Kunio Kataoka

Emulsion polymerization of styrene in a continuous Taylor vortex flow reactor

Abstract A continuous emulsion polymerization of styrene was tried in a Taylor vortex flow reactor which has characteristics of a plug flow reactor. The Taylor vortex flow reactor has the mixing characteristics appropriate for this reaction system. The steady-state conversion, the average molecular weight and the size distribution of latex particles can be controlled by the flow condition as well as by the reaction temperature.

Effective mass diffusion over cell boundaries in a Taylor-Couette flow system

Abstract Effective mass diffusion over cell boundaries in a Taylor-Couette flow system was investigated ranging from singly periodic wavy vortex flow to weakly turbulent wavy vortex flow by a salt-solution tracer technique. In order to determine experimentally the intercell mixing coefficient k CB between the neighbouring pairs of vortices, an appropriate model was formulated. As a result, k CB depends not only on Taylor number but also on axial wavelength with fluid viscosity. In the singly periodic wavy vortex flow region, the intermixing is enhanced by periodic fluctuations resulting from azimuthally travelling waves on the cell boundaries. With increasing Taylor number in the doubly periodic wavy vortex flow and weakly turbulent wavy vortex flow regions, the mixing characteristics go toward axial turbulent diffusion. In these two flow regions, the correlation between k CB and effective diffusion coefficient D z based on an axial diffusion model has been obtained as D z = 2 λk CB .

Controlling particle size by self-sustained oscillations in continuous emulsion polymerization of vinyl acetate

This work examined the controllability of the size of polymer particles and its distribution by taking advantage of the self-sustained oscillations of monomer conversion in continuous emulsion polymerization of vinyl acetate in a CSTR. The emulsifier concentration was primarily varied as a control parameter of the experimental condition below the critical micelle concentration. Regularly periodical oscillations in monomer conversion occurred with a long period as compared to the mean residence time of the CSTR. Time-dependent size distribution of polymer particles observed by TEM varied in form synchronously with the periodical oscillations of monomer conversion. These results suggest that particles can be formed intermittently owing to the temporal variation of the concentration of free emulsifier in the condition below CMC. It has also been confirmed that the particle size distribution (PSD) is made quite narrow in the condition for regularly periodical oscillations but considerably wide in the condition for irregular oscillations. It has been successfully indicated that the self-sustained oscillations in continuous emulsion polymerization will be profitable not only for controlling the size of latex particles but also for raising the monomer conversion.

Intercellular mass transfer in wavy/turbulent Taylor vortex flow

Abstract Axial mass transfer or mixing through trains of cellular vortices has been observed in the range of time-dependent wavy vortex flow with the aid of visualization technique of wave motion, salt-tracer response technique, and spectral analysis of fluctuating velocity-gradients. There appear multiple stable flow states even at the same Reynolds number owing to the hysteresis of the flow system, depending upon the start-up operation. Intercellular mass transfer depends upon the axial wavelength and wave motion as well as the Reynolds number in the range of singly (SPWVF) and doubly periodic wavy vortex flow (DPWVF) whereas it is controlled mainly by turbulent motion in the range of weakly turbulent wavy vortex (WTWVF) and fully turbulent Taylor vortex flows (TTVF). Intracellular mixing increases monotonically with Reynolds number, regardless of the flow state.

CHARACTERISTICS OF CONVECTIVE HEAT TRANSFER IN NONISOTHERMAL, VARIABLE-DENSITY IMPINGING JETS

Convective heat transfer is experimentally studied in the impingement region where a free jet of high-temperature burned gas impinges normally on a circular flat plate cooled from the back. Taking into account the effect of jet-to-ambient fluid density ratio on the jet development, a generalized, design-oriented model is proposed, which permits local prediction of the wall heat-fluxes over a wide range of the initial density ratio.

Laser-optical observation of chaotic mixing structure in a stirred vessel

The purpose of the present work was to observe the chaotic mixing structure in a stirred vessel via flow-visualization using laser-induced fluorescence. Under laminar flow conditions in the stirred vessel, two types of mixing region were observed, i.e. the active mixing region (AMR) and the isolated mixing region (IMR). The IMRs clearly took the form of two toroidal vortices respectively above and below the turbine impeller in a range of less than Reynolds number (Re) = 100. These regions did not exchange much fluid material with the AMR. From a cross sectional view, it was found that the good mixing in the AMR resulted from the stretching and folding motion of the turnstile-lobe-like regions generated by each stroke of the turbine blades. Under the nearly same rotational conditions, a set of three stable filaments surrounding the core torus of the IMRs was found in the case of the six-bladed turbine, while a set of four filaments was found in the case of the four-bladed turbine. Hence it can be considered that these structures depend on the periodical perturbations caused by the rotating turbine blades. In order to observe the internal structure of the ring-doughnut-shaped core regions, an unsteady rotation procedure was applied. Another set of filaments was observed to exist inside the core. It was found that the IMRs had complex multi-structures consisting of various Kolmogorov, Anold, and Moser (KAM) tori. The rotating period of an island P i,and the passing period of turbine blade P t had a rational relationship. Furthermore, the rational number of the ratio, P i/ P t, corresponded to the number of islands. These results clearly show the structure complicated with stable/unstable manifolds obtained from the Poincare-Birkhoff theorem.

Electrochemical observation of instabilities of the Belousov-Zhabotinskii reaction in CSTR

The instabilities of the Belousov-Zhabotinskii reaction were studied in an isothermal CSTR by varying the space velocity as bifurcation parameter. The time-dependent concentration of bromide ion and redox potential were observed, respectively, by a Ag-AgBr electrode and a platinum-wire electrode under reaction-controlling conditions. The single-peak periodic and the chaotic oscillations occur alternately with increasing space velocity. The multipeak oscillations were also observed at higher space velocities. Two kinds of chaotic oscillations were observed, chaotic oscillations with amplitudes varying irregularly in the periodic-chaotic sequence region and chaotic mixing of large and small amplitude in the multipeak oscillations region. An analysis of the phase portraits for these chaotic oscillations indicates that they correspond to low dimensional and fractal structures.

Analysis of Orderliness in Higher Instabilities Toward the Occurence of Chaos in a Taylor-Couette Flow System

Tbe purpose of the experimental work is to elucidate the mechanism for the occurrence of chaos in a Taylor-Couette flow system. Tbe attention was focused on the higher instability region from the doubly-periodic to the weaklyturbulent wavy vortex flow. In order to take note of the effect of hysteresis, the inner cylinder rotation was accelerated at a constant rate from rest until a specified Reynolds number was reached. Tbe test section with the radius ratio of 0.625 had an annular gap width of 22.5 mm and an aspect ratio of 4. A fiberoptic laserDoppler velocimeter was employed to observe a time-dependent, peripheral component of velocity at the central region of vortex ceHs. At the same time, timedependent peripheral component of velo city gradients on the wall of the stationary outer cylinder were measured in the neighborhood of one of the outflow ceH boundaries with a hot-film shear sensor embedded flush with the inside cylindrical surface. Four vortex ceHs were always formed regardless of the acceleration rate of the inner cylinder rotation tested in the start-up operation, but the axial wavelength of the two central vortices was shorter than that of the remaining two end vortices. The amplitudes of the fluctuations of velocity and velocity-gradient varied irregularly whereas the first fundamental frequency was maintained in proportion to the inner cylinder rotation as long as the azimuthaIly-traveling waves existed. It has been conc1uded that chaos occurs firstly at the inflow cell boundaries as a result of instabiIity in the viscous interaction of end vortices with the fixed bottom and top surfaces and that the chaotic turbulence is propagated along the secondary flow streamlines toward the central vortices and penetrated very slowly toward the center of vortex cells.