Mixer Configuration Research Articles

Performance of the Caltech Submillimeter Observatory Dual-Color 180–720 GHz Balanced SIS Receivers

In this paper, we report on balanced SIS receivers covering the astronomical important 180-720 GHz submillimeter atmospheric window. To facilitate remote observations and automated spectral line surveys, fully synthesized local oscillators are employed. High-current-density Nb-AlN-Nb superconducting-insulating-superconducting (SIS) tunnel junctions are used as the mixing element. The measured double-sideband (DSB) 230 GHz receiver noise temperature, uncorrected for optics loss, ranges from 50 K at 185 GHz, 33 K at 246 GHz, to 51 K at 280 GHz. In this frequency range the mixer has a DSB conversion gain of 0 ±1.5 dB. The measured 460 GHz double-sideband receiver noise temperature, uncorrected for optics loss, is 32 K at 400 GHz, 34 K at 460 GHz, and 61 K at 520 GHz. Similar to the 230 GHz balanced mixer, the DSB mixer conversion gain is 1 ±1 dB. To help optimize performance, the mixer IF circuits and bias injection are entirely planar by design. Dual-frequency observation, by means of separating the incoming circular polarized electric field into two orthogonal components, is another important mode of operation offered by the new facility instrumentation. Instrumental stability is excellent supporting the LO noise cancellation properties of the balanced mixer configuration. In the spring of 2012 the dual-frequency 230/460 SIS receiver was successfully installed at Caltech Submillimeter Observatory (CSO), Mauna Kea, HI, USA.

Using tomography to assess the efficiency of the coaxial mixers in agitation of yield-pseudoplastic fluids

The mixing performances of five anchor coaxial mixers (anchor-Scaba 6SRGT, anchor-Rushton, anchor-Spiral, anchor-ARI, and anchor-A200), utilized for the agitation of non-Newtonian fluids, were evaluated in the laminar and transitional regime. To achieve this goal, power consumption and mixing time were measured as a function of the design parameters. An electrical resistance tomography (ERT) system was used to measure the mixing time. The non-Newtonian fluid was 2.0% xanthan gum solution (pseudoplastic fluid possessing yield stress). It was found that for all five configurations there was a critical speed ratio (RN=central impeller speed/anchor speed), which beyond it the mixing time did not decrease anymore with an increase in the speed ratio. Prior to this critical speed ratio, mixing time was proportional to RN0.4 regardless of the coaxial mixer configurations. The new correlations developed for the generalized Reynolds and power numbers of the coaxial mixers were tested successfully for all studied configurations. The power consumption and the mixing time data revealed that the Scaba-anchor coaxial mixer in the co-rotating mode was the most efficient mixer among the coaxial mixers explored in this study.

Pump Capacity and Power Consumption of Two Commercial In-line High Shear Mixers

Two main commercial in-line high shear mixer (HSM) configurations, including the dual rows ultrafine teethed and the single-row blade-screen in-line units, were investigated under the pump-fed mode in order to disclose the pump capacity and power consumption characteristics. Results indicate that the pump capacity of the teethed in-line HSM is rather poor, with maximum pumping heads of 2.31–2.72 m and a maximum pumping efficiency of 1.5%. By contrast, the blade-screen in-line HSM demonstrates maximum heads around 4.33–4.76 m and a maximum pumping efficiency of 7.3%. The power number data of both units with the bearing loss subtracted can be correlated by the Froude number modified power consumption model. The predicted power numbers show good agreement with the experimental data for both in-line HSMs. The results obtained here are fundamental for the performance assessment as well as the design and selection of in-line HSMs.

Design of a Low Loss RF Mixer in Ku-Band (12 - 18 GHz)

The goal of this paper is to design and develop low conversion loss mixers at Ku Band (12 - 18 GHz) in microstrip line configuration. The Ku-band (Kurtz-under band) is primarily used for satellite Communications, particularly for editing and broadcasting satellite television. CAD tools (Agilent’s Advance Design System software) have been used for simulation and optimization of the circuits. 180 degree balanced mixer configuration has been adopted due to better RF to LO isolation requirement. The circuit is designed on microstrip line using RT Duroid (Dielectric Constant = 2.22). Initially a rat race coupler (180 degree hybrid) was designed and simulated and optimized for required performance successfully.

The influence of cam geometry and operating conditions on chaotic mixing of viscous fluids in a twin cam mixer

AbstractSmooth particle hydrodynamica (SPH) simulations were used to better understand the mixing performance of a class of two‐dimensional Twin Cam mixers. The chaotic manifolds of the flow are used to describe the mixing and to identify isolated regions. For an equilateral triangle cam geometry, a figure‐eight manifold structure traps a layer of fluid against the cam boundaries. Changes in the differential rotation and phase offsets between the cams results in modest improvements in the mixing rate across the manifold barrier. Reducing the apex angle of the triangle changes the manifold structure and allows the trapped layer of fluid to mix more effectively with the rest of the domain. This article shows that examining the chaotic manifolds within a typical industrial mixer can provide valuable insight into both the transient and long‐term mixing processes, leading to a more focused exploration of possible mixer configurations and to practical improvements in mixing efficiency. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Study of biomolecules partition coefficients on a novel continuous separator using polymer-salt aqueous two-phase systems

A novel experimental prototype device was evaluated for the continuous operation of an aqueous two-phase extraction protocol. As proof-of-concept, preliminary tests were performed using an organic blue and Gentian violet dyes, to demonstrate the capacity of the system for solute partitioning and continuous phase separation. Different experimental configurations were established by changing tubular separator length (3.0 and 5.0 m) and static mixer configurations (single Beads-filled tube, zig-zag, 3 Serial Beads-filled and tube Spiral/single Beads-filled tube). The use of different static mixer configurations ensured total organic dyes transfer from bottom to top phase with shorter equilibration time (1.0–4.0 min) than batch system. The turbulent regime created at the entrance of the device by the static mixer, contributed to an efficient mass transfer that resulted in improvement of product partition coefficient (Kp) previously obtained from batch systems, when bovine serum albumin (BSA) was used as a model protein. A complex protein extract, namely whey protein extract (WPI), characterized by the presence of two main proteins (α-lactalbumin and β-lactoglobulin) with different phase affinities was successfully processed, resulting in differential protein partitioning with total recoveries up to 90% (top + bottom phase) and minimal protein precipitation at the interface. The obtained results suggested that the concentration of protein products in a defined phase could be feasible, by controlling the PEG-rich or salt-rich phase flow rates. These findings demonstrated the potential application of the proposed separator device for the continuous protein recovery using aqueous two-phase systems.

Quantification of mixing efficiency in turbulent supercritical water hydrothermal reactors

This paper presents a mathematical model able to quantify mixing efficiency in Supercritical Water Hydrothermal Reactors (SWHR) for the production of different types of nanoparticles. In fact, mixing plays a crucial role in determining the final particle size distribution and therefore the final product quality. In this work, mixing of supercritical water streams is studied with Computational Fluid Dynamics (CFD) by using the Reynolds Averaged Navier Stokes (RANS) approach coupled with an equation of state and a micromixing model, to take into account the effect of molecular mixing. The performance of the model is investigated in three different scenarios, corresponding to very different values of the Richardson number and very different mixer configurations. The main results show how mixing can be quantified by means of a global mixing time and how turbulence enhances the process, leading to better final product characteristics, especially in terms of lower mean particle size and narrower particle size distributions. This confirms previous research on this topic, highlighting the fact that both the mean particle size and the particle size distribution are strongly dependent on the mixing features of the SWHR.

Quantification of mixing efficiency in turbulent supercritical water hydrothermal reactors

Abstract This paper presents a mathematical model able to quantify mixing efficiency in supercritical water hydrothermal reactors (SWHR) for the production of different types of nanoparticles. In fact, mixing plays a crucial role in determining the final particle size distribution and therefore the final product quality. In this work, mixing of supercritical water streams is studied with Computational Fluid Dynamics (CFD) by using the Reynolds Averaged Navier Stokes (RANS) approach coupled with an equation of state and a micromixing model, to take into account the effect of molecular mixing. The performance of the model is investigated in three different scenarios, corresponding to very different values of the Richardson number and very different mixer configurations. The main results show how mixing can be quantified by means of a global mixing time and how turbulence enhances the process, leading to better final product characteristics, especially in terms of lower mean particle size and narrower particle size distributions. This confirms previous research on this topic, highlighting the fact that both the mean particle size and the particle size distribution are strongly dependent on the mixing features of the SWHR

Characterizing continuous powder mixing using residence time distribution

Continuous powder mixing is an efficient alternative in high volume manufacturing of powder-based products. A new method is communicated in this paper to determine the effects of different operating conditions and mixer configurations on mixing performance. The main idea of the proposed methodology is the utilization of experimental residence time distribution (RTD) measurements to (a) determine the contributions of feeding variability, powder segregation and RTD variability on output composition variance and (b) develop a predictive model of the output variance of a continuous mixer. The method is illustrated using experimental data for mixing acetaminophen and lactose in convective continuous mixer.

Mixing of particles and powders: Where next?

Industrial mixers for powders and granular materials operate with no effective control of mixture quality and lack scientific design. The last twenty years have seen growth in understanding of mixing and mixers. However, research falls far short of what is needed for on-line characterisation of mixture quality. Secondly, although theoretical descriptions of a few mixer types have been reported, these fall far short of what is needed for equipment design. Two thrusts could revolutionise this situation. One is a scientific characterisation of mixer structure applicable to industrial scale as well as laboratory scale equipment; this is now within our grasp using digital imaging. The other is the development of ideas to overcome the restricted number of particles that can be used in the Distinct Element Method (DEM) for mixers. The goal should be to take the designer through a sequence of steps to the most appropriate mixer size, configuration and operating conditions for a given process duty.

Digital mixer capable of programming mixer configuration, mixer configuration editing apparatus, and control application program to control digital mixer

A digital mixer has a processor capable of operating in accordance with a program to constitute a sound signal processing module and executing a program corresponding to mixer configuration data defining a mixer configuration of the sound signal processing module to perform a sound signal processing operation of the mixer configuration. In the digital mixer, a current memory stores an operation data set having a data structure corresponding to the mixer configuration data. A control section controls the sound signal processing operation of the sound signal processing module based on the operation data set stored in the current memory. A storage is provided for storing a plurality of operation data sets and attribute information indicative of data structures of the respective operation data sets. A select section selects one of the operation data sets stored in the storage. A converting section converts the selected operation data set from the data structure indicated by the attribute information of the selected operation data set into a data structure corresponding to the mixer configuration data, and recalls the converted operation data set to the current memory.

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.

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

The objective of this study is to propose a scale-up factor for a mean drop diameter in batch rotor.stator mixers. We define a homogenization index (H.I.) as a scale-up factor obtained from a local energy dissipation rate of turbulence and a circulation number. The local energy dissipation rate is calculated using the volume of the homogenization region, and the local power consumption is obtained from the measured net power consumption and the flow rate.We also measure the mean drop diameter using certain time interval for different configurations of mixers and different operating conditions in order to evaluate the validity of the scale-up index using H.I. Experimental results show that H.I. could well account for the mean drop diameter under different rotor speed conditions (13–27 m/s), with a different gap width between the rotor and the stator (0.15–0.25 mm) and different sizes of mixers and production volume (rotor diameters were 30 and 57 mm; production scale was 1.5 and 9 L). These results indicate that H.I. can be used to predict the mean drop diameter. Our results also suggest that the scale-up criteria for the mean drop diameter in relation to mixing time is based on H.I., and not necessarily on geometrical similarities, same rotor tip speed, or gap width in the case of similar mixer configurations and our experimental range (1 to 10 L) used for our model product, which is similar to typical dairy foods.

A K-Band CMOS Quadrature Frequency Tripler Using Sub-Harmonic Mixer

A low-power frequency tripler is designed by using the sub-harmonic mixer configuration for K-band applications. The proposed circuit features quadrature signal generation, applicable to LO signal synthesis in millimeter-wave wireless transceivers. It achieves conversion gain of -5.7 dB at the output frequency of 21 GHz. Implemented in a 0.18 mum CMOS technology, the circuit consumes power of 7.5 mW with 1.5 V supply voltage. The entire die occupies an area of 1000times1050 mum2.

Numerical investigation of flow mixture enhancement and infrared radiation shield by lobed forced mixer

For the exhaust system of turbo-fan engine, the numerical calculation is used to investigate the different mixer configurations. The method using forward–backward ray-tracing and narrow-band model to predict the radiation from engine exhaust has been developed. The scheme has been validated in accuracy for spectral radiation intensity predictions, and some useful results of practical importance have been obtained to establish its ability for infrared signature analysis of exhaust system. A series of computations on exhaust system model have been conducted to obtain the effects of mixer configuration on the aerodynamic performances and infrared radiation intensity. The results indicate that the lobed forced mixer can increase the mixing efficiency by 65%, decrease the thrust coefficient by 3% only, but the infrared radiation of plum can reduce about 40% relative to confluent mixer at zero degree aspect (normal to nozzle outlet), especially. That means the lobed forced mixer has the remarkable ability to shelter the infrared radiation from the inside enclosure of nozzle.

Angle-Resolved Particle Image Velocimetry Measurements of Flow and Turbulence Fields in Small-Scale Stirred Vessels of Different Mixer Configurations

Angle-resolved particle image velocimetry measurements were conducted at one degree intervals in miniature vessels of four different configurations used in high-throughput experimentation. The four vessels—standard fully baffled, unbaffled, off-center or eccentric impeller, and square section—were agitated by an up-pumping six-blade 45° pitched blade turbine (PBT). The effect of periodicity was revealed in all configurations but was restricted to the impeller discharge and inflow regions. The square vessel achieved the strongest axial-radial flow field among all configurations. The smallest overestimation in the computation of turbulent kinetic energy by the ensemble time average method, otherwise referred to as pseudoturbulence, was achieved in the eccentric and square configurations. The up-pumping PBT shed trailing vortices mainly in a radial direction with relatively little axial movement. The highest axial vortex position was achieved in the square vessel, which may be partly responsible for its lower mixing time compared to other configurations. The measurements obtained here in the high-transitional regime suggest that the square configuration performs better than other configurations and can be a good replacement for the fully baffled vessel in commercial high-throughput experimentation units where baffles are usually prohibited. This result was confirmed from mixing time measurements made using planar laser induced fluorescence where the superiority of the square vessel was demonstrated.

Active micromixer based on artificial cilia

We propose a design for an active micromixer that is inspired by the motion of ciliated micro-organisms occurring in nature. The conceptual design consists of an array of individually addressable artificial cilia in the form of microactuators covering the channel wall. The microactuators can be set into motion by an external stimulus such as an electric or a magnetic field, inducing either a primary or secondary motion in the surrounding fluid. To validate the concept and to help to design the precise mixer configuration, we developed a computational fluid-structure model. This model is based on a fictitious domain method that couples the microactuator motion to the concomitant fluid flow, fully capturing the mutual fluid-structure interactions. The simulated flow patterns resulting from the motion of single and multiple actuated elements (in a microchannel filled with a Newtonian fluid) under the action of a time-periodic forcing function are analyzed using dynamical systems theory to quantify the mixing efficiency. The results show that with a proper actuation scheme, two microactuators placed on the same wall of a microchannel can indeed induce effective mixing by chaotic advection; their distance should be small, but collisions should be avoided, and they can be actuated in a rather broad regime around 90° out of phase. Placing actuators on opposite walls also induces exponential stretching in the fluid, but if their length is relatively small, of the order of 20% of the channel height, mixing effectiveness is higher when they are arranged on the same wall.

Inline Bitumen Emulsification Using Static Mixers

Highly concentrated bitumen-in-water emulsions were produced with static mixers in continuous mode. The effect of the following process parameters on the average droplet size was studied: emulsion flowrate, static mixers configuration, and surfactant concentration as well as bitumen hardness, concentration, and temperature. Several static mixer configurations were investigated consisting of combinations of SMX (Sulzer Chemtech Ltd.) and helical elements with empty sections. The drop size results revealed that the mean droplet size could be scaled with the energy or the power draw depending on the static mixer configuration. Moreover, it was shown that the energy draw could capture the effect of emulsion flowrate and bitumen concentration on the mean droplet size, whereas the power draw (or the specific power) captured the effect of the emulsion flowrate and bitumen temperature. It was also demonstrated that the specific energy, or pressure drop, was minimized when SMX mixers were inserted after helical mixers.

Experimental and Numerical Analysis of Power Consumption for Mixing of High Viscosity Fluids with a Co-Axial Mixer

An experimental and numerical programme has been carried out to explore and determine design and mixing performance characteristics of co-axial agitation systems. Power consumption analyses in Newtonian and non-Newtonian fluids in laminar regime for a co-axial mixer configuration for chemical processes are discussed. An anchor impeller was used in combination with a dual set of pitched blade turbines in co-rotating mode. It was demonstrated that the power consumption of the proximity impeller is affected by the tip speed ratio, but no influence of the proximity impeller speed on the power drawn by the pitched blade turbines was observed. Computational fluid dynamics (CFD) was employed to calculate the flow field created by the co-axial mixer. CFD was able to predict well the power consumption of the co-axial mixing system. Power and Reynolds number were adapted to obtain the power characteristics of co-axial mixers. The approach employed to obtain a single master power curve succeeded for the investigated co-axial mixer configuration and is a useful engineering tool to predict the power consumption of co-axial mixing systems.

Prediction of a non-isothermal three-dimensional mixing layer created by a scarfed lobed mixer

The work presented here considers the complex mixing processes associated with a three-dimensional non-isothermal convoluted mixing layer such as produced by scarfed lobed mixers as used in aero-engine gas turbine exhaust ducts. Numerical simulations of the compressible Navier-Stokes equations in Reynolds-averaged form with a k-ε turbulence model are conducted. The discretization of the high-Reynolds-number form of the k-ε model for the unstructured mesh numerical solver used is described. The discretization was verified against two elemental flows that represent subcomponents of lobed mixer problems: a planar shear layer and a developing boundary layer. A grid dependency study is also presented for different grid types: purely quadrilateral, a purely triangular, and a mixed grid, to assess the influence of different mesh types on predictions. Results for a two-dimensional planar shear layer flow indicated that quadrilateral grids yielded best results for a given grid resolution. This result was confirmed in the numerical simulations of three-dimensional convoluted shear layers created by a generic lobed mixer geometry in which hexahedral grids yielded the most accurate results relative to a purely tetrahedral grid and a mixed grid. The model was finally used to simulate the flow field in an engine-representative scarfed mixer configuration under non-isothermal flow conditions representative of current engine practice. Results showed that the scarfed mixer introduced strong flow asymmetries in the azimuthal direction. This caused adjacent vortical structures produced by the alternating short and long gullies of the lobes to interact with one another and this behaviour dominated the flow evolution. Detailed comparisons between predicted and measured temperature fields were also carried out and generally showed encouraging agreement and capture of correct trends. The evolution of the predicted thermal mixing layer slightly lagged the measured data as was also the case for the velocity fields, indicating that improvements in the prediction of the thermal mixing layer may be strongly dependent on correct prediction of the momentum transport process as well as improved modelling of the turbulent heat fluxes.