Computational Fluid Dynamics plays an important role in industries as it analyzes the results without performing the actual experiments. A model of an external loop airlift photobioreactor with a cross-shaped sparger was developed using FLOTRAN software as per the design. Flow patterns of Anabaena ambigua culture were studied inside external loop airlift photobioreactor for different velocities viz., 1 m/s, 1.5 m/s, 2 m/s, 2.5 m/s, and 3 m/s. The velocity contour plots give information on dead zones, zones with maximum velocity, zones with minimum velocity, and whether the circulation of fluid is possible or not. From the simulation studies, it can be concluded that for the above said velocities viz., 1 m/s, 1.5 m/s, 2 m/s, 2.5 m/s, and 3 m/s the culture was displaced upward along the riser and came down through the external loop under the influence of gravity. As the model was working, an external loop airlift photobioreactor was fabricated according to the design and real-time experiments were carried out. From real-time experiments, the biomass formation was estimated at different velocities and was observed that maximum biomass was obtained at a velocity of 1.5 m/s.