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

La tensione di vapore, che influenza l'ebollizione e la cavitazione, è la pressione esercitata da un vapore in equilibrio con il suo liquido ad una data temperatura e indica la tendenza delle molecole a fuoriuscire dalla superficie del liquido.
In un contenitore chiuso ed evacuato, le molecole liquide fuoriescono nello spazio, aumentando la pressione fino al raggiungimento dell'equilibrio, dove la velocità di fuga delle molecole è uguale alla velocità di ritorno. Questa pressione di equilibrio è la pressione di vapore.
La pressione del vapore dipende dalla temperatura. All'aumentare della temperatura, le molecole guadagnano energia cinetica, superando le forze intermolecolari e sfuggendo più facilmente nella fase di vapore, aumentando la pressione del vapore.
Ad esempio, l'acqua a 100°C ha una pressione di vapore di 101,3 kPa, che corrisponde alla pressione atmosferica a livello del mare, provocandone l'ebollizione. Ad altitudini più elevate, con una pressione atmosferica più bassa, l'acqua bolle a temperature più basse perché la sua pressione di vapore corrisponde più rapidamente alla pressione atmosferica ridotta.
Il monitoraggio della pressione del vapore è fondamentale nella progettazione e nel funzionamento di pompe e turbine per prevenire la cavitazione.
La cavitazione si verifica quando la pressione locale del fluido scende al di sotto della pressione del vapore, formando bolle di vapore che collassano violentemente, danneggiando le apparecchiature.

pressione di vapore di un fluido

La pressione di vapore di un fluido è un concetto cruciale nella meccanica dei fluidi, poichè influenza fenomeni come l'ebollizione e la cavitazione. La pressione di vapore, indica la pressione esercitata da un vapore in uno stato di equilibrio termodinamico con la sua fase liquida, corrispondente a una temperatura specifica. Rappresenta la tendenza delle molecole a fuoriuscire dalla superficie del fluido, nella fase di vapore.

Quando un liquido viene posto in un contenitore chiuso con un piccolo spazio d'aria e lo spazio viene evacuato, le molecole di vapore si muoveranno dal liquido allo spazio. Man mano che più molecole fuoriescono, la pressione nello spazio aumenta fino a raggiungere un equilibrio, in cui la velocità delle molecole che fuoriescono dal liquido, è uguale alla velocità delle molecole che vi ritornano. Questa pressione di equilibrio, è la pressione di vapore del liquido.

La pressione di vapore dipende dalla temperatura. All'aumentare della temperatura, l'energia cinetica delle molecole aumenta, con una quantità maggiore di molecole in grado di superare le forze intermolecolari e relativo passaggio nella fase di vapore. Ne consegue che la pressione di vapore aumenta con la temperatura. Ad esempio, l'acqua a 100°C ha una pressione di vapore di 101,3 kPa (1 atm), che le consente di bollire alla pressione atmosferica standard. Tuttavia, ad altitudini più elevate, dove la pressione atmosferica è inferiore, l'acqua bolle a temperature più basse, perché in altitudine la sua pressione di vapore è uguale alla pressione atmosferica ridotta.

Pressione di Vapore di un Fluido

La tensione di vapore, che influenza l'ebollizione e la cavitazione, è la pressione esercitata da un vapore in equilibrio con il suo liquido ad una data temperatura e ...

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Fluid Properties

Proprietà dei fluidi

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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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