From the viewpoint of modeling of coated film drying, research papers by the author and colleagues, published mainly in Kagaku Kogaku Ronbunshu, on binder segregation estimation, the temperature-change method and a drying characteristic model are reviewed and future prospects are discussed under the keyword of “correlation model.” A correlation model by the lumped parameter system was recently proposed that aimed to provide rapid feedback to production of research results into complicated phenomena of coated film drying. Here, “correlation” means the interrelationships among variables in the phenomena on the basis of mass- and energy-balance equations. In the correlation model, establishment of an appropriate balance domain obviates the need for parts (a) or all (b) of transport properties or transport mechanisms (c), in contrast to the prediction model, in which transport mechanisms and properties are all indispensable for simulation of the phenomena. The correlation model may allow research results to be fed back rapidly to production. This review discusses the temperature-change method to estimate drying rate by using the temperature history of wet material during drying as an example of (c), and the method for estimation of binder segregation within dried material by using drying rate history during drying as examples of (a) and (b). Both proposed methods are based on models of the lumped parameter system. Combination of the two methods may allow estimation of binder segregation by using material temperature history.
Dispersion and agglomeration of particles with a drastic change in fluid flow differs from those under a steady shear flow. In this study, the development and destruction of particle agglomerates with step-wise shear rate change were investigated by microscopic observation, and the results were compared with particle dispersibility predicted from rheological data. Polystyrene particles with strong agglomerative properties could be controlled by addition of small amount of carboxymethylcellulose (CMC). Once the particles were sufficiently dispersed, the agglomeration process was dominated by the collision of particles and was not affected by polymer concentration. When the amount of adsorbed CMC was sufficient to prevent the aggregation of particles, agglomerates readily dispersed to an agglomerative state corresponding to the applied shear rate. However, insufficient adsorption of CMC resulted in a heterogeneous agglomeration process that took longer time to attain steady agglomerated state. Slurry viscosity was employed to evaluate agglomerative nature except under conditions of complete dispersion.
Fluid mixing is generally judged to be complete when two or more different fluid materials are uniformly distributed over the whole system. In practice, mixing time in mixing processes is often measured by detecting color change due to a chemical reaction. However, the conceptual mixing time does not necessarily coincide with the time of completion of color change. In the present study, we reconsidered the relation between the conventional concepts of fluid mixing and experimentally measured mixing time. In addition, by comparing the difference in the spatiotemporal concentration change between an irreversible decolorizing reaction and a reversible color reaction, we investigated the possibility that mixing times measured by use of these reactions may differ. Experimentally, the completion time of color change in the reversible reaction was found to be longer than that of the irreversible reaction. In a reversible reaction, an initial color change may be reversed until the concentration becomes uniform in the system. Hence, the completion time of color change agrees well with the mixing time in a reversible reaction. On the other hand, in an irreversible reaction, a region once decolorized cannot be colored again even if the concentration in the system is not homogeneous. Thus, error may arise if an irreversible reaction alone is used to conclude that mixing is complete. Moreover, the difference in mixing time measured by irreversible and reversible reactions becomes larger as Reynolds number increases.
In order to apply the lattice Boltzmann method to a flow problem of magnetic suspensions, we investigated the feasibility of employing a viscosity-modifying method to refine the activation of particle Brownian motion based on fluctuation hydrodynamics. We examined a magnetic suspension in thermodynamic equilibrium to clarify the influences of various factors such as the roughness of a lattice system and the volumetric fraction of magnetic particles on the scaling coefficient of viscosity. Snapshots and pair correlation functions of magnetic particles confirmed that the viscosity-modifying method can show good agreement with the results of Monte Carlo method both quantitatively and qualitatively. This agreement is almost independent of the roughness of a lattice system if a relatively fine lattice system is used. The scaling coefficient of viscosity is almost constant and independent of the strengths of magnetic particle-field and particle-particle interactions, and is also almost constant for the variation of the volumetric fraction for a given lattice system unless a coarse lattice system is used. We conclude from these results that the lattice Boltzmann method with the viscosity-scaling procedure is potentially applicable for simulating a flow problem of magnetic particles under a non-uniform applied magnetic field.
Mixtures of microbubbles (particle size, 20 μm) with water or dilute polymer solutions were passed through micro-orifices of 100–400 μm. Pressure drops were measured, and elastic stresses were estimated. The pressure drops of Polyethylene Oxide solutions alone were less than those of water, while the pressure drops of microbubble mixtures with Polyethylene Oxide were greater than those of Polyethylene Oxide solutions alone. This phenomenon was thought to arise from hindrance by microbubbles of the association of polymer chains in the solution; and this idea was supported by the estimated elastic stresses.
Polyamic acid particles, the precursors of polyimide particles, are basically prepared by a precipitation polymerization in which diamine and tetracarboxylic acid dianhydride are irradiated with supersonic waves at room temperature. Polyimide particles are then produced by thermal processing of the polyamic acid particles. Such polyimide particles are characterized by their size uniformity and spherical shape. The physical properties of polyamic acid particles such as size, size variation and shape vary are reported to depend on the reaction solvent, but a detailed investigation of this effect has not been reported. In this study, the effect of reaction solvent on mean size of polyamic acid particles was investigated by using Hansen Solubility Parameters (HSP). It was found that the mean size of polyamic acid particles was correlated with the HSP distance between reaction solvent and polymer. Also, calculation of the constituent energies of the HSP suggested that δd, the energy from the dispersion force between molecules, was dominant. As a result, it was concluded that the HSP could be used to control the mean size of polyamic acid particles.
A new method for spray combustion simulation was proposed in which the state of a droplet is divided into two modes: the combustion mode and the evaporation mode. The combustion mode assumes single droplet combustion, and the evaporation mode assumes group combustion or evaporation. First, single droplet combustion analysis was carried out and a database of evaporation rate, flame radius and heat transferred into the droplet was prepared. Evaporation rate in the combustion mode was calculated from the database, and evaporation rate in the evaporation mode was calculated with a conventional evaporation model. In this study, a simulation of heavy oil spray combustion was carried out, and the calculated results were compared with experimental findings. The result showed that it is possible to calculate heterogenous combustion, suggesting that our method is effective for spray combustion simulation of low-volatility fuel.
The influences of dissolved oxygen and shearing force on the production of extracellular polysaccharides by Polianthes tuberosa callus were evaluated independently by use of a fixed-bed reactor. Oxygen consumption rate of the callus increased with increasing dissolved oxygen (DO) concentration, while the polysaccharide productivity peaked at DO concentration of 7.6 g/m3. When DO concentration was kept around 7.6 g/m3, the maximized polysaccharide productivity was observed with respect to shearing force generated by the flow of medium. Assessment of culture performance in an industrially conventional vessel with aeration and agitation showed that DO concentration could be controlled around 7.6 g/m3 under a stable operation condition of shearing force, though a desirable condition of shearing force was difficult to achieve.
To clarify the effect of agitation on the leakage rate of intracellular substances from Spirulina platensis and Chlorella pyrenoidosa, we measured the ultraviolet absorption of culture media after agitation and subsequent removal of cells by filtration. The leakage rate of the intracellular substances from S. platensis was proportional to algal concentration to the power of 1.0 and to blade number to the power of 1.3. For Reynolds numbers in the range of 1.1–2.2×104, the leakage rate constant of intracellular substances of S. platensis was 7×10−3 m3 · kg−1 · h−1, which was 1.4 times that of C. pyrenoidosa.
A washing method utilizing high-speed movement of microbubbles under ultrasound irradiation was studied. Air microbubble movement was observed under ultrasound irradiation of 20 kHz and 600 W with a high-speed camera. Microbubbles were observed to move at high velocities and cluster together. Copper plates with oil-based ink dirt or carbon dirt were prepared and used for the washing experiments. High-speed movement of microbubble clusters under ultrasound irradiation showed a cleaning effect with both samples. Spot damage by ultrasound cavitation of the sample surface did not occur in the presence of microbubbles, probably due to the covering of microbubble clusters near the sample surface. The results indicate that low-frequency (20 kHz) ultrasonic cleaning with microbubbles is suitable for weakly adhering dirt and for weak sample surfaces.