Study On Dynamics Of Gas-liquid Dispersion In High-viscosity Non-newtonian Fluids With A Novel Impeller

Microbial polysaccharide with the properties of high viscosity and pseudo-plastic characteristic belongs to a sort of widely used mass products, which is usually fermented with renewable resources. Meanwhile, some traits like high viscosity and complex rheological behavior severely hinder the normal function of fermentation process in the aspects of mixing, heat-conduction, oxygen-transfer, and so on, and accordingly impact the stability and output of the whole process. As a result, it is developing applicable mixing equipments for high viscous fluids that possesses the key points of improving the productivity of microbial polysaccharides industry.Efficiency of design and application of mixing and blending equipments has been significantly boosted since computational fluid dynamics (CFD) was implemented. It has been widely proved that taking CFD combined with last-phase experimental validation can effectively cut down the input of labor and research investments. According to the reasons above mentioned, the hydrodynamic behaviors of a novel impeller which was designed for high viscous fluids was studied in this work, and then, the optimal configuration of this impeller was put forward subsequently. At last, the cost-effective mixing systems with high effectivity for non-Newtonian, especially pseudo-plastic, fluids were made up and investigated.Firstly, the configuration of the symmetric sawtooth double pitch blade turbine (SPT) was optimized based on CFD technique while taking 2% wt xanthan gum solution with ventilation of 1 vvm as the computing model. As the results showed, the capabilities of mixing and gas-liquid dispersion were evidently affected by the included angle of the placket between upper and downer blades. A 60 degree of the included angle was verified having the best score when the power consumption, pumping capacity, gas hold-up, volumetric oxygen transfer rate and oxygen transfer efficiency were taken into account.Secondly, comparison between the optimized SPT and a disk turbine (DT) in a series of spinning speeds and ventilation rates was made to evaluate the rheological behaviors and oxygen transfer capabilities of the two impellers in the test system established at the first stage. Comparing with the operation data of DT, there was a 35% decline in power consumption of unit volume coming up with a 10% increase in oxygen transfer capability when SPT was adopted in the whole testing range.At last, the mixing behaviors of six sets of three-stage impeller combination were investigated. These sets included several elaborately selected combination of SPT, DT and a four-twist-blade impeller (KSX, named in accordance with the manufacturer). As the results exhibited, the SPT-KSX-KSX set gave the maximum oxygen transfer efficiency among the six tested runs, and obtained up to 23% increase of the efficiency comparing with the DT-DT-DT set which was in widespread use in the mixing industry. Meanwhile, all the relative deviations of the six runs between simulation and experiment data were within the range of 10%, which represented a criterion of acceptable errors. Although the SPT-KSX-KSX set didn't reach the highest level of volumetric oxygen transfer coefficient, the far lower power consumption compensated the deficiency well, which expressed a potential advantage of cost in high viscous fermentation industry.