【作者】 刘建军；

【导师】 包雨云； 郑畴军；

【作者基本信息】 北京化工大学 ， 材料与化工（专业学位）， 2023， 硕士

【摘要】 颗粒-水体系搅拌在化工、食品、催化和制药等领域中是重要的单元操作,搅拌桨式混合器广泛应用于这类操作中。在搅拌混合器内颗粒-水体系搅拌轴功率消耗是该类设备设计的重要参数。建立轴功率消耗预测模型是研究颗粒-水体系搅拌轴功率消耗的重要方法,该方法可用于工业生产中搅拌混合器的设计和放大。本研究以平均粒径分别为1至5 mm的玻璃珠为实验物料,使用平叶桨、框式桨和双螺带桨三种搅拌桨,在内径为210 mm的平底圆柱形搅拌混合器内采用控制变量法研究了物料特性相关参数和搅拌参数对颗粒-水体系搅拌过程中功率消耗特性的影响,建立了功率消耗预测模型。将颗粒-水体系搅拌和高黏流体搅拌联系起来,借鉴流体黏度的概念,提出了一种表征颗粒-水体系黏性程度的参数——颗粒-水体系表观黏度,以此来研究颗粒-水体系在搅拌过程中的流动行为和流变特性。研究结果表明:随着自由液体体积比增加,颗粒-水体系搅拌功率消耗呈现先增加后减小直到减小至低于干颗粒搅拌时功率值的变化规律,并在自由液体体积比为0.2008时达到最大功率消耗值。随着物料装填相对高度增加,功率消耗和单位质量功率消耗均增加;直叶桨搅拌干颗粒体系会出现再循环区域,随物料装填相对高度增加而逐渐消失。干颗粒体系搅拌时,功率消耗随颗粒平均粒径增大而增加;颗粒-水体系搅拌时,对于粒径为1 mm、2 mm和3 mm的玻璃珠,随着颗粒粒径增大,功率消耗随之降低;加入少量水搅拌,1 mm玻璃珠的颗粒床层孔隙度会增加。随着搅拌转速的增加,不同自由液体体积比下,颗粒-水体系搅拌功率消耗均增加,且呈凹函数形式增加速度越来越快。通过量纲分析法建立的颗粒-水体系功率消耗预测模型,相对误差在25%以内;通过模型分析法建立的功率消耗预测模型,相对误差在10%以内。在层流搅拌过程中,颗粒-水体系表观黏度随搅拌转速的增加而降低,与屈服假塑性流体有相似之处。屈服应力随自由液体体积比增加呈现先增加后减小的变化规律,与含水率对功率消耗的影响规律相同。更多还原

【Abstract】 Stirring of particle-water system is an important unit operation in many fields,such as chemical,food,catalysis and pharmaceutical,and stirred tank mixers are widely used in these industries.The stirring shaft power consumption of particle-water systems in stirred mixers is important parameter in design of mixer.The establishment of shaft power consumption prediction model is an important method to study the stirring shaft power consumption in particle-water systems.This method can be used for the design and scale-up of stirred mixers in industrial applications.In this study,glass beads with an average particle size from 1 to 5 mm were used as experimental materials,and three different types of impellers,i.e.,flat blade impeller,frame impeller and double helical ribbon,were used,in a flat-bottom cylindrical stirred mixer with an inner diameter of 210 mm.The effects of material characteristics and stirring parameters on the power consumption characteristics of particle-water systems were studying by using the control variable method.Considering the effects of each variable on power consumption,a shaft power consumption prediction model was establishment.Based on the concept of fluid viscosity,the apparent viscosity of particle-water systems,a parameter characterizing the viscosity of particle-water systems,is proposed to study the flow behavior and rheological properties of particle-water systems in stirred mixers.The results show that with the increase of the free liquid volume ratio,the power consumption of particle-water systems increases first and then decreases to lower than that in stirring dry particle systems,and reaches the maximum power consumption when the free liquid volume ratio is 0.2008.With the increase of the relative material filling height,both the power consumption and the unit mass power consumption increase.The recirculation zone appears in the dry particle system stirred by flat blade impeller,and gradually disappears with the increase of the material filling relative height.When the dry particle systems is stirred,the power consumption increases with the increase of the average particle size;however,when the particle-water system is stirred,the power consumption decreases with the increase of particle size for glass beads with particle size of 1 mm,2 mm and 3mm.Adding a small amount of water to particles,the porosity of the particle bed of 1 mm glass beads will increase.With the increase of agitation speed,the stirring power consumption of particle-water systems increases under different free liquid volume ratios,and the increase rate becomes faster in the form of concave function.The power consumption prediction models of particle-water system were established by dimensional analysis and model analysis,respectively,with the relative errors of prediction within 25%,and10%,respectively.In laminar stirring,the apparent viscosity of particle-water system decreases with the increase of rotation speed,which is similar to the yield pseudoplastic fluid.The yield stress increases first and then decreases with the increase of free liquid volume ratio,which is the same as the influence of water content on power consumption.更多还原