New research may revise a theory of reacting flow

The research team of Tokyo University of Agriculture and Technology (TUAT) for the first time clearly demonstrates that the effect on the flow reverses according to the degree of change in the properties due to the reaction in a reacting flow with production of viscoelastic material, through experiments involving high-precision rheological measurements and a newly proposed theory. This is achieved by that the viscoelastic properties differently affect flow dynamics depending on the elasticity of the viscoelastic material.

These researchers published their results in Physical Review Fluids on February 16^th, 2022.

Reacting flows in which chemical reactions occur within a flowing fluid, can be seen in a wide variety of fields, such as in industrial, environmental, and biological applications. In reacting flows, changes in fluid physical properties induced by chemical reactions can alter the flow dynamics. “Generally, flows change more significantly with larger changes in properties. However, this study demonstrates a reacting liquid flow where the flow reverses in response to changes in the physical properties,” said Dr. Nagatsu, one of the authors on the paper, Professor in the Department of Chemical Engineering at TUAT.

The research team experimentally investigates viscous fingering (VF) with gel (a viscoelastic material) production by a chemical reaction as a reacting flow. In VF, the interface forms a finger-like pattern when a more-viscous fluid is displaced by a less-viscous one in porous media or Hele–Shaw cells. “Our team demonstrates that the gel production affects the VF dynamics in an opposite manner depending on the gel elasticity by combining with rheological measurements of the gel produced at the liquid–liquid interface. The VF pattern is approximately the same as the non-reactive one when the gel elasticity is low, narrower when the elasticity is medium, and wider when the elasticity is high (see Figure),” Nagatsu explained. “In addition, our team proposes a model that explains the opposite effects considering the gel viscoelastic properties,” said Dr. Suzuki, the corresponding author on the paper, Assistant Professor in the Department of Chemical Engineering at TUAT. “In this model, VF becomes thinner when the shear thinning viscosity of the gel is effective (blue region in Fig.(d)) and wider when the gel behaves as a solid material, thus reducing the permeability of the porous media, which corresponds to the shear thickening viscosity of the gel being effective (red region in Fig.(d)). These viscoelastic properties are based on actual viscosity measurements of the gel bulk itself (see Figure). The experimental results and theoretical considerations indicate that the opposite effects are driven by the multiple rheological properties, which are mainly responsible for the flow dynamics, depending on the gel elasticity.”

“This result overturns the common understanding of reacting flow research that the flow monotonically changes more significantly as the change in the fluid properties due to the reaction is larger, and leads the research of the reacting flow to a new stage,” Nagatsu said. “Control of flow dynamics utilizing change in fluid properties induced by chemical reaction is called chemical control of flow. The chemical control of flow is based on such common understanding.  However, this study shows that such common understanding is not always correct in chemical control of flow with production of viscoelastic material. Therefore, this study will open new avenues for flow control using chemical reactions.”

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About Tokyo University of Agriculture and Technology (TUAT)

TUAT is a distinguished university in Japan dedicated to science and technology. TUAT focuses on agriculture and engineering that form the foundation of industry, and promotes education and research fields that incorporate them. Boasting a history of over 140 years since our founding in 1874, TUAT continues to boldly take on new challenges and steadily promote fields. With high ethics, TUAT fulfills social responsibility in the capacity of transmitting science and technology information towards the construction of a sustainable society where both human beings and nature can thrive in a symbiotic relationship. For more information, please visit http://www.tuat.ac.jp/en/.