Solution containing high-molecular-weight polymer or surfactant forming rod-like micelles show very complex flow behavior. Non-linear flow behavior became prominent especially under high shear rates or high extensional rates. That is due to non-uniform structure of dilute polymer or rod-like micelles solution, which is enhanced under the condition of high strain rates.
In this study, in order to detect non-uniform structure in complex fluids, optical tweezers was used to measure local viscosity of several Newtonian and viscoelastic solutions. Ethylene glycol solution, polyethyleneoxide (PEO, Mw = 3,500,000) solution and cationic surfactant solution were prepared as Newtonian and viscoelastic solutions. The cationic surfactants form rod-like micelles in the solution with the presence of counter ion supplier, which became highly viscoelastic. The average values of the local viscosity of these solutions measured by the optical tweezers were consistent with the viscosity measured by a rheometer. Then, distributions of the local viscosities were also obtained to quantify non-uniform structure of the solution. The local viscosity distributions of viscoelastic solutions were wider than that of Newtonian fluids. Especially, the distribution of rod-like micelles solution was much wider than that of the other solutions. The results suggest that the local viscosity distribution of each solution has non-uniformity information of viscoelastic complex fluids.
For the production of self-adhesive labels, high speed coating of adhesives is necessary to increase the productivity of labels. It is also required that the coated adhesives is as thin as possible to reduce the use of adhesives. Curtain coating is one of the candidate to achieve high speed and thin coating. However, curtain coating can cause some troubles like air entrapment resulting in the defect of the products. In this study, three-dimensional numerical simulations of curtain coating were carried out in order to investigate the mechanism of entrapment of air to coated films. The OpenFOAM tool box with VOF method was used for the simulation.
Simulation results reproduced four different regimes in curtain coating: coatable, heel formation, air entrainment, and air entrainment with heel formation. They are mapped on the diagram of the curtain Reynolds number versus the velocity ratios between coating speed (substrate speed) and impingement one. We will discuss the mechanism of air entrapment using numerically visualized flow fields.
In fluid processes in engineering fields, flow pattern characters are essential in the process performance, and are largely controlled by the geometric structures of the channel and/or driving element. In melt mixing in polymer processing, various elements, including screw and mixing elements, defines the channel geometry, and the resulting flow patterns are responsible for different mixing characteristics. Analyzing the flow pattern should be useful in understanding the mixing characteristics in connection with the different geometric structures of the mixing elements. Mathematically, the classification of flow field can be analyzed by the eigen-analysis of the deformation rate tensor [1,2]. However, such analysis technique have not been commonly applied in fluid processing. We have developed a simplified flow classification scheme based on the invariants of the strain-rate tensor and the vorticity tensor, which is frame-invariant [3,4] . The spatial distributions of these quantities offer an essential tool in understanding the flow pattern structure, and therefore can be useful to get insights into the connection between the geometry and the process performance.
[1] Tanner, R. I., and R. R. Huilgol, Rheol. Acta 14.11 (1975) 959–962.
[2] Chong, Min S., Anthony E. Perry, and Brian J. Cantwell, Phys. Fluids A 2.5 (1990) 765–777.
[3] Nakayama, Y., et al. AIChE J. 62.7 (2016) 2563–2569.
[4] Nakayama, Y., et al., AIChE J. 64.4 (2018) 1424–1434.
Ice cream is one of the most popular deserts in the world. Its physical and sensory properties depend on the microstructure of ice cream. Ice cream consists of bubble, ice, fat and the freeze-concentrated continuous phase. Because all the phases intricately interact each other, it is quite difficult to construct the precise principle for the control of ice cream properties in the production process. The microstructure of ice cream is determined in freezing process. During freezing process of the ice cream mix in an ice cream freezer, air is whipped into the mix. Air taken in the ice cream is broken down to small bubbles by the shear force. Also, the shear force induces fat globules coalescence which affects ice cream properties. Therefore, it can be considered that the shear force generated by the agitation operation dominates the microstructure of ice cream. In order to control ice cream properties from the perspective of agitation, in this study, the effect of agitation speed on the viscosity of the ice cream and the bubble size in the ice cream was investigated.
The commercial batch ice cream freezer with an impeller was used. During freezing process, the torque was monitored by a torque meter (ST3000II, SATAKE Chemical Equipment MFG. LTD.). Based on the measured torque, the apparent viscosity was estimated. The bubbles size in the ice cream was calculated from the image acquired by a digital micro scope (DMS1000B, Leica Microsystems LDT.).
The apparent viscosity decreased with the increase in the agitation speed. This means the agitation speed has an influence on the sensed creaminess during consumption. Furthermore, it was found that the increase in the agitation speed leads the increase in smaller bubbles with a narrower size distribution. These results imply that the rheological properties can be controlled by the agitation operation.
The gas-solid fluidized beds have been broadly studied, both experimentally and theoretically because they are widely applied in several industrial applications. However, most of the previous studies reported their findings based upon spherical particles while in practice, particles in gas-solid fluidized beds are generally non-spherical. In this study, the combined approach of CFD-DEM (Computational Fluid Dynamics - Discrete Element Method) is used to simulate the gas-solid fluidization process of ellipsoidal particles to analyse the effect of particle shape on bubble dynamics. Simulations for single jet fluidized bed by injecting gas jet only through central orifice showed that the bubbles for ellipsoidal particles are larger in size, have a greater bubble size distribution and higher bubble break-up frequency. The bubbles for ellipsoidal particles have lateral drift, therefore, while rising through the bed they travel away from bed centreline. Simulations for uniform gas injection demarcated that the bubble and solid flow patterns are asymmetrical for ellipsoidal particles compared to spherical particles. The bubble size is smaller and the bubble size distribution is broader for ellipsoidal particles. Both types of simulations exhibited that the difference in particle shape can result in different bubble behaviour, for example, a region of bubble formation, bubble trajectory and bubble properties. Moreover, ellipsoidal particles have preferred orientation which can depend upon the development of bubbles. The ellipsoidal particles align parallel to the fluid flow direction around the bubbles while they align perpendicular to the fluid flow direction at the top of the bubble. The findings deduced from this study can aid in the understanding of particle shape effect on gas-solid fluidized beds.
