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Fluid Mechanics for a Non-technical Audience


Yu-Li Sim

on 12 October 2012

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Transcript of Fluid Mechanics for a Non-technical Audience

FLUID MECHANICS 101 An Introduction to Fluid Mechanics Welcome to
"Fluid Mechanics"?
Fluid Mechanics is a branch of physics.

It focuses on the effect of forces on fluids. How is Fluid Mechanics used in today's society? Let's begin with the first law of thermodynamics!
First Law of Thermodynamics:
Energy cannot be created or destroyed
In Fluid Mechanics we consider: Placing the previous equations
together gives: Since Total Energy is CONSTANT 1/2(mv^2) + mgh + mP/p = C'

Now, we can divide through by m to get:

1/2(v^2) + gh + P/p = C

(Where C is a constant) Things to remember about Bernoulli's Equation: Why is Bernoulli's Equation Important? Let's revisit the real world applications of Fluid Mechanics we saw earlier... Using what we have learnt, we can solve for the velocity of a fluid in a chemical plant drain pipe Chemical plants and oil refineries. Sewage and water treatment plants Hydraulic Power systems - Kinetic Energy
KE = (mv^2)/2 - Potential Energy
PE = mgh and Pressure Energy
E(pressure) = mP/p Where:
m is mass in kg
v is velocity in m/s
P is pressure in Pa
p is density in kg/m^3
g is gravitational acceleration, g= 9.81m/s^2
h is height in m BUT! ... ... It can change form! Ever wondered at what
speed the water comes out
of a drain pipe when it rains? Probably not.....

We will work it out anyway. This is known as BERNOULLI's EQUATION! Bernoulli's equation is generally applied between two chosen points in a system containing fluid. When using Bernoulli's equation, we assume:
- There is no energy lost from point 1 to point 2.
- The fluid in the system is incompressible
- The flow is inviscid and laminar. From Bernoulli's Equation, the "Mechanical Work Equation" can be derived: The Mechanical Energy Equation accounts for:
1. Work both in and out of a system.

2. Energy losses L, which occur between two arbitrary points 1 and 2 in a system. Total Energy = KE + PE + E(pressure)
= 1/2(mv^2) + mgh + mP/p Imagine this is a drainpipe. So the pressure at this point is 101326.47Pa

And the water isn't moving so the velocity is
0m/s The drain pipe is full of water!!! And the height of the drain pipe is
5m We also know the density of water is
1000kg/m^3 Also the acceleration due to gravity is
9.81m/s^2 So we can insert the values we know into Bernoullis equation The height is 0m because we have reached the ground.

The Pressure is atmospheric pressure.

The pressure is still the same and so is the acceleration due to gravity.

But we don't know the velocity so we must find v. Then at the end of the pipe we know We find the velocity (v) by rearranging Bernoullis equation and substituting what we already know. Then we find v 9.9m/s So we have found that the velocity of the water leaving the pipe is... This is just one of many applications of Bernoulli's equation and fluid mechanics. Thanks for Watching That's all Folks Slide from: Google Images, Viewed 8th October 2012 <https://www.google.com.au/search?q=fluid+mechanics&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a> Slide from: Google Images, 'Chemical Plants' Viewed 9th October 2012 <https://www.google.com.au/search?q=chemical+plants&hl=en&client=firefox-a&hs=kl9&sa=X&rls=org.mozilla:en-US:official&channel=fflb&prmd=imvns&tbm=isch&tbo=u&source=univ&ei=u2R3UJDLD--NiAeGxoHgBw&ved=0CEEQsAQ&biw=1440&bih=719> Slide from: Google Images, 'Hydraulic power systems' Viewed 9th October 2012 <https://www.google.com.au/search?q=hydraulic+power+systems&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=N2Z3UKnQK_CUiQep-YDACw&biw=1440&bih=719&sei=QGZ3UN6eGKnpiAevt4HIDg> Slide from: Google Images, 'Bolivar wastewater treatment plant' Viewed 9th October 2012 <https://www.google.com.au/search?q=bolivar&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb#hl=en&client=firefox-a&hs=n8o&rls=org.mozilla:en-US%3Aofficial&channel=fflb&sclient=psy-ab&q=bolivar+wastewater+treatment+plant&oq=bolivar+wa&gs_l=serp.3.0.0l4.5757.8726.0.10752.,or.r_gc.r_pw.r_qf.&fp=4c9f4bbd916d9831&bpcl=35277026&biw=1440&bih=719> Slide from: Muson, BR, Young, DF, Okiishi, TH & Huebsch, WW 2009, Fundamentals of Fluid Mechanics, 6th edn, John Wiley and Sons.
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