PLIF Research On Mixing And Mass Transfer Characteristics In A Solid-liquid Stirred Tank

Solid-liquid two phase mechanical agitation is a common unit operation in chemical process.It plays an important role in strengthening the mixing and mass transfer between materials,and its industrial application is very extensive.At present,the research on solid liquid stirred tank is mainly aimed at the characteristics of liquid phase flow field and the analysis of particle concentration and velocity characteristics.The study of solid and liquid mixing characteristics and two phase mass transfer characteristics in this kind of stirred tank is less.In order to improve the cognition of solid-liquid mixing and mass transfer,this paper uses a visual experimental means of planar laser induced fluorescence(PLIF)to study the mixing and mass transfer characteristics of solid liquid two phases under different working conditions in a stirred tank.In the experiment,the continuous phase is 1:1 ratio of sucrose aqueous solution.The solid phase is a mixture of PVPK30,mannitol and sucrose with a ratio of 3:1:1.The physical compression method and melting method are used to form cylindrical particles.The stirred tank is the 120 mm cube structure of the border length,and the blade is a standard Rushton turbine propeller.By changing the Reynolds number of the blade operation speed adjustment,the Reynolds number of the blade ranges from 73 to 450.In this paper,the influence of the Reynolds number and the phase angle of the blade on the mixing and mass transfer characteristics during the start and operation of the blades is studied by using the PLIF technique,and the typical flow field characteristics are tested by using the particle image velocimetry(PIV)technique.The study shows that the fluid near the bottom of the impeller moves to the center of the trough and the hub directly.When Re is greater than 323,the flow pattern and mixture are distributed irregularly.When the horizontal plane of the blade center is the interface,when Re is less than 290,the mixing and mass transfer are mainly concentrated in the region below the interface.The probability of mixing and mass transfer at the bottom of the interface is small and the velocity is slow.The periodic rotation of blades will cause the change of jet direction and angle at the tip of the blade,thus promoting the mixing and mass transfer of the material below and below the interface.When Re is more than 295,the interfacial phenomena in the vertical section disappear,and the mixing and mass transfer rates are faster in the range of the whole grooves,but the region near the bottom of the trough and the top of the trough is still the low velocity region of mixing and mass transfer.The PIV experiment and CFD numerical simulation of the flow field in a stirred tank under laminar flow show that the velocity distribution of the two is in good agreement,which lays a foundation for the further use of the CDF method to carry out the study of mass transfer characteristics.