The Study Of Mixing, Heat Transfer And Power Consumption Performance Of A Coaxial Mixer

As the most fundamental element process, mixing is widely used in process industries. The impeller is crucial to perfect the mixing process and required to have good mixing performance and heat transfer characteristic. Most traditional agitators are single axis agitators applicable to a small viscosity range, while the coaxial mixers have wide adaptability to viscosity. However, there are few studies on the performance of a coaxial mixer, and its design and application are shortage of adequate guidance. Combined with actual conditions and needs, the mixing, power consumption and heat transfer performances of a coaxial mixer consisting of a frame and two Rushton turbines were investigated for different rotating modes in laminar and transition flow regimes.The experiments were done in a coaxial mixer plat, which was composed of a stainless steel cylinder shell and standard ellipsoidal head with1000mm height and diameter. Half coil jacket was equipped on the outer wall and full of circulating conduction oil or cooling water for the heating or cooling the medium in the tank. The heat transfer performance of coaxial mixer under three different modes (single inner impeller, co-rotating and counter-rotating) was experimentally studied, and the average heat transfer coefficient of inner wall surface was calculated and compared. Through regress of experimental data, the correlative expression of heat transfer coefficient was derived.Performances of mixing, power consumption and heat transfer of the coaxial mixer were numerical simulated using the commercial software Fluent. Based on the comparison of the results of mixing characteristics (flow field, velocity field, mass flow rate, shear rate and flow number) and power consumption under different conditions, the appropriate rotating mode and operating parameters were determined. In addition, the local heat transfer coefficient of inner surface was also obtained with the help of numerical simulation, which was useful to understand the heat transfer performance of the coaxial mixer.The results of experiment and numerical simulation indicated that the overall performance of the coaxial mixer was better than that of a single impeller, and the co-rotating mode was recommend for the coaxial mixer. These quantitative and qualitative research results are beneficial to optimize the design and operation of the coaxial mixer and promote its change from experience design to rule design.