FLUCTUATIONS IN THE PRE‐BREAKDOWN REGION OF DOUBLE INJECTIONP‐I‐NDIODES

1965 ◽  
Vol 6 (7) ◽  
pp. 126-128 ◽  
Author(s):  
A. G. Jordan ◽  
R. W. Knepper
Keyword(s):  
Breakdown Region

ON THE MECHANISMS OF POROUS SILICON COMBUSTION IN OXYGEN AND AIR ATMOSPHERE WHEN SODIUM PERCHLORATE IS INCORPORATED IN PORES

2020 ◽  
Author(s):  
V. N. MIRONOV ◽  
◽  
O. G. PENYAZKOV ◽  
P. N. KRIVOSHEYEV ◽  
I. A. IVANOV ◽  
...  
Keyword(s):  
Porous Silicon ◽  
Porous Layer ◽  
Sodium Perchlorate ◽  
Spark Ignition ◽  
Joule Heat ◽  
Air Atmosphere ◽  
Breakdown Region ◽  
Ignition And Combustion ◽  
Heating Up

The processes of pSi ignition and combustion in oxygen are described. When spark ignition in the porous layer releases the Joule heat, it leads to a significant heating-up of the breakdown region.

scholarly journals Computation of Energy Absorption and Residual Voltage in a Fourth Rail LRT Station Arresters in EMTP-RV: A Comparative Study

2021 ◽  
Author(s):  
Farah Asyikin Abd Rahman ◽  
Mohd Zainal Abidin Ab Kadir ◽  
Ungku Anisa Ungku Amirulddin ◽  
Miszaina Osman
Keyword(s):  
Electromagnetic Transients ◽  
Lightning Strike ◽  
Voltage Gradient ◽  
Urban Transit ◽  
Residual Voltage ◽  
Voltage Ratio ◽  
Lightning Channel ◽  
Breakdown Region ◽  
Current Region ◽  
Performance Results

AbstractThis paper presents a study on the performance of a fourth rail direct current (DC) urban transit affected by an indirect lightning strike. The indirect lightning strike was replicated and represented by a lightning-induced overvoltage by means of the Rusck model, with the sum of two Heidler functions as its lightning channel base current input, on a perfect conducting ground. This study aims to determine whether an indirect lightning strike has any influence with regard to the performance of the LRT Kelana Jaya line, a fourth rail DC urban transit station arrester. The simulations were carried out using the Electromagnetic Transients Program–Restructured Version (EMTP–RV), which includes the comparison performance results between the 3EB4-010 arrester and PDTA09 arrester when induced by a 90 kA (9/200 µs). The results demonstrated that the PDTA09 arrester showed better coordination with the insulated rail bracket of the fourth rail. It allowed a lower residual voltage and a more dynamic response, eventually resulting in better voltage gradient in the pre-breakdown region and decreased residual voltage ratio in the high current region.

Describing the Mechanism of Instability Suppression Using a Central Pilot Flame With Coupled Experiments and Simulations

2021 ◽  
Author(s):  
Jihang Li ◽  
Hyunguk Kwon ◽  
Drue Seksinsky ◽  
Daniel Doleiden ◽  
Jacqueline O’Connor ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Vortex Breakdown ◽  
Eddy Simulation ◽  
Breakdown Region ◽  
Large Eddy ◽  
Rate Oscillations ◽  
Combustion Oscillation ◽  
The Stability ◽  
The Impact

Abstract Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stability of the main flame. This hypothesis is based on a series of experimental results that show that pilot efficacy is a strong function of pilot equivalence ratio but not pilot flow rate, which would indicate that the temperature of the pilot gases as well as the combustion intensity of the pilot flame play more of a role in oscillation stabilization than the length of the pilot flame relative to the main flame. Further, the pilot flame efficacy increases with pilot flame equivalence ratio until it matches the main flame equivalence ratio; at pilot equivalence ratios greater than the main equivalence ratio, the pilot flame efficacy does not change significantly with pilot equivalence ratio. To understand these results, we use large-eddy simulation to provide a detailed analysis of the flow in the region of the pilot flame and the transport of radical species in the region between the main flame and pilot flame. The simulation, using a flamelet/progress variable-based chemistry tabulation approach and standard eddy viscosity/diffusivity turbulence closure models, provides detailed information that is inaccessible through experimental measurements.

Effect of 3d eddy currents on stray field in plasma breakdown region

2000 ◽  
Vol 8 (2) ◽  
pp. 79-94 ◽  
Author(s):  
A. Belov ◽  
V. Belyakov ◽  
V. Kokotkov ◽  
V. Kukhtin ◽  
K. Lobanov ◽  
...  
Keyword(s):  
Eddy Currents ◽  
Stray Field ◽  
Breakdown Region ◽  
Plasma Breakdown

scholarly journals The Role of Tip Leakage Vortex Breakdown in Compressor Rotor Aerodynamics

1998 ◽  
Author(s):  
Masato Furukawa ◽  
Masahiro Inoue ◽  
Kazuhisa Saiki ◽  
Kazutoyo Yamada
Keyword(s):  
Flow Rate ◽  
Peak Pressure ◽  
Vortex Breakdown ◽  
Pressure Rise ◽  
Suction Surface ◽  
Tip Leakage Vortex ◽  
Rotor Aerodynamics ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Breakdown Region

The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier-Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubble-like recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending to the upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow resulting from the contraction of the bubble-like structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at near-stall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise and pitchwise directions. The growth of the breakdown causes the blockage and the loss to increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.

Messung und Deutung extrem hoher Rauschtemperaturen von Siliciumdioden im Durchbruchbereich.

1964 ◽  
Vol 19 (5) ◽  
pp. 563-572
Author(s):  
H. Melchior ◽  
M. J. O. Strutt
Keyword(s):  
Field Emission ◽  
Noise Temperature ◽  
Thermal Fluctuations ◽  
Internal Field ◽  
Switching Noise ◽  
Noise Spectral Density ◽  
Avalanche Behavior ◽  
Sufficient Energy ◽  
Breakdown Region ◽  
Stable Burning

Semiconductor-diodes operated in the breakdown region show large noise fluctuations. The noise fluctuations associated with the onset of astable burning microplasmas are well known. The noise spectral density for such statistical switching microplasma pulses has been calculated and agrees with measured values. ZEXER-diodes, in which internal field emission is the cause of the breakdown or ZENER-diodes with stable burning microplasmas, the so-called avalanches diodes, show large noise fluctuations too. These spontaneous fluctuations of voltage and current can be explained by the thermal fluctuations of the breakdown-carriers heated up by the high field in the transition region of a p-n junction. ZENER-diodes break down by internal field emission, when the measured noise temperature does not exceed about 18 000 °K. In this case the aequivalent noise temperature grows proportional to the square root of the breakdown current. When the noise temperature of the breakdown is higher than about 18 000°K, the carriers have sufficient energy to produce electron-hole pairs by ionization. The stable parts of breakdown characteristics with noise temperatures above about 18 000°K show avalanche behavior. Often microplasma switching noise is observed. In the stable burning parts of avalanche breakdown characteristics, noise temperatures as high as 105 to 107°K are measured. These high noise temperatures can not be fully explained by thermally heated carriers in the breakdown region. It is believed that fluctuations of the ionization breakdown contribute to these noise temperatures.

Shear Layer Flame Stabilization Sensitivities in a Swirling Flow

2012 ◽  
Author(s):  
I. Chterev ◽  
C. W. Foley ◽  
D. R. Noble ◽  
B. A. Ochs ◽  
J. M. Seitzman ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Shear Layer ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Shear Layers ◽  
Flame Stabilization ◽  
Preheat Temperature ◽  
Swirl Number ◽  
Breakdown Region ◽  
Detailed Kinetics

A variety of different flame configurations and heat release distributions can exist in high swirl, annular flows. Each of these different configurations, in turn, has different thermoacoustic sensitivities and influences on combustor emissions, nozzle durability, and liner heating. These different configurations arise because at least three flame stabilization locations are present, associated with the inner and outer shear layers of the annulus, and the stagnation point of the vortex breakdown region. This paper focuses on the sensitivities of the outer shear layer stabilization point to bulkhead temperature, flow velocity, swirl number, preheat temperature, and fuel/air ratio. It also characterizes the hysteresis that is present in conditions where the outer shear layer locally re-attaches and blows off. The sensitivities to bulkhead temperature, preheat temperature and fuel/air ratio follow the expected trends. Moreover, the strong bulkhead temperature sensitivities show that computations must include heat transfer to combustor hardware in order to capture flame stabilization correctly. The preheat temperature and fuel/air ratio sensitivities are captured with detailed kinetics calculations of the extinction stretch rate of the mixture. Somewhat counter intuitively, there is little variation in transition conditions with swirl number for the Sm∼0.6 and 0.8 swirlers analyzed here. Finally, velocity sensitivities are in many cases much weaker than what would be predicted assuming that the fluid mechanic straining time scales as 1/u.

scholarly journals Noise Parameter Analysis of SiGe HBTs for Different Sizes in the Breakdown Region

2016 ◽  
Vol 2016 ◽  
pp. 1-5
Author(s):  
Chie-In Lee ◽  
Yan-Ting Lin ◽  
Wei-Cheng Lin
Keyword(s):  
Heterojunction Bipolar Transistors ◽  
Silicon Germanium ◽  
Noise Figure ◽  
Rf Circuits ◽  
Bipolar Transistors ◽  
Parameter Analysis ◽  
Noise Performance ◽  
Noise Spectral Density ◽  
Breakdown Mechanism ◽  
Breakdown Region

Noise parameters of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) for different sizes are investigated in the breakdown region for the first time. When the emitter length of SiGe HBTs shortens, minimum noise figure at breakdown decreases. In addition, narrower emitter width also decreases noise figure of SiGe HBTs in the avalanche region. Reduction of noise performance for smaller emitter length and width of SiGe HBTs at breakdown resulted from the lower noise spectral density resulting from the breakdown mechanism. Good agreement between experimental and simulated noise performance at breakdown is achieved for different sized SiGe HBTs. The presented analysis can benefit the RF circuits operating in the breakdown region.

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