Model Validation for Photosynthetically Active Radiation Transport and Multiphase Flow in Algal Photobioreactors

Iowa State University, Ames IA

Investigators

Abstract

CBET-1236676 Vigil Recent interest in algaculture is largely driven by the desire to acquire renewable alternatives for petroleum-based products. However, the development of commercially-viable algal biorefineries requires significant advancements not only in the bioengineering of robust, fast-growing microorganisms tuned to produce high-value products, but also substantial improvements in process engineering for more rapid and efficient production of algal products. Breakthroughs in the design and optimization of algal photobioreactors can be achieved through the implementation of highly accurate and computationally efficient numerical models of radiation transport and complex multiphase fluid phenomena that characterize these reactors. This research project directly addresses the need to develop reliable computational models capable of being used for the design and scale-up of algal photobioreactors. In particular, state-of-the-art two-phase computational fluid dynamics simulations of buoyancy-driven bubbly flows commonly found in photobioreactors will be validated by using index-of-refraction matching methods to carry out particle image velocimetry experiments with sufficient temporal and spatial resolution to rigorously test simulation predictions and to determine the importance of including various interface force models for drag, lift, virtual mass, rotation, and strain. The three-dimensional distribution of light in algal photobioreactors will be simulated by developing a novel spectral radiation transport model (based upon the method of discrete ordinates) that also accounts for the presence of bubbles and the optical effects of transparent reactor walls. Validation of the spectral radiation transport model will be achieved by carrying out a series of light measurements in a cylindrical algal bioreactor illuminated by filtered light sources that pass radiation with narrow bands of wavelengths in the photosynthetically active regime. After the computational fluid dynamics and radiation transport simulations have been validated, the interplay between the fluid dynamics and the radiation transport in the reactor will be explored by carrying out Lagrangian particle tracking simulations to compute light absorption histories experienced by individual algal cells, which is of paramount importance in determining the rate of production of biomass by these microorganisms. Algaculture is an increasingly attractive alternative for producing fuels and chemicals derived from petroleum, but the development of economically viable algal biorefineries requires significant improvements in both the engineering of elite microorganisms and in the design and scaleup of photobioreactors. This project will employ experimental methods and computer simulations to improve the understanding of how fluid motion and light distribution in algal photobioreactors impacts the production of biomass, and the results will form the basis for constructing a simulation tool for improving the design of production-scale equipment used in algaculture. The research will also provide educational opportunities for graduate and undergraduate students in a research area of strategic national importance.