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Research Papers

A Transient Thermography Method to Separate Heat Loss Mechanisms in Parabolic Trough Receivers

[+] Author and Article Information
Marc Röger

German Aerospace Center (DLR),
Institute of Solar Research,
Plataforma Solar de Almería,
Tabernas 04200, Spain
e-mail: marc.roeger@dlr.de

Peter Potzel

Institute of Thermodynamics and Thermal
Engineering (ITW),
University of Stuttgart,
Stuttgart 70550, Germany

Johannes Pernpeintner

German Aerospace Center (DLR),
Institute of Solar Research,
Cologne 51147, Germany

Simon Caron

German Aerospace Center (DLR),
Institute of Solar Research,
Plataforma Solar de Almería,
Tabernas 04200, Spain

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received January 14, 2011; final manuscript received May 13, 2013; published online xx xx, xxxx. Assoc. Editor: Eckhard Luepfert.

J. Sol. Energy Eng 136(1), 011006 (Jul 16, 2013) (9 pages) Paper No: SOL-11-1024; doi: 10.1115/1.4024739 History: Received January 14, 2011; Revised May 13, 2013

This paper describes a transient thermography method to measure the heat loss of parabolic trough receivers and separate their heat loss mechanisms. This method is complementary to existing stationary techniques, which use either energy balances or glass envelope temperature measurements to derive overall heat losses. It is shown that the receiver heat loss can be calculated by applying a thermal excitation on the absorber tube and measuring both absorber tube and glass envelope temperature signals. Additionally, the emittance of the absorber selective coating and the vacuum quality of the annulus can be derived. The benefits and the limits of the transient method are presented and compared to the established stationary method based on glass envelope temperature measurements. Simulation studies and first validation experiments are described. A simulation based uncertainty analysis indicates that an uncertainty level of approximately 5% could be achieved on heat loss measurements for the transient method introduced in this paper, whereas for a conventional stationary field measurement technique, the uncertainty is estimated to 17–19%.

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References

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Figures

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Fig. 1

Heat transfer system overview

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Fig. 2

Sketch of the lumped capacitance model for the glass envelope tube

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Fig. 3

Simulation results for five receivers with different characteristics under various external air velocities ranging from 0.2 to 10 m/s

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Fig. 4

Illustration of the three-dimensional model discretization scheme, fluid mass flow, and heat transfer mechanisms, labeled from 1 to 7

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Fig. 5

Annulus heat loss (gas heat conduction and natural convection) at different annulus pressures for a PTR 70. Ta = 350 °C, Tamb = 25 °C; Tg variable, wind 0 m/s

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Fig. 6

Receiver heat loss (left) and glass envelope temperature (right). Comparison of NREL experimental data [2] (circle) with simulation results (numerical model, Sec. 3, cross) and experimental results (transient measurements, triangle) for an intact Schott PTR 70 receiver.

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Fig. 7

Radiation shield design

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Fig. 8

Temperature oscillation measured for the absorber tube (continuous line) and the glass envelope (dashed line) during the experiment 2 (T¯a = 386 °C; T¯g = 91 °C)

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