Viscosity is like the “thickness” or “stickiness” of a liquid, determining how easily it flows. Imagine pouring honey and water; honey flows much more slowly because it has a higher viscosity compared to water. This concept applies to all liquids and gases, affecting how they move through pipes, over surfaces, or when being mixed.
What Is Viscosity, and How Is It Relevant to My Product or Process?
In technical terms, viscosity measures a fluid’s resistance to deformation at a given rate, such as when it’s flowing or being mixed. For fluids like water or air (known as Newtonian fluids), viscosity is constant and doesn’t change with the speed of flow or how forcefully they’re mixed. However, for non-Newtonian fluids, like ketchup or gels, their viscosity can change when they’re squeezed, mixed, or shaken – they can become thinner (less viscous) or thicker (more viscous) under stress.
Samples of viscosity
These values represent the viscosity of the materials listed, providing a comparison from very fluid substances like water to very thick materials like window putty. Each fluid’s viscosity measurement is dependent on factors like temperature and the specific composition of the fluid.
These examples span a range of common household and industrial liquids to illustrate how viscosity varies across different materials.
Viscosity behaviour for Newtonian, Thixotropic and Dilatant
Viscosity behaviour describes how the thickness of a fluid (its viscosity) changes under different conditions. Here’s an explanation of the behaviour for Newtonian, Thixotropic, and Dilatant fluids:
1. Newtonian Fluids: – These fluids have a constant viscosity, regardless of the force applied to them or the rate at which they are stirred or moved. – A common example is water. Whether you stir it slowly or quickly, it feels just as ‘thick’ or ‘thin’ – it doesn’t change its resistance to flow.
2. Thixotropic Fluids: – Thixotropic fluids become less viscous, or thinner, over time when a constant force is applied. – Imagine a jar of honey or ketchup. When you first try to pour it, it moves slowly. But as you shake or stir it, it flows more easily. Once you stop stirring, over time, it will thicken up again.
3. Dilatant Fluids: – Dilatant fluids are the opposite of thixotropic. They become more viscous, or thicker, when a force is applied. – Think of a mixture of cornstarch and water. When you press on it or move your hand through it quickly, it feels solid. But if you move slowly, it feels liquid. The faster the force, the thicker it becomes.
These behaviours are important in industrial processes where the flow of materials is critical, such as in mixing, pumping, or during chemical reactions. Understanding and controlling viscosity behaviour ensures that processes run smoothly and efficiently.
What does high viscosity mean?
High viscosity means that a fluid is thick and flows slowly. A high-viscosity fluid, like honey or molasses, resists motion due to internal friction – its molecules don’t move past each other easily. This is in contrast to low-viscosity fluids, like water or alcohol, which are thin and flow quickly. High-viscosity substances require more force to pour, spread, or stir compared to low-viscosity substances.
What does density mean?
Density is a measure of how much mass is contained in a given volume. It is often expressed in kilograms per cubic meter (kg/m³) or grams per cubic centimetre (g/cm³). You can think of density as how tightly packed or how heavy something is for its size. For example, a rock is denser than a piece of cork; even if they’re the same size, the rock will be heavier because it has more mass packed into the same amount of space. Density is an important concept in physics and engineering because it affects how substances interact with each other, including whether they will float or sink when placed in a fluid.
How does the temperature change viscosity?
Temperature has a significant impact on the viscosity of liquids and gases:
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For Liquids: As temperature increases, the viscosity of a liquid typically decreases. This occurs because the increased thermal energy allows the molecules to move more freely, reducing the internal friction that resists flow. In other words, heat makes the liquid’s molecules more energetic and less sticky to each other, making the liquid thinner and flow more easily. For example, heating honey or oil makes it runnier than when it is cold.
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For Gases: Unlike liquids, the viscosity of gases increases with temperature. As the temperature rises, gas molecules move faster and collide more often, which leads to an increase in the transfer of momentum across the gas. This increased activity and interaction between the molecules cause the viscosity to go up.
💡These changes in viscosity in response to temperature variations are important to consider in applications such as lubrication, chemical processing, and in the design of equipment where fluids are used or processed.
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