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

粘度は、流体の層が互いに移動するときに、流体が内部摩擦によって流れに抵抗する方法を測定します。
例えば、蜂蜜は粘度が高いためゆっくり流れますが、水は粘度が低いため流れやすいです。
粘度には、動的粘度と運動学的粘度の2つの主要なタイプがあります。動的粘度は、1つの流体層を別の流体層上に移動するのに必要な力を測定します。
たとえば、かき混ぜると、蜂蜜は水よりもスプーンに抵抗します。動粘度は、流体の動的粘度とその密度の比率であり、流体が重力下でどのように広がるかを表します。
水や空気などの最も一般的な流体は、加えられた力に関係なく一定の粘度を持っています。
ただし、ケチャップのように、加えられる力によって粘度が変化する液体もあります。ケチャップは、ボトルを振ると流れやすくなります。
温度は粘度に大きく影響し、オイルがスムーズに流れるパイプラインの設計に不可欠です。
対照的に、サウナ内の暖かい空気は、温度が高くなるとガスの粘度がどのように増加するかを示しています。

流体の粘度

粘度は、流体が流れや変形に対して示す抵抗を測定します。これは、流体の層が互いに相対的に動くことで生じる内部摩擦によって生じます。ギリシャ文字のミュー (μ) で表される粘性係数は、ある流体層を別の層の上に移動させるために必要な力を数値化します。水や空気などのニュートン流体の場合、せん断応力とせん断ひずみ率の関係は線形です。つまり、加えられた応力に関係なく、粘度は一定のままです。ケチャップ、歯磨き粉、流砂などの非ニュートン流体は、せん断率の変化に応じて粘度が変化します。

 温度は粘度に大きく影響します。温度が高いと、分子間力が弱まり、流体がより流れやすくなるため、液体の粘度は低下します。例として、加熱したシロップは、冷たいときよりも簡単に注ぐことができます。逆に、温度が高いと、分子の活動と層間の運動量の交換が増加するため、空気の粘度は増加します。サウナで暖かい空気がより濃く感じられるのと同様です。

 流体の挙動を正確に予測するには、これらの温度の影響を考慮する必要があります。これは、パイプラインや自動車エンジンなどのシステムの設計において非常に重要です。パイプラインでは、オイルがスムーズに流れる必要があり、自動車エンジンでは、適切なオイル粘度によって適切な潤滑と効率が確保されます。これを理解することで、エンジニアはさまざまな温度下でより効果的にシステムを設計および操作できるようになります。

粘度は、流体の層が互いに移動するときに、流体が内部摩擦によって流れに抵抗する方法を測定します。
例えば、蜂蜜はゆっくり流れます......

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Fluid Properties

流体の特性

KEY TERMS AND CONCEPTS

主要用語と概念

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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