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Research Papers

An Air-Based Cavity-Receiver for Solar Trough Concentrators

[+] Author and Article Information
Roman Bader

Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland

Maurizio Barbato

Department of Innovative Technologies, SUPSI, 6928 Manno, Switzerland

Andrea Pedretti

 Airlight Energy Holding SA, 6710 Biasca, Switzerland

Aldo Steinfeld1

Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland; and Solar Technology Laboratory, Paul Scherrer Institute, 5232 Villigen PSI, Switzerlandaldo.steinfeld@ethz.ch

1

Corresponding author.

J. Sol. Energy Eng 132(3), 031017 (Jun 29, 2010) (7 pages) doi:10.1115/1.4001675 History: Received March 28, 2010; Revised April 14, 2010; Published June 29, 2010; Online June 29, 2010

A cylindrical cavity-receiver containing a tubular absorber that uses air as the heat transfer fluid is proposed for a novel solar trough concentrator design. A numerical heat transfer model is developed to determine the receiver’s absorption efficiency and pumping power requirement. The 2D steady-state energy conservation equation coupling radiation, convection, and conduction heat transfer is formulated and solved numerically by finite volume techniques. The Monte Carlo ray-tracing and radiosity methods are applied to establish the solar radiation distribution and radiative exchange within the receiver. Simulations were conducted for a 50 m-long and 9.5 m-wide collector section with 120°C air inlet temperature, and air mass flows in the range 0.1–1.2 kg/s. Outlet air temperatures ranged from 260°C to 601°C, and corresponding absorption efficiencies varied between 60% and 18%. Main heat losses integrated over the receiver length were due to reflection and spillage at the receiver’s windowed aperture, amounting to 13% and 9% of the solar power input, respectively. The pressure drop along the 50 m module was in the range 0.23–11.84 mbars, resulting in isentropic pumping power requirements of 6.45×1040.395% of the solar power input.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Cross-sectional view of the cavity-receiver configuration: (1) absorber inner surface, (2) absorber outer surface, (3) cavity inner surface, (4) window inner surface, (5) window outer surface, and (6) shell outer surface

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Figure 2

(a) Half profile of the CCT concentrator and (b) simulated radiative flux distribution at the focal plane of CCT and ideal parabolic trough concentrators. Focal length fconcentrator=3.5 m and rim angle ϕrim=73.6 deg.

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Figure 3

Air outlet temperature Tair,out, receiver absorption efficiency ηabsorption, and mechanical pumping power requirement Wp,s, for air mass flow rates in the range 0.1–1.2 kg/s

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Figure 4

Heat flows by modes in %, normalized by the total concentrated incident solar power Qsolar; the diagram reports the useful energy gain and specifies the different contributions to energy losses for air mass flow rates in the range 0.1–1.2 kg/s

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Figure 5

Thermal losses and air temperature (black curve) as a function of position along the receiver axis x, mair=0.4 kg/s

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Figure 6

Local absorption efficiency as a function of the local air temperature; parameter is the air mass flow rate; for comparison, the absorption efficiency of a commercial Schott PTR70 receiver is shown in (16)

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Figure 7

Electric pumping power requirement in % of estimated electric power output for one module of given length; parameter is the absorber tube radius

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