Research On Design Methodology And Performance Of The Vertical Kneading Mixers

Mixing operation is an important procedure of solid propellant manufacture, and the vertical kneading mixer is the key device to fulfill this procedure. In this dissertation, according to differential geometry, rheology, stochastic process theory and computational fluid dynamics (CFD), some key techniques existing in the design of vertical kneading mixers and performance analysis are systematically investigated by combining theoretical analysis with engineering practice.Firstly, some crucial problems existing in the design process of the vertical kneading mixers are proposed by analyzing the material characteristic of solid propellant and its mixing requirements. Then, the configuration and operating mechanism of the device are investigated. On the basis of the results mentioned above, methods and indices to analyze and evaluate the performance of the vertical kneading mixers, namely torque, pumping capacity, mixing efficiency, reliability and etc, are also presented.Secondly, methods to numerically simulate and analyze the fluid field in the mixing tank of the vertical kneading mixers are proposed by means of application geometry, rheologic theoretic and finite element methods. The methods include developing 3D modeling process of the kneading blades by analyzing the transmission characteristics of the self-rotating speed and the planetary revolution speed of them, establishing the physical and mathematical models of the flow field in the mixing tank of vertical kneading mixers, determining the boundary conditions of numerical simulation, and deeply investigating the characteristics of velocity field, flow pattern, pressure distribution and viscosity distribution of the mixing field numerically simulated by means of CFD software such as ANSYS CFX10.0.Thirdly, the selecting ranges and design rules of some key structural parameters are proposed by investigating their influence on the vertical kneading mixers via numerical simulation and theoretical analysis. The influence of the ratio of the planetary revolution speed to the self-rotating speed of the hollow kneading blade is studied at first, the studied results show that better mixing performance can be achieved if the speed ratio is designed to be lower enough. The helix angle of the kneading blade is then investigated, and the results illustrate that the preferable torque characteristic, higher pumping capacity and steady shearing rate can be achieved when the value of the helix angle of the hollow kneading blade is chosen between 42°and 48°. Also, the investigation of the mixing clearance shows that small mixing clearance can improve the mixing performance of the vertical kneading mixers, and that the lowest power consumption can be achieved if diversified mixing clearances have the same value when the other parameters are determined.Furthermore, to investigate the relationship of the processing parameters and the mixing performance of the vertical kneading mixers, numerical simulation models diversified with different processing parameters which include rotating direction of the kneading blades, rotation speed, and solid constituent proportion in the mixtures, are established. The mixing uniformity experiments are then designed to investigate the influence of the processing parameters on the mixing uniformity of the mixture, and some simulating results can be validated by them. Research results show that favorable mixing efficiency can be achieved if the rotating directions of the kneading blades are altered non-periodically, and that the mixing uniformity of the mixture and the mixing efficiency of the devices arise when the rotation speed is increased. Also, it is advantageous for improving the mixing performance of the mixing devices to increase the solid constituent proportion in the mixtures properly.Finally, methods and techniques to analyze, evaluate, and optimize the system reliability of the vertical kneading mixer are studied in detail. On the assumption that all reliability data , for example, the life cycle of a component, are determinate, a method to analyze the system reliability of the devices and their sub-systems is established, and this procedure is illustrated by using it to solve the reliability problem of the condition monitoring system for the vertical kneading mixers. Nevertheless, in the engineering practice, the test data of the vertical kneading mixers and their components are deficient and the reliability estimate information is uncertain. With consideration of this matter, reliability estimate methods of the vertical kneading mixer and its components are proposed by means of reliability mathematics and Bayesian methods. Application cases are used to illustrate these procedures. In addition, methods to enhance the reliability and safety of the vertical kneading mixer are presented due to forenamed studies. Engineering applications indicate that the system reliability analyzing, estimating and optimizing methods proposed in this dissertation are significant for reliability design of the vertical kneading mixer.The achievements of this dissertation provide significant theoretic foundation and guidance for the development of the optimum design, manufacture and operation of the vertical kneading mixer. Also, it is practical and valuable to apply these achievements to the solid propellant mixing processes.