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

Un volumen de control es una región definida en el espacio donde se analizan las interacciones que involucran masa, energía o momento.
Considere el agua que fluye a través de una tubería. El volumen de control sería una sección de la tubería y la superficie de control sería el límite de esta sección.
A medida que el agua entra y sale de este volumen de control, se utilizan leyes de conservación de masa, momento y energía para estudiar el flujo sin rastrear partículas de agua individuales.
El volumen de control permanece fijo mientras el fluido se mueve a través de él, lo que reduce la complejidad.
Por el contrario, un sistema se refiere a una masa específica de fluido que se sigue a lo largo del tiempo. Considere un tanque de agua que contiene una cantidad fija de agua.
El agua dentro del tanque representa el sistema. A medida que el agua se drena o se llena, se realiza un seguimiento del mismo sistema de agua, centrándose en su comportamiento y cambios con el tiempo.
La representación del sistema permite un análisis de esta masa fija de agua, incluso cuando cambia el estado del tanque.
Mientras que el sistema sigue la masa de fluido específica, el enfoque de volumen de control permanece estacionario y se centra en una región particular del espacio.

representaciones del volumen de control y del sistema

Para analizar la transferencia de masa, energía y momento se emplean dos marcos fundamentales: el enfoque del volumen de control y el enfoque del sistema. Estos marcos ofrecen diferentes perspectivas, dependiendo de si el enfoque se centra en una región específica del espacio (enfoque del volumen de control) o en una masa definida de fluido (enfoque del sistema). El enfoque del volumen de control considera una región estacionaria del espacio por la que fluye el fluido. Esta región está delimitada por una superficie de control. Por ejemplo, en el caso del agua que fluye por una tubería, el volumen de control sería una sección fija de la tubería y la superficie de control sería el límite de esta sección. Este marco simplifica el análisis del flujo de fluidos al aplicar las leyes de conservación de masa, energía y momento en todo el volumen de control. La ventaja clave es que se centra en las propiedades macroscópicas del fluido sin necesidad de rastrear partículas individuales del fluido. A medida que el agua entra y sale del volumen de control, los cambios en sus características de flujo se evalúan en los límites de la superficie de control, lo que lo convierte en una herramienta poderosa para estudiar las condiciones de flujo estable o inestable. El enfoque de sistemas, por el contrario, se ocupa de una masa fija de fluido que se sigue a lo largo del tiempo. Un ejemplo práctico de esto es el agua en un tanque. El agua dentro del tanque representa un sistema y, a medida que se drena o se llena, se analiza la misma masa de agua. El comportamiento del sistema se estudia a medida que las fuerzas externas y las transferencias de energía provocan cambios en el estado del fluido. Este enfoque es particularmente útil al analizar procesos termodinámicos donde la masa exacta y su contenido de energía o momento son críticos, como en los escenarios de transferencia de calor o cambio de fase de sistema cerrado. Mientras que el volumen de control está fijo en el espacio y se centra en el intercambio de cantidades a través de su superficie, el enfoque de sistemas rastrea la evolución de una masa específica de fluido. Estas metodologías son complementarias y ofrecen flexibilidad en la dinámica de fluidos y el análisis termodinámico.

Representaciones del volumen de control y del sistema

Un volumen de control es una región definida en el espacio donde se analizan las interacciones que involucran masa, energía o momento.
Considere el agua que fluye a través de una tubería. ...

control-volume-and-system-representations

Education

Educación

JoVE Core

Civil Engineering

Ingeniería Civil

Unit 1

Unidad 1

Fluid Kinematics

Cinemática de Fluidos

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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.

civil engineering

Tracking Fluid Through Space or Mass

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