Numerical Simulation Of Mixing Characteristics In A Stirred Tank With Turbine Impellers

Agitation equipments are commonly used in industrial mixing applications such as chemical industry, foodstuff, metallurgy, paper making, petroleum and water disposal, etc. Liquid-liquid mixing is one of the most important processes in stirred operations. Disc turbine agitation equipments are widely adopted in industries because of their simpler manufacture and better mixing effect, especially, the pitched blade turbines (PBT) with the lower power consumption is paid more attention. However, the choices to the structures and the rotating speeds are usually based on the experience so that the expected purposes can not be attained. Because of these factors, the mixing characteristics in turbine stirred tank are simulated by using FLUENT in the paper, and the detailed information of mixing and fluid flow in the stirred tank is studied.In the paper, multi-reference frame (MRF) is used to simulate the impellers, and standard k -εturbulent model and the resolve method of apart the velocity field from concentration field are used in the simulation. The characteristics of R-1 turbine agitation in the tank, which is widely used in the industry, are studied in the paper. The mainly studies are follows:The simulation results of the standard six straight blades turbine agitation are in good agreement with the experiment results in the literatures, which prove the correctness of simulation in the paper. With decreasing of the distance between the impeller and bottom of tank, the state of flow in the standard six straight bladed turbine mixing tank would change from the radial type to axial type. And by comparing the mixing effects of flow state of axial type with that of radial type, the results show that the number of mixing time of axial type is lower than radial type about 32.7%.The respondences of different observation points to mixing effects of agitators with 6 blades of lean angle of 90°,60°,45°and 30°are studied, the results show that the mixing time of observation in the surface is longer than the observation near the impellers, and the difference become more obvious with the lean angle of impellers increasing. The influence on mixing effects of different injected points of tracer and different rotating speeds of agitators with 6 blades of lean angle of 60°and 45°in the mixing tank are researched in the paper, and it is obtained that the relations between the mixing time and the power consumption in the double logarithm coordinate is linear. The type of flow, the vector distribution of velocity and the power consumption in the tank under different distance between impeller and bottom of tank are researched, and the results show that the type of flow changes when the C/T is separately 0.241 and 0.278 to PBT agitators with 6 blades of lean angle of 60°and 45°. The power consumption of impellers is lowest when the type is changed. By comparing the mixing effects and its respondence curves at different observation points in the conditions of impellers with lean angles of 90°,60°,45°and 30°, it is approved that the mixing energy of unit volume of agitator with 6 blades of lean angle of 45°is lowest.The research results in the paper provide guidance for the choice and optimized design to the mechanical mixing operations.