Experimental facility dedicated to high temperatures thermophysical properties measurement: validation of the temperature measurement by multispectral method (original) (raw)
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Review of Scientific Instruments
Experimental research into severe nuclear accidents often requires the accurate measurement of high temperatures of molten materials. Measurements of very high temperatures (1500–2500 °C) in liquid materials using standard pyrometry can entail uncertainties in the order of 5%–10%. Pyroreflectometry is a powerful technique with the potential to significantly reduce these uncertainties. A method is proposed to optimize pyroreflectometry temperature measurements in the 1500–2500 °C range and to allow more easily the detection of the solid–liquid phase transition. The originality of this research essentially relies on the use of pyroreflectometry based on two wavelengths (1.3 and 1.55 μm) and its application to liquid materials at high temperature, which implies to adapt technological elements and metrological procedures. The proposed procedure first requires temperature calibration, which is undertaken using three eutectic fixed-point cells, reducing temperature uncertainty. Second, p...
Development of a Special Multi-Wavelength Pyrometer for Temperature Distribution Measurements in
2002
Previously a fast multi-wavelength pyrometer was developed in a collaboration between the Harbin Institute of Technology of China and Rome University of Italy. The main features of the instrument include the use of a dispersing prism and a photodiode array to cover the entire spectral band. Following this experience, a new type of six-target eight-wavelength pyrometer for solid propellant rocket engine plume temperature distribution measurements has been developed. The instrument can record the radiation fluxes of eight wavelengths for six different uniformly distributed points on the target surface, which are well defined by holes on a field stop. The fast pyrometer with a specially designed synchronous data acquisition system can assure that the recorded thermal radiation fluxes of different spectral regions are at the same time and the same true temperature, even with dramatically changed targets.
On-line thermocycles measurements in laser applications
Le Journal de Physique IV, 1994
The thermal state of material in the zone of laser action is one of the main integrated parameters t o determine the evolution of physicochemical processes and structural phase transformations. The conditions of temperature measurements in laser machining are among the most severe even for noncontact technique of optical pyrometry. From a general point of view, the absence of on-line control and monitoring is one of the main limitations of laser technology integration into modern industry. Data on surface temperature dynamics obtained by pyrometry could be widely used to: (a) understand and optimize the laser processes (i.e. define of the links between surface temperature history and the properties of treated materials); (b) create process control on-line including feedback from a pyrometer. The main technical parameters of high speed pyrometer (HSP) are the following : brightness temperature range 1 1 50K(1550K)-3500K (threshold sensitivity depends on selected wavelength); error of measurement 1 %; response time 190 ps; 200 pm spatial resolution at 350 mm distance of pyrometer from the zone of temperature measurements; wavelength variation in 2 colour channels from 0.5 to 1.1 pm. The opportunities of actual temperature measurements by high speed high spatial resolution pyrometer system in wide range of laser applications are illustrated by : heat treatment, welding, cladding, and pulsed action.
Theoretical aspects of the integration of thermography and pyrometry methods
2008
Both thermovision and pyrometric measuring are widely used for the control of industrial process thermo modes, the technical service and diagnostics of equipment as well as the works on security and safety provision. The objective of thermovision measuring is the visualization and research of an object thermo field on the basis of temperature gradient identification at defined temperature sensitivity. The main purpose of pyrometric measuring is the identification of temperature values in certain object points with certain accuracy. Nowadays, it is expediently to solve the complex task based on both methods advantages’ unification in many technological processes: identification of object thermo field point temperature values with the needed accuracy. For this purpose it is necessary to integrate the methods of thermography and pyrometry on the basis of usage of these methods’ advantages as well as common disadvantages’ correction. Both thermovision and pyrometric measuring are tightl...
High Accuracy Multicolor Pyrometry for High Temperature Surfaces
An evaluation of previously proposed least-squares multi-color pyrometry methods was carried out to determine their highest achievable accuracy. The study was limited to the visible spectrum and the temperature range of 1700 to 3000 K, typical of electrode surfaces in high-power electric propulsion thrusters. A Monte-Carlo simulation of the various methods showed the eects that the number of colors of the pyrometer, the errors associated with noise and calibration, and the number of measurements have on the uncertainty of the predicted temperature. Some of these methods were found to lead to inaccurate results, an underestimate of the uncertainty of the predicted temperature, or yield larger uncertainties than single-color pyrometry. The two methods that were found to yield the highest accuracy without underestimating the uncertainty are based on tting the intensity versus wavelength data with three free parameters (temperature and the two coecien ts of the emissivity versus wavelen...
Successful Pyrometry in Investment Casting
2007
The FAR Expert System SpectroPyrometer has accurately measured solid and liquid metal temperatures in investment casting. The problems it has solved are significant and explain the skepticism investment casters have toward non-contact temperature measurement. The problems are caused by the nature and behavior of the target: a solid metal charge changes phase into a turbulent liquid. Liquids, especially turbulent liquids, give conventional pyrometry problems because the changing microscopic shape of the surface governs the radiation characteristics, i.e., the emissivity. Metals as a class, whether solid or liquid, are the most difficult for pyrometry due to the behavior of their emissivity: it changes with wavelength (color) in addition to all the other variables that affect it. Put the two together and no instrument that requires emissivity information beforehand or assumes constant emissivity (or constant relative emissivity) has a chance of success. The SpectroPyrometer has shown ...
The Open Corrosion Journal, 2011
The heating parts of thermogravimetry curves performed for cast alloys in air at high temperatures were analysed, after correction from the effects of air buoyancy variation, to characterize the transient oxidation before reaching the targeted temperature for the isothermal stage usually applied thereafter. This was done here for three binary M-30Cr alloys, six ternary M-30Cr-0.4 and 0.8%C alloys, and three M-30Cr-0.4C-6Ta quaternary alloys, heated in synthetic air at 20 K min-1 until 1000, 1100 or 1200°C. The cobalt alloys begin to be oxidized with a sufficient mass gain to be detected by thermogravimetry, earlier than the nickel or iron alloys (i.e. at lower temperatures). The temperature of oxidation start is lowered by the presence of tantalum for the three families of alloys. When the carbon content (or the carbides density) increases in the alloy, the temperature of oxidation start decreases for the cobalt alloys and remains almost constant for the nickel or iron alloys, while the total mass gain due to oxidation during heating increases for the nickel and cobalt alloys and decreases for the iron alloys.
In-situ Temperature Measurement using a Multi-sensor Camera during Laser Welding
QUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY, 2015
The aim of this study was to develop a temperature measurement technique during welding using a developed multi-sensor camera based on a two-color thermometry method. This technique has specific features, such as in-situ temperature measurement, high response speed, two-dimensional (2D) noncontact measurement, and flexibility. Accurate in-situ temperature 2D distribution and its history can be acquired based on the selection of a suitable combination of band-pass filters for laser welding and the welded material. In addition, a clear visible image can be captured with the 2D temperature distribution using the developed multi-sensor camera even when a high welding speed is employed.
The features of contactless measurements of the surface temperature of bodies by the method of two-colour pyrometry of samples activated by periodic laser pulses are considered. The requirements imposed on the parameters of laser radiation and a measuring circuit are formulated. It is shown experimentally that surface temperatures close to room temperature can be measured with an error not exceeding 3 % after elimination of the superêuous static component of the excess temperature. The sensitivity of the method is estimated. Advantages of laser photothermal radiometry with repetitively pulsed excitation of surfaces over the case when samples are subjected to harmonic amplitude-modulated laser radiation are discussed.
Review of Temperature Measurement Techniques
Biomedical Journal of Scientific & Technical Research, 2021
Rapid development in the area of temperature measurement techniques arises from various applications, such as the sessile drop, which is of interest in several fields including coating, combustion, and cooling facilities. Accurate depiction of the physical phenomenon entails improvement in the temperature measurement resolution, where average temperature measurements fail to capture, due to their spatial limitation. In the current paper, various optical techniques are reviewed in contrast to conventional measurement approaches, such as thermocouples and microheater arrays. The optical techniques include Infrared thermography and fluorescing materials, such as quantum dots and Temperature sensitive paint. The advantages and shortcomings of such techniques are examined in depth, with respect to their applications in previous works.