A New Design of a (3D) Fresnel Collector With Fixed Mirrors and Tracking Absorber

[+] Author and Article Information
A. B. Larbi

Conservatoire National des Arts et Métiers, laboratoire de Thermique Industrielle, 292, rue Saint-Martin, 75141 Paris cedex 03, Francee-mail: benlarbi@cnam.fr

J. Sol. Energy Eng 122(2), 63-68 (May 01, 2000) (6 pages) doi:10.1115/1.1286364 History:
Copyright © 2000 by ASME
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Artist view of a (3D) Fresnel collector with fixed mirrors and tracking absorber
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Quadrant (oxy) of (3D) Fresnel concentrator. Only one elementary mirror is shown for clarity of illustration. (xi,yj)=Cartesian coordinates of the elementary mirror in the (x,y,z) reference. φ=azimuth angle of the elementary mirror. l=length of the elementary mirror. c=center of the elementary mirror.
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Optical analysis. Only one elementary mirror is shown. The effective solar half-angle θs is grossly exaggerated for clarity of illustration. (z0,z1,z2,z3)=corners of the elementary mirror. (I1̰,I2̰,I3̰,I4̰)=incident rays. (R1̰,R2̰,R3̰,R4̰)=reflected rays. N̰=normal to the elementary mirror. W=West direction. S=South direction.
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(a) Optimization method parameters. z01=intersection point of P(z01,di,dj) with the optic axis of the collector. (hs±di)=rotation of P(z01,di,dj) around the y-axis. (δ±dj)=rotation of P(z01,di,dj) around the x-axis. hs=local solar-hour angle. F=focal length. E=East direction. S=South direction. W=West direction. (b) Optimization method. A schematic illustration of the positions occupied by the plane P(z01,di,dj) for the case of normal incident rays (hs=0 and δ=0). The tinted parts represent the intersection of the reflected rays with P(z01,di,dj) (it is not a real presentation of the spots of points). dy=diameter of the absorber.
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Optimal design of the Fresnel concentrator. It represents the set of elementary mirrors in the circle for which the diameter is equal to the length of the basic square concentrator. The number of elementary mirrors is reduced to 400 instead of 484.
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Variation of the concentration ratio (CR) as a function of the incidence angle (i) (solar declination=0) and the number of elementary mirrors, for two types of Fresnel concentrators with the same total area of reflecting mirrors and the same focal length (or rim half-angle). One of the concentrators is built with flat elementary mirrors and the other with curved ones.
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Flux density along the receiver surface as a function of the incidence angle. The concentrator is built with 400 curved elementary mirrors. The total area of reflecting mirrors is 9 m2 .
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Energy delivery by unit absorber area as a function of the position along the absorber and the incidence angle. The concentrator is built with 400 curved elementary mirrors. The total area of reflecting mirrors is 9 m2 .




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