Total Pressure Measurements Research Articles

Vapor–Liquid Equilibria of Binary Mixtures Containing 1-Butanol and Hydrocarbons at 313.15 K

Total pressure measurements made at 313.15 K by the static method for five binary mixtures 1-butanol + heptane, 2,2,4-trimethylpentane, dodecane, cyclohexane, and methylbenzene are presented. Data reduction by Barker's method provides correlations for GE, using the four-parameter Margules equation; also the Wilson, nonrandom two-liquid (NRTL), and universal quasichemical activity coefficient (UNIQUAC) models have been used for fitting binary systems. The five investigated mixtures exhibit a positive deviation from ideality. No azeotrope has been detected for 1-butanol + dodecane, and the other systems show positive azeotropy. Good results are obtained in the prediction of total pressure for these systems.

Investigations of a method for determining pumping speed and sorption capacity of nonevaporable getters based on in situ calibrated throughput

This paper presents a gas-sorption method, based on an in situ calibrated throughput, for characterizing nonevaporable getters (NEGs) of Ti- and Zr-based alloys. The main characteristics of the method are the adjustment of a constant injected gas flow, the prompt calibration of a throughput, and the measurement of an increasing sorption pressure. It is essential that inert vacuum gauges be selected for measurements of total pressure to prevent contamination of a test gas and poisoning of an NEG under test. A capacitance diaphragm gauge is used for preparation of the injected gas flow by filling the gas reservoir with a test gas and adjusting the conductance of a variable leak valve. A spinning rotor gauge (SRG) is used for in situ calibration of the throughput by means of an integrated gas-flow calibration facility and the rate-of-pressure-rise method, and by continuous measurement of the sorption pressure in a test chamber. A getter pumping speed and a sorbed quantity are calculated while considering the throughput, the sorption pressure, and the sorption time. The throughput must be selected in accordance with both the sorption characteristics of a particular NEG type and the measurement capabilities of the SRG. At room temperature, porous thick-film NEGs and structured thin-film NEGs exhibit an initial getter pumping speed on the order of 1 and 0.1 l s−1 cm−2, respectively. The corresponding sorption capacity of a few times 10−4 mbar l cm−2 is comparable for all chemically active gases except for H2, which amounts to a few times 100 × 10−3 mbar l cm−2 in the case of porous NEGs and ∼1 × 10−3 mbar l cm−2 in the case of structured NEGs. Detailed analysis of uncertainties of SRG pressure measurements below 1 × 10−3 mbar gives an expanded uncertainty of the getter pumping speed and the sorbed quantity of 1.9% and 3.5%, respectively. While temporally interrupting the throughput, the setup enables discrete measurements of the background pressure, which increases because of the accumulation of nongetterable gases. After completion of the gas-sorption test, a qualitative determination of the accumulated inert gas composition is performed by the gas-burst method using a quadrupole mass spectrometer (QMS) mounted on a vacuum system. The quantitative analysis is enabled by the use of a QMS calibrated in situ by known amounts of a certain gas such as H2, CH4, CO, Ar and Kr.

Automated Prescription of an Optimal Imaging Plane for Measurement of Cerebral Blood Flow by Phase Contrast Magnetic Resonance Imaging

This study describes and evaluates a semiautomated method for prescribing an optimal imaging plane that is located as close as possible to the skull base, and is simultaneously nearly perpendicular to the four arteries leading blood to the brain [internal carotid arteries (ICAs) and vertebral arteries (VAs)]. Such a method will streamline and improve reliability of the measurement of total cerebral blood flow and intracranial pressure by velocity encoding phase-contrast magnetic resonance imaging. The method first extracts the vessels' centerline from a 2-D time-of-flight magnetic resonance angiogram of the neck by performing distance transformations. An anatomical marker, the V2 segment of the VAs, is then identified to guide the imaging plane to be as close and below the skull base. An imaging plane that is nearly perpendicular to the ICAs and V2 segment of VAs is then identified by minimizing a misalignment value, estimated by a weighted mean of the angles between the plane's normal and the vessel axes at the vessel-plane intersections. The performance of the semiautomated method was evaluated by comparing manually selected planes to those found semiautomatically in nine magnetic resonance angiogram datasets. The semiautomated method consistently outperformed manual prescription with a significantly smaller misalignment value, 8.6° versus 20.7° (P < 0.001), respectively, and significantly improved reproducibility.

Vapor−Liquid Equilibrium in Diluted Polymer + Solvent Systems

Vapor−liquid equilibrium data were determined for five polymer + methylbenzene systems under isothermal conditions between (333.15 and 373.15) K. The polymers studied include copolymers and terpolymers of octadecyl propenoate, propenoic acid, ethenylbenzene, and 1-vinyl-2-pyrrolidone because of their practical importance as flow improvers for crude oil and/or derivatives. An all-glass microebulliometer with circulation of the liquid phase was used for measurements of total pressure over polymer + methylbenzene mixtures. Two predictive group-contribution models (entropic−free volume and group contribution−Flory) were applied to estimate the phase behaviors of two polymer solutions; good agreement with the experimental data was achieved.

Computational and experimental study of intake ground vortices

AbstractThe ground vortices generated by an intake under both headwind and crosswind configurations have been investigated using computational and experimental approaches. The flow field of a scale-model intake was experimentally studied using stereoscopic particle image velocimetry to measure the ground vortex in conjunction with induct total pressure measurements for the internal flow. The computational predictions were performed using an unsteady Reynolds averaged Navier-Stokes approach. The experimental results show that under crosswind conditions a single ground vortex forms which becomes stronger as the crossflow velocity is increased. Under headwind conditions the measured ground vortex strength initially increases with freestream velocity before it reaches a local maximum and then reduces thereafter. The computations also exhibit the same characteristics and show good agreement with the measurements for some configurations. Based on the predictions, the complex flow field topology is investigated and a detailed flow model of the vortex flow field under crosswind conditions is proposed.

Ground vortex aerodynamics under crosswind conditions

An experimental study was performed to investigate ground vortex formation under crosswind conditions using stereoscopic particle image velocimetry and in-duct total pressure measurements. The effect of velocity ratio, non-dimensional height, approaching boundary layer thickness and yaw angle are assessed using vortex strength and in-duct distortion descriptors. The flow-field is characterized by a single ground vortex which increases in strength as the velocity ratio is reduced. The vortex characteristics depend on the ground clearance with a stronger vortex observed at lower intake heights. For a high ground clearance, the vortex strength reaches a local maximum before reducing towards zero as the capture streamtube no longer interacts with the ground plane. At a low ground clearance, the vortex strength is strong enough to induce a lip separation. The approaching boundary layer thickness has no notable influence on the vortex characteristics. Reducing the intake yaw angle from a crosswind to a headwind configuration leads to a monotonic decrease in vortex strength with the data following a sin3(ψ) relationship, where ψ is the yaw angle. The distortion coefficient was also monotonic with yaw angle; however, the dependence was sin6(ψ).

High-Fidelity Numerical Analysis of Per-Rev-Type Inlet Distortion Transfer in Multistage Fans—Part I: Simulations With Selected Blade Rows

Demands for improved performance and operability of advanced propulsion systems require an understanding of the physics of inlet flow distortion transfer and generation and the subsequent engine response. This also includes developing a high-fidelity characterization capability and suitable tools/rules for the design of distortion tolerant engines. This paper describes efforts to establish a high-fidelity prediction capability of distortion transfer and fan response via high-performance computing. The current CFD capability was evaluated with a focus of predicting the transfer of prescribed inlet flow distortions. Numerical simulations, comparison to experimental data, and analysis of two selected three-stage fans are presented. The unsteady Reynolds-Averaged Navier-Stokes (RANS) code PTURBO demonstrated remarkable agreement with data, accurately capturing both the magnitude and profile of total pressure and total temperature measurements. Part I of this paper describes the establishment of the required numerical simulation procedures. The computational domains are limited to the first three blade rows for the first multistage fan and the last three blade rows for the second fan. This paper presents initial validation and analysis of the total pressure distortion transfer and the total temperature distortion generation. Based on the established ground work of Part I, the entire two multistage fans were simulated with inlet distortion at normal operating condition and near stall condition, which is Part II of this paper. Part II presents the full range validation against engine test data and in-depth analysis of distortion transfer and generation mechanisms throughout the two fans.

High-Fidelity Numerical Analysis of Per-Rev-Type Inlet Distortion Transfer in Multistage Fans—Part II: Entire Component Simulation and Investigation

Part I of this paper validated the ability of the unsteady Reynolds-Averaged Navier-Stokes (RANS) solver PTURBO to accurately simulate distortion transfer and generation through selected blade rows of two multistage fans. In this part, unsteady RANS calculations were successfully applied to predict the 1/rev inlet total pressure distortion transfer in the entirety of two differently designed multistage fans. This paper demonstrates that high-fidelity computational fluid dynamics (CFD) can be used early in the design process for verification purposes before hardware is built and can be used to reduce the number of distortion tests, hence reducing engine development cost. The unsteady RANS code PTURBO demonstrated remarkable agreement with the data, accurately capturing both the magnitude and the profile of total pressure and total temperature measurements. Detailed analysis of the flow physics identified from the CFD results has led to a thorough understanding of the total temperature distortion generation and transfer mechanism, especially for the spatial phase difference of total pressure and total temperature profiles. The analysis illustrates that the static parameters are more revealing than their stagnation counterpart and that pressure and temperature rise are more revealing while the pressure and temperature ratio could be misleading. The last stage is effectively throttled by the inlet distortion even though the overall engine throttle remains unchanged. The total temperature distortion generally grows as flow passes through the fan stages.

Time Resolved Spectroscopic Characterization of a-C:H Deposition by Methane and Removal by Oxygen Inductively Coupled RF Plasma

The deposition of amorphous hydrogenated carbon thin films by inductively coupled radio frequency (IC RF) pure methane plasma and its subsequent removal by IC RF pure oxygen plasma have been studied within a cylindrical glass tube. Both processes were simultaneously monitored by optical emission spectroscopy, light transmission through thin film deposits, temperature of the discharge tube and total gas pressure measurements. Comparing the time evolution of all parameters, various stages of oxygen plasma cleaning process were established. The transitions between E-mode and H-mode of plasma induced by the presence of cleaning products impurities were observed and discussed.

Experimental Investigation of Intake Ground Vortices During Takeoff

A quantitative experimental investigation has been conducted to simulate intake ground vortex formation during aircraft takeoff under headwind conditions. The experiments were performed using a small-scale intake model in conjunction with a rolling ground plane in a low-speed wind tunnel. The Reynolds number was fixed at 1.26 x 10 6 based on the inner diameter and average intake velocity. Stereoscopic particle image velocimetry was used to measure the ground vortex velocity field, and in-duct total pressure measurements have been performed to assess the internal flow. Measurements were taken for an extensive range of configurations, including a static and simulated moving intake under a variety of headwind conditions. A moving intake was simulated in the wind tunnel by synchronizing the ground and tunnel wind velocities and using extensive suction to remove the approaching boundary layer. The results show that at high velocity ratios there are no substantial differences due to the moving ground plane. At low velocity ratios, the simulated moving intake results in a significantly different flowfield in which the ground vortex is weaker, steadier in space, and more symmetric relative to the static ground case. These results indicate the relative importance of the ground vortex vorticity sources and highlight the importance of including the effects of a moving ground when simulating an aircraft takeoff.

Serum ghrelin and the prediction of the development of impaired glucose regulation and Type 2 diabetes in middle-aged subjects

Ghrelin is a peptide hormone which has been shown to associate with obesity, hypertension and Type 2 diabetes (T2DM) in cross-sectional studies. To study whether total ghrelin levels have predictive value for the incidence of impaired glucose regulation (IGR) or T2DM. The subjects of this prospective follow-up study (no.=201) belonged to a population-based cohort collected in Northern Finland. Oral glucose tolerance tests (OGTT) and measurements of fasting serum total ghrelin, lipids, blood pressure and body mass index were performed at the beginning and at the end of the study. The mean follow-up time was 5.1 yr. The subjects had normal glucose tolerance (NGT) at the beginning of the study. T2DM developed in 6 (3%), impaired fasting glucose (IFG) in 6 (3%) and impaired glucose tolerance (IGT) in 35 (17.4%) subjects. The baseline ghrelin concentrations did not differ between the two studied groups: median fasting serum total ghrelin concentration was 733 pg/ml (25th-75th percentiles: 571-961 pg/ml) among those who maintained NGT, and 661 pg/ml (25th-75th percentiles: 527- 878 pg/ml) among those who developed IGR (IFG and/or IGT) or T2DM (p=0.421). The baseline ghrelin concentrations did not explain the changes in the 0-h or 2-h blood glucose concentrations in regression models. Our findings suggest that fasting serum total ghrelin levels measured at one time point might not have predictive value for the development of abnormalities in glucose tolerance.

Measurement techniques for in situ stresses around underground constructions in a deep clay formation

Disposal in deep underground geological formations is internationally recognized as the most viable option for the long-term management of high-level radioactive waste. In Belgium, the Boom clay formation is extensively studied in this context, in particular at the 225 m deep HADES Underground Research Facility in Mol. A cost-effective design of deep underground structures requires an accurate assessment of the in situ stresses; a good estimation of these stresses is also essential when interpreting in situ experiments regarding the hydro-mechanical behaviour of the host formation. Different measurement techniques are available to provide data on the stress evolution and other mechanical properties of the geological formation. The measurement can be direct (measurement of total pressure), or it can be an indirect technique, deriving the stress from related quantities such as strain (changes) in structural members. Most total stress measurements are performed through permanently installed sensors; also once-only measurements are performed through specific methods (e.g. pressuremeter). Direct measurement of the stress state is challenging due to the complex mechanical behaviour of the clay, and the fact that the sensor installation inevitably disturbs the original stress field. This paper describes ways to deal with these problems and presents the results obtained using different techniques at HADES.

Microramps Upstream of an Oblique-Shock/Boundary-Layer Interaction

To examine the potential of micro vortex generators for shock/boundary-layer interaction control, a detailed experimental and computational study in a supersonic boundary layer at M = 3.0 was undertaken. The experiments employed a flat-plate boundary layer with an impinging oblique shock with downstream total-pressure measurements. The moderate Reynolds number of 3800 allowed the computations to use monotone-integrated large eddy simulations. The monotone-integrated large eddy simulations predictions indicated that the shock changes the structure of the turbulent eddies and the primary vortices generated from the microramp. Furthermore, they generally reproduced the experimentally obtained mean velocity profiles, unlike similarly resolved Reynolds-averaged Navier-Stokes computations. The experiments and monotone-integrated large eddy simulations results indicate that the microramps, for which the height is h ≈ 0.5δ, can significantly reduce boundary-layer thickness and improve downstream boundary-layer health as measured by the incompressible shape function H. Regions directly behind the ramp centerline tended to have increased boundary-layer thickness, indicating the significant three-dimensionality of the flowfield. Compared with baseline sizes, smaller microramps yielded improved total-pressure recovery. Moving the smaller ramps closer to the shock interaction also reduced the displacement thickness and the separated area. This effect is attributed to decreased wave drag and the closer proximity of the vortex pairs to the wall.

Thrust Measurement of the Hybrid Electric Thruster TIHTUS by a Baffle Plate

A novel, two-stage, electric thruster is under development at Institut fiir Raumfahrtsysteme at Universitat Stuttgart. The first stage is an arcjet, and the second stage uses inductive heating of the arcjet plume. Because of the complex setup of the thruster, it is impossible to mount the two-stage system on a thrust stand without causing unwanted momentum onto the stand by the numerous supply lines. Thrust is, therefore, inferred using a baffle plate by means of a variation of power- and mass-flow ratios between the two stages. To interpret the results, the present paper also provides radially resolved measurement of total pressure from which thrust can be determined. It is shown that the thrust obtained from the two measurement methods are in good agreement with each other and range between 1.7 and 2.5 N for the respective operating conditions of the thruster. At constant total input power of 50 kW to the thruster, thrust decreases as power is diverted from the first stage to the second (inductive) stage at a constant mass-flow rate. However, when power is applied to both stages, thrust increases as the mass-flow rate is diverted to the second stage at a constant total mass-flow rate of 300 mg/s.

Experimental Investigation of Embedded Crossflow Fan for Airfoil Propulsion/Circulation Control

This experimental study examines the feasibility and effectiveness of using a crossflow fan embedded in an airfoil for simultaneous propulsion and circulation control. In an earlier computational fluid dynamics study, results indicated that a 34% thick airfoil equipped with a trailing-edge-embedded crossflow fan can operate stall-free up to 40 deg angle of attack and achieve lift coefficients upward of 6–7. This study seeks to experimentally verify the computational fluid dynamics results and provide further insight into the fan’s behavior in providing circulation control to the airfoil. Through flow-visualization techniques, surface static pressure, and wake total pressure measurements, the degree to which the fan can influence the flow is determined. Surface pressure distributions are studied for a wide range of fan operating points and angles of attack, leading ultimately to the calculation of the relative improvement in the airfoil’s lift-coefficient curves for the cases studied. Finally, the experimental setup and geometry were reproduced in the computational fluid dynamics package FLUENT for direct comparison with the acquired data. Good agreement between the experimental data and computational fluid dynamics results was found and both confirm the viability of the proposed propulsive/circulation-control airfoil concept.

Cross Determination of the Vapor Liquid Equilibrium of Formaldehyde Aqueous Solutions by Quadrupole Mass Spectrometry and Infrared Diode Laser Spectroscopy

Quantitative measurements of the partial vapor pressure of formaldehyde are performed above aqueous H2CO solutions of different concentrations (from 10(-5) to 0.3 molar fraction) using mass spectrometry and IR diode laser spectroscopy. Both experimental techniques allow direct probing of the gas phase concentration collected at equilibrium above the aqueous solutions. A correlation is observed between the polymerization processes occurring in the solution and the partial pressure of H2CO measured at vapor liquid equilibrium (VLE). A similar correlation is observed from total pressure measurements for which the equilibrium vapor pressure decreases as [VLE XH2CO]liq is increased. A saturation regime of the H2CO partial pressure is reached as the dissolved fraction of formaldehyde increases above approximately 0.15 mol frac. Henry's law constants are derived at 295K for the diluted solutions.

Oxygen plasma flow properties deduced from laser-induced fluorescence and probe measurements

Estimation of the local dissociation degree and the local mass-specific enthalpy of a pure oxygen plasma flow determined mainly from laser-induced fluorescence measurements are reported. Measurements have been conducted for several generator parameters in an inductively heated plasma wind tunnel. Additional probe measurements of total pressure together with the deduced translational temperature are used to estimate the local mass-specific enthalpy. For a reference condition, full dissociation has been measured. The measured translational temperature of atomic oxygen for this condition is T = 3500 K. Subsequently, the local mass-specific enthalpy has been derived using these local density and temperature measurements. For the reference condition the estimated value of h = 27 MJ/kg is in good agreement with the probe measurements and results from diode laser absorption spectroscopy.

Aerodynamic and Heat Flux Measurements in a Single-Stage Fully Cooled Turbine—Part II: Experimental Results

This paper presents measurements and the companion computational fluid dynamics (CFD) predictions for a fully cooled, high-work single-stage HP turbine operating in a short-duration blowdown rig. Part I of this paper (Haldeman, C. W., Mathison, R. M., Dunn, M. G., Southworth, S. A., Harral, J. W., and Heltland, G., 2008, ASME J. Turbomach., 130(2), p. 021015) presented the experimental approach, and Part II focuses on the results of the measurements and demonstrates how these results compare to predictions made using the Numeca FINE/Turbo CFD package. The measurements are presented in both time-averaged and time-accurate formats. The results include the heat transfer at multiple spans on the vane, blade, and rotor shroud as well as flow path measurements of total temperature and total pressure. Surface pressure measurements are available on the vane at midspan, and on the blade at 50% and 90% spans as well as the rotor shroud. In addition, temperature and pressure measurements obtained inside the coolant cavities of both the vanes and blades are presented. Time-averaged values for the surface pressure on the vane and blade are compared to steady CFD predictions. Additional comparisons will be made between the heat transfer on cooled blades and uncooled blades with identical surface geometry. This, along with measurements of adiabatic wall temperature, will provide a basis for analyzing the effectiveness of the film cooling scheme at a number of locations.

Investigation of ionization gauges with carbon nanotube (CNT) field-emitter cathodes

The use of field emitter arrays (FEA) in XHV partial or total pressure measurement so far did not pass the laboratory stage. The reasons are costly manufacturing in comparison to thermionic cathodes and the susceptibility of microtip cathodes to degradation at higher pressures. Today, electron sources based on carbon nanotube (CNT) field emitters are a true alternative to FEAs with microtip cathodes. CNTs with a diameter below 20 nm possess the best field emission properties and are very robust mechanically, which justifies their use in field emission cathodes for vacuum sensors. Starting from basic research to characterize field emission properties, long term stability and stress of CNT field emitters, we present investigations of CNT field emitter electron sources of different provenance in an ionization gauge. We used emission currents of 1 mA and an upper pressure limit of 1 Pa. We compare the results with those of Dong and discuss advantages to a Bayard-Alpert gauge (BAG) with thermionic cathodes. Focus of the presentation is on the investigation of the CNT cathode for applications in ionization gauges.

Synthesis of the titanium phosphide telluride Ti 2PTe 2: A thermochemical approach

The phosphide telluride Ti 2PTe 2 can be synthesised from the elements or from oxides in a thermite type reaction. Both ways have been optimised by consideration of the thermodynamic behaviour of the compound. Hence, the investigation of phase equilibria in the ternary system Ti/P/Te and of the thermal decomposition of Ti 2PTe 2 was necessary. This investigation was performed by using different experimental approaches as total pressure measurements, thermal analysis and mass spectrometry. The results were supported and further analysed by thermodynamic modelling of the ternary system. It was shown that Ti 2PTe 2(s) decomposes to Ti 2P (s) and Te 2(g) in six consecutive steps. The growth of single crystals of Ti 2PTe 2 is thermodynamically described as a chemical vapour transport with TiCl 4(g) acting as the transport agent.