Byard Wood

Design and Performance of a Solar Photobioreactor Utilizing Spatial Light Dilution

A photobioreactor with an optical system that spatially dilutes solar photosynthetic active radiation has been designed, built, and tested at the Utah State University Biofuels Center. This photobioreactor could be used to produce microalgal biomass for a number of purposes, such as feedstock for an energy conversion process, or high-value products, such as pharmaceuticals and nutraceuticals. In addition, the reactor could be used to perform services such as removing nitrates, phosphates, and other contaminants from waste water, as well as scrubbing toxic gases and carbon dioxide from flue gas. Preliminary tests were performed that compared growth and productivity kinetics of this reactor with that of a control reactor without spatial light-dilution. Tests indicated higher specific growth rates and higher areal and volumetric yields compared with the control reactor. The maximum specific growth rate, volumetric yield, and areal yield were 0.21 day ―1 , 0.059 gm l ―1 day ―1 , and 15 gm m ―2 day ―1 , respectively. Over 10 days of sequential-batch operation, the prototype photobioreactor converted direct-normal solar energy to energy stored in biomass at an average efficiency of 1 %. The areal productivity, as mass per aperture per time, was three times higher than that of the control reactor, indicating the photobioreactor design investigated holds promise.

Dynamic Prescribed Vortex Wake Model for AERODYN/FAST

A new aerodynamic wake model has been developed for horizontal axis wind turbines. The aim is to develop an engineering tool for investigation and design of furling turbines. The prescribed vortex wake code HAWTDAWG, developed at the University of Glasgow, has been extended for dynamic flow conditions. This dynamic prescribed wake model is built into the aerodynamic code AERODYN and linked to the structural dynamics code FAST. The new model has been compared to unsteady aerodynamic experiment Phase VI wind tunnel data. Comparisons are also made to blade element momentum and generalized dynamic wake models built into AERODYN. Results are encouraging and justify further investigation.

Prediction of light-transmission losses in plastic optical fibers

A theoretical expression is derived, based on a geometrical optics approach, with which to predict light-transmission losses in multimode plastic optical fibers for office or home lighting. Two types of optical ray arrangement, meridional ray and skew ray, are evaluated, and five loss mechanisms are identified and considered. The meridional arrangement results in a lower overall loss of light than the skew ray arrangement. The theoretical results were compared with experimental measurements taken for a 0.5-cm-diameter polymer optical fiber. For optical rays entering the fiber at incident angles of less than 20 degrees, the theoretical results are in good agreement with the empirical results.

Optical Design of an Infrared Non-Imaging Device for a Full-Spectrum Solar Energy System

A full-spectrum solar energy system is being designed by a research team lead by Oak Ridge National Laboratory and the University of Nevada, Reno. [1,2] The benchmark collector/receiver and prototype thermophotovoltaic (TPV) array have been built [3J, so the work performed here is to match the two systems together for optimal performance. It is shown that a hollow, rectangular-shaped non-imaging (NI) device only 23 cm long can effectively distribute the IR flux incident on the TPV array mounted behind the secondary mirror. Results of the ray-tracing analysis of the different systems tested are presented.

Economic Analysis of a Vertical Sheet Algal Photobioreactor for Biodiesel Production

The combination of a 100% increase in diesel fuel prices since 2002 and a new photobioreactor technology has renewed interest in producing biodiesel, a direct petroleum diesel fuel substitute, from microalgae. A new photobioreactor technology in which the microalgae are grown on vertically suspended membranes promises to increase algal productivity per acre ten-fold compared to microalgae ponds, and 400-fold compared to soybeans. This paper describes the general photobioreactor concept and assesses the economic viability of such technology given the current crude oil prospects. The majority of the data necessary for assessment are obtained from published articles, with experimental results providing the remaining necessary information. Analysis results indicate that the photobioreactor would need to be constructed and operate on the order of dollars per square foot per year.Copyright

Computational Fluid Dynamics Analysis of Vertical Mixing in Algae Biofuel Raceways Through the Addition of Delta Wings at Angle-of-Incidence

CFD calculations of experimental algae raceways under consideration for biofuel production studies were performed in an effort to assess the effectiveness of delta wing vortex formation as a means of enhancing vertical mixing. The impact of delta wings on the level of turbulence dissipation rate in these raceways was also investigated. All simulations were completed at a constant level of power input into the raceway. Velocity profiles as well as characteristic mixing times were used to analyze and quantify the vertical mixing both with and without delta wings. The velocity profiles and turbulent dissipation rate calculations suggest that delta wings are a viable method of increasing vertical motion. However, the mixing time results for the configuration of delta wings tested suggest that the additional mixing was insignificant to the raceway as a whole. Additional work on optimizing the use of delta wings is suggested.Copyright

Effect of Solids Removal From Dairy Manure Feedstock on Biogas Production in Anaerobic Digesters

Many modern anaerobic digesters in developed countries consist of a digestion process in which solids are reduced to biogas, followed by mechanical separation that removes the majority of the remaining solids from the effluent. Experience has shown that such systems are often plagued with plugging due to excessive solids in the digester influent. Moreover, the mechanical separation equipment is prematurely degraded due to the elevated temperatures and corrosive compounds in the digester effluent. Reversing the order of separation and digestion offers a proven method of eliminating these problems, but at the expense of lower biogas production. The work presented in this paper quantifies this difference in biogas production by comparing the biogas yields of dairy wastewater feedstocks with and without prior mechanical solids separation through a 0.75-mm screen. Laboratory-scale batch digesters were operated up to 40 days at 35–40 °C and monitored for mass of volatile solids consumed and biogas production. Although the initially separated influent contained only half as much volatile solids, the ultimate biogas yield was only 25% less than that obtained with non-separated influent, demonstrating some tradeoff between higher energy production and system reliability.Copyright

Design and Performance of a Photobioreactor Utilizing Spatial Light Dilution

A photobioreactor with an optical system that spatially dilutes solar photosynthetic active radiation has been designed, built, and tested at the Utah State University Biofuels Center. This photobioreactor could be used to produce microalgal biomass for a number of purposes, such as feedstock for an energy conversion process or high-value products such as pharmaceuticals and nutraceuticals. In addition, the reactor could be used to perform services such as removing nitrates, phosphates, and other contaminants from waste water, as well as scrubbing toxic gases and carbon dioxide from flue gas. Preliminary tests were performed that compared growth and productivity kinetics of this reactor with that of a control reactor simulating a pond. Tests indicated higher specific growth rates and higher areal and volumetric yields compared with the control reactor. The maximum specific growth rate, volumetric yield, and areal yield were 0.21 day−1 , 0.059 gm L−1 day−1 , and 15 gm m−2 day−1 , respectively. Over 10 days of sequential-batch operation, the prototype photobioreactor converted direct-normal solar energy to energy stored in biomass at an average efficiency of 1%. The areal productivity, as mass per aperture per time, was three times higher than that of the control reactor, indicating the photobioreactor design investigated holds promise.Copyright

Ray Trace Analysis for Concentrating Sunlight Onto an Optical Fiber Bundle

A two-axis concentrating solar collector/receiver is being designed to concentrate visible solar irradiance and distribute it inside a building for daylighting via a bundle of polymer optical fibers. This paper is concerned with the optics that will provide uniform illuminance of the visible spectrum on the entrance of the fiber optic bundle. A fiber optic bundle made of 3mm diameter fibers and a non-imaging device along with the solar collector’s primary and secondary mirrors has been modeled in a ray-tracing software package, TracePro 3.3. Fiber optic bundles of two different geometries were considered, viz. a square bundle with 225 fibers and a round bundle consisting of 126 fibers. The purpose of this research is to determine the optimum length of the non-imaging device that could provide uniform illuminance on the entrance area of the fiber optic bundles. Sensitivity analyses are conducted to see the variations in the output due to different possible off-set conditions, such as distance between the primary and the secondary mirror, the secondary mirror off-set from the primary mirror optical axis, and misalignment due to tracking error. The results of the sensitivity analyses are presented, and recommendations are made for the design of the non-imaging device. It is shown that the square non-imaging device and fiber bundle is superior to the round non-imaging device and fiber bundle.Copyright

Demonstration of Thermophotovoltaics for a Full-Spectrum Solar Energy System

A non-imaging (NI) device and thermophotovoltaic (TPV) array for use in a full-spectrum solar energy system has been designed, built, and tested [1,2,3]. This system was designed to utilize the otherwise wasted infrared (IR) energy that is separated from the visible portion of the solar spectrum before the visible light is harvested. The IR energy will be converted to electricity via a gallium antimonide (GaSb) TPV array. The experimental apparatus for the testing of the IR optics and TPV performance is described. Array performance data will be presented, along with a comparison between outdoor experimental tests and laboratory flash tests. An analysis of the flow of the infrared energy through the collection system will be presented, and recommendations will be made for improvements. The TPV array generated a maximum of 26.7 W, demonstrating a conversion efficiency of the IR energy of 12%.Copyright