Flow Field Characteristics And Field Synergy Analysis Of Flexible-Bionic-Blade Impeller

The mixing process is an important basic unit operation in chemical industries.Attention is being paid to the green economy as climate problems have become more and more serious.The energy utilization of mixing equipment is becoming more and more important.Low energy consumption and high efficiency have become the requirements for mixing technology.Some studies show that the bionic corrugated groove structure and flexible materials which can play the role of fluid-structure coupling have certain advantages in reducing energy consumption.In nature,there are grooves in the flippers of humpback whales and the caudal fins of fish.The bionic shape can stabilize eddy currents and reduce energy dissipation and noise.The flexible material makes the blade have self-adaptive ability when working,and deforms with different speed,reduces the shear force at blade tip,makes the energy transfer smoother.In order to reduce the consumption and increase the efficiency of the mixing process,this thesis designs seven new stirring blades with corrugated groove bionic structure based on the bionics knowledge and analyses by CFD numerical simulation.Among them,the PBDT-V stirring paddle is selected,a flexible material(rubber)was used to make a flexible bionic blade in order to replace the rigid blade of PBDT-V.The improvement of mixing effect was studied by the fluid-solid interaction simulation and electrical resistance tomography solid-liquid suspension experiment.The flow resistance and mass transfer capacity were analyzed by the synergy angle.Seven bionic blades were designed based on the bionic structure,and their power consumption and circulating flow intensity were compared and analyzed by numerical simulation.In terms of power consumption,each bionic impeller scheme can effectively reduce the stirring power consumption,which can be reduced by 8.767%at most.From the point of view of circulating flow strength,the bionic scheme with corrugated groove at the edges of the blades obviously improved the circulating strength of the stirred tank.From the perspective of velocity and pressure field synergy,the synergy angle of velocity and pressure gradient at the bottom of the bionic impeller stirred tank will decrease slightly,thus enhancing the mass transfer effect at the bottom area.Taking the bionic impeller with wavy structure on the blade edge as an example,the flow field characteristics at different moments in the mixing process were analyzed.The velocity in flow field of the bionic impeller was larger at the initial mixing stage,and the component dispersion effect was better.In the process of mixing,the synergy angle between velocity and concentration gradient in the flow field of bionic impeller is smaller than traditional impeller,which further reveals the reason for better mass transfer effect of the bionic impeller.The bionic impeller with wavy structure on the blade edge was selected,and the rigid blade was replaced by the flexible material.The bionic flexible blade impeller was simulated by the two-way fluid-solid interaction technology,and compared with the rigid blade impeller and the flexible straight blade impeller.The results show that it has certain adaptive ability because of the deformation of flexible blade.It’s power consumption reduced because of the flexible blades,but the average velocity of the flow field reduced too.The deformation of the flexible blade changes with time,causing an unstable flow field,increasing the flow velocity in the low-speed region and reducing the dead zone.According to the field synergy angle distribution,it can be found that the flexible blade increases the velocity and pressure gradient synergy angle near the impeller,thus reducing the flow resistance and energy loss.For the region far away from the impeller,the synergy angle is reduced,which is beneficial to mass transfer.The solid-liquid suspension experiment of rigid straight blade impeller,rigid bionic blade impeller,flexible straight blade impeller,flexible bionic blade impeller was designed by the electrical resistance tomography technology.The conductivity data can be converted to the data of the non-conducting solids concentration distribution by Maxwell equation.The results show that the axial distribution of solid concentration of the flexible bionic impeller is smoother,which means a better axial solid-liquid suspension ability of the flexible bionic impeller.