Impact of Dropwise Condensation on the Biomass Production Rate in Covered Raceway Ponds

Jack Hoeniges, Keyong Zhu, Jeremy Pruvost, Jack Legrand, El-khider Si-Ahmed and Laurent Pilon
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Jack Hoeniges: Mechanical and Aerospace Engineering Department, Henry Samueli School of Engineering and Applied Science, University of California, Los Angeles, CA 90095, USA
Keyong Zhu: School of Aeronautical Science and Engineering, Beihang University, Beijing 100191, China
Jeremy Pruvost: Université de Nantes, Oniris, CNRS, GEPEA, UMR 6144, F-44600 Saint-Nazaire, France
Jack Legrand: Université de Nantes, Oniris, CNRS, GEPEA, UMR 6144, F-44600 Saint-Nazaire, France
El-khider Si-Ahmed: Université de Nantes, Oniris, CNRS, GEPEA, UMR 6144, F-44600 Saint-Nazaire, France
Laurent Pilon: Mechanical and Aerospace Engineering Department, Henry Samueli School of Engineering and Applied Science, University of California, Los Angeles, CA 90095, USA

Energies, 2021, vol. 14, issue 2, 1-23

Abstract: This study investigates the effect of condensed water droplets on the areal biomass productivity of outdoor culture systems with a free surface, protected by a transparent window or cover to prevent contamination and to control the growth conditions. Under solar radiation, evaporation from the culture causes droplets to condense on the interior surface of the cover. To quantify the effect of droplets on the system’s performance, the bidirectional transmittance of a droplet-covered window was predicted using the Monte Carlo ray-tracing method. It was combined with a growth kinetics model of Chlorella vulgaris to predict the temporal evolution of the biomass concentration on 21 June and 23 September in Los Angeles, CA. A droplet contact angle of 30 ∘ or 90 ∘ and a surface area coverage of 50% or 90% were considered. Light scattering by the condensed droplets changed the direction of the incident sunlight while reducing the amount of light reaching the culture by up to 37%. The combined effect decreased the daily areal biomass productivity with increasing droplet contact angle and surface area coverage by as much as 18%. Furthermore, the areal biomass productivity of the system was found to scale with the ratio X 0 / a of the initial biomass concentration X 0 and the specific illuminated area a , as previously established for different photobioreactor geometries, but even in the presence of droplets. Finally, for a given day of the year, the optical thickness of the culture that yielded the maximum productivity was independent of the window condition. Thus, the design and operation of such a system should focus on maintaining a small droplet contact angle and surface area coverage and an optimum optical thickness to maximize productivity.

Keywords: light transfer; photobioreactor; biofuel; bioprocess engineering; design; modeling (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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