Blackbody Furnace Research Articles

Estimation of radiative properties and temperature distributions in coal-fired boiler furnaces by a portable image processing system

This paper presented an experimental investigation on the estimation of radiative properties and temperature distributions in a 670t/h coal-fired boiler furnace by a portable imaging processing system. The portable system has been calibrated by a blackbody furnace. Flame temperatures and emissivities were measured by the portable system and equivalent blackbody temperatures were deduced. Comparing the equivalent blackbody temperatures measured by the portable system and the infrared pyrometer, the relative difference is less than 4%. The reconstructed pseudo-instantaneous 2-D temperature distributions in two cross-sections can disclose the combustion status inside the furnace. The measured radiative properties of particles in the furnace proved there is significant scattering in coal-fired boiler furnaces and it can provide useful information for the calculation of radiative heat transfer and numerical simulation of combustion in coal-fired boiler furnaces. The preliminary experimental results show this technology will be helpful for the combustion diagnosis in coal-fired boiler furnaces.

Measurements on flame temperature and its 3D distribution in a 660 MWe arch-fired coal combustion furnace by visible image processing and verification by using an infrared pyrometer

In order to verify the 3D temperature distribution of combustion in large-scale, coal-fired boiler furnaces visualized through a visible flame image processing system, a carefully calibrated portable flame temperature measuring system adopting the same flame image processing technique was developed, which is more convenient for industrial flame measurements. Furthermore, the temperatures and emissivities measured by the portable system were compared with the results by an infrared pyrometer which was used to measure the equivalent blackbody temperatures of the flames. The relative differences of the predicted temperatures and emissivity for a blackbody furnace by the portable system are less than 1% and 3%, respectively, showing a good accuracy for its application in the combustion industry. The equivalent blackbody temperatures deduced from the flame temperatures and emissivities measured by the portable system from 12 flame-observing ports in a 660 MWe arch-fired boiler in three horizontal sections at different elevations were compared with those measured by the infrared pyrometer. The relative differences are less than 7%, an acceptable agreement for measurements in the case of a coal-fired furnace. The cross-section-averaged temperatures deduced from the 3D temperature distribution acquired by the visualizing system were verified by those measured by the portable flame measuring system, and the two sets of results matched each other reasonably. This revealed that the coal combustion in the furnace was suffering from seriously delayed ignition of coal, leading to a lower efficiency of fuel utilization.

A simple measurement method of temperature and emissivity of coal-fired flames from visible radiation image and its application in a CFB boiler furnace

The two-color method is widely used in non-contact temperature measurement of combustion flames from radiation images, traditionally based on the spectroscopic characteristics of the image sensor, and/or the representative wavelengths for the red, green and blue filters of the image-forming devices, for example, Charge Coupled Device (CCD) cameras. In this paper, a new method to derive the temperature and emissivity images from a color CCD image is presented for coal-fired combustion processes, which is independent of the spectroscopic characteristics and the representative wavelengths of the CCD and the image processing system. In this method, it is only necessary to capture image information by the image processing system from a blackbody furnace at different temperatures which cover the possible temperature range of the combustion processes to be measured. In a 480 ton/h coal-fired circulating fluidized bed (CFB) boiler experiments are conducted. The temperature measured by this method is validated by that obtained by thermocouple, and it varies obviously with the load the boiler. The flame emissivity provided by this system is worthy for further study.

112 温度制御された黒体炉とふく射伝熱解析による放射温度計の高精度計測(学生賞II)

112 温度制御された黒体炉とふく射伝熱解析による放射温度計の高精度計測(学生賞II)

Optical Diffraction Corrections in Radiometric Thermodynamic Temperature Determination

One of the main components of uncertainty in high-temperature thermometry arises because of the size-of-source effect (SSE). This effect makes the temperature measurement sensitive to the geometry of the radiating environment. It is caused by optical diffraction and especially by light scattering off/from, and inter-reflections between, optical components inside the pyrometer. The LNE-INM/CNAM is involved in extending the thermometry temperature scale to very high temperatures (T > 2000 °C) and has developed eutectic-based fixed points (Sadli et al. (in: Zvizdic (ed.) Proceedings of TEMPMEKO 2004, 9th International Symposium on Temperature and Thermal Measurements in Industry and Science, 2004)) and a thermodynamic temperature measurement capability based on absolute radiometric methods (Briaudeau et al. (in: D. Zvizdic (ed.) Proceedings of TEMPMEKO 2004, 9th International Symposium on Temperature and Thermal Measurements in Industry and Science 2004)). A new measurement technique that uses an optical fiber has been developed and tested, allowing the determination of the SSE at any defocusing plane, with high resolution. A model based on optical diffraction has been developed to simulate the SSE in a real situation, considering the contribution to the pyrometer signal of the whole “3D” optical scene inside the blackbody furnace. Using the same approach, it has been demonstrated that optical scattering in a simple radiance meter can be estimated from accurate optical diffraction measurement.

Optimization of a Graphite Tube Blackbody Heater for a Thermogage Furnace

Design modifications are presented for a 289-mm long, 25.4-mm inner diameter blackbody heater element of a 48 kW Thermogage blackbody furnace, based on (i) cutting a small “heater zone” into the ends of the tube and (ii) using a mixture of He and Ar or N2 to “tune” the heat losses and, hence, gradients in the furnace. A simple numerical model for the heater tube is used to model and optimize these design changes, and experimental measurements of the modified temperature profile are presented. The convenience of the Thermogage graphite-tube furnace, commonly used in many NMIs as a blackbody source for radiation–thermometer calibration and as a spectral irradiance standard, is limited by its effective emissivity, typically between 99.5% and 99.9%. The design simplicity of the furnace is that the blackbody cavity, heater, and electrical and mechanical connections are achieved through a single piece of machined graphite. As the heater also performs a mechanical function, the required material thickness leads to significant axial heat flux and resulting temperature gradients. For operation at a single temperature, changes to the tube profile could be used to optimize the gradient. However, it is desired to use the furnace over a wide temperature range (1,000–2,900°C), and the temperature-dependence of the electrical conductivity and thermal conductivity, and that of the insulation, makes this approach much more complex; for example, insulation losses are proportional to T4, whereas conduction losses are proportional to T. In the results presented here, a slightly thinner graphite region near each end of the tube was used to “inject heat” to compensate for the axial conduction losses, and the depth, width, and position of this region was adjusted to achieve a compromise in performance over a wide temperature range. To assist with this optimization, the insulation purging gas was changed from N2 to He at the lower temperatures to change the thermal conductivity of the felt insulation, and the effectiveness of this approach has been experimentally confirmed.

Experimental investigations on visualization of three-dimensional temperature distributions in a large-scale pulverized-coal-fired boiler furnace

By using a novel flame image processing technique, the 3-D temperature distributions of combustion in the pulverized-coal-fired boiler furnace of a 200 MW power generation unit were visualized experimentally. With the assumption of gray radiation, multiple color flame image detectors were used to capture approximately monochromatic radiation intensity images under the visible wavelengths of red (R), green (G), and blue (B), and a blackbody furnace was used to calibrate the color images. A way to calculate the radiation intensity using the Monte Carlo method was used to establish the relationship between the radiation flame images and the 3-D temperature distribution inside the furnace, given the radiative parameters such as the absorption and scattering coefficients of the combustion medium. A modified Tikhonov regularization method was used to reconstruct the 3-D temperature distribution from the 2-D flame temperature images transformed from the color flame images. Eight flame image detectors were mounted close to the four corners in four layers in different heights in the furnace, the 3-D temperature distribution in 1200 discrete meshes in 12 layers along the height of the furnace was reconstructed from the eight flame images, and the visualization result was updated within 5 s. The errors between some local temperatures visualized by the present system with those measured by a suction thermocouple were within ±5%, showing applicability of the method. On-line monitoring results demonstrated that the average temperature inside the furnace changed directly proportionally with the load of the unit. The preliminary results show that this technology will be useful for the combustion diagnosis and control in coal-fired power generation plants.

Development Method to Estimate the Complex Index of Refraction of Dielectric Aerosols

A method to estimate the complex refractive indices of dielectric aerosols is developed. The three-dimensional radiative transfer problem in an absorbing-scattering medium is solved by the Monte Carlo method. Mie scattering theory is used to handle particle scattering and absorption. Magnesium oxide aerosol, with its well-known complex index of refraction, is selected as an example of a dielectric aerosol. Magnesium is burnt to produce MgO aerosol and the transmission of the radiation from a black body furnace through the aerosol layer is measured. The analytical results of the transmitted energy profiles along the wall facing the emission source, a black body furnace, were obtained for a wide range of complex indices of refraction

A transportable blackbody furnace for the accurate realization of the fixed points of indium, tin and zinc

The design of a compact blackbody furnace that allows temperature fixed points to be realized to a high degree of accuracy is described. Using this apparatus, the standard uncertainty in the calibration of a precision infrared thermometer at the fixed-point temperatures of indium, tin and zinc was estimated to be about C. This furnace can be used as a travelling standard for intercomparisons as well as laboratory apparatus for the calibration of precision infrared thermometers.

熱赤外多素子検出器の背景放射低減と放射温度計の零点安定化

Infrared radiation thermometers measuring low temperature have an inherent problem of background radiation originated in themselves because inner parts of radiation thermometers radiate as bright as measurement objects. The problem is important to multielement radiation thermometers.To investigate background radiation of a multielement detector, angular dependence of responsivity of a 10-element InSb linear array was measured. The detector elements responded to radiation incidence from the outside of the field of view. Radiation from the outside of the field of view is mainly background radiation in an actual radiation thermometer.We developed a new optical method to reduce background radiation incidencee of thermal infrared detectors with cooling. A mirror iris was used in the method; it was a concave mirror having an aperture for signal radiation at the center. When the mirror iris is inserted into an optical pass between the detector and a lens, the detector observes the cold image reflected in the mirror surface.A thermal infrared radiation thermometer having the InSb array detector and the mirror iris was developed to evaluate the effect of the optical method. Zero drift of the radiation thermometer was largely reduced by the mirror iris without an optical chopper.Stability of the radiation thermometer observing a blackbody furnace maintained at 40°C was measured. The indicated temperature drift was less than ±0.9°C when the room temperature was varied in a range of ±6°C alternatively. The drift was improved to less than ±0.2°C with a compensation using the inner temperature of the radiation thermometer.

Modelling of the effective emissivity of a graphite black body

Measurements of the effective radiance temperature of a high-temperature graphite tube black-body furnace are compared with those calculated from two theoretical models. The first model extends the conventional annular zone model by including effects of vignetting and temperature gradients. Because the black-body surface is not a perfect diffuse reflector, this is found to be insufficiently accurate and a Monte-Carlo integration with a diffuse/Fresnel-specular surface model is presented, which gives good agreement with the measured data.

Measurement of Excited Oxygen (O2:1.DELTA.g) Concentration by Spontaneous Emission.

The concentration of excited oxygen (1Δg) generated by microwave discharge in a pure oxygen flow has been measured from the intensity of spontaneous emission. The conversion factor to density was determined from spectroscopic analysis of the rotational structure and calibration of the emission intensity using a black-body furnace as light source. Good agreement was found between the observed profiles and those calculated from spectroscopic data, and it was shown that the absolute concentration is obtainable by coupling band analysis and the calibration method. The concentration of excited oxygen at the microwave discharge cavity was estimated to be around 1% in the pressure range from 0.5 torr to 2 torr. Also, the comparison of the profiles calculated at different temperatures showed that the band profile can be a good indicator of gas temperature when the signal-to-noise ratio is high.

Infrared Detection by Si‐Ti‐C‐O Fibers

Electrical resistivity at 20° to 90°C and infrared (IR) responses (thermal time constant and responsivity of electrical resistance changes) were measured on Si‐Ti‐C‐O fibers. The fibers showed negative temperature coefficient resistance‐temperature characteristics, and the thermistor constant B was 890 to 4760 K. A fast and steady output (resistance change) was observed in response to IR radiation from a 600 K blackbody furnace. The IR response was affected markedly by detector structure; the thermal time constant decreased with decreasing length of the fibers, and the responsivity increased with decreasing number of the fibers. In an IR detector with a separate arrangement of a few (n=10) fibers with a short length (1 mm) and a low resistivity (80 Ω·cm), a thermal time constant of 3.5 ms and a responsivity of 63 V/W were obtained. A fast and steady IR response of Si‐Ti‐C‐O fibers suggests the possibility of detecting both stationary and moving IR sources.

Determining the integrated cavity emissivity of blackbody furnaces

An apparatus has been constructed for determining the integrated cavity emissivity of blackbody furnace simulators near 500 K and for calibrating infrared detectors. A difference-ratio method is described for measuring the radiant emission characteristics of the simulator by using a high-quality heat-pipe blackbody as a standard radiant source operated at 500 K and a water-immersed cavity as a reference source operated at a lower temperature. It is verified that the total uncertainties of the method are less than 0.6% for determining the integrated cavity emissivity and 0.5% for determining irradiance from the 500-K standard blackbody on the detectors.

A simple secondary standard radiation thermometer for use in industrial standards laboratories

A design of radiation thermometer is described which has been developed to transfer the calibration from fixed-point primary standard black-body sources to industrial black-body furnaces. Accurate interpolation can be achieved by a simple four-term polynomial. The thermometers are sufficiently stable to act as secondary standards in an industrial laboratory, with an uncertainty of better than ±0.5 K over the range 400–1250°C. The operation, evaluation and calibration of three thermometers are discussed.

Bandwidth effective emissivities of a nonisothermal blackbody furnace for calibrating broadband pyrometers

Bandwidth effective emissivities of a nonisothermal blackbody furnace for calibrating broadband pyrometers

放射温度計校正用標準黒体炉

A standard blackbody furnace for the calibration of commercially available radiation thermometers has been developed. This furnace has a cavity of chrome plated copper walls with an opening of 60mm in diameter. The furnace is designed so that the temperature of the cavity can be easily estimated by a resistance thermometer. It is shown that the furnace has an accuracy of 1K through the comparison with two fixed point blackbodies when the effective emissivity, the size-of-source effect and the absorption by water vapor of the air are corrected for.

Noncontact True temperature measurement

AbstractA laser pyrometer has been developed for acquiring the true temperature of a levitated sample. The laser beam is first expanded to cover the entire cross-sectional surface of the target. For calibration of such a system, the reflectivity signal of an ideal 0.95cm diameter gold-coated sphere (reflectivity = .99) is used as the reference for any other real targets. The emissivity of the real target can then be calculated. The overall system constant is obtained by passively measuring the radiance of a blackbody furnace (emissivity = 1.0) at a known, arbitrary temperature. Since the photo sensor used is highly linear over the entire operating temperature range, the true temperature of the target can then be computed. Preliminary results indicate that true temperatures thus obtained are in excellent correlation with thermocouple measured temperatures.

Experiments to Develop Large Aperture Blackbody Furnaces for Examination of Radiation Thermometers

Experiments to Develop Large Aperture Blackbody Furnaces for Examination of Radiation Thermometers

シリコン単色高温計

The practical standard in high temperature is maintained by tungsten strip lamps. In the past to use these lamps as standard, it was necessary to calibrate these lamps with other radiance sources using an intermediate instrument, the optical pyrometer. But the accuracy of an optical pyrometer is limited and insufficient for calibration; especially this instrument is not adequate for the calibration of blackbody furnaces. And the limitations impede the establishment of traceability of standard for commercial radiation thermometers.This pyrometer is on trial to remove the limitations of an optical pyrometer. This pyrometer adopts a silicon photocell as detector and operates with monochromatic light by an interference filter (λmax=0.649μm, Δλ=18nm) so as to calibrate the photocell directly to the tungsten strip, the effective wavelength of this pyrometer corresponds approximately to that of a lamp.The luminance temperature range is 1000°C to 2000°C with a resolution of 0.1°C and the stability is 0.2°C/month. This pyrometer may be useful as practical standard instrument.