Study On Mixing Performance Of High Viscosity Solid-liquid Fluid Intensified By Rigid-flexible Combination Impeller

Mixing equipments are ubiquitous in the chemical industrial productions. Primarily,they import mechanical energy through the rotating agitator which could form suitableflow field. Hence, heat transfer and mass transfer strengthened and mixing efficiencyimproved. High viscosity solid-liquid two-phase mixing is a common unit operation inthe field of petroleum, food, pharmaceutical, polymer materials and so on. Existingproblems are when power consumption (Pv) is small, easy accumulation of particles cannot effectively disperse, when Pvis large, the two phase achieve good mixing, but theshaft bearing torque is too large that easy to cause mechanical loss, especially notsuitable for shear sensitive polymer system. Therefore, it is necessary to explore a wayto gain good mixing of high viscosity solid-liquid in the moderate power consumption.It is well known that impeller is a core component of the mixing equipment, energyinput to tank fluid by rotating impeller, so designing a suitable impeller is a reasonableway to obtain efficient mixing. This work aimed to enhance fluid mixing by reformingstirred impeller, based on the traditional rigid impeller, a new type of rigid-flexiblecombination impeller formed with addition of flexible components, this new impellerwould reduce dead volume by utilizing the rigid-flexible-fluid coupling action to spreadenergy fully to the whole tank.In this paper, glycerol was used as the liquid phase and PP particles as the solidphase. A torque sensor collected torque signal and then the largest Lyapunov exponent（LEmax）was calculated with Matlab to analyze the chaotic characteristics of fluids instirred tank. Acid and alkali chemical bleaching method was used to determine systemmixing time（tmix）which was reference to analyze mixing performance.Fluent was usedto simulate flow field structure to search the characteristics of the internal structure offluid. Combined with experimental study and numerical simulation, to determine wetherrigid-flexible combination impeller was better for mixing of high viscosity solid-liquidthan the traditional rigid impeller. The specific contents were as follows:①The acquisition of torque time series data of each system with virtual torquesensor was used to calculate LEmax, compared the chaotic mixing of floating particlesystem and sinking particle system caused by rigid impeller and combination impeller,results showed as follows: combination impeller could bring good chaotic mixing whenthe power consumption was low（Pv<3000w·m-3）, chaotic mixing for rigid impeller would not have obvious change with increase of solid holding-up（Cv）,but forcombination impeller system, chaotic mixing enhanced with the increasing of Cv.②Used acid and alkali chemical bleaching method to determine mixing time（tmix）of each system, analysis the influence of different impeller on mixing performance, alsodifferent length of flexible component was investigated such as2cm,3cm,4cm. Theexperimental results were logtmixand logPvshowed good linear relationship which hadnothing to do with impeller type; compared with the rigid impeller, combinationimpeller could greatly shorten tmix, and the longer flexible component, the better mixingefficiency; when the two types impeller had the same length, combination impeller hadobvious advantages, it could effectively reduce tmix.③The flow field structure of rigid impeller and combination impeller was simulatedby Fluent. With study of velocity contours, velocity vector diagram and speed scatterplots, it could see that flow field showed good axial symmetry structure for differentimpeller; for the determine combination impeller, too small or too large Pvcould notcause ideal result, system mixing effect was better when Pvwas3500w·m-3; when thetwo types impeller had the same length, combination impeller had obvious advantageswith its roll force than the shearing action that caused by rigid impeller.④Compared with experimental and simulation results, it showed that rigid-flexiblecombination impeller could effectively promote the mixing of high viscositysolid-liquid than the rigid impeller.