Tom; Trushyk, Mike

    1999-01-01

    We propose experiments that might be set up to detect the increase in the velocity of light in a vacuum in the laboratory frame for photons travelling between (and perpendicular to) the Casimir plates in a vacuum. The Casimir plates are two closely spaced, conductive plates, where an attractive force is observed to exist between the plates called the 'Casimir Force'. We propose that the velocity of light in a vacuum increases when propagating between two transparent Casimir Plates. We call this effect the 'Light Velocity Casimir Effect' or LVC effect. The LVC effect happens because the vacuum energy density in between the plates is lower than that outside the Casimir plates. The conductive plates disallow certain frequencies of electrically charged virtual particles to exist inside the plates, thus lowering the inside vacuum particle density, compared to the density outside the plates. The reduced (electrically charged) virtual particle density results in fewer photon scattering events inside the plates, whic...

  14. Insights on tephra settling velocity from morphological observations

    Science.gov (United States)

    Alfano, Fabrizio; Bonadonna, Costanza; Delmelle, Pierre; Costantini, Licia

    2011-12-01

    In this study we present a systematic and detailed morphological characterization of tephra particles from different eruptions (Fontana Lapilli, Masaya, Nicaragua; Keanakāko'i Formation, Kilauea, USA; recent dome explosions of Soufriere Hills volcano, Montserrat) and the calculation of their Terminal Fall Velocity (TFV) as obtained based on different drag prediction models (i.e., Wilson and Huang, 1979; Haider and Levenspiel, 1989; Ganser, 1993; Dellino et al., 2005). In particular, particle sphericity, and, therefore, particle surface area, is essential for the calculation of TFV of irregular-shape particles but is of complex determination. Various attempts have been proposed. According to our results, 2D morphological characterization of volcanic particles is a fast and simple application for a wide range of particle size and provides consistent sphericity and settling-velocity values. 3D scanning also provides a promising tool for lapilli-sized tephra (> 2 cm). In contrast, gas-adsorption-derived surface area is not suitable for the calculation of TFV of volcanic particles mostly because it mainly describes the surface contribution of nanometric pores that are not expected to affect significantly TFV and because bulk-sample analysis is representative of neither individual particles nor of the whole particle population. Settling velocities calculated using values of surface area derived from gas adsorption analyses are up to two orders of magnitude lower than the values obtained through 2D analysis. In addition, our results also show how the influence of particle shape on TFV increases with particle size. In particular, calculated TFV converges at small particle sizes (≥ 3 ϕ) regardless of the model applied, suggesting that the spherical assumption is appropriate for this size fraction (discrepancies with the spherical model are within 10%). Discrepancies with the spherical model increase with particle size up to about 50% and depend on the choice of both the

  15. 超音速火焰喷涂Fe基合金涂层的抗汽蚀性能%Cavitation erosion resistance of Fe-based alloy coating by HVOF thermal spraying

    Institute of Scientific and Technical Information of China (English)

    陈怡; 吴玉萍; 梁伟灿; 刘博; 钱玲; 楼益龙

    2011-01-01

    采用超音速火焰(HVOF)喷涂在1Cr18Ni9Ti不锈钢基体上制备了200 pm厚的Fe基(含Cr、Ni等)合金涂层.采用金相显微镜、扫描电镜、显微硬度计、磁致伸缩汽蚀仪对涂层的组织、硬度和抗汽蚀性能进行了研究.结果表明,Fe基合金涂层组织均匀致密,孔隙率低,具有层状结构,涂层的平均硬度为993 HV0.1,是基体硬度的5.8倍;Fe基涂层抗汽蚀性能明显优于1Cr18Ni9Ti不锈钢,1Cr18Ni9Ti不锈钢汽蚀沿晶界和孪晶界破坏,而Fe基合金涂层汽蚀沿表面微小孔隙破坏,破坏由孔隙边缘向外扩展,损伤程度由汽蚀试样表面中心向外递减,最终不同损伤程度的汽蚀坑分布于表面.%Fe-based (including Cr, Ni, etc. ) alloy coating was prepared by HVOF thermal spraying method on ICr18Ni9Ti stainless steel with thickness of 200 μm, and the microstructure, microhardness, cavitation erosion resistance of the Fe-hased alloy couting were inwestigated by optical microscopy ( OM ), scanning electron microscopy ( SEM ), microhandness tester and magnelostrictive cavitation device. The results show that the coating Ires uniform density, low porosity, high hardness and lamellar stricture. The. Average hardness of the Fe-based alloy coating is 993 HV0.1, which is 5.8 times of the steel substrate. The cavitation erosion resistance of the Fe-based coating is higher than that of ICr18Ni9Ti stainless steel. The mass loss of ICrl8NigTi steel initiated at the grain boundary and twin boundary, while cavitation erosion damage of the Fe-based alloy cooling began at the edge of small pores and extended toward outside and reduced gradually from the center to the outside of the sample, eventually the surface of the sample was filled with different depth of pits.

  16. Microestructura y oxidación cíclica en atmósferas con contenidos de oxígeno variables de un recubrimiento NiCrBSiFe proyectado térmicamente por plasma y HVOF

    Directory of Open Access Journals (Sweden)

    Higuera-Hidalgo, V.

    2006-12-01

    Full Text Available The influence of thermal spraying procedure (plasma and HVOF on the microstructure, high temperature oxidation resistance and adherence of NiCrBSiFe coatings has been examined. Two different series of oxidation tests have been carried out, in air (21% oxygen at 800 and 1,000 ºC (1,073 y 1,273 K and in a simulated gas turbine environment (10% oxygen representative of a combined-cycle power generation plant, at the same temperatures.
    Coating microstructure, porosity, oxide content and microhardness are highly dependent on the spraying procedure and coating hardness also significantly decreases after long maintenances at high temperature (1,000 ºC. Finally, the oxidation weight gain and the adherence of NiCrBSiFe coatings are also dependent on the morphology of the coating but, nevertheless, the oxidation behaviour of these coatings was very good as protective chromium and silicon oxides were always formed.

    Se ha llevado a cabo un estudio experimental sobre la influencia del proceso de proyección en la microestructura, resistencia a la oxidación y adherencia de los recubrimientos NiCrBSiFe proyectados térmicamente por plasma y llama a alta velocidad (HVOF, para lo que se han realizado ensayos en dos ambientes diferentes: en una atmósfera convencional (21 % de O2, a 800 y 1000 ºC (1.073 y 1.273 K, respectivamente, y en un ambiente simulativo de una turbina de gas y del generador de vapor de una central eléctrica de ciclo combinado (10-11 % de O2, a las mismas temperaturas. Se ha puesto de manifiesto que la microestructura, porosidad, contenido de óxidos y microdureza de estas capas varían significativamente con el sistema de proyección utilizado y que la microdureza de estas capas disminuye apreciablemente tras largos mantenimientos a alta temperatura (1.000 ºC. También, la ganancia de peso por oxidación de los recubrimientos NiCrBSiFe y la adherencia entre la capa y el sustrato dependen de la morfología del recubrimiento

  17. Measuring Oscillatory Velocity Fields Due to Swimming Algae

    CERN Document Server

    Guasto, Jeffrey S; Gollub, J P

    2010-01-01

    In this fluid dynamics video, we present the first time-resolved measurements of the oscillatory velocity field induced by swimming unicellular microorganisms. Confinement of the green alga C. reinhardtii in stabilized thin liquid films allows simultaneous tracking of cells and tracer particles. The measured velocity field reveals complex time-dependent flow structures, and scales inversely with distance. The instantaneous mechanical power generated by the cells is measured from the velocity fields and peaks at 15 fW. The dissipation per cycle is more than four times what steady swimming would require.

  18. Measurement of velocity field in parametrically excited solitary waves

    CERN Document Server

    Gordillo, Leonardo

    2014-01-01

    Paramerically excited solitary waves emerge as localized structures in high-aspect-ratio free surfaces subject to vertical vibrations. Herein, we provide the first experimental characterization of the hydrodynamics of thess waves using Particle Image Velocimetry. We show that the underlying velocity field of parametrically excited solitary waves is mainly composed by an oscillatory velocity field. Our results confirm the accuracy of Hamiltonian models with added dissipation in describing this field. Remarkably, our measurements also uncover the onset of a streaming velocity field which is shown to be as important as other crucial nonlinear terms in the current theory. The observed streaming pattern is particularly interesting due to the presence of oscillatory meniscii.

  19. Superconducting spoke cavities for high-velocity applications

    Energy Technology Data Exchange (ETDEWEB)

    Hopper, Christopher S. [Old Dominion U.; Delayen, Jean R. [Old Dominion U., JLAB

    2013-10-01

    To date, superconducting spoke cavities have been designed, developed, and tested for particle velocities up to {beta}{sub 0}~0.6, but there is a growing interest in possible applications of multispoke cavities for high-velocity applications. We have explored the design parameter space for low-frequency, high-velocity, double-spoke superconducting cavities in order to determine how each design parameter affects the electromagnetic properties, in particular the surface electromagnetic fields and the shunt impedance. We present detailed design for cavities operating at 325 and 352 MHz and optimized for {beta}{sub 0}~=0.82 and 1.

  20. Leading-Edge Velocities and Lifted Methane Jet Flame Stability

    Directory of Open Access Journals (Sweden)

    W. Wang

    2010-01-01

    Full Text Available Current interest exists in understanding reaction-zone dynamics and mechanisms with respect to how they counterpropagate against incoming reactants. Images of flame position and flow-field morphology are presented from flame chemiluminescence and particle image velocimetry (PIV measurements. In the present study, PIV experiments were carried out to measure the methane jet lifted-flame flow-field velocities in the vicinity of the flame leading edge. Specifically, velocity fields within the high-temperature zone were examined in detail, which complements previous studies, whose prime focus is the flow-field upstream of the high-temperature boundary. PIV data is used not only to determine the velocities, but, along with chemiluminescence images, to also indicate the approximate location of the reaction zone (further supported by/through the leading-edge flame velocity distributions. The velocity results indirectly support the concept that the flame is anchored primarily through the mechanism of partially premixed flame propagation.

  1. Visual control of walking velocity.

    Science.gov (United States)

    François, Matthieu; Morice, Antoine H P; Bootsma, Reinoud J; Montagne, Gilles

    2011-06-01

    Even if optical correlates of self-motion velocity have already been identified, their contribution to the control of displacement velocity remains to be established. In this study, we used a virtual reality set-up coupled to a treadmill to test the role of both Global Optic Flow Rate (GOFR) and Edge Rate (ER) in the regulation of walking velocity. Participants were required to walk at a constant velocity, corresponding to their preferred walking velocity, while eye height and texture density were manipulated. This manipulation perturbed the natural relationship between the actual walking velocity and its optical specification by GOFR and ER, respectively. Results revealed that both these sources of information are indeed used by participants to control walking speed, as demonstrated by a slowing down of actual walking velocity when the optical specification of velocity by either GOFR or ER gives rise to an overestimation of actual velocity, and vice versa. Gait analyses showed that these walking velocity adjustments result from simultaneous adaptations in both step length and step duration. The role of visual information in the control of self-motion velocity is discussed in relation with other factors.

  2. Dynamic Strengthening During High Velocity Shear Experiments with Siliceous Rocks

    Science.gov (United States)

    Liao, Z.; Chang, J. C.; Boneh, Y.; Chen, X.; Reches, Z.

    2011-12-01

    It is generally accepted that dynamic-weakening is essential for earthquake instability, and many experimental works have documented this weakening. Recent observations revealed also opposite trends of dynamic-strengthening in experiments (Reches & Lockner, 2010). We present here our experimental results of this dynamic-strengthening and discuss possible implications to earthquake behavior. We ran hundreds of experiments on experimental faults made of siliceous rock including granite, syenite, diorite, and quartzite. The experimental fault is comprised of two solid cylindrical blocks with a raised-ring contact of 7 cm diameter and 1 cm width. We recognized general, three regimes of strength-velocity relations: (I) Dynamic weakening (drop of 20-60% of static strength) as slip velocity increased from ~0.0003 m/s (lowest experimental velocity) to a critical velocity, Vc=0.008-0.16 m/s; (II) Abrupt transition to dynamic strengthening regime during which the fault strength almost regains its static strength; and (III) Quasi-constant strength with further possible drops as velocity approaches ~1 m/s. The critical velocity depends on the sample lithology: Vc is ~0.06 m/s for granite, ~0.008 m/s for syenite, ~0.01 m/s for diorite, and ~0.16 m/s for quartzite. The strengthening stage is associated with temperature increase, wear-rate increase, and the occurrence of intense, high frequency stick-slip events (Reches & Lockner, 2010). Sammis et al., (this meeting) attributed this strengthening to dehydration of the thin water layer that covers the gouge particles as the temperature increases. On the other hand, we note that tens of experiments with dolomite samples (non-siliceous), which were deformed under similar conditions, did not exhibit the velocity strengthening (unpublished). Based on the analyses by Andrews (2004, 2005), we speculate that velocity strengthening may bound the slip velocity. The numerical models of Andrews show that the slip velocity along a slip

  3. Percolation velocity dependence on local concentration in bidisperse granular flows

    Science.gov (United States)

    Jones, Ryan P.; Xiao, Hongyi; Deng, Zhekai; Umbanhowar, Paul B.; Lueptow, Richard M.

    The percolation velocity, up, of granular material in size or density bidisperse mixtures depends on the local concentration, particle size ratio, particle density ratio, and shear rate, γ ˙. Discrete element method computational results were obtained for bounded heap flows with size ratios between 1 and 3 and for density ratios between 1 and 4. The results indicate that small particles percolate downward faster when surrounded by large particles than large particles percolate upward when surrounded by small particles, as was recently observed in shear-box experiments. Likewise, heavy particles percolate downward faster when surrounded by light particles than light particles percolate upward when surrounded by heavy particles. The dependence of up / γ ˙ on local concentration results in larger percolation flux magnitudes at high concentrations of large (or light) particles compared to high concentrations of small (or heavy) particles, while local volumetric flux is conserved. The dependence of up / γ ˙ on local concentration can be incorporated into a continuum model, but the impact on global segregation patterns is usually minimal. Partially funded by Dow Chemical Company and NSF Grant No. CBET-1511450.

  4. Diffusive transport by thermal velocity fluctuations.

    Science.gov (United States)

    Donev, Aleksandar; Bell, John B; de la Fuente, Anton; Garcia, Alejandro L

    2011-05-20

    We study the contribution of advection by thermal velocity fluctuations to the effective diffusion coefficient in a mixture of two identical fluids. We find good agreement between a simple fluctuating hydrodynamics theory and particle and finite-volume simulations. The enhancement of the diffusive transport depends on the system size L and grows as ln(L/L₀) in quasi-two-dimensional systems, while in three dimensions it scales as L₀⁻¹ - L⁻¹, where L₀ is a reference length. Our results demonstrate that fluctuations play an important role in the hydrodynamics of small-scale systems.

  5. Particle Dispersion Behaviors of Dense Gas-Particle Flows in Bubble Fluidized Bed

    Directory of Open Access Journals (Sweden)

    Sihao Lv

    2013-01-01

    Full Text Available An Euler-Euler two-fluid model incorporating a developed momentum transfer empirical coefficient is developed to study the particle dispersion behaviors of dense gas-particle flows in gas-fluidization reactor. In this model, the four-way couplings among gas-particles, particle-gas, and particle-particle collisions are fully considered based on kinetic theory of granular flows and an improved smooth continuous drag coefficient is utilized. Gas turbulent flow is solved by large eddy simulation. The particle fraction, the time-averaged axial particle velocity, the histogram of particle fluctuation velocity, and the wavelet analysis of pressure signals are obtained. The results are in good agreement with experimental measurements. The mean value and the variance of axial particle velocity are greater than those of radial particle velocities. Particle collision frequencies at bubble vibrant movement regions along axial direction are much higher than those of radial direction and attenuated along height increase. Low-frequency component of pressure signal indicating the bubble movement behaviors in the center of reactor is stronger than wall regions. Furthermore, the negative values represent the passed bubble and positive peak values disclose the continuous motion of single bubble.

  6. Ice particle collisions

    Science.gov (United States)

    Sampara, Naresh; Turnbull, Barbara; Hill, Richard; Swift, Michael

    2017-04-01

    Granular interactions of ice occur in a range of geophysical, astrophysical and industrial applications. For example, Saturn's Rings are composed of icy particles from micrometers to kilometres in size - inertial and yet too small to interact gravitationally. In clouds, ice crystals are smashed to pieces before they re-aggregate to for snow floccules in a process that is very much open to interpretation. In a granular flow of ice particles, the energy spent in collisions can lead to localized surface changes and wetting, which in turn can promote aggregation. To understand the induced wetting and its effects, we present two novel experimental methods which provide snippets of insight into the collisional behaviour of macroscopic ice particles. Experiment 1: Microgravity experiments provide minute details of the contact between the ice particles during the collision. A diamagnetic levitation technique, as alternative to the parabolic flight or falling tower experiments, was used to understand the collisional behaviour of individual macroscopic icy bodies. A refrigerated cylinder, that can control ambient conditions, was inserted into the bore of an 18 Tesla superconducting magnet and cooled to -10°C. Initial binary collisions were created, where one 4 mm ice particle was levitated in the magnet bore whilst another particle was dropped vertically from the top of the bore. The trajectories of both particles were captured by high speed video to provide the three-dimensional particle velocities and track the collision outcome. Introducing complexity, multiple particles were levitated in the bore and an azimuthal turbulent air flow introduced, allowing the particles to collide with other particles within a coherent fluid structure (mimicking Saturn's rings, or an eddy in a cloud). In these experiments, a sequence of collisions occur, each one different to the previous one due to the changes in surface characteristics created by the collisions themselves. Aggregation

  7. Development of an optimal velocity selection method with velocity obstacle

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Min Geuk; Oh, Jun Ho [KAIST, Daejeon (Korea, Republic of)

    2015-08-15

    The Velocity obstacle (VO) method is one of the most well-known methods for local path planning, allowing consideration of dynamic obstacles and unexpected obstacles. Typical VO methods separate a velocity map into a collision area and a collision-free area. A robot can avoid collisions by selecting its velocity from within the collision-free area. However, if there are numerous obstacles near a robot, the robot will have very few velocity candidates. In this paper, a method for choosing optimal velocity components using the concept of pass-time and vertical clearance is proposed for the efficient movement of a robot. The pass-time is the time required for a robot to pass by an obstacle. By generating a latticized available velocity map for a robot, each velocity component can be evaluated using a cost function that considers the pass-time and other aspects. From the output of the cost function, even a velocity component that will cause a collision in the future can be chosen as a final velocity if the pass-time is sufficiently long enough.

  8. Gaseous Detectors: Charged Particle Detectors - Particle Detectors and Detector Systems

    CERN Document Server

    Hilke, H J

    2011-01-01

    Gaseous Detectors in 'Charged Particle Detectors - Particle Detectors and Detector Systems', part of 'Landolt-Börnstein - Group I Elementary Particles, Nuclei and Atoms: Numerical Data and Functional Relationships in Science and Technology, Volume 21B1: Detectors for Particles and Radiation. Part 1: Principles and Methods'. This document is part of Part 1 'Principles and Methods' of Subvolume B 'Detectors for Particles and Radiation' of Volume 21 'Elementary Particles' of Landolt-Börnstein - Group I 'Elementary Particles, Nuclei and Atoms'. It contains the Subsection '3.1.2 Gaseous Detectors' of Section '3.1 Charged Particle Detectors' of Chapter '3 Particle Detectors and Detector Systems' with the content: 3.1.2 Gaseous Detectors 3.1.2.1 Introduction 3.1.2.2 Basic Processes 3.1.2.2.1 Gas ionization by charged particles 3.1.2.2.1.1 Primary clusters 3.1.2.2.1.2 Cluster size distribution 3.1.2.2.1.3 Total number of ion pairs 3.1.2.2.1.4 Dependence of energy deposit on particle velocity 3.1.2.2.2 Transport of...

  9. Sound Velocity and Release Behaviour of Shock-Compressed LY12 Al

    Institute of Scientific and Technical Information of China (English)

    YU Yu-Ying; TAN Hua; DAI Cheng-Da; HU Jian-Bo; CHEN Da-Nian

    2005-01-01

    @@ A velocity interferometer system for any reflector (VISAR) is used to measure the sound velocity of LY12 Al shock-compressed to peak pressures of 20, 32, 55 and 71 GPa. Unloading wave velocities from these pressures are obtained from the observed particle velocity profiles at the LY12 Al/LiF window interface; and the longitudinal,bulk and shear sound velocities at the initial Hugoniot state are well determined. The histories of stress, strain,density or volume, and particle velocity along the release paths are calculated by the impedance-matching method based on the unloading sound velocity data. It is revealed that the release behaviour of shocked LY12 Al departures obviously from the elastic perfectly-plastic response.

  10. Fuzzy logic particle tracking velocimetry

    Science.gov (United States)

    Wernet, Mark P.

    1993-01-01

    Fuzzy logic has proven to be a simple and robust method for process control. Instead of requiring a complex model of the system, a user defined rule base is used to control the process. In this paper the principles of fuzzy logic control are applied to Particle Tracking Velocimetry (PTV). Two frames of digitally recorded, single exposure particle imagery are used as input. The fuzzy processor uses the local particle displacement information to determine the correct particle tracks. Fuzzy PTV is an improvement over traditional PTV techniques which typically require a sequence (greater than 2) of image frames for accurately tracking particles. The fuzzy processor executes in software on a PC without the use of specialized array or fuzzy logic processors. A pair of sample input images with roughly 300 particle images each, results in more than 200 velocity vectors in under 8 seconds of processing time.

  11. Examples of Vector Velocity Imaging

    DEFF Research Database (Denmark)

    Hansen, Peter M.; Pedersen, Mads M.; Hansen, Kristoffer L.

    2011-01-01

    To measure blood flow velocity in vessels with conventional ultrasound, the velocity is estimated along the direction of the emitted ultrasound wave. It is therefore impossible to obtain accurate information on blood flow velocity and direction, when the angle between blood flow and ultrasound wa...... with a 90° angle on the vessel. Moreover secondary flow in the abdominal aorta is illustrated by scanning on the transversal axis....

  12. Comparison of in vitro behavior of as-sprayed, alkaline-treated and collagen-treated bioceramic coatings obtained by high velocity oxy-fuel spray

    Energy Technology Data Exchange (ETDEWEB)

    Melero, H., E-mail: hortensia.melero.correas@gmail.com [Thermal Spray Centre, Universitat de Barcelona, Martí i Franqués, 1, 08028 Barcelona (Spain); Garcia-Giralt, N. [URFOA, IMIM (Institut Hospital del Mar d’Investigacions Mèdiques), RETICEF, Doctor Aiguader, 80, 08003 Barcelona (Spain); Fernández, J. [Thermal Spray Centre, Universitat de Barcelona, Martí i Franqués, 1, 08028 Barcelona (Spain); Díez-Pérez, A. [URFOA, IMIM (Institut Hospital del Mar d’Investigacions Mèdiques), RETICEF, Doctor Aiguader, 80, 08003 Barcelona (Spain); Servei de Medicina Interna, Hospital del Mar, Barcelona (Spain); Guilemany, J.M. [Thermal Spray Centre, Universitat de Barcelona, Martí i Franqués, 1, 08028 Barcelona (Spain)

    2014-07-01

    Hydroxyapatite (HAp)–TiO{sub 2} samples obtained using high velocity oxy-fuel spray (HVOF), that had previously shown excellent mechanical behaviour, were innovatively surface treated in order to improve their biological performance. The chosen treatments were an alkaline treatment to increase –OH radicals density on the surface (especially on TiO{sub 2} zones), and a collagen treatment to bond collagen fibrils to the –OH radicals present in hydroxyapatite. These coatings were analysed using scanning electron microscopy, energy-dispersive X-ray spectroscopy and infrared spectroscopy, and tested for human osteoblast biocompatibility and functionality. In the case of the alkaline treatment, although the –OH radicals density did not increase compared to the as-sprayed coatings, a nanostructured layer of sodium hydroxycarbonate precipitated on the surface, thus improving biological behaviour due to the nanoroughness effect. For the collagen-treated samples, collagen fibrils appeared well-adhered to the surface, and in vitro cell culture tests showed that these surfaces were much more conducive to cell adhesion and differentiation than the as-sprayed and alkaline-treated samples. These results pointed to collagen treatment as a very promising method to improve bioactivity of HAp–TiO{sub 2} thermal-sprayed coatings.

  13. Ice Particle Impacts on a Moving Wedge

    Science.gov (United States)

    Vargas, Mario; Struk, Peter M.; Kreeger, Richard E.; Palacios, Jose; Iyer, Kaushik A.; Gold, Robert E.

    2014-01-01

    This work presents the results of an experimental study of ice particle impacts on a moving wedge. The experiment was conducted in the Adverse Environment Rotor Test Stand (AERTS) facility located at Penn State University. The wedge was placed at the tip of a rotating blade. Ice particles shot from a pressure gun intercepted the moving wedge and impacted it at a location along its circular path. The upward velocity of the ice particles varied from 7 to 12 meters per second. Wedge velocities were varied from 0 to 120 meters per second. Wedge angles tested were 0 deg, 30 deg, 45 deg, and 60 deg. High speed imaging combined with backlighting captured the impact allowing observation of the effect of velocity and wedge angle on the impact and the post-impact fragment behavior. It was found that the pressure gun and the rotating wedge could be synchronized to consistently obtain ice particle impacts on the target wedge. It was observed that the number of fragments increase with the normal component of the impact velocity. Particle fragments ejected immediately after impact showed velocities higher than the impact velocity. The results followed the major qualitative features observed by other researchers for hailstone impacts, even though the reduced scale size of the particles used in the present experiment as compared to hailstones was 4:1.

  14. Velocity field calculation for non-orthogonal numerical grids

    Energy Technology Data Exchange (ETDEWEB)

    Flach, G. P. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2015-03-01

    Computational grids containing cell faces that do not align with an orthogonal (e.g. Cartesian, cylindrical) coordinate system are routinely encountered in porous-medium numerical simulations. Such grids are referred to in this study as non-orthogonal grids because some cell faces are not orthogonal to a coordinate system plane (e.g. xy, yz or xz plane in Cartesian coordinates). Non-orthogonal grids are routinely encountered at the Savannah River Site in porous-medium flow simulations for Performance Assessments and groundwater flow modeling. Examples include grid lines that conform to the sloping roof of a waste tank or disposal unit in a 2D Performance Assessment simulation, and grid surfaces that conform to undulating stratigraphic surfaces in a 3D groundwater flow model. Particle tracking is routinely performed after a porous-medium numerical flow simulation to better understand the dynamics of the flow field and/or as an approximate indication of the trajectory and timing of advective solute transport. Particle tracks are computed by integrating the velocity field from cell to cell starting from designated seed (starting) positions. An accurate velocity field is required to attain accurate particle tracks. However, many numerical simulation codes report only the volumetric flowrate (e.g. PORFLOW) and/or flux (flowrate divided by area) crossing cell faces. For an orthogonal grid, the normal flux at a cell face is a component of the Darcy velocity vector in the coordinate system, and the pore velocity for particle tracking is attained by dividing by water content. For a non-orthogonal grid, the flux normal to a cell face that lies outside a coordinate plane is not a true component of velocity with respect to the coordinate system. Nonetheless, normal fluxes are often taken as Darcy velocity components, either naively or with accepted approximation. To enable accurate particle tracking or otherwise present an accurate depiction of the velocity field for a non

  15. Velocity Profiles between Two Baffles in a Horizontal Circular Tube

    Institute of Scientific and Technical Information of China (English)

    Tae-Hyun Chang; Hae-Soo Lee; Keon-Je Oh; Doeg Hee Doh; Chang-Hoan Lee

    2014-01-01

    The shell and tube heat exchanger is an essential part of a power plant for recovering heat transfer between the feed water of a boiler and the wasted heat.The baffles are also an important element inside the heat exchanger.Internal materials influence the flow pattern in the bed.The influence of baffles in the velocity profiles was observed using a three-dimensional particle image velocimetry around baffles in a horizontal circular tube.The velocity of the particles was measured before the baffle and between them in the test tube.Results show that the flows near the front baffle flow were parallel to the vertical wall,and then concentrate on the upper opening of the front baffle.The flows circulate in the front and rear baffles.These flow profiles are related to the Reynolds number (Re) or the flow intensity.The velocity profiles at lower Re number showed a complicated mixing,concentrating on the lower opening of the rear baffle as front wall.Swirling flow was employed in this study,which was produced using tangential velocities at the inlet.At the entrance of the front baffle,the velocity vector profiles with swirl were much different from that without swirl.However,velocities between two baffles are not much different from those without swirl.

  16. Superconducting accelerating structures for very low velocity ion beams

    Energy Technology Data Exchange (ETDEWEB)

    Xu, J.; Shepard, K.W.; Ostroumov, P.N.; Fuerst, J.D.; Waldschmidt, G.; /Argonne; Gonin, I.V.; /Fermilab

    2008-01-01

    This paper presents designs for four types of very-low-velocity superconducting accelerating cavity capable of providing several MV of accelerating potential per cavity, and suitable for particle velocities in the range 0.006 < v/c < 0.06. Superconducting TEM-class cavities have been widely applied to CW acceleration of ion beams. SC linacs can be formed as an array of independently-phased cavities, enabling a variable velocity profile to maximize the output energy for each of a number of different ion species. Several laboratories in the US and Europe are planning exotic beam facilities based on SC linacs. The cavity designs presented here are intended for the front-end of such linacs, particularly for the post-acceleration of rare isotopes of low charge state. Several types of SC cavities have been developed recently to cover particle velocities above 0.06c. Superconducting four-gap quarter-wave resonators for velocities 0.008 < {beta} = v/c < 0.05 were developed about two decades ago and have been successfully operated at the ATLAS SC linac at Argonne National Laboratory. Since that time, progress in simulation tools, cavity fabrication and processing have increased SC cavity gradients by a factor of 3-4. This paper applies these tools to optimize the design of a four-gap quarter-wave resonator for exotic beam facilities and other low-velocity applications.

  17. Superconducting accelerating structures for very low velocity ion beams

    Directory of Open Access Journals (Sweden)

    J. Xu

    2008-03-01

    Full Text Available This paper presents designs for four types of very-low-velocity superconducting (SC accelerating cavity capable of providing several MV of accelerating potential per cavity, and suitable for particle velocities in the range 0.006velocity profile to maximize the output energy for each of a number of different ion species. Several laboratories in the U.S. and Europe are planning exotic beam facilities based on SC linacs. The cavity designs presented here are intended for the front end of such linacs, particularly for the postacceleration of rare isotopes of low charge state. Several types of SC cavities have been developed recently to cover particle velocities above 0.06c. Superconducting four-gap quarter-wave resonators for velocities 0.008<β=v/c<0.05 were developed about two decades ago and have been successfully operated at the ATLAS SC linac at Argonne National Laboratory. Since that time, progress in simulation tools, cavity fabrication, and processing have increased SC cavity gradients by a factor of 3–4. This paper applies these tools to optimize the design of a four-gap quarter-wave resonator for exotic beam facilities and other low-velocity applications.

  18. Velocity profiles between two baffles in a horizontal circular tube

    Science.gov (United States)

    Chang, Tae-Hyun; Lee, Hae-Soo; Oh, Keon-Je; Doh, Doeg Hee; Lee, Chang-Hoan

    2014-12-01

    The shell and tube heat exchanger is an essential part of a power plant for recovering heat transfer between the feed water of a boiler and the wasted heat. The baffles are also an important element inside the heat exchanger. Internal materials influence the flow pattern in the bed. The influence of baffles in the velocity profiles was observed using a three-dimensional particle image velocimetry around baffles in a horizontal circular tube. The velocity of the particles was measured before the baffle and between them in the test tube. Results show that the flows near the front baffle flow were parallel to the vertical wall, and then concentrate on the upper opening of the front baffle. The flows circulate in the front and rear baffles. These flow profiles are related to the Reynolds number (Re) or the flow intensity. The velocity profiles at lower Re number showed a complicated mixing, concentrating on the lower opening of the rear baffle as front wall. Swirling flow was employed in this study, which was produced using tangential velocities at the inlet. At the entrance of the front baffle, the velocity vector profiles with swirl were much different from that without swirl. However, velocities between two baffles are not much different from those without swirl.

  19. Motion of Euglena gracilis: Active fluctuations and velocity distribution

    Science.gov (United States)

    Romanczuk, P.; Romensky, M.; Scholz, D.; Lobaskin, V.; Schimansky-Geier, L.

    2015-07-01

    We study the velocity distribution of unicellular swimming algae Euglena gracilis using optical microscopy and active Brownian particle theory. To characterize a peculiar feature of the experimentally observed distribution at small velocities we use the concept of active fluctuations, which was recently proposed for the description of stochastically self-propelled particles [Romanczuk, P. and Schimansky-Geier, L., Phys. Rev. Lett. 106, 230601 (2011)]. In this concept, the fluctuating forces arise due to internal random performance of the propulsive motor. The fluctuating forces are directed in parallel to the heading direction, in which the propulsion acts. In the theory, we introduce the active motion via the depot model [Schweitzer, et al., Phys. Rev. Lett. 80(23), 5044 (1998)]. We demonstrate that the theoretical predictions based on the depot model with active fluctuations are consistent with the experimentally observed velocity distributions. In addition to the model with additive active noise, we obtain theoretical results for a constant propulsion with multiplicative noise.

  20. Three Kinds of Velocity Structure Function in Turbulent Flows

    Institute of Scientific and Technical Information of China (English)

    LIU Wei; JIANG Nan

    2004-01-01

    Based on the local multi-scale eddy structures in turbulent flows, we elucidate the essential difference between the real turbulent field with a finite Reynolds number and the Kolmogorov fully developed random field. The motion of fluid particles in the real turbulent field is not fully random. There exist multi-scale structures due to the effect of viscosity. Actually the movements of fluid particles in the turbulent field are restricted by such eddy structures. Furthermore, concept of the locally averaged velocity structure function is put forward to describe the relative strain distortion of two adjacent turbulent eddy structures at a certain scale. The time sequence of the longitudinal velocity component at different vertical locations in turbulent boundary layer has been elaborately measured by the constant temperature anemometry of model IFA-300 in a wind tunnel. The experiment proves that the locally averaged velocity structure function is in agreement with the wavelet-coefficient structure function.

  1. Asymmetry of Coordinate and Velocity in Noisy Oscillator

    Institute of Scientific and Technical Information of China (English)

    SONG Yan-Li; BAO Jing-Dong; WANG Hai-Yan; JI Qing

    2005-01-01

    The velocity variable of a noise oscillator as an internal or external noise is proposed, the spectrum of which is quite different from that of the coordinate variable of the same noise oscillator. The former leads to ballistic diffusion for a free particle in long time limit and the asymptotical results of the system are sensitive to the initial condition. However, diffusion process induced by the coordinate of noise oscillator is a normal one and depends on the initial condition only in the transient time. This allows us to classify two kinds of non-Markovian processes: normal one and strong one, just like the processes induced by the coordinate and the velocity of noise oscillator, respectively.Applying to a correlation ratchet, we have found that the steady current of a particle subjected to the velocity of noise oscillator is opposite to that subjected to its coordinate, thus the former shows greenness and the latter redness.

  2. Velocity and rotation measurements in acoustically levitated droplets

    Energy Technology Data Exchange (ETDEWEB)

    Saha, Abhishek [University of Central Florida, Orlando, FL 32816 (United States); Basu, Saptarshi [Indian Institute of Science, Bangalore 560012 (India); Kumar, Ranganathan, E-mail: ranganathan.kumar@ucf.edu [University of Central Florida, Orlando, FL 32816 (United States)

    2012-10-01

    The velocity scale inside an acoustically levitated droplet depends on the levitator and liquid properties. Using Particle Imaging Velocimetry (PIV), detailed velocity measurements have been made in a levitated droplet of different diameters and viscosity. The maximum velocity and rotation are normalized using frequency and amplitude of acoustic levitator, and droplet viscosity. The non-dimensional data are fitted for micrometer- and millimeter-sized droplets levitated in different levitators for different viscosity fluids. It is also shown that the rotational speed of nanosilica droplets at an advanced stage of vaporization compares well with that predicted by exponentially fitted parameters. -- Highlights: ► Demonstrates the importance of rotation in a levitated droplet that leads to controlled morphology. ► Provides detailed measurements of Particle Image Velocimetry inside levitated droplets. ► Shows variation of vortex strength with the droplet diameter and viscosity of the liquid.

  3. Sodium Velocity Maps on Mercury

    Science.gov (United States)

    Potter, A. E.; Killen, R. M.

    2011-01-01

    The objective of the current work was to measure two-dimensional maps of sodium velocities on the Mercury surface and examine the maps for evidence of sources or sinks of sodium on the surface. The McMath-Pierce Solar Telescope and the Stellar Spectrograph were used to measure Mercury spectra that were sampled at 7 milliAngstrom intervals. Observations were made each day during the period October 5-9, 2010. The dawn terminator was in view during that time. The velocity shift of the centroid of the Mercury emission line was measured relative to the solar sodium Fraunhofer line corrected for radial velocity of the Earth. The difference between the observed and calculated velocity shift was taken to be the velocity vector of the sodium relative to Earth. For each position of the spectrograph slit, a line of velocities across the planet was measured. Then, the spectrograph slit was stepped over the surface of Mercury at 1 arc second intervals. The position of Mercury was stabilized by an adaptive optics system. The collection of lines were assembled into an images of surface reflection, sodium emission intensities, and Earthward velocities over the surface of Mercury. The velocity map shows patches of higher velocity in the southern hemisphere, suggesting the existence of sodium sources there. The peak earthward velocity occurs in the equatorial region, and extends to the terminator. Since this was a dawn terminator, this might be an indication of dawn evaporation of sodium. Leblanc et al. (2008) have published a velocity map that is similar.

  4. Deposition and Resuspension of Particles

    DEFF Research Database (Denmark)

    Lengweiler, P.; Nielsen, Peter V.; Moser, A.

    To investigate the physical process of deposition and resuspension of particles in the indoor environment, scale experiments are used and a sampling method is established. The influences of surface orientation and turbulence and velocity of the air on the dust load on a surface are analysed....

  5. Spatiotemporal properties of Sub-Rayleigh and supershear rupture velocity fields: Theory and experiments

    Science.gov (United States)

    Mello, Michael; Bhat, Harsha S.; Rosakis, Ares J.

    2016-08-01

    Fundamental spatiotemporal field properties and particle velocity waveform signatures of sub-Rayleigh and supershear ruptures were experimentally investigated through a series of laboratory earthquake experiments. We appeal to dynamic rupture theory to extract and highlight previously unnoticed aspects and results, which are of direct relevance to our new experiments. Kinematic relationships derived from both singular and non-singular solutions are applied to analyze and interpret various features observed in these experiments. A strong correspondence is demonstrated between particle velocity records obtained in lab experiments and synthetic particle velocity waveform profiles derived from theory. Predicted temporal profiles, sense of particle motion, and amplitude decay properties of sub-Rayleigh and supershear particle velocity waveforms are experimentally verified. In a particular set of supershear rupture experiments, the fault-normal (FN) and fault-parallel (FP) velocity waveforms were simultaneously recorded at fixed, off-fault field points as a shear Mach front swept these locations. Particle velocity records collected over a broad range of stable supershear rupture speeds validate the predicted scaling relationship δu˙1s / δu˙2s =√{Vr2 / Cs2-1 } =βs, between the FP (δu1ṡ) and the FN (δu2ṡ) velocity jumps propagated by a shear Mach front. Additional experimental findings include detailed rupture speed measurements of sub-Rayleigh and supershear ruptures and the observation of a supershear daughter crack with vanishing shear Mach front.

  6. Introduction to vector velocity imaging

    DEFF Research Database (Denmark)

    Jensen, Jørgen Arendt; Udesen, Jesper; Hansen, Kristoffer Lindskov;

    Current ultrasound scanners can only estimate the velocity along the ultrasound beam and this gives rise to the cos() factor on all velocity estimates. This is a major limitation as most vessels are close to perpendicular to the beam. Also the angle varies as a function of space and time making...

  7. Instantaneous Velocity Using Photogate Timers

    Science.gov (United States)

    Wolbeck, John

    2010-01-01

    Photogate timers are commonly used in physics laboratories to determine the velocity of a passing object. In this application a card attached to a moving object breaks the beam of the photogate timer providing the time for the card to pass. The length L of the passing card can then be divided by this time to yield the average velocity (or speed)…

  8. SIMULATION OF TRANSLATIONAL - ROTATIONAL MOTION OF WOOD PARTICLES DURING THE PROCESS OF PARTICLE ORIENTATION

    Directory of Open Access Journals (Sweden)

    Sergey PLOTNIKOV

    2014-09-01

    Full Text Available The simulation from the motion of flat particle revealed that the fall depends on the height of the drop, the thickness and density of the particles and does not depend on its length and width. The drop in air is about 20% longer than in vacuum. During orientation from angular particles the velocity of rotating particles with a length of 150mm is reduced by 18%, for particles with a length of 75mm by 12%. This reduction increases linearly with decreasing density of particles. A velocity field acting on the particle in the fall and rotation was presented. The results of the study prove the possibility to reduce the scatter of the particles during the mat's formation, that in turns can increase the board’s bending strength.

  9. Experimental study of high temperature particle dropping in coolant liquid

    Institute of Scientific and Technical Information of China (English)

    LI Tianshu; YANG Yanhua; LI Xiaoyan; HU Zhihua

    2007-01-01

    A series of experiments of the premixing stage of fuel-coolant interactions (FCI), namely the particles falling into water, were carried out. The force on the particles during the course of falling has been studied. The dropping character of hot particle was influenced by three main parameters, i.e., particle temperature, particle diameter and coolant subcooling that varied over a wide range. A high-speed camera recorded the falling speed of the particle and the moving curves were obtained. The experimental results showed that for the film boiling on the surface of particle and water, the temperature increase of either particle or coolant would slow down the particle falling velocity. The falling velocity of particle in small diameter is lower than that of the bigger particle. The present work can provide an experimental foundation for further investigation of high-speed transient evaporation heat transfer.

  10. Streamwise decrease of the 'unsteady' virtual velocity of gravel tracers

    Science.gov (United States)

    Klösch, Mario; Gmeiner, Philipp; Habersack, Helmut

    2017-04-01

    Gravel tracers are usually inserted and transported on top of the riverbed, before they disperse vertically and laterally due to periods of intense bedload, the passage of bed forms, lateral channel migration and storage on bars. Buried grains have a lower probability of entrainment, resulting in a reduction of overall mobility, and, on average, in a deceleration of the particles with distance downstream. As a consequence, the results derived from tracer experiments and their significance for gravel transport may depend on the time scale of the investigation period, complicating the comparison of results from different experiments. We developed a regression method, which establishes a direct link between the transport velocity and the unsteady flow variables to yield an 'unsteady' virtual velocity, while considering the tracer slowdown with distance downstream in the regression. For that purpose, the two parameters of a linear excess shear velocity formula (the critical shear velocity u*c and coefficient a) were defined as functions of the travelled distance since the tracer's insertion. Application to published RFID tracer data from the Mameyes River, Puerto Rico, showed that during the investigation period the critical shear velocity u*c of tracers representing the median bed particle diameter (0.11 m) increased from 0.36 m s-1 to 0.44 m s-1, while the coefficient a decreased from the dimensionless value of 4.22 to 3.53, suggesting a reduction of the unsteady virtual velocity at the highest shear velocity in the investigation period from 0.40 m s-1 to 0.08 m s-1. Consideration of the tracer slowdown improved the root mean square error of the calculated mean displacements of the median bed particle diameter from 8.82 m to 0.34 m. As in previous work these results suggest the need of considering the history of transport when deriving travel distances and travel velocities, depending on the aim of the tracer study. The introduced method now allows estimating the

  11. Rainbow Particle Imaging Velocimetry

    KAUST Repository

    Xiong, Jinhui

    2017-04-27

    Despite significant recent progress, dense, time-resolved imaging of complex, non-stationary 3D flow velocities remains an elusive goal. This work tackles this problem by extending an established 2D method, Particle Imaging Velocimetry, to three dimensions by encoding depth into color. The encoding is achieved by illuminating the flow volume with a continuum of light planes (a “rainbow”), such that each depth corresponds to a specific wavelength of light. A diffractive component in the camera optics ensures that all planes are in focus simultaneously. With this setup, a single color camera is sufficient to track 3D trajectories of particles by combining 2D spatial and 1D color information. For reconstruction, this thesis derives an image formation model for recovering stationary 3D particle positions. 3D velocity estimation is achieved with a variant of 3D optical flow that accounts for both physical constraints as well as the rainbow image formation model. The proposed method is evaluated by both simulations and an experimental prototype setup.

  12. Diffraction imaging and velocity analysis using oriented velocity continuation

    KAUST Repository

    Decker, Luke

    2014-08-05

    We perform seismic diffraction imaging and velocity analysis by separating diffractions from specular reflections and decomposing them into slope components. We image slope components using extrapolation in migration velocity in time-space-slope coordinates. The extrapolation is described by a convection-type partial differential equation and implemented efficiently in the Fourier domain. Synthetic and field data experiments show that the proposed algorithm is able to detect accurate time-migration velocities by automatically measuring the flatness of events in dip-angle gathers.

  13. Analysis of Enhanced Velocity Signals Observed during Solar Flares

    Indian Academy of Sciences (India)

    Brajesh Kumar; B. Ravindra

    2006-12-01

    Solar flares are known to release a large amount of energy. It is believed that the flares can excite velocity oscillations in active regions. We report here the changes in velocity signals in three active regions which have produced large X-class flares. The enhanced velocity signals appeared during the rise time of the GOES soft X-ray flux. These signals are located close to the vicinity of the hard X-ray source regions as observed with RHESSI. The power maps of the active region show enhancement in the frequency regime 5–6.5 mHz, while there is feeble or no enhancement of these signals in 2–4 mHz frequency band. High energy particles with sufficient momentum seem to be the cause for these observed enhanced velocity signals.

  14. Reconstructing the three-dimensional local dark matter velocity distribution

    CERN Document Server

    Kavanagh, Bradley J

    2016-01-01

    Directionally sensitive dark matter (DM) direct detection experiments present the only way to observe the full three-dimensional velocity distribution of the Milky Way halo local to Earth. In this work we compare methods for extracting information about the local DM velocity distribution from a set of recoil directions and energies in a range of hypothetical directional and non-directional experiments. We compare a model independent empirical parameterisation of the velocity distribution based on an angular discretisation with a model dependent approach which assumes knowledge of the functional form of the distribution. The methods are tested under three distinct halo models which cover a range of possible phase space structures for the local velocity distribution: a smooth Maxwellian halo, a tidal stream and a debris flow. In each case we use simulated directional data to attempt to reconstruct the shape and parameters describing each model as well as the DM particle properties. We find that the empirical pa...

  15. Microstructure, Processing, Performance Relationships for High Temperature Coatings

    Energy Technology Data Exchange (ETDEWEB)

    Thomas M. Lillo

    2011-04-01

    This work evaluates the suitability of iron aluminide coatings for use in high temperature fossil fuel combustion environments, such as boiler applications. The coatings are applied using High Velocity Oxy-Fuel (HVOF) thermal spray techniques. Iron aluminide coatings, with the nominal composition of Fe3Al, were applied to various high temperature structural materials (316 Stainless Steel, 9Cr-1Mo steel and Inconel 600) that typically lack inherent resistance to environmental degradation found in fossil fuel combustion atmospheres. Coating/substrate combinations were subjected to thermal cycling to evaluate the effect of HVOF parameters, coating thickness, substrate material and substrate surface roughness on the resistance to coating delamination and cracking. It was found that substrate surface roughness had a profound influence on the performance of a given substrate/coating system and that surface preparation techniques will need to be tailored to the specific substrate material. Also, higher particle velocity during HVOF thermal spray deposition of the iron aluminide coatings tended to result in better-performing coating/substrate systems with less delamination at the coating/substrate interface. Some combinations of HVOF parameters, coating thickness and substrate materials were found to perform extremely well even at temperatures up to 900oC. However, in some cases, substantial reactions at the interface were observed.

  16. Effects of Particles Collision on Separating Gas–Particle Two-Phase Turbulent Flows

    KAUST Repository

    Sihao, L. V.

    2013-10-10

    A second-order moment two-phase turbulence model incorporating a particle temperature model based on the kinetic theory of granular flow is applied to investigate the effects of particles collision on separating gas–particle two-phase turbulent flows. In this model, the anisotropy of gas and solid phase two-phase Reynolds stresses and their correlation of velocity fluctuation are fully considered using a presented Reynolds stress model and the transport equation of two-phase stress correlation. Experimental measurements (Xu and Zhou in ASME-FED Summer Meeting, San Francisco, Paper FEDSM99-7909, 1999) are used to validate this model, source codes and prediction results. It showed that the particles collision leads to decrease in the intensity of gas and particle vortices and takes a larger effect on particle turbulent fluctuations. The time-averaged velocity, the fluctuation velocity of gas and particle phase considering particles colli-sion are in good agreement with experimental measurements. Particle kinetic energy is always smaller than gas phase due to energy dissipation from particle collision. Moreover, axial– axial and radial–radial fluctuation velocity correlations have stronger anisotropic behaviors. © King Fahd University of Petroleum and Minerals 2013

  17. Are There Faster Than Light Particles?

    Science.gov (United States)

    Kreisler, Michael N.

    1969-01-01

    Based upon recent relativistic theory, the researcher describes the search for tachyons, particles having velocities greater than that of a light. The properties of these particles are speculated upon. The author delineates the difficulties anticipated in their detection and the assumptions underlying their methodology. (RR)

  18. Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

    Science.gov (United States)

    Luo, Jun; Cai, Zhenbing; Mo, Jiliang; Peng, Jinfang; Zhu, Minhao

    2016-05-01

    Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed (HVOF) technique WC-17Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffractrometry (XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy (OM), and surface topography. The experimental results reveal that the WC-17Co coating adjusted the boundary between the partial slip regime (PSR) and the slip regime (SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate's coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating's higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17Co coating in prevention of rotational fretting wear.

  19. Flow of colloid particle solution past macroscopic bodies and drag crisis

    Energy Technology Data Exchange (ETDEWEB)

    Iordanskii, S. V., E-mail: iordansk@itp.ac.ru [Russian Academy of Sciences, Landau Institute for Theoretical Physics (Russian Federation)

    2013-11-15

    The motion of colloid particles in a viscous fluid flow is considered. Small sizes of colloid particles as compared to the characteristic scale of the flow make it possible to calculate their velocity relative to the liquid. If the density of a colloid particle is higher than the density of the liquid, the flow splits into regions in which the velocity of colloid particles coincides with the velocity of the liquid and regions of flow stagnation in which the colloid velocity is higher than the velocity of the fluid. This effect is used to explain qualitatively the decrease in the drag to the flows past macroscopic bodies and flows in pipes.

  20. Dynamics of finite size neutrally buoyant particles in isotropic turbulence

    Energy Technology Data Exchange (ETDEWEB)

    Elhimer, M; Jean, A; Praud, O; Bazile, R; Marchal, M; Couteau, G, E-mail: elhimer@imft.fr [Universite de Toulouse, INPT, UPS, IMFT - Institut de Mecanique des Fluides de Toulouse, Allee Camille Soula, F-31400 Toulouse (France); CNRS, IMFT, F-31400 Toulouse (France)

    2011-12-22

    The dynamics of neutrally buoyant particles suspended in a turbulent flow is investigated experimentally, with particles having diameters larger than the Kolmogorov length scale. To that purpose, a turbulence generator have been constructed and the resulting flow characterized. The fluid was then seeded with polystyrene particles of diameter about 1 mm and their velocity measured separately and simultaneously with the surrounding fluid. Comparison of the velocities statistics between the two phases shows no appreciable discrepancy. However, simultaneous velocity measurement shows that particles may move in different direction from the underlying flow.