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

Um volume de controle é uma região definida no espaço onde as interações envolvendo massa, energia ou momento são analisadas.
Considere a água fluindo através de um cano. O volume de controle seria uma seção do tubo e a superfície de controle seria o limite dessa seção.
À medida que a água entra e sai desse volume de controle, as leis de conservação de massa, momento e energia são usadas para estudar o fluxo sem rastrear partículas de água individuais.
O volume de controle permanece fixo enquanto o fluido se move através dele, reduzindo a complexidade.
Em contraste, um sistema refere-se a uma massa específica de fluido que é seguida ao longo do tempo. Considere um tanque de água contendo uma quantidade fixa de água.
A água dentro do tanque representa o sistema. À medida que a água escoa ou enche, o mesmo sistema de água é rastreado, concentrando-se em seu comportamento e mudanças ao longo do tempo.
A representação do sistema permite uma análise dessa massa fixa de água, mesmo quando o estado do tanque muda.
Enquanto o sistema segue a massa específica do fluido, a abordagem do volume de controle permanece estacionária e se concentra em uma região específica do espaço.

volume de controle e representações do sistema

Duas estruturas principais são empregadas para analisar a transferência de massa, energia e momento: a abordagem do volume de controle e a abordagem do sistema. Essas estruturas oferecem perspectivas diferentes, dependendo se o foco está em uma região específica no espaço (abordagem do volume de controle) ou em uma massa definida de fluido (abordagem do sistema).

A abordagem do volume de controle considera uma região estacionária no espaço através da qual o fluido flui. Esta região é delimitada por uma superfície de controle. Por exemplo, no caso de água fluindo por um cano, o volume de controle seria uma seção fixa do cano, e a superfície de controle seria o limite desta seção. Esta estrutura simplifica a análise do fluxo de fluido aplicando leis de conservação para massa, energia e momento em todo o volume de controle. A principal vantagem é que ela se concentra nas propriedades macroscópicas do fluido sem exigir o rastreamento de partículas individuais do fluido. À medida que a água entra e sai do volume de controle, as mudanças em suas características de fluxo são avaliadas nos limites da superfície de controle, tornando-a uma ferramenta poderosa para estudar condições de fluxo estáveis ​​ou instáveis.

A abordagem do sistema, por outro lado, está preocupada com uma massa fixa de fluido rastreada ao longo do tempo. Um exemplo prático disso é a água no tanque. A água no tanque representa um sistema e, à medida que drena ou enche, a mesma massa de água é analisada. O comportamento do sistema é estudado à medida que forças externas e transferências de energia causam mudanças no estado do fluido. Essa abordagem é particularmente útil ao analisar processos termodinâmicos onde a massa exata e seu conteúdo de energia ou momento são críticos, como em cenários de transferência de calor ou mudança de fase em sistema fechado.

Enquanto o volume de controle é fixo no espaço e se concentra na troca de quantidades através de sua superfície, a abordagem do sistema rastreia a evolução de uma massa específica de fluido. Essas metodologias são complementares, oferecendo flexibilidade em dinâmica de fluidos e análise termodinâmica.

Volume de controle e representações do sistema

Um volume de controle é uma região definida no espaço onde as interações envolvendo massa, energia ou momento são analisadas.
Considere a água fluindo através de um cano. ...

control-volume-and-system-representations

Education

JoVE Core

Civil Engineering

Engenharia Civil

Unit 1

Unidade 1

Fluid Kinematics

Cinemática dos Fluidos

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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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