| The medium with impurity in experiment device needs to be fully stirred in the stirring tank to ensure the maintenance and control of impurity concentration in the area of equipment to be inspected.However,due to the settling characteristics of impurity particles,during the long-term experiment process,the stirring dead zone often occurs due to the uneven stirring flow field,resulting in impurity deposition and affecting the experiment.Therefore,how to improve the mixing uniformity of the impurity stirring tank and avoid the deposition of impurity particles has become an urgent problem to be studied in the impurity experiment device.In this paper,based on the numerical simulation technology of multiphase flow in free-surface stirred tank,through reasonable simplification,the numerical model of double impeller free-surface stirred tank is established,and the influence of mixing impeller position parameters,the setting of mixing tank turbulence baffles and other aspects on the flow field is studied.An optimization scheme is proposed for the existing experimental device.Finally,the feasibility of the optimization scheme is verified through experiments.The main research contents are as follows:(1)To establish a model for the existing experimental device,under the premise of low concentration of solid components,the method of gas-liquid two-phase flow coupling particle deposition velocity analysis is used as a substitute for the three-phase flow model for numerical simulation.The results show that the mixing uniformity of the existing device is poor.The dead zone of mixing occurs in the area between the right-angle edge of the rectangular mixing tank and the mixing impeller,and in the area between the two mixing impellers.The flow rate is lower than the particle deposition velocity,resulting in the deposition effect of impurity particles.(2)Based on “Orthogonal Experimental Design”,9 groups of comparative experiments were designed with adjustable device variables of field devices,and the effects of various factors on the three-dimensional flow field were qualitatively studied.At the same time,the uniformity of the mixing flow field is quantitatively determined based on the root mean square method of relative deviation.The results show that under certain conditions,the smaller the distance between impellers,the better the mixing characteristics between impellers in the double impeller and square mixing tank system.The suppression effect of the square stirring tank on the circulation improves the mixing characteristics in the region between impellers and tank side walls,thus the impeller spacing becomes the dominant factor affecting the uniformity of the flow field compared with the impeller height.On the other hand,if the volume of the mixing tank permits,a larger right-angle baffle will obtain higher flow field uniformity.(3)Based on the existing experimental device and the improved device with the optimized design scheme,stirring and sampling experiments are carried out,and the sampling analysis data of the two experiments are compared.The results show that in the long-term experiment of the existing device,the sampling concentration continuously decreases and tends to be stable at a random low value point.After drainage,more particles deposit at the bottom corner and the middle area of the tank,and the stirring characteristics are poor.However,according to the modified device of the optimization scheme,the sampling data fluctuates stably at a higher value,and the sediment at the bottom of the tank is less after drainage,so the optimization scheme is feasible. |
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