Low Open Area Research Articles

Theoretical study of particle and energy balance equations in locally bounded plasmas

Abstract In this study, new particle and energy balance equations have been developed to predict the electron temperature and density in locally bounded plasmas. Classical particle and energy balance equations assume that all plasma within a reactor is completely confined only by the reactor walls. However, in industrial plasma reactors for semiconductor manufacturing, the plasma is partially confined by internal reactor structures. We predict the effect of the open boundary area (A_L,eff') and ion escape velocity (u_i) on electron temperature and density by developing new particle and energy balance equations. Theoretically, we found a low ion escape velocity (u_i/u_B≈0.2) and high open boundary area (A_L,eff'/A_T,eff)≈0.6) to result in an approximately 38% increase in electron density and a 8% decrease in electron temperature compared to values in a fully bounded reactor. Additionally, we suggest that the velocity of ions passing through the open boundary should exceed ω_pi *λ_De under the condition (E_0)^2≪(Φ/λ_De)^2.

Permeability decline by fines migration near sand control screens in steam assisted gravity drainage: A numerical assessment

The near-wellbore permeability loss caused by the release and migration of naturally fine particles impairs the well productivity in oil reservoirs. The damage would be intensified in the presence of restrictions such as sand control screens due to retardation and accumulation of fine particles resulting from flow convergence and high volumetric flux.This study focuses on the experimental investigation and mathematical modeling of the permeability impairment near the sand control screens under a representative fines migration process for the SAGD well conditions. For this purpose, the single-phase flow experiments were conducted on unconsolidated sand packs in a sand retention testing (SRT) setup. The testing used different sand screens and considered the chemical effect of the fines migration process and different salinity for the saturating brine and flowing fluid. A 3D numerical model incorporating governing fluid and particle transport equations in porous media and an empirical permeability loss equation was established to simulate the fines migration process.The results show that the sand screens with a low open flow area and narrow aperture size cause higher permeability loss under the same flow conditions. Higher salinity reduction yields higher mobilized fines concentration, causing high near-screen permeability loss. For the salinities above 800 ppm, no significant pressure drops were observed. Furthermore, changing salinity to deionized water (DI) caused almost complete plugging of the sand pack, masking the flow performance of the sand control screen. A good match was obtained between the measured and calculated dimensionless pressure drops from the experimental and numerical models. The calibrated model could accurately enough predict the dimensionless pressure drops for the near-screen interval. It was confirmed that the porous medium's model parameters were nearly independent of the sand screen. However, different results were obtained for different salinities, confirming the 'parameters' dependency on not just porous medium but also fluid properties.

Understanding the coupling between the moisture loss and surface temperature in an evaporating leaf-type surface

We experimentally report evaporation characteristics from leaf-like surfaces having low open (exposed) area ratio. Even at much lower (1–10%) exposed areas, higher transpiration rates (60–70% compared to a bare water source) are sustained by a leaf. We mimic stomata, tiny openings present on the leaves using holes punched on silicon wafers (SW). The leaf-mimics have different opening diameters, ranging from to but nearly the same open area of The leaf-mimic with the smallest opening size was found to evaporate the most, while for the larger opening sizes it seems to decrease. In all the cases, evaporation ratio (ratio of the evaporation rate from the leaf-mimic to that of from a bare water surface at the same net incident radiation) increased with decreasing pore sizes; we compute this ratio based on three different definitions including one for the isothermal cases. In non-isothermal cases, we recognized that the variation in surface temperature led to nonlinear variation in the surface water vapor concentration. The effect of increased surface temperature, compared to a bare water surface in similar conditions, is missing in defining the evaporation ratios in previous approaches and thus we include it.

Pressure Drop Through Orifices for Single- and Two-Phase Vertically Upward Flow—Implication for Metering

Pressure drop has been measured for upward single- and two-phase gas–liquid flow across an orifice in a vertical pipe. A conductance probe provided average void fraction upstream of the orifice. Six orifices with different apertures/thickness were mounted in turn in a 34 mm diameter transparent acrylic resin pipe. Gas and liquid superficial velocities of 0–4 m/s and 0.3–0.91 m/s, respectively, were studied. For single-phase flow, pressure drop, expressed as an Euler number, was seen to be independent of Reynolds number in turbulent region. The Euler number increased with decreasing the open area ratio/orifice thickness and increasing velocity. The pressure drop was well predicted by the correlation of Idel'chik et al. (1994, Handbook of Hydraulic Resistances, 3rd ed., CRC Press, Boca, Raton, FL.), which uses a form of Euler number. The corresponding two-phase flow pressure drop depends on the flow pattern. Decreasing open area ratio/orifice thickness increased the pressure drop. For a given liquid superficial velocity, the pressure drop increases with gas superficial velocity except for low open area ratio where this increase is followed by a decrease beyond a critical superficial gas velocity for the high liquid superficial velocities. Relevant correlations were assessed using the present data via a systematic statistical approach. The two-phase multiplier equations of Morris (1985, “Two-Phase Pressure Drop Across Valves and Orifice Plates,” European Two Phase Flow Group Meeting, Marchwood Engineering Laboratories, Southampton, UK.) and Simpson et al. (1983, “Two-Phase Flow Through Gate Valves and Orifice Plates,” International Conference on Physical Modelling of Multiphase Flow, Coventry, UK.) are the most reliable ones.

Relation of Aortic Valve Morphologic Characteristics to Aortic Valve Insufficiency and Residual Stenosis in Children With Congenital Aortic Stenosis Undergoing Balloon Valvuloplasty

Aortic valve morphology has been invoked as intrinsic to outcomes of balloon aortic valvuloplasty (BAV) for congenital aortic valve stenosis. We sought to use aortic valve morphologic features to discriminate between valves that respond favorably or unfavorably to BAV, using aortic insufficiency (AI) as the primary outcome. All patients who underwent BAV at 2 large-volume pediatric centers from 2007 to 2014 were reviewed. Morphologic features assessed on pre-BAV echo included valve pattern (unicuspid, functional bicuspid, and true bicuspid), leaflet fusion length, leaflet excursion angle, and aortic valve opening area and on post-BAV echo included leaflet versus commissural tear. Primary end point was increase in AI (AI+) of ≥2°. Eighty-nine patients (median age 0.2years) were included in the study (39 unicuspid, 41 functional bicuspid, and 9 true bicuspid valves). Unicuspid valves had a lower opening area (p <0.01) and greater fusion length (p= 0.01) compared with functional and true bicuspid valves. Valve gradient pre-BAV and post-BAV were not different among valve patterns. Of the 16 patients (18%) with AI+, 14 had leaflet tears (odds ratio 13.9, 3.8 to 50). True bicuspid valves had the highest rate (33%) of AI+. On multivariate analysis, leaflet tears were associated with AI+, with larger opening area pre-BAV and lower fusion length pre-BAV. AI+ was associated with larger pre-BAV opening area. Gradient relief was associated with reduced angle of excursion. Valve morphology influences outcomes after BAV. Valves with lesser fusion and larger valve openings have higher rates of leaflet tears which in turn are associated with AI.

What maximum permeability can be measured with a monitoring well?

The PVC screens of recent monitoring wells (MWs) have thin slots and a low open area, usually in the 2–8% range. The MW screen and filter pack may cause important head losses which are not taken into account when interpreting the data of permeability tests performed using the MW. The equivalent hydraulic conductivity K of usual PVC screens was defined by hydraulic tests in a water tank, which have shown that gas micro-bubbles, a common problem in MWs and filter packs, contribute to increase the parasitic head losses. Closed-form equations and numerical models are used to explain by how much a field permeability test in a MW under evaluates an aquifer K value due to parasitic head losses in the screen and filter pack. The MW can properly measure the local soil K value only if it is markedly lower than the maximum MW value as obtained in a water tank. The MW measuring capacity can reach 5×10−3m/s for large slots and deaired water, but is most often between 10−5 and 10−4m/s for small slots in field conditions, and it can be only 10−6m/s for poorly designed and installed MWs. The limited measuring capacity may yield artificial permeability scale effects as often registered in environmental studies.

On the acoustic performance of rectangular splitter silencers in the presence of mean flow

Dissipative splitter silencers are often used to reduce the noise emitted in ventilation and gas turbine systems. It is well known that the acoustic performance of a splitter silencer changes under the influence of the convective effects of a mean gas flow and so in this article a theoretical model is developed to include the effects of mean flow. The theoretical model is based on a hybrid finite element method which enables the inclusion of bull nose fairings and a perforated screen separating the mean gas flow from a bulk reacting porous material. Predictions are compared against experimental measurements obtained both with and without mean flow. Good agreement between prediction and measurement is generally observed in the absence of mean flow, although it is seen that for silencers with a low percentage open area the silencer insertion loss is over predicted at higher frequencies. When mean flow is present, problems with the experimental methodology are observed at relatively modest mean flow velocities, and so comparison between prediction and experiment is limited to relatively low face velocities. However, experiment and theory both show that the insertion loss reduces at low frequencies when mean flow is in the direction of sound propagation, and at high frequencies the influence of mean flow is generally much smaller. Following additional theoretical investigations it is concluded that the influence of mean flow on splitter silencer performance should be accounted for at low frequencies when silencer airway velocities are greater than about 20m/s; however, at higher frequencies one may generally neglect the effect of mean flow, even at higher velocities. Predictions obtained using the hybrid method are also compared to a simplified point collocation approach and it is demonstrated that the computationally efficient point collocation method may be used to investigate the effects of mean flow in a splitter silencer without loss of accuracy.

Endpoint Detection in Low Open Area TSV Fabrication Using Optical Emission Spectroscopy

Through-silicon via (TSV) technology is a key enabler for 3-D and 2.5-D integration, which provides low-power and high-bandwidth chip-to-chip communication. During TSV fabrication, over-etching may cause notching at the base of the TSVs, resulting in TSV diameter variations. Endpoint detection (EPD) techniques are critical for controlling TSV diameter, and detecting the endpoint for low open areas presents a serious challenge to process engineers. In this paper, a hybrid partial least squares-support vector machine model for optical emission spectroscopy data are successfully demonstrated for an EPD of low open area TSVs. Accurate EPD results are shown for 120, 80, and 25 \(\mu\) m diameter TSVs.

Theory of Compressor Stability Enhancement Using Novel Casing Treatment, Part I: Methodology

This paper proposes a novel casing treatment, designated a stall precursor-suppressed casing treatment. It is designed to suppress stall precursors to realize stall margin enhancement in turbomachinery. This paper first presents a physical and mathematical model to describe the casing treatment configuration as a wall boundary condition and then establishes the stability equation with its effect. The sensitivity of stall inception to different boundary conditions is considered numerically for both subsonic and transonic axial flow fan/compressors. One important finding from this numerical prediction and analysis is that such a casing treatment can be used to change stall inception even when using a casing treatment configuration with low open area ratio. Thus, a reduction of momentum loss due to recirculating flow can be realized, in comparison with a conventional recessed casing treatment with more than 50% open area ratio. It is thus theoretically possible to design an advanced casing treatment to affect the evolution of stall precursors and finally change stall inception without significantly changing the efficiency of the fan and compressors.

OES를 이용한 질화막/산화막의 식각 스펙트럼 데이터 분석

As semiconductor device technology continuously shrinks, low-open area etch process prevails in front-end etch process, such as contact etch as well as one cylindrical storage (OCS) etch. To eliminate over loaded wafer processing test, it is commonly performed to emply diced small coupons at stage of initiative process development. In nominal etch condition, etch responses of whole wafer test and coupon test may be regarded to provide similar results; however, optical emission spectroscopy (OES) which is frequently utilize to monitor etch chemistry inside the chamber cannot be regarded as the same, especially etch mask is not the same material with wafer chuck. In this experiment, we compared OES data acquired from two cases of etch experiments; one with coupon etch tests mounted on photoresist coated wafer and the other with coupons only on the chuck. We observed different behaviors of OES data from the two sets of experiment, and the analytical results showed that careful investigation should be taken place in OES study, especially in coupon size etch.

Endpoint Detection in Low Open Area Ratio Plasma Etching Using Hybrid Method

In current semiconductor manufacturing, as the feature size of integrated circuit (IC) devices continuously shrinks, detecting endpoint in low open area plasma etch process is more difficult than before. For endpoint detection, various kinds of sensors are installed in many semiconductor manufacturing equipment, and sensor data sampled with predefined sampling rate. To solve this problem, a combination of Signal to Noise Ratio (SNR), Principal Component Analysis (PCA) and Expanded Hidden Markov model (eHMM) technique is applied to optical emission spectroscopy (OES) signals.

Analytical models for evaluating buoyancy-driven ventilation due to stack effect in a shaft considering heat transfer from shaft interior boundaries

Stack effect is a dominant driving force for building natural ventilation. Analytical models were developed for the evaluation of stack effect in a shaft, accounting for the heat transfer from shaft interior boundaries. Both the conditions with constant heat flux from boundaries to the airflow and the ones with constant boundary temperature were considered. The prediction capabilities of these analytical models were evaluated by using large eddy simulation (LES) for a hypothetical shaft. The results show that there are fairly good agreements between the predictions of the analytical models and the LES predictions in mass flow rate, vertical temperatures profile and pressure difference as well. Both the results of analytical models and LES show that the neutral plane could locate higher than one half of the shaft height when the upper opening area is identical with the lower opening area. Further, it is also shown that the analytical models perform better than KLOTE’s model does in the mass flow rate prediction.

Endpoint Detection in Plasma Etching Using Principal Component Analysis and Expanded Hidden Markov Model

In current semiconductor manufacturing, plasma processes such as etch and CVD take the portion at least 40% throughout of integration processes. As the feature size of integrated circuit (IC) devices continuously shrinks, detecting endpoint in low open area plasma etch process becomes more difficult. To solve this problem, a combination of Principal Component Analysis (PCA) and Expanded Hidden Markov model (eHMM) technique is applied to optical emission spectroscopy (OES) signals. Selected patterns are used in PCA, which reduces dimension of the raw data and increases gap between classes. The eHMM is employed to detect endpoint using output of PCA. The eHMM combines the semi-Markov model to enable an arbitrary distribution on the location of the change-point and the segmental HMM to model the configuration in each segment. After modeling using eHMM, real-time OES data were fed to this model to detect endpoint.

Emission effects of three different ventilation control strategies—A scale model study

The objectives of this paper are to determine the effects of varying the ventilation rates on ammonia emission using three different control strategies: constant inlet opening area, constant inlet air velocity and constant inlet air jet momentum. In addition, methods for estimation of air exchange rates between the headspace and the room are investigated. The work is based on scale model experiments in three different floor configurations. The model was made to scale 1:12.5 of a sub-section of a pig house with double rows of pens. Ventilation air was supplied through adjustable slats at two sides beneath the ceiling spanning the whole width of the model. Ammonia water was added in the scale model bottom to serve as a reservoir providing measurable gas emission. In addition to no-floor, two types of slatted floor were investigated with opening area 33.3% and 16.7%. The effect on the emission of increasing the ventilation rate is seen to greatly depend on the control strategy. The highest emission rate was found for constant inlet opening. The emission was reduced considerably when the inlet opening was adjusted to maintain constant inlet velocity, and when the inlet opening was adjusted to maintain constant momentum the emission was nearly independent of ventilation rate. The maximum emission was found with no slatted floor and the minimum emission was found for the slatted floor with the lower opening area.

Feature extraction of particle density in a pipeline with tomography and wavelets

A concept to extract a feature of solid-air two-phase flow in a pipeline has been launched with a combination of a capacitance-computed tomography and wavelets transform. With this concept, particle distribution images obtained by CT are transformed with discrete wavelets multiresolution. As a result, in the case of low open area ratios of the pipe cross-section, high particle densities are shown in secondary dominant levels as well as a substantial space level. The high value in the secondary level resulted from inhomogeneous density due to collision between particles.

キャパシタンスCTとウェーブレット多重解像度を用いた管路内固気二相流の特徴抽出

A concept to extract a feature of solid-air two-phase flow in a pipeline has been launched with a combination of a capacitance-computed tomography and wavelets transform. With this concept, particle distribution images obtained by CT are transformed with discrete wavelets multiresolution. As a result, in the case of low open area ratio of the pipe cross-section, high particle densities are shown in secondarily dominant levels as well as a substantial space level. The high value in the secondary level results from unhomogeneous density due to collision between particles and wall. In the experiment, the CT acquires the capacitances between 12 electrodes distributing around the outside of the pipeline. Clay is attached inside the pipeline in order to verify the open area ratio. The images are reconstructed from the capacitances with a linear back projection method.

Low open-area endpoint detection using a PCA-based T/sup 2/ statistic and Q statistic on optical emission spectroscopy measurements

Examines an approach for automatically identifying endpoint (the completion in etch of a thin film) during plasma etching of low open area wafers. Because many end-pointing techniques use a few manually selected wavelengths or simply time the etch, the resulting endpoint detection determination may only be valid for a very short number of runs before process drift and noise render them ineffective. Only recently have researchers begun to examine methods to automatically select and weight spectral channels for estimation and diagnosis of process behavior. This paper will explore the use of principal component analysis (PCA)-based T/sup 2/ formulation to filter out noisy spectral channels and characterize spectral variation of optical emission spectroscopy (OES) correlated with endpoint. This approach is applied and demonstrated for patterned contact and via etching using digital semiconductor's CMOS6 (0.35-/spl mu/m) production process.

FOAMING OF SPRAYS WITH THE USE OF SCREENS

ABSTRACT Transformation of liquid sprays into foamed sprays was achieved with the use of a nozzle that contained a screen placed at a distance from the nozzle orifice. The quality of transformation was controlled by the percent open area of the screen with its optimum value being around 46%. Other important spray characteristics that affect the quality of foamed sprays are the spray velocity and distance between screen and orifice. The mechanism responsible for the transformation of liquid droplets into foamed particles is considered to be that of collisions between the liquid droplets and liquid bridges formed in the screen openings. The neck thickness of the liquid bridges depends on the percent open area of the screen. A low percent open area screen results in thick liquid bridges that cannot be effectively penetrated by the liquid droplets. On the other hand, a high percent open area screen results in very thin liquid bridges that are penetrated by the liquid droplets without transforming them into foamed particles.