A numerical framework to predict the performances of a tubular photobioreactor from operating and sunlight conditions

International audienceA framework model is proposed to evaluate the actual overall growth rate of microalgae in an outdoor tubular photobioreactor. A Monte Carlo-based radiative transfer modeling approach describes the local distribution of light energy inside the broth as a function of static (reactor geometry, location) and dynamic solar radiation parameters (angle of incidence, direct and diffuse solar contribution, incident radiation intensity). The light fields are coupled to a Lagrangian discrete random walk tracking of the cells to give the light variations experienced by each microalga for different broth flow rates. The cell light experiments are combined with a dynamic biological model to statistically calculate the actual overall growth rate. Using this model, 380 numerical experiments were performed for a wide range of geographic, light, biomass concentration, and broth flow turbulence conditions. Correlations for a normalized growth rate, Gamma, relating the actual overall growth rate to its asymptotic behaviors (i.e., the instantaneous response and the full integration response), are proposed. The results clearly show that, for a fixed broth flowrate, Gamma does not change with cell concentration variation. Under given light conditions, the level of turbulence linearly manages Gamma, and thus the efficiency of sunlight utilization by the photobioreactor biomass can be tuned by the broth flow rate in the tubular photobioreactor. Gamma also increases linearly with the diffuse fraction of solar radiation. A simple correlation is proposed for fast calculation of the actual overall growth rate

Characterization of a low pressure capacitively coupled RF discharge in N₂-H₂

Discharges operated in mixtures of hydrogen and nitrogen are nowadays used as a source of active species for various kinds of applications from etching of low-k materials to modifications of polymer surfaces for biomedical applications. Moreover these kinds of discharges can provide information relevant for studies of planetary atmospheres. The present work involves the study of a low pressure capacitively coupled RF discharge operated in variable mixtures of N2 and H2 at variable pressures and powers. The systematic measurements of electron density, RF voltage, self bias and the observation of several molecular bands by means of optical emission spectroscopy gave us important information about basic processes relevant for the understanding and application of such kind of discharges. The experimental results are interpreted by means of a hybrid model, namely the effect of admixing hydrogen into a N2 discharge

Longitudinal Hierarchy Co3O4 Mesocrystals with High-dense Exposure Facets and Anisotropic Interfaces for Direct-Ethanol Fuel Cells

Novel electrodes are needed for direct ethanol fuel cells with improved quality. Hierarchical engineering can produce catalysts composed of mesocrystals with many exposed active planes and multi-diffused voids. Here we report a simple, one-pot, hydrothermal method for fabricating Co 3 O 4 /carbon/substrate electrodes that provides control over the catalyst mesocrystal morphology (i.e., corn tubercle pellets or banana clusters oriented along nanotube domains, or layered lamina or multiple cantilevered sheets). These morphologies afforded catalysts with a high density of exposed active facets, a diverse range of mesopores in the cage interior, a window architecture, and vertical alignment to the substrate, which improved efficiency in an ethanol electrooxidation reaction compared with a conventional platinum/carbon electrode. On the atomic scale, the longitudinally aligned architecture of the Co 3 O 4 mesocrystals resulted in exposed low- and high-index single and interface surfaces that had improved electron transport and diffusion compared with currently used electrodes