Name: how temperature changes fluid viscosity
Uploaded: 2025-02-13T15:43:08.000Z
Duration: 1 min 19 s
Channel: JoVE

La viscosité mesure la résistance d’un fluide à s’écouler en raison du frottement interne lorsque les couches du fluide se déplacent les unes sur les autres.
Par exemple, le miel s’écoule lentement car il a une viscosité élevée, tandis que l’eau s’écoule facilement avec une faible viscosité.
Il existe deux principaux types de viscosité : dynamique et cinématique. La viscosité dynamique mesure la force nécessaire pour déplacer une couche de fluide sur une autre.
Par exemple, lorsqu’il est remué, le miel résiste plus à la cuillère que l’eau. La viscosité cinématique est le rapport entre la viscosité dynamique d'un fluide et sa densité, décrivant comment le fluide se propage sous l'effet de la gravité.
La plupart des fluides courants, tels que l’eau et l’air, ont une viscosité constante, quelle que soit la force appliquée.
Cependant, certains fluides, comme le ketchup, changent de viscosité en fonction de la force appliquée ; le ketchup s’écoule plus facilement lorsque la bouteille est secouée.
La température affecte considérablement la viscosité, cruciale dans la conception des pipelines, où l’huile doit s’écouler sans heurts.
En revanche, l’air chaud d’un sauna montre comment des températures plus élevées augmentent la viscosité des gaz.

viscosité d'un fluide

La viscosité mesure la résistance qu'un fluide oppose à l'écoulement et à la déformation. Elle résulte du frottement interne entre les couches de fluide en mouvement les unes par rapport aux autres. La viscosité dynamique, désignée par la lettre grecque mu (μ), quantifie la force nécessaire pour déplacer une couche de fluide sur une autre. Pour les fluides newtoniens comme l'eau et l'air, la relation entre la contrainte de cisaillement et le taux de déformation de cisaillement est linéaire, ce qui signifie que leur viscosité reste constante quelle que soit la contrainte appliquée. Les fluides non newtoniens, comme le ketchup, le dentifrice et les sables mouvants, présentent une viscosité qui change avec les taux de cisaillement variables.

La température affecte considérablement la viscosité. Des températures plus élevées diminuent la viscosité des liquides car les forces intermoléculaires s'affaiblissent, ce qui permet au fluide de s'écouler plus facilement. Un exemple est le sirop chauffé, qui s'écoule plus facilement que lorsqu'il est froid. Inversement, des températures plus élevées augmentent la viscosité des gaz, car l'activité moléculaire et l'échange de quantité de mouvement entre les couches augmentent, de la même manière que l'air chaud semble plus épais dans un sauna.

Pour prédire avec précision le comportement des fluides, il faut tenir compte des effets de la température, ce qui est essentiel dans la conception de systèmes tels que les pipelines et les moteurs de voiture. Dans les pipelines, l'huile doit s'écouler en douceur, tandis que dans les moteurs de voiture, la viscosité correcte de l'huile garantit une lubrification et une efficacité adéquates. Cette compréhension aide les ingénieurs à concevoir et à exploiter des systèmes plus efficacement sous des températures variables.

Viscosité d'un fluide

La viscosité mesure la résistance d’un fluide à s’écouler en raison du frottement interne lorsque les couches du fluide se déplacent les unes sur les autres.
Par exemple, le miel coule lentement...

Education

Enseignement

JoVE Core

Civil Engineering

Génie civil

Unit 1

Unité 1

Fluid Properties

Propriétés des fluides

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

Viscosity of Fluid

how temperature changes fluid viscosity

Viscosity describes how much a fluid resists flow and deformation. It comes from internal friction between fluid layers that move past each other. Dynamic viscosity, shown by the Greek letter mu (μ), measures the force needed to move one layer over another.

Newtonian fluids, such as water and air, have a linear relationship between shearing stress and the rate of shearing strain. Their viscosity stays constant, even when the applied stress changes. Non-Newtonian fluids, like ketchup, toothpaste, and quicksand, do not behave this way. Their viscosity changes as the shear rate changes.

Temperature also has a strong effect on viscosity. For liquids, higher temperature lowers viscosity because intermolecular forces weaken and the fluid flows more easily. Heated syrup is a simple example. It pours more readily when warm than when it is cold.

For gases, the pattern is different. Higher temperature increases viscosity because molecular activity and momentum exchange between layers rise. Warm air can feel thicker, like the air in a sauna. Engineers need to account for these temperature effects when predicting fluid behavior.

This is important in systems such as pipelines and car engines. Oil in a pipeline must move smoothly. In a car engine, the right oil viscosity helps with lubrication and efficiency. Understanding viscosity helps engineers design and operate these systems under changing temperatures.

How Temperature Changes Fluid Viscosity

characteristics of fluids

Fluid Behavior in Liquids and Gases

Fluids include liquids and gases, and they behave differently from solids because of how their molecules are arranged. In solids, molecules are tightly packed and held by strong intermolecular forces. That structure helps solids keep their shape and resist deformation. Fluids have molecules that are farther apart and held by weaker forces. Because of this, they can flow and change shape easily. A fluid is any substance that deforms continuously when shearing stress is applied. Shearing stress...

density, specific weight, specific gravity and compressibility of fluid

density-specific-weight-specific-gravity-and-compressibility-of-fluid

Fluid Properties: Density, Weight and Compression

Density, specific weight, specific gravity, and compressibility are key fluid properties. Density is the mass per unit volume of a fluid. It helps describe how much mass a fluid system contains and affects buoyancy, pressure, flow behavior, viscosity, thermal conductivity, and sound propagation. In pipeline design, knowing density helps engineers make sure the pipe can support the fluid’s mass. Specific weight is the weight per unit volume. It is found by multiplying density by gravitational...

viscosity of fluid

Viscosity describes how much a fluid resists flow and deformation. It comes from internal friction between fluid layers that move past each other. Dynamic viscosity, shown by the Greek letter mu (μ), measures the force needed to move one layer over another. Newtonian fluids, such as water and air, have a linear relationship between shearing stress and the rate of shearing strain. Their viscosity stays constant, even when the applied stress changes. Non-Newtonian fluids, like ketchup,...

types of fluids

Newtonian vs Non-Newtonian Fluid Behavior

Fluids can be grouped by how they respond to shear stress. Shear stress is a force that acts across a material, and shear strain rate describes how quickly it changes shape or flows. In this lesson, fluids are divided into Newtonian and non-Newtonian types. Newtonian fluids follow Newton’s law of viscosity. Their shear stress changes in a linear way as the shear rate changes. That means their viscosity stays constant, so their flow is predictable and easier to analyze. Water, air, oil, and...

newtonian fluid: problem solving

Newtonian Fluid Viscosity and Shear Stress

Newtonian fluids have a constant viscosity, so their shear stress and shear strain rate stay directly proportional. This creates a linear, predictable link between force and flow. Water, air, and light oils are common examples of Newtonian fluids. A simple way to study this behavior is to place the fluid between two parallel plates. One plate stays still, and the other moves at a constant velocity. The fluid forms a velocity gradient, which is the change in speed across the distance between...

vapor pressure of fluid

Vapor Pressure and Boiling Behavior

Vapor pressure and boiling behavior are closely linked in fluids. Vapor pressure is the pressure a vapor exerts when it is in thermodynamic equilibrium with its liquid at a given temperature. It shows how strongly molecules tend to leave the liquid surface and move into the vapor phase. A closed container helps show how vapor pressure forms. If a liquid sits in a sealed space with a small air gap, and that space is evacuated, vapor molecules escape from the liquid into the empty space. The...

surface tension of fluid

Why Water Drops and Needles Float

Surface tension helps explain why water forms drops, supports small objects, and moves in thin tubes. It is a property of fluids at the boundary between a liquid and a gas, or between two immiscible liquids. At the surface, molecules are pulled inward by neighboring molecules. That inward pull makes the surface act a little like a stretched elastic membrane. Inside a fluid, molecules are attracted in all directions. Surface molecules do not have the same balance of forces. They feel a net...

capillarity in fluid

Capillary Action in Narrow Spaces

Capillary action is the movement of liquid through narrow spaces without any outside force. It depends on surface tension and adhesion between the liquid and nearby solid surfaces. This effect is common in narrow tubes, porous materials, and fine particles. Surface tension comes from cohesive forces between liquid molecules at the liquid-air boundary. These forces create a thin skin that resists outside pressure. When a capillary tube is placed in a liquid, the liquid level changes because of...

design example: deciding thickness of lubricating fluid in a shaft

design-example-deciding-thickness-of-lubricating-fluid-in-a-shaft

Lubricant Film Thickness for Shaft Bearings

Lubricant film thickness for shaft bearings is calculated to keep a rotating shaft from touching its bearing housing. A controlled layer of lubricant reduces friction, wear, and energy loss. It also helps the machine run smoothly by preventing metal-to-metal contact. The calculation starts with the shaft’s tangential velocity. First, the rotational speed is converted to angular velocity. Then that value is multiplied by the shaft radius. The result is the shaft’s linear speed at its surface...

key terms and concepts

Learn how viscosity changes with temperature in liquids and gases, and why Newtonian and non-Newtonian fluids matter in pipelines and car engines.

How Temperature Changes Fluid Viscosity | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

How Temperature Changes Fluid Viscosity

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