The extensional flow has attracted attention in dispersing the nanofillers and immiscible polymer blends on the nanoscale since the extensional flow enables the direct stretch of the nanofillers and polymer droplets without rotation. Based on the fundamental analysis, we have revealed the dispersion effect of extensional flow. Furthermore, we proposed a new mixing element of a twin-screw extruder, fixed Blister Disc (XBD), that enables generating a strong extensional flow field. This paper reviewed the previous studies and introduced the case studies of compounding the nanocomposites and polymer blends using a twin-screw extruder equipped with the XBD mixing element.

We investigated birefringence of suspended cellulose nanofiber (CNF) liquids with constant flow rate owing to flow-induced orientation change of the suspensions passing through a rectangular channel with a tapered contraction. For rheological properties, non-Newtonian viscosity and gel-like behavior of CNF-suspensions exhibited. Velocity in the flow direction and elongational rate increased around the inlet of contraction. The experimental results of CNF-suspensions were independence of tapered angle for the contraction. However, overshoot behavior of tapered angle = 120° alone exhibited. Moreover, the resultant birefringence was dependence of the tapered angle. For understanding the experimental results, we discussed flow behavior (flow path line) and relationship between velocity and birefringence. Possibility of existence of corner-vortex before contraction was discussed. Furthermore, the experimental results were compared with those of a polymer solution (aqueous solution of Xanthan-Gum). The difference between two test fluids was obtained.

Understanding multiphase flows with phase change is of fundamental importance for the optimal design and operation of polymer processing. However, the study of multiphase flows with phase change is challenging in practice because polymers have complex physical properties and it is difficult to obtain precise thermal-hydraulic measurements of multiphase flows with phase change due to the high temperatures involved in polymer processing. Computational simulations overcome many of these difficulties and thus provide an essential alternative to study intricate thermal-hydraulic mechanisms not easily observed in a laboratory setting. In this article, I review the current state-of-the-art as well as outstanding challenges in the study of multiphase flows with phase change in polymer processing through the author’s computational studies on the motion of bubbles and drops with phase change.

Recently, plastic problems related to global warming and ocean pollution have become serious social problems. In order to confront the plastic problems, efforts are being made world widely to develop various technologies aimed at realizing recycling-oriented society. The use of naturally derived polymer material such as CA (Cellulose Acetate) is expected to be an effective way to solve the plastic problems. In the present research, a simulation technology for predicting the morphology of CA/PVA (Polyvinyl Alcohol) polymer blend formed in a twin screw extruder is proposed. The effectiveness of the technology was verified by comparing with the experimental data collected under various operating conditions of a twin screw extruder.

To elucidate the dynamic contact angle behavior in the transient state of the contact line motion, we conducted experimental investigations in which the cylindrical rod vertically intersecting the liquid surface was immersed with constant acceleration into the liquid and captured images of the meniscus. We found that the contact angles just after the initiation of the motion of the rod deviates from those measured with constant immersing velocity of the rod. The deviation is found to continues until the capillary number increased up to a certain value, which can be expressed as a form of Ca^*mReⁿ, with Ca^* modified capillary number, Re Reynolds number, m and n fitting coefficients.

Cryogenic fluid such as liquid hydrogen is used as the propellant for rockets. Cryogenic fluids are easy to boil and become gas-liquid two phase flow. Cavitation instability that occurs in cryogenic fluid has been a serious problem in pumps of rockets. However, this phenomenon is not fully understood. Therefore, revealing cavitation instability is an urgent matter. Previous research suggests that cavitation instability is likely to occur in conical diffusers. In this research, application of non-contact capacitive void fraction sensor to a tapered tube was attempted to measure the volume fluctuation of cavitation instability. The sensor was designed based on electric field analysis (EFA). EFA was conducted with two types of electrodes, and two fluid models. The result suggested that parallel type electrode was superior to spread out type electrode. However, low sensitivity of the sensor at the edge of electrode remained as a problem. To confirm the effect of the low sensitivity at the edge, the additional EFA was conducted. According to the results, the accuracy was the poorest when gas phase concentrated at the edge. Furthermore, flow experiment was performed to verify the accuracy of the void fraction sensor. Void fraction was measured in five flow patterns and the measurement was compared with void fraction calculated by using Smith’s equation and Thom’s equation. The result of the experiment corresponded with the void fraction from each equation within the margin of error.

The dynamics of a gas pore within a rotating metal droplet are elucidated through two-dimensional numerical simulations of a liquid-gas two-phase flow model. It was observed that gas pores are ejected earlier for the high rotational speed cases, indicating that the rotational motion of a droplet facilitates the ejection. Detailed investigation of the ejection mechanism reveals that the droplet gradually deforms into an elliptical shape as it spins, and the pores protrude in the direction of its minor axis, eventually leading to ejection. The deformation of pores is found to be caused by the formation of a local low pressure region in the thin liquid film between the pores and the gas phase region outside the droplet. Simulations were also performed by varying the viscous coefficient of the droplet, and it was found that the larger the viscous coefficient, the more suppressed the pore ejection becomes. It was suggested that the suppression of high-speed motion of the liquid phase prevents the formation of localized low-pressure regions, resulting in the suppression of pore ejection. On the other hand, simulations were performed by varying the surface tension coefficient, and the smaller the surface tension coefficient, the longer the time required for pore evacuation. This suggests that the smaller the surface tension coefficient, the longer the time scale of the second-order mode becomes, which is relatively strongly affected by viscosity.

The formation of fragments resulting from the breakup of a single droplet owing to a high-velocity gas flow behind a shock wave was captured through high-resolution imaging with temporal and spatial accuracy. The process of fragment formation was also examined. The catastrophic breakup of a droplet in the high Weber number region is characterized by an upstream interfacial wave with a wavelength larger than the critical wavelength of the Kelvin-Helmholtz instability in the stability region. The observed wavelength is consistent with the theoretical wavelength of the Rayleigh-Taylor instability. Therefore, the upstream interfacial wave of the droplet is generated by the development of small disturbances owing to the Rayleigh-Taylor instability. The measured fragment diffusion widths were found to be independent of Weber number.