Low-pressure Mode Research Articles

Features of stabilization of soft soils at the base of emergency deformed buildings using finely powdered injection materials in low pressure mode

At present, the strengthening of the soil base is often performed by high-pressure injection - injection of a solution under pressure that exceeds the structural strength of the soil (hydraulic fracturing mode). High-pressure injection makes it possible to successfully solve various geotechnical problems, but it has a number of disadvantages, first of all, the uncertainty of the shape and size of injection bodies created in the soil mass, as well as the impossibility of predicting the final deformation and strength characteristics necessary for design. It should be noted that directly from the production of injection works in the uncontrolled hydraulic fracturing mode, unpredictable technological deformations (rise followed by uneven settlement) of the Objects are observed, the base of which is stabilized, as a result of which crack formation processes in above-ground structures and fragmentary destruction of load-bearing elements develop. The article considers the possibility of solving the problem of predictable increase in the mechanical properties of stabilized soils on the example of a pilot production site in the central region of St. Petersburg. The proposed method makes it possible to ensure the absence of technological deformations from the production of injection works by using the author's kinematic scheme for the production of works and the use of modern solutions based on fine binders in the impregnation mode with an element of soil microfracture, that is, in the mode of controlled hydraulic fracturing at a reduced injection pressure of the injection solution.

Production of H2 via sorption enhanced auto-thermal reforming for small scale Applications-A process modeling and machine learning study

Small scale production of H2 via sorption enhanced auto-thermal reforming (SEATR) of methane is simulated using Ni based catalyst and CaO sorbent for the capturing of CO2. One dimensional heterogeneous reactor model was developed using gPROMS model builder to study the performance of SEATR reactor. At low pressure mode, the process was evaluated for varying temperature, pressure, gas flux and steam to carbon ratio. Chemical equilibrium with application (CEA), an equilibrium based software was employed so as to compare both equilibrium and simulation results. Under a range of temperature (500–1000 K), pressure (1–10 bar), S/C ratio (1–6), and O/C ratio (0.2–0.6) close to equilibrium conditions, model outputs satisfactory results with regard to CH4 conversion, CO2 capturing, H2 yield and purity. At 750 K, 2.9 bar, Gs of 0.4 kg/m2 s, S/C of 3 and O/C of 0.45, H2 purity and CH4 conversion achieved was 97% and 94% respectively in comparison with 66% and 77% from conventional auto-thermal reforming. In Bayesian Regularization (BR), Mean square error(MSE) and R value is minimum for neural network algorithm comparison. It accounts for 1.2e−10 and 0.999 respectively. BR produces minimum error with increase in Epochs and gradients values highlighting maximum performance with optimize computation time for process modeling data-integration studies and generalization.

SP Gas Well Development Strategy at Offshore B Flowstation Using Analytical Hierarchy Process

This research is focused on analyzing strategies for developing SP well production in the B Flowstation offshore platform. The development in question is the construction of platforms and SP gas well production facilities based on the application of the SP gas well production operation mode to the existing Bravo Flowstation production system. The application of the SP well production operation mode will determine the design of the production facility and the amount of investment the company has to operate the SP well. The mode of production operation also affects the continuity and stability of SP gas well production in meeting the company's production targets. Based on seismic results and studies from the company that wells have capacity of 53.5 BCF with a gas production rate of 30 MMSCFD and is capable of producing for 6 years. Incorrect application of operating modes has the potential to cause premature production, which means that production from the well cannot last for 6 years. That is because the occurrence of water coning which has an impact on gas production is hindered by the rate of water production. In addition, the application of the operation mode also affects the continuity of gas well production. Gas production activities may be halted due to production shutdowns due to a mismatch of the SP well production line technology design that is applied to an existing production system. The cessation of SP well gas production activities can also be caused by operational activities such as maintenance activities. From the potential problems that arise, a qualitative analysis is needed by considering every aspect of the problem. With the complexity of things that must be considered in the production development strategy used the AHP (Analytic Hierarchy Process) method. 4 alternative choices of SP well operation modes are determined by the expert. The alternatives include: high pressure mode; low pressure mode; medium pressure mode; and combine high low pressure mode. Criteria identified by the expert include: technology; capital costs; the impact of existing production; operating costs; decline reservoir. From the data obtained in the field as a reference for experts to determine the weighting in the AHP method, the dominant alternative is the development of SP wells based on the combining high low pressure operation mode. The high low pressure operating mode provides continuous production without being affected by existing production processes and has the potential for a medium for water coning. With a sizeable investment the SP well development strategy can be on target in production and on return on investment.

Role of thermionic emission in the formation of negative electric potential and oscillations in low pressure discharges

In this paper, we discuss the results from the two-dimensional computational investigation of the role of thermionic cathode emission in the formation of the negative (reverse) potential near the emissive cathode (LaB6 tablet). Two modes of discharge behavior are considered—high- and low-pressure modes. We show that the region of the negative potential (for that of the emitting cathode) is enclosed in a semi-sphere bounded by the line where the electric field changes its direction. This sheath region was distorted by the movement of the emitting points in horizontal and vertical directions. The unstable behavior of the high pressure discharge and self-excited oscillations of plasma parameters were observed. At low pressure the potential reversal and oscillations were not so pronounced.

The impact of processing parameters on the properties of Zn-bonded Nd–Fe–B magnets

We report on the effect of loading factor and pressure on the density and the magnetic properties of Zn-bonded Nd–Fe–B magnets produced by pulsed-electric-current sintering (PECS). The idea behind this study is to fabricate bonded magnets with a metallic binder in order for the bonded magnet to operate at temperatures higher than 180°C: the current upper-limit for polymer-bonded magnets. These composites are made of hard-magnetic powder in the form of melt-spun ribbons bonded with the low-melting-point metal Zn. The binder additions were varied from 10 to 30wt%, and pressures of 50 and 500MPa were applied. The high-pressure mode with 20wt% Zn resulted in a 24% increase of Jr, compared to the low-pressure mode. The magnetic measurements revealed a maximum remanence of 0.64T for 10wt% Zn, while the coercivity is largely unaffected by the processing conditions. The density of the composites was up to 7.0g/cm3, corresponding to 94% of the theoretical density. Compared to commercial polymer-bonded magnets, the Zn-bonded counterparts exhibit a slightly lower Jr, but the coercivity is retained. We show that there is a minor diffusion of Zn into the Nd–Fe–B, forming a 1μm thin transition layer, but it does not harm the magnetic properties. These metal-bonded Nd–Fe–B magnets are ideal for use in high-temperature automotive applications like under-the-hood sensors and other magnet-based devices that are close to the engine.

Active multi-effect vertical solar still: Mathematical modeling, performance investigation and enviro-economic analyses

In this paper, year round performance and enviro-economic analyses of active multi-effect vertical solar still were carried out using the developed comprehensive mathematical model. The optimum number of effects, mass flow rate of feed water and gap between the effects were found to be five, 7.20kg/h and 0.05m, respectively. Maximum annual average distillate yield of 6.78 and 21.29kg/m2-d was noticed for the optimized unit under normal mode and low pressure mode operation. Maximum annual average Performance ratio (PR) and Solar energy Coefficient of Performance (SCP) of 5.59 and 3.03 was noticed under evacuated mode operation. Energy payback time and distilled water production cost of the evacuated unit treating 5wt% saline water was around 1.37yrs and Rs.2272.00/m3 (33.00USD/m3), respectively and it can effectively mitigate at least 81.81tons of CO2 emission during its life time of 20yrs. Distilled water production cost of the evacuated unit was found to reduce from Rs.2270.00/m3 (33.00USD/m3) to Rs.1310.00/m3 (19.00USD/m3) by decreasing the interest rate from 12% to 5%. Salinity of feed water and interest rate at which the unit was financed played a major role in distilled water production cost.

Scaling analysis of PMR200 reactor cavity cooling system

The reactor cavity cooling system (RCCS) of the PMR200, a demonstration plant of very high temperature reator (VHTR), removes the residual heat, which amounts to 0.3–0.6% of the reactor full power, at both high and low pressure modes, by means of radiation and natural convection. Its operation has to be passive to eliminate any accidents associated with human errors. Prior to the experimental performance verification of the RCCS, a scaling analysis has been performed. In the present study, the scaling was based on the cavity radiation number. Based on it, the scaling laws between the model and prototype were derived, and applied to the RCCS down-scaling.

ESEM modifications to LEO SUPRA 35 VP FESEM

A LEO SUPRA 35VP FESEM has been modified to significantly improve image quality in the low pressure mode of operation. It is further shown that the same conversion can allow the machine to operate also as a fully fledged environmental scanning electron microscope with specimen chamber pressures in excess of 2000Pa. This is achieved by a diamagnetic insert with a thin pressure limiting aperture at the bottom of the pole-piece. The insert allows the use of various size apertures in addition to the existing 1mm differential diaphragm.

Extendibility Study of a PVD Cu Seed Process with Ar+ Rf-Plasma Enhanced Coverage for 45nm Interconnects

ABSTRACTWe present the results of a systematic benchmarking study, using 45nm-groundrule structures, of a commercially-available ionized PVD Cu technology which employs an in-situ Ar+ radio-frequency (Rf) plasma capability for enhanced coverage, and compare its performance and extendibility against the same seedlayer process operated in conventional low-pressure mode. Studies of single-damascene lines and dual-damascene via structures indicate that the PVD Cu seedlayer with Rf-Plasma enhancement enables a reduction of the PVD Cu seed thickness on the order of 35%, based on studies of Cu voiding, via-yield degradation, and transmission-electron microscopy (TEM). These results illustrate the critical importance of the Rf-plasma resputter capability in extending the PVD Cu process to advanced groundrules at 45nm and beyond.

Clinical effectiveness of a low-tech versus high-tech pressure-redistributing mattress

To compare the effectiveness of a high-specification foam mattress (control) with a high-tech (Duo2, Hill Rom) alternating/continuous low-pressure mattress (treatment) in the prevention of pressure ulceration. The study also evaluated if there is a difference in performance between the two working modalities (alternating and continuous low pressure) of the high-tech mattress in a comparable sample of patients. Thirty-three patients were observed for two weeks in the control group. In the treatment group, 86 patients were randomised to receive alternating low pressure and 84 continuous low pressure. Incidence of pressure ulcers in both arms was recorded. Student's t-test was used to compare all Braden scores, and the chi-square test and Fisher's exact test to evaluate differences between groups. There was a high difference in the number of new pressure ulcers in the control group when compared with the treatment group. There was no difference in performance between the alternating and continuous low-pressure modes. However, the sample size is too small to prove or disprove a statistically significant difference between the two modalities. The high-tech mattress was markedly more effective than the high-specification foam mattress in preventing the onset of pressure ulcers. Initial data suggest that the use of alternating or continuous low pressure made little or no difference to the results.

Low pressure mode combined with OsO4 vapor fixation and sputter-coating for the preservation of delicate aerial hyphae and conidia in the ESEM

The newer generation of environmental scanning electron microscopes (ESEMs) allows samples to be viewed under a range of different vacuum conditions. No specific sample preparation protocols are required with the ESEMs, as fresh, unfixed samples are used and discarded later. We have worked out a method that preserves aerial hyphae on biltong that closely resemble fresh specimens and may be stored for viewing at a later date. Another advantage is that fixed samples are more resilient to the variable vacuum encountered in the ESEM. When biltong samples with fungal growth were first studied, we observed that vacuum-related artifacts were induced unless vacuum conditions and changes in pressure were carefully controlled. Damage readily occured in conidia and its delicate hyphae. Fresh, unfixed samples are very vulnerable to these artifacts. In addition, biltong proved to be a problematic study sample because of its high salt content, its hygroscopic nature as well as being laden with spices. To eliminate these artifacts, the preservation of specimens by OsO4 vapor fixation combined with a special sputter-coating technique is described. Previous studies confirmed that OsO4 vapor fixation is superior to traditional immersion fixation methods for the examination of hyphae and conidia of various fungi in a conventional SEM. However, both preparation methods induce sample shrinkage. We observed that OsO4 vapor fixation followed by Au coating under strictly controlled vacuum conditions induced fewer artifacts and gave the best images with minimum distortion in low pressure (LP) mode. The proposed method allows samples to be viewed both in ESEM and LP mode. There are however some disadvantages inherent to ESEM mode. Even when viewing fixed, coated samples, care should be taken to maintain a pressure of not lower than 0.2 Torr in the specimen chamber. It is critical that different samples have the same vacuum exposure history, as shrinkage and collapse were found to be directly related to the lowest pressure the samples were subjected to, both in the sputter coater chamber and in the electron microscope specimen chamber.

A filamentless ion source for materials processing

A dual-stage, multiaperture gas ion source with 5 cm beam diameter has been built and characterized. The first discharge stage is a constricted glow discharge injecting a plasma stream into a discharge cavity supporting a Penning ion gauge discharge in the low pressure mode. Both discharge stages and ion extraction are fed by a single, grounded power supply. This simplifies the electrical setup and reduces costs. Various gases have been tested including nitrogen, oxygen, and argon. The ion beam current density is 250 μA/cm2, i.e., the beam current is about 5 mA, at an extraction voltage of 3.0 kV and a discharge current of 59 mA. Measurements of the ion beam current as a function of various parameters such as the discharge voltage and current, gas flow, and magnetic field are presented. The source is compact and can be easily adapted to various materials modification applications in which ion energies of a few keV are required.

Predicted performance characteristics of a variable cycle turbofan

AbstractThe selective bleed turbofan is a two shaft, three compressor, variable cycle aircraft engine. Its bypass ratio (BPR) can be modulated to suit the operating flight conditions. At subsonic flight speeds it operates as a medium bypass turbofan (low pressure mode or LPM). It becomes a low bypass turbofan (high pressure mode or HPM) when flying faster and is capable of supersonic cruise without reheat (RH).The aim of this paper is to describe the selection of the main engine design parameters in the HP mode and to outline the challenges to be met to enable the powerplant to operate in the other mode. The components have to perform satisfactorily over a wide range of varying conditions. The resulting demands are reflected in many ways, for example in the operating lines of the low pressure compressors and in the overall efficiency changes with increased bypass ratio. In the case of the present investigation the two bypass ratios selected are 0·3 for the high pressure mode and 0·7 for the low pressure mode. The latter was selected after an examination of a choice of bypass ratios ranging from 0·4 to 1·0. The change in variable stators required to achieve the LP mode cycle is indicated.The effect of changing bypass ratio on engine performance and handling is shown. The main conclusion is that the design of this engine seems to be feasible within current technological capabilities and further investigation is encouraged because it appears to yield significant benefits.

Operating characteristics of a 100 kV, 100 kW plasma ion implantation facility

Plasma ion implantation of gaseous ion species is conducted in two different operating modes corresponding to two different gas pressure regimes, a low-pressure mode (1.33 × 10-3 -1.33 × 10-2Pa (10-5 -10-4Torr)) and a high-pressure mode (1.33 × 10-2 -0.133 Pa (10-4 -10-3Torr)). In the low-pressure operating mode, the plasma production and ion implantation processes are decoupled, i.e. a part to be implanted is immersed in a separately generated nitrogen plasma and then independently pulse biased to -100 kV to implant ions. The current-pulse waveform continuously decays from an initial high-current-spike value (300 A) to a low relatively steady-state value (30 A). A wide dynamic range of operation is possible in this mode. Pulse durations can extend from 10 to 50 us and frequencies can range from 100 to 1000 Hz. Total power levels of 100 kW have been demonstrated. In the high-pressure operating mode, the plasma production and ion implantation processes are coupled, i.e. the part is immersed in a gas, and the voltage used to pulse bias the part both initiates and sustains the plasma production process, as well as implanting ions. The current-pulse waveform increases during the initial part of the pulse duration and can attain a near-steady value of 150 A at 100 kV. The higher near-steady-state pulsed current of the high-pressure mode potentially allows faster implantation of parts as well as a smaller more conformal plasma sheath compared with the low-pressure mode. However, the dynamic range in this mode differs from the low-pressure mode. At 100 kV, pulse durations are limited to less than 5 μs at a frequency of less than 100 Hz. In this paper, we present the operating characteristics for both operating modes, as well as their implications for faster treatment and more conformal implants of complex-shaped parts.

High sensitivity mass spectrometer system for contaminant measurement in high purity gases

A mass spectrometer beam system using a double focusing sector analyzer and an electron impact ion source has been developed for trace analysis. The molecular beam, formed through a focusing glass capillary array, serves as the gas inlet of the system. Closed cycle cryopumps and ion pumps are used to generate the high vacuum. System roughing is achieved using sorption pumps. Clean and oil free vacuum was obtained by nonmechanical pumping. System normal mode sensitivity is about 107 counts/s/Torr. System low pressure mode sensitivity can be three orders of magnitude higher when sample pressures are below 30 mTorr. A parts-per-billion range system detection capability was accomplished. Slow response time for adsorptive species measurements is a major drawback of the sample inlet system.

A simple electron cyclotron resonance ion sourcea)

A simple, all permanent magnet, 2.45 GHz electron cyclotron resonance ion source has been developed for the production of stable beams of low charge state ions from gaseous feed materials. The source can produce ∼1 mA of low energy (3 kV) singly charged ion current in the 10−4 Torr pressure range. The source can also be operated in a more efficient low-pressure mode at an order of magnitude lower pressure. In this latter range, for example, the ionization efficiency of Ar is estimated to be 1% with charge states up to Ar8+ present. Operation in the low-pressure mode requires low power input (∼20 W). These features make the source especially suited for use with small accelerator systems for a number of applications including ion implantation, mass spectrometry, and atomic collision experiments where multiply charged ions are desirable. Design details and performance characteristics of the source are presented.

A simple electron cyclotron resonance ion source (abstract)a)

A simple, all permanent magnet, 2.45 GHz electron cyclotron resonance ion source has been developed for the production of stable beams of low charge state ions from gaseous feed materials. The source can produce ∼1 mA of low energy (3 kV) singly charged ion current in the 10−4 Torr pressure range. The source can also be operated in a more efficient low-pressure mode at an order of magnitude lower pressure. In this latter range, for example, the ionization efficiency of Ar is estimated to be 1% with charge states up to Ar8+ present. Operation in the low-pressure mode requires low power input (∼20 W). These features make the source especially suited for use with small accelerator systems for a number of applications including ion implantation, mass spectrometry, and atomic collision experiments where multiply charged ions are desirable. Design details and performance characteristics of the source are presented.

Observation of a very high electron current extraction mode in a hollow cathode discharge

Earlier results by Hershcovitch, Kovarik, and Prelec in J. Appl. Phys. 67, 671 (1990) proved that, in a low-pressure operating mode, hollow cathode discharges can have a two-component electron population, one of which is that of ‘‘fast’’ electrons having an energy corresponding to the cathode potential and a thermal spread of about 0.13 eV, which could form a basis for an excellent electron gun. Investigations of extracted electron currents in this low pressure mode indicate the existence of a narrow pressure range characterized by very high electron current extraction.

On the low-pressure mode transition in electron cyclotron heated plasmas

The properties of plasmas created and sustained by electron cyclotron heating (ECH) have often been found to undergo an abrupt change as the ambient gas pressure is reduced below a value that is typically around 10−5–10−4 Torr. A model is presented in which ambipolar transport of particles and energy are balanced by electron impact ionization and microwave power absorption, respectively. In the absence of magnetic-mirror confinement of high energy electrons, the equilibria predicted by the model exist only for gas pressures greater than a value determined by the ionization rate constant, the average ion mass, and the axial length (along the steady magnetic field) of the discharge. At the critical pressure, the equilibria bifurcate into high-temperature/low-density and low-temperature/high-density branches. Magnetic-mirror confinement of high-energy electrons can lower the critical pressure and modify the bifurcation somewhat. In all cases the equilibrium electron temperature is governed primarily by gas pressure while the plasma density is proportional to the microwave power density absorbed by the plasma.

Optimization and performance of a saddle field ion source

The saddle field ion source operates at low gas pressure and requires neither magnetic field nor filament. We have designed a cold cathode saddle field ion source and characterized the discharge with hydrogen in the oscillating (‘‘low pressure’’) mode and in the transition mode. The anode design was optimized for maximum electrostatic confinement of the electrons and thus also maximum discharge current. A discharge current of 100 mA was obtained at a pressure of 0.5 Pa (3.8 mTorr) and a voltage of 10 kV. The discharge anisotropy was investigated and the discharge was found to be mainly an axial one in which the electrons oscillate near the axis. A highly peaked radial profile of current was measured at the end cathodes in the low pressure mode, and was dependent upon the operating pressure. A phenomenological explanation of these results is presented.