Stator Holes Research Articles

High shear mixer works as a heat exchanger enhancing the liquid–liquid direct contact heat transfer

As an indispensable unit equipment in industrial production, the design of efficient heat exchangers is of great significance to improve energy utilization rate. In this paper, the in-line high shear mixer (HSM) was investigated as a heat exchanger for the first time by experiments and assisted with CFD simulations, and the heat transfer performance was measured using kerosene and thermal water as the heat transfer fluids. Effects of operational parameters, including rotor speed, fluids temperature and flow rate, as well as the structural parameters, involving the rotor teeth number, teeth height, and the shear gap, were studied on the volume heat transfer coefficient and the heat transfer efficiency of such inline HSM. The results indicated that the volume heat transfer coefficient can be significantly improved by increasing the rotor speed and the flow rate of the heat transfer fluids, but reducing the heat transfer temperature difference, whereas increasing the thermal fluid flow rate deteriorates heat transfer efficiency. Furthermore, the structural parameters including rotor teeth number and teeth height, the shear gap within the stator and rotor were optimized to enhance the heat transfer of HSM. The optimal HSM possesses a shear gap of 0.5 mm, a teeth height of 10 mm and a teeth number of 6, which can generate larger turbulent energy dissipation rate and higher shear rate, meanwhile make more fluids jet out of the shear gap and stator hole. The maximum volume heat transfer coefficient and heat transfer efficiency can be up to 2522.8 kW·m−3·°C−1 and 92.4% with the optimal structure. Finally, the dimensionless correlations of heat transfer performance were established to guide the operating mode and structural design of high-efficiency high shear mixer.

Numerical Studies of Batch and Inline High Shear Melt Conditioning Technology Using Different Rotors

When casting aluminum alloy billets, high shear melt conditioning (HSMC) technology refines the resulting grain size, reduces the number of defects, and improves mechanical properties without the need to add polluting and expensive chemical grain refiners. These resultant improvements spring from the high shear rates that develop in the rotor–stator gap and the stator holes facing the leading edge of the rotor. Despite the growing literature on rotor–stator mixing, it is unclear how the different rotor–stator parameters affect the performance of high shear treatment. To upscale this technology and apply it to processes that involve large melt volumes, an understanding of the performance of the rotor–stator design is crucial. In this paper, we present the results of computational fluid dynamics (CFD) studies of high shear melt conditioning in continuous and batch modes with different rotor designs. These studies build upon our earlier work by studying the effect of rotor variation in a stator design consisting of rows of small apertures at different rotor speeds spanning from 1000 to 10,000 revolutions per minute. While no clear-cut linear pattern emerges for the rotor performance (as a function of the design parameters), the rotor geometry is found to affect the distributive mixing of microparticles, but it is insignificant with regards to their disintegration.

Nanoparticle de-agglomeration in viscous fluids using different high shear mixer geometries

In the present work, the effect of batch high shear mixer (HSM) geometries is studied on nanoparticles deagglomeration and power draw in water and aqueous glycerol solutions. The kinetics and mechanism of cluster break-up are investigated for disintegrated (less number of larger stator holes), and mesh (higher number of smaller stator holes) heads at different rotor speeds. Mesh head geometry is found to be more efficient for fines generation than disintegrated head. A bi-modal particle size distribution and erosion as dominant break-up mechanism is found. The size of the smallest fines is found to be ≈30 nm for mesh head and ≈50 nm for the disintegrated head. Z-average ranges from 180 to 310 nm for given operating and process conditions. The power draw is more in mesh head and increased with an increase in viscosity. Further, power draw increased with an increase in viscosity of continuous media and rotor speed.

Effect of stator geometries on flow fields and mixing performance for viscous fluids

High shear mixers (HSMs) find wide applications in industrial processes where intense mixing and dispersion of fluids play a vital role. In this work, the flow fields and mixing performance is analyzed in different batch HSMs with varying stator heads, such as disintegrated, slotted, and mesh. Further, the effect of viscosity, flow behavior and rotor speed on hydrodynamics and mixing performance is assessed through numerical investigations. The turbulent flow fields and mixing enhancement are characterized using standard k-ɛ turbulence model with multiple reference frames approach for various HSMs. The turbulent statistics like turbulent kinetic energy are found to be maximum in the stator hole region and varied with flow behavior. The energy dissipation within the rotor vicinity is found higher for mesh head geometry followed by disintegrated and slotted heads. The effect of tracer injection locations is evaluated to gain comprehensive information on the mixing performance inside the mixing tank. Mixing time (t95) was evaluated and correlated with the existing results. For viscous fluids, complete mixing is hard to achieve due to the presence of cavern effect in smaller stator holes HSM. Moreover, the results provided guidance for further selection, design and development of HSMs for process industries.

Design and characterization of a thin linear ultrasonic motor for miniature focus systems

We present a miniature linear piezoelectric ultrasonic motor with a thin and hollow design, which can serve as an essential component of autofocusing features in next-generation camera modules. It consists of a thin square stator with a hole and an elastic cylindrical slider with a slit. The motor design, in which the slider inserted into the stator hole expands outward, enables a hollow structure for centering a lens and an optimal preload for enhancing the motor thrust force. In this study, we model the relationship between the dimensions and the preload statically to quantify the preload value and clarify the design methodology of the motor. After optimizing the preload empirically, we evaluate the fundamental characteristics experimentally. The stator with a side length of 4.5 mm and a thickness of less than 1 mm provides a thrust force of 12.9 mN that leads to a quick response, which is a requirement of autofocusing. Finally, the motor drive system with visual feedback control is used to demonstrate the positioning of an actual lens group in front of an image sensor to obtain clearer images.

Influence of Unbalanced Electromagnetic Force and Air Supply Pressure Fluctuation in Air Bearing Spindles on Machining Surface Topography

Air bearing spindles (ABS) can meet high accuracy demands for the precise rotation motion, which adopt air bearings to support spindle shaft, and the spindle shaft directly connects the motor rotor. The unbalanced electromagnetic force caused by motor rotor eccentricity (MRE) and air pressure fluctuation (APF) are two important influential factors to the dynamic performance of the spindle system and machining surface quality. This paper addresses the problems of measuring the MRE and APF in an ABS through testing machining surface topography. A permanent magnet synchronous motor (PMSM) was modelled by finite element simulation (FES). Through FES it found that the MRE between the motor rotor and stator hole produced a radial magnetic force (RMF), which could cause ABS to periodically vibrate in the axial direction. Besides, the change of the air supply caused the stiffness variation of ABS and result in the tilt error motions of the spindle shaft. A theoretical model of machining surface topography considering MRE and APF was then proposed for the first time, which revealed that the MRE and APF resulted in the periodic fluctuations of the machining surface topography. The overall surface topography then became grooved surfaces. The above findings were finally validated by measurement results of ultraprecision diamond turning experiments.

On The Possibility of Grinding Solid Particles of a Dispersed-Phase Suspension in a High-Speed Rotary Disperser

Conditions for grinding particles comprising the dispersed phase of a suspension when it moves in the holes of the rotor and stator of a high-speed rotary disperser are considered. The obtained dependences are used to determine the conditions for the destruction of the particles into smaller components at the moment of their impact on the faces of the rotor and stator holes, allowing the selection of rational technical disperser parameters.

Numerical Assessment of In-Line Rotor\u2013Stator Mixers in High-Shear Melt Conditioning (HSMC) Technology

High shear melt conditioning technology refines the as-cast structure of light alloy melts, thereby improving the mechanical properties of the casting and reducing the occurrence of defects, without requiring chemical grain refiners. To upscale the technology and apply it to processes involving larger melt volumes, a computational fluid dynamics study is conducted with three rotor–stator mixers operating in both batch and continuous modes. Analysis of the results show that rotor–stator mixers with smaller stator holes outperform those with larger ones because of larger shear rates—increasing the deagglomeration rate—and larger volume flow rates—increasing the dispersion of the intensively sheared melt in the bulk liquid. Compared with batch mode, continuous operation results in lower mass flow rate through the mixer and reduced mixing, although the mixer design has a larger impact on both measures.

Analysis of the Motion of Fluid in the Annular Gap between the Rotor and Stator of a High-Speed Disperser

The conditions of motion of the liquid medium in the annular gap between the rotor and stator of a disperser are considered. Analytical dependences for calculating the flow rate in the gap, the friction force, and the value of the tangential stress between the layers of the liquid are determined. A model of fluid flow in the annular gap between the rotor and stator is developed, which allows to determine the time of coincidence of the axes of the rotor and stator holes for the exit of liquid streams, as well as the times when they overlap.

Analysis of Dispersed Liquid Medium Motion in Rotor and Stator Holes

The parameters of liquid medium motion in holes of rotor and stator of a high-speed rotor disperser are studied.

Flow, turbulence and potential droplet break up mechanisms in an in-line Silverson 150/250 high shear mixer

Angle resolved 2-D PIV measurements were performed to characterise the flow and turbulence as well as indicate potential droplet break up mechanisms in an in-line Silverson 150/250 high shear mixer, using water as the working fluid in the turbulent regime (120,000 < Re < 420,000). Distributions of Reynolds stresses, turbulent kinetic energy (TKE), and energy dissipation rates (ε) were examined. The regions of interest (ROI) were: A – jet emanating from a stator hole and B – the rotor swept volume. The complex flow pattern can cause droplet break up under either laminar or turbulent conditions depending on the characteristic length and velocity in the ROI; break up due to turbulence in the inertial regime was identified as the dominant mechanism in this study. Evaluated energy dissipation rates obtained assuming either a fully resolved velocity field (DE) or using the Smagorinsky closure model (SGS) were found to depend on rotor speed e.g. ε∝Nb with b exponents of 1.59–1.90 (DE) and 2.42–2.84 (SGS), which are comparable to existing literature values. The influence on ε of the rotor speed, external pump flow rate and induced backpressure on the mixer outlet, were also investigated. Analysis revealed that the intensity and propensity of ε is dictated by the dominant flow in the mixing head e.g. radial flow at high pump flow rates, prominent in ROI A or tangential flow at high rotor speeds and when backpressure is induced, prominent in ROI B.

Turbulent statistics of flow fields using large eddy simulations in batch high shear mixers

Large eddy simulations (LES) have been carried out for the first time to characterize the flow and turbulent characteristics in three different batch high shear mixers (HSMs) at a constant rotor speed of 4000rpm. Three HSMs having different stator heads such as circular, square and inclined stator head with 6, 92 and 210 numbers of stator holes, respectively have been investigated. Dynamic Smagorinsky model with sliding mesh method is used for the sub-grid scale stresses at a Reynolds number of 52,000, to overcome the prediction of RANS models. Numerical methodology is validated, in terms of Power number with the available numerical and experimental studies and found in fairly good agreement. The velocity flow patterns and fluctuations at different planes are predicted and vortexes have been observed within the stator holes and bulk fluid. It is observed that velocity magnitude fluctuation is a function of rotor rotations and stator holes size, and fluctuations in one jets emerging from stator holes affect the fluctuations in other plane jets. Further, it is found that smaller the stator holes size, greater is the energy distribution and hence greater will be the drop size distribution in the mixer. Therefore, the inclined stator head HSM can be used for the uniform size distribution in application to de-agglomeration and dispersion. It is found that the energy spectrum of Kolmogorov is followed over the entire length scale for all HSMs and LES provided the richer flow and turbulent information as compared to RANS model.

Numerical and experimental evaluation of droplet breakage of O/W emulsions in rotor-stator mixers

Emulsification of a high viscosity oil in water mixture was studied in a rotor-stator mixer. Experimental characterization of drop sizes and high-speed visualizations of drop breakup phenomena were performed, combined with computational fluid dynamics analysis of the flow field and population balance modeling. Single-phase flow simulations were carried out with a sliding mesh CFD model and combined with analysis of streamlines, turbulent eddy dissipation fields and high-speed visualizations of drop breakage. From frames taken over few seconds, with the oil-water system initially fully segregated, three drop breakage mechanisms were identified, supported by the CFD analysis: (i) a combination of the large scale circular motion in the tank and the fluid jet emanating from the stator holes; (ii) droplets that are pulled into the rotor – stator system from the bottom and flow through the gap between the stator and rotor, undergoing extremely high shear stresses, being expelled through the stator slots in several fragments, and iii) droplets that remain caught at the recirculation zones in the stator holes, increasing exposure time to high shear during the rotor blade passage. Finally, an optimization algorithm was coupled to a population balance model and the measured drop size distributions were reproduced in good agreement with experimental data, including the bimodal behavior attributed to the generation of satellite droplets.

Hydrodynamics and mixing characterization in a novel high shear mixer

In the present study hydrodynamics and mixing characteristics in a novel batch rotor-stator mixer (RSM), which is very simple in construction and design, is investigated at different rotor speeds (2000, 4000 and 6000rpm). The proposed RSM design is comprised of tilted jets/holes in the stator, for the deep penetration in the mixing vessel. For the optimization of operating as well as geometrical parameters of the proposed mixer design, simulations are carried out using transient sliding mesh with k-ε turbulence model at different rotor speeds. It was observed that besides radial and tangential flows jets emerging from stator holes impinge the bulk fluid above and below the stator, which improves mixing and reduces dead zones. Further, the flow parameters such as mass flow rate, Power number, Flow number, pumping efficiency and energy dissipation rate increased with an increase in rotor speed. Further, the energy dissipation rate is found maximum in the rotor swept region. It is observed that the amplitude fluctuations in flowrate and torque, with blade position, increased with the rotor speed. Further, mixing characterization in the novel RSM is studied for the first time in a batch RSM to predict the dead zones in the RSM.

Experimental investigations of turbulent fragmenting stresses in a rotor-stator mixer. Part 1. Estimation of turbulent stresses and comparison to breakup visualizations

Despite large industrial relevance, the relation between rotor-stator geometry, hydrodynamics and drop breakup is poorly understood, partly since no methods for measuring the fragmenting stresses acting on drops have been established. This study attempts to bridge this gap by developing, applying and evaluating two approaches for estimating local turbulent stresses based on particle image velocimetry data: namely one traditional but indirect approach based on the dissipation rate of turbulent kinetic energy, and another more direct approach based on the spatial turbulent spectrum that has proven useful in other high-intensity emulsification processing. The approaches are evaluated in terms of validity of underlying assumptions, how they compare to breakup visualizations in the same geometry and with regard to the reliability of primary measurables.Results show three consistent regions of high stress in the rotor-stator region: in a plume extending into the stator-hole from the trailing edge, in the shear layers of the jet exiting the hole and in the macroscopic flow structure formed after the rotor blocks a stator hole. Following a drop travelling along an average velocity flow field, the measurement predict disrupting stresses exceeding the stabilizing stress at the stator hole exit, at approximately the same position where drop breakup is observed in breakup visualizations. Both methods are therefore able to predict the most likely breakup positions. It is also concluded that both methods have limitations, and that average stress alone cannot describe all aspects of the fragmentation process in rotor-stator mixers.

次世代型人工筋肉を目指したフレキシブル超音波モータの開発

We present a flexible ultrasonic motor that generates linear motion as a novel soft actuator. This motor is comprised of a single cube stator with a through-hole, and a flexible coil spring inserted into the hole. The coil spring, which has a diameter of 10 mm and length of 200 mm, is translated by a vibration generated in the stator. A preload between the stator and the coil spring is important for improving the motor performance. The coil spring inserted into the stator hole generates the preload by expanding in a radial direction. We build a prototype flexible ultrasonic motor, and examine its basic performance parameters such as thrust force, velocity, response time, resolution and flexibility. To demonstrate flexibility, we show the stable thrust force and velocity even when the coil spring is bent to a bending radius of 15 mm.

Hydrodynamic difference between inline and batch operation of a rotor‐stator mixer head ‐ A CFD approach

AbstractRotor‐stator mixers (RSMs) can be operated in either batch or inline mode. When operating a rotor‐stator geometry in batch mode, it typically experiences an order of magnitude higher volumetric flow through the stator than in inline mode. This is expected to cause differences in the flow and turbulence in the rotor‐stator region. This study uses computational fluid dynamics (CFD) to study the hydrodynamic differences in and near the stator hole as a function of volumetric flow rates between those experienced in inline and batch modes of operation. It is concluded that both radial flow profiles and turbulent kinetic energy across a range of rotor speeds and flow rates can be described by a velocity ratio: average tangential fluid velocity in the stator hole divided by the rotor tip speed. Moreover, the position where dissipation of turbulent kinetic energy takes place—and hence the effective region of dispersion or mixing—differs between the two modes of operation. The relative importance of the two regions can be described in terms of the velocity ratio and the transition can be predicted based on the relative power input due to rotational and pumping power of the mixer. This study provides a starting point for understanding differences between emulsification efficiency between inline and batch modes of operation with relevance for both equipment design and process scale‐up.

Study of Rotary-Linear Ultrasonic Motor Output Shafts

We propose output shafts with a preload generation mechanism to improve the output torque and thrust force of the rotary-linear ultrasonic motor. The stator is comprised of a single metallic cube with a through-hole, and the output shafts are inserted into the hole to generate motion in both its circumferential and axial directions arbitrarily. In this paper, two design concepts for optimizing the preload using the output shafts are examined. The first involves a cylinder shaft with micron-order accuracy diameter realization. The cylinder shaft makes contact with the entire inner surface of the stator and generates a preload between the stator and shaft. The second concept employs a spring shaft having a slightly larger diameter than the stator hole, which expands in the radial direction and generates the preload. Experiments show that these design concepts improve the output torque and thrust force.

The limits of operation modes for apparatuses with cavitation excitation

Cavitation in the chamber of a rotor apparatus with flow modulation was considered. A method was proposed for determining the limits of precavitation and cavitation, cavitation and supercavitation operation modes for apparatuses with pulsed cavitation excitation as a key factor of production process stimulation. The experimental dependence of the critical cavitation number on the excess liquid pressure in the chamber of a rotor apparatus was given and showed an insignificant hysteresis of the critical cavitation number. The dependences of the amplitude of the first cavitation pressure pulse on the generalized cavitation number at different rotor apparatus modulator shuttering rates and temperatures of water (up to 99°C) flowing through one stator hole and of the integrated cavitation noise pressure on the excess liquid pressure (up to 2 MPa) in the chamber of a modified rotor apparatus at constant volumetric flow rates (up to 27 m3/h) were also reported.

Scale-Up Factor for Mean Drop Diameter in Batch Rotor-Stator Mixers with Internal Circulation

The aim of the present study is to propose a scale-up factor for the mean drop diameter in internally circulated batch rotor–stator mixers. The total energy dissipation rate (εt) is used as the scale-up factor for the mean drop diameter. εt is calculated from the power number, flow number, rotational speed, number of rotor blades, and number of stator holes. Because it is difficult to measure the circulation flow rate of an internally circulated mixer directly, the flow rate of a production-scale mixer is estimated by measuring the time required for complete mixing—termed “mixing time”—and taking into account the power number of the production- and pilot-scale mixers and the flow number of the pilot-scale mixer. Our experimental results indicate that εt could influence the mean drop diameter. Theoretical verification suggests that εt includes information on the mixer configuration (rotor diameter, stator hole diameter, stator wall thickness, stator opening ratio, and gap width) and manufacturing conditions (operating time: t; rotational speed: N; and total product volume: V). Our results show that a decrease in the mean drop diameter is proportional to t, N4, and V−1. Further, we estimate the mean drop diameter of the production-scale mixer by performing a model product experiment with a pilot-scale mixer. The above results also indicate that the scale-up criteria for the mean drop diameter can be determined on the basis of εt and in terms of the operating time and not necessarily in terms of the geometric similarities between mixer configurations, a constant rotor tip speed, or a constant clearance between the rotor and stator.