Showing papers on "Chamber pressure published in 2009"

Acoustics, Vortex Shedding, and Low-Frequency Dynamics Interaction in an Unstable Hybrid Rocket

Abstract: This paper deals with an experimental investigation into the stability behavior of a hybrid rocket where gaseous oxygen is fed with either an axial conical subsonic nozzle or a radial injector. The influence of the oxidizer-injection configurations on the motor stability is thoroughly examined. These distinct oxidizer-injection techniques allowed unveiling key and so far unreported features of the hybrid rocket combustion stability, especially emphasizing the role of vortex shedding which occurs in both the pre- and postcombustion chamber. Axial and radial injectors caused completely stable and unstable combustor operations, respectively, and this fact has been attributed to the fluid dynamics and unsteady heat release at the entrance of the fuel grain port. In particular, the unstable combustion in the radial-flow injector motor was dominated by low-frequency pressure oscillations, around 10-20 Hz. These low-frequency pressure oscillations were always accompanied by longitudinal acoustic modes. In some cases, the pressure oscillations abruptly increased, reaching peak-to-peak amplitude close to 70% of the mean chamber pressure, which is somewhat unusual for hybrid engines. Vortex shedding in the aft-mixing chamber is considered as the main driving mechanism of this latter behavior.

Coupled Analysis of Flow and Surface Ablation in Carbon-Carbon Rocket Nozzles

Abstract: A study is conducted to predict C/C nozzle recession behavior in solid rocket motors for broad variations of propellant formulations and motor operating conditions. The numerical model considers the turbulent flow in the nozzle, heterogeneous chemical reactions at the nozzle surface, variable transport and thermodynamic properties, and heat conduction in the nozzle material. Results show that the recession rate is largely determined by the diffusion of the major oxidizing species (H2O, CO2, OH) to the nozzle surface. Both the concentration of the major oxidizing species -affected by the aluminum content of the propellant- and the chamber pressure exert a strong influence on the recession rate. The erosion rate increases almost linearly with chamber pressure and decreases with propellants with higher aluminum content. The calculated results show a very good agreement with the experimental data from the BATES motor firings.

Film Cooling of Accelerated Flow in a Subscale Combustion Chamber

Abstract: Experimental investigations have been carried out to examine film cooling effectiveness of an accelerated hot gas in a subscale rocket combustion chamber. In support of future first-stage high-performance rocket combustion chambers, a Vulcain2-like test case has been examined with combustion pressure levels up to 12 MPa. The effectiveness of an almost tagentially injected film of hydrogen with an initial temperature of approximately 280 K has been determined. Axial distributions of temperature were measured inside the copper liner as well as on the chamber surface in the convergent and divergent parts of the nozzle segment. An existing film cooling model has been modified for application in a combined convective and filmcooled combustion chamber with an accelerated hot gas. The new model predicts film cooling effectiveness at different combustion-chamber pressures and film blowing rates at sub-, trans-, and supersonic conditions.

Influence of Heavy Fuel Properties on Spray Atomization for Marine Diesel Engine Applications

Abstract: In the present work, a model with the thermophysical properties of Heavy Fuel Oil, typically used in marine diesel engines, has been developed and implemented into the KIVA CFD code The effect of fuel properties on spray atomization is investigated by performing simulations in a constant-volume high-pressure chamber, using the E-TAB and the USB breakup models Two different nozzle sizes, representative of medium- and low-speed marine diesel engines, have been considered The simulations have been performed for two values of chamber pressure, corresponding to operation at partial and full engine load The results indicate that, in comparison to a diesel spray, the Heavy Fuel spray is characterized by comparable values of penetration length, and larger droplet sizes These findings are correlated to experimental results from the literature

Gas jet assisted vapor deposition of yttria stabilized zirconia

Abstract: A gas jet assisted electron beam evaporation process for synthesizing yttria stabilized zirconia (YSZ) coatings has recently been reported. The process uses a rarefied inert gas jet to entrain and transport vapor to a substrate. The gas jet enables the lateral spreading of the flux to be controlled and large fractions of the vapor to be deposited on samples of relatively small size. When the gas pressure is high, coatings grown at 1050°C and below have a columnar structure and a high pore fraction. The total pore volume fraction, the morphology of the inter- and intracolumn pores and the coating texture are all observed to be a strong function of the gas pressure in the chamber with increasing chamber pressure leading to larger intercolumnar pore spacings, wider pores, a higher total pore volume fraction, and a reduction in the coating texture. A direct simulation Monte Carlo simulation approach has been used to investigate vapor transport for the various gas pressures explored in this study. The simulati...

Investigation of etching and deposition processes of Cl2/O2/Ar inductively coupled plasmas on silicon by means of plasma?surface simulations and experiments

Abstract: In this paper, a simulation method is described to predict the etching behaviour of Cl2/O2/Ar inductively coupled plasmas on a Si substrate, as used in shallow trench isolation for the production of electronic devices. The hybrid plasma equipment model (HPEM) developed by Kushner et al is applied to calculate the plasma characteristics in the reactor chamber and two additional Monte Carlo simulations are performed to predict the fluxes, angles and energy of the plasma species bombarding the Si substrate, as well as the resulting surface processes such as etching and deposition. The simulations are performed for a wide variety of operating conditions such as gas composition, chamber pressure, power deposition and substrate bias. It is predicted by the simulations that when the fraction of oxygen in the gas mixture is too high, the oxidation of the Si substrate is superior to the etching of Si by chlorine species, resulting in an etch rate close to zero as is also observed in the experiments.

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.

Low-Temperature, Low-Pressure Chemical Vapor Deposition and Solid Phase Crystallization of Silicon–Germanium Films

Abstract: Low-pressure chemical vapor deposition of silicon–germanium Si1−xGex and its SPC below 400°C are investigated. The effects of precursor ratio SiH4/SiH2Cl2 DCS :GeH4 , pressure, and temperature are examined with the goals of film composition tunability and high deposition rates. SiH4 is found to be a better source gas than DCS because the decomposition rate of SiH4 is faster than that of DCS during the deposition process. In the SiH4:GeH4 system, the binary deposition mechanism is well explained by the “enhancement” model. The deposition temperature and chamber pressure affect the conversion factor, enabling independent tuning of the film composition and deposition rate. Amorphous Si0.7Ge0.3 and Si0.5Ge0.5 films are obtained at 350 and 400°C by adjusting the deposition conditions while keeping the deposition rates high. Compositional effects of the SiGe films on the SPC are also investigated. © 2008 The Electrochemical Society. DOI: 10.1149/1.3008009 All rights reserved.

Vacuum processing chambers incorporating a moveable flow equalizer

Abstract: A method and apparatus for vacuum processing of a workpiece, the apparatus including a flow equalizer disposed in a vacuum processing chamber between a workpiece support pedestal and a pump port located in a wall of the vacuum processing chamber. In an embodiment, the flow equalizer has a first annular surface concentric about the workpiece support pedestal to provide conductance symmetry about the workpiece support even when the pump port is asymmetrically positioned within the vacuum processing chamber. In an embodiment, the flow equalizer has a second annular surface facing a lower surface of the workpiece support pedestal to restrict conductance as the flow equalizer is moved is response to a chamber pressure control signal. In an embodiment, the apparatus for vacuum processing of a workpiece includes tandem vacuum processing chambers sharing a vacuum pump with each tandem chamber including a flow equalizer to reduce cross-talk between the tandem chambers.

A method to measure the total scattering cross section and effective beam gas path length in a low-vacuum SEM.

Abstract: A method is presented to determine the total scattering cross section of imaging gases used in low-vacuum scanning electron microscopy or environmental scanning electron microscopy. Experimental results are presented for water vapor, nitrogen gas and ambient air for primary beam electron energies between 5 and 30 keV. The measured results are compared and discussed with calculated values. This method allows the effective beam gas path length (BGPL) to be determined. The variations of the effective BGPL with varying chamber pressure are presented. SCANNING 31: 107–113, 2009. © 2009 Wiley Periodicals, Inc.

Model for Heat and Mass Transfer in Freeze-Drying of Pellets

Abstract: Lyophilizing frozen pellets, and especially spray freeze-drying, have been receiving growing interest. To design efficient and safe freeze-drying cycles, local temperature and moisture content in the product bed have to be known, but both are difficult to measure in the industry. Mathematical modeling of heat and mass transfer helps to determine local freeze-drying conditions and predict effects of operation policy, and equipment and recipe changes on drying time and product quality. Representative pellets situated at different positions in the product slab were considered. One-dimensional transfer in the slab and radial transfer in the pellets were assumed. Coupled heat and vapor transfer equations between the temperature-controlled shelf, the product bulk, the sublimation front inside the pellets, and the chamber were established and solved numerically. The model was validated based on bulk temperature measurement performed at two different locations in the product slab and on partial vapor pressure measurement in the freeze-drying chamber. Fair agreement between measured and calculated values was found. In contrast, a previously developed model for compact product layer was found inadequate in describing freeze-drying of pellets. The developed model represents a good starting basis for studying freeze-drying of pellets. It has to be further improved and validated for a variety of product types and freeze-drying conditions (shelf temperature, total chamber pressure, pellet size, slab thickness, etc.). It could be used to develop freeze-drying cycles based on product quality criteria such as local moisture content and glass transition temperature.

Experiment and Semi-Empirical Modeling of Lab-Scale Hybrid Rocket Performance

Abstract: A simplified semi-empirical predictive model was developed to aid in the determination of operating parameters and chamber specifications for a lab-scale hybrid rocket engine and test sled design. The model combines user defined initial operating and system design parameters with empirically derived regression rate correlations, NASA CEA2000 combustion equilibrium analysis results, and conservation of mass derivations. The model facilitates parametric optimization of oxidizer flow, chamber pressure and nozzle throat diameter, through a time resolved series of functions, deriving output parameters including characteristic velocity, combustion temperature, efficiency, chamber pressure, thrust, and specific inertia. Experiments were conducted using polymethyl methacrylate (PMMA), hydroxyl-terminated polybutadiene (HTPB) and gaseous oxygen. Experimental results indicates HTPB regression rate exceeds PMMA by a factor of 2 for a given oxidizer flow rate and nozzle parameters. Additionally, the results show, a simplified model of the hybrid combustion system is sufficient to adequately predict combustion parameters in a lab-scale hybrid rocket motor.

Fluctuation characteristics of arc voltage and jet flow in a non-transferred dc plasma generated at reduced pressure

Abstract: A torch with a set of inter-electrode inserts between the cathode and the anode/nozzle with a wide nozzle exit was designed to generate plasma jets at chamber pressures of 500?10?000?Pa. The variation of the arc voltage was examined with the change in working parameters such as gas flow rate and chamber pressure. The fluctuation in the arc voltage was recorded with an oscilloscope, and the plasma jet fluctuation near the torch exit was observed with a high-speed video camera and detected with a double-electrostatic probe. Results show that the 300?Hz wave originated from the tri-phase rectified power supply was always detected under all generating conditions. Helmholtz oscillations over 3000?Hz was detected superposed on the 300?Hz wave at gas flow rates higher than 8.8?slm with a peak to valley amplitude lower than 5% of the average voltage value. No appreciable voltage fluctuation caused by the irregular arc root movement is detected, and mechanisms for the arc voltage and jet flow fluctuations are discussed.

Effect of Humidity on Drying of Porous Materials in Fluidized Bed under Reduced Pressure

Abstract: For fluidized bed drying under a reduced pressure, the effect of the humidity of the drying gas on the drying characteristics of porous materials immersed in the bed was examined experimentally and theoretically. The temperature at the sample center increased with the humidity at relatively high pressures in the drying chamber (101.3 and 50 kPa), and the degree of the increment in the temperature with the humidity increased with the chamber pressure. The effect of the humidity on the temperature at the sample center and the drying time was insignificant at a relatively low chamber pressure (20 kPa).

Spray generated by an airblast atomizer: atomization, propagation and aerodynamic instability

Abstract: This thesis presents a study that has been performed to investigate different phenomena exhibited by a spray generated by an airblast atomizer. Three main subjects are addressed: • Characterization of the spray generated by an airblast atomizer at various operating conditions, including ambient pressure, airflow rate and liquid flow rate. • Investigation of instationary phenomena in spray, its natural and forced oscillations • Modelling of spray atomization inside the nozzle Characterization of both liquid and gas phases of the two-phase flow of an airblast spray is performed using high-speed video imaging, Particle Image Velocimetry and the phase Doppler technique. Three velocity components profiles and size distribution of the droplets in the spray are obtained. The effect of three parameters on the velocity profile and the size distribution, namely; chamber pressure, liquid flow rate and airflow rate has been thoroughly investigated. The collected data can be used for the validation of the numerical Euler-Lagrange code developed for simulation of spray propagation. Next, spray fluctuations at various chamber pressures are characterized using two techniques, namely; Proper Orthogonal Decomposition of time-resolved images and spectral analysis of laser Doppler velocity data. The airblast spray frequency exhibited a strong dependency on the chamber pressure and the gas-phase flow rate and is totally independent of the liquid phase flow rate. The obtained frequencies from both techniques match each other closely. Scaling analysis of the spray frequency demonstrates that it depends only on the average air velocity at the nozzle outlet and on the atomizer geometry. A specific Strouhal number is proposed which could be used as a predictive tool for the determination of spray frequencies at various operational conditions. The value of the Strouhal number depends only on the geometry and type of the atomizer. For the atomizer used in this study the empirical value of the Strouhal number is determined as . The effect of oscillating downstream pressure conditions on the airblast spray is qualitatively investigated. It is found that small pressure oscillating magnitudes has a noticeable effect on the spray behavior. Furthermore, the penetration velocity of the spray under the oscillating pressure conditions is estimated by analyzing the high-speed video images. It is found that the penetration velocity and the oscillation frequency increase when increasing the chamber pressure. Then, in order to better understand the mechanism of film formation in an airblast atomizer with pre-filmer, an auxiliary series of spray impact experiments onto inclined targets experiments are performed the outcome of the impingement process is investigated. The film thickness of the residual liquid on the target is estimated by processing high-speed video images whereas the ejected droplets are characterized using the phase Doppler technique. The experimental data is used to express the film thickness as function of the primary spray parameters. Finally, a novel scaling analysis for the droplet size in the airblast spray is proposed based on the energy balance principle in the framework of the chaotic disintegration theory. The model is validated by the comparison with the experimental data from this and other studies.

Device and method for regulating the gas supply or the gas transport in a gas storage system

Abstract: A device for regulating the gas supply in a gas storage system of a biogas system, wherein the gas storage system has gas stores connected in series in a cascade-like manner with an intermediate chamber between a gas store membrane and a protective cover. The device comprises gas supply mechanisms, intermediate chamber pressure measuring mechanisms and at least one regulating mechanism, each gas store is assigned at least one gas supply mechanism, each gas store is assigned at least one intermediate chamber pressure measuring mechanism with which the gas pressure in the intermediate chamber of the respective gas store can be measured, and the measured values of the intermediate chamber pressure measuring mechanisms are transmitted to at least one regulating mechanism, and the regulating mechanism is designed to regulate the gas pressure in the intermediate chambers of the gas stores by controlling the gas supply mechanisms assigned to gas stores.

Process optimization of CF4/Ar plasma etching of Au using I-optimal design

Abstract: In this paper, reactive ion etching of Au is performed with CF4/Ar gases, and process optimization method is suggested using a statistically established process model. The I-optimal design was employed to set up the etching experiment with operating parameters, namely, gas composition, RF power and chamber pressure. Its analysis was performed on individual parameters of the etch rate, selectivity, and profile. In addition, process optimization, including all three responses of interest, is provided simultaneously. We confirmed that a nonvolatile by-product AuFx was re-deposited on the surface, but controlling the amount of carbon fluoride provided a good etch rate with a satisfactory sidewall profile by reducing by-products. Although RF power is closely related with etch rate, increased power gives poor selectivity due to increased physical etching. Pressure and gas flows strongly interact with each other, affecting sidewall characteristics. Suggested optimization simultaneously considers three responses of interests, which is crucial in process development and optimization for quickly ramping up high volume manufacturing.

Inkjet recording apparatus and method

Abstract: The inkjet recording apparatus includes: an inkjet recording head which includes a nozzle through which liquid is ejected; a pressure regulating unit which includes a liquid chamber that communicates with the nozzle and a gas chamber that is partitioned from the liquid chamber by a flexible film; and a liquid chamber pressure controlling device which controls a pressure of the liquid chamber to a predetermined negative pressure when carrying out back pressure control in which back pressure is applied to the liquid inside the nozzle, wherein: the flexible film causes change in the pressure of the liquid chamber when the liquid is supplied for at least a predetermined supply amount to the liquid chamber in a state where the gas chamber is open to air; and the liquid chamber pressure controlling device carries out the back pressure control after controlling the pressure of the liquid chamber to a predetermined value of positive pressure by supplying the liquid of at least the predetermined supply amount to the liquid chamber.

Automatic control system for balancing shield machine excavation chamber pressure

Abstract: The utility model relates to an automatic control system for balancing shield machine excavation chamber pressure, which comprises a compressed air pressure control system and a spiral conveyer rev automatic control system. The compressed air pressure control system includes an air pressure transmitter, a pneumatic controller, a pressure control valve, an air source processing module, an air source, an air exhaust regulating valve assembly and an air inlet regulating valve assembly. A spiral conveyer hydraulic control system is connected with a programmable logic controller (PLC). The PLC is connected with an excavation chamber earth pressure sensor, a hydraulic control system pressure sensor and a motor rev sensor. The utility model has the advantage that the pressure of the shield machine excavation chamber and the water-earth pressure of the excavation face are balanced automatically and accurately.

Combustion Characteristics of the Cylindrical Multi-port Grain for Hybrid Rocket Motor

Abstract: The purpose of this experimental research is to investigate combustion characteristics of cylindrical multi-port grain of a hybrid rocket motor. The physical model of concern includes an oxidizer supply system, a multi-port fuel grain, and a combustor with preand post chamber. Gaseous oxygen and polymer (PE and PMMA) are applied as the oxidizer and the fuel, respectively. In geometric points of view, the effects of the port number and the distance between ports on a regression rate are taken into account. Internal combustion performance was analyzed using smalland large scale motors: one is motor diameter of 50 mm and the other is 96 mm, with oxidizer mass flux ranging from 10 kg/m-sec to 300 kg/msec for both cases. The port number positively shifts the O/F ratio to near its optimum value as well as the oxidizer mass flux to the typical range influenced by pressure effects so that the fuel regression rate becomes fast as the port number increases to a typical number up to 4 ports. Emphasis was placed on merging effects among fuel gain ports having 4 and 5 port to analyze how port geometrical configuration may influence the chamber pressure and thrust drop.

Subscale Tool for Determining Transverse Combustion Response

Abstract: Experimental results of a transverse combustion instability rating tool using gas-center swirl-coaxial injectors are presented. A 2D rectangular chamber that produces strong transverse instability waves was used to determine the feasibility as a stability rating tool for a minimum representative set of elements. Four different configurations were tested to determine the modes driven most in the chamber. With the driving modes determined, the chamber was set up to determine its ability to be used as a tool to study other element’s responses to the transverse acoustic combustion waves. When limited driving injectors were used results show that the chamber acoustic waves are driven at the primary frequency from the outer injectors, which are located near a pressure anti-node. It was also observed that the oxidizer only portions of the chamber tended to dampen the acoustic waves. The case where only four outer injectors (two on each side) flowed propellant was the most unstable case producing peak-to-peak oscillations greater than chamber pressure, indicating that this configuration could be used to study and measure the combustion response of a centrallylocated minimum representative set of injector elements to high-amplitude velocity oscillations. From these series of tests it was determined that the chamber and injector designs can be used as a tool to drive acoustic waves and allow a study element to be placed in the chamber to determine its response to the instability.

Partially Confined FC-72 Spray-Cooling Performance: Effect of Dissolved Air

Abstract: The objective of this paper was to investigate the heat transfer performance of a partially confined FC-72 spray with varying dissolved-air concentrations. An experimental test rig consisting of a spray chamber coupled to a fluid-delivery-loop system was used to obtain temperature, pressure, and critical heat flux data. A downward-facing nozzle within the spray chamber allowed the FC-72 fluid to be sprayed onto an upward-facing thick-film resistor heater. The heater was mounted onto a glass post, with a sump system to allow removal of excess fluid. Type-E thermocouples were embedded in the post to obtain temperature data. The parametric ranges for experimental testing were as follows: volume-percent concentration of dissolved air was 5 ≤ C m ≤ 18%, chamber pressure was 6.90 x 10 4% ≤ P ch ≤ 8.27 x 10 1 N/m 2 (10 ≤ P ch , ≤12 psia), liquid subcooling was 2≤ ΔT sc ≤ 12°C, and volumetric flow rate was 6.3 0.0 gph). Test data were obtained for comparison of critical heat flux with varying C while controlling the spray chamber pressure. The applicability of Henry's law to the current system was investigated, and air concentration measurements using Henry's law were compared with those obtained using a direct sample method. An empirical mathematical relationship allowing for determination of surface heat flux with varying flow rate was also developed. The relationship was obtained using test data at flow rates of V = 6.31, 8.41, and 10.5 cm 3 /s and was validated using experimental data obtained for flow rates of V = 7.36 and 9.46 cm 3 /s (7.0 and 9.0 gph).

Mixing Enhancement of Liquid Rocket Engine Injector Flow

Abstract: An investigation of the mixing enhancement behavior of N2 shear coaxial jets between two injector geometries is presented. A total of 20 cases with one injector geometry and 15 with the other, corresponding to different momentum flux ratios (J values) at subcritical, nearcritical and supercritical pressures are analyzed and compared. The measurements are extracted from 998 backlit images for each data point. Acoustic excitation is used to analyze the response of the system to velocity and pressure perturbations. The frequency of the system varied from 2.90 to 3.11 kHz and the maximum peak-to-peak pressure perturbation as a percentage of the mean chamber pressure was 4%. It was found that the geometry differences between the two injectors had a large impact on their behavior. The qualitative response of one of the injectors to acoustics at low J values in the subcritical regime was completely different to the other. In contrast, when comparing cases with very similar J values for different pressures, it was found that the normalized dark core length between these cases remains close regardless of phase angle for the two injectors despite the fact that the relative acoustic excitation intensities for subcritical pressures were up to eight times stronger than those at near and supercritical chamber pressures.

On the Design of an In-Line Control System for a Vial Freeze-Drying Process: The Role of Chamber Pressure

Abstract: This paper is focused on the design of an in-line control system for the freeze-drying process of pharmaceuticals in a vial. The goal is to minimize the duration of the primary drying, when most of the water is removed by sublimation while maintaining the product temperature below the maximum value allowed by the product. The pressure in the drying chamber and the temperature of the fluid that is used to heat (or to cool) the product can be manipulated; the pressure rise test and the DPE (Dynamic Parameters Estimation) algorithm are used to estimate the product temperature and the residual ice fraction, i.e. the controlled variables. Both an open-loop controller, using constant values of fluid temperature and chamber pressure, and a closed-loop controller, based on the in-line optimization of the fluid temperature, will be described and tested. Finally, the possibility of manipulating in-line the pressure in the drying chamber will be discussed.