Optimization Of Tubular Microalgal Photo-bioreactors With Spiral Fins

Nowadays,with the increasingly prominent environmental problems,microalgae gradually come to people's visions as potential clean energy resources.That microalgae will not occupy food-crop lands and are raw materials for many products make it more room for development relative to other energy crops.At present,the large scale cultivation of microalgae is limited by the development of photobioreactors.Tubular photobioreactor(PBR)is the promising one because continuous cultivation and systematical control and management can be realized in it.The yield of microalgae is related to light/dark(L/D)cycle frequency in PBRs and thus improving the frequency is exactly the object of many designs and optimizations of PBRs.In this thesis,spiral fins were introduced in tubular PBRs so as to improve the average L/D cycle frequency.The CFD technology was used to simulate the flow fields while the software,Matlab,was adopted to do postprocessing.The influences of microalgal PBRs' structural and operating parameters on L/D cycle performances were studied.The optimum combination of factors was obtained through orthogonal experimental design,that is,the combination of unilateral illumination,PBRs with one spiral fin whose inclined angle is 60 ° and the inlet velocity of microalgae suspension is 0.5m/s.Under these conditions,the average L/D cycle frequency is 2.28 Hz and the L/D cycle enhancement efficiency is 1.22.Among all the simulated particles,73.6 % of them finish their L/D cycles and among which,47.6 % of particles experience L/D cycles with the frequency of 2~3 Hz.The simulation results under the light conditions of unilateral illumination and bilateral illumination at a constant total light intensity were compared and analyzed.It was concluded that the average L/D cycle frequency of algae could not be enhanced by introducing spiral fins in PBRs under bilateral illumination.It is necessary to increase the number of algae that experience L/D cycle and the L/D cycle frequency of individual cells so that the average L/D cycle frequency can be increased.It can be achieved by adjusting the position of L/D boundary in the light field combining with the flow field.