Pyrometer Technique Research Articles

Deflagration characteristics of freely propagating flames in magnesium hydride dust clouds

The flame propagation processes of MgH2 dust clouds with four different particle sizes were recorded by a high-speed camera. The dynamic flame temperature distributions of MgH2 dust clouds were reconstructed by the two-color pyrometer technique, and the chemical composition of solid combustion residues were analyzed. The experimental results showed that the average flame propagation velocities of 23 μm, 40 μm, 60 μm and 103 μm MgH2 dust clouds in the stable propagation stage were 3.7 m/s, 2.8 m/s, 2.1 m/s and 0.9 m/s, respectively. The dust clouds with smaller particle sizes had faster flame propagation velocity and stronger oscillation intensity, and their flame temperature distributions were more even and the temperature gradients were smaller. The flame structures of MgH2 dust clouds were significantly affected by the particle sinking velocity, and the combustion processes were accompanied by micro-explosion of particles. The falling velocities of 23 μm and 40 μm MgH2 particles were 2.24 cm/s and 6.71 cm/s, respectively. While the falling velocities of 60 μm and 103 μm MgH2 particles were as high as 15.07 cm/s and 44.42 cm/s, respectively, leading to a more rapid downward development and irregular shape of the flame. Furthermore, the dehydrogenation reaction had a significant effect on the combustion performance of MgH2 dust. The combustion of H2 enhanced the ignition and combustion characteristics of MgH2 dust, resulting in a much higher explosion power than the pure Mg dust. The micro-structure characteristics and combustion residues composition analysis of MgH2 dust indicated that the combustion control mechanism of MgH2 dust flame was mainly the heterogeneous reaction, which was affected by the dehydrogenation reaction.

Flame propagation and temperature distribution characteristics of magnesium dust clouds in an open space

In order to explore the flame propagation behaviors and temperature characteristics of magnesium dust clouds, the measurement system and the two-color pyrometer technique were used to study the spatial-temporal distribution of flame temperature fields and flame propagation behaviors with different particle sizes. The experiment results showed that the flame propagation characteristics largely depended on the particle size and the flame propagation velocity was higher with decreasing particle sizes. The flame temperatures of the leading edges were kept stable between 3100 and 3300 K, and the average flame temperature was related to the dust concentrations and particle sizes. The average flame temperature of −400 mesh magnesium with 830 g/m3 dust concentration was the highest, and the descent speed of the average flame temperature had a negative correlation with the particle size. The two-color pyrometer technique could evaluate the severity of magnesium dust clouds explosion, which provides a theoretical basis for the prevention.

Explosion temperature mapping of emulsion explosives containing TiH2 powders with the two-color pyrometer technique

In the study, the two-color pyrometer technique was used to measure the transient temperature field of emulsion explosives with different contents of TiH2 powders. The experimental results showed that the introduction of TiH2 powders could significantly increase the explosion temperature and fireball duration of emulsion explosive. When emulsion explosives were ignited, the average explosion temperature of pure emulsion explosive continuously decreased while emulsion explosives added with TiH2 powders increased at first and then decreased. When the content of TiH2 powders was 6 mass%, the explosion average temperature reached its maximum value of 3095 K, increasing by 43.7% as compared with that of pure emulsion explosive. In addition, the results of air blast experiment and explosion heat test showed that the variation trends of shock wave parameters, explosion heat and theoretical explosion temperature of emulsion explosives with different contents of TiH2 powders were basically consistent with that of explosion temperature measured by the two-color pyrometer technique. In conclusion, the two-color pyrometer technique would be conducive to the formula design of emulsion explosive by understanding the explosion temperature characteristics.

An investigation on the dust explosion of micron and nano scale aluminium particles

A series of dust explosion were conducted to compare the flame structure between nano and micron aluminium dusts. Two-color pyrometer technique is applied to have qualitative observation of flame development. Measurement of temperature indicates that explosion in micron aluminium dust clouds start in a single spot at 3000 K, in contrast, explosion in nano aluminium dust clouds start when hot powder accumulated to a certain amount at lower temperature of 2600 K. For micron aluminium dust clouds, flame at leading edge has the highest temperature and propagates in all directions. On the other hand, flame in nano aluminium dust clouds propagate only upward with the hottest part left behind at the downside. As flame propagates, the temperature at top edge gradually decreases from 2600 K to finally 2000 K, but temperature at bottom edge maintains in 3000 K with no significant displacement. The unevenness of flame structure is considered as the consequence of different particle densities, which suggests that the reaction of nano aluminium particles stays in molten state, meanwhile, the high surface area also leads to unignorable heat loss.

A Methodology for Temperature Correction When Using Two-Color Pyrometers - Compensation for Surface Topography and Material

In this investigation, the applicability of the two-color pyrometer technique for temperature measurements in dry hard turning of AISI 52100 steel was studied, where both machined surfaces as well as cutting tools were considered. The impacts of differing hard turned surface topography on the two-color pyrometer readings was studied by conducting temperature measurements on reference samples created using cutting tools with different degrees of tool flank wear. In order to conduct measurements in a controlled environment, a specially designed furnace was developed in which the samples were heated step-wise up to 1,000 °C in a protective atmosphere. At each testing temperature, the temperatures measured by the two-color pyrometer were compared with temperatures recorded by thermocouples. For all materials and surfaces as studied here, the two-color pyrometer generally recorded significantly lower temperatures than the thermocouples; for the hard turned surfaces, depending on the surface topography, the temperatures were as much as ~20 % lower and for the CBN cutting tools, ~13 % lower. To be able to use the two-color pyrometer technique for temperature measurements in hard turning of AISI 52100 steel, a linear approximation function was determined resulting in three unique equations, one for each of the studied materials and surfaces. By using the developed approximation function, the measured cutting temperatures can be adjusted to compensate for differing materials or surface topographies for comparable machining conditions. Even though the proposed equations are unique for the hard turning conditions as studied here, the proposed methodology can be applied to determine the temperature compensation required for other surface topographies, as well as other materials.

Shock induced polymorphism phase transitions in high density glass

Plate impact experiments are conducted on high density glass (HDG) with an initial density of ～4.817g/cm3 (Brand ZF6) at a two-stage light gas gun facility. A copper flyer plate is used as a standard sample. Experimental shock pressure is between 52.1GPa and 167.8GPa. A multi-wavelength pyrometer and optical analyzer technique are used to determine the Hugoniot curve, sound velocity and shock temperature of HDG. The experiment results reveal that polymorphism phase transitions occur in HDG under compression, and the onset pressures are ～23, ～78 and ～120GPa, respectively. The measured sound velocity first increases and arrives at about 78GPa, then decreases rapidly, and increases again with pressure increasing. Beyond ～120 GPa, the longitudinal sound velocity turns in to bulk sound velocity, indicating the melting of HDG. Measured shock temperatures also show discontinuities at ～78 and ～120GPa, after which its increase rate becomes small and consistent with the calculated Lindemann melting line, confirming the above HDG phase transformation behaviors. Our Hugoniot data are consistent well with LASL shock Hugoniot data of HDG, which shows discontinuity only at about 23GPa, indicating that the phase transitions at 78 and 120GPa are not first-order ones. Our shock data and the gained knowledge of dynamic response behavior of HDG are valuable for improving the accuracies in sound velocity measurements for metals and non-metals at pressures over a megabar range.

Two colour pyrometer technique for coal particle temperature measurements in pressurised pulverised coal flame

The present paper describes the development and application of two modifications of a two colour pyrometer for the measurement of coal particle temperatures in a pressurised pulverised coal combustor operating at a maximal thermal power of 400 kW and pressures up to 10 bars. The mean diameter of coal particles ranged from 40 to 100 μm. Slag tap and dry dust firing modes were used. The first system for slag tap firing conditions consists of an achromatic lens system arranged outside the combustor and it is coupled to the pyrometer by an optical fibre. The second system preferably for dry dust firing is a probe configuration and consists of an achromatic lens which is integrated into a water cooled radially movable probe with a cooled background to exclude the effect of the combustion wall radiation. Several series of measurements at a pressure of 3 bars for different coal types were carried out at the pressurised pulverised coal combustion test facility of RWTH Aachen University.

In situ diagnostic methods for thin‐film fabrication: utilization of heat radiation and light scattering

AbstractDeposition processes of Cu(In,Ga)Se2 (CIGS) thin films were observed by informative and low‐cost in situ monitoring means; the pyrometer technique, and the spectroscopic light‐scattering (SLS) technique. Intensities of thermal radiation and scattered white light were profiled from outside the vacuum chamber during growth, using a monochromatic pyrometer and a small CCD spectrometer. The deposition process was studied by systematic variations of major process parameters of CIGS, such as the substrate temperature, Ga concentration and Se supply. Various film properties, including the deposition speed, thickness, compositional ratios, surface roughness and precipitation of Cu‐rich phases have been monitored in situ. Copyright © 2004 John Wiley & Sons, Ltd.

Thermal Radiation Spectroscopy Diagnosis for Temperature and Microstructure of Surfaces

Surface microstates of real surfaces of solid materials change in industrial environments, or they are changed in industrial surface processes positively. A real time diagnosis technique for the surface microstates should be developed for the process control. We propose a diagnosis technique for temperature and microstructure of real surfaces on a basis of the hardware performance of our wide-spectral-range high-speed spectrophotometer system. With respect to the temperature, an active spectral pyrometer technique is adopted, in which the reflection of the surface is measured as well as the self-emission. With respect to the microstructure, an attention is paid to the interference and diffraction of radiation in a new real surface model. An experiment is made on a metal surface in a high-temperature oxidation process to verify the performance of this technique. Spectra of emission and reflection energy of radiation in a near-infrared through infrared region are measured at every 2s, and analyzed. Time transition of the surface temperature of an order of 1100K is estimated within an inaccuracy of 10K. The average thickness d and rms roughness σI of the surface film are estimated to be in regions of d=0.08∼3.8µm and σI=0.01∼0.71µm, respectively.

Thermal Radiation Spectroscopy Technique for Diagnosis of Temperature and Microstructure of Real Surfaces

Surface microstates of real surfaces of solid materials change in industrial environments, or they are changed in industrial surface processes positively. A real time diagnosis technique for the surface microstates should be developed for the process control. We propose a diagnosis technique for temperature and microstructure of real surfaces on a basis of the hardware performance of our wide-spectral-range high-speed spectrophotometer system. With respect to the temperature, an active spectral pyrometer technique is adopted, in which the reflection of the surface is measured as well as the self-emission. With respect to the microstructure, an attention is paid to the interference and diffraction of radiation in a new real surface model. An experiment is made on a metal surface in a high-temperature air-oxidation process to verify the performance of this technique. Spectra of emission and reflection energy of radiation in a near-infrared through infrared region are measured at every 2 s, and analyzed. Time transition of the surface temperature of an order of 1100 K is estimated within an inaccuracy of 10 K. The average thickness d and rms roughness σ1 of the surface film are estimated to be in regions of d=0.08∼3.8 μm and σ1=0.01∼0.71 μm, respectively.

High-temperature infrared properties of sapphire, AlON, fused silica, yttria, and spinel

A vacuum emissometer, utilizing a carbon dioxide laser for high-temperature sample heating, has been designed and built for use with a Fourier Transform spectrometer. A two-color pyrometer technique is used to measure sample surface temperature. Oxides such as sapphire, spinel, yttria, aluminum oxynitride, and fused silica are experimentally characterized in temperature from 600 to 2000 K and in frequency from 500 to 5000 cm −1. A glowing yttria sample has also been characterized over the spectral range of 8500 to 13 500 cm −1. Good agreement with temperature dependent classical oscillator and quantum mechanical multiphonon models for the complex index of refraction is obtained.

Study of the Convective Heat Transfer in a Rotating Coolant Channel

An experimental and theoretical study of convective heat transfer in a rotating coolant channel was inspired by the potential application to cooled turbine rotor blades. The flow that circulates into the internal cavity of the blade is subjected to Coriolis and centrifugal forces, in addition to pressure and friction forces. In this study, the channel is a rectangular-sectioned duct that rotates around an orthogonal axis. The experimental rig is composed of a vacuum enclosure, which includes an electric furnace, and the test section, heated by radiative flux. The temperatures of the wall test section are measured with thermocouples and the infrared pyrometer technique still under development. The convective heat transfer coefficients are determined with transient or steady-state techniques. It is shown that Coriolis acceleration has a beneficial influence on mean heat transfer. Locally, along the pressure side, the transfer increases strongly and on the contrary along the suction side, it decreases slightly. These effects are analyzed theoretically with a Navier-Stokes three dimensional (with mixing length model of turbulence) and explained by the influence of Coriolis force, which induces a secondary flow and distorts the velocity and temperature profiles. Experimental and theoretical results are presented and discussed.

In-flight measurement of particle size and temperature

Two coincidence techniques for simultaneously obtaining particle size and temperature in a plasma torch are described. The absolute magnitude of scattered laser light is used to determine particle size while particle temperature is determined using a two-colour pyrometer technique. Typical results on alumina particles injected into a 7 kW plasma torch are presented.

Simultaneous Measurement of Particle Size and Temperature in a Plasma Torch

ABSTRACTTwo coincidence techniques for simultaneously obtaining particle size and temperature in a plasma torch are described. The absolute magnitude of scattered laser light is used to determine particle size and particle temperature is determined from a two-color pyrometer technique. Typical results on alumina particles injected into a 7 kW plasma torch are presented.

On the temperature and reaction rate of burning pulverized fuels

A two-color pyrometer technique has been used to measure the temperature of burningpulverized fuel particles flowing in dilute suspension on the centerline of a laminar flow reactor. The transparent reactor is fed by a premixed flat flame fueled with CH 4 −H 2 −O 2 −N 2 mixtures, which permit widely variable post-flame temperatures and oxygen concentrations to be obtained. The two-color system employs an optical-electronic system which includes two monochromators to acquire light emission intensity at two wavelengths simultaneously from individual burning particles passing through a 1 mm square area on the centerline of the reactor. Planck's law and the gray body assumption (verified here by measurements) are used to compute particle temperatures, and the average temperature is then determined by averaging the values for some 500 individual particles. Particle temperatures have been determined for various gas temperatures over a range ofoxygen mole fractions from 0 to 0.2 for size-graded (90 μm mean diameter) samples of a petroleum coke and a flash pyrolysis char. Particle burning rates per unit external surface area were determined from the measured temperatures by a heat balance analysis. The functional variation in burning rate with temperature was then used to infer whether the burning rate was controlled by chemical rates (Zone I), the combined effects of chemistry and pore diffusion (Zone II), or bulk diffusion (Zone III). For the petroleum coke, both zone I and Zone II conditions were observed, and chemical rate coefficients for each zone were derived. For the char, Zone II and a transition to Zone III conditions were observed, and a chemical rate coefficient for Zone II was derived. Reaction orders and activation energies were in the range expected from previous oxidation studies, and the chemical rates for both samples were in good agreement with previous measurements by a different method in another laboratory. The results show that careful temperature measurements can provide a sensitive method for the determination of pulverized fuel burning rates.

Vapour Pressure Studies Over Liquid Uranium Oxide and Uranium Plutonium Oxide Up to 5000 K

AbstractThe estimation of the energy release in a hypothetical fast breeder reactor core meltdown accident requires a detailed analysis of the disassembly process. Since the vapour pressure presents the ultimate shut‐down mechanism, the required data are given by the equation of state of the irradiated fuel.The pressure over the ternary uranium‐plutonium oxide was determined to log p(atm) = 7.966 – 28,137/T, yielding a heat of evaporation of ΔHevap = 128.7 kcal/mol, fully consistent with the heat of sublimation of ΔHsub = 148.4 kcal/mol below the melting point, and the heat of fusion of 19.4 kcal/mol. The corresponding equation for liquid UO2 was determined as log p(atm) = 7.7 – 27,900/T, with a heat of evaporation of ΔHevap = 127.6 kcal/mol, again in consistency with the assessed data below the melting point of ΔHsub= 144.1 kcal/mol, and the heat of fusion of 17.7 kcal/mol. For this a new high‐energy laser technique, including fast temperature recording in the microsecond range, was developed. The first quantitative measurements on (U, Pu)O2 above 4000 K were reported to the IAEA Symposium on Thermodynamics of Nuclear Materials in Vienna.The investigation of the total temperature range from 3000 K to Te = 7560 K revealed two principle experimental difficulties, a liquid layer movement at temperatures below 4000 K, and optical absorption due to increasing thermal ionisation above 5000 K. A new double intensity laser pulse technique is presented, which allows the extension of measurements to below 4000 K. In addition a multi‐wavelength pyrometer technique has been developed to eliminate, and at a later stage to determine, spectral emissivities above the melting point, during laser heating within pulse times of micro and nanoseconds.