喷射式液液混合器与静态混合器复合应用研究

喷射式液液混合器和静态混合器都是混合过程强化的重要设备。合理设计具有喷射式混合器、静态混合器的复合结构的新混合器,可以解决生产上的难题。新混合器能直接进行两种不同压力流体的混合,使压力较低流体混合后的压力有所提高,保证较好的混合效果,降低能耗,提高经济效益,简化流程。降低投资。     

Nonisothermal modeling of heat transfer inside an internal batch mixer

A nonisothermal transient process of temperature increase due to viscous heating was simulated for a 69 cm³ internal batch mixer (BM) using a computational fluid dynamics (CFD) software, Polyflow 3.9 form ANSYS, Inc., to obtain the temporal temperature distribution and characterize the heat transfer between polymer melt and mixer wall. The melt temperature obtained from simulation was verified with experiments. Starting from a uniform temperature of 463 K, when a rotation speed of 5.24 rad/s is imposed, viscous heating caused a maximum temperature rise of 3 K for a polyethylene (PE) resin, and 6 K for a polystyrene (PS) resin. The transient flow fields inside the batch mixer were characterized with velocity profiles and a mixing index parameter, which show that laminar flow dominates inside the mixer while a small percentage of elongational flow, converging flow, and recirculation flow is also present. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Expression for turbulent power draw of an in-line Silverson high shear mixer

We report the validation of an expression to accurately describe the power draw of an in-line rotor–stator mixer over a range of flow rates and rotor speeds. The expression consists of a term which reflects the power required to rotate the shaft in response to the liquid resistance and a term to reflect the power convected away from the mixing chamber. A specially commissioned high speed (12,000 rpm), instrumented 150/250 MS Silverson mixer has been developed with power draw determined from both torque and calorimetric measurements. Experiments are carried out using water over a range of independently controlled flow rates and rotor speeds with losses for both techniques carefully accounted for. For the torque measurement the value of the constants for the two terms above are Po_z=0.197 and k₁=9.35, respectively. For the calorimetric technique the measured temperature rise was similar to some of the corrections and losses over a significant range of the experimental space but nevertheless with careful experimentation constants similar to those for the torque technique were obtained, Po_z=0.229 and k₁=7.46. Allowing the calibration of the temperature probes to be a fit parameter in the regression routine increased the value of k₁=8.10 but did not affect the value of Po_z. A simple graphical method is also proposed using a dimensionless form of the expression which yielded slightly higher value of Po_z but a slightly lower value of k₁. The accuracy of both measurement techniques improves with rotor speed and the differences between the constants is attributed to the better accuracy of the torque technique at higher flow rates whereas the calorimetric technique is more accurate at low flow rates where the temperature rise is larger. Several repeats of the calorimetric technique with a reduced set of experimental points show good reproducibility. Finally at low flow rates (<10% of the maximum) the power unexpectantly increases and a modification to the expression is proposed by considering the pumping efficiency.     

Polydisperse granular flows in a bladed mixer: Experiments and simulations of cohesionless spheres

The flow and segregation of polydisperse, spherical particle mixtures in a bladed mixer was investigated using experimental and computational techniques. Discrete element simulations were able to reproduce the qualitative segregation profiles and surface velocities observed experimentally. For a binary system with a 2:1 size ratio, segregation by size occurs due to a sieving mechanism. Segregation in the binary system is fast, with a fully segregated system observed after just 5 revolutions. However, the numerical simulations showed that the extent of segregation in the bladed mixer can be reduced by introducing intermediate particle sizes in between the smallest and the largest particles. Addition of intermediate particle sizes increases convective and diffusive particle motion promoting a mixing mechanism that reduces segregation via the sieving mechanism. Void fraction within the bladed mixer increases as the degree of polydispersity is increased allowing the particles to move more freely throughout the particle bed. Higher void fractions also increase the ability of large particles to penetrate deeper into the particle bed. Normal and shear stresses are also affected by particle size distributions, with lower average values obtained for the system with the largest number of particle species. Differences in the amount of stress generated by each particle species were observed. However, the difference in stresses is reduced as the number of particle species in the system is increased.     

A novel microfluidic mixer using aperiodic perturbation flows

A novel technique is proposed for enhancing the mixing performance of a ‘crisscross’ microfluidic mixer by means of aperiodically-varying perturbation flows. The effects of the perturbation and geometry parameters on the fluid flow characteristics and mixing performance are analyzed numerically. In performing the simulations, the flow field and species concentration field are obtained by solving the two-dimensional time-dependent Navier–Stokes equations and the convection–diffusion equation, respectively. In addition, the oscillating source used to modulate the perturbation flows is modeled using the Sprott system. The results show that the irregularly-alternating flow perturbations cause a repeated stretching and folding of the species streams and enhance the mixing performance as a result. It is shown that an effective improvement in the mixing performance can be obtained through a suitable choice of the Sprott system scaling factor. Moreover, it is shown that having assigned an appropriate scaling factor, the mixing performance can be further improved by specifying suitable values of the geometry and perturbation parameters.     

Relationship between droplet size and fluid flow characteristics in miniemulsion polymerization of methyl methacrylate

Static mixer (SM) can be applied for emulsification, but the fundamental understanding of the nature of fluid flow and mixing in static mixers, is however poor. Droplet size is a very important parameter in miniemulsion systems and affects strongly the mechanism of particle formation in polymerization reactions. In this study, static mixer was used as homogenization device for emulsification of methyl methacrylate (MMA). Re number (Re) was obtained for SM inserted tube in different flow rates. It was demonstrated the nature of fluid flow was turbulent under our experimental conditions. The relationship between droplet size—the most important variable in our study—and Weber number (We) was investigated. The results showed that the ratio of the droplet size to the pipe diameter was fit as an exponential function with an order of −0.35. The polymerization of created droplets under certain We values by SM showed that it is possible to obtain a reasonable 1 : 1 copy of droplets to the particles. All these, indicate that using relationship between We and droplet size allow one to obtain acceptable condition of droplet nucleation in miniemulsion polymerization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

化工行业常用搅拌器研究热点

归纳了近年来化工行业常用搅拌器的研究热点,将其总结为8个方面:大型化、微型化、连续化、高黏度化、节能化、数值模拟、智能化和反求工程.分析了搅拌器发展的多样性以及各个研究热点的优越性,提出尚待解决的问题,并展望了搅拌器未来的发展方向.     

高粘度介质静态混合器的设计计算

给出了高粘度介质静态混合器研发过程中旋转段和分散段的设计计算,混合段的设计选型原则。该设计计算为结构设计提供了参数,也可作为进行混合器试验结果分析和改进设计的依据。     

Rv470残渣浓缩器的设计

介绍了TDI残渣浓缩器的应用及特点,通过对该设备运行情况的调查,对其设计过程提出了一些建议。     

浮法玻璃混合机设备的选用与改进

介绍了浮法玻璃生产中所使用混合机的作用,混合机的类型、选择与使用,以及对进口混合机设备的国产化改造。