Enhancing microalgal biomass productivity with an optimized flow field generated by double paddlewheels in a flat plate photoreactor with CO 2 aeration based on numerical simulation.

•An optimized flow field was generated by double paddlewheels in a photoreactor.•Bubble size reduced by 24.4%, and bubble rising velocity reduced by 10.6%.•Flash cycle frequency increased by 3.46-fold in the optimized flow field.•Microalgal biomass accumulation improved by 62.3%.