Name: tracking fluid through space or mass
Uploaded: 2025-02-13T15:43:18.000Z
Duration: 1 min 16 s
Channel: JoVE

制御ボリュームは、質量、エネルギー、または運動量が関与する相互作用が解析される空間内の定義された領域です。
パイプを通って流れる水を考えてみましょう。制御ボリュームはパイプのセクションであり、制御サーフェスはこのセクションの境界になります。
水がこの制御ボリュームに出入りすると、質量、運動量、エネルギーの保存則を使用して、個々の水粒子を追跡せずに流れが研究されます。
制御ボリュームは、流体が移動している間も固定されたままであるため、複雑さが軽減されます。
対照的に、システムとは、時間の経過とともに追跡される特定の質量の流体を指します。一定量の水を保持している水タンクを考えてみましょう。
タンク内の水はシステムを表しています。水が排水または満たされると、同じ水システムが追跡され、その挙動と時間の経過に伴う変化に焦点を当てます。
システム表現により、タンクの状態が変化しても、この固定された水の質量を分析できます。
システムは特定の流体質量に従いますが、制御ボリュームアプローチは静止したままで、空間の特定の領域に焦点を合わせます。

制御体積とシステム表現

質量、エネルギー、および運動量の伝達を分析するために、制御体積アプローチとシステムアプローチという 2 つの主要な枠組みが採用されています。これらの枠組みは、焦点が空間内の特定の領域 (制御体積アプローチ) にあるか、流体の定義された質量 (システムアプローチ) にあるかに応じて、異なる視点を提供します。

 制御体積アプローチでは、流体が流れる空間内の静止領域を考慮します。この領域は、制御面によって境界が定められています。たとえば、パイプを流れる水の場合、制御体積はパイプの固定セクションになり、制御面はこのセクションの境界になります。この枠組みでは、制御体積全体にわたって質量、エネルギー、および運動量の保存則を適用することで、流体の流れの分析を簡素化します。主な利点は、個々の流体粒子を追跡する必要なく、流体のマクロ特性に焦点を当てていることです。水が制御体積に出入りすると、制御面の境界でその流れ特性の変化が評価されるため、定常または非定常の流れ状態を研究するための強力なツールになります。

 対照的に、システムアプローチは、一定量の流体を時間とともに追跡します。この実例としては、タンク内の水が挙げられます。タンク内の水はシステムを表し、水が排出または満たされるときに、同じ量の水が分析されます。外部の力とエネルギーの移動によって流体の状態が変化するため、システムの動作が研究されます。このアプローチは、特に、密閉系の熱伝達や相変化のシナリオなど、正確な質量とそのエネルギーまたは運動量の内容が重要な熱力学的プロセスを分析する場合に役立ちます。

 制御堆積は空間内で固定されており、その表面を通じた量の交換に焦点を当てていますが、システムアプローチは特定の量の流体の変化を追跡します。これらの方法論は補完的であり、流体力学と熱力学の分析に柔軟性をもたらします。

制御ボリュームは、質量、エネルギー、または運動量が関与する相互作用が解析される空間内の定義された領域です。
パイプを通って流れる水を考えてみましょう。...

control-volume-and-system-representations

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Fluid Kinematics

流体運動学

KEY TERMS AND CONCEPTS

主要用語と概念

Control Volume and System Representations

tracking fluid through space or mass

Fluid analysis often uses two linked ideas: the control volume approach and the system approach. Both help describe mass, energy, and momentum transfer, but they focus on different things. One follows a region in space. The other follows a fixed mass of fluid over time.

The control volume approach looks at a stationary area in space through which fluid moves. That area is bounded by a control surface, which is the outer edge of the region. A pipe with water flowing through it is a clear example. In that case, the control volume is a fixed section of the pipe.

This method makes it easier to apply conservation laws for mass, energy, and momentum. It does not require tracking each fluid particle. Instead, it studies how fluid enters and exits the control surface. This makes it useful for both steady flow and unsteady flow.

The system approach uses a different viewpoint. It tracks a specific mass of fluid as conditions change. Water in a tank is a good example. As the tank drains or fills, the same mass of water is treated as the system.

This approach is especially useful in thermodynamics. It helps when the exact mass and its energy or momentum content matter, such as in closed-system heat transfer or phase change. The system changes because external forces and energy transfers act on it.

Together, the control volume and system approaches give students flexible ways to study fluid dynamics and thermodynamics. One focuses on what crosses a boundary in space. The other focuses on how one mass of fluid changes over time.

Tracking Fluid Through Space or Mass

eulerian and lagrangian flow descriptions

eulerian-and-lagrangian-flow-descriptions

Tracking Fluid Motion in Space and Time

Fluid flow can be described with the Eulerian and Lagrangian methods. These two approaches give different views of the same moving fluid. They are useful in science and engineering because the best method depends on the problem being studied. The Eulerian method looks at fixed points in space. At each location, it measures fluid properties such as velocity, pressure, and temperature as the fluid moves past. This stationary view is useful when studying how a fluid interacts with a solid object.

introduction to types of flows

Flow Patterns by Direction and Time

Fluid flow can be grouped by direction and by how it changes over time. The simplest case is one-dimensional flow. In this type, properties such as velocity and pressure change along only one axis. Water moving through a straight pipe is a common example, because changes in other directions are very small. Two-dimensional flow changes in two directions. It varies in both length and height, so the analysis is more complex than one-dimensional flow. Air moving over a flat surface, such as a...

streamlines, streaklines, and pathlines

Tracing Fluid Motion: Three Flow Paths

Streamlines, streaklines, and pathlines are three ways to describe fluid motion. Each one shows flow from a different angle. Together, they help students compare how a fluid moves in steady and unsteady flow. A streamline is a line that stays tangent to the fluid’s velocity vector at each point. That means the fluid velocity points along the streamline. Streamlines give an instant picture of the flow field, so they are useful for showing the overall direction of flow in a fluid system. In...

control volume and system representations

Fluid analysis often uses two linked ideas: the control volume approach and the system approach. Both help describe mass, energy, and momentum transfer, but they focus on different things. One follows a region in space. The other follows a fixed mass of fluid over time. The control volume approach looks at a stationary area in space through which fluid moves. That area is bounded by a control surface, which is the outer edge of the region. A pipe with water flowing through it is a clear...

velocity and acceleration in steady and unsteady flow

velocity-and-acceleration-in-steady-and-unsteady-flow

How Flow Changes Affect Particle Motion

Velocity and acceleration help describe how a fluid particle moves in steady and unsteady flow. A fluid particle follows a pathline, and its velocity depends on both position and time. Acceleration is found by differentiating velocity with respect to time, so it shows how the particle’s motion changes. In a flow field, acceleration can be written using three perpendicular components. These components show how velocity changes over time in different spatial directions. This gives a general way...

reynolds transport theorem

Reynolds Transport and Control Volumes

Reynolds transport theorem links a fluid system to a control volume. It helps explain how the time rate of change of a property can be tracked in fluid dynamics. The theorem uses extensive properties, such as mass, velocity, acceleration, temperature, and momentum. These properties depend on the size of the system. Their intensive forms are the values per unit mass. The total amount of an extensive property in a system at any instant is the sum of the amounts carried by each tiny fluid...

design example: flow through a fire extinguisher

design-example-flow-through-a-fire-extinguisher

Fire Extinguisher Nozzle Flow and Pressure

A pressurized water fire extinguisher uses fluid dynamics to create a fast stream of water. The water is stored at a much higher pressure inside the extinguisher than the surrounding air. When the extinguisher is activated, that pressure difference forces water to flow out quickly. Bernoulli's equation helps predict the exit speed of the water. This equation links pressure and velocity. As pressure drops, velocity increases. In the extinguisher, the high internal pressure is converted into the...

key terms and concepts

Learn how the control volume and system approaches analyze mass, energy, and momentum in fluids, using examples like water in a pipe or tank.

Tracking Fluid Through Space or Mass | 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.

Tracking Fluid Through Space or Mass

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