Showing papers on "Chamber pressure published in 2021"

Impact of chamber pressure and Si-doping on the surface morphology and electrical properties of homoepitaxial (100) β-Ga2O3 thin films grown by MOVPE

Abstract: The influence of chamber pressure and Si-doping on the growth rate, surface morphology and Hall mobility was investigated for β-Ga2O3 thin films homoepitaxially grown by metalorganic vapor phase epitaxy on Mg-doped β-Ga2O3 (100) substrates with 4° miscut. Transitions from step-bunching to step-flow to 2D island growth modes were achieved by varying the chamber pressure from 10 mbar to 40 mbar and/or by varying the O2/Ga ratio. High-quality β-Ga2O3 homoepitaxial thin films with a high charge carrier mobility of 153 cm2/Vs have been obtained at a chamber pressure of 25 mbar and a growth rate of 3.6 nm/min. All Si-doped samples show n-type conducting behavior with carrier concentrations in the range of 1Χ1017 to 2Χ1019 cm-3. When increasing the chamber pressure to 40 mbar step-flow growth mode and high charge carrier mobility can only be preserved by adjusting the O2/Ga ratio and increasing the Ar push gas flow. SIMS and Hall measurements for Si and carrier concentration, respectively, revealed Si compensation at higher tetraethyl orthosilicate flux.

Performance Characterization of a Natural Gas–Air Rotating Detonation Engine

Abstract: An experimental study of a rotating detonation engine (RDE) operating with natural gas and air at elevated chamber pressures and air preheat temperatures was conducted to quantify its performance a...

Face Stability Analysis of EPB Shield Tunnels in Dry Granular Soils Considering Nonuniform Chamber Pressure and a Dynamic Excavation Process

Abstract: The support pressure at the tunnel face of earth pressure balance (EPB) shield machines is usually assumed to be uniform from the crown to the invert, which is a notable simplification of ...

Double Fed Induction Generator Control Design Based on a Fuzzy Logic Controller for an Oscillating Water Column System

Abstract: Oscillating water column (OWC) systems are water power generation plants that transform wave kinetic energy into electrical energy by a surrounded air column in a chamber that changes its pressure through the waves motion. The chamber pressure output spins a Wells turbine that is linked to a doubly fed induction generator (DFIG), flexible devices that adjust the turbine speed to increase the efficiency. However, there are different nonlinearities associated with these systems such as weather conditions, uncertainties, and turbine stalling phenomenon. In this research, a fuzzy logic controller (FLC) combined with an airflow reference generator (ARG) was designed and validated in a simulation environment to display the efficiency enhancement of an OWC system by the regulation of the turbine speed. Results show that the proposed framework not only increased the system output power, but the stalling is also avoided under different pressure profiles.

Numerical simulation of plasma jet characteristics under very low-pressure plasma spray conditions

Abstract: Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, velocity and pressure fields. However, as PS-PVD is generally operated at pressures below 500 Pa, a question rises about the validity of the CFD predictions that are based on the continuum assumption. This study dealt with CFD simulations for a PS-PVD system operated either with an argon-hydrogen plasma jet at low-power (<50 kW) or with an argon-helium plasma jet at high-power (≥50 kW). The effect of the net arc power and chamber pressure on the plasma jet characteristics and local gradient Knudsen number (Kn) was systematically investigated. The Kn was found to be lower than 0.2, except in the region corresponding to the first expansion shock wave. The peak value in this region decreased rapidly with an increase in the arc net power and the width of this region decreased with an increase in the deposition chamber pressure. Based on the results of the study, the local Knudsen number was introduced for detecting conditions where the continuum approach is valid under PS-PVD conditions for the first time and the CFD simulations could be reasonably used to determine a process parameter window under the conditions of this study.

Experimental Investigation of Wall Heat Flux in a Rotating Detonation Rocket Engine

Abstract: An experimental test campaign was conducted for a rotating detonation rocket engine (RDRE) using gaseous oxygen and RP-2 at operating pressures of 3–18 atm. The copper chamber outer wall was instru...

Regression Rate Enhancement of Hybrid Rockets by Introducing Novel Distributed Tube Injector

Abstract: Low fuel regression rate is one of the major drawbacks of hybrid rocket motors. In this study, a novel injector concept is proposed to provide a substantial enhancement in the fuel regression rate....

Finding the optimum design of the planar cutoff probe through a computational study

Abstract: A new plasma diagnostic tool called the planar cutoff probe (PCP), recently developed by Kim et al. [Plasma Sources Sci. Technol. 28, 015004(2019)], can be embedded into a chamber wall or wafer chuck electrode for non-invasive electron density measurements. The application feasibility of the probe has so far been demonstrated in terms of signal-to-noise ratio; however, for the successful application of the PCP to real plasma processing, its design should first be optimized based on a comprehensive investigation of its characteristics. Therefore, in this paper, the effects of various parameters on the measurement characteristics of the PCP are investigated and analyzed via 3D full electromagnetic wave simulation. Results show that PCP measurement discrepancies vary by numerous controllable parameters, namely, wafer thickness and relative dielectric constant, antenna distance, input electron density, and chamber pressure. Based on these findings, the condition with the smallest measurement discrepancy and where PCP measurement performance is least affected by the parameters is found and discussed.

Experimental Response of Capillary Tube Attenuated Pressure Measurements Under High-Amplitude, Nonlinear Forcing

Abstract: The response behavior of capillary tube attenuated pressure sensor arrangements is studied using a rotating detonation engine as a nonlinear pressure wave source. The resulting measured pressures a...

Experimental Investigation of Viscosity and Combustion Characteristics of N-Butanol/Diesel Blends

Abstract: Bio-derived butanol is a potential CO2 neutral alternative fuel to be applied in internal combustion engines. However, the physical and combustion characteristics have to be fully understood before it can be used efficiently in engines. This work investigates the viscosity and the combustion characteristics of n-butanol/diesel fuel blends, with a particular focus on the combustion property at low load performance. N-butanol was mixed with diesel from 20 vol% up to 80 vol% blend ratio. Tests were performed in a combustion research unit (constant volume) at fixed chamber pressure that mimic a low load condition. The effects of various chamber temperatures and ambient oxygen concentrations (21%, 13%, and 11%) are evaluated. As expected, the viscosity of n-butanol/diesel fuel blends decreases at high temperature. The decrease is non-linear with the blend ratio. The results from the combustion research unit (CRU) show that the ignition delay of n-butanol/diesel fuel blends increases non-linearly as blend ratio increases and decreases as chamber temperature increases when operated with no exhaust gas recirculation (EGR). At low oxygen concentration (EGR-like conditions), the elongated mixing time contributes to more low temperature heat release and longer burn duration. It indicates that inlet heating or low n-butanol blend ratio is necessary to prevent misfire in engine condition. It is interesting to find that the definition of ignition delay as applied in the CRU analysis is not appropriate for low reactivity fuel, especially at low oxygen concentration conditions. When 80 vol% n-butanol and 20 vol% diesel operated at 13% and 11% O2, the chamber pressure rise from the low temperature heat release causes actually a shorter ignition delay for the 550oC case than that of 565oC and 580oC cases. Thus a new definition for start of combustion is suggested (for this case, 1.3 bar above initial chamber pressure).

Theoretical Method of Chamber Pressure for EPB Shield Tunneling Under-Crossing Existing Metro Tunnels

Abstract: As an increasing number of metro lines have been planned or executed in urban area, new tunnel undercrossing existing tunnels has been commonly practiced. Construction of the existing tunnel causes disturbance to the surrounding soil and hence affects the operational parameters of undercrossing tunneling especially the chamber pressure of EPB machine. However, very limited research studies this effect. To fill the gap of knowledge, this paper proposed a new method for calculating the chamber pressure of EPB tunneling machine in undercrossing project. First, the effect of existing tunnel on surrounding soil is classified as removal-and-replacement effect, excavation-induced-disturbance effect, and elastic foundation beam effect. Second, based on analysis of the mutual interaction between existing tunnel and the undercrossing tunneling, three zones have been identified to study the chamber pressure of EPB machine. Next, a new method is proposed to calculate the chamber pressure in the process of undercrossing existing tunnel. Finally, the proposed method has been verified with measured data from two engineering cases. The comparison results show that the proposed method is in good agreement with the measured data, indicating that it is reasonable with high accuracy.

Investigation of Deep Dry Etching of 4H SIC Material for MEMS Applications Using DOE Modelling

Abstract: In this paper the reactive ion etching (RIE) of 4H silicon carbide (SiC) with an SF 6 /O 2 /He gas mixture is investigated in an inductively coupled plasma etcher (ICP). Objective is the analysis of the manufacturing process of a SiC diaphragm for a bulk micromechanical pressure sensor, by etching a cavity into silicon carbide wafer. In addition, the selectivity of etching masks made from Nickel and Copper against SiC are examined. By means of Design of Experiments (DOE) in the software JMP, a test series with 29 recipes is set up. The process is varied over the parameters chamber pressure, source power, platen power, SF 6 flow rate, O 2 flow rate, clamp cooling and mask material. To evaluate the etched samples quantitatively, cross sections of 29 specimens are made. The results are used to create a mathematically model for the prediction of etching rate, profile angle and occurring micro masking. The model is evaluated by etching samples. Etching a cavity with an opening width of 800 µm to a depth of 300 µm with a maximum etching rate of 4 µm/min, vertical profile walls and a smooth and even etched base is demonstrated. The selectivity of the modelled process is 115 compared to Cu, the observed selectivity of Cu is higher compared to Ni.

Equipment Capability Measurement of Laboratory Freeze-Dryers: a Comparison of Two Methods.

Abstract: The objective of this investigation was to evaluate two methods for measuring the maximum sublimation rate that a freeze-dryer will support—the minimum controllable pressure method and the choke point method. Both methods gave equivalent results, but the minimum controllable pressure method is preferred, since it is easier, faster, and less subjective. The ratio of chamber pressure to condenser pressure corresponding to the onset of choked flow was considerably higher in this investigation (up to about 20:1) than in previously published reports. This ratio was not affected by the location of the pressure gauge on the condenser; that is, on the foreline of the vacuum pump versus on the body of the condenser itself. The total water loss due to sublimation as measured by tunable diode laser absorption spectroscopy was consistently within 5% of gravimetrically determined weight loss, regardless of whether the measurement took place during choked versus non-choked process conditions.

Toward Semi-Autonomous Stiffness Adaptation of Pneumatic Soft Robots: Modeling and Validation

Abstract: The constant stiffness of the soft medical robots imposes a cap on their force transmission capacity. To address this limitation, the objective of this study was to investigate the effects of chamber pressure on the stiffness of pneumatic soft robots. To this end, a single-chamber pneumatic soft robot was designed and fabricated. Afterward, a mechanistic model of the robot under external force and chamber pressure was developed. The model was solved as an initial value problem with homogeneous Neumann and Dirichlet boundary conditions. Comparison of the theoretical findings with experimental results for tip displacement and stiffness showed similar trends with a maximum error of 8.7%. The findings confirmed the feasibility of stiffness adaptation through chamber pressure regulation.

Hybrid perovskite films deposited by thermal evaporation from a single source

Abstract: Hybrid perovskites, such as MAPbI3, are very promising materials to fabricate highly efficient and low-cost solar cells and photodetectors. In this work, we propose a new method of deposition of hybrid perovskite thin films through thermal evaporation of MAPbI3 powder from a single source for which was evaluated the effect of evaporation parameters (distance, time, substrate temperature, chamber pressure, and crucible heating rate) on the structural, optical, and morphological properties. It was found that it is necessary to control adequately the chamber partial pressure, substrate temperature, and the crucible heating rate in order to obtain single-phase MAPbI3 perovskite films. Also, it was studied the solvent annealing treatment as a method to increase the grain size of evaporated films. Finally, a study of transient and steady-state photoconductivity allowed verifying that the evaporated MAPbI3 films present fast band to band photogeneration and bimolecular recombination, and also that the grain size growth leads to an increase of the photoconductivity intensity due to the improvement of the diffusion length.