Viscoelastic Fluids Show Promise for Boosting Efficiency in Industrial Heat and Mixing Systems

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Fluids are vital to industrial processes involving heating, cooling, and mixing. While Newtonian fluids—with constant viscosity—have traditionally been used in these applications, industries are increasingly turning to viscoelastic fluids. These materials exhibit both liquid and elastic characteristics and are capable of suppressing turbulence in simple flows, such as through straight pipes or channels. This so-called "drag reduction effect" has gained attention for its potential to improve energy efficiency.


To unlock the full potential of viscoelastic fluids in industrial systems, a deeper understanding of how they behave in turbulent conditions is essential.


In this context, Associate Professor Shumpei Hara of Doshisha University, along with Professor Takahiro Tsukahara and Emeritus Professor Yasuo Kawaguchi of Tokyo University of Science, conducted an experimental study focused on viscoelastic fluid flow through a backward-facing step (BFS)—a benchmark scenario for analyzing turbulence and separation. Their findings were recently published in the International Journal of Heat and Mass Transfer.


“Unlike Newtonian fluids, viscoelastic fluids have a unique relaxation time, and their behavior depends on how this time scale interacts with the natural dynamics of the flow,” said Dr. Hara. “Our goal was to investigate instabilities and flow characteristics of BFS turbulence using these materials.”


The researchers conducted experiments in a closed-circuit water system featuring a two-dimensional channel with a 20 mm height and a 1:2 expansion ratio at the BFS. They used particle image velocimetry to observe fluid movement, a capillary breakup extensional rheometer to measure relaxation time, and T-type thermocouples to track heat transfer performance.


In a BFS flow, turbulence typically generates unstable shear layers that lead to eddy formation and the production of turbulent kinetic energy. When viscoelastic fluids are used, their relaxation properties can interact with this turbulent structure in unexpected ways—leading to phenomena such as inertia-viscoelastic meandering motion.


By manipulating the Reynolds number (related to flow speed) and the Weissenberg number (related to fluid elasticity), the team identified three distinct flow regimes: low, middle, and high diffusivity states.


In the low diffusivity regime, the fluid maintained a high-speed flow with minimal turbulence and poor heat transfer performance due to low Reynolds shear stress. In the middle state, turbulence levels and heat transfer resembled those seen in Newtonian fluids. The most striking findings occurred in the high-diffusivity state, where the main flow developed a vertically oscillating, wavelike motion—referred to as meandering. This behavior significantly enhanced fluid mixing and heat transfer efficiency.

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The vertical meandering of the flow increased momentum and thermal diffusion, reducing temperature gradients and promoting uniform mixing. These effects make viscoelastic fluids particularly appealing for use in heat exchangers, reactors, and mixers across industries such as chemical processing, food production, and pharmaceuticals.


Looking ahead, the research team plans to study various viscoelastic formulations to better understand how they can be tailored for specific industrial needs and optimized for energy-saving applications.


“Our work opens new doors for designing turbulence control strategies using viscoelastic fluids,” Dr. Hara concluded. “By enhancing heat and mass transfer processes, we can improve product quality and energy efficiency in advanced manufacturing systems.”