Microalgae Culture Panel Reactor Flow And Mass Transfer Numerical Simulation

Microalgae has great value in various fields such as food, pharmacy, chemical industry, environment protection, biofuel and so on, however, it's difficult to provide continuous, adequate and cheap biomass for the large-scale commercial use of microalgae during current research period of microalgal cultivation. So, it's of great importance to advance the culture technology of microalgae, especially the technology of reactor, which is crucial to realize the cultivation of high proficiency and low cost. Panel reactor is a kind of closed reactor for microalgal culture. Because of the complexity of the reactor's internal flow and mass transfer, its design and amplification still largely depend on experience and theoretical guidance, meanwhile cost higher and need long period of design. Therefore, the research for flow and mass transfer of reactor is particularly pressing. This paper used CFD (Computational Fluid Dynamics) on studying its flow characteristics of the panel reactor, in order to provide for high-density cultivation of microalgae with excellent performance and technical parameters of the reactor.Firstly, this paper used Fluent software, Eulerian-Eulerian model to simulate the gas-liquid two phase flow field in the panel reactor, make mesh-independent test and establish the number of mesh. The comparison between simulation experimental values demonstrated the feasibility and reliability of CFD simulation.Cultivation experiments of Scenedesmus dimorphu in different panels with and without single baffles had been carried out, and the results showed that more algal biomass had been reached with baffled panels. Under the aeration ratio of 0.1～0.6 vvm, the simulation results showed that the fluid flow field was divided into riser and the downcomer by the single baffle. Liquid circulated around the baffle and liquid velocity increased with the increase of aeration ratio. The bubbles mainly concentrated in the riser, and gas holdup and kLa drawn almost linearly with the increase of aeration ratio.Under the aeration ratio of 0.3 vvm, baffle location had a significant effect on the flow and mass transfer. When the A_d / A_r was less than 0.5, large vortex and the swing bubbles were observed. When the A_d / A_r = 2, it achieved the maximum liquid mass transfer coefficient 2.65×10^-3 s^-1 . The length of the baffle made little difference on the liquid flow field, average gas holdup and kLa, but influenced the liquid velocity. When the length of baffle was 0.28 m ,it reached the maximum liquid velocity in both the riser and downcomer.Panel with double vertical baffles improved the liquid velocity compared with that with single baffle, however, the averaged gas holdup and kLa had no significant difference. However the panel installed double waved-baffles had higher gas holdup and mass transfer coefficients , increased by 14.9% and 14.6% compared with that with double vertical baffles, respectively. The flow velocity contour and flow vector with double waved-baffles and double vertical baffles were almost same, but better liquid circulation around baffles, faster liquid velocity in the riser and comparatively slower liquid velocity in the downcomer were reached . With the increase of aeration ratio, liquid velocity, the averaged gas holdup and kLa increased near linearly.Waved-baffle enhanced the volumetric mass transfer of the panel. A good linear relationship between the kLa and the energy input per unit volume of the waved-baffle panel reactor had been obtained..Through a comprehensive analysis including the average gas holdupεg, volumetric mass transfer coefficient kLa and liquid cycle time ratioθbetween riser and downcomer of the wave-baffled panel by simulation, an optimal structure of waved-baffle panel reactor had been determined as follows: A_d / A_r = 1.62,h₀ = 260 mm,h₁ = 20 mm, and the parameters h₀, h₁ greatly impacted on mass transfer of the panel reactor.