(237w) Characterization of Bubble Dynamics and Local Gas Holdup in a Cylindrical Airlift Photobioreactor during Microalgae Culturing

Airlift photobioreactors have been widely used in chemical and biochemical fields. However, in the literature, the details of bubble properties and local gas hold up in this kind of reactors, unfortunately, are still unclear because of the limitations of the classical measurement techniques, and that too mostly in air-water process. Thus, during real culturing systems, the bubble dynamics properties such as interfacial area, bubble chord length, bubble velocity, and bubble passage frequency, and also the local gas holdup are required [1-3]. In this study, a 5.5 inches diameter of cylindrical split internal-loop photobioreactor as shown in Figure 1 was used at different superficial gas velocities which varying between 1.0 to 2.8 cm/s when the green Scenedesmus sp microalgae were culturing, and along the axial height for split-photobioreactor at the radial direction in the center for both, the downcomer and the riser sections. As shown in Figure 2, an advanced four-point optical fiber probe has been used for this measurements. The culturing medium was monitored by using optical density device and the viscosity and surface tension properties were monitored as well. as a result, the local gas holdup was increased as well as with the interfacial area and bubble passage frequency, all are visible in this system with also a rise up in superficial gas velocity, and decrease at the optical density which is related to the growth of microalgae, while there is no a big change in surface tension in this experiment. On the other hands, the values of the bubble velocity and bubble chord length have been seen bigger at higher superficial gas velocity and higher optical density; but at the same time, there is no considerable difference in the axial direction for the properties of the bubble. Moreover, these results were shown in the riser section, an axial different in these properties were obtained in the downcomer due to the reduced in the bubbles' number of inclined in the downcomer section.