Special Experimental Method Research Articles

Analysis of Thermo-Acoustic Instabilities Induced by Hydrogen Swirling Flames

Abstract A considerable research effort has been concerned combustion dynamics of systems fed with hydrocarbon fuels. The case of pure hydrogen/air flames deserves to be specifically considered because hydrogen is highly reactive, has a tendency to develop thermo-diffusive instabilities, is envisaged in many future applications, most notably in gas turbines, and is less well documented. Thermo-acoustic instabilities of pure hydrogen flames are here investigated in a configuration where hydrogen is injected in-crossflow in a swirling stream of air. The study is focused on operating conditions that lead to oscillatory regimes. Using Abel-transformed phase-averaged images of OH* emission and visible light emission in burnt gases, it is shown that the OH* signal evolves approximately in phase with the heat release rate. This signal is then used to determine the local Rayleigh source term that feeds acoustic energy in the oscillation. The contributions of this term are examined using a space–time analysis based on an integration of the source term in the transverse direction. This procedure allows a detailed analysis of the processes that contribute to the acoustic energy in the system, showing, in particular, that a strong positive addition of acoustic energy results from a roll-up of the flame tip and from the quick cyclic back propagation of the flame to the injector tip. A global integration of the Rayleigh source term is then used together with a volume-integrated acoustic energy to estimate the growth rate associated with these driving processes and estimate the damping rate. A special experimental method is then exploited to determine the effective growth rate of the instability. The system allowing a sweep in frequency, self-sustained instabilities obtained at different frequencies are used to extract the specific instability frequency band of the burner. Finally, the flame is externally forced in order to measure its flame-describing function.

Theoretical and experimental study on the rheological properties of WIS grout and the dispersion and sealing mechanism

Recently a new grout material called water inflow sealing (WIS) was invented for sealing water inflow in tunneling and underground constructions. In this study, a special experimental method called intubated counter grouting (ICG) was proposed to investigate the influence of water dispersion on the rheological properties of the grout during the grouting process, and to testify the sealing performance of the grout, such as instant gelling ability (IGA) and anti-dispersion ability (ADA). In the experiment, dispersion was restricted in the downstream of the channel with a high turbulence intensity. The influences of ADA and IGA were therefore decoupled and evaluated separately. Experimental results revealed two distinctive sealing mechanisms of WIS. For a low initial velocity of water, WIS turned the shear flow of water into an overall movement of a plug by absorbing water into the particles. For a high initial velocity and the situation that the particles reached the outlet before sufficiently expanding, WIS modified the rheology of the water in the channel and reduced its velocity till the static state. The distinctive feature of WIS brings a reformation on the sealing mechanism and provides an effective way to control water inflow with high pressure and velocity.

Characterization of new primary air kerma standards for dosimetry in Co-60, Cs-137 and Ir-192 gamma ray sources

Introduction. To be better suited for measurements at air kerma rates which are common for the calibration of detectors for dosimetry in brachytherapy and radiation protection, two graphite-wall, air-filled cavity ionization chambers (PS-10 and PS-50 built by PTW of Freiburg, Germany) were characterized for use as primary standards at the Physikalisch-Technische Bundesanstalt (PTB) for 60Co, 137Cs and 192Ir gamma ray sources. Methods. Applying experimental or Monte Carlo methods, corrections were determined for wall effects, stem scattering effects, point-source non-uniformity, saturation effects, and deviations from Spencer-Attix cavity theory. The geometrical cavity volume of the ionization chambers was determined by a special experimental method. Non-charge-collecting parts of the volume were calculated by finite-element simulations. In addition, mass electronic stopping powers and mass-energy absorption coefficients were reevaluated in close agreement with ICRU 90. To compare the results to an already established air kerma standard, measurements of air kerma rates were taken for gamma rays from all three sources. Results. In contrast to the standards currently in use, the newly characterized ionization chambers show significant wall effects up to 4.17% (192Ir). For the PS-10 ionization chamber, the geometric volume differs by 0.42% from the charge collecting volume. For the ^192Ir source, Spencer-Attix corrections were applied exceeding 0.30% for both ionization chambers. Applying the derived corrections factors, air kerma rates measured with the two ionization chambers at the three sources did not differ by more than 0.13%. Comparing the results to an already established air kerma standard, deviations ranged up to 0.61%. The uncertainty budget for the determination of air kerma rates resulted in a relative combined standard uncertainty of 0.35%. Conclusion. Both ionization chambers can be used as primary air kerma standards for 60Co, 137Cs and 192Ir gamma ray sources using the values of corresponding physical quantities and correction factors derived in this work.

Studying the Mutual Influence of a Set of Strikers during Simultaneous High-Velocity Entry into Water

High-velocity motion of a set of supercavitating kinetic strikers during their simultaneous entry into water has been experimentally studied. A special experimental method of launching supercavitating kinetic strikers and studying their high-velocity motion under hydroballistic test setup conditions has been developed. Experimental data on the motion of two identical supercavitating strikers in the initial stage of trajectory at velocities about 1100 m/s have been obtained, which demonstrate the possibility of stable propagation of a set of such strikers in water until reaching an underwater target.

Experimental Study on the Brittle-Ductile Response of a Heterogeneous Soft Coal Rock Mass under Multifactor Coupling

After a gas drainage event causes different degrees of initial porosity in the coal seam, the heterogeneity of the coal mass becomes much more obvious. In this paper, soft coal testing samples with different degrees of heterogeneity were prepared first by a new special experimental research method using hydrogen peroxide in an alkaline medium to generate oxygen. Then, a series of mechanical tests on the soft coal mass samples were carried out under multiple factor coupling conditions of different heterogeneities and confining pressures. The results show that with a low strength, the ductility failure characteristic and a kind of rheology similar to that for soft rock flow were reflected for the soft coal; i.e., the stress-strain curve of the coal mass had no apparent peak strain and residual strength. An interesting phenomenon was found in the test process: there was an upwardly convex critical phase, called the brittle-ductile failure transition critical phase, for the heterogeneous soft coal mass between the initial elastic compression phase and the ductile failure transition phase in the stress-strain curve of the coal mass. An evolution of the brittle-ductile modulus coefficient of the soft coal was developed to analyze the effect of the internal factor (degree of heterogeneity) and external factors (confining pressure) on the transition state of the brittle-ductile failure of soft coal. Further analysis shows that the internal factor (heterogeneity) was also one of the essential factors causing the brittle-ductile transition of soft coal.

Investigation of performance and cutting properties of carbide tool with nanostructured multilayer Zr-ZrN-(Zr0.5,Cr0.3,Al0.2)N coating

The study involved the investigation of the properties of the cutting tool with nanostructured multilayer Zr-ZrN-(Zr0.50,Cr0.30,Al0.20) N coating, deposited using the technology of filtered cathodic vacuum arc deposition (FCVAD). The scratch-test method was applied to study the coating failure pattern. The microstructure and nanostructure of the samples were analyzed with a high-resolution transmission electron microscope (TEM) and a scanning electron microscope (SEM). The X-ray diffraction analysis (XRD) was performed with a diffractometer with CuKα radiation. A special experimental method was used to determine the adhesion (molecular) component of the coefficient of friction (COF) fM within a range of temperatures of 450–950 °C. The results of the cutting tests in turning steel AISI 1045 demonstrated a significantly higher wear resistance of the tool with the coating under study compared to the tool with the reference ZrN monolayer coating (the tool life parameter was two times higher). The study also involved the investigation of the failure and wear pattern of a tool with the coating under study in turning and the investigation of the diffusion and oxidation processes. It was found that the coating under study was characterized by the combination of high hardness and wear resistance with good plasticity and resistance to brittle fracture. This combination of the properties makes it possible to effectively apply the coating to improve the tool life of a cutting tool.

The Stress Triaxiality Effect under Large Plastic Deformation of a Polybutylene Terephthalate (PBT)

In this work, we focus on a new generation of polymer named Polybutylene terephthalate (PBT). In order to analyse and determine true behaviour of this polymer, a special experimental method was used. Hence, the true stress/strain responses are investigated under a large plastic deformation in different stress triaxiality frameworks with a particular attention on the volumetric strain evolution, with their decomposition to an elastic volumetric strain, plastic volumetric strain and the pure shear. Moreover, the effect of stress triaxiality on the plastic instability and the fracture strain is also examined. With the plastic instability analysis, it was found that plastic strain hardening increases gradually with the triaxiality. Finally, in order to evaluate the damage of this polymer, a theoretical damage formula is proposed.

Novel Carbon Porous Material with Nanostructural for Separation of Arsenic(III) from Water with Highest Adsorption Capacity

Arsenic is a heavy metal and exists in an oxidation state of -3, 0, +3 or +5 which the As (III) is more toxic than other. Due to the extreme toxicity of As(III) in drinking water many research was done to find natural and economical adsorber for removing it from the water. Porous carbonaceous nanostructural materials have been widely used in the adsorption of contaminated water, gas storage, separation, and purification. By special experimental method were produced in Beshel Activated Carbon Industry (BACI) a new carbon adsorber material (BACI-2017) with nano pores, for removal of As (III) in contaminated water. Because of existing an appropriate pores and surface area, the new adsorber has shown a high tendency for adsorption of Arsenic (III) from water. Experiment: Two different particle sizes, mesh 4x8 and mesh 100 and greater than 100 mesh, were used. The separation of As(III) were done with 0.5 gram of BACI-2017 with mesh 4x8 and 0.1 gram of BACI-2017 with 100 mesh and greater than100 mesh and six different concentrations of As(III) solution, 5, 10, 20, 30, 50, 100 and 100, 200, 300, 400, 500, 1000 ppm respectively. In all experiments the pH was about 8.5. The results showed that the maximum adsorption capacity of As(III) calculated from Langmuir isotherm was found 41.48 mg/g for 0.5 gram of GRG-2017 with mesh 4x8 and 0.1 gram of BACI-2017 calculated from Freundlich isotherm was 455 mg/g for 100 mesh and greater than 100 mesh. The contact time in all experiments was 15 minutes. The study showed that the adsorption capacity of arsenic is strongly depending on the particle size of adsorber. The results: The BACI-2017 nanopores adsorber for removal of As (III) from aqueous solution shown that the As (III) can be separated from water with a high capacity of 455 mg/g or 455 g of As (III) per kg of adsorber BACI-2017. This is a world record with highest adsorption capacity in comparison with other studies till now, March 2017.

Ferro-Antiferromagnetic Coupling and Enhancement of Magnetoresistance in La<sub>0.67</sub>Ca<sub>0.33</sub>MnO<sub>3</sub>/LaMnO<sub>3</sub> Composites

The samples with the nominal composition of (1-x)La0.67Ca0.33MnO3/xLaMnO3 with x=0.00, 0.05, 0.15 and 0.25 were fabricated using a special experimental method. The electrical transport behaviour and magnetoresistance (MR) were studied for the composites in magnetic fields H=0.3T, 3T. Experimental results show that with the increasing LaMnO3 doping level, the metal–insulator（M-I） transition temperature TP shifts to lower temperature and the resistivity increases sharply in zero magnetic field. Meanwhile, a significant enhancement in MR is observed for the composites especially in the low temperature range（below TP）. Specially, the maximum MR at 3 T increased from 35% for the pure La0.67Ca0.33MnO3 to 92% for the sample with x=0.25. We suggest that such enhancement in MR is attributed to the strong ferro-antiferromagnetic coupling effects in the composite system, which increase the magnetic disorder at the grain surface and boundary, will improve the spin-polarized tunneling process of the conducting electron between adjacent grains, and thus enhance the MR effects.

ON-LINE MEASUREMENT OF DISSOLVED METHANE CONCENTRATION DURING METHANE FERMENTATION IN A LOOP BIOREACTOR

A dissolved methane sensor based on silicone tube was designed, constructed and optimized.�The silicone tube diameter, silicone tube length and helium flow rate (as the carrier gas � were considered as process parameters to be optimized. A continuous stream of helium (50 mL/min) was directed through the tubing, sweeping out the dissolved methane which diffused through the walls of the tubing from the fermentation broth. The probe was made of silicone rubber tubing, 10 cm in length with inner and outer diameters of 0.25 cm and 0.35 cm, respectively (Detakta Company; NO. 02502). A semi-conductor methane gas sensor (Figaro TGS 2611) - which is highly sensitive and selective to methane gas - was used to measure the dissolved methane continuously. Henry's law along with a special circuit experimental method was applied for calibration. The output concentration was displayed in mg/l (or ppm) of dissolved gas. The accuracy and response time of this system are ± 2 % and 2 minutes, respectively. Moreover, a control system was installed for recycling methane gas during fermentation.

Electrical Transport and Giant Magnetoresistance in (1 - x) La 0.67 Ca 0.33 MnO 3/ x CuO Composites

Samples with nominal composition of (1 - x) La 0.67Ca 0.33MnO 3 (LCMO)/xCuO ( x = 0%, 2%, 4% and 20%) were made using a special experimental method. The temperature dependence of the resistivity (ρ) of the composites was investigated in the temperature range of 10 ∼ 300 K and different magnetic fields of H = 0, 0.1, 0.3, 0.5. 1.0 and 3.0 T. The results showed that CuO percentage x had important effects on metal-insulator transition temperature ( T p), zero field peak resistivity (ρ max), and magnetoresistance ( MR) properties of the composites. T P shifted sharply towards low temperature with the increase of x in the range of x ≤ 4%, but was almost independent of x at high level of CuO content. Composites with x = 4% and 20% exhibited similar electrical transmission behavior. Compared with pure LCMO, enhanced magnetoresistance could be clearly observed even in a quite low magnetic field of 0.3 T. For x = 4% and 20% samples, the MR value at 0.3 T could reach as high as ∼ 88% and ∼ 90%, respectively. XRD and SEM analysis showed that the substantial enhancement of MR, especially near T p, was because of local spin disorder between contiguous LCMO ferromagnetic particles caused by the addition of CuO.

Physicochemical parameters of the oldest boninite melts

Ophiolites of the southeastern Sayan region, the oldest formations in Central Asia (1020 Ma [1]), include unique information on early stages of Paleoasian Ocean evolution. The presence of boninites in the ophiolites indicates that a suprasubduction environment similar to that of the present-day Pacific island-arc systems existed as early as 1 Ga ago. Therefore, investigations of magmatic systems responsible for the formation of such ancient rock complexes are of great scientific interest. In order to elucidate physicochemical parameters of boninite melts of the southeastern Sayan region, we examined melt inclusions in chrome spinels of boninite samples from rock complexes of the “dike-indike” type in the Dunzhugursk sector. We are not able to check the inclusions in the course of heating, because the studied chrome spinels are virtually transparent. Therefore, we developed a special experimental method and designed a microchamber based on a silite heater. The high-temperature experiments were carried out in accordance with the methods of melt inclusion studies [2, 3]. Inclusions detected by the microscopic examination in reflected light were analyzed with a Camebax-Micro microprobe at the United Institute of Geology, Geophysics, and Mineralogy (Novosibirsk). Contents of rare elements (RE), rare earth elements (REE), and water in melt inclusions were determined by secondary ion mass spectrometry using an IMS-4f microprobe at the Institute of Microelectronics of the Russian Academy of Sciences (Yaroslavl), according to the method reported in [4]. Primary melt inclusions (15‐50 µ m) are uniformly distributed in the chrome spinel grain. Round equilibrium inclusions often show negative faceting and are mainly composed of glass with round gaseous bubbles. Pure homogeneous sectors of the inclusions burn away under the laser beam suggesting their glassy state. Table 1 presents the compositions of glass in heated melt inclusions in boninite-hosted chrome spinels from the southeastern Sayan region. In terms of the SiO 2 content, the studied homogeneous inclusions make up a series ranging from basalts and basaltic andesites to andesites. This is consistent with data on dikes and volcanics of the Dunzhugursk sector. In the MgO‐SiO 2 diagram (Fig. 1), data points of chromite-hosted melt inclusions from the eastern

Experimental investigation on Marangoni drop migrations using drop shaft facility

Experimental hardware has been developed to perform the experiments of drop Marangoni migration in the case of intermediate Reynolds numbers in a microgravity environment. The experiments were completed using the drop shaft free fall facility with a 4.5 s microgravity period in the Microgravity Laboratory of Japan. A special experimental method was designed for experimenting with a short microgravity period. In this experiment, the thermocapillary velocity of drop migration, driven only by the thermocapillary effect, was obtained. Experimental results show that Marangoni migration velocity depends on the temperature gradient and the drop diameter for fixed experimental mediums; the thermocapillary velocity of this present experiment is obviously smaller than the one suggested by YGB linear theory. This conclusion agrees. in general, with that of the ground-based experiment.

Plasma parameters in pulsed laser-plasma deposition of thin films

In this paper the first results of an experimental study of the dependence of some plasma parameters (plasma density, degree of ionisation, energy distribution of the ions) on the laser parameters (light flux density, wavelength) for two laser types (TEA-CO2 and excimer laser) are presented. A special experimental method has been developed for absolute measurement of some plasma parameters, such as plasma flux density, ion energy, multicharge ion content and ionization degree. The results obtained show the possibility to control the parameters of plasma fluxes over the deposition conditions and herewith to control the properties of the deposited films.

Diagnostics of Pulsed Plasma Fluxes in Laser Deposition of Thin Films

ABSTRACTThis paper presents the main results of an experimental study of the dependence of some important plasma parameters (plasma flux density, multicharge ion content, degree of ionization, energy distribution of the ions) on some laser parameters (light flux density, wavelength) for two laser types (TEA-CO2- and excimer laser). A special experimental method has been developed for an absolute and simultaneous measurement of the plasma parameters. The results obtained show the possibility to control the parameters of plasma fluxes over the deposition conditions and herewith to control the properties of the deposited films.

Charge relaxation in structures containing non-polar polymer-metal interfaces

The excess charge relaxation in electret structures based on Teflon-FEP films, particularly the charge behaviour in the region of polymer-metal contact, has been investigated. Measurements were made using both the standard electret techniques and a special experimental method, based on observation of the partial recovery of voltage of sandwich electret structures during reheating after forced corona-discharge. It has been found that a specific macro-non-uniformity region exists near the FEP-Al interface, where deep trapping of charges drifting through the FEP film occurs. Using experimental measurements and an appropriate analysis, the authors determine the energy distribution of the traps located near the FEP-Al interface estimate the dimensions of this region to be about 0.3.-0.75 mu m from the Al electrode.

Hyperfine field vectors and hyperfine field distributions in FeNi Invar alloys

We present Mössbauer effect measurements carried out on statistically disordered ferromagnetic fcc FeNi Invar alloys in the concentration range of 30–36 at% Ni. By use of a special experimental method, 57Fe Mössbauer spectroscopy with polarized γ-radiation, we get information on the hyperfine field vectors at the iron nuclei. We find these vectors at lattice sites with more than 10 nearest iron neighbors to be oriented antiparallel to the normal direction of hyperfine field vectors in a ferromagnetic sample, with magnitudes of about 10 T. We calculate P( H) distributions considering the vector character of the hyperfine field. Our results give direct evidence for the existence of antiparallel as well as frustrated magnetic moments of Fe atoms. The existence of different electronic states of the Fe atoms, however, can be excluded by considering results of isomer shift measurements in addition.

Average Triton Energy Deposited in Silicon per Electron-Hole Pair Produced

The average triton energy required to produce an electron-hole pair in silicon was measured. The measured value was 3.64\ifmmode\pm\else\textpm\fi{}0.04 eV. This is the first published measurement of this quantity. Precision charge calibration of the amplifier system, plus a special experimental method for correcting for dead-layer losses in the detector, was used to improve the accuracy of the result.

Temperature Variation in a Circular Cylinder of Finite Length due to Heating at an End Part (6th Report)

In the previous report, an approximate formula giving the transient temperature variation in a circular cylinder of finite length, since the immersion of its lower end part to a high temperature bath, was deduced analytically. Now, its result is compared with the experiment. For this purpose, a special experimental method is used. One of its speciality is the direct observability of the shape and growth of the isothermal line in the cylinder. And the other, the isothermal lines thus obtained are free from the disturbances which will be aroused, if many thermocouple wires were inserted into the cylinder. A specimen is composed of two semicircular cylinders of glass, and one joinning plane (neutral layer) is painted in the thermo-colour. Then, a boundary between changed and unchanged colour region represents itself an isothermal line. Since the instance of immersion of the specimen into a bath, isothermal lines are observed from time to time. Comparing the group of isothermal lines thus obtained with the corresponding lines calculated, very good agreement is recognized.

一端部を熱した場合の有限長円〓内の温度変化(第1報)

In the previous report, an approximate formula giving the transient temperature variation in a circular cylinder of finite length, since the immersion of its lower end part to a high temperature bath, was deduced analytically. Now, its result is compared with the experiment. For this purpose, a special experimental method is used. One of its speciality is the direct observability of the shape and growth of the isothermal line in the cylinder. And the other, the isothermal lines thus obtained are free from the disturbances which will be aroused, if many thermocouple wires were inserted into the cylinder. A specimen is composed of two semicircular cylinders of glass, and one joinning plane (neutral layer) is painted in the thermo-colour. Then, a boundary between changed and unchanged colour region represents itself an isothermal line. Since the instance of immersion of the specimen into a bath, isothermal lines are observed from time to time. Comparing the group of isothermal lines thus obtained with the corresponding lines calculated, very good agreement is recognized.