Constant Gas Pressure Research Articles

An investigation of constant-pressure gas well testing influenced by high-velocity flow

This paper presents the results of a study of transient pressure analysis of gas flow under either constant bottom-hole pressure conditions or the constant wellhead pressure conditions. The effects of formation damage, wellbore storage and high-velocity flow are included in the model. The analysis of simulated well tests showed that the interpretation methods used for liquid flow are generally accurate when the m( p) is used. For these conditions, a graph of 1/ q D vs. log t D presents gradually lower values of 1.1513 as the value of p wf decreases: for pressure buildup conditions, a graph of m D(1, Δ t a D )/ q D(Δ t a D = 0) vs. ( t a D + Δ t a D )/Δ t a D shows values of this slope within 1% of the 1.1513 value. However, when high-velocity flow influences constant pressure production tests, the slope can yield errors up to 13%. This upper limit occurs when the formation has a relatively ‘high’ permeability (around 1 mD) and the rate performance test is affected by high-velocity flow. It was found that pressure buildup tests are superior to rate performance tests because high-velocity flow does not affect the slope of the straight line portion of the buildup curve. Derivative analysis of simulated buildup tests showed that the skin factor is considerably miscalculated when the high-velocity flow effect is significant. This problem could lead to errors in the calculation of the skin factor, s, up to 300%.

A nonlinear control method for resin transfer molding

AbstractIn performing permeability measurements on the fiber reinforced preforms typically used in the resin transfer molding (RTM) process, two types of fluid injection are commonly utilized: constant fluid pressure and constant fluid flow rate. The constant pressure condition is often enforced by placing the test fluid within a pressure pot and supplying a constant gas pressure, thereby forcing the fluid into the mold under a constant pressure. In the case of constant fluid flow rate, the fluid is often supplied by forcing a piston through a fluid‐filled cylinder at a constant rate of displacement through the use of a press or Instron machine. This paper presents a nonlinear control method for providing constant flow rate RTM processes with a pressure pot solely through the use of a regulator. Computer simulations of the control examined the effect of various parameters on the ability to maintain constant flow rate. Rectilinear flow experiments were carried out to evaluate the theoretical development. Experimental results are in good agreement with the computer simulations. Both computer simulations and experiments show significant promise for the proposed control methodology.

The effects of pulsed introduction of buffer gas on ion storage and detection efficiencies in a quadrupole ion trap

The quadrupole ion trap is commonly operated with a constant background pressure of an inert, low molecular weight buffer gas. This inclusion of a buffer gas has been shown to increase the sensitivity and mass resolution of the instrument. Research to gain an understanding of these effects, both experimental and through simulations, has typically assumed that it is optimal to maintain a constant buffer gas pressure throughout the entire experiment This article describes the effects of the pulsed introduction of buffer gas at strategic points within the analytical scan and evaluates those events during which the presence of buffer gas is critical. By incorporating a pulsed valve within the ion trap manifold, both the presence and pressure of the buffer gas can be controlled and varied during the individual steps of the scan. The presence of helium buffer gas just before the ion ejection and detection event showed a greater increase in intensity of the ion signal than at any other time in the analytical scan. In addition, this increase in intensity upon pulsed introduction of buffer gas prior to detection is constant over a wide range of pulsed valve open times (i.e., pressures), whereas the signal enhancement upon pulsed introduction of the buffer gas before ionization is observed only over a narrow range of pulsed valve open times.

Arc erosion characteristics of Cu-W contact at load current range in SF6 gas

Development of SF6 gas-insulated switches that have a long service life and are highly reliable at medium voltage ratings require arc erosion of contacts in SF6 gas to be decreased. The effects of SF6 gas pressure and magnetic field for arc blow-out on erosion were studied experimentally in detail using sintered Cu-W contacts. The test current, SF6 pressure and magnetic field were 100 to 400 A, 0.1 to 0.6 MPa and 0 to 50 mT, respectively. The results show that the arc erosion rate increased linearly with the SF6 pressure. The magnetic field effectively reduced anode erosion (i.e., the application of a mere 50 mT lowered the erosion rate to 1/3 to 1/4). These phenomena may be attributed, respectively, to the increase in evaporation rate according to the shrinkage of arcing spot areas caused SF6 pressure and a decrease of the evaporation rate correlating to high-speed movement of the arcing spot on the anode by the magnetic field. However, the cathode erosion was insensitive to the magnetic field. The influence of both W grain size and composition ratio, Cu:W, on the erosion rate was also studied. The smaller W grain at Cu content of 50 to 70 wt.% was found to be best for suppression of erosion under the present conditions. Further, the increase of N2 mixture ratio to SF6 under constant total gas pressure greatly decreased contact erosion. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (1): 41–51, 1997

赤外吸収法による燃焼火炎場の化学種濃度計測法に関する研究

This study describes a novel technique for obtaining transient measurements of a chemical species in combustion fields by applying the infrared absorption method. Thus, it is expected that the actual chemical species and fuel vapor concentrations in the flame should be detected in situ inside the combustion engines as well as in gas turbine engines. In general, the absorption spectrum of the chemical species depends on the pressure, concentration, temperature, and optical path length. As a first step, the absorption spectrum of the chemical species (CH4, CH2, CO) was measured with calibra-tion cell by means of the FTIR (Fourier Transform Infrared Spectroscopy) method. The temperature ranged from 300 K to 800 K under constant pressure and constant gas concentration. The tempera-ture dependence of the absorption spectrum was applied to the measurement of the chemical species in a CH4-Air premixed steady-state burner flame at the atmosphere state. The validity of this measurement method was investigated.

A novel automated method for the determination of membrane permeability in gas-liquid transfer applications

A novel automated test method for determining the gas transmission rates of sheet membranes is described. The experimental conditions are relevant to applications involving a hydrophobic membrane barrier separating a liquid phase and a gas phase, such as an oxygenator for use in heart-lung bypass. Steady state transfer is accomplished by passing the test gas tnder isobaric condition tthrough the membrane into a recirculating reaction solution. The gas transfer rate is given by the timed volumetric displacement of the test gas which is logged by a microcomputer. The microcomputer also implements a controller which maintains constant (atmospheric) gas pressure. Oxygen and carbon dioxide permeabilities of microporous flat sheet polypropylene (Celgard ® 2400 and 2500 series, Hoechst Celanese Corp.) and polydimethylsiloxane (Scimed Life Systems Inc.) membranes were evaluated using this method. As expected, the transfer rate of the homogeneous membrane was found to be lower than that of the microporous membranes, while the results for microporous membranes point towards the importance of liquid “plugs” in the pores in influencing permeability. The method was found to give rapid and reproducible results, and automation facilitated the transfer of data for analysis.

SF<sub>6</sub>ガス中Cu-W接点の負荷電流域におけるアーク消耗特性

Development of SF6 gas-insulated switches that have a long service life and are highly reliable at medium voltage ratings require arc erosion of contacts in SF6 gas to be decreased. The effects of SF6 gas pressure and magnetic field for arc blow-out on erosion were studied experimentally in detail using sintered Cu-W contacts. The test current, SF6 pressure and magnetic field were 100 to 400 A, 0.1 to 0.6 MPa and 0 to 50 mT, respectively. The results show that the arc erosion rate increased linearly with the SF6 pressure. The magnetic field effectively reduced anode erosion (i.e., the application of a mere 50 mT lowered the erosion rate to 1/3 to 1/4). These phenomena may be attributed, respectively, to the increase in evaporation rate according to the shrinkage of arcing spot areas caused SF6 pressure and a decrease of the evaporation rate correlating to high-speed movement of the arcing spot on the anode by the magnetic field. However, the cathode erosion was insensitive to the magnetic field. The influence of both W grain size and composition ratio, Cu:W, on the erosion rate was also studied. The smaller W grain at Cu content of 50 to 70 wt.% was found to be best for suppression of erosion under the present conditions. Further, the increase of N2 mixture ratio to SF6 under constant total gas pressure greatly decreased contact erosion. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (1): 41–51, 1997

Carbothermal reduction of sillimanite

Preliminary studies on the carbothermal reduction of sillimanite (Al2O3SiO2) powders are reported. The effects of various reaction parameters, e.g. reaction temperature (1550–1700 °C), C: Si molar ratio (4.5–9.0) in the reactant mixtures, the nature and source of carbon (carbon black or activated charcoal) and the reaction atmosphere (argon or nitrogen under a constant positive gas pressure of 0.15 MPa), on the carbothermal reduction have been investigated. It has been observed that Al2O3 and β-silicon carbide whiskers [β-SiC(w)] are the ultimate products formed in an argon atmosphere. Under a nitrogen atmosphere, β′-sialons are also formed. In all cases, mullite forms as the first intermediate phase at lower temperatures, which later converts progressively to the higher-temperature products.

Characterization of SiGe Alloy Nanocrystallites Prepared by Pulsed Laser Ablation in Inert Gas Ambient

AbstractWe report nanometer-sized silicon germanium (SiGe) alloy crystallites prepared by excimer laser ablation in constant-pressure inert gas. Size distribution of the SixGelxultrafine particles decreases with decreasing x under fixed conditions of deposition such as ambient gas pressure. Raman scattering spectra of the deposited SiGe ultrafine particles show three peaks intrinsic to crystalline SiGe alloys, and the linewidths of these peaks broaden due to the reduced size of the crystallites. Furthermore, a visible photoluminescence (PL) band with a peak at around 2.2 eV is obtained at room temperature after an annealing process.

Effects of Substrate Temperature and Oxygen Partial Pressure on the Properties of Sputtered Zirconium Titanate Thin Films

We report the effects of substrate temperature and O2/Ar ratios on the properties of ZrTiO4 thin films prepared by RF magnetron sputtering. The films were deposited at a constant gas pressure (0.133 Pa) with various substrate temperatures (25-450° C) and different O2/Ar ratios from 0/100 to 20/80. The deposition rate decreases with increasing oxygen partial pressure and substrate temperature. Moreover, the higher O2 content increases the surface roughness of deposited films, which reduces the transmittance of the films. The effects of substrate temperature and oxygen partial pressure on the stoichiometric composition, optical constant, crystallinity phase, surface morphology, and adhesion have also been systematically investigated.

95/04984 Conversion of BKZ-210-140 boiler in Chelyabinsk heat and power plant-2 to natural gas firing with separate burners and air supply ducts

This chapter discusses different aspects of elementary thermometry. The different types of thermometers include: (1) liquid-in-glass thermometer, (2) constant-pressure gas thermometer, (3) constant-volume gas thermometer, (4) platinum-resistance thermometer, and (5) thermoelectric thermometers. Mercury is particularly suitable to construct a liquid-in-glass thermometer and to devise a scale of temperature. To mark off a scale of temperature on the instrument, the level of the mercury is marked when the bulb is placed in melting ice. This is a fixed temperature called the lower fixed point. The chapter also highlights experiments that conclude that two scales of temperature will not agree except at the fixed points unless the property upon which one is based varies uniformly with temperature as defined using the other property. Mercury is considered a suitable thermometric liquid because: (1) it does not wet glass and so mercury is not left behind on the glass as the temperature falls, (2) it is liquid over a wide range of temperature, and (3) it requires no coloring matter to render it visible. For the purpose of defining a temperature scale, it is required to use some property of a substance, or substances, the variation of which with temperature is common to many substances so that the same scale is defined whichever substance is used in the thermometer.

Pulmonary Blood Flow Model Coupled with Breathing Dynamics.

A mathematical model for pulmonary circulation is established taking into account the mechanical behavior coupled with breathing dynamics. The blood flow models in the arterial and venous trees are established by assembling the tube-flow model in each elastic vessel. These models are combined with the sheet-flow model which expresses the blood flow in the capillary network. The finite-element discretization based on adjoint variational principle is applied to solve the model numerically. First, the pulmonary blood flow under a constant gas pressure in the lung is measured using rabbit lungs, and the decrease in blood flow due to gas pressure is observed. The simulation model is verified by comparing the experimental observations with the simulated results, and the causality among the decrease in blood flow, the capillary collapsing and the pressure distribution is discussed. Next, the pulmonary circulation model is coupled with the breathing model to examine the input impedance in normal breathing and to evaluate the effect of varying the inhaled gas pressure in artificial ventilation. It is shown that the results obtained in the simulation correspond to the impedance characteristics observed in experiments in different species. The simulation of artificial ventilation demonstrates that the inhaled gas pressure affects the blood flow not only in arteries and veins but also in the capillaries. These results indicate that the simulation based on the proposed model can be used to investigate the internal mechanical behavior of the pulmonary circulation taking into account the variation due to individuality of the geometry and material properties.

Measurement of Sidewall Roughness of InP Etched by Reactive Ion Beam Etching

We have quantitatively measured the sidewall roughness of InP etched by reactive ion beam etching (RIBE) for the first time. An electron probe surface roughness analyzer was employed. The minimum value of average sidewall roughness appeared to be 1 nm and the peak-to-peak roughness appeared to be 6 nm. The etching conditions were an ion extraction voltage of 400 V and a Cl2 gas pressure of 1.2× 10-3 Torr. It is found that the etched sidewall roughness is decreased by lower-ion-extraction-voltage etching in a constant gas pressure, as well as by higher-gas-pressure etching with a constant ion extraction voltage.

Electron energy distribution function in DC magnetron axially symmetric discharges: evidence of spatial anisotropy

Experimental measurements of the second derivative d2i/dv2 of the probe current i versus probe voltage v were performed in an axially symmetric magnetron sputtering gas discharge plasma in order to determine the electron energy distribution function. The measurements were performed using a cylindrical Langmuir probe oriented in two directions, along and across the discharge axis. The experiments were carried out at a constant argon gas pressure of 3 mTorr and at a constant discharge current of 1 A to a molybdenum cathode. Three different magnetic field configurations in the discharge region were investigated and these were achieved by superimposing an external magnetic field on the original magnetron magnetic field. By varying the magnetic field distribution and, in particular, the respective axial component of the magnetic induction Bz at the probe position, the second derivative d2i/dv2 was significantly altered. Certain differences in d2i/dv2 were also established with the probe oriented in radial and axial directions. A spherical spatial plasma isotropy of the electron energy distribution function was thus found for the opposed superimposed magnetic field (Bz=-31 G) while for both the original (Bz=36 G) and the supporting (Bz=103 G) magnetic field configurations, a plasma anisotropy was established. The degree of anisotropy was quantified by comparison of the respective average electron energies (E) evaluated for each of the three magnetic field configurations. It was found that assumption of spherical isotropy during determination of the electron energy distribution function leads to overestimation of (E) by up to 10% under the experimental conditions used.

Study on radio frequency reactive sputtering deposition of silicon nitride thin films

A rf magnetron sputtering apparatus operating at constant gas pressure was used to deposit silicon nitride thin films in an Ar–N2 plasma. The nitrogen partial pressure, incident rf power, and the deposition time were varied to obtain various sets of films. In analyzing the stoichiometry and thickness of the silicon nitride films by Rutherford backscattering spectroscopy, several correlations among deposition parameters and film characteristics could be found. The results can be discussed by adapting a reactive sputtering theoretical model to the present conditions. An alternative method to grow films with the same stoichiometry but under different deposition rates was tested.

Deterministic onset of chaos in a gas discharge

Sequences of bifurcations in the radiation intensity of a discharge plasma on the boundary between regular and chaotic ionization waves regions were observed by varying the discharge current at a constant gas flow velocity and pressure. Fundamental constants of the Feigenbaum scenario were measured in the experiment as δ = 4.6±0.1 and α = 2.6±0.6 by means of recording succeeding period doublings.

Effect of residence time on microwave plasma chemical vapor deposition of diamond

We have investigated the effects of reactant residence time on the properties of microwave-assisted chemical vapor deposited diamond films. Using a constant gas pressure of 40 Torr and gas composition of 1% CH4 in H2, the total gas flow rate was adjusted from 25 to 800 sccm which corresponds to apparent chamber residence times of 3–100 s for our reactor. The flow rate is one of the few parameters in the microwave plasma deposition system that is decoupled from all others, making this a relatively clean study on the effects of a single process variable. Two distinct types of diamond films were prepared in this work. One set was deposited directly on diamond-seeded silicon wafers. A second set was prepared separately, and under otherwise identical diamond film growth conditions, but deposited on a layer of microcrystalline diamond (MCD). The 5-h growths resulted in continuous polycrystalline diamond films of ∼2 μm thickness which were analyzed with scanning electron microscopy, Raman scattering and photoluminescence (PL) spectroscopies, infrared (IR) transmission, and x-ray diffraction. The Raman and PL spectra, and x-ray diffraction data exhibited flow-dependent behavior, while the electrical resistivity, IR transmission spectra, and deposition rate of the films, as well as the optical emission spectra of the deposition plasmas, were relatively insensitive to the flow rate. The x-ray diffraction results revealed that the diamond films were textured, although the preferred orientation was not particularly related to the surface morphology. The surfae preparation strongly affected the texture, with films deposited on MCD exhibiting a [110] texture while those on Si had a [111]-preferred orientation. Furthermore, the extent of texture for the films on Si varied with the gas flow rate, unlike that of the films on MCD. The Raman and PL spectra varied with flow for both the films on Si and on MCD. Flow modeling showed the importance of convective flow in our reactor, and the insensitivity of deposition rate on gas flow rate can be rationalized by the flow pattern. The presence of vortices above the growth surface complicates the concept of residence time for this system. We argue that variation in the concentrations of gas-phase diamond growth species, arising from changes in gas residence time, are responsible for the flow-dependent variation in diamond film material properties.

THE [NE III]-[O II] SPECTRUM AS AN IONIZATION INDICATOR IN NEBULAE

ABSTRACT The usefulness of the Ne III-O II forbidden-line spectrum as a helium ionization correction factor (ICF) indicator in low-density nebulae, such as H II regions, is examined, and the results of an extensive grid of photoionization simulations which have a 'blister'-like geometry are presented. Fully filled constant pressure gas, Orion dust, and H II region abundances are used, along with a very wide variety of ionizing continua. As suggested by the ionization potentials, the He ICF is small when the Ne III 3869/O II 3727 forbidden line ratio, an easily measured line pair, reaches above 0.20. The 'eta' parameter, a ratio of ratios of oxygen and sulfur lines, is probably strongly affected by low-temperature dielectronic recombination, a basic process which has no reliable rate coefficients for third-row elements.

Broad NA D emission in QSOs and the profile of He I 5876 A

For six QSOs, the H-alpha profile was fit to the position of He I 5876 A and Na I 5890, 5896 doublet. The implied Na I/H-alpha ratio ranged between 0.004 and 0.042. Photoionization models were run with a variety of parameters, including density, column density, ionization parameter, two different incident spectra, and either constant density or constant gas pressure. The models use zone results from Ferland's code Cloudy and solved for the sodium emission. The set of cloud parameters that can produce approximately the observed Na I/H-alpha ratios consist of only the high-density clouds, with n(H) about 10 to the 11th/cu cm and only at column densities N(H) = 10 exp 23.5/sq cm or more. The highest Na I/H-alpha ratios are found in models where the sodium is shielded. The large range of observed Na I/H-alpha ratios implies a corresponding range of cloud conditions. 23 refs.

Stability of YBa 2Cu 3O 7, Y 2Ba 4Cu 7O 15 and YBa 2Cu 4O 8 superconductors under varying oxygen partial pressure, total gas pressure and temperature

The phase stability of a YBCO type superconductor has been studied for different total gas pressures, oxygen partial pressures and temperatures by using a oxygen-hot-isostatic-process. A total gas pressure versus temperature phase diagram at constant oxygen partial pressure (10 Wit), and an oxygen partial pressure versus temperature phase diagram at constant total gas pressure (200 MPa) were obtained. The dependence of the phase transformation temperature of the YBCO type superconductor on the oxygen partial pressure and the total gas pressure was examined. The phase stability analysis reveals for the first time that the transformation temperature of this YBCO type superconductor depends on both the total gas pressure and the oxygen partial pressure.