| Agitation equipment, especially the mechanical agitation equipment, are widely used in various process industries in order to realize the transfers of momentum, heat and mass, and the chemical reaction among gaseous, liquid and solid materials simultaneously. The main purpose for investigating the dynamic characteristics of the agitation system is to find out the characteristics and rules of the interaction between the fluids in the stirred vessel and the agitation system, which can be used as important references for the optimum design of the industrial agitation equipment. The key issues of the research are:(1) calculation of the critical speed in agitation system and the analysis of the relevant factors;(2) analysis of the dynamic forces applied to the agitation system and their effects on the system. Because of the complexity of the interaction between solid and fluid, it is impossible to theoretically analyze and calculate the key issues mentioned above until now. Therefore, investigation on the dynamic characteristic in the agitation system is mainly carried out by means of the combination of experimental, analytical and numerical simulation methods.An integrated and optimized experiment system for dynamic characteristics of varies agitation systems, designed, manufactured and installed all by this work, was established to measure the critical speed of the agitation system studied and the loads applied to the system. The experiment system consists of twenty-four high speed data capture channels and high precision laser optical displacement sensors, which can be used to realize the synchronizing measurement of bending moment, torque, axial force, deflection and rotating speed with fast data transmission speed and good stability. Simultaneously, the experimental modal analysis of the critical speed in the agitation system can be realized. The term of key phase was firstly introduced to the measuring method which applies for the agitation system successfully by which we can gain the agitator axis load and swing with any rotating number of turns. The experiment system implements modularizing management based on the data demanded for the practical application, establishes the analysis method and the processing program separately, and predigests the analysis operation of the dynamic characteristic in agitation system.The comparison between the experimental results of the critical speed and various analysis calculations shows that first order critical speeds calculated by the Kuilse method and the finite element are in good agreement with the experimental result of modal method when the agitation system is rotating in the air. However, the calculation error for the first order critical speed is much bigger while using the HG/T20569standard method. When the agitation system is rotating in the water, the error of measuring the attenuation vibration is within5%on the basis of the data gained by the experimental modal method; whereas the measurement error based on the finite element calculation is much bigger. The equivalent annexation mass calculation methodology was proposed so as to correct the mass factor in the finite element modal for the axial flow CBY impeller.The supporting rigidity of the agitation system has significant influence on the critical speed and the corresponding swing style. When the supporting rigidity is poor, the numerical value of the critical speed in every order descends evidently and moves to the low frequency area so that the probability of the sympathetic vibration and the existence of the critical speed in low frequency range increases. From the sight of XY plane which is vertical to the agitator shaft, the distribution rule of the critical speed in every order was determined by the supporting rigidities distribution of the agitation system rotating with X and Y axes. When difference of the supporting rigidities in X and Y directions is very small, the critical agitation speeds pair with almost same values is existed. Otherwise, the critical speeds in the pair are different.Bending moment is an unstable load, the direction and value of which in different cross section of agitation shaft is changed totally random. The distribution of bending moment vs time is different from that of the torque. The fluctuating range based on the average value of the bending moment is even larger than the average value itself. The trajectory curve of vector terminal of the bending moment not only has a circumference of the average value, but also has an enveloping circumference. The size and direction of the radial vibrating displacement in the agitation shaft change in a completely random way. Similar as the trajectory curve of vector terminal of the bending moment, a circumference of the average value and an enveloping circumference exist in the trajectory curve of the agitation shaft.The concept of "design bending moment" is proposed based on the statistic phenomenon that the enveloping circle of bending moment exits. The probability that actual bending moment is larger than the designed bending moment is<0.2%on conditioned that the designed bending moment is defined as the sum of the mean value of the bending moment and2.6times of the standard deviation and the ratio of the agitation speed to the critical agitation speed is less than80%. The assumption of the designed bending moment can be used in the industrial design. The dimensionless designed bending moment coefficient CmL is first time defined as:(?) which is an improvement for the radial flow force coefficient in the literatures and valuable for engineering design. It considers the interaction between the flow and the solid synthetically under the operational condition, and covers the variety regulations of the bending moment in the agitation shaft for different operations.In order to the further study on the interaction between fluid and solid, the flow patterns were studied by means of PIV experiments and CFD numerical simulation in a stirred tank with single or dual PBT impellers. The high turbulent kinetic energy region for single PBT is smaller than that of dual PBT for the same liquid level, impeller diameter and Renault number. The dimensionless turbulent kinetic energy regions of0.02for the dual PBT have the tendency to converge. There is a single trailing vortex structure behind PBT, in which the displacement in radial direction is smaller than that in axial direction. The energy was transferred from the impeller to the bulk flow by means of the high turbulent kinetic energy region moving together with the trailing vortex. The velocity and structure of trailing vortex for single PBT predicted by the standard k-ε model is consist with those from PIV experiments. However, the predicted turbulent kinetic energy was lower than that from experiment. |
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