Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.iecr.5c00469

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

The effect of bubble-bearing state on fluid flows on an inclined plane is clarified. The deceleration or acceleration compared to the single-phase state is determined by a non-dimensional parameter Π, a ratio of the gravity-induced shear stress to the restoring force originated by the surface tension. At Π<O(1), the spherical bubbles contribute to increasing the viscosity and decelerating the flow. At Π>O(1), the deformed bubbles decrease the viscosity and accelerate the flow. The result is validated in experiments under the former condition, and this framework is applied to predict the arrival time of the bubble-bearing fluid flows. Through this work, it is shown that extending the application of the rheology model beyond just materials science to fluid mechanics offers new avenues for elucidating the underlying physics of bubble-bearing fluid flows across diverse disciplines.

DOI： 10.1063/5.0261398

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Rheology  

As representatives of fluid foods containing millimeter-sized ingredients, three kinds of rice porridge are examined by velocity-profiling-assisted rheometry (VPAR). The obtained flow curves of the plain, egg, and bean porridge are well characterized by the power-law model, where the plain porridge has the highest consistency, the bean porridge is the second, and the egg porridge has the lowest viscosity. These are also time dependent properties; the consistency and the degree of shear-thinning decrease as the measurement repetition proceeds. With these rheology data, spreading and descending behaviors, which are fundamental and important flows in the eating and swallowing process, are discussed. Spreading behavior in the conventional line spread test and descending behavior in a simplified artificial throat model are predicted based on the rheological data identified by VPAR and simple physical models. The spreading behavior is validly described by the consistency, and the descending velocity is evaluated to have high correlation with the representative shear rate predicted. Through the rheological measurement and its application to rationalize the flow behaviors, VPAR is expected to be a practical tool in both rheology and fluid mechanics of complex fluid foods.

DOI： 10.1122/8.0000919

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

We propose a method for estimating volume fraction of emulsions based on ultrasonic velocity profiling viscometry and validate its feasibility through a series of experiments. The experiments involve emulsions composed of silicone oil as continuous phase and tap water with volume fractions ranging from 10vol% to 30vol%. We introduce the viscosity model for this emulsion to establish the mathematical relationship between volume fraction and viscosity. Subsequently, we calibrate this relationship using ultrasonic spinning rheometry (USR). The identified equation is then applied in estimating the inline volume fraction using ultrasonic velocity profiling combined with pressure drop measurement. The key idea is that by measuring the viscosity in a pipeline the volume fraction is then indirectly estimated employing the identified equation. Through the collection and analysis of experimental data, we confirmed that the USR can capture the characteristics of the emulsion viscosity accurately. Moreover, we found that this method demonstrates applicability and accuracy in measuring volume fractions of emulsions. The results indicate that the mean relative error for this estimation is 24.06% at a volume fraction of 10vol%, and 4.78% at a volume fraction of 30vol%.

DOI： 10.1088/1361-6501/ad78f2

Other Link： https://iopscience.iop.org/article/10.1088/1361-6501/ad78f2/pdf

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

Cost-effective production method for making density-controllable monodisperse spheres is demonstrated. A sodium alginate aqueous solution containing gelatin is emulsified with canola oil. The droplet surface is covered with a calcium alginate membrane by dropping the emulsion into a calcium lactate aqueous solution. The content of the canola oil can control the sphere's density. To demonstrate the applicability of the spheres to experimental research, rheological measurements of the suspensions of the spheres were performed. The effective viscosity agrees with the theoretical formula at volume fractions of 0.7%–11.7%. The demonstration highlights that the spheres can function as neutrally buoyant solid particles in studies for the physics of fluids.

DOI： 10.1063/5.0226393

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Rheology  

We propose a torque rheometer coupled with an ultrasonic velocity profiler (UVP) for evaluating multiphase fluids as bulk rheology in oscillatory shear flows. The rheometer mainly consists of wide-gap coaxial cylinders, where the outer cylinder is sinusoidally oscillated and the inner cylinder is fixed to a torque sensor for measuring the wall shear stress. Based on Cauchy’s equation of motion, the spatiotemporal distribution of the shear stress is obtained from the velocity information and the wall shear stress as a boundary condition. This rheometer was applied to a carboxymethyl cellulose aqueous solution and compared with a standard torque-type rheometer. The results of the evaluated viscoelastic properties agreed well with each other, indicating the validity of the proposed rheometry. To further investigate the applicability of the rheometer to multiphase fluids, suspensions of solid spherical particles with a diameter of 220μm with volume fraction of 0.8–3.4% were measured, which are out of the applicable ranges of the standard rheometer. For volume fractions up to 3% where the UVP measurement is available, the relative viscosity agrees well with a theoretical formula. This indicates the applicability of the method to examine multiphase fluids.

DOI： 10.1122/8.0000818

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Cambridge University Press (CUP)  

The viscoelasticity of a dilute bubble suspension is theoretically derived from the constitutive equation originally for a dilute emulsion proposed by Frankel & Acrivos (J. Fluid Mech., vol. 44, issue 1, 1970, pp. 65–78). Non-dimensionalization of the original tensor equation indicates that the viscoelasticity is systematized for a given void fraction by the capillary number $Ca$ and dynamic capillary number $Cd$ , representing the bubble deformability and unsteadiness of bubble deformation. Comprehensive evaluation of the viscoelasticity according to the volume fraction, $Ca$ and $Cd$ reveals that whether the viscosity increases or decreases depends on whether $Ca$ or $Cd$ exceeds a common critical value. In addition, it is indicated that the bubble suspension has the most prominent viscoelasticity when the time scale of the shear deformation is the same as the relaxation time of the suspended bubble and when the bubbles keep a spherical shape, that is, $Ca \ll 1$ and $Cd = 1$ . The applicability of this theory in flow prediction was examined in a Taylor–Couette system, and experimentally good agreement was confirmed.

DOI： 10.1017/jfm.2024.171

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00348-022-03561-z

Other Link： https://link.springer.com/article/10.1007/s00348-022-03561-z/fulltext.html

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.iecr.2c03022

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00348-022-03489-4

Other Link： https://link.springer.com/article/10.1007/s00348-022-03489-4/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.iecr.2c01792

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Abstract

We have developed an effective method for evaluating time‐resolved rheological functionalities of swallowed foods using ultrasonic spinning rheometry (USR). USR can obtain variations over time in the rheological properties of fluids despite the fluids being in heterogeneous and nonequilibrium conditions. In addition, USR can evaluate time variations of shear‐thinning property changing in a few seconds. Demonstrations were conducted with typical thickener solutions: starch, guar gum, and xanthan gum‐based solutions, with alpha‐amylase as a digestive enzyme. The flow curve of the starch‐based solutions lowered with time, and a few minutes after addition of the amylase, the viscosity dropped to one‐hundredth of the original value. In contrast, the guar gum‐ and xanthan gum‐based solutions maintained the original viscosities as generally known. Applying the power law fitting to series of these flow curves, the time variation of the shear‐thinning property is quantitatively characterized by the plots on typical K‐n space, where K and n are parameters in the model, consistency index and power law exponent. The qualitative characteristics of the thickeners are successfully quantified in the K‐n space, and this will be a practical tool for evaluating the time‐resolved rheological properties of swallowed foods.

DOI： 10.1111/jtxs.12679

Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1111/jtxs.12679

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Society of Rheology Japan  

DOI： 10.1678/rheology.50.3

Open Access

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00348-022-03382-0

Other Link： https://link.springer.com/article/10.1007/s00348-022-03382-0/fulltext.html

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/transjsme.22-00115

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/transjsme.20-00242

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Kohei Ohie, Taiki Yoshida, Yuji Tasaka