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Potential Applications of Concentrated Solar Photons (1991)

Chapter: Appendix D: Intensity Influence

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Suggested Citation:"Appendix D: Intensity Influence." National Research Council. 1991. Potential Applications of Concentrated Solar Photons. Washington, DC: The National Academies Press. doi: 10.17226/1843.
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APPENDIX D
Intensity Influence

The photocatalytic process at a TiO2 particle can be schematically represented in a simplified reaction scheme as:

The actual reaction mechanism is more complicated and can involve a number of intermediates, such as hydroxyl radicals species adsorbed on the TiO2 surface, radicals, and radical ions.

A summary of literature and Solar Energy Research Institute data [1] for the effect of intensity [irradiance (photons/area-time)] on the photocatalyzed rate of oxidation indicates that at or above I sun near-ultraviolet equivalence, the reaction rate varies as the square root of intensity. This square root dependence can be rationalized by the increased importance of processes like e-h+ recombination [Eq. (4)] and the reaction of photogenerated e- and h+ with intermediates. A collector also brings a reflectance loss. The impact of these two phenomena on the achievable rate is now estimated (see Figure D-1).

A. Photon Rate Arriving at Catalyst

i. Plate: (direct + diffuse)(area)

= (Id + 0.25Id)(1.0)

= 1.25 Id (photons/time)

ii. Concentrator:

(direct)(collector x-section) + (diffuse)(tube x-section)

(0.8 Id)(1.0) + (0.25Id)(0.1)

(reflectance = 0.8)

= 0.825Id

Suggested Citation:"Appendix D: Intensity Influence." National Research Council. 1991. Potential Applications of Concentrated Solar Photons. Washington, DC: The National Academies Press. doi: 10.17226/1843.
×

FIGURE D-1 Illustration of calculation for configurations and concentrator.

B. Rate Loss

Let PR = photon rate

RA = reactor area

Since intensity I = PR/RA and rate per unit area varies as the square root of I,

Rate = (rate per area)(area)

Suggested Citation:"Appendix D: Intensity Influence." National Research Council. 1991. Potential Applications of Concentrated Solar Photons. Washington, DC: The National Academies Press. doi: 10.17226/1843.
×

REFERENCE

1. Turchi, C., and Ollis, D.F. J. Catal. 119, 483 (1989).

Suggested Citation:"Appendix D: Intensity Influence." National Research Council. 1991. Potential Applications of Concentrated Solar Photons. Washington, DC: The National Academies Press. doi: 10.17226/1843.
×
Page 64
Suggested Citation:"Appendix D: Intensity Influence." National Research Council. 1991. Potential Applications of Concentrated Solar Photons. Washington, DC: The National Academies Press. doi: 10.17226/1843.
×
Page 65
Suggested Citation:"Appendix D: Intensity Influence." National Research Council. 1991. Potential Applications of Concentrated Solar Photons. Washington, DC: The National Academies Press. doi: 10.17226/1843.
×
Page 66
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This book reviews current work and assesses the state of the art in potential applications of concentrated solar energy in nonelectric areas, such as water and waste treatment, photochemical processes, and materials processing. It identifies and recommends research needed for further development of promising applications.

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