scholarly journals Contactless Ultrasonic Cavitation in Alloy Melts

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3610 ◽  
Author(s):  
Koulis Pericleous ◽  
Valdis Bojarevics ◽  
Georgi Djambazov ◽  
Agnieszka Dybalska ◽  
William D. Griffiths ◽  
...  
Keyword(s):  
High Frequency ◽  
Electromagnetic Induction ◽  
Acoustic Resonance ◽  
Grain Refiner ◽  
Melt Treatment ◽  
Treatment Volume ◽  
Added Benefit ◽  
Flow Heat ◽  
Higher Temperature ◽  
Software Coupling

A high frequency tuned electromagnetic induction coil is used to induce ultrasonic pressure waves leading to cavitation in alloy melts. This presents an alternative ‘contactless’ approach to conventional immersed probe techniques. The method can potentially offer the same benefits of traditional ultrasonic treatment (UST) such as degassing, microstructure refinement and dispersion of particles, but avoids melt contamination due to probe erosion prevalent in immersed sonotrodes, and it can be used on higher temperature and reactive alloys. An added benefit is that the induction stirring produced by the coil, enables a larger melt treatment volume. Model simulations of the process are conducted using purpose-built software, coupling flow, heat transfer, sound and electromagnetic fields. Modelling results are compared against experiments carried out in a prototype installation. Results indicate strong melt stirring and evidence of cavitation accompanying acoustic resonance. Up to 63% of grain refinement was obtained in commercial purity (CP-Al) aluminium and a further 46% in CP-Al with added Al–5Ti–1B grain refiner.

scholarly journals Hyperfine structure in the arc spectrum of cæsium and nuclear rotation

1928 ◽  
Vol 121 (787) ◽  
pp. 432-447 ◽  
Keyword(s):  
Hyperfine Structure ◽  
Nuclear Spin ◽  
High Frequency ◽  
Principal Series ◽  
Very High Frequency ◽  
Nuclear Rotation ◽  
Higher Temperature ◽  
The Difference ◽  
Mechanical Moment ◽  
Very High

The arc spectrum of cæsium was investigated with the object of finding whether any of its lines possessed hyperfine structure, resulting from a nuclear magnetic moment, due to a quantised nuclear spin. The lines belonging to the principal series should, owing to the greater degree of penetration of the electron in the (1 s or 6 1 ) orbit, and the correspondingly greater interaction, show the greatest effect. The lines of the principal series are very easily broadened if the vapour pressure of the metal becomes high, so that great care had to be used in obtaining the spectrum of cæsium at a sufficiently low temperature. The most satisfactory method of excitation was found to be the application by means of external electrodes of a very high frequency alternating current to a tube filled with helium at about 2 mm. pressure containing a small quantity of cæsium. The tube required slight heating to bring out the cæsium lines; without this the helium spectrum was very much stronger than the metallic spectrum. At a very low vapour pressures of cæsium the discharge was blue in colour. Under these conditions the lines of the principal series showed no broadening greater than that due to thermal agitation, but at a slightly higher temperature the colour of the discharge became purple and the lines broadened. The lines belonging to the principal series were found to be very close doublets with very nearly constant frequencies differences. A theory is worked out which explains the origin of these doublets, assuming a nuclear spin of one half quantum; by correlating the difference in the separation of the hyperfine structure doublets in the 1 s — m 2 p 3/2 lines and the 1 s — m 2 p 1/2 lines, it is shown that a ratio of the magnetic to the mechanical moment of the nucleus about twice as great as the corresponding ratio for the electron would account for the observed frequency differences. The spectral notation used throughout is that of Hund. The results are compared with those found for the hyperfine structure of some of the bismuth lines by Back and Goudsmid, and are found to be in satisfactory agreement. A selection principle is found which applies both to the bismuth and the cæsium spectrum.

A hybrid coil system for high frequency electromagnetic induction sensing

2017 ◽  
Author(s):  
John B. Sigman ◽  
Benjamin E. Barrowes ◽  
Yinlin Wang ◽  
Hollis J. Bennett ◽  
Janet E. Simms ◽  
...  
Keyword(s):  
High Frequency ◽  
Electromagnetic Induction ◽  
Coil System

Coil design considerations for a high-frequency electromagnetic induction sensing instrument

2016 ◽  
Author(s):  
John B. Sigman ◽  
Benjamin E. Barrowes ◽  
Yinlin Wang ◽  
Hollis J. Bennett ◽  
Janet E. Simms ◽  
...  
Keyword(s):  
High Frequency ◽  
Electromagnetic Induction ◽  
Coil Design ◽  
Design Considerations

scholarly journals Flame response to high-frequency oscillations in a cryogenic oxygen/hydrogen rocket combustor

2019 ◽  
Author(s):  
N. Fdida ◽  
J. Hardi ◽  
H. Kawashima ◽  
B. Knapp ◽  
M. Oschwald ◽  
...  
Keyword(s):  
High Frequency ◽  
Acoustic Resonance ◽  
High Amplitude ◽  
Operating Conditions ◽  
Test Facility ◽  
Response Analysis ◽  
Rocket Engines ◽  
Acoustic Oscillations ◽  
Spatially Resolved ◽  
Flame Response

Experiments presented in this paper were conducted with the BKH rocket combustor at the European Research and Technology Test Facility P8, located at DLR Lampoldshausen. This combustor is dedicated to study the effects of high magnitude instabilities on oxygen/hydrogen flames, created by forcing high-frequency (HF) acoustic resonance of the combustion chamber. This work addresses the need for highly temporally and spatially resolved visualization data, in operating conditions representative of real rocket engines, to better understand the flame response to high amplitude acoustic oscillations. By combining ONERA and DLR materials and techniques, the optical setup of this experiment has been improved to enhance the existing database with more highly resolved OH* imaging to allow detailed response analysis of the flame. OH* imaging is complemented with simultaneous visible imaging and compared to each other here for their ability to capture flame dynamics.

Simulation And Development Of Electronic Ballast for High Pressure Discharge Lamps

2021 ◽  
pp. 86-92
Author(s):  
Vladimir G. Kulikov ◽  
Albert A. Ashryatov
Keyword(s):  
High Pressure ◽  
High Frequency ◽  
Acoustic Resonance ◽  
High Frequency Current ◽  
Electronic Ballast ◽  
Advantages And Disadvantages ◽  
Test Operation ◽  
Pressure Discharge ◽  
Frequency Current ◽  
High Pressure Discharge

The advantages and disadvantages of using electromagnetic ballasts for power supply of high pressuredischarge lamps (HPDL) are considered. The advantages of using electronic ballasts for supplying HPDL are shown. The analysis is fulfilled of the operation of the HPDL when powered by a high-frequency current, in particular, high-pressure sodium lamps (HPSL). It is indicated that when high-pressure discharge lamps are supplied with a high-frequency current, acoustic resonance may appear. The basic requirements to be met by electronic ballasts for HPSL have been determined. The topology of construction of electronic ballasts for supplying HPDL with a capacity of up to 1 kW has been selected. It has been established that half-bridge converters with inductive ballast and active power factor corrector (PFC) allow maintaining a stable power on the lamp while changing its parameters and efficiency. Mathematical modelling of the electronic ballast based on a half-bridge converter and an ignition device for the sodium discharge lamps DNaT type has been carried out. According to the proposed topology, the electronic ballast was developed for a DNaT 600 lamp powered from the 380 V network. Test operation of the lamps confirmed the reliability of the proposed electronic ballast topology.

A design methodology for acoustic resonance-free, high-frequency, dimmable electronic ballast for high-pressure sodium-vapour lamps

2019 ◽  
Vol 52 (4) ◽  
pp. 524-539
Author(s):  
B Gupta Bakshi ◽  
B Roy
Keyword(s):  
High Pressure ◽  
High Frequency ◽  
Design Methodology ◽  
Power Level ◽  
Harmonic Distortion ◽  
Acoustic Resonance ◽  
Electrical Characteristics ◽  
Electronic Ballast ◽  
Lamp Current ◽  
Sodium Vapour

This paper presents a methodology to design acoustic resonance-free, high-frequency, dimmable electronic ballasts for high-pressure sodium vapour (HPSV) lamps having a range of rated wattage (70–400 W). After estimation of the ‘quiet window’ of an HPSV lamp, the proposed iterative algorithm is able to determine the acoustic resonance-free driving frequencies of a design ballast corresponding to 50%–100% power level. On the other hand, a developed wattage and voltage independent HPSV lamp model facilitates finding the required electrical characteristics of HPSV lamps without performing laboratory experimentation. Using the estimated driving frequencies of a design ballast and the synthesized electrical characteristics of the lamp, the design circuit parameters of an electronic ballast are determined. Performance evaluation of the designed ballasts, carried out on the Matlab–Simulink platform, indicates several important attributes, viz. higher power control accuracy (deviation ≤3.69%), near-unity lamp power factor (≥0.98), lower lamp current crest factor (<1.7) and lower lamp current total harmonic distortion (≤12.63%). Results establish the effectiveness of the proposed design methodology to design lightweight and compact electronic ballasts for HPSV lamps with less effort than conventional design practice.

scholarly journals High-Frequency Electromagnetic Induction (HFEMI) Sensor Results from IED Constituent Parts

2019 ◽  
Vol 11 (20) ◽  
pp. 2355 ◽  
Author(s):  
Benjamin Barrowes ◽  
Mikheil Prishvin ◽  
Guy Jutras ◽  
Fridon Shubitidze
Keyword(s):  
High Frequency ◽  
Electromagnetic Induction ◽  
Low Frequency ◽  
Test Site ◽  
Frequency Range ◽  
Discrimination Capability ◽  
Metal Detectors ◽  
Metallic Parts ◽  
Ground Penetrating ◽  
Improvised Explosive

The detection and classification of subsurface improvised explosive devices (IEDs) remains one of the most pressing military and civilian problems worldwide. These IEDs are often intentionally made with either very small metallic parts or less-conducting parts in order to evade low-frequency electromagnetic induction (EMI) sensors, or metal detectors, which operate at frequencies of 50 kHz or less. Recently, high-frequency electromagnetic induction (HFEMI), which extends the established EMI frequency range above 50 kHz to 20 MHz and bridges the gap between EMI and ground-penetrating radar frequencies, has shown promising results related to detecting and identifying IEDs. In this higher frequency range, less-conductive targets display signature inphase and quadrature responses similar to higher conducting targets in the LFEMI range. IED constituent parts, such as carbon rods, small pressure plates, conductivity voids, low metal content mines, and short wires respond to HFEMI but not to traditional low-frequency EMI (LFEMI). Results from recent testing over mock-ups of less-conductive IEDs or their components show distinctive HFEMI responses, suggesting that this new sensing realm could augment the detection and discrimination capability of established EMI technology. In this paper, we present results of using the HFEMI sensor over IED-like targets at the Fort AP Hill test site. We show that results agree with numerical modeling thus providing motives to incorporate sensing at these frequencies into traditional EMI and/or GPR-based sensors.

Research on Acoustic Emission Signals Characteristics of Pitting Corrosion on 304 Stainless Steel

2013 ◽  
Author(s):  
Zhongzheng Zhang ◽  
Hua Liang ◽  
Cheng Ye ◽  
Wensheng Cai ◽  
Jun Jiang ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Acoustic Emission ◽  
Pitting Corrosion ◽  
High Frequency ◽  
Low Frequency ◽  
Ferric Chloride Solution ◽  
304 Stainless Steel ◽  
Flexural Wave ◽  
Higher Temperature ◽  
Ae Signals

In order to study acoustic emission (AE) signals waveform characteristics of pitting corrosion on 304 stainless steel under higher temperature than lower one, Pitting corrosion process on 304 stainless steel in 6% ferric chloride solution at 70°C was monitored by AE technology. Wavelet transform and mode acoustic emission technology were combined to deal with recorded AE signals, and micromorphologic observation was performed for further verification. The results showed that signal waveform was mainly composed of low-frequency (<100KHz) flexural wave with larger amplitude & energy and high-frequency (>100KHz) expansion wave with lesser amplitude & energy. The research results have some certain significance for AE monitoring of pitting corrosion on 304 stainless steel.

Scrutinization of 3D flow and nonlinear radiative heat transfer of non-Newtonian nanoparticles over an exponentially sheet

2019 ◽  
Vol 30 (4) ◽  
pp. 2051-2062 ◽  
Author(s):  
Ganesh Kumar K.
Keyword(s):  
Numerical Modeling ◽  
Prandtl Number ◽  
Numerical Technique ◽  
Three Dimensional ◽  
Content Type ◽  
Flow Heat ◽  
Higher Temperature ◽  
Exponentially Stretching Surface ◽  
Exponentially Stretching

Purpose This paper aims to explore the consequence of chemical reaction on three-dimensional flow, heat and mass transfer of a Casson nano liquid over exponentially stretching surface. A numerical technique of RKF-45 method is applied to resolve the nonlinear ordinary differential equations, which are obtained by applying the similarity transformation to the nonlinear partial differential system. Design/methodology/approach Role of significant parameters on flow fields are observed graphically. Also, the strength of heat exchange (Nusselt number) and the strength of mass exchange (Sherwood number) are analyzed. Findings The results of numerical modeling showed that, the Prandtl number plays a key role in reducing the temperature of the system. Further, the radiation parameters manufacture a lot of heat to operating fluid and higher temperature exponent parameter and enhance the temperature of the fluid. Originality/value The results of numerical modeling showed that, the Prandtl number plays a key role in reducing the temperature of the system. Further, the radiation parameters manufacture a lot of heat to operating fluid and higher temperature exponent parameter and enhance the temperature of the fluid.

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