6.3.1 - Pressure Difference Calculation
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Introduction to Pressure Difference Calculation
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Today, we'll talk about pressure difference and its importance in fluid dynamics. Can anyone tell me why we calculate pressure differences?
It's necessary to understand how fluids move and how they exert forces!
Exactly! We use Bernoulli's principle and momentum equations for this. Let’s start with Bernoulli’s equation, which relates pressure, velocity, and elevation.
How does Bernoulli's equation actually help in calculating forces?
Great question! Bernoulli's equation can give us velocities that help compute the force acting on surfaces due to fluid flow.
"Let’s remember,
Momentum Equations
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
Now, let’s apply linear momentum equations. Who can describe how we use these in fluid flow problems?
They help us compute the net forces acting on a fluid control volume!
Exactly! So, when we consider momentum flux, what's the formula we generally start with?
It's the sum of momentum influx minus the outflux, right?
Right! We can visualize this using control volumes. Let's move on to an example involving a water jet striking a plate.
Applying Bernoulli's and Momentum
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
In our water jet example, we need to find the angle of impact when the flow rate is given. How do we set this problem up?
We can use the momentum equations and apply Bernoulli’s from two points!
Correct! And what does the flow classification look like?
It's steady, incompressible, and ideally frictionless.
Exactly! So if we simplify the equations appropriately, we can solve for the angle θ.
Venturi Meter Calculations
🔒 Unlock Audio Lesson
Sign up and enroll to listen to this audio lesson
How many of you are familiar with venturimeters? They're crucial for flow measurement. What basic principle do they rely on?
They use Bernoulli's equation to calculate pressure differences.
Exactly! Now, if we know the diameters and the flow rate, how can we find the discharge coefficient?
By comparing the actual flow rate to the theoretical flow rate!
Great summary! Remember this relationship: C_d = Q_actual / Q_theoretical.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, we explore the concepts behind calculating pressure differences in fluid systems. It covers the application of Bernoulli's principle and linear momentum equations in practical examples, illustrating how these theories can be used to derive values such as force components and angles of impact in various fluid dynamics scenarios.
Detailed
In the Pressure Difference Calculation section, we start with a fundamental understanding of fluid motion along a horizontal surface, using continuity and Bernoulli's equations for fluid flow analysis. The section emphasizes the importance of Reynolds transport theorems in simplifying the analytical process for linear momentum equations. Key examples, including a scenario involving water jets striking a plate and venturimeter calculations, demonstrate the practical application of theoretical concepts. The section concludes with the derivation of force components and resultant forces through a comprehensive understanding of mass and momentum fluxes, and pressure drop across a venturimeter, reinforcing the critical role of pressure difference calculations in engineering applications.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Introduction to Pressure Difference Calculation
Chapter 1 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
And here as you know it we have considered it is a horizontal surface. So z equal to z. That is what we cancelled out. And we are just substituting the mass conservation equation and the Bernoulli’s equations to compute what will be the Q value.
Detailed Explanation
In this chunk, we set the stage for calculating pressure differences by assuming a horizontal surface, which simplifies our calculations as the elevation terms cancel out. We then reference the equations we will use: the mass conservation equation (which deals with how mass is conserved in fluid flow) and Bernoulli’s equations (which relate pressure, velocity, and elevation). This foundational setup is crucial for calculating flow rates and subsequently the forces acting on the system.
Examples & Analogies
Think of a water pipe running straight and level; if the pipe isn’t going up or down, you can disregard gravity's effect on the water flow. This simplification makes it easier to understand how pressure changes from one point in the pipe to another.
Applying the Reynolds Transport Theorem
Chapter 2 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
So based on Reynolds transport theorems, we can write for linear momentum equations. We can write that the sum of the force is acting is equal to the same path change of is equal to since it is a one inflow and one outflow.
Detailed Explanation
The Reynolds Transport Theorem allows us to relate the change in momentum to the forces acting on a control volume. Since we are focusing on one inflow and one outflow, we can mathematically express how the forces acting on the system are equal to the change in momentum across the control surface. This equation is fundamental in analyzing fluids in motion, allowing us to quantify how pressure changes in response to flow variations.
Examples & Analogies
Imagine a water balloon with a small hole in it. As water flows out, the pressure inside changes. Using the Reynolds Transport Theorem helps us calculate how fast the balloon deflates based on the forces acting on the remaining water.
Momentum Outflux and Influx
Chapter 3 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
So that is what is outflux, mass outflux. Sorry, this is what momentum outflux and this is what momentum influx components.
Detailed Explanation
In this part, we differentiate between momentum outflux and influx. Momentum outflux is the momentum leaving our control volume, while influx is the momentum entering it. Understanding these concepts is crucial because they directly relate to how pressure differences are created in fluid systems—more momentum leaving than entering results in a drop in pressure, and vice versa.
Examples & Analogies
Think of a crowded elevator: when people leave (momentum outflux), it becomes lighter and the pressure inside decreases. If more people enter (momentum influx), the pressure inside increases as space and air become limited.
Computing Forces in the X-Direction
Chapter 4 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
So we will play along the x directions to get it. If I apply in the x-direction, we will get the sum of the force F x will be...
Detailed Explanation
Here, we focus on calculating the forces in the x-direction. This involves understanding how the momentum flux affects the forces we need to consider when analyzing pressure differences. By following through with calculations, we can clearly express how the flow through the system influences the resultant forces, ultimately allowing us to predict necessary adjustments to maintain desired flow conditions.
Examples & Analogies
If you push against a swing while someone is swinging back and forth, your force applied alters their momentum in that direction. Similarly, in fluid dynamics, the forces create changes in velocity and flow, which we quantify in our equations.
Resultant Force Calculation
Chapter 5 of 5
🔒 Unlock Audio Chapter
Sign up and enroll to access the full audio experience
Chapter Content
As we know this F x and F y value then we can compute resultant force which will be...
Detailed Explanation
Once we have our force values in both x and y directions, we can compute the resultant force using the Pythagorean theorem. This resultant force is key because it reflects the total impact of our pressure calculations, highlighting how these combined forces affect flow dynamics. Understanding resultant forces is essential for design and analysis of fluid systems.
Examples & Analogies
Picture a bow and arrow: the force pulling back the string and releasing it creates a resultant force that determines how fast and far the arrow flies, much like how fluid pressure pushes the liquid through pipes and systems.
Key Concepts
-
Pressure Difference: The difference in pressure between two points in a fluid system, critical for determining flow characteristics.
-
Bernoulli’s Principle: Relates pressure, velocity, and elevation in fluid flow, essential for analyzing fluid systems.
-
Momentum Equations: Framework used to analyze fluid behavior by accounting for momentum changes in control volumes.
-
Venturimeter: Instrument used to measure fluid flow rates by using the principle of pressure difference across varying diameters.
Examples & Applications
Calculating the resultant force exerted by a fluid jet on a plate using momentum equations and Bernoulli’s principle.
Applying the venturimeter formula to find the discharge coefficient given the pressure difference and flow rate.
Memory Aids
Interactive tools to help you remember key concepts
Rhymes
Speed raises high, pressure must fall; Bernoulli's rule applies to them all!
Stories
Imagine a water park where the slides are narrow and steep. As you zoom down, you feel lighter—this is Bernoulli's effect in action!
Memory Tools
P for Pressure, V for Velocity, and H for Height—remember it as PVH for Bernoulli's equation!
Acronyms
Remember 'BEEP' for Bernoulli's Equation
Balance Energy
Equal Path!
Flash Cards
Glossary
- Bernoulli’s Equation
A principle stating that in a steady flow, the total mechanical energy along a streamline remains constant.
- Momentum Flux
The rate at which momentum crosses a unit area.
- Venturimeter
A device used to measure the flow rate by observing the pressure difference created by a reduction in pipe diameter.
- Control Volume
A specified region in space through which fluid may flow.
Reference links
Supplementary resources to enhance your learning experience.