The high cost of microalgae cultivation is one of the major hurdles in large scale production of microalgal biofuels. Cultivation in closed photobioreactors (PBR) to achieve high culture concentrations is a potential solution. However, existing PBR designs do not have the desired efficiencies, and lead to high material and energy costs. Therefore, novel PBR designs need to be developed and benchmarked against existing designs. This work has proposed a novel PBR design by combining two existing designs, namely, the airlift and flat plate PBRs. The novel design uses the concept of riser and downcomer from the airlift PBR. However, the downcomer has flat surfaces resembling a flat plate PBR The hydrodynamic performance of the novel PBR was studied using Computational Fluid Dynamics (CFD), and the performance was compared with that of the conventional airlift PBR. The dimensions of the novel design were then optimized using CFD simulations. The results showed that the novel design had superior liquid circulation properties that resulted in a regular and alternative exposure to light and dark regions of the PBR. The novel design also had about 7% higher surface area to volume ratio as compared to a conventional airlift PBR. (C) 2014 Elsevier Ltd. All rights reserved.