Search

We propose a groove-embedded partitioned pipe mixer (GPPM) and conduct an in-depth numerical study on the flow and mixing characteristics of the GPPM in the creeping flow regime. The GPPM is a variant of a previously reported mixer, the barrier-embedded partitioned pipe mixer (BPPM), and is designed to achieve better energy-efficient mixing compared to the BPPM. In this paper, we first introduce the working principle of the GPPM and its mixing protocols. Then, the flow system affected by mixing protocols and geometrical parameters of the GPPM is investigated using Poincare sections. As for mixing characteristics, the flux-weighted intensity of segregation is employed for quantitative mixing analysis. It turns out that a GPPM with a proper set of design parameters can indeed lead to a globally chaotic mixing. More importantly, the best GPPM showed better mixing in terms of energy consumption compared to its counterpart, the best BPPM.

In order to investigate how particle aggregation affects tensile mechanical performance of composite, a ductile biopolymer (poly(caprolactone)) was melt-compounded with CaCO3 particles over a wide concentration range from 10 to 60 wt.%. The aggregation of CaCO3 particles in poly(caprolactone) (PCL) is investigated depending on particle concentration and surface modification (with stearic acid (2.5 wt.%)) based on rheological assessment. If the composite is mixed with a high concentration of particles (> 30 wt.%), morphological observations and a thermal behavior analysis do not find a difference in the particle aggregation regardless of particle surface modification. However, the linear viscoelastic moduli of the composites distinguishes the difference in particle aggregation regarding to surface modification, indicating induced aggregation behavior with surface-modified CaCO3 (sCC). The composite with sCC starts to form network structure of particles at a lower concentration (30 wt.%) than that with unmodified particles (40 wt.%). When particles form the network structure above the particle percolation threshold, the yield strength of the composite begins to decrease even though Young’s modulus is still increasing. In contrast to the expectation of the better dispersion of particles by surface modification as well as improved tensile mechanical performance with better dispersion, sCC rather induced aggregation with a lower concentration of particle than unmodified particles which resulted in decrease in yielding performance. This study showed that rheological study, especially for the composite with high concentration of particles, is useful to figure out the particle dispersion against a limit at morphology observation.

In this paper we investigated numerically the flow and mixing characteristics of the barrier-embedded partitioned pipe mixer (BPPM) in non-creeping flow conditions. Numerical simulations are conducted for three mixing protocols of the BPPM, co-rotational, mirrored co-rotational, and counter-rotational protocols in the range of the Reynolds number (Re), 0.1≤Re≤300, focusing on the effect of the Reynolds number, the barrier height, and the mixing protocols on the mixing in the BPPM. Each mixing protocol creates two crosssectional flow portraits with crossing streamlines. Poincare sections were plotted to investigate the flow system affected by the Reynolds number and the barrier height. Mixing in a specific BPPM is characterized using the intensity of segregation in terms of the compactness and the energy consumption. The dependency of the barrier height and the Reynolds number on the final mixing state of the BPPMs was identified by mixing analyses. The co-rotational protocol results in an efficient mixing in the creeping flow regime. Meanwhile, mirrored co-rotational and counter-rotational protocols, which lead to poor mixing in the creeping flow regime, turned out to be efficient protocols in the higher Reynolds number regime.

Time-dependent viscoelastic properties of Oldroyd-B fluid were investigated by lattice Boltzmann method (LBM) coupled with advection-diffusion model. To investigate the viscoelastic properties of Oldroyd-B fluid, realistic rheometries including step shear and oscillatory shear tests were implemented in wide ranges of Weissenberg number (Wi) and Deborah number (De). First, transient behavior of Oldroyd-B fluid was studied in both start up shear and cessation of shear. Stress relaxation was correctly captured, and calculated shear and normal stresses agreed well with analytical solutions. Second, the oscillatory shear test was implemented. Dynamic moduli were obtained for various De regime, and they showed a good agreement with analytical solutions. Complex viscosity derived from dynamic moduli showed two plateau regions at both low and high De limits, and it was confirmed that the polymer contribution becomes weakened as De increases. Finally, the viscoelastic properties related to the first normal stress difference were carefully investigated, and their validity was confirmed by comparison with the analytical solutions. From this study, we conclude that the LBM with advection-diffusion model can accurately predict time-dependent viscoelastic properties of Oldroyd-B fluid.

Butt-fusion welding is an effective process for welding polymeric pipes. The process can be simplified into two stages. In heat soak stage, the pipe is heated using a hot plate contacted with one end of the pipe. In jointing stage, a pair of heated pipes is compressed against one another so that the melt regions become welded. In previous works, the jointing stage that is highly related to the welding quality was neglected. However, in this study, a finite element simulation is conducted including the jointing stage. The heat and momentum transfer are considered altogether. A new numerical scheme to describe the melt flow and pipe deformation for the butt-fusion welding process is introduced. High density polyethylene (HDPE) is used for the material. Flow via thermal expansion of the heat soak stage, and squeezing and fountain flow of the jointing stage are well reproduced. It is also observed that curling beads are formed and encounter the pipe body. The unique contribution of this study is its capability of directly observing the flow behaviors that occur during the jointing stage and relating them to welding quality.

In this paper, the flow pattern of viscoelastic fluids flowing inside a 4:1 planar contraction microchannel was investigated and quantitatively analyzed. A wide range of Weissenberg number flows of poly(ethylene oxide) solutions were observed while maintaining low Reynolds number (0.01 > Re). As the shear rate or fluid elasticity was increased, a transition from steady to unsteady flow was observed. In the steady flow region, the flow pattern was Newtonian-like, progressed to a divergent flow where the upstream flow pattern was distorted due to elasticity, and then a vortex developed at the upstream corners. The vortex, which was stable at first, fluctuated with a certain period as the Weissenberg number increased. The oscillating vortex was symmetric at first and became asymmetric with various patterns. As the elasticity increased further, the vortex randomly fluctuated without any time period. The Lyapunov exponent for the change in vortex size was positive, meaning that the flow was spatially chaotic. This paper systematically analyzed the flow patterns of the elastic fluids in the micro-contraction flow, which included; Newtonian-like flow, divergent flow, oscillating flow with symmetry, oscillating flow with asymmetry, and chaotic flow.

Changes in flow pattern were investigated for a viscoelastic fluid (polyethylene oxide) in various-sized micro-fabricated planar 4:1 contraction channels. The flow pattern changed from a Newtonian-like flow to a flow with a vortex growth region, during which a divergent flow and lip vortex were also observed depending on the elasticity number (El) and aspect ratio. When the aspect ratio was large, the lip vortex was observed only in a limited number of cases, and the flow pattern occurring before the vortex growth was more diverse. When the elasticity number was large, the divergent flow was not observed unlike the cases in which the Elasticity number was small. The flow pattern in the contraction microchannel was found to be diverse and abundant depending on the aspect ratio and elasticity number.

We investigated the nonlinear and nonsymmetric responses of viscoelastic fluids under large amplitude oscillatory squeeze (LAOSQ) flow. The nonlinear and nonsymmetric stress response is a unique feature of oscillatory squeeze (OSQ) flow under larger deformation, but has rarely been investigated. The goal of this study is to systematically characterize the responses of viscoelastic fluids at larger deformation under oscillatory squeeze flow and to provide a platform for the analysis of nonsymmetric stress signals. We report a framework for the analysis of nonlinear-and-nonsymmetric stress signals at larger strain amplitude under oscillatory squeeze flow. The storage and loss modulus showed strain thinning behavior as the strain amplitude increases in both oscillatory shear and oscillatory squeeze flow. However the normal stress under LAOSQ was found to be nonsymmetric in both magnitude and shape unlike the shear stress under oscillatory shear flow. In addition the energy dissipation was found to be larger in extension than in compression. This study is expected to provide a platform to understand the nonlinear and nonsymmetric characteristics of complex fluids under LAOSQ flow.

Oscillatory shear flow has been widely used to investigate the flow properties of a wide range of complex fluids. The flow is useful because experimental platform is already fixed and its analysis has sound theoretical background. However it is too simple compared to the complex flows encountered in industry. Accordingly, the rheological response of complex fluids needs to be investigated in more complicated flow field. There were several reports on the superimposed flows in which oscillatory flow was applied either parallel or perpendicular to the steady shear flow. In this paper, we propose dynamic helical squeeze flow (DHSQ) which superimposes oscillatory shear and oscillatory squeeze between parallel plates. The nonlinear response in DHSQ was studied by comparing DHSQ with oscillatory shear (OS) and with oscillatory squeeze (OSQ) in terms of stress shape and Lissajous plot. In DHSQ, both stress curve and Lissajous plot of shear and normal stresses showed nonsymmetric characteristics unlike shear stress in large amplitude oscillatory shear (LAOS). The normal stress in DHSQ was more distorted than that of OSQ. The shear stress in DHSQ showed the onset of nonlinearity at lower strain amplitude than that of oscillatory shear flow (OS). It is due to the coupling of shear and squeeze flows, and the effect was more pronounced in the shear stress than in the normal stress.

Dynamic oscillatory shear flow tests, i.e. small, medium, and large amplitude oscillatory shear (SAOS, MAOS, and LAOS), are useful to study polymer composite systems. In this study, MAOS and LAOS tests were used to investigate the dynamic behavior of electrically activated polypropylene (PP)/Clay nanocomposites. The morphology of PP/Clay nanocomposites could be controlled by the applied time, type (AC and DC), and strength of the electric field. Various electrically activated PP/Clay nanocomposites were compared in terms of I3/1, which was determined from FT-Rheology within the MAOS and LAOS region. Nonlinear-Linear viscoelastic Ratio (NLR), which developed by Lim et al. (2011), was calculated to measure the dispersion quality of the PP/Clay nanocomposites.

Dynamic self-assembly of droplets, regular structure formation of moving deformable objects in a confinement environment is a challenging problem in nonlinear dynamics and engineering patterned structure. In the current work, we investigated how the local kinematic history affects the dynamic self-assembly of picoliter-sized droplets near the expansion regions in microfluidic devices. The local kinematic history was controlled by the shape of the expansion region and characterized using computational fluid dynamics. Sizecontrolled aqueous droplets in light mineral oil were continuously generated at T-junction microchannel and transported toward the expansion region. The fast dynamics of the droplets was tracked using high-speed video microscopy. We found three types of dynamic droplet arrays: 1D, 2D zigzag, and irregular. The orderdisorder transition was associated not only with the droplet size, but also with the controlled local kinematic history, which results in the transient deformation of droplet and droplet-droplet interactions. The present results provide us with insight into the dynamic self-assembly of droplets and could be a useful guide for practical applications of droplet-based microfluidics.