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Research Papers

Pyrometric Temperature Measurement in Concentrated Sunlight With Emissivity Determination

[+] Author and Article Information
Nathan B. Crane

Department of Mechanical Engineering, University of South Florida, Tampa, FL 33620

J. Sol. Energy Eng 132(1), 011007 (Dec 21, 2009) (8 pages) doi:10.1115/1.4000351 History: Received October 17, 2008; Revised September 02, 2009; Published December 21, 2009

Pyrometers are commonly used for high temperature measurement, but their accuracy is often limited by uncertainty in the surface emissivity. Radiation heating introduces additional errors due to the extra light reflected off the measured surface. While many types of specialized equipment have been developed for these measurements, this work presents a method for measuring high temperatures using single color pyrometers when the surface emissivity is unknown. It is particularly useful for correcting errors due to reflected light in solar heating applications. The method requires two pyrometers and is most helpful for improving measurement accuracy of low cost commercial instruments. The temperature measurements of two pyrometers operating at different wavelengths are analyzed across a range of sample temperatures to find the surface emissivity values at each wavelength that minimize the difference in temperature measurements between pyrometers. These are taken as the surface emissivity values, and the initial temperature measurements are corrected using the calculated emissivity values to obtain improved estimates of the surface temperature. When applied to temperature data from a solar furnace, the method significantly decreased the difference in the temperature measurements of two single color pyrometers. Simulated temperature data with both random noise and systematic errors are used to demonstrate that the method successfully converges to surface emissivity values and reduces temperature measurement errors even when subjected to significant errors in the model inputs. This method provides a potential low cost solution for pyrometric temperature measurement of solar-heated objects. It is also useful for temperature measurement of objects with unknown emissivity.

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Figures

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Figure 1

Typical solar furnace data set

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Figure 2

Detector response of the pyrometers used in the test (18) (arbitrary units)

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Figure 3

Estimated errors from single color approximation for short and long wavelength pyrometers. Two single color wavelength values for the long wavelength pyrometer are compared.

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Figure 4

Solar furnace temperature data after emissivity adjustment and temperature correction.

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Figure 5

Distribution of the accuracy of the emissivity and temperature solutions for different error types when applied to temperature data from 400–2200°C: (a) 5.21 μm pyrometer temperature, (b) 1.56 μm pyrometer temperature, (c) 5.21 μm pyrometer emissivity, and (d) 1.56 μm pyrometer emissivity. Data sets: noise only—random temperature error; Noise+Model—adds a systematic pyrometer model error; 10% flux error—simulates a 10% error in the flux input to the model; zero flux—applies to the case without a solar flux on the sample.

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Figure 6

Distribution of the accuracy of the emissivity and temperature solutions for different error types when applied to temperature data from 1600–1800°C: (a) 5.21 μm pyrometer temperature, and (b) 1.56 μm pyrometer temperature data sets: noise only—random temperature error; Noise+Model—adds a systematic pyrometer model error; 2% emissivity error—simulates a 2% variation in the emissivity across the temperature range; zero flux—applies to the case without a solar flux on the sample

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