The mixing process in a 0.42-m diameter transparent stirred tank with improved double Intermig impellers was experimentally studied using the decolorization method with four di erent tracer injection points. The time dependence of the tracer concentration distribution was recorded using a high-speed camera. The turbulent ow and tracer dispersion were calculated by a large eddy simulation (LES) combined with the dynamic Smagorinsky-Lilly model. The tracer di usion process, tracer concentration response, and mixing time in the tank stirred with the improved double Intermig impellers were investigated. The results showed that the mixing process predicted by LES was consistent with that by the decolorization method experiment. The predicted mixing time was 14% longer than the experimental time. The mixing time was the shortest when the injection point was in the middle of two impellers. The mixing time increased when the injection point moved to the top or bottom of the tank. The mixing times at the monitoring points near the injection point were shorter than those at distant points. The bottom of the tank with the improved double Intermig impellers was the crucial region that was di cult to mix. The mixing times at the monitoring points at the bottom were the longest for all the injection points. Increasing the mixing speed could promote the mixing process of the medium in the stirred tank and reduce the mixing time without changing the ow eld structure. Therefore, the results could serve as a guide for the design and engineering application of such a stirred tank.

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The heat transfer of a reactor with improved Intermig impellers was numerically investigated by the finite element method (FEM) simulation software Fluent (V.19). A turbulence model utilized the standard k-ε model, and the turbulent flows in two large vortexes between vertical tubes were collided to form a strong convection. The influence of heat and mass transfer developing from the impeller diameters, the distance between the two impellers (C1), the rotational speed and the installation height of the bottom impeller (C2) were studied. The reactor was equipped with special structure vertical tubes to increase the heat exchange areas. The rate of heat transfer, including criteria such as the convective heat transfer coefficient, the Nusselt number of outside vertical tubes, and the temperature boundary layer thickness, assured the accurate control of the heat exchange mixing state. The experimental testing platform was designed to validate the simulated results, which revealed the influence order of related factors. The Nusselt number Nu was affected by various related factors, resulting in the rotation and diameter of impellers extending far beyond the distance between the two impellers (C1) and the installation height of the impeller (C2). The average temperature boundary layer thicknesses of the symmetrical and middle sections were 3.24 mm and 3.48 mm, respectively. Adjusting the appropriate parameters can accurately control the heat exchange process in such a reactor, and the conclusions provide a significant reference for engineering applications.

The heat transfer process in a stirred tank of diameter T=0.5m equipped with dual-layer improved Intermig impellers and helical coils was investigated by experiment and numerical simulation methods. The temperature field, the temperature boundary layer lateral to the coil and the heat transfer coefficient were measured at different rotational speeds. The standard k-ε turbulence model and multiple reference frames combined with a sliding mesh method were adopted in the numerical simulation. The results show that the temperature errors between numerical simulation and experimental measurement were within 2K. The temperature in the stirred tank gradually rose from top to bottom and inside to outside, and the maximum temperature difference was within 2K. The average thickness of the temperature boundary layer outside the helical coil is 3.66 mm. According to the experiments and numerical simulations, the heat transfer coefficient correlations, including Nu and Re, Nu and ε of the helical coil outer side, were obtained, and the trends of heat transfer coefficients are consistent and regular. The correlation of the heat transfer coefficient lateral to the coil was acquired from the experimentally measured data. The research results can serve as a guide for the design and engineering application of mass and heat transfer processes in stirred tanks with improved Intermig impellers.