Indian Institute of Technology Kharagpur - 1.3 | 14. Fluid Dynamics | Hydraulic Engineering - Vol 1
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Bernoulli's Equation and Fluid Flow

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0:00
Teacher
Teacher

Today, we will apply Bernoulli's equation to analyze water flow through a tapered pipe. Can anyone tell me how Bernoulli's equation relates pressure and velocity?

Student 1
Student 1

Is it that higher velocity corresponds to lower pressure?

Teacher
Teacher

Exactly! This principle helps us simplify our calculations. We are given a discharge of 120 liters per second through a tapered pipe. Let's find the deflection h in a mercury manometer. First, can you recall the assumptions we make while applying Bernoulli’s equation?

Student 2
Student 2

We neglect the friction, right?

Teacher
Teacher

Correct! By neglecting friction, we can directly use Bernoulli's equation. Now let's set up the equation for our problem using the relative density of mercury.

Student 3
Student 3

What is relative density again?

Teacher
Teacher

Good question! Relative density is the ratio of the density of a substance to the density of a reference substance. For mercury, it's 13.6. Now let's calculate h.

Student 4
Student 4

After calculating, we'll see how it relates to fluid properties?

Teacher
Teacher

Absolutely! Let's wrap up this session by summarizing that we’ve applied Bernoulli’s to deduce physical flow characteristics.

Understanding Fluid Properties

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Teacher
Teacher

Let’s discuss fluid properties. Who can define extensive and intensive properties?

Student 1
Student 1

Isn’t extensive property something that depends on the size of the system, like mass?

Teacher
Teacher

Correct! Extensive properties are dependent on the mass of fluid. Intensive properties, like temperature, do not depend on the system size. Why do you think this distinction is important?

Student 2
Student 2

It helps in understanding flow characteristics at different scales?

Teacher
Teacher

Exactly! Now let's consider the Reynolds transport theorem and how it relates extensive properties to time rates of change.

Student 3
Student 3

How do we measure these changes in a control volume?

Teacher
Teacher

Great question! We observe time rates of change using calculations based on the fluid flow across a control surface. Let's apply this to a problem.

Deriving Reynolds Transport Theorem

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Teacher
Teacher

Today we will derive the Reynolds transport theorem. Can anyone summarize the Reynolds transport theorem for me?

Student 1
Student 1

It relates the rate of change of extensive properties in a system to those in a control volume?

Teacher
Teacher

Exactly! Let’s derive it. Start with the definition of an extensive property. If B represents the extensive property, how do we express it for a system?

Student 2
Student 2

B is equal to the mass times the property per unit mass?

Teacher
Teacher

Well done! Now, we introduce control volume and how it differs from a system. Can someone define control volume?

Student 3
Student 3

It's a fixed volume through which fluid flows?

Teacher
Teacher

Exactly! Now, let’s derive how we measure the change of B over time within this control volume.

Student 4
Student 4

What happens during this derivation?

Teacher
Teacher

We see how inflow and outflow affect the extensive property B. By doing this step-by-step, we will arrive at a generalized form of the theorem.

Applications of Reynolds Transport Theorem

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Teacher
Teacher

Having derived the Reynolds transport theorem, let's discuss its applications. Who can give examples of where it's applied?

Student 1
Student 1

In engineering systems involving fluid flow?

Teacher
Teacher

Correct! It's widely used in hydraulics and aerodynamics. Can someone explain how this relates to the conservation laws?

Student 2
Student 2

It shows how properties like momentum are conserved in a control volume?

Teacher
Teacher

Exactly! It’s essential to understand flow through systems with multiple inlets and outlets. Let’s explore a problem that illustrates this.

Student 3
Student 3

How does varying velocity change our calculations?

Teacher
Teacher

That's crucial, and it shows the role of velocity in calculating inflow and outflow rates. Great insights, everyone.

Consolidation and Review

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Teacher
Teacher

Let's review what we've learned. Can someone summarize the key points from Bernoulli’s equation and the Reynolds transport theorem?

Student 1
Student 1

Bernoulli relates pressure and velocity, while Reynolds connects system properties with control volumes.

Teacher
Teacher

Exactly right! Now, let's solve a quick problem together. If we have a flow through a pipe, how do we calculate the deflection in a manometer?

Student 2
Student 2

By applying Bernoulli's equation after finding velocities?

Teacher
Teacher

Correct! Remember to consider relative densities in these calculations. What’s another essential takeaway from today's session?

Student 3
Student 3

Understanding the distinction between extensive and intensive properties helps in analyzing fluid behavior.

Teacher
Teacher

Perfect! This foundational knowledge prepares you for fluid dynamics problems ahead. Well done, everyone!

Introduction & Overview

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Quick Overview

This section covers the application of Bernoulli’s equation and the Reynolds transport theorem within fluid mechanics, with practical examples and derivations.

Standard

The section delves into practical applications of Bernoulli's equation, including how to calculate fluid flow through tapered pipes, and introduces the Reynolds transport theorem, explaining the relationship between extensive and intensive properties of fluids and their time rates of change within a control volume.

Detailed

Fluid Mechanics at Indian Institute of Technology Kharagpur

In this section, we explore practical applications of Bernoulli's equation in fluid mechanics, specifically for fluid flow through tapered pipes. We start by solving a problem where the flow of water through a pipe is analyzed using Bernoulli's principle, allowing us to neglect friction to simplify the calculations. The relationship between pressure variations and flow characteristics is derived, culminating in the determination of deflection in a mercury manometer.

The discussion transitions to the Reynolds transport theorem, a fundamental theorem in fluid dynamics that relates the time rate of change of an extensive property (e.g., mass, momentum) of a system to the rate of change of that property within a control volume. By understanding the concepts of extensive and intensive properties, such as B (extensive property) and b (intensive property), students can grasp how physical parameters interact in fluid systems.

Utilizing mathematical expressions and integrals, we derive the Reynolds transport theorem's form applicable to fluid flow in varying control volumes. This theorem implies the conservation principles over control volumes and is essential for analyzing complex fluid dynamics problems. Hence, the section not only reinforces Bernoulli's equation but also integrates foundational concepts necessary for deeper understanding in fluid dynamics.

Audio Book

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Reynolds Transport Theorem Introduction

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So, to start fluid dynamics, one of the most important theorems that generally is not taught in fluid mechanics is Reynolds transport theorem. So, what we are going to do, we are going to derive this Reynolds transport theorem in a little bit more detail. So, all physical laws are stated in terms of various physical parameters. So, if B represents any of these, these parameters can be velocity, acceleration, mass, temperature, momentum, anything etc.

Detailed Explanation

The Reynolds transport theorem (RTT) is crucial for understanding fluid dynamics. It expresses how properties of fluids change over time within a control volume as fluid flows through it. The variables such as velocity, mass, and temperature are essential in fluid mechanics. In this chunk, the lecture emphasizes the importance of this theorem in analyzing fluid flow and prepares the audience for a detailed derivation.

Examples & Analogies

Think of a river as a control volume. The Reynolds transport theorem helps you understand how the water's properties, like speed or temperature, change as water flows downstream. Just as you wouldn't expect the street to stay clean when it rains, properties of the fluid don’t stay constant; they change as the fluid moves.

Extensive and Intensive Properties

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So, what it says is, let B represent any of these fluid parameter capital ‘B’ and small ‘b’ represent the amount of that parameter per unit mass, that is, B is equal to m into b, where m is the mass of the portion of the fluid of interest, b will be 1 if B is equal to m. So, B is the amount of that parameter per unit mass. The parameter B, capital B is termed as extensive property and the parameters b is termed as intensive property.

Detailed Explanation

In fluid mechanics, properties of substances are categorized into extensive and intensive. Extensive properties (B) depend on the amount of fluid present, such as mass or volume. In contrast, intensive properties (b) are independent of the quantity of fluid, such as temperature or pressure. Understanding these distinctions helps in analyzing fluid behavior correctly.

Examples & Analogies

Imagine you have two cups of water: one full and one half full. The total weight of the full cup (an extensive property) is more than that of the half cup. However, the temperature of the water (an intensive property) remains the same whether you measure it in one cup or the other.

Calculating Extensive Properties

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The amount of an extensive property that the system possesses at a given instant B, sys so, basis is the amount of the extensive property that a system will have at any given instant. And how that can be found out? It can be determined by adding up the amount associated with each fluid particle in the system, it is very simple. So, B system can be calculated by summing up different B s, you know, capital B, capital B of each particle.

Detailed Explanation

To find the total quantity (B_sys) of an extensive property in a system, we sum up the property values of each fluid particle. For a large number of particles, this summation evolves into an integral as particle sizes approach zero. This mathematical approach allows for precise calculations in fluid dynamics.

Examples & Analogies

Think of a classroom full of students. To find the total number of students in the classroom (an extensive property), you just count each one by one. If you had a camera that could take a picture of everyone together and then zoomed in to see each student as an individual particle, you would be summing them up visually!

Time Rate of Change

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Thus, we often encounter terms such as dB sys dt. So, not only B system is important with that is the summation of so, B summation B sys was integral system rho b d V. So, this is important but not only this, the derivative of this B sys this is also important because in many times we require that mass rate of change of mass or rate of change of momentum.

Detailed Explanation

In fluid dynamics, it is often crucial to calculate how the extensive properties change over time (dB_sys/dt). This derivative helps us understand how factors like momentum or mass evolve as fluid flows. For practical applications, knowing these rates can aid in predicting the behavior of fluids under varying conditions.

Examples & Analogies

Imagine a tub being filled with water. The rate at which the water rises (change in height over time) is like the rate of change for momentum or mass in fluid dynamics. If you had a slow faucet, the water might rise gradually, while a fast faucet would cause a rapid rise.

Deriving Reynolds Transport Theorem

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So, now we are, I mean, this is the prelude to but now we are going to derive Reynolds transport theorem. We consider the control volume to be that stationary volume within the pipe or duct between section 1 and 2. So, this figure have been taken from Munson, Young and Okiishi, but yeah, so, you can refer to that book for the derivation of Reynolds transport theorem as well.

Detailed Explanation

The derivation of the Reynolds transport theorem begins by defining a control volume in a flow system, such as within a pipe. This prepares for a detailed exploration of how fluid properties are influenced within this defined space, accounting for in- and out-flow across the boundaries of the control volume.

Examples & Analogies

Think of a water balloon. The balloon itself is like the control volume, holding the water inside. As we squeeze it (similar to flow in a pipe), water squirts out. Just as we can visually analyze what's happening inside the balloon, the Reynolds transport theorem allows us to analyze properties inside any flow system.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Bernoulli's Equation: Describes the relationship between fluid velocity and pressure, critical in fluid mechanics.

  • Reynolds Transport Theorem: Essential for analyzing the dynamics of fluid flow in control volumes.

  • Extensive vs Intensive Properties: Understanding these distinctions aids in fluid property analysis.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Calculating the deflection h in a mercury manometer using Bernoulli's principle.

  • Deriving the change of extensive property using the Reynolds transport theorem in a control volume.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • In Bernoulli's flow, swift and light, Pressure drops when speed takes flight.

📖 Fascinating Stories

  • A water park slide is steep and fast; as water rushes down, the pressure won’t last – just like in Bernoulli's grand tale where fast fluid means pressure frail.

🧠 Other Memory Gems

  • B.E.P.V.H - Bernoulli's Equation relates Pressure, Velocity, and Height.

🎯 Super Acronyms

R.T.T - Reynolds Transport Theorem connects Rate, Time, and Transport properties.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Bernoulli's Equation

    Definition:

    A principle that describes the conservation of energy in fluid flow, establishing a relationship between pressure, velocity, and height.

  • Term: Relative Density

    Definition:

    The ratio of the density of a substance to the density of a reference substance, typically water.

  • Term: Extensive Property

    Definition:

    A property that depends on the amount of material in a system, such as mass and volume.

  • Term: Intensive Property

    Definition:

    A property that does not depend on the amount of material present, such as density and temperature.

  • Term: Reynolds Transport Theorem

    Definition:

    A theorem that relates the rate of change of an extensive property in a system to its flow across a control volume.