Buoyancy and velocity slip effects on squeezing fluid flow conveying ternary hybrid nanoparticles and gyrotactic microorganisms between two circular disks with convective boundary condition
This study investigates the effects of buoyancy and velocity slip on the squeezing flow of a ternary hybrid nanofluid containing Nickel, magnetite, and diamond nanoparticles with gyrotactic microorganisms between two convectively heated circular disks, utilizing the Homotopy Analysis Method and numerical simulations to demonstrate that buoyancy accelerates surface velocity while velocity slip enhances local skin friction, mass transfer, and microorganism density.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine a world where the movement of liquids is not just about water flowing in a pipe, but about how tiny, invisible particles suspended in that liquid change the way heat and force travel. This is the realm of fluid dynamics, a branch of physics that studies how liquids move and interact with their surroundings. In many modern machines, from the hydraulic brakes in a car to the cooling systems in a power plant, engineers rely on a specific type of flow called "squeezing flow." This happens when a liquid is trapped between two surfaces that move closer together or pull apart, forcing the fluid to change shape and speed. While this process is fundamental to engineering, adding complex ingredients to the fluid—such as microscopic solid particles or living organisms—makes the physics significantly more intricate. Understanding how these mixtures behave under pressure is crucial for designing more efficient cooling systems, better lubricants, and advanced medical devices.
A team of researchers at the Federal University of Technology Akure recently set out to explore a particularly complex version of this scenario. They investigated what happens when a liquid is squeezed between two circular disks, but with a twist: the liquid contains a mixture of three different types of microscopic solid particles, along with tiny swimming organisms. The solids they chose were nickel, magnetite, and diamond. These materials were selected because they are known for their ability to hold and transfer heat efficiently. The living components were gyrotactic microorganisms, which are single-celled creatures that naturally swim in response to gravity and fluid currents. The researchers wanted to see how these ingredients behaved when the disks moved, specifically looking at how the fluid's own weight (buoyancy) and the way the fluid slips against the disk surfaces influenced the flow.
To study this, the team created a mathematical model of the system. They imagined two circular plates, one moving toward the other, with a water-based fluid sandwiched between them. This fluid was loaded with the three types of nanoparticles and the swimming microorganisms. The setup included realistic conditions, such as the plates being heated from the outside and the fluid having a slight tendency to slip rather than sticking perfectly to the metal surfaces. Using powerful computer software, the researchers solved a series of complex equations that describe how the fluid moves, how heat spreads, how the particles distribute, and how the microorganisms swim. They did not perform a physical experiment with actual disks and water; instead, they ran detailed simulations to predict the behavior of this mixture under various conditions.
The simulations revealed several clear patterns. When the researchers increased the "squeezing" speed—meaning the plates moved together faster—the fluid's overall movement slowed down. The temperature of the fluid dropped, and the concentration of both the solid particles and the microorganisms decreased. Essentially, squeezing the fluid faster pushed the heat and the particles away from the center, making the flow less active. However, the story changed when they looked at buoyancy. Buoyancy is the upward force that objects feel in a fluid, similar to how a balloon rises in the air. The researchers found that when buoyancy was stronger, the fluid at the surface actually moved faster. The natural tendency of the fluid to rise due to heat helped push the flow along, counteracting some of the slowing effects of the squeezing.
Another key discovery involved the "slip" of the fluid. In many standard models, it is assumed that fluid sticks perfectly to a solid surface, moving at the same speed as the surface itself. In this study, the researchers allowed for a "slip" condition, where the fluid can slide slightly over the surface. They found that when this slipping occurred, it had a surprising effect: it increased the friction at the surface, improved the rate at which mass was transferred, and actually increased the density of the microorganisms near the wall. This suggests that allowing a fluid to slip slightly can make the system more efficient at moving heat and particles, rather than hindering it.
The study also examined how the heat applied to the disks affected the system. When the heat transfer from the outside was stronger, the temperature of the fluid rose, creating a warmer environment. This heating also influenced the movement of the microorganisms and the solid particles, though the effects were more subtle than the changes caused by the squeezing speed or the buoyancy. The researchers confirmed that their mathematical approach was reliable by comparing their simulation results with established numerical methods, finding that the two matched closely.
Ultimately, this work provides a clearer picture of how complex mixtures behave in confined spaces. The findings suggest that by carefully controlling the speed of the squeezing motion, the strength of the buoyancy forces, and the slip conditions at the surface, engineers could potentially design better systems for cooling or transporting fluids. The study confirms that adding a mix of high-performance nanoparticles and living microorganisms to a squeezing flow creates a dynamic system where heat, motion, and biology interact in predictable ways. While the research remains a theoretical simulation, the insights it offers into the behavior of these ternary hybrid fluids could guide future designs in industries ranging from automotive engineering to biotechnology.
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