Study On Mixing Characteristics Of Gas-liquid Two Phase Flow In Tubular Photobioreactor With Combined Rotors

As one of the microalgae industrialized cultivation technology products,biodiesel is considered as a clean renewable energy source with broad development prospects.As a microalgae cultivation equipment for large-scale,industrialized biodiesel raw materials,photobioreactor(PBR),it should have the characteristics of low cost,high output,and easy maintenance.The tubular photobioreactor(T-PBR)stands out from many types of PBR because of its advantages of large specific surface area,closed antifouling and good maneuverability.However,there are also problems such as poor mass transfer performance,easy deposition of microalgae,and difficulty in amplification.For these defects,by improving the internal structure of the T-PBR and optimizing the flow field,the volume of the reactor is increased,the effect of mixing and mass transfer of the fluid is improved,the distribution of the microalgae in the pipe is improved,and the overall performance of the T-PBR is improved.This is a great significance for improving the production of microalgae and guiding large-scale production.This article briefly introduced the research progress of biodiesel preparation by microalgae and the factors affecting the growth of microalgae.The structure,advantages and disadvantages,and application prospects of typical PBRs are described in detail.The structure,principle and application of the "JIE NENG XIN" combined rotor for improving the mixing characteristics of T-PBR fluids are mainly described.The combination of computational fluid dynamics(CFD)simulation analysis and visual experimental verification is used to optimize the structure of T-PBR with combined rotors and promote the mixing of gas-liquid two phase flow.In this paper,a fin rotor with arc-shaped hem structure is designed and compared with the two-blade rotor.The results show that the special structure of the fin rotor can significantly increase the gas holdup rate in T-PBR and improve the gas liquid.The mass transfer effect between the two phases,compared with the two-bladed rotor tube and the light pipe,increased the gas holdup by 53.77%and 26.5%respectively,which is favorable for the absorption of carbon sources by microalgae.This paper analyzes the gas-liquid two phase flow mixing characteristics of T-PBR at different inclination angles(0°,30°,60°,and 90°).The results show that gas velocity and turbulent kinetic energy increase with the increase of inclination angle.The effect of the built-in rotor is even more obvious.Therefore,under the condition of 90° inclination and built-in rotor,the mixing ability of the gas-liquid two phase flow fluid is stronger,which is more conducive to the growth of microalgae.In this paper,a large-diameter multi-rotor series T-PBR is simulated.Explore the influence of factors such as the number of rotor strings,rotor arrangement,and rotor type on the flow field.The results show that the different rotor arrangement patterns that can be overlapped by rotation do not affect the mixing performance of the liquid-phase fluid,but have a greater influence on the gas-phase fluid;within a certain range,there are multiple sets of rotor-string-type piping arranged in a single ring.The mixing performance is better than the mixing performance of the same number of rotor strings in the annular arrangement of inner and outer rings;under the premise of unchanged pipe diameter and without affecting the normal rotation of the rotor,increasing the number of rotor strings can significantly improve the mixing performance of the T-PBR.In this paper,a visual experiment of large-diameter multi-rotor string T-PBR is carried out,and the accuracy of simulation methods and results is verified intuitively.It is concluded that the rotational symmetry of combined rotor arrangement forms a difference in the continuous-phase flow field.Small;under the experimental conditions,appropriate increase in the number of rotor strings can significantly increase the mixing effect on the liquid phase fluid;after the gas phase floats on the top of the pipeline,the uppermost rotor can agitate the rotor arrangement form of the gas-liquid interface,mixing effect better.