Showing papers on "Chamber pressure published in 2018"

High-Precision Solvent Vapor Annealing for Block Copolymer Thin Films.

Abstract: Despite its efficacy in producing well-ordered, periodic nanostructures, the intricate role multiple parameters play in solvent vapor annealing has not been fully established. In solvent vapor annealing a thin polymer film is exposed to a vapor of solvent(s) thus forming a swollen and mobile layer to direct the self-assembly process at the nanoscale. Recent developments in both theory and experiments have directly identified critical parameters that govern this process, but controlling them in any systematic way has proven non-trivial. These identified parameters include vapor pressure, solvent concentration in the film, and the solvent evaporation rate. To explore their role, a purpose-built solvent vapor annealing chamber was designed and constructed. The all-metal chamber is designed to be inert to solvent exposure. Computer-controlled, pneumatically actuated valves allow for precision timing in the introduction and withdrawal of solvent vapor from the film. The mass flow controller-regulated inlet, chamber pressure gauges, in situ spectral reflectance-based thickness monitoring, and low flow micrometer relief valve give real-time monitoring and control during the annealing and evaporation phases with unprecedented precision and accuracy. The reliable and repeatable alignment of polylactide cylinders formed from polystyrene-b-polylactide, where cylinders stand perpendicular to the substrate and span the thickness of the film, provides one illustrative example.

Experimental Aspects of Measuring the Vial Heat Transfer Coefficient in Pharmaceutical Freeze-Drying

Abstract: One of the current methods for cycle optimization in primary drying to is develop a graphical design space based on quality by design (QbD). In order to construct the design space, the vial heat transfer coefficient (Kv) is needed. This paper investigated experimental factors that can affect the Kv result, examined the relationship between the batch average Kv and Kv values for individual vials, and recommended best practices for measuring Kv. Factors investigated included the technique for measuring ice temperature, shelf temperature, the use of a radiation shield on the door of the freeze-dry chamber, and shelf spacing. All experiments reported here used a chamber pressure of 100 mTorr. The most important factor was the technique for ice temperature measurement, where it is important to assure that any restrictions to vapor flow at the top of the vial are the same between monitored and non-monitored vials. Another factor that was found to play a role was the shelf temperature whereby the lower the shelf temperature, the larger the "edge effect," and the larger the average Kv. Factors that were found to not have a significant effect were the use of a radiation shield inside the chamber door and the shelf spacing. Being aware of these factors and knowing best practices when determining the vial heat coefficient will lead to more accurate design spaces and better cycle optimization.

Linear Acoustic Analysis of Main Combustion Chamber of an Oxidizer-Rich Staged Combustion Engine

Abstract: A comprehensive linear acoustic analysis of the main combustion chamber of an oxidizer-rich staged combustion engine is presented. The theoretical basis is an acoustic wave equation derived from th...

Dynamic vacuum pressure tracking control with high-speed on-off valves:

Abstract: A vacuum pressure tracking system with high-speed on-off valves is a discontinuous system due to the discrete nature of high-speed on-off valves. Chamber pressure changes in the system are determin...

Optimization of pressure paths in hydrodynamic deep drawing assisted by radial pressure with inward flowing liquid using a hybrid method

Abstract: Hydroforming is a convenient method for applying fluid to produce parts with high strength-to-weight ratio. Hydrodynamic deep drawing assisted by radial pressure with inward flowing liquid process is considered as a type of hydroforming. In this method, radial and chamber pressures are two most important parameters. The values of these parameters at any moment play important roles on the quality of final part. In this study, based on a hybrid method, the chamber and radial pressure paths in hydrodynamic deep drawing assisted by radial pressure with inward flowing liquid process are optimized. In this method, an adaptive simulation that is integrated with the fuzzy control system with the artificial bee colony (ABC) algorithm is used to determine the optimized radial and chamber pressure paths. The achievement of a conical part with minimum thinning and without wrinkling has been defined as the optimization goal. The validity of radial and chamber pressure paths obtained from optimization algorithm is verified through an experiment. Results showed that utilization of the optimized loading path yields a part with lower maximum thinning and without wrinkling.

Influence of combustion chamber size (L*) on characteristic exhaust velocity (c*) for a N2O/C2H4 premixed green propellant

Abstract: Currently several so called “green propellants” are under investigation to replace the toxic monopropellant hydrazine (N2H4). Aside alternatives as Ammonium dinitramide (ADN)-based propellants, Hydroxylammonium nitrate (HAN)-based mixtures or high concentrated hydrogen peroxide (H2O2), a further promising propellant is a mixture of hydrocarbons with nitrous oxide - called HyNOx or NOFBX. Compared to classical hydrazine N2O/hydrocarbon mixtures offer a high Performance (Isp, c*) a negligible toxicity and low propellant costs. Those substances are also called “premixed monopropellants”: oxidizer and fuel are stored premixed in one tank. To gain experience with a propellant mixture consisting of nitrous oxide (N2O) and ethene (C2H4), DLR is conducting hot gas combustion tests with an experimental combustor. The paper summarizes the results of 134 combustion tests conducted with the premixed propellant injected in gaseous state. Calculated and measured performance (c* and eta c*) depending on mixture ratio, characteristic combustion chamber length (L*) and chamber pressure are shown and discussed. Furthermore the residence time scales of the propellant mixture inside the combustion chamber are normalized by the chemical time scale of the combustion process. Thus combustion efficiencies depending on dimensionless Damkohler numbers are derived.

Observation of wet specimens sensitive to evaporation using scanning electron microscopy.

Abstract: Wet specimens are notoriously difficult to image in scanning electron microscopes (SEM) owing to evaporation from the required vacuum of the specimen chamber. Traditionally, this issue has been addressed by increasing the specimen chamber pressure. Unfortunately, observation under high specimen chamber pressure cannot prevent the initial evaporation effects. The wet cover method, where the original surface water is retained (and, therefore, considered wet), provides a way to introduce and subsequently image specimens that are sensitive to evaporation within a SEM, while preventing evaporation-related damage, and to observe interesting specimen-water interactions.

High-Speed Flame Radiation Imaging of Thermoacoustic Coupling in a High Pressure Research Thrust Chamber

Abstract: This work addresses the nature of supercritical hydrogen-oxygen flame coupling to acoustics through visualization under conditions representative of upper stage rocket engines A research thrust chamber which shows self-excited combustion instabilities for certain operating conditions was used Previous analysis proved that the instabilities are connected to injector acoustics In this study a small optical access window was mounted in the chamber wall High-speed flame radiation imaging of OH* and blue wavelengths has been applied in order to analyze the acoustic-flame interaction of one of the 42 flames Dynamic mode decomposition results for a case with 80 bar chamber pressure showed that the flame dynamics are strongly influenced by the LOX injector acoustics, whereas for a 50 bar chamber pressure load point no flame response to injector acoustics was observed A potential source of acoustic excitation for the oxygen injectors based on hydrodynamic effects is consistent with the contradictory behavior of the two load points

Tuning the Coupled-Domain Response for Efficient Ultrasonic Droplet Generation

Abstract: Acoustic microfluidic devices encompass mechanical, fluidic, and electromechanical domains. Complicated multidomain interactions require the consideration of each individual material domain, as well as coupled behaviors to achieve optimal performance. Herein, we report the co-optimization of components comprising an ultrasonic droplet generator to achieve the high-efficiency liquid atomization for operation in the 0.5–2.5-MHz frequency range. Due to the complexity of the real system, simplified 2-D representations of the device are investigated using an experimentally validated finite element analysis model. Ejection modes (i.e., frequencies at which droplet generation is predicted) are distinguished by maxima in the local pressure at the tips of an array of triangular nozzles. Resonance behaviors of the transducer assembly and fluid-filled chamber are examined to establish optimal geometric combinations concerning the chamber pressure field. The analysis identifies how domain geometries affect pressure field uniformity, broadband operation, and tip pressure amplitude. Lower frequency modes are found to focus the acoustic energy at the expense of field uniformity within the nozzle array. Resonance matching yields a nearly threefold increase in maximum attainable tip pressure amplitude. Significantly, we establish a set of design principles for these complex devices, which resembles a classical half-wave transducer, quarter-wave matching layer, and half-wave chamber layered system.

Transition of subcritical liquid jets in single and multicomponent systems

Abstract: The fundamental mechanisms which cause the behavior of a liquid jet to alter from classic spray atomization to diffusion-dominated mixing, especially in multicomponent systems at critical conditions, are investigated. In the present experimental study, the behavior of a subcritical laminar fluoroketone liquid jet injected into its own environment and in a mixture of N2-fluoroketone environment at varying Reynolds number (490-3700) and chamber pressure (subcritical to supercritical) conditions is investigated. The present work utilizes high-speed imaging techniques to understand the jet behavior, and the fractal analysis of the jet boundary is employed to comprehend the mixing nature of the liquid jet. The results show that the composition of fluids in the chamber environment plays a critical role in altering the jet behavior. The thermodynamic transition of the liquid jet depends upon the injecting Reynolds number and chamber pressure for a single component system, whereas in a binary component system, transition depends heavily on the partial pressure of the respective fluid in the chamber environment.

Design and Evaluations of 3D-Printed Microthrusters with Nanothermite Propellants

Abstract: We design, analyze, evaluate, characterize and test microthrusters and thruster arrays which are fabricated using an additive three-dimensional printing. Open questions in structural design, propellants synthesis, system-level integration, sensing and controlling electronics are addressed. For aerial, aerospace, surface and underwater platforms, additively-printed solid-propellant rockets and engines may ensure desired capabilities and meet mission-specific requirements. Adequate thrust to weight ratio, specific impulse, total impulse and thrust are ensured by nanothermite. The synthesized optimally-structured nanoenergetic solid propellants are encapsulated in a combustion chamber. Controlled ignition, combustion reaction rate, chamber pressure, exhaust velocity and thrust are accomplished for studied microthrusters with synthesized propellants. The proposed nanothermite is a composition of the copper iodate and aluminum nanoparticles which are the oxidizer and fuel, respectively. The interconnect, sensing, electronics and power management components are studied to ensure sequential ignition. Experiments are performed to research sensing, data acquisition, diagnostics and control schemes. We measured spatiotemporal temperature, burning rate, pressure, thrust and specific impulse.

Combustion chamber simulation experiment device

Abstract: The utility model discloses a combustion chamber simulation experiment device, including fuel feeding way, air feed way, controller, simulation combustion chamber and oil return way. The fuel feedingsets up flow control valve, mass flow meter and nozzle on the road for adjust and supply oil flow, air compressor, gas holder, air drying filter, filter relief -pressure valve, high -voltage electrical proportional valve, vacuum that the air feed route connected gradually are constituteed with the water filtration ware, liquid level changer, pressure transmitter and safety gas valve are equipped with to the simulation combustion chamber to the simulation combustion chamber contains 4 visual windows, the oil return sets up unloading valve and relief valve on the road. Combustion chamber simulation experiment device, can realize the simulation of chamber pressure under the gas turbine different work condition to realize the more true accurate fuel control and the visual observation of fuel atomization effect.

Morphology and Structure of Carbon Films Deposited at Varying Chamber Pressures

Abstract: Depositing thin and thick films through different deposition technology systems has been a topic of great interest. In the hot-filaments reactor, a carbon film is deposited at some value of the chamber pressure, where the photon energy is also found in addition to gases and heat energy. Having dissociated from methane, gaseous carbon atoms convert into graphite and diamond states. Increase in chamber pressure from 3.3 kPa to 14 kPa alters the morphology and structure of carbon films. Increasing the chamber pressure upto 8.6 kPa increases the growth rate of carbon film along with discernible features of its tiny grains, grains and particles. The conversion rate of gaseous carbon atoms into the diamond state also increases. At high set chamber pressures, i.e., 11.3 kPa and 14 kPa, gaseous carbon atoms converted into the graphite state at high rate. However, the films with low growth rates had deposited. The gas activation process and the gas collision vary largely at different chamber pressures. Hence, the morphology and structure of carbon films got deposited with different nucleation and growth rates. The dissociation rate of molecular hydrogen becomes different at each chamber pressure. Consequently, the amount of formation of typical energy varies. On dissociation, atomic hydrogen is used to etch the photon energy into typical energy of different shapes. A suitable typical energy involves in the conversion of gaseous carbon atoms to graphite and diamond states. Graphite atoms get bound by the same involved energy. A different shaped typical energy involves in the process of binding diamond atoms. Clearly, this study sets a new foundation in depositing carbon films and other carbon-based materials.

Determination of etching parameters for pulsed XeF 2 etching of silicon using chamber pressure data

Abstract: A technique is presented for determination of the depletion of the etchant, etched depth, and instantaneous etch rate for Si etching with XeF2 in a pulsed etching system in real time. The only experimental data required is the pressure data collected temporally. Coupling the pressure data with the knowledge of the chemical reactions allows for the determination of the etching parameters of interest. Using this technique, it is revealed that pulsed etching processes are nonlinear, with the initial etch rate being the highest and monotonically decreasing as the etchant is depleted. With the pulsed etching system introduced in this paper, the highest instantaneous etch rate of silicon was recorded to be 19.5 µm min−1 for an initial pressure of 1.2 Torr for XeF2. Additionally, the same data is used to determine the rate constant for the reaction of XeF2 with Si; the reaction is determined to be second order in nature. The effect of varying the exposed surface area of Si as well as the effect that pressure has on the instantaneous etch rate as a function of time is shown applying the same technique. As a proof of concept, an AlN resonator is released using XeF2 pulses to remove a sacrificial poly-Si layer.

Deposition Chamber Pressure on the Morphology of Carbon Films

Abstract: Depositing thin and thick films in different coating technology units is the beauty of deposition technology where every process deals chamber pressure In hot-filament reactor, in addition to force, chamber pressure deals heat and photon energy settling into available mass per unit area or volume Temperature of substrate material and filaments under fixed input power vary as per residence time under set pressure of entered dissociating CH4 and H2 gases Dynamics of carbon atoms along with their transformation rate from gas state to other states vary largely under varying chamber pressure which influences their deposition rate in addition to content-specific structural evolution The increase in the chamber pressure from 25 torr to 105 torr influences morphology of films comprising tiny grains, grains and crystallites The increase in the chamber pressure to 65 torr increases the growth rate of carbon film along with discernible features At intermediate range of pressure, gas state carbon atoms transformed into diamond state at high rate At high chamber pressures, gas state carbon atoms transformed into graphitic state at high rate where low growth rate of films resulted Deposited carbon films are investigated under the investigation of original line of experimental results opening abundant avenues of materials research

Ignition characteristics and combustion performances of a LO2/GCH4 small thrust rocket engine

Abstract: A 500 N model engine filled with LO2/GCH4 was designed and manufactured. A series of ignition attempts were performed in it by both head spark plug and body spark plug. Results show that the engine can be ignited but the combustion cannot be sustained when head spark plug applied as the plug tip was set in the gaseous low-velocity zone with thin spray. This is mainly because flame from this zone cannot supply enough ignition energy for the whole chamber. However, reliable ignition and stable combustion can be achieved by body spark plug. As the O/F ratio increases from 2.61 to 3.49, chamber pressure increases from 0.474 to 0.925 MPa and combustion efficiency increases from 57.8% to 95.1%. This is determined by the injector configuration, which cannot produce the sufficiently breakup of the liquid oxygen on the low flow rate case.