Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Designing and constructing CPCs for solar photocatalytic applications

Solar collectors are the key component in any solar installation. After the identification of constructive, structural, mechanical and optical problems of different non-concentrating solar collectors systems, Compound Parabolic Concentrators (CPC) were selected as the best option for photocatalytic processes. CPC non-imaging concentrators, extensively employed for evacuated tubes, are static collectors with a reflective surface following an involute around a cylindrical reactor tube and have been found to provide the best optics for non-concentration systems.

The static behaviour of CPC solar collectors are a good technological solution in large volume of water treatment systems which adds to its capability to capture UV sunlight, coming with the diffuse as well as the direct beam; as the UV radiation is not absorbed by water, when clouds are present, an important portion of solar UV radiation reaches the earth surface as diffuse light.

This means that the Solar Detoxification process could works with solar light even in cloudy days. CPC design was optimized by performing a set of optical calculations, using tray-tracing tools, to stress the optical behaviour of this collector type. These calculations support the final design of the UV collection system and help on decisions taken for the design and constructive solutions selected, initially to collector�s prototypes and later to the final system design.

Final CPC reflectors, made of electropolished anodized aluminium, were constructed based on the following data design:
Acceptance angle 90º Truncation angle 90º
Concentration ratio 1.0 Optical gap 1.4mm
Ext. absorber radius 16.0mm Int.absorber radius14.6mm

The CPC reflector is made in high reflective anodised aluminium and collector frame is constructed with galvanised sheet frame and with 16 parallel tubes of 1.5 m length. Tubular reactor tubes are made of borosilicate glass with low iron content to enhance the transmissivity in the region of 300-400 nm. Each tube has at its end an appropriate connector for the tube of next adjacent collector. A complete module is formed by a series of collectors connected in a row. Collectors are designed to constitute long linear modules and treatment plants would be formed by parallel rows of modules with East-West orientation. Collectors and modules are also designed with a small structural tilt (1%) in the same E-W orientation as a way to dry-out and to avoid the accumulation of rain water on the CPC troughs. Fig. 2 shows the supporting structure of collectors, with different inclination angle capability.

System design is completely modular. Collectors are connected in series using HDPE quick connections between reactor glass tubes absorbers. Water flows simultaneously by all parallel tubes and modules have no limit in the number of collectors components. Two manifolds at the module extremes serve to water input and output.

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