Akio Yamada

Bio: Akio Yamada is an academic researcher from Kyushu University. The author has contributed to research in topics: Shear rate & Dimensionless quantity. The author has an hindex of 1, co-authored 1 publications receiving 15 citations.

Evaluation of performance of mixing apparatus for high viscosity fluids

Abstract: There exists no universally accepted technique for evaluating the functional status of equipment for high-viscosity mixing based upon generalized basic information such as flow patterns and shearing deformation characteristics. This paper deals with the measurement of flow patterns. After obtaining the overall flow patterns in a mixing vessel, circulation capacity and fluid deformations which cover information about energy dissipation were correlated with the homogenizing time. The physical meanings of C1=nTM and C2=TM √Pυgc/μ are interpreted by using a concept of striation thickness. A measure of an averaged dimensionless shear rate number √Pυgc/μ/n is plotted against the dimensionless nearest distance between moving part and fixed wall in the mixing vessel. This diagram could give an useful comparison as to averaged shear rate characteristics for any device for high-viscosity mixing regardless of geometrical configuration. A novel technique is also proposed for quick evaluation of the shear distribution in a given apparatus.

CFD simulation of stirred tanks: Comparison of turbulence models. Part I: Radial flow impellers

Abstract: A critical review of the published literature regarding the computational fluid dynamics (CFD) modelling of single-phase turbulent flow in stirred tank reactors is presented. In this part of review, CFD simulations of radial flow impellers (mainly disc turbine (DT)) in a fully baffled vessel operating in a turbulent regime have been presented. Simulated results obtained with different impeller modelling approaches (impeller boundary condition, multiple reference frame, computational snap shot and the sliding mesh approaches) and different turbulence models (standard k − e model, RNG k − e model, the Reynolds stress model (RSM) and large eddy simulation) have been compared with the in-house laser Doppler anemometry (LDA) experimental data. In addition, recently proposed modifications to the standard k − e models were also evaluated. The model predictions (of all the mean velocities, turbulent kinetic energy and its dissipation rate) have been compared with the experimental measurements at various locations in the tank. A discussion is presented to highlight strengths and weaknesses of currently used CFD models. A preliminary analysis of sensitivity of modelling assumptions in the k − e models and RSM has been carried out using LES database. The quantitative comparison of exact and modelled turbulence production, transport and dissipation terms has highlighted the reasons behind the partial success of various modifications of standard k − e model as well as RSM. The volume integral of predicted energy dissipation rate is compared with the energy input rate. Based on these results, suggestions have been made for the future work in this area.

Circulation and mixing times for helical ribbon impellers. Review and experiments

Abstract: The purpose of this paper is to extend basic information on mixing and circulation times for mixing systems equipped with helical ribbon impellers. In a first part, from a survey of existing literature, we have reviewed the different effects of the geometrical parameters of the helical mixing systems (clearance-wall, pitch size ratio, blade width, number of blades) on the mixing process. From this qualitative analysis, useful guidelines are provided on the influence of the helical impeller geometry on the mixing effectiveness. In a second part, the homogenization effectiveness of an atypical helical ribbon impeller was investigated and compared with the performance of classical helical ribbons impellers.

Theory of mixing sections in single screw extruders

Abstract: A discussion of the effect of deformation on mixing leads to reorientation of fluid interfaces as a proposed mechanism for special “mixing sections” in single screw extruders. Based on the kinematics of mixing it is shown how a mixing section can greatly decrease the amount of work necessary to accomplish extensive mixing through orienting the fluid more favorably for mixing by subsequent shear. Mathematical development quantitatively describes favored configurations of mixing sections. An upper bound for the mixing performance of a simple model of an extruder with special sections is shown to be similar to turbulent mixing. Based on this theory the key actions of the special sections are identified.

An upper bound on the performance of plane strain mixers

Abstract: Consideration of the basic equation for mixing in plane strain laminar flow shows that mixing can proceed much more rapidly than has been commonly accepted. While linear rates of mixing have been predicted previously, exponential rates of mixing are possible. An upper bound for, the rate of mixing in plane strain laminar flow is shown to be an exponential. The geometry of the flow which produces this most rapid mixing is shown to be plane strain extensional flow, sometimes called pure shear flow, with all interfaces aligned normally to the smallest principle axis of the deformation.