Chamber pressure

About: Chamber pressure is a research topic. Over the lifetime, 2988 publications have been published within this topic receiving 30725 citations.

Study of dry etching for GaN and InGaN-based laser structure using inductively coupled plasma reactive ion etching

Abstract: Dry etching of undoped, n-GaN, p-GaN and InGaN laser structure was investigated by inductively coupled plasmas reactive ion etching (ICP-RIE) using Ni mask. As Cl 2 /Ar gas flow rates were fixed at 10/25 sccm, the etched surface roughness has the lowest value of 0.2 nm at constant ICP/bias power=300/100 W and 5 mTorr chamber pressure for undoped GaN. The highest etching rate of 12,000 A/min for n-GaN was achieved at 30 mTorr, 300 W ICP, 100 W bias power using low Cl 2 flow rate (Cl 2 /Ar=10/25 sccm) gas mixtures. The surface roughness was dependent of bias power and chamber pressure, and shows a low root mean square (rms) roughness value of about 1 nm at 50 W of bias power for n-GaN and p-GaN. For etching of InGaN laser structure using high Cl 2 flow rate (Cl 2 /Ar=50/20 sccm) and low chamber pressure 5 mTorr, a smooth mirror-like facet of InGaN laser diode structure was obtained. Using these etching parameters, mirror-like facets can be obtained which can be used for the fabrication of nitride-based laser diodes. Moreover, at the fixed Cl 2 /Ar flow rate of 10/25 sccm, ICP/bias power of 200/100 W and chamber pressure of 30 mTorr, the InGaN-based materials nanorods were fabricated with a density of about 10 8 cm −2 and dimension of 50–100 nm.

Acoustic Attenuation Experiments on Subscale, Cold-Flow Rocket Motors

Abstract: Acoustic dissipation studies were undertaken using a subscale cold-flow rocket motor model to determine the effect of purely geometric variables on the acoustic performance leading to axial mode combustion instability. Cold air served as the working fluid to simulate the internal flow and to obtain a critical nozzle throat. By using interchangeable parts, it was possible to vary the nozzle throat diameter and to simulate the geometry of a cylindrical-bore grain at various motor burn times. The model was acoustically driven by three separate methods: pulse decay, steady-state decay, and steady-state resonance. The methods are compared, and the applicability of each is discussed. Test results show that the transmission of acoustic energy through the nozzle was the largest source of loss for the axial mode and that the losses increase linearly with / (ratio of nozzle throat area to grain port area). Acoustic bulk and wall losses were negligible compared with the nozzle losses. The results also showed that the nozzle losses are independent of the way Jis changed and thus can be scaled. The test equipment has been established as a semi-automated facility to evaluate models with more complex geometries, to test chamber damping devices, and to gather design and research data. Nomenclature a* = critical nozzle velocity, m/sec c = velocity of sound at stagnation conditions, m/sec cp = specific heat at constant pressure, joules/kg °C D = diameter of the grainport channel, m /o = first mode resonant frequency, cps fltf2 = half-power frequencies, cps J = ratio of nozzle throat area to grain port area L = length of motor chamber, m M = Mach number p = acoustic or a.c. pressure (p-to-p), newton/m2 po = initial acoustic or a.c. pressure (p-to-p), newton/m2 pr = Prandtl number Q = quality factor t = time, sec V = d.c. or mean chamber gas velocity, m/sec a = temporal damping constant, sec"1 7 = ratio of specific heats K = thermal conductivity of gas, joule/m sec°C IJL = viscosity, newton sec/m2 TT '= 3.1416 p = d.c. or mean gas density, kg/m3 PO = stagnation gas density at nozzle, kg/m3 p* = d.c. gas density at sonic nozzle throat, kg/m3 co = angular frequency, r ad/sec UQ = angular resonant frequency, rad/sec

Combustion Effects in Confined Explosions

Abstract: Results of shock-dispersed-fuel (SDF) explosion experiments are presented. The SDF charge consisted of a spherical 0.5-g PETN booster surrounded by 1 g of fuel, either flake aluminum (Al) powder or TNT. The charge was placed at the center of a sealed chamber. Three cylindrical chambers (volumes of 6.6, 20, and 40 l with L/D = 1) and three tunnels (L/D = 3.8, 4.65, and 12.5) were used to explore the influence of chamber volume and geometry on completeness of combustion. Detonation of the SDF charge created an expanding cloud of explosion product gases and hot fuel (Al or TNT). When this fuel mixed with air, it formed a turbulent combustion cloud that consumed the fuel and liberated additional energy (31 kJ/g for Al or 15 kJ/g for TNT) over and above detonation of the booster (6 kJ/g) that created the explosion. Static pressure gauges were the main diagnostic. Pressure and impulse histories for explosions in air were much greater than those recorded for explosions in nitrogen—thereby demonstrating that combustion has a dramatic effect on the chamber pressure. This effect increases as the confinement volume decreases and the excess air ratio approaches values between 2 and 3.5.

Lean Partially Premixed Combustion Investigation of Methane Direct-Injection Under Different Characteristic Parameters

Abstract: The effects of hydrogen addition, diluent addition, injection pressure, chamber pressure, chamber temperature and turbulence intensity on methane–air partially premixed turbulent combustion have been studied experimentally using a constant volume combustion chamber (CVCC). The fuel–air mixture was ignited by centrally located electrodes at given spark delay times of 1, 5, 40, 75 and 110 milliseconds. Experiments were performed for a wide range of hydrogen volumetric fractions (0% to 40%), exhaust gas recirculation (EGR) volumetric fractions (0% to 25% as a diluent), injection pressures (30–90 bar), chamber pressures (1–3 bar), chamber temperatures (298–432 K) and overall equivalence ratios of 0.6, 0.8, and 1.0. Flame propagation images via the Sclieren/Shadowgraph technique, combustions characteristics via pressure derived parameters and pollutant concentrations were analyzed for each set of conditions. The results showed that peak pressure and maximum rate of pressure rise increased with the increase in chamber pressure and temperature while changing injection pressure had no considerable effect on pressure and maximum rate of pressure rise. The peak pressure and maximum rate of pressure rise increased while combustion duration decreased with simultaneous increase of hydrogen content. The lean burn limit of methane–air turbulent combustion was improved with hydrogen addition. Addition of EGR increased combustion instability and misfiring while decreasing the emission of nitrogen oxides (NOx).Copyright © 2013 by ASME