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

Der Dampfdruck, der das Sieden und die Kavitation beeinflusst, ist der Druck, den ein Dampf im Gleichgewicht mit seiner Flüssigkeit bei einer bestimmten Temperatur ausübt und gibt die Tendenz von Molekülen an, aus der Flüssigkeitsoberfläche zu entweichen.
In einem geschlossenen, evakuierten Behälter entweichen flüssige Moleküle in den Weltraum und erhöhen den Druck, bis ein Gleichgewicht erreicht ist, bei dem die Rate der entweichenden Moleküle der Rückkehrrate entspricht. Dieser Gleichgewichtsdruck ist der Dampfdruck.
Der Dampfdruck hängt von der Temperatur ab. Mit steigender Temperatur gewinnen die Moleküle an kinetischer Energie, überwinden intermolekulare Kräfte und entweichen leichter in die Dampfphase, was den Dampfdruck erhöht.
Zum Beispiel hat Wasser bei 100 °C einen Dampfdruck von 101,3 kPa, was dem atmosphärischen Druck auf Meereshöhe entspricht, was dazu führt, dass es kocht. In größeren Höhen mit niedrigerem Atmosphärendruck siedet Wasser bei niedrigeren Temperaturen, da sein Dampfdruck schneller dem reduzierten Atmosphärendruck entspricht.
Die Überwachung des Dampfdrucks ist bei der Konstruktion und dem Betrieb von Pumpen und Turbinen von entscheidender Bedeutung, um Kavitation zu verhindern.
Kavitation tritt auf, wenn der lokale Flüssigkeitsdruck unter den Dampfdruck sinkt und Dampfblasen bilden, die heftig kollabieren und die Ausrüstung beschädigen.

dampfdruck einer flüssigkeit

Der Dampfdruck eines Fluids ist ein entscheidender Begriff in der Strömungsmechanik, der Phänomene wie Sieden und Kavitation beeinflusst. Dampfdruck bezeichnet den Druck, den ein Dampf in einem Zustand thermodynamischen Gleichgewichts mit seiner entsprechenden flüssigen Phase bei einer bestimmten Temperatur ausübt. Er stellt die Tendenz von Molekülen dar, von der Flüssigkeitsoberfläche in die Dampfphase zu entweichen.

Wenn eine Flüssigkeit in einen geschlossenen Behälter mit einem kleinen Luftraum gegeben wird und der Raum evakuiert wird, entweichen Dampfmoleküle aus der Flüssigkeit in den Raum. Wenn mehr Moleküle entweichen, steigt der Druck im Raum, bis ein Gleichgewicht erreicht ist, bei dem die Rate der Moleküle, die aus der Flüssigkeit entweichen, der Rate der Moleküle entspricht, die in sie zurückkehren. Dieser Gleichgewichtsdruck ist der Dampfdruck der Flüssigkeit.

Der Dampfdruck ist temperaturabhängig. Mit steigender Temperatur steigt die kinetische Energie der Moleküle, was dazu führt, dass mehr Moleküle intermolekulare Kräfte überwinden und in die Dampfphase entweichen. Daraus folgt, dass der Dampfdruck mit der Temperatur steigt. Beispielsweise hat Wasser bei 100 °C einen Dampfdruck von 101,3 kPa (1 atm), sodass es bei normalem atmosphärischem Druck sieden kann. In höheren Lagen, wo der atmosphärische Druck niedriger ist, siedet Wasser jedoch bei niedrigeren Temperaturen, da sein Dampfdruck dem reduzierten atmosphärischen Druck in der höheren Lage entspricht.

Dampfdruck einer Flüssigkeit

Der Dampfdruck, der das Sieden und die Kavitation beeinflusst, ist der Druck, der von einem Dampf ausgeübt wird, der sich im Gleichgewicht mit seiner Flüssigkeit bei einer bestimmten Temperatur und ...

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JoVE Core

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Unit 1

Einheit 1

Fluid Properties

Fluideigenschaften

KEY TERMS AND CONCEPTS

ZENTRALE BEGRIFFE UND KONZEPTE

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

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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,...

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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

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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...

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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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