Dynamical Particle Motions in Vortex Flows

Circular vortex flows generate interesting self-organizing phenomena of particle motions, that is, particle clustering and classification phenomena. These phenomena result from interaction between vortex dynamics and relaxation of particle velocity due to drag. This chapter introduces particle clustering in stirred vessels and particle classification in Taylor vortex flow based on our previous research works. The first part of this chapter demonstrates and explains a third category of solid-liquid separation physics whereby particles spontaneously localize or cluster into small regions of fluids by taking the clustering phenomena in stirred vessels as an example. The second part of this chapter discusses particle classification phenomena due to shear-induced migration. Finally, this chapter discusses about process intensification utilizing these self-organizing phenomena of particle motions in vortex flows

Vortex Dynamics in Complex Fluids

The present chapter provides an overview of vortex dynamics in complex fluids by taking examples of Taylor vortex flow. As complex fluids, non-Newtonian fluid is taken up. The effects of these complex fluids on the dynamic behavior of vortex flow fields are discussed. When a non-Newtonian shear flow is used in Taylor vortex flow, an anomalous flow instability is observed, which also affects heat and mass transfer characteristics. Hence, the effect of shear-thinning on vortex dynamics including heat transfer is mainly referred. This chapter also refers to the concept of new vortex dynamics for chemical process intensification technologies that apply these unique vortex dynamics in complex fluids in Conclusions

Thermal treatment of starch slurry in Couette-Taylor flow apparatus

In this paper, thermal processing of starch slurry in a Couette-Taylor flow (CTF) apparatus was investigated. Gelatinized starch dispersion, after treatment in the CTF apparatus, was characterized using such parameters like starch granule diameters (or average diameter), starch granule swelling degree (quantifying the amount of water absorbed by starch granules) and concentration of dissolved starch. These parameters were affected mostly by the process temperature, although the impact of the axial flow or rotor rotation on them was also observed. Moreover, the analysis of results showed a relatively good correlation between these parameters, as well as, between those parameter and apparent viscosity of gelatinized starch dispersion. Meanwhile, the increase in the value of the apparent viscosity and in shear-tinning behaviour of dispersion was associated with the progress of starch processing in the CTF apparatus. Finally, the CTF apparatuses of different geometries were compared using numerical simulation of the process. The results of the simulation indicated that the apparatus scaling-up without increasing the width of the gap between cylinders results in higher mechanical energy consumption per unit of processed starch slurry

Improvement of separation performance by fluid motion in the membrane module with a helical baffle

Pressure-driven membrane filtration processes such as microfiltration and ultrafiltration are still hindered by concentration polarization and membrane fouling. Generally in these filtration processes, concentration polarization causes decline of permeate flux and rejection, and fouling leads to permeate flux decline with the increase of rejection. The use of high shear stress for cross flow filtrations has long been considered one of the most efficient methods for overcoming these problems. However, circumferential fluid motion of the hollow fiber membrane surface is also important to avoid formation of a high concentration layer on the surface. In this study, ultrafiltration of humic acid aqueous solution using a polyethersulfone hollow fiber membrane was selected as a model case, and a membrane module with a helical baffle installed around the membrane was used. With the insertion of the baffle, normalized permeate flux and rejection became higher than those without the baffle at the wide range of the feed flow rate. In order to identify the cause of the improvement, CFD simulation was conducted for different baffle geometries. Swirling flow motion generated by the helical baffle around the membrane became more dominant with the lower aperture ratio of the cross sectional area, and there existed the optimum value for the swirling flow generation in terms of the variation of the helical baffle pitch length. The intensity of this fluid motion was characterized by Swirl number and it was found out that high separation performance was obtained at the high Swirl number