Particulate light scattering dependence upon solute compound in atomic flame spectrometry

The relative intensities of light by compounds of 46 elements have been measured following irradiation, by electrodeless discharge lamps, of the particles formed in H₂-air and C₂H₂-air flames. A procedure which enables signals from the detector to be normalized allows comparison of results which vary greatly in absolute magnitude. Scattering by unseeded flames is shown to be significant when the flame is not in thermal equilibrium with the environment. In an H₂-air flame, scattering resulting from the nebulization of 0.05 m solutions containing the following elements is found to decrease in the series Th > La > Al > Si > Ir > U > Pt > Rh ? Ru > Ti > Zr ? Ce ? Ca > Os ? Mn ? Tl ? Pd. Compounds of other elements investigated did not lead to significant scattered radiation. The scattering is dependent upon flame composition and temperature, the form of the element as nebulized and apparently the extent of cohesion between non-volatile particles. Light scattering by the Pt group metals is considered to occur as a result of interatomic bonding.     

Nitrogen determination in coal and coke with an ammonia electrode

The selective-electrode procedure described for determining 0.2-2.5% of nitrogen in coal and coke offers significant advantages over Kjeldahl distillation and titration. The Kjeldahl digest is diluted, neutralized, cooled, diluted to volume, adjusted to a standard temperature and rendered alkaline prior to measurement with an ammonia-selective electrode. Accuracy and precision of 1% relative are demonstrated by comparative analyses of a range of samples. Important experimental aspects discussed include the role as neutralization indicator played by vanadium derived from the catalyst, precision of the mV-meter, the influence of solution temperature and concentration, the repeatability of the readings, and interferences.     

The sound generated by a square cylinder with a splitter plate at low Reynolds number

The generation of aerodynamic sound by the interaction of flow at a Reynolds number of 150 and a Mach number of 0.2 with a rigid square cylinder attached to a rigid thin flat plate is numerically investigated. When the length of the plate is varied from L=0.5D to 6D, where D is the side length of the square cylinder, the results can be grouped into three distinct regimes. For the first regime (L?D), the sound levels decrease with increasing plate length. A 3 dB sound reduction is obtained when the length of the plate is D. For the second regime (1.25D?L?4.75D), the sound levels increase with increasing plate length. For the third regime (5D?L?6D), the sound levels decrease as the length of the plate increases but the levels are higher than for the other regimes. Results also show that the lift fluctuation is the dominant sound source. These acoustic results can be explained in terms of the fluid mechanics occurring in the near wake of the cylinder.     

X-ray emission from clusters of galaxies and cosmological parameters

Clusters of galaxies are excellent probes of cosmic structure and evolution. X-ray studies of clusters provide some of their key parameters, viz., temperature of the hot intra-cluster gas, its metallicity, X-ray luminosity and surface brightness giving mass distribution and mass-flow rate in the case of cooling flows. X-ray measurements for a large sample of clusters have lead to estimates of the total gravitating mass in them, which can be compared to the virial masses derived from dynamical considerations and gravitational lensing in some of them. X-ray derived total masses are consistent with masses obtained from the other methods after the effects due to the presence of cooling flows are taken into account in the analyses. Estimated virial masses, lack of evolution in X-ray properties, and detection of several very hot clusters at high redshifts indicate a Universe with a low value (≤ 0.3) for the Ω parameter.     

On-line dual-wavelenth instrumentation for antomatic correction of light scattering interference in dispersive atomic fluorescence spectrometry

The design basis of a dual detection channel spectrometer for general application in atomic fluorescence analysis is discussed. Low frequency modulation of the radiation from a single light source is employed with one channel set at a fluorescence wavelength while the second channel measures the magnitude of scattering at a non-fluorescent wavelength. The instrument has been applied to the analysis of trace Au and Cd in high scattering matrix solutions. The statistical treatment of data, and the method of calculating detection limits, is discussed.     

The determination of traces of mercury in solid fuels by high-temperature combustion and cold-vapour atomic absorption spectrometry

A high-temperature combustion technique is described for the determination of mercury in coal, coal products including ash, and other samples of environmental interest. The liberated mercury is absorbed in an acidified potassium permanganate solution and determined by cold-vapour atomic absorption spectrometry. The vapour generation assemblage is constructed of standard ground-joint glassware, and is designed to produce non-transient signals suitable for either analog or digital recording devices. Accuracy and precision for 1-g coal samples is 0.02 μg g^-1.     

Computational bluff body aerodynamic noise prediction using a statistical approach

A new method for calculating the aerodynamic noise generated by bluff bodies is presented in this paper. The methodology uses two-dimensional, unsteady Reynolds averaged Navier Stokes turbulent flow simulations to calculate the acoustic source terms. To account for turbulent flow effects that are not resolved by the flow simulation, a statistical approach has been developed and applied to introduce narrow band random noise. Spanwise de-correlation of flow information is accounted for using a correction method based on a de-correlation length scale. Curle’s compact acoustic analogy is used to calculate the far-field noise. To illustrate the effectiveness of the method, the turbulent flow and noise about two test cases are calculated and compared with experimental results from the literature.     

Flow-induced noise of a wall-mounted finite airfoil at low-to-moderate Reynolds number

This paper presents an experimental investigation of the flow-induced noise created by a wall-mounted finite airfoil at low-to-moderate Reynolds number and zero angle of attack. Far-field noise measurements have been taken at a single observer location and with two perpendicular microphone arrays in an anechoic wind tunnel at Reynolds numbers of _Rec=9.2×10⁴–1.6×10⁵${\mathit{Re}}_c=9.2\times {10}^4–1.6\times {10}^5$, based on chord, and for a variety of airfoil aspect ratios (length to chord ratio of L/C=0.2–2$L/C=0.2–2$, corresponding to length to thickness ratio of L/T=1.7–16.7$L/T=1.7–16.7$). Additionally, surface oil-film visualisation images and unsteady velocity measurements taken in the near trailing edge wake are related to far-field noise measurements to determine the flow mechanisms responsible for noise generation. The results show that the wall-mounted finite airfoil radiates noise similar to a two-dimensional airfoil when L/T>8.3$L/T>8.3$. Despite the incoming boundary layer height at the junction being 1.30≤δ/T≤1.46$1.30\le \delta /T\le 1.46$, junction and tip flow suppresses tonal noise production for airfoil?s up to L/T=8.3$L/T=8.3$ at _Rec=9.2×10⁴–1.2×10⁵${\mathit{Re}}_c=9.2\times {10}^4–1.2\times {10}^5$. Trailing edge noise is found to be the dominant airfoil noise generation mechanism at frequencies above 1 kHz with the position of the noise source along the trailing edge determined by the proportion of the airfoil span influenced by flow at the airfoil–wall junction.     

Measurements of the orthogonal blade–vortex interaction using a particle image velocimetry technique

This paper describes the results of application of a particle image velocimetry (PIV) technique to an orthogonal blade–vortex interaction experiment. To help resolve the problem of vortex meander during the tests, two PIV systems were used, which produced two velocity vector maps closely separated in time. During the PIV analysis an image-based vector validation scheme was used, which was shown to reduce significantly the number of wild vectors reaching the vector map. Preliminary results from the tests showed that, close to the blade, a significant radial outflow was superimposed on the vortex flow field. The radial flow is thought to be due to the dispersion of the vortex axial core flow during vortex cutting, which distorts the vortex flow field and enlarges the vortex. Further away from the blade, no significant radial flow was detected and the vortex remained undisturbed. Received: 26 April 1999/Accepted: 9 November 1999     

High-temperature kinetics of thermal decomposition of acetic acid and its products

Kinetics of the thermal decomposition of acetic acid vapor dilute in argon have been studied over the temperature range of 1300–1950 K in a single-pulse shock tube. The acid was found to decompose homogeneously and molecularly via two competing firstorder reaction channels at nearly equal rates, to form methane and carbon dioxide on the one hand, and ketene and water on the other. Fall-off behavior has been taken into account and limiting high-pressure rate constants for both channels have been derived. Ketene was found to decompose both unimolecularly to methylene radicals and carbon monoxide and also by a radical reaction with CH₂ to form ethylene and carbon monoxide. The rate constant derived for the unimolecular reaction was found to be in good agreement with an earlier shock tube measurement by H. G. Wagner and F. Zabel [Ber. Bunsenges Phys. Chem., 75 , 114 (1971)]. The bimolecular reaction of ketene to produce allene and carbon dioxide, important in lower temperature reaction systems, has been found to be unimportant under the present conditions. A computer model for the decomposition kinetics involving 46 reactions of 21 species has been found to simulate the experimental yield data substantially. Sensitivity analyses have been used to identify reactions which make important contributions to the overall mechanism and yields of major products. Methylene radicals play important roles in determining yields of major species.