Journal of Thermodynamics & Catalysis
Open Access

Role of Viscosity in Fluid Dynamics

Yang Zhang^{* *}Correspondence: Yang Zhang, Department of Chemical Engineering, University of Kazan Federal, Kazan, Russia, Email:

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Description

The concept of viscosity can be compared to the internal friction within a fluid. It arises due to the cohesive forces between the molecules constituting the fluid. When these molecules slide past each other, they experience resistance, preventing the fluid's flow. This resistance is what distinguishes fluids with high viscosity, like honey or the substance, from those with low viscosity, such as water or air. One of the most iconic displays presenting viscosity is the simple experiment involving different liquids poured over an inclined surface. Observing the behaviour of each liquid as it flows down the rise provides a visual representation of viscosity. Thicker fluids exhibit slower movement, forming a steady and consistent stream, while thinner fluids flow more rapidly, spreading out in a thinner layer. The quantification of viscosity depends on the concept of shear stress and shear rate. This fundamental parameter characterizes a fluid's resistance to flow under an applied force. Viscosity is not a constant property and can vary with factors such as temperature, pressure, and composition. In most cases, an increase in temperature tends to decrease viscosity, as higher temperatures enhance molecular motion, thereby reducing internal friction. However, this trend may not hold for all substances, some fluids, like certain polymers, might exhibit an increase in viscosity with rising temperature due to complicated molecular interactions. Fluids can be categorized based on their viscosity into Newtonian and non-Newtonian fluids. Newtonian fluids, like water and most gases, have a constant viscosity regardless of the applied shear stress. Their behaviour is described by Newton's law of viscosity, which states that the shear stress is directly proportional to the shear rate. On the other hand, non-Newtonian fluids, such as ketchup or toothpaste, showcase variable viscosity under different conditions. They can be further classified into various types based on their specific flow behaviour, such as shear-thinning, shearthickening, and viscous fluids. The significance of viscosity extends far beyond theoretical understanding, playing a crucial role in diverse real-world applications. In industries like petroleum, where the flow of crude oil through pipelines is viscous, understanding viscosity helps optimize transportation and processing methods. Similarly, in pharmaceuticals, the viscosity of drug formulations impacts drug delivery systems, influencing dosage accuracy and absorption rates within the body. Biological systems also heavily rely on viscosity. Blood, a complex fluid, exhibits a unique viscosity crucial for its function. Its viscosity directly affects the flow through blood vessels, impacting circulation and overall health. Disorders altering blood viscosity, such as polycythemia or anemia, can have profound health implications. In the state of materials science, the control and manipulation of viscosity are central in developing new materials and improving existing ones. Tailoring viscosity allows for the creation of products with specific flow characteristics, enhancing their performance and usability. The study of viscosity has led to the development of various techniques to measure and manipulate this property. Viscometers, devices designed directly for viscosity measurement, come in different types such as capillary viscometers, rotational viscometers, and falling ball viscometers. Each type caters to specific applications and provides insights into fluid behaviour under varying conditions. Viscosity stands as a fundamental property governing the behaviour of fluids, influencing a number of natural and industrial processes. Its comprehension holds immense importance across various fields, from engineering and medicine to materials science and beyond. As technology advances, a deeper understanding of viscosity continues to unlock new possibilities, driving innovations that shape our world.