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The Impact of Air Flow Rate on Photobioreactor Sparger/Diffuser Bubble Size(s) and Distribution

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  131620764,  2013 Kansas City, Missouri, July 21 - July 24, 2013. (doi: http://dx.doi.org/10.13031/aim.20131620764) @2013
Authors:   Anil R. Kommareddy, Gary A. Anderson, Stephen P. Gent, Ghazi S. Bari
Keywords:   Photobioreactor mixing bubble diameter bubble regime sparger bubble size determination image analysis superficial gas velocity homogenous flow regimes heterogeneous flow regimes system design

Abstract. Air with carbon dioxide is often bubbled through photobioreactors (PBR) growing green and blue-green algae to mix the growth medium with the suspended algae. The mixture of bubbles (1) maintains alga, nutrient, and temperature distribution uniformity, (2) removes oxygen from the growth medium produced as a byproduct of photosynthesis, and (3) adds carbon dioxide to the growth medium to replace carbon dioxide consumed in photosynthesis. The air often enters the PBR growth medium as bubbles through a sparger/diffuser located near the bottom of the reactor. The bubbles rise up through the growth medium in the reactor, mix and exchange gases with the growth medium and exit through the top of the reactor. Mixing with bubbles needs to be understood to improve the efficiency of the PBR system. Bubble diameters are need for the understanding of the volumetric mass transfer coefficient in the system. A PBR was tested with flow rates of 2-8 liter/min from the sparger and the bubble sizes are determined using high speed video camera data and image analysis tools in Matlab software. The bubble size distribution spaned from 1 to 3 mm for flow rates of 2 – 8 liter/min. The bubble regime was determined to be homogenous regime.

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