Name: how temperature changes fluid viscosity
Uploaded: 2025-02-13T15:43:08.000Z
Duration: 1 min 19 s
Channel: JoVE

צמיגות מודדת כיצד נוזל מתנגד לזרום עקב חיכוך פנימי כאשר שכבות של הנוזל עוברות זו על פני זו.
לדוגמה, דבש זורם לאט כי יש לו צמיגות גבוהה, בעוד מים זורמים בקלות עם צמיגות נמוכה.
ישנם שני סוגים עיקריים של צמיגות: דינמית וקינמטית. צמיגות דינמית מודדת את הכוח הדרוש כדי להעביר שכבת נוזל אחת על פני אחרת.
לדוגמה, כאשר מערבבים, הדבש מתנגד לכפית יותר מאשר מים. צמיגות קינמטית היא היחס בין צמיגותו הדינמית של הנוזל לצפיפותו, ומתארת כיצד הנוזל מתפשט תחת כוח הכבידה.
לרוב הנוזלים הנפוצים, כגון מים ואוויר, יש צמיגות קבועה ללא קשר לכוח המופעל.
עם זאת, נוזלים מסוימים, כמו קטשופ, משנים את צמיגותם בהתאם לכוח המופעל; קטשופ זורם בקלות רבה יותר כאשר הבקבוק מזועזע.
הטמפרטורה משפיעה באופן משמעותי על צמיגות, קריטית בתכנון צינורות, שבהם הנפט חייב לזרום בצורה חלקה.
לעומת זאת, אוויר חם בסאונה מדגים כיצד טמפרטורות גבוהות יותר מגבירות את צמיגות הגזים.

צמיגות של נוזל

<div style="direction:rtl">צמיגות מודדת את ההתנגדות של נוזל לזרימה ולעיוות. היא נובעת מחיכוך פנימי בין שכבות הנוזל הנעות זו ביחס לזו. צמיגות דינמית, המסומנת באות היוונית μ (מו), מודדת את הכוח הנדרש כדי להזיז שכבת נוזל אחת מעל שכבה אחרת. נוזלים ניוטוניים כמו מים ואוויר מקיימים קשר ליניארי בין מאמץ הגזירה לבין קצב עיוות הגזירה, כך שהצמיגות שלהם נשארת קבועה ללא תלות בעומס. לעומתם, נוזלים לא ניוטוניים כמו קטשופ, משחת שיניים וחול טובעני משנים את צמיגותם בהתאם לשינוי בקצבי הגזירה. הטמפרטורה משפיעה באופן משמעותי על הצמיגות. בטמפרטורות גבוהות יותר, הצמיגות של הנוזלים יורדת, מכיוון שכוחות המשיכה הבין מולקולריים נחלשים, והזרימה נעשית קלה יותר. דוגמה לכך היא סירום מחומם שנשפך בקלות רבה יותר מסירופ קר. מנגד, בגזים, צמיגות עולה בטמפרטורות גבוהות יותר, שכן פעילות מולקולרית והחלפת התנע בין שכבות גוברות, בדומה לאוויר חם שמרגיש ״כבד״ יותר בסאונה. התחשבות בהשפעות הטמפרטורה על הצמיגות חשובה במיוחד לתכנון מערכות כמו צינורות ומנועי רכב. בצינורות, יש להבטיח זרימה חלקה, ובמנועי רכב, צמיגות נכונה של השמן מבטיחה שימון תקין ותפקוד יעיל. הבנה זו מאפשרת למהנדסים לתכנן ולתפעל מערכות ביעילות בתנאים משתנים.</div>

צמיגות מודדת כיצד נוזל מתנגד לזרום עקב חיכוך פנימי כאשר שכבות של הנוזל עוברות זו על פני זו.
לדוגמה, דבש זורם לאט ...

Education

JoVE Core

Civil Engineering

הנדסה אזרחית

Unit 1

יחידה 1

Fluid Properties

תכונות נוזלים

KEY TERMS AND CONCEPTS

מונחי מפתח ומושגים

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, toothpaste, and quicksand, do not behave this way. Their viscosity changes as the shear rate changes.

Temperature also has a strong effect on viscosity. For liquids, higher temperature lowers viscosity because intermolecular forces weaken and the fluid flows more easily. Heated syrup is a simple example. It pours more readily when warm than when it is cold.

For gases, the pattern is different. Higher temperature increases viscosity because molecular activity and momentum exchange between layers rise. Warm air can feel thicker, like the air in a sauna. Engineers need to account for these temperature effects when predicting fluid behavior.

This is important in systems such as pipelines and car engines. Oil in a pipeline must move smoothly. In a car engine, the right oil viscosity helps with lubrication and efficiency. Understanding viscosity helps engineers design and operate these systems under changing temperatures.

How Temperature Changes Fluid Viscosity

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

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

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 viscosity changes with temperature in liquids and gases, and why Newtonian and non-Newtonian fluids matter in pipelines and car engines.

How Temperature Changes Fluid Viscosity | 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

How Temperature Changes Fluid Viscosity

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