Varying Chamber Pressure Research Articles

1-D 시뮬레이션을 활용한 핀틀추력기의 성능해석 -I : 정상상태 특성

This paper describes how to apply one-dimensional simulation to predict unsteady state characteristics of the cold-gas pintle thruster. Mass flow rate, chamber pressure, and nozzle exit pressure are key parameters for thrust control. Chamber pressure rose and fell monotonously with the pintle stroke variation, while thrust variation was different from chamber pressure variation. During the forward pintle stroke operation, the thrust value tended to decrease initially and returned to increase when pintle speed and chamber free volume exceed some specified value. Even though one-dimensional simulation has the limitations to predict unsteady state characteristics, it is still useful for initial performance assessment of various thrusters which adopt an altitude compensation nozzle such as a dual-bell nozzle, prior to experiment or numerical analysis.

1-D 시뮬레이션을 활용한 핀틀추력기의 성능해석-II : 비정상상태 특성

본 연구는 공압시험용 핀틀추력기의 비정상상태 특성을 예측하기 위한 1-D 시뮬레이션 적용법을 기술한다. 추력을 제어하기 위해 질량유량, 챔버압력, 노즐출구 압력은 핵심 매개변수이다. 챔버압력은 핀틀 스트로크 변화에 따라 단조롭게 증감하였지만, 추력은 챔버 압력의 변화와 다른 양상을 보였다. 핀틀이 전진할 때 핀틀 속도와 챔버 자유체적이 특정 값을 초과하면 추력 값은 초기에 감소하다가 다시 증가하는 경향을 보였다. 1-D 시뮬레이션은 비정상 상태 특성을 예측하는데 한계가 있지만 실험이나 수치해석 이전에 듀얼벨 노즐과 같은 다양한 고도보정노즐 추력기의 초기 성능 평가에 여전히 유용하다. This paper describes how to apply one-dimensional simulation to predict unsteady state characteristics of the cold-gas pintle thruster. Mass flow rate, chamber pressure, and nozzle exit pressure are key parameters for thrust control. Chamber pressure rose and fell monotonously with the pintle stroke variation, while thrust variation was different from chamber pressure variation. During the forward pintle stroke operation, the thrust value tended to decrease initially and returned to increase when pintle speed and chamber free volume exceed some specified value. Even though one-dimensional simulation has the limitations to predict unsteady state characteristics, it is still useful for initial performance assessment of various thrusters which adopt an altitude compensation nozzle such as a dual-bell nozzle, prior to experiment or numerical analysis.

Modeling of End-Burning Solid Propellant Gas Generator

The Solid Propellant Gas Generator (SPGG) is widely used for special military and space applications, in view of its simplicity, light weight, size and high reliability. A mathematical model that describes the burning characteristics inside the SPGG has been established and validated through the implementation of appropriate software. These two methods enabled to predict the performance and to draw the time variation of chamber pressure. An experimental work is carried out in order to prove the functionality and check the validity of the developed techniques. The comparison between the computational results and the experimental measured parameters showed a deviation error less than 4%. The presented software is considered as a powerful tool for selecting the SPGG design parameters in the stages of preliminary design and for performing further sensitivity analyses.

Lumped model of MEMS diaphragm compressors

This article presents a quasi-static lumped model of MEMS circular and square/rectangular diaphragm compressors subjected to a specified peak actuation pressure. In this work equations necessary for determining the pressure rise vs. flow rate relationship for a specific peak actuation pressure are provided. In addition, equations are also presented for determining the temporal variation of chamber pressure and volume. The results of the quasi-static lumped model are found to be in good agreement with that of the results of a transient three-dimensional model studied using COMSOL Multiphysics 4.2a. The independent variables of this model are the geometric, material and operating parameters associated with the MEMS compressor. The geometric parameters are compressor chamber dimensions while the material properties include the diaphragms Young’s modulus and Poisson’s ratio and the ratio of specific heats of the gas. The operating parameters are the operating frequency and peak actuation pressure; actuation pressure is assigned a sinusoidal form. The performance of MEMS compressors improves with increase in peak actuation pressure when all other parameters are held constant. With increase in the depth of the compression chamber the performance characteristics of MEMS compressors degrade provided all parameters are maintained constant. The model also predicts that increase in just the planar dimensions of the diaphragm reduces the maximum achievable pressure ratio. It is found that the performance of the MEMS compressor is inversely related to Young’s Modulus and the thickness of the diaphragm; thus it would be appropriate to make MEMS compressors with materials of low Young’s modulus or thin diaphragms or a combination of both. Based on the model it is observed that the temporal variation of diaphragm deflection significantly varies from that of the actuation pressure for all operating conditions, unlike assumed in literature, except for those operating conditions existing at the extremes of a performance characteristics curve.

Analytical modeling of microscale diaphragm compressors

This article presents a set of simple equations for determining the performance of microscale diaphragm compressors. Equations applicable to circular and square/rectangular microscale diaphragm compressors are provided. Using the model it is possible to determine the influence of material, geometric and operating parameters, under the constraint of constant stroke, on the pressure rise vs. flow rate relationship as well as temporal variation of chamber pressure and volume and actuation pressure. Material parameters considered include Young's modulus and Poisson's ratio of the compressor material and the ratio of the specific heats of the gas. Geometric parameters considered are shape, planar dimensions and depth of compression chamber and thickness of the oscillating diaphragm. For a specific stroke of the diaphragm the least clearance ratio possible for cylindrical microscale compressors is determined to be 2 and correspondingly the maximum pressure ratio, for most gases, is determined to be around 1.76 using the model. For square microscale compressors the least clearance ratio is 2.5 and the corresponding pressure ratio is 1.6. For rectangular microscale compressors, reduction in aspect ratio of the diaphragm below unity increases and decreases the clearance ratio and the pressure ratio, respectively. Moreover, the model predicts that the actuation pressure, for a specific operating condition, increases with increase in discharge pressure and flexural rigidity of the diaphragm. Thus it is best to realize microscale diaphragm compressors with materials of low Young's Modulus or thin diaphragms or a combination of both.

Patent Foramen Ovale: A Potential Cause of Refractory Hypoxemia in Off-Pump Coronary Artery Bypass Surgery

Patent Foramen Ovale: A Potential Cause of Refractory Hypoxemia in Off-Pump Coronary Artery Bypass Surgery

Combustion Experiments of HTPB/RFNA Mixed Hybrid Propellants

A series of combustion experiments have been conducted for investigating the regression rates of propellants using Red Fuming Nitrous Acid (RFNA) as liquid oxidizer and Hydroxyl-Terminated Polybutadiene (HTPB) with the addition of Ammonium Perchlorate (AP) upto 20 percent as the solid fuel. HTPB is the state-of-theart binder used in solid propellant rocket motors and is considered to be a potential candidate fuel for rocket applications due to its higher regression rate characteristics, greater fuel value, higher carbon/hydrogen ratio and solid loading capability. One of the effective ways of increasing the regression rates in hybrids is the addition of solid oxidizer such as AP in the fuel in small percentages. This type of configuration is called mixed hybrid and regression rate enhancement upto 100% is obtained. A series of static tests are conducted to establish the ignition and combustion in the mode. It is seen that the propellant has burnt smoothly. The ignition pressure could also be controlled and kept to a reasonable value. Stable combustion within a variation of chamber pressure ±2% and combustion efficiency above 0.95 was achieved. The characteristics of the combustion products are calculated using the NASA CEA code. Regression rate correlations for the different combinations are obtained using the experimental data and ballistic code developed for predicting the performance of system.

액체로켓엔진 연소기를 이용한 고고도 환경 모사용 디퓨저 시동특성 연구

본 연구에서는 액체 로켓 엔진의 고온 연소 가스를 이용하여 축소형 고고도 환경 모사용 초음속 디퓨저 성능 실험을 수행하였다. 실험 장치는 연소실, 진공 챔버, 디퓨저로 구성되어 있다. 고고도 환경 모사 시험은 연소실 압력이 약 26, 29, 32barg 세 조건으로 수행하였고, 세가지 조건에서 모두 디퓨저는 성공적으로 시동되었으며 진공 챔버 압력이 약 140torr로 형성하였다. 이전의 상온 고압 가스를 이용한 디퓨저의 시동 특성과 비교하였을 때 시동 압력과 압력 분포 등의 시동 특성의 경향성은 유사하였으나, 고온 환경으로 인하여 진공 챔버에 형성되는 압력은 2배 정도 높은 것을 확인하였다. 본 연구 결과는 향후 실물형 고고도 환경 모사 시험 설비를 구축하는데 기초 자료로 활용될 수 있을 것으로 판단된다. Performance tests of a supersonic exhaust diffuser were conducted by using a liquid rocket engine for simulating high-altitude environment. The experimental setup consisted of a combustion chamber, a vacuum chamber and a diffuser. The combustion tests for simulating high-altitude environment were carried out at three cases by chamber pressure variation(26, 29, 32barg). The test results showed that the diffuser was started at all case and vacuum chamber pressures were approximately 140torr. The starting pressure using combustion gas was similar with that of cold gas, but the vacuum chamber pressure was relatively high because of high temperature in the vacuum chamber. The results of this test can be used as an essential database for the design of real-scale high-altitude simulation test facility in the future.

Experimental modelling of the venous muscle pump

One of the most interesting phenomena in the venous circulatory system is the vein pump mechanism in the legs. The veins in this area are surrounded by the calf muscle, which periodically deforms the vein walls and squeezes blood out of the section. Venous valves prevent the blood from backflow. A measuring rig was designed to model and measure the periodic pulsation of the veins. The device contains a chamber containing a collapsible tube. In this paper the diameter of the tube was examined under periodically varying chamber pressure. Pictures were taken of the viscoelastic tube during the pulsation. The diameter as a function of time is calculated and compared with the pressure-time series. Also the operation of the check valves of the measuring rig is observed. The results are presented and discussed. DOI: 10.17489/biohun/2010/2/03

Effects of chamber pressure variation on the grid temperature in an inertial electrostatic confinement device

Inertial electrostatic confinement fusion devices are compact sources of neutrons, protons, electrons, and x rays. Such sources have many applications. Improving the efficiency of the device also increases the applications of this device. Hence a thorough understanding of the operation of this device is needed. In this paper, we study the effect of chamber pressure on the temperature of the cathode. Experimentally, the grid temperature decreases as the chamber pressure increases; numerical simulations suggest that this is caused by the reduction of the hot ion current to the cathode as the pressure increases for constant power supply current. Such an understanding further supports the conclusion that the asymmetric heating of the cathode can be decreased by homogenizing the ion flow around the cathode.

Experimental study of helium leakage parameters in flexible composite

AbstractThe helium leakage characterizations of flexible composites are experimentally studied in this article. Three data processing techniques (Defining method, Fourier series method, and Fast series method) are used to evaluate the helium leakage parameters including the diffusion coefficient D, the solubility S, and the permeant rate k. The chamber pressure variation for helium permeation in flexible composite is measured by the differential pressure method. The results indicate that Fast series method is an effective technology in extracting the helium leakage parameters for flexible composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Analysis of Forces and Moments in Gerotor Pumps

This article presents the analyses of the forces and moments between gears in contact with a gerotor pump. The objective was to reach a more accurate solution for the problems related to load distribution in trochoidal pumps with fixed shaft axes. Calculation of contact forces is complex due to the simultaneous contact of several trochoidal teeth during the load transfer and additional compressive fluid forces that act on the teeth flanks. A simple physical model and a suitable analytical model are used for this analysis. Compressive fluid forces are simulated with single force applied in the middle of the line that separates the suction and upward pressure zone. During the teeth engagement there is also a change in fluid volumes between teeth. This creates pressure change that needs to be considered and calculated at an arbitrary moment of the engagement process. Finite element analysis (FEA) was used to determine the reaction forces that depend on instantaneous moments as well. Analysis shows that if a chamber pressure variation is taken into account, higher values of driving moment and support reaction forces will be generated. Designers can use the obtained results to develop a higher efficiency gerotor pumps.

The Minimization of Generator Output Variations by Impulse Chamber Pressure Control during Turbine Valve Test

This paper describes the actual application of a feedback control loop as a means for minimizing turbine impulse chamber pressure variation during the turbine steam valve tests at a 1,000 MW nuclear power plant. The chamber pressure control loop was implemented in the new digital control system which was installed as a replacement for the old analog type control system. There has been about 40MW of the generator output change during the steam valve tests, especially the high pressure governing valve tests, because the old control system had not the impulse chamber pressure control so the operators had to compensate steam flow drop manually. The process of each valve test consists of a closing process and an reopening process and the operators can make sure that the valves are in their sound conditions by checking the valves movement. The control algorithm described in this paper contributed to keep the change in megawatt only to 6MW during the steam valve tests. Thereby, the disturbance to reactor control was reduced, and the overall plant control system's stability was greatly improved as well.

추력 30톤급 액체산소/케로신 로켓엔진 연소장치 개발(II)-가스발생기

추력 30톤급 펌프공급방식 액체로켓엔진을 위한 가스발생기 개발 과정에 관하여 기술하였다. 액체산소와 케로신을 추진제로 연료 과농 조건에서 작동하는 가스발생기의 개발을 위해 분사기 개발에서부터 시작하여 축소형, 실물형 개발시제를 거쳐 가스발생기 단품 개발을 성공적으로 완료하였다. 가스발생기 설계 과정에서 다양한 해석적 방법을 적용하였으며 점화 시험, 연소성능 및 연소안정성 평가시험, 내구성 평가시험 등을 통해 가스발생기의 성능요구사항을 시험적으로 검증하였다. 개발된 가스발생기는 연소압 및 혼합비 운용 영역 내에서 안정적으로 작동하며 성능 및 수명 요구조건을 만족시킴을 확인하였다. The development process of a gas generator for a 30-tonf pump-fed space liquid rocket engine is described. Starting from the development of an injector, followed by subscale and full-scale test specimens, the development of LOx/kerosene fuel-rich gas generator has been concluded successfully. Various analytical methods have been utilized in the course of design and the performance requirements have been verified experimentally through ignition tests, combustion performance and stability assessment tests and duration tests. The gas generator has proven its workability and stability within a defined operation window of varying chamber pressure and mixture ratio and demonstrated compliance to the performance and life time requirements.

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

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.

Controlled Growth of Gold Nanoparticles on Silica Nanowires

Production of gold nanoparticles with the specific goal of particle size control has been investigated by systematic variation of chamber pressure and substrate temperature. Gold nanoparticles have been synthesized on SiO2 nanowires by plasma-enhanced chemical vapor deposition. Determination of particle size and particle size distribution was done using transmission electron microscopy. Average nanoparticle diameters were between 4 and 12 nm, with particle size increasing as substrate temperature increased from 573 to 873 K. A bimodal size distribution was observed at temperatures ≥723 K indicating Ostwald ripening dominated by surface diffusion. The activation energy for surface diffusion of gold on SiO2 was determined to be 10.4 kJ/mol. Particle sizes were found to go through a maximum with increases in chamber pressure. Competition between diffusion within the vapor and dissociation of the precursor caused the pressure effect.

Influence of process parameters on the properties of TEOS–PECVD-grown SiO 2 films

The influence of chamber pressure, substrate temperature and mass flow ratio on growth rate, refractive index and stress of plasma-enhanced chemical vapor deposition (PECVD) grown SiO 2 films has been investigated. In this study, the silicon dioxide films were grown by homemade PECVD system by carrying three different sets of processes for variation in chamber pressure (70–240 Pa), substrate temperature in the range of 523–673 K and flow rate ratio (O 2/TEOS) of 2–10. In these processes, liquid tetraethoxysilane (TEOS) has been used as a source of Si instead of SiH 4 to avoid difficult handling of SiH 4. The growth rate (by measuring thickness for specified time process), refractive index and stress of the deposited SiO 2 films have been determined by ellipsometry technique. The present study reveals that, in order to grow good quality SiO 2 films for their microelectronics applications, where stress is of prime importance, deposition processes of TEOS–PECVD should be carried out with substrate temperature and flow ratio variations. However, for optoelectronics applications, the growth processes carried out with varying chamber pressure are believed to be highly desirable, they allow precise control of the refractive index and a higher thickness.

Si(CH3)4로부터 SiC의 레이저 화학증착에 관한 연구

The purpose of the present study was to examine some basic aspects of laser chemical vapor deposition that will be ultimately utilized for solid freefom1 fabrication of three dimensional objects. Specifically, deposition of silicon carbide (SiC) using tetramethylsilane (TMS) as precursor was studied for a rod grown by CO₂ laser-assisted chemical vapor deposition. First. temperature distribution for substrate was analyzed to select proper substrate where temperature was high enough for SiC to be deposited. Then, calculations of chemical equilibrium and heat and mass now with chemical reactions were perfonned to predict deposition rates, deposit profiles, and deposit components. Finally, several rods were experimentally grown with varying chamber pressure and compared with the theoretical results.<br/>

A study of methods for moving particles in RF processing plasmas

Methods for moving charged particles in RF processing plasmas are investigated. These methods include varying RF power, varying chamber pressure, attraction and repulsion by an electrostatic probe, and movement with magnetic fields. Varying RF power changes the depth of the potential wells where particles are trapped. The RF power affects shape and location of the traps and the bulk plasma potential. Increasing the chamber pressure moves the sheath edge closer to the wafer being processed. Since particle traps are found at the plasma sheath edge increasing the chamber pressure will move the particle traps (and any trapped particles) closer to the wafer being processed. The Langmuir probe can repel particles when under negative bias and attract them when positively biased. This probe can also distort the sheath edge when the tip resides within the sheath. Applying a magnetic field can change the characteristics of the particle traps and produce a force on the charged dust particles. >

On the problem of sulfur losses during PIXE analysis

Investigations of laboratory aerosols of H 2SO 4, (NH 4) 2SO 4, and NH 4HSO 4, which are important compounds of ambient aerosol, show that there are experimental conditions allowing the complete determination of sulfate sulfur using the PIXE method, but that there are also such experimental parameters, yielding high sulfur losses ( > 50%). Both experimental regimes can well be involved in PIXE analytical routine. No sulfur losses are observed with proton current densities below ∼ 150 nA/cm 2 for target backings of cellulosic acetate membrane filters of 5 mg/cm 2 thickness at proton energies E p = 2 MeV and a reaction chamber vacuum of approximately 0.01 mbar. The dependence of sulfur losses on proton current density is discussed for several useful experimental conditions and aerosol filter materials. Preliminary results on the influence of varying chamber pressure are outlined.