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Research Papers

Analysis of a New Compound Parabolic Concentrator-Based Solar Collector Designed for Methanol Reforming

[+] Author and Article Information
Xiaoguang Gu

School of Mechanical and
Manufacturing Engineering,
The University of New South Wales, Sydney,
New South Wales 2052, Australia
e-mail: xiaoguang.gu@unsw.edu.au

Robert A. Taylor

School of Mechanical and
Manufacturing Engineering,
School of Photovoltaic and
Renewable Energy Engineering,
The University of New South Wales, Sydney,
New South Wales 2052, Australia
e-mail: rtaylor99@gmail.com

Gary Rosengarten

School of Aerospace, Mechanical, and
Manufacturing Engineering,
RMIT University,
115 Queensberry Street,
Carlton, Melbourne,
Victoria 3053, Australia
e-mail: gary.rosengarten@rmit.edu.au

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received November 19, 2013; final manuscript received May 21, 2014; published online June 11, 2014. Assoc. Editor: Dr. Akiba Segal.

J. Sol. Energy Eng 136(4), 041012 (Jun 11, 2014) (9 pages) Paper No: SOL-13-1344; doi: 10.1115/1.4027767 History: Received November 19, 2013; Revised May 21, 2014

Methanol reforming is a well-known method of producing hydrogen for hydrogen-based fuel cells. Since methanol reforming is an endothermic process, requiring an energy input, it is possible to use this reaction as a way to store primary energy. In this paper, we propose that this reaction can be driven with a vacuum packaged, nonimaging solar collector which has high overall efficiency. The linear compound parabolic concentrator (CPC) collector was designed with a half angle of 27.4 deg and a concentration ratio between 1.5 and 1.75 over this entire cone angle. Furthermore, due to its small size (90 mm × 72.6 mm × 80 mm), the design is portable. Selective surfaces, black chrome and TiNOX, are analyzed for the receiver to absorb solar (short wavelength) radiation while minimizing emission of thermal (long wavelength) radiation. Importantly, this design uses a vacuum layer between the receiver and the frame to minimize the convective heat loss. A ray-tracing optical analysis shows an optical efficiency of 75–80% over the entire half incident angle range. Stagnation tests show that under vacuum conditions, temperature up to 338 °C is achievable. Overall, the proposed design can achieve high temperatures (up to 250 °C) without tracking—which reduces overall cost, operational limitations, and enables a portable design.

Copyright © 2014 by ASME
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References

Figures

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Fig. 1

Schematic of the micro solar concentrator (not to real scale): (a) a cross section of the collector and (b) a close up schematic of the copper receiver, and (c) a cross section of the combined tube

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Fig. 2

Two-dimensional cross section schematic of designed CPC collector and flat absorber

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Fig. 3

Reflectance measurements of potential reflective surfaces

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Fig. 4

Reflectivity for varying incident angles as a function of wavelength

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Fig. 5

Reflectance of selective surface TiNOx and black chrome

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Fig. 6

Power received on bottom detector verses number of rays assumed in the model (note: grid independence is assumed at 200,000 rays)

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Fig. 7

Total gained power with and without a glass cover for an entrance aperture of about 47 cm2

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Fig. 8

Effect of mirror reflectivity on absorbed power

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Fig. 9

Ray paths in ray-tracing results for various transversal angles (the acceptance angle is 27.4 deg)

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Fig. 10

Energy flux distributions along the receiver width for different transversal angles ((a)–(f) correspond to 0, 10, 20, 25, 27.4—CPC acceptance angle and 30 deg, respectively)

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Fig. 11

Optical efficiency and heat flux as a function of longitudinal angle θL (θT = 0 deg)

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Fig. 12

Prototype of the designed CPC collector: (a) front view of prototype after milling in CNC system, (b) prototype with 3 M solar mirror film attached to its inside surface, and (c) assembled prototype of the designed micro collector

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Fig. 13

Experimental setup (not to scale)

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Fig. 14

Testing vacuum system

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Fig. 15

Stagnation temperatures for various heat fluxes

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