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

ضغط البخار ، الذي يؤثر على الغليان والتجويف ، هو الضغط الذي يمارسه البخار في حالة توازن مع سائله عند درجة حرارة معينة ويشير إلى ميل الجزيئات إلى الهروب من سطح السائل.
في حاوية مغلقة تم إخلاؤها ، تهرب الجزيئات السائلة إلى الفضاء ، مما يرفع الضغط حتى يتحقق التوازن ، حيث يساوي معدل هروب الجزيئات معدل العودة. ضغط الاتزان هذا هو ضغط البخار.
يعتمد ضغط البخار على درجة الحرارة. مع ارتفاع درجة الحرارة ، تكتسب الجزيئات طاقة حركية ، وتتغلب على القوى بين الجزيئات وتهرب إلى مرحلة البخار بسهولة أكبر ، مما يزيد من ضغط البخار.
على سبيل المثال ، الماء عند 100 درجة مئوية له ضغط بخار يبلغ 101.3 كيلو باسكال ، والذي يتطابق مع الضغط الجوي عند مستوى سطح البحر ، مما يؤدي إلى غليانه. في الارتفاعات العالية ، مع انخفاض الضغط الجوي ، يغلي الماء في درجات حرارة منخفضة لأن ضغط بخاره يتطابق مع الضغط الجوي المنخفض بسرعة أكبر.
تعد مراقبة ضغط البخار أمرا بالغ الأهمية في تصميم وتشغيل المضخات والتوربينات لمنع التجويف.
يحدث التجويف عندما ينخفض ضغط السائل المحلي إلى ما دون ضغط البخار ، مما يشكل فقاعات بخار تنهار بعنف ، مما يؤدي إلى إتلاف المعدات.

الضغط البخاري للموائع

<div style="direction:rtl">يعتبر الضغط البخاري للموائع مفهومًا بالغ الأهمية في ميكانيكا الموائع، حيث يظهر تأثيره على ظواهر مثل الغليان والتكهف. يشير الضغط البخاري إلى الضغط الذي يمارسه البخار الذي في حالة توازن ديناميكي الحراري مع الطور السائل المقابل له عند درجة حرارة معينة. وهو يمثل ميل الجزيئات للهروب من سطح السائل إلى الطور البخاري. عند وضع سائل في وعاء مغلق به مساحة هوائية صغيرة، وعند تفريغ تلك المساحة، فإن جزيئات البخار ستهرب من السائل إلى الفراغ. ومع هروب المزيد من الجزيئات، يزداد الضغط في الفراغ حتى يتم الوصول إلى حالة توازن، حيث يكون معدل الجزيئات التي تهرب من السائل مساويًا لمعدل الجزيئات التي تعود إليه. هذا الضغط المتوازن هو الضغط البخاري للسائل. يعتمد الضغط البخاري على درجة الحرارة. مع زيادة درجة الحرارة، تزداد الطاقة الحركية للجزيئات، مما يؤدي إلى تغلب المزيد من الجزيئات على القوى البين جزيئية والهروب إلى الطور البخاري. ويترتب على ذلك زيادة الضغط البخاري مع زيادة درجة الحرارة. على سبيل المثال، يبلغ الضغط البخاري للماء عند 100 درجة مئوية حوالي 101.3 كيلو باسكال (1 ضغط جوي)، مما يسمح له بالغليان عند الضغط الجوي القياسي. ومع ذلك، عند الارتفاعات الأعلى، حيث يكون الضغط الجوي أقل، يغلي الماء عند درجات حرارة أقل لأن ضغطه البخاري سيساوي حينها الضغط الجوي المنخفض عند الارتفاع الأعلى.</div>

ضغط البخار ، الذي يؤثر على الغليان والتجويف ، هو الضغط الذي يمارسه البخار في حالة توازن مع سائله عند درجة حرارة معينة و ...

Education

JoVE Core

Civil Engineering

الهندسة المدنية

Unit 1

الوحدة الأولى

Fluid Properties

خصائص الموائع

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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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