New CPC Solar Collector for Planar Absorbers Immersed in Dielectrics. Application to the Treatment of Contaminated Water

[+] Author and Article Information
Julio Chaves

 Lpi-Light Prescription Innovators, 16662, Hale Av., Irvine, CA 92606

Manuel Collares Pereira

 INETI-DER, Edificio G, Az. dos Lameiros, 1649-038, Lisboa, Portugal

J. Sol. Energy Eng 129(1), 16-21 (Nov 18, 2005) (6 pages) doi:10.1115/1.2390949 History: Received June 24, 2005; Revised November 18, 2005

The most energetic part of the solar radiation spectrum can be used in the presence of a catalyst (Photo Catalysis) or in Photo Fenton techniques to treat chemically or biologically contaminated water. This process requires an efficient optics to collect and deliver solar radiation to the liquid to be treated. Non Imaging Optics provides the most efficient way to collect solar radiation and in the present paper we describe one optical solution for absorbing surfaces holding the catalyst and immersed in the water to be treated. The water circulates in UV and blue transparent glass tubes and the absorber is a flat fin parallel to the optical axis of the system. An optical solution is derived, achieving maximum concentration without rays being geometrically rejected. However, it is shown that this concentration falls short by a small margin of the maximum concentration predicted by ideality in Non Imaging Optics because of caustic formation inside the dielectric. In the paper we present an example developed for the investigation of photocatalysis in the treatment of biologically contaminated waters.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Concentrator for a vertical fin. The mirror has two sections. The parabolic arc from B to Q reflects to tip F of the receiver the edge rays of the incoming radiation. Portion QR of the mirror is an arc of circumference with center F.

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Figure 2

In order to maximize the entrance aperture dimension, the angle α must be as large as possible at every point P on the mirror. This means minimizing angles β and γ that the incoming ray r and the reflected ray make to the horizontal.

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Figure 3

In order to maximize angle α, angles γ and β must be minimized, restricted by the conditions that all the radiation must be captured and that there should be no losses

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Figure 4

Circular receiver of radius ri surrounded by a layer of dielectric of external radius re. If ri=re∕n, a ray tangent to the outer surface is refracted tangent to the inner receiver. In this case, all the radiation hitting the outer surface ends on the receiver.

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Figure 5

The first portion of the mirror, extending from R to P2, reflects to point F the light coming from that same point

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Figure 6

The edge rays perpendicular to the plane wave front w form a caustic inside the tube. Therefore, these rays cannot be used to continue the design of the mirror.

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Figure 7

A new section of the mirror is obtained by reflecting to edge F of the receiver the rays tangent to the mirror (a). The new portion of the mirror is calculated by constant optical pathlength, as shown in (b).

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Figure 8

From point P4 on, the edge rays perpendicular to wave front w are visible from the mirror and can be used to design it by constant optical pathlength

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Figure 9

For small acceptance angles, the mirror has an extra portion that concentrates rays at the angle θ to the tip F of the receiver

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Figure 10

If the height of the receiver is larger than re+ri, not all the rays exiting F will exit the tube, but will TIR. Therefore, for the portion of the tube between P1 and P4, the light will not be directed by the mirror to point F, but will be reflected tangent to the tube.

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Figure 11

The designs presented above are not ideal and therefore can accept light rays outside the acceptance angle. From a bundle of parallel rays beyond the acceptance angle, as rays r1 and r2 and r3 in this figure, some may be accepted (r1 and r2) and some rejected (r3).

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Figure 12

There is a “dark” angle δ for the receiver points between T and R. The receiver cannot receive light coming from outside the tube inside this angle. The edge rays of the receiver are shown in (b). “Dark” angle δ is related to angle φ by φ=δ∕2.

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Figure 13

Radiation coming from outside the tube and that the receiver can capture

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Figure 14

The ratio between the etendue of the radiation captured by the collector and the maximum the receiver can accept

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Figure 15

Effect of considering a tube surrounding and holding the water



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