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Abstract

Recently, fossil fuel depletion and global warming have become critical issues in need of urgent solutions. One approach toward this, the use of new and renewable energy, has attracted considerable attention. Among renewable energy sources, bio-fuel developed using microalgae is considered promising. This thesis presents results of optical design and fabrication of light guiding plates (LGPs) to be used as illumination systems for photobioreactors, with which mass production of microalgae is commonly accomplished. First, modeling of light sources, reflection films, and LGP patterns was performed. The LGP patterns were modeled as Lambertian scatterer. The modeling parameters (Reflectance: 50 %, Scatterer Width: 1.8 mm) were determined through matching simulations with the experimentally measured illuminance distribution for a test LGP. LGPs for an LED (light emitting diode) source and sunlight were designed with the extracted model parameters. In the case of the LGP for sunlight, a linear Fresnel lens was employed for light focusing. Design parameters for the LGPs included maximum pattern spacing, minimum pattern spacing, and the width of the Gaussian function for pattern spacing. LGPs for photobioreactors were fabricated using a CNC (computerized numerical control) machine. In the case of the LGP (size: 500 mm × 500 mm × 10 mm) for an LED source, the driving circuits for LEDs and plates for the heat sink were also designed and fabricated. In the case of the LGP (size: 500 mm × 600 mm × 10 mm) for sunlight, a mechanical frame for holding the Fresnel lens and the LGP was designed and fabricated. Two types of LGPs were fabricated and tested for LED source. The average illuminance for these two LGPs was 20,300 lx (photon flux density: 261 μE/(m^2·s)) and 17,150 lx (photon flux density: 198 μE/(m^2·s)) and the uniformity of the illuminance distribution was 71.8 % and 50.1 %, respectively. For the LGP for sunlight, the average illuminance and the uniformity of illuminance distribution were 21,110 lx (photon flux density: 372 μE/(m^2·s)) and 67.8 %, respectively. The LGPs fabricated in our work are presently being utilized as an illumination system for a flat-panel photobioreactor developed at the Biorefinery Center, Chosun University. This photobioreactor is being used to grow Chlorella and Dunaliella, and bio-diesel will be extracted from the biomass produced by these microalgae species. Modification of the light collecting system for sunlight and development of the LED-solar hybrid type LGPs are actively underway.