Name: vapor pressure and boiling behavior
Uploaded: 2025-02-13T15:43:08.000Z
Duration: 1 min 28 s
Channel: JoVE

A pressão de vapor, que influencia a ebulição e a cavitação, é a pressão exercida por um vapor em equilíbrio com seu líquido a uma determinada temperatura e indica a tendência das moléculas de escaparem da superfície do líquido.
Em um recipiente fechado e evacuado, as moléculas líquidas escapam para o espaço, aumentando a pressão até que o equilíbrio seja alcançado, onde a taxa de moléculas escapando é igual à taxa de retorno. Essa pressão de equilíbrio é a pressão de vapor.
A pressão do vapor depende da temperatura. À medida que a temperatura aumenta, as moléculas ganham energia cinética, superando as forças intermoleculares e escapando para a fase de vapor com mais facilidade, o que aumenta a pressão do vapor.
Por exemplo, a água a 100 ° C tem uma pressão de vapor de 101,3 kPa, que corresponde à pressão atmosférica ao nível do mar, fazendo com que ela ferva. Em altitudes mais elevadas, com pressão atmosférica mais baixa, a água ferve em temperaturas mais baixas porque sua pressão de vapor corresponde à pressão atmosférica reduzida mais rapidamente.
O monitoramento da pressão de vapor é crucial no projeto e operação de bombas e turbinas para evitar a cavitação.
A cavitação ocorre quando a pressão do fluido local cai abaixo da pressão do vapor, formando bolhas de vapor que colapsam violentamente, danificando o equipamento.

pressão de vapor do fluido

A pressão de vapor de um fluido é um conceito crucial na mecânica dos fluidos, influenciando fenômenos como ebulição e cavitação. A pressão de vapor se refere à pressão exercida por um vapor em um estado de equilíbrio termodinâmico com sua fase líquida correspondente a uma temperatura específica. Ela representa a tendência das moléculas de escapar da superfície do fluido para a fase de vapor.

Quando um líquido é colocado em um recipiente fechado com um pequeno espaço de ar, e o espaço é evacuado, as moléculas de vapor escapam do líquido para o espaço. A medida que mais moléculas escapam, a pressão no espaço aumenta até que um equilíbrio seja alcançado, onde a taxa de moléculas que escapam do líquido é igual à taxa de moléculas retornando a ele. Essa pressão de equilíbrio é a pressão de vapor do líquido.

A pressão de vapor depende da temperatura. À medida que a temperatura aumenta, a energia cinética das moléculas aumenta, resultando em mais moléculas superando as forças intermoleculares e escapando para a fase de vapor. Conclui-se que a pressão de vapor aumenta com a temperatura. Por exemplo, a água a 100°C tem uma pressão de vapor de 101,3 kPa (1 atm), permitindo que ela ferva na pressão atmosférica padrão. No entanto, em altitudes mais elevadas, onde a pressão atmosférica é menor, a água ferve em temperaturas mais baixas porque sua pressão de vapor é igual à pressão atmosférica reduzida na altitude mais alta.

Pressão de vapor do fluido

A pressão de vapor, que influencia a ebulição e a cavitação, é a pressão exercida por um vapor em equilíbrio com seu líquido a uma determinada temperatura e ...

Education

JoVE Core

Civil Engineering

Engenharia Civil

Unit 1

Unidade 1

Fluid Properties

Propriedades dos Fluidos

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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 pressure rises as more molecules collect there. Soon, the rate of molecules leaving the liquid equals the rate returning to it. That balance creates the vapor pressure of the liquid.

Temperature changes vapor pressure. When temperature increases, the molecules gain kinetic energy. More molecules can overcome intermolecular forces and escape into the vapor phase. For that reason, vapor pressure increases as temperature increases.

Water gives a clear example. At 100°C, water has a vapor pressure of 101.3 kPa, or 1 atm. That is why it can boil at standard atmospheric pressure. At higher elevations, atmospheric pressure is lower. Water then boils at a lower temperature because its vapor pressure reaches the reduced outside pressure sooner.

Vapor Pressure and Boiling Behavior

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

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,...

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 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 vapor pressure forms, why it rises with temperature, and how it explains boiling in water at sea level and higher elevations.

Vapor Pressure and Boiling Behavior | 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

Vapor Pressure and Boiling Behavior

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