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RESEARCH PAPERS

# Pyrometric Temperature Measurements on Solar Thermal High Temperature Receivers

[+] Author and Article Information
Markus Pfänder, Eckhard Lüpfert, Peter Heller

Institute of Technical Thermodynamics, German Aerospace Center (DLR), PSA, Apartado 39, E-04200 Tabernas, Spain

J. Sol. Energy Eng 128(3), 285-292 (Apr 06, 2006) (8 pages) doi:10.1115/1.2210499 History: Received June 21, 2005; Revised April 06, 2006

## Abstract

The knowledge of the absorber surface temperature distribution is essential for efficient operation and further development of solar thermal high temperature receivers. However, the concentrated solar radiation makes it difficult to determine the temperature on irradiated surfaces. Contact thermometry is not appropriate and pyrometric measurements are distorted by the reflected solar radiation. The measurement in solar-blind spectral ranges offers a possible solution by eliminating the reflected solar radiation from the measurement signal. The paper shows that besides the incoming solar radiation and the absorber emittance, the bi-directional reflection properties and the temperature of the object are determining for the required selectivity of the spectral filter. Atmospheric absorption affects the solar blind pyrometric measurements in absorption bands of $CO2$ and water vapor. The deviation of temperature measurement due to atmospheric absorption is quantified and the possibilities and limitations of accounting for the atmospheric absorption with models based on radiation transfer calculations are discussed.

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## Figures

Figure 1

Concentrated solar spectrum based on LOWTRAN calculated AM1 spectrum, concentrator reflectance and blackbody irradiances at typical operation temperatures

Figure 2

Relative temperature errors of a pyrometer (CW=4.56μm, HW=0.08μm) due to solar reflections (solid lines) and due to emittance uncertainties (dashed lines) as function of temperature

Figure 3

Solar radiance after reflection at concentrator compared to blackbody irradiances and the transmittance of fused quartz (GE214, d=8mm)

Figure 4

Transmittance of the solar blind filter together with an AM1.5 solar radiance spectrum

Figure 5

Relative changes in effective atmospheric band transmittance for the 2.625μm filter as a function of the H2O column density. For an ambient temperature of T=293K and pressure P=96kPa the dependence of the effective transmittance on the mixing ratio and path length is shown.

Figure 6

Nomogram for the determination of the temperature error after atmospheric correction resulting from a measurement uncertainty in atmospheric water content

Figure 7

Experimental setup of the temperature measurement at the pressurized volumetric receiver

Figure 8

Temperature distribution of the high temperature volumetric absorber at an air outlet temperature of approximately 800°C

Figure 9

Temperature distribution on the quartz window at an air outlet temperature of approximately 800°C

Figure 10

Experimental setup of the pyrometric temperature measurement at the EuroTrough test loop

Figure 11

(a)–(c) Infrared images of the UVAC absorber tube (above), the Schott-PTR-70 (middle), and the temperature profile across the absorber tube

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