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Numerical analysis of the effects of air on light distribution in a bubble column photobioreactor
McHardy, Christopher,Luzi, Giovanni,Lindenberger, Christoph,Agudo, Jose R.,Delgado, Antonio,Rauh, Cornelia Elsevier 2018 Algal research Vol.31 No.-
<P><B>Abstract</B></P> <P>Light distribution inside photobioreactors (PBR) is a crucial parameter for the determination of growth of phototropic microorganisms and reactor productivity. In order to compute the light propagation inside PBR, scattering due to the presence of microorganisms is often neglected, since it is difficult to measure experimentally and it is not trivial to handle numerically. Moreover, absorption is usually assumed constant, but it is affected by the concentration of microorganisms and the presence of gas bubbles. In the present contribution we study how the flow hydrodynamics and local gas fractions inside a bubble column PBR affect the light distribution. First, we perform numerical simulations of a bubble column flow at different gas superficial velocities. Afterwards, we use instantaneous air volume fractions to calculate the effective scattering and absorption coefficient of the mixture, as well as the effective scattering phase function. Finally, we compute the polychromatic light distribution inside the PBR by means of a Lattice-Boltzmann solver. On the one hand, we find that gas bubbles affect both spatial distribution and magnitude of the light intensity field and their impact increases at higher gas superficial velocity. On the other hand, we also observe that the biomass counteracts these effects already at concentrations less than 1 kg/m<SUP>3</SUP> so that the role of the gas phase on light fields seems to be of minor importance in PBR.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hybrid numerical simulation of fluid flow and light distribution in a photobioreactor. </LI> <LI> Spatial distribution of gas bubbles affect symmetry and magnitude of the light intensity field. </LI> <LI> Increasing biomass concentration suppresses the effects of the gas phase. </LI> <LI> Role of the gas phase on light fields is of minor importance for cell growth in photobioreactors. </LI> </UL> </P>
Rioja, Marí,a J.,Dodson, Richard,Jung, TaeHyun,Sohn, Bong Won,Byun, Do-Young,Agudo, Ivá,n,Cho, Se-Hyung,Lee, Sang-Sung,Kim, Jongsoo,Kim, Kee-Tae,Oh, Chung Sik,Han, Seog-Tae,Je, Do-Heung,Ch American Institute of Physics 2014 The Astronomical journal Vol.148 No.5
<P>The Korean VLBI Network (KVN) is a new millimeter VLBI dedicated array with the capability to simultaneously observe at multiple frequencies, up to 129 GHz. The innovative multi-channel receivers present significant benefits for astrometric measurements in the frequency domain. The aim of this work is to verify the astrometric performance of the KVN using a comparative study with the VLBA, a well-established instrument. For that purpose, we carried out nearly contemporaneous observations with the KVN and the VLBA, at 14/7 mm, in 2013 April. The KVN observations consisted of simultaneous dual frequency observations, while the VLBA used fast frequency switching observations. We used the Source Frequency Phase Referencing technique for the observational and analysis strategy. We find that having simultaneous observations results in superior compensation for all atmospheric terms in the observables, in addition to offering other significant benefits for astrometric analysis. We have compared the KVN astrometry measurements to those from the VLBA. We find that the structure blending effects introduce dominant systematic astrometric shifts, and these need to be taken into account. We have tested multiple analytical routes to characterize the impact of the low-resolution effects for extended sources in the astrometric measurements. The results from the analysis of the KVN and full VLBA data sets agree within 2σ of the thermal error estimate. We interpret the discrepancy as arising from the different resolutions. We find that the KVN provides astrometric results with excellent agreement, within 1σ, when compared to a VLBA configuration that has a similar resolution. Therefore, this comparative study verifies the astrometric performance of the KVN using SFPR at 14/7 mm, and validates the KVN as an astrometric instrument.</P>