Transient Measurement Techniques Research Articles

Mechanical and Thermal Behavior of Fibrous Carbon Materials.

The ability of various commercial fibrous carbon materials to withstand stress and conduct heat has been evaluated through experimental and analytical studies. The combined effects of different micro/macro-structural characteristics were discussed and compared. Large differences in mechanical behavior were observed between the different groups or subgroups of fibrous materials, due to the different types of fibers and the mechanical and/or chemical bonds between them. The application of the Mooney–Rivlin model made it possible to determine the elastic modulus of soft felts, with a few exceptions, which were studied in-depth. The possible use of two different mechanical test methods allowed a comparison of the results in terms of elastic modulus obtained under different deformation regimes. The effective thermal conductivity of the same fibrous materials was also studied and found to be much lower than that of a single carbon fiber due to the high porosity, and varied with the bulk density and the fiber organization involving more or less thermal contact resistances. The thermal conductivity of most materials is highly anisotropic, with higher values in the direction of preferential fiber orientation. Finally, the combination of compression and transient thermal conductivity measurement techniques allowed the heat conduction properties of the commercial fibrous carbons to be investigated experimentally when compressed. It was observed that thermal conductivity is strongly affected under compression, especially perpendicular to the main fiber orientation.

Experimental Study on Heat Transfer of Leading Edge Film-Cooling With Counter-Inclined Cylindrical and Laid-Back Holes

AbstractThe heat transfer coefficient of counterinclined film holes fed by different intake structures on the turbine vane leading edge (LE) model is experimentally investigated in this paper. A semicylinder model is adopted to model the vane leading edge, which is arranged with one single row of film holes per side, which are located from the stagnation at a 15-deg angle. The four leading edge models, which are the combinations of the hole-shapes (cylindrical hole and laid-back hole) and intake structures (plenum and impingement), are tested at four blowing ratios M. The contours of the heat transfer coefficient, which are characterized by the Frössling number Fr, since it includes the Reynold number effect, are acquired by the transient measurement technique based on double thermochromic liquid-crystals (LCs). The lateral-averaged Fr of the nonfilm-cooled model is provided by using the same experimental platform with an identical main-flow condition. It is then compared with the published data, which indicates the reliability of the present transient measurement techniques. The results illustrate that a core region with a higher heat transfer appears in the hole-exit downstream, and its distribution is slightly skewed to the inclination direction of the film holes. The shape of the high heat transfer region gradually inclines in the spanwise direction as M increases. The heat transfer in the region where the jet core flows through is relatively low, while the jet edge region is relatively high. The effect of impingement leads to the outflow of each hole becoming increasingly uniform, which can reduce the difference in the heat transfer between the region where the jet core flows through and the jet edge. The heat transfer strength may increase due to the intense turbulence caused by the introduction of the impingement. Compared with the cylindrical hole, the laid-back hole has a spanwise expansion feature, which makes the shape of the high heat transfer region wider in the spanwise direction and increases the heat transfer level. Additionally, the magnitude of the enhancement increases with an increasing M.

A highly reliable physics-based SPICE compact model of IGZO memristor considering the dependence on electrode metals and deposition sequence

In this work, a SPICE compact model of indium-gallium-zinc oxide (IGZO) memristor in consideration of IGZO and electrode materials having non-quasi-statically updated Schottky barrier heights has been developed. In order for compact modeling of an analog memristor with higher accuracy, understanding of its switching characteristics and conduction behaviors needs to be preceded. It has been empirically revealed that they are dependent on metal species of the electrodes and processing approach. The switching characteristics are more weightedly determined by the interface between the switching layer and the metal with lower workfunction out of two electrode metals and interface status has been controlled by an Ar bombardment in this work. In order for identifying the conduction mechanism, a series of device simulations have been performed and the internal electric field distribution over the device structure has been closely investigated. It has been shown that the conduction behaviors are mainly determined by the thermionic emission taking place between Pd electrode and IGZO switching layer. For preparing the model parameters, along with the experimental results, transient measurement techniques have been cultivated at the same time, which has made possible to tell the difference between sets of model parameters obtained by theory and the techniques. In consequence, a highly reliable physics-based modeling for IGZO memristor has been developed through identification of switching and conduction mechanisms and extraction of the model parameters with the simultaneous help of Verilog-A equation build-up, which has demonstrated a plausible agreement with the measurement results.

RETRACTED ARTICLE: Data transmission and real-time information acquisition based on fine-grained algorithm and wireless network

With the advent of the 5G era, wireless network data transmission and real-time information acquisition face certain technical challenges. Simultaneously, how to ensure fast and safe information transmission becomes the research topic of the information age. The improvement of this research is based on the traditional fine-grained algorithm, and this study uses spatial constraints and evaluation scores to obtain the bounding box positions of objects and objects. Simultaneously, Part-based R-CNN is used to extract convolution features for each filtered bounding box and join the local features to form a feature representation vector. In addition, the research is based on the application of high-resolution acquisition of information entropy, abnormal signal detection and transient signal measurement methods and techniques in typical time domain test instruments, that is, digital oscilloscope, and this study is experimentally verified. The research indicates that the method proposed in this paper is scientific and can provide theoretical reference for subsequent related research.

Investigation of Various Pressure Transient Techniques on Permeability Measurement of Unconventional Gas Reservoirs

An evaluation of fluid flow behavior in porous media is necessary considering its widespread applications in geo-engineering projects, such as reservoir productivity and hydraulic fracturing. In order to improve the understanding of gas flow characteristics in porous media, particularly permeability estimation of unconventional gas reservoirs, various pressure transient measurement techniques were numerically evaluated in this study based on the established mathematical models, closely representing each experimental design of these transient techniques. Given that both compressive storage and sorption capacity of unconventional reservoirs vary at different pressures, the practicability of the conventional pulse decay method (PDM), initially adopted by Brace et al. (J Geophys Res 73(6):2225–2236, 1968), was examined. The results showed that compressive storage and sorption effect are the limiting factors in the application of the conventional PDM for permeability measurement of sorptive rocks. Meanwhile, the degree to which these factors affect the accuracy of pressure response and permeability were investigated quantitatively. It was found that pulse size, rock porosity, gas compressibility and reservoir volumes are the main parameters influencing compressive storage and sorption effect, and thus the application of the conventional PDM. A comprehensive numerical investigation was also conducted on Metwally and Sondergeld’s technique, a modified PDM, initially proposed for measuring low permeabilities of gas sands and shales. Considering limitations in the derived permeabilities of sorptive rocks when using the conventional PDM techniques and Metwally and Sondergeld’s technique, an optimized PDM was then proposed by creating dual-pressure pulses to avoid the pressure disturbance due to compressive storage, and ad-/de- sorption during the course of measurement. To verify the feasibility of the optimized PDM, a suite of numerical investigation was carried out for various PDM techniques, and the pressure responses were also compared with calculated data obtained from the mathematical model and experimental results. Both numerically calculated and experimental results exhibit the practicality of the optimized PDM, providing a fast, accurate and reliable approach for permeability measurement of sorptive rocks.

Characterization of nickel catalysts with transient methods

The Ni surface area is a key factor in catalytic performance of supported Ni catalysts employed in heterogeneously catalyzed reactions. For its characterization, transient measurement techniques are powerful but need a proper experimental design and a high level of accuracy. In this study, several transient methods, namely temperature programmed desorption of H2 (H2-TPD), pulsed H2 chemisorption and N2O chemisorption, were applied and evaluated for the characterization of Ni catalysts. Results were compared with those from static H2 chemisorption. Ni powder, as well as NiAlOx and Ni/γ-Al2O3 with varying Ni loadings, synthesized via precipitation and incipient wetness impregnation, respectively, were used as model catalysts. H2-TPD within the temperature range from 84 to 753K is able to completely describe the interaction of H2 with supported Ni. However, a quantitative analysis of the specific Ni surface area based on H2-TPD is difficult whereas pulsed H2 chemisorption leads to comparable results as obtained from static measurements. Adsorption and pre-treatment conditions have a strong impact on the desorption spectra. Reversible morphologic changes of the Ni surface were revealed by H2-TPD when changing the gas atmosphere during pre‐treatment. N2O chemisorption occurs in three steps including fast oxygen uptake, growth of the oxide layer and subsequent layer thickening due to subsurface and bulk oxidation. A separation of surface and subsurface/bulk oxidation of NiAlOx and Ni/γ-Al2O3, both of which are readily oxidized even under mild conditions, is only achievable at temperatures between 190 and 195K. In this temperature range, the ratio of adsorbed oxygen atoms, O, and the number of Ni surface atoms, NiS, (O/NiS) is 0.38±0.07, which can be applied for specific Ni surface area determination. The experimental mode of N2O chemisorption (flow or titration mode) does not influence the extent of subsurface oxidation. The separation of surface and subsurface/bulk oxidation is more feasible in the case of Ni powder. Here, a suitable temperature for Ni surface area determination lies within 265 and 285K with an O/NiS ratio of 0.96±0.05.

Structure-Independent Proton Transport in Cerium(III) Phosphate Nanowires.

Understanding of water-related electrical conduction is of utmost importance in applications that utilize solid-state proton conductors. However, in spite of the vast amount of theoretical and experimental work published in the literature, thus far its mechanism remained unsolved. In this study, the structure-related ambient temperature electrical conduction of one-dimensional hydrophilic nanostructures was investigated. Cerium phosphate nanowires with monoclinic and hexagonal crystal structures were synthesized via the hydrothermal and ambient temperature precipitation routes, and their structural and surface properties were examined by using high-resolution transmission electron microscopy, X-ray diffractometry, nitrogen and water sorption, temperature-programmed ammonia desorption, and potentiometric titration techniques. The relative humidity (RH)-dependent charge-transport processes of hexagonal and monoclinic nanowires were investigated by means of impedance spectroscopy and transient ionic current measurement techniques to gain insight into their atomistic level mechanism. Although considerable differences in RH-dependent conductivity were first found, the distinct characteristics collapsed into a master curve when specific surface area and acidity were taken into account, implying structure-independent proton conduction mechanism in both types of nanowires.

Thermal conductivity measurements using 1ω and 3ω methods revisited for voltage-driven setups

1ω and 3ω methods are widely established transient measurement techniques for the characterization of thermal transport in bulk-materials, thin films, and 1D nano-objects. These methods are based on resistance oscillations of a heater caused by Joule-heating from a sinusoidal current at frequency 1ω which lead to changes in the 1ω voltage and produce a voltage component at 3ω. Although the usual formalism for analyzing the measurement data assumes an ideal current source, voltage-driven measurement setups are employed in many cases. In this context, we find that there has been lack of clarity if a correction generally has to be considered when analyzing the measurement data from voltage driven setups. In this work, Fourier-analysis is employed to show that a correction is not required for 1ω methods and for 3ω measurements that use common-mode-subtraction. Experimental results are presented for a line heater on a fused silica substrate with known thermal properties, and for an individual nickel wire with diameter of 150 nm.

A study on the 65‐35 brass corrosion inhibitor

AbstractThe influence of new inhibitor namely 1,3‐bis‐diethylamino‐propan‐2‐ol (DEAP) on the dezincification corrosion of 65‐35 brass in simulated atmospheric water was studied by potentiostatic current transient measurement, solution analysis and surface evaluation techniques. Potentiostatic current transient results showed that the investigated inhibitor can effectively inhibit the chemical dissolution of brass in simulated atmospheric water. Solution analysis revealed that the weigh loss of brass electrode remarkably decreased in the presence of DEAP, changing from 7.375 × 10−3 mg (blank) to 9.567 × 10−4 mg (10−2 M). The scanning electron microscope (SEM) and electron probe microanalyzer (EPMA) measurements showed that DEAP may better adsorb to zinc component than to copper component, inhibiting the dezincification of brass in solution by a mixed complex film of Zn(II)‐DEAP and Cu(I)‐DEAP. The nature of the inhibited film was analyzed by an X‐ray photoelectron spectroscope (XPS) analyzer.

Water hammer and condensation hammer scenarios in power plants using new measurement system

This contribution presents experimental results of the investigation of water hammer and cavitational hammer at the pipeline test facility at Fraunhofer UMSICHT in the context of the EURATOM project WAHALoads. The main objective of this running project is the prediction of the strain on equipment and support structures caused by water and condensation hammer. Thus, some typical scenarios of power plants are conducted. For this purpose the test facility at Fraunhofer UMSICHT (PPP) was modified in order to simulate a piping system and associated supports that are typical for a power plant. For a better understanding of thermohydraulic processes, new wire mesh sensors with thermocouples for the measurement of condensation heat transfer and other innovative transient measurement techniques were implemented into PPP additionally.

Transient Method for Convective Heat Transfer Measurement With Lateral Conduction—Part II: Application to an Isolated Spherical Roughness Element

The effect of lateral conduction on convective heat transfer measurements using a transient infrared technique over an isolated spherical roughness element (bump) is evaluated. Comparisons are made between a full 3D finite-volume analysis and a simpler 1D transient conduction model. The surface temperature history was measured with a high resolution infrared camera during an impulsively started hot-gas flow at a flow Reynolds number of 860,000. The boundary layer was turbulent with the bump heights equivalent to 0.75, 1.5, and 3 times the boundary layer momentum thickness. When considering transient conduction effects only in the bump wake, the 1D approximate method underestimates the actual Stanton number estimated with the 3D model. This discrepancy is only 10% for a 75% change in St number occurring over a surface distance of 10 mm (the half-width of the wake). When the actual bump topology is accounted for in estimating the Stanton number on the bump itself with the 3D analysis technique, the increased surface area of the finite-volume cells on the protruding bump actually decreases the predicted value of St locally. The net result is that the two effects can cancel each other, and in some cases the 1D approximate technique can provide a reasonably accurate estimate of the surface heat transfer without the added complexity of the 3D finite-volume method. For the case of the largest bump tested, with maximum surface angularity exceeding 60 deg, the correction for 3D topology yields a 1D St estimate that is within 20–30% of the 3D estimate over much of the bump surface. These observed effects are valid for transient measurement techniques while the opposite is true for steady-state measurement techniques.

Picosecond transient absorption measurement of anthrylphenoxide anions in solution phase

By using picosecond transient absorption and fluorescence spectral measurement techniques, we have investigated fluorescence state of 3-(9-anthryl)phenoxide and 3-(9-anthryl)-5-(2,2-dimethyl-1-oxopropyl)phenoxide anions in 1,4-dioxane and acetonitrile. The fluorescence spectra of these compounds are broad and structureless and show strong solvatochromic shift. Since the S n ← S 1 absorption spectra of the anions are similar to the absorption band of the anthracene radical anion, the negative charge of the anions in the S 1 state is essentially localized in the anthracene moiety. On the contrary, in the T 1 state the anthracene moiety is neutral and the negative charge may be localized in the phenoxy moiety.

The WAHA Code : a numerical tool for water hammer in two-phase flow – some simulations of experiments

The WAHA computer code has been developed during the WAHALoads project in the frame of the 5th European Program. The main purpose of the WAHA code is to predict various mechanisms of single- and two-phase water hammer transients in piping systems. The WAHA code can simulate thermal-hydraulic transients with one-dimensional six-equation two-fluid model approximations and calculate the hydraulic forces on the piping system due to water hammers in two-phase flow. In the first part of the present paper, the main features of the WAHA code and its capabilities are presented : basic equations, specific closures laws, numerical scheme, possible boundary conditions, some basic results of water hammers induced by a rapid valve closure. In the second part of the paper, a description of the UMSICHT test facility PPP which has been used for water hammer tests inducing bubble condensation is given. The installation has been equipped with a new measurement technology including new wire mesh sensors with thermocouples for the measurement of condensation heat transfer and other innovative transient measurement techniques. From the UMSICHT data bank,some basic data have been chosen as reference case for validating the WAHA code. The third part deals with the simulation of several test cases using the WAHA code : Edwards pipe - Discharge of a hot liquid from a horizontal pipe. PPP water hammer tests – Depressurisation inducing cavitation water hammer initiated by a fast valve closure. Super Moby Dick experiment – Critical two-phase flow through a long nozzle. The results of these simulations are systematically compared with the experimental data, when available. It is concluded that the WAHA code has the abilitity to correctly predict various mechanisms of transients flows occurring in piping systems.

Compact laser flash photolysis techniques compatible with ultrafast pump-probe setups

Two new transient absorption measurement techniques are described which use commercially available pulsed laser diodes or high-power light-emitting diodes (LEDs) as monitoring beam. The semiconductor devices substitute the probe in a kilohertz-repetition-rate ultrafast pump-probe setup. A fully functional and highly compact laser flash photolysis system reaching the nanosecond to millisecond time scale is thereby added to a state-of-the-art femtosecond system. The sample is excited with UV-Vis tunable femtosecond pulses, and for the electronically synchronized probing light either subnanosecond pulsed laser diodes for selected wavelengths or LEDs covering the visible to near infrared and UV regions are used. The applicability and reliability of the devices are demonstrated for various probe wavelengths in the visible by the investigation of excited-state decay or photoinduced bimolecular reactions. The time resolution is found to be 400 ps for the pulsed laser diodes and a few nanoseconds for the LEDs. This provides overlap to the accessible time range of the ultrafast pump-probe experiment. In this way full reaction cycles of photo-physical or -chemical processes can be monitored with identical excitation conditions.

Photoionization and Ion Pair Formation of N,N-Diethyl-p-phenylenediamine in Various Polar Solvents

Abstract By using transient absorption and photoconductivity measurement techniques, we have investigated the photoionization process of N,N-diethyl-p-phenylenediamine in various polar solvents. Significant excitation wavelength and excitation intensity effects were observed in alcoholic solvents. The slowly rising component of the photoconductivity in hundreds of nanoseconds or longer time scale is ascribed to the dissociation of the monophotonically produced ion pairs. In addition, a photoconductivity signal that has almost the same duration as the excitation laser pulse and is due to the geminate pair formed via the two-photon ionization is clearly observed with the 248-nm excitation. On the other hand, the biphotonic process was negligible with the 351-nm excitation in ethanol and 1-propanol. The monophotonically formed long-lived ion pair did not contribute to the conductivity. The long lifetime of the ion pair indicates that not only the Coulombic interaction but also the exciplex-like specific interaction is important.

Comparative study on electrical properties of atomic layer deposited high-permittivity materials on silicon substrates

Deep level transient spectroscopy, capacitance–voltage and conductance transient measurement techniques have been applied in order to evaluate the electrical quality of thin high-permittivity oxide layers on silicon. The oxides studied included HfO2 film grown from two different oxygen-free metal precursors and Ta2O5 and Nb2O5 nanolaminates. The interface trap densities correlated to the oxide growth chemistry and semiconductor substrate treatment. No gap state densities induced by structural disorder were measured in the films grown on chemical SiO2. Trap densities were also clearly lower in HfO2 films compared to Ta2O5–Nb2O5.

A fractal model for predicting permeability around perforation tunnels using size distribution of fragmented grains

A methodology to predict the permeability distribution around the perforation tunnels is presented. The resulting equation describes the permeability by modeling the distribution of grain fragments and by fractal concepts. The equation allows the calculation of permeability from the particle size data obtained from the rock material surrounding the tunnel. The fractal model constructs a flow equation for an incompletely fragmented porous media by describing the geometry and size of the pores using the grain size distribution and setting up a hierarchical scaling concept for fragmentation to eliminate the extra porosity of a completely fragmented fractal porous medium. Predicted permeabilities (as compared to measured ones for the 2.4- and 5.1-MPa underbalance shots) using the developed equation showed that the predictions are successful at almost all radial positions around the tunnel. Relative errors between predictions and measurements increase towards the tunnel wall. This may be attributed to the unfavorable particle shapes, which are assumed to be spherical in the model, and aspect ratios of fragmented grains. It also was observed that predictions for higher underbalance test are better due to better surge flow cleaning, which eliminates most of the small particles affecting the calculations due to their unfavorable shapes. The developed equation provides an easier and cheaper way of mapping the permeability distribution around the perforation tunnels compared to the viscous fluid injection and pressure transient measurement techniques. The proposed technique can be valuable to obtain permeability distribution data for near-wellbore modeling of specific formations perforated at laboratory conditions and also for the assessment of the permeability damage created by different charge and gun designs.

Influence of Surface Roughness on Heat Transfer and Effectiveness for a Fully Film Cooled Nozzle Guide Vane Measured by Wide Band Liquid Crystals and Direct Heat Flux Gages

The influence of surface roughness on heat transfer coefficient and cooling effectiveness for a fully film cooled three-dimensional nozzle guide vane (NGV) has been measured in a transonic annular cascade using wide band liquid crystal and direct heat flux gages (DHFGs). The liquid crystal methods were used for rough surface measurements and the DHFGs were used for the smooth surfaces. The measurements have been made at engine representative Mach and Reynolds numbers and inlet free-stream turbulence intensity. The aerodynamic and thermodynamic characteristics of the coolant flow have been modeled to represent engine conditions by using a heavy “foreign gas” (30.2 percent SF6 and 69.8 percent Ar by weight). Two cooling geometries (cylindrical and fan-shaped holes) have been tested. The strategies of obtaining accurate heat transfer data using a variety of transient heat transfer measurement techniques under the extreme conditions of transonic flow and high heat transfer coefficient are presented. The surfaces of interest are coated with wide-band thermochromic liquid crystals, which cover the range of NGV surface temperature variation encountered in the test. The liquid crystal has a natural peak-to-peak roughness height of 25 μm creating a transitionally rough surface on the NGV. The time variation of color is processed to give distributions of both heat transfer coefficient and film cooling effectiveness over the NGV surface. The NGV was first instrumented with the DHFGs and smooth surface tests preformed. Subsequently the surface was coated with liquid crystals for the rough surface tests. The DHFGs were then employed as the means of calibrating the liquid crystal layer. The roughness of 25 μm, which is the typical order of roughness for the in-service turbine blades and vanes, increases the heat transfer coefficient by up to 50 percent over the smooth surface level. The film cooling effectiveness is influenced less by the roughness. [S0889-504X(00)00804-7]

Annealing of the deep recombination center in GaInP/AlGaInP quantum wells grown by solid-source molecular beam epitaxy

Time resolved photoluminescence and deep level transient spectroscopy have been used to monitor the effect of rapid thermal annealing on bulk GaInP and GaInP/AlGaInP quantum wells grown by solid source molecular beam epitaxy similar to those used in 650 nm range lasers. Following rapid thermal annealing at temperatures up to 875 °C, reductions in the concentration of several deep level traps are observed. Correlation of these data with photoluminescent intensity and lifetime measurements indicate that the defect labeled N3, 0.83 eV below the conduction band, is the dominant recombination center. The combination of these two transient spectroscopy measurement techniques is therefore not only able to measure the change in deep level concentration, but also to correlate this change with improved carrier lifetimes and, ultimately, reduced threshold current densities in quantum well lasers. There is also evidence to suggest that this same defect, possibly a phosphorous vacancy or a related complex, plays an important role in other GaInP based devices.

Energy gap dependence of the S 2→S 1 internal conversion of α, ω-diphenylpolyenes ( N=3–8) in solution phase

By using femtosecond and picosecond transient absorption measurement techniques, we have investigated the dynamic behavior of the S 2 state of all-trans- α, ω-diphenylpolyenes, from diphenylhexatriene ( N=3) to diphenylhexadecaoctaene ( N=8), in solution. The S 2 state lifetimes, which were determined from the decay of the S n ←S 2 absorption band around 700 nm, were similar for N=3–7. The observed small energy gap dependence of the S 2→S 1 internal conversion rate can be an indication of the large difference in the molecular geometry of the S 1 and S 2 states.