1GHz-9GHz混波室的结构和统计特性的研究

混波室(Reverberation Chamber)作为一种新型的电磁兼容的测量设备,由于其自身的优越性,受到越来越多的关注。混波室测量技术与混波室中场分布的统计特性有着密切关系。本文提出一种工作频率为1GHz-9GHz的三维混波室结构,采用有限元法(FEM),利用AnsoftHFSS9.2软件进行建模仿真,重点研究了混波室内场分布的统计特性,并与实测结果相比较,与三维混波室理论场分布特性相一致。同时,比较了不同的扇叶取样数下混波室内场分布的情况,指出扇叶取样数对统计特性的影响。

Transfer Characteristics in Mechanically Stirred Airlift Loop Reactors with or without Static Mixers

The mechanically stirred internal loop airlift reactors equipped with or without static mixers are devised for intensification of gas-liquid mass transfer rate. The influences of superficial gas velocity, agitation or static mixers on gas hold-up, mixing time, liquid circulating velocity and volumetric mass transfer coefficient have been investigated with tap water and carboxymethyl cellulose (CMC) aqueous solution. The experimental results indicate that mechanical agitation is more efficacious than static mixer in highly viscous media for improving mass transfer in airlift reactors. The empirical correlation of volumetric mass transfer coefficient with apparent viscosity, and energy consumption for mechanical agitation and aeration is developed.

Graphene stirrer with designed movements:Targeting on environmental remediation and supercapacitor applications

Beyond the traditional focus on improvements in mechanical, electronic and absorption properties, controllability, actuation, and dynamic response of monoliths have received increasing attentions for practical applications. However, most of them could only realize simple response to constant conditions(e.g. a stationary magnetic field) while carrying out humdrum motions. By controlling distribution of metal organic framework obtained carbon-enriched Fe304 nanoparticles in self-assembly reduced graphene oxide(RGO) monoliths, we could achieve two distinctive RGO-Fe_3 O_4 stirrers that could dynamically respond to the rapidly changing magnetic field while executing designed movements precisely: rotating with lying down posture or standing straight posture. These stirrers can not only be applied in environmental remediation(e.g.suction skimmer), but also be recycled as electrode active materials for supercapacitors after fulfilling their destiny, realizing transformation of trash to treasure, which will inspire other dynamically responsive monoliths for various applications.

Numerical and experimental analyses of a stirred vessel for a large volumetric flow rate of sparged air

Computational fluid dynamics(CFD)and experimental analyses of some of the basic characteristics of air sparging in a tall stirred vessel equipped with a three-stage impeller are presented.The impeller was assembled from a radial ABT impeller as the lower,a turbine 6 PBT45 as the middle and an axial Scaba-type 3SHP1 impeller as the upper.All the impellers were of the same diameter,i.e.,225 mm,while the vessel diameter was 450 mm.The impeller’s rotational speed was 178 r·min-1.The aeration regime was established with an air volumetric flow rate of 28.3 m3·h-1.To the best of our knowledge,this study is the first to consider the very high gassing rate by means of CFD in a tank stirred by three-stage axial/radial impellers.The numerical simulation was performed using the ANSYS Fluent(R17.2,2016)code for solving the governing equations of fluid dynamics in single-and multi-phase systems.While discussing the bubble size distribution,a discrete population balance model(PBM)was used.Adopting CFD,the stirring power and the total void fraction(the total gas holdup)were calculated.The results were in good agreement with the measured values using a laboratory experimental device.

Effect of flow field distribution on the synthesis of sub-micron ZSM-5 molecular sieve in a quasi-solid system

Scale-up synthesis of sub-micron ZSM-5 molecular sieve in a quasi-solid system was investigated. Compared with traditional hydrothermal synthesis, the synthesis in a quasi-solid system has the advantages of high yield, short crystallization time, low energy consumption as well as low emissions. However, the high solid content in the quasi-solid system can cause the mass and heat transfer problems and make scalable production difficult. In order to solve the problem, we have developed a method for the optimization of the mass and heat transfer. By this method one can vary the flow field in the reactor by changing the stirrer speed. Scale-up synthesis of the sub-micron ZSM-5 molecular sieve in a quasi-solid system was carried out in a 5 L reactor with double propeller-type agitators. The process was investigated with product characterization using X-ray diffraction （XRD） and scanning electron microscopy （SEM） and the flow field information was collected using laser Doppler velocimetry （LDV）. The results showed that the flow field patterns can be tuned by using different stirrer speeds, the morphology and size of assynthesized of ZSM-5 can be effectively controlled.

DEM analysis of the influence of stirrer design on die filling with forced powder feeding

Die filling is a critical stage during powder compaction,which can significantly affect the product quality and efficiency.In this paper,a forced feeder is introduced attempting to improve the filling performance of a lab-scale die filling system.The die filling process is analysed with a graphics processing units(GPU)enhanced discrete element method(DEM).Various stirrer designs are assessed for a wide range of process settings(i.e.,stirrer speed,filling speed)to explore their influence on the die filling performance of free-flowing powder.Numerical results show that die filing with the novel helical-ribbon(i.e.,type D)stirrer design exhibits the highest filling ratio,implying that it is the most robust stirrer design for the feeder configuration considered.Furthermore,die filling performance with the type D stirrer design is a function of the stirrer speed and the filling speed.A positive variation of filling ratio(ηf>0%)can be ensured over the whole range of filling speed by adjusting the stirrer speed(i.e.,increasing the stirrer speed).The approach used in this study can not only help understand how the stirrer design affects the die filling performance but also guide the optimization of feeder system and process settings.

Numerical Study of Temperature Development of Slurry of Al-Si Alloy in Double-Axis-Electromagnetic Stirrer

Flow and temperature fields of slurry of A1-Si alloy in the process of cup-cast method is numerically simulated. The simulation results agree with the experiment by Shimasaki et al.under an estimated value of the overall heat transfer coefficient between the alloy and the cup.

Numerical Simulation of Electromagnetic Field and Flow Pattern in a Continuous Slab Caster with In-roll Type Strand Electromagnetic Stirring

The electromagnetic field and flow analysis model were developed to simulate the electromagnetic field and the flow pattern in a vertical curved continuous slab caster with the in-roll type strand electromagnetic stirring. The transient electromagnetic field distribution and the induced electromagnetic force were numerically described. The effects of stirring current, stirring frequency, and different stirrer configurations on the electromagnetically driven flow field in the strand were investigated and the optimization of the stirring parameters was discussed by performing a relative comparison of numerical results. Results show that the in-roller type strand electromagnetic stirrer （S- EMS） pair generates the fluctuating magnetic fields, penetrating through the cast slab and periodically parallel shift- ing along the slab wide face w!th time evolution. The transient induced electromagnetic forces travels toward the magnetic flux shifting direction, Different stirring parameters （i. e. current and frequency） and stirrer configurations affect the stirring strength and the flow rbcirculation pattern in the strand, which are closely related to metallurgical performances of the stirrers. There is an optimum frequency to obtain the maximum stirring. The present model pro vides a relatively theoretical insight into the in-roll type strand electromagnetic stirring system for best operating.

Effect of Magnetic Stirrer Imposed in the Inner-Mold on Continuous Casting Hollow Billet

In order to improve the quality of continuous casting hollow steel billet,especially the inner surface quality,the technology of installing magnetic stirrer in the inner-mold during the hollow billet continuous casting was put forward,and structure and electrical parameter of magnetic stirrer were studied by numerical simulation method,and static simulation experiment was done,the results show that:1)the greater the current strength,the solidification rate and temperature gradient of molten metal are lower,and therefore it helps to form fine equiaxial crystal structure,however when the current strength is too large,it is not obvious to change the equiaxial crystal size,and the excessive velocity of the melt will result in segregation defects.2)Three-phase magnetic stirrer has higher stirring effect than that of two-phase one.3)Tooth width of yoke should be small to improve the stirring effect.The numerical simulation results can provide the theory basis to optimize the electromagnetic continuous casting technology.