【作者】 徐双庆；

【导师】 张金利；

【作者基本信息】 天津大学 ， 化工过程机械， 2012， 博士

【摘要】 高剪切混合器是一种新型过程强化设备，局部超高的湍动和剪切作用使其具有强化传递限制的快速化学反应过程的巨大潜质。本文对中试规格管线型高剪切混合器流体力学性能及返混特性进行了实验测定和计算流体力学模拟，对于该类新型化学反应器的设计、选型和优化具有指导意义。首先，利用激光多普勒测速仪测定了中试规格、双圈超细齿管线型高剪切混合器（定子后弯斜齿）外圈定子射流区的径向和切向速度分量。采用扭矩-转速传感器测定了高剪切混合器的功率消耗。对混合器内单相流动过程进行了计算流体力学模拟，考察了不同湍流模型和差分格式对预测精度的影响。对于高剪切混合器内高度三维化、强烈旋转、壁面约束和各向异性流动，大涡模拟比标准k-ε模型能更准确其内部平均流场和二次流动特征。在混合器的定-转子区域、外圈定子射流区以及转子紧固螺母附近的射流区，流动都明显偏离各向同性湍流。其次，基于非理想脉冲示踪-响应实验与去卷积算法得到超细齿管线型高剪切混合器的本征停留时间分布，并采用大涡模拟与组分输运相结合的方法对其进行了预测。实验与模拟的停留时间分布曲线在响应峰出峰位置以及肩峰等主体特征上相似，各操作条件下平均停留时间吻合良好，表明大涡模拟与组分输运相结合的方法准确可靠。高剪切混合器接近于全混流，其内部存在明显的滞留区。增加转速或流量都有助于提高混合度并能消除微弱的沟流，但是可能产生增强的内部环流。齿合管线型高剪切混合器的几何参数对其返混特性有重要影响。具有较大剪切间隙宽度、较大齿尖-基座间距、单圈定-转子或者直齿型定子的高剪切混合器，可能会存在沟流、短路和/或流体夹带的弊端。最后，实验测定了不同操作模式下定-转子齿合型与叶片-网孔型高剪切混合器在不同转速、流量和流体粘度下的扬程、泵效率、输入轴功及功率曲线，建立了弗鲁德数校正的Kowalski功耗预测模型。两种混合器在低转速下泵送能力均较差，增加转速后叶片-网孔型高剪切混合器的泵送性能优于齿合型。无转子时，流体流经两种混合器均产生压力降；处理不同粘度的工作流体时，两种混合器中定子的局部阻力相近。在湍流区相同流量准数下，超细齿高剪切混合器比类似规格的双圈细网孔Silverson能多输出超过50%的净功率。泵送模式单圈叶片-网孔型高剪切混合器与双圈标准网孔Silverson的湍流功耗相近；完全自吸模式单圈叶片-网孔型与双圈细网孔Silverson的湍流功耗相近。更多还原

【Abstract】 As a novel type of process intensification equipment, high shear mixers (HSMs)have great potential to intensify chemical reactions with fast inherent reaction ratesbut relatively slow mass transfer, due to their locally intense turbulence and shear.Hydrodynamics and backmixing properties of pilot-scale in-line HSMs, instructive forthe design, selection and optimization of these novel chemical reactors, were bothexperimentally and numerically investigated in this thesis.Firstly, the radial and tangential velocities in the jet flow region of a pilot-scalein-line HSM with single stage, double rows of ultra-fine teeth (backward inclinedstator teeth) were measured using LDA. Power consumptions of the mixer wereinvestigated by the torque based method. The single phase flow field in the HSM wasestimated through CFD simulations for the assessments of the predictive capabilitiesof different turbulence models and discretization schemes. It is found that, for thehighly three-dimensional, strongly rotating, wall-bounded and anisotropic turbulentflow in the HSM, LES captures more accurately the mean and secondary flowcharacteristics than the standard k-ε turbulence model. Obvious deviation fromisotropic turbulence is observed in the rotor-stator region, as well as the jet regionsnear the outer stator and the clamp nut.Secondly, the intrinsic RTDs of the ultra-fine teethed in-line HSM were obtained bythe stimulus-response experiments with imperfect tracer pulse and a deconvolutiontechnique. The LES and combined species transport method was adopted for the RTDpredictions. The experimental and simulated RTD curves share overall features in theresponse peaks, and the predicted mean residence times approximate to the measuredvalues, indicating reliable CFD predictions of the RTDs. Results show that the teethedin-line HSM behaves like a mixed flow reactor with stagnant regions. The increase ofeither the rotor speed or the flowrate leads to improvement of the mixedness andelimination of the trivial channeling defect, but also increase of internal recirculation.Geometric parameters of the teethed in-line HSM have significant influences on theRTDs. The defects of channeling, short circuiting and fluid re-entrainment are resultedfrom inefficient geometric designs of HSMs, such as those with large shear gapwidths, large tip-to-base clearances, single rows of rotor and stator teeth, or axiallystraight stator teeth. Lastly, the pumping heads, pumping efficiencies, input shaft powers and powercurves were measured under both the pump-fed and free-pumping modes for therotor-stator teethed and blade-screen in-line HSMs under different rotor speeds,flowrates and fluid viscosities. The power number of both units with the bearing losssubtracted can be correlated by the Froude number modified Kowalski’s powerconsumption model. Both HSMs do not pump well at lower rotor speeds. While athigher rotor speeds, better pumping capacity is observed for the blade-screen unitover the teethed unit. Both units demonstrate pressure drops when operated withoutthe rotors attached. Local resistances from the teethed and screen stators areapproximate at different fluid viscosities. In the fully turbulent flow region with thesame flow number, the dual-row ultra-fine teethed HSM draws over50%net power tofluid than the Silverson with dual fine screens. The single-row blade-screen HSM hasapproximate turbulent power draw to the dual standard Silverson under the pump-fedmode, and to the dual fine Silverson when operated under the free-pumping mode.更多还原