All language subtitles for 01_CourseIntroduction

Registro, condividi, questo condividi.

Ok, registration should be on, should be
written somewhere.

Qualcuno lo vede se sto registrando?

No? Ok, good.

So besides client, your note,
registration, you will

also have a lecture note. Ok?

By Matteo.

Good. You can call me on the phone or
write me by email.

I don't really know the phone number of
Matteo.

Probably it's on the official website of
Polimi, or you can write Matteo.

It's better you write. I'm not that
often in office, so I won't be able to

answer you as you would like.

Okay?

Good. This is, okay, it's updated.

This is how the course is organized.

So, on Monday and Wednesday morning, no,

first off, we, no, on Monday we will
have lesson, on Wednesday you will have

training with Matteo, except first week,
so we start with two lessons, okay?

And from, say, beginning of October on,
once the training is finished, for

those who like it, you will have slides
online, so don't take pictures.

If you want, tell me, I laugh, you get a
nice picture for your collection.

From 1st of October on, for those
interested, I will introduce seminars.

or additional topics. Of course, these
additional topics are not required for

the exams.

Okay? So, if you would like to attend,
fine. If not, fine as well.

Okay? As you see, we will start with
fluid power actuators. Fluid power, I

introduce it in a couple of minutes, are
hydraulic and pneumatic actuators.

Then we will go on to electromagnetic
actuators, C.

motors, electric motors and voice coils.

Okay? Then we will go on to smart
actuators, which are those

actuators that couple different physical
domains.

This is why they are called smart.

In practice, these are electric
actuators, restrictive shape

memory alloys.

There are much more. We don't have time
to introduce them all. Okay?

So the course is divided in three
families of actuators.

Okay? Then there are vacations. Then,
unfortunately, there's graduation day.

we lose this to one lesson and one
training.

And down here we will have Christmas.

Each of us at our own home.

Okay. The exam.

The exam is done.

Both written and oral. Final mark is the
mean value of the two results.

Okay?

You know how to do the mean between two
numbers?

Great. And then with some approximation,
of course.

So, for the written, you will be given
an exercise, a numerical one.

A numerical doesn't mean you need a
calculator nor a computer.

Okay?

Simple calculations.

most of which are, say, you don't even,
you are not even required to

end up with a number.

Okay? Okay.

You have to choose during this victim
which type of actuator to use. Now,

sometimes it's required which type of
pump, which type of battery, which type

whatsoever. Okay? So, the problem,
engineering problem is stated up to you

determine how to actuate that system.

Okay? With all the auxiliaries that go
with that system. Okay? With that

model. Then there's the oral. The oral
is there to understand whether you have

understood the course.

Okay? So, we will ask you topics that
were

introduced in the course. It may happen
that you are asked topics that

you may extrapolate from the course.

Okay? So now you are a master of
science, switch on the brain.

Okay? So it's not like if I don't tell
you something, then you

don't need to know it. If you can end up
with that knowledge by putting together

pieces of the course, this is required.

Okay?

Of course, nothing difficult, but in
some parts of the course, we skip

proofs and so on, and you may be
required to do them. No proofs, I don't

ask, but we put pieces together.

Of course, to go to the Europe, you need
to have done the written, and passed

the written, which means mark greater or
equal than.

18. If it's less than 18, you cannot do
the oral.

Then you have to finish the exam within
the session, which means you can do the

written first, say, on January, and do
the oral end of

February, so at the final possibility,
second call.

But if you do the written in February,
then you have to do the oral in

If you asked me to do the oral on June,
you have to do the written again.

Okay? Clear? So exam finished within the
session.

So January, February, one session.

June, July, second session.

September, end of October, September,
third session. That's it.

Okay? Good.

Please remember to register for the
exam, else I won't be able to register

final mark if it's positive.

If it's negative, then of course I won't
register it. Okay?

Questions? Clear?

Okay, good.

I believe you may register for several
exams in parallel. If so, please do.

Okay? I'm not counting the students, so
I'm not checking whether you registered

in January and in February. If you are
allowed to, then register for both

January and February sessions.

Okay, folks.

Clear?

Okay, this is, now let's start with the
course. That's the general

book for actuators.

It's written by Jan Locha, a German.

It's for, it doesn't go that deep into
actuators, so it's a general

for actuators.

I'm not telling you to buy this book.

I'm telling you the Copertina is nice,
and

if you look carefully on the internet,
you may find it online.

Okay? Understood?

Okay. For sure, don't buy this book.

Okay? But that's the general
introduction. So, it gives you the...

The classification of all possible
actuators you will see in your life.

Okay.

Now, the course Actuating Devices is
within the track

Mechatronics. Why is it within the track
Mechatronics and Robotics? Let's

introduce the term Mechatronics. It was
first introduced by a Japanese

engineer back in 1969.

And it's the combination, as you may
see, of two words,

mechanisms and electronics.

You join them together, you end up with
mechatronics.

Still, we don't see why actuating
devices course is within this

Okay, let's say a few words more about
mechatronics.

Over the years, this concept, the
original concept evolved.

to describe the philosophy of
engineering technology rather than a

itself. So, mechatronics is not
electromagnetism, okay?

It's a way of thinking machines that
combine not only the mechanical part,

also, for sure, the electronic part.

And, going on, also the computer control
part, okay?

So we have the mechanical part, the
electronic part, and the

logic that moves the system.

So if you design a machine that combines
all these components together, then you

are designing a mechatronic system.

If you just design a bike without the
motor, without anything, that's a

mechanical system.

If you design a bike with an electric
motor, with a torque sensor, okay, to

power on the motor, with some other
sensors to give you the right

then the bike becomes a mechatronic
device.

Clear? Okay.

And, of course, if you have electronics,
if you have, say,

quantum logic inside, then...

The control logic is typically not there
just to store data and pop -up lights,

okay? To say you are doing well, great,
go on, like this watch here, that always

tells me to do more training, okay?

If you have this phone, then typically
you want to act on the system, okay?

Modify the system's state.

And to do this, you need actuators. So
today, a mechatronic system...

It's not only a mechanical system with
an electronic board on which some logic

is running, okay? It also has sensors
and actuators, okay? These are the

four components that come into a
mechatronic system, okay?

Good.

Ah, yeah, the stupid question I always
ask is, can

you sight?

pure mechanical system, just to give you
the feeling of how important

mechatronic systems are today.

Can you cite one single mechanical, one
pure mechanical system?

Okay, the bike, the old bike I already
said.

Other examples?

You can think of?

Yeah. Expensive watches are the pure
mechanical systems, and in

fact they are jewels. If you buy this
watch, okay, that's more a mechatronic

system, since you have electronic
scenes, you have a quartz clock that

the timing, so no, yeah, some gears
still in, but the core is electronic,

okay? So if you think of mechatronic
systems, you will see they are all

us. Most mechanical systems are today
mechatronic systems.

Okay. Now, actuators are everywhere from
household appliances to cars,

airplanes, rockets, and they are an
indispensable component for

implementing mechatronic systems.

They are as necessary as sensors.

Sensors provide information, the input
to the control logic, actuators provide

the output of the control logic.

Okay?

At the end of the course, you will be
able to not exactly design

actuators, some yes, some others no, but
at least to identify which is the right

actuator for the given problem.

Okay? And you will also be able...

In most engineering cases, there's no
one single solution.

There are several optimal solutions
depending on the results

you would like to obtain.

And thus you will be able to compare
different actuators depending on the

budget you have, the performance you
want to obtain, and so on and so forth.

Okay? Okay.

enjoy introducing the actuators also
from a historical

perspective, and this is what's coming
next, okay, to give you a flavor of

how long mankind, since how long mankind
started to develop actuators.

Okay, so for fluid -powered actuators,
some more

references, okay.

Where is it? This one here is the Bible
of hydraulic

actuators. So if you fall in love with
hydraulic actuators, then, besides going

to a good psychologist, you may buy this
book.

Okay? The others are, yeah, of interest,
but I

wouldn't buy them, for sure.

Okay?

The slides you would see next are taken
from

this book here.

Okay? Most of the information is taken
from there.

Good.

What else should I say here?

No, nothing.

For pneumatic actuators, instead, two
books.

The faster ones you download from
online, for sure.

and they are for free. The rest are for
free.

Not that much. But still you can find
them online.

Populmatics, there is no Bible as there
is for hydraulic actuators.

So this is the best book I found.

Still not as interesting as the other
one.

So then the information for this slide
comes from more than these two books.

So not all the information you will find
on these books.

Still, reference book is missing.

Okay? Yeah, some few words now.

Yeah, fluid. We talked about fluid power
actuators.

Fluids are both gases and liquids.

Okay? So a fluid is a state of matter
that is capable of

flowing. To adjust, to the, say, volume
given.

The, say, counterpart are solids.

They affect, they don't adapt, they
don't flow, they don't adapt to the

volume. But this you know from, say,
kindergarten, right?

Okay.

Pneumatics and hydraulics are similar in
many respects.

and are often described with the general
term of fluid -powered systems.

Of course, pneumatics, the working fluid
is gas.

Hydraulics, the working fluid is liquid.
It doesn't mean it's water, okay?

Although hydraulics may give you the
idea the fluid

is water, it's not.

Water is not used in hydraulic
actuators. It's mineral oil, typically.

The most important property of fluids is
the conversion,

simple conversion, of pressure into
force and displacement.

They are of simple design.

So there are many, many different...

actuators on the market. They are
simple.

They may be quite fast.

Okay? And they do not overheat even if
stalled or blocked. Okay?

Since there is some fluid running around
and fluid brings away the heat. Okay?

So the good thing of hydraulic or fluid
powered actuators is they do not

overheat.

And the

Power to weight ratio is very high,
okay? Which means you can produce very

compact actuators that are able to
generate huge forces of torque.

Much better than electric motors, okay?

So small actuator, enormous force, okay?

Clear? And that's the market niche in
which still today...

pneumatic and hydraulic actuators are
used.

Else, the rest of the market has been
taken over by electric motors.

Okay.

In hydraulics, we use high pressure up
to 120 bars.

In Europe, Italy, typically we use up to
300 bars.

Okay? Well, not that high.

They are...

they applied for relatively low
velocities, because you have to draw the

inside your actuators, and this takes
time due to internal viscosity, okay?

So not that fast. Huge forces, not that
fast.

Hydraulic actuators are used whenever
large forces or torques are required.

Lower pressures for pneumatic actuators
up to 10 bars.

That's common.

Okay. In Italy we use 10 bars.

They can obtain much higher flow
velocities, less internal viscosity,

so they are faster than hydraulic
actuators.

Okay.

There are other fluid power actuators.

There are fluid power actuators for

absolute pressure lower than 0 .1, okay,
which are called

vacuum actuators, okay, so the gas
within, typically they are,

the fluid is gas, some type of gas, is
very rarefied, so you cannot use Navier

-Stokes equation, you need special
equation for vacuum actuators, vacuum

systems.

So we won't deal with these types of
actuators.

Clear? Okay. Another family of fluid
-powered actuators

are those for which you have an internal
chemical reaction

of the fluid, being it gas, being it
liquid, being it even solid.

Okay? Of course...

The thermodynamics there is definitely
non -stationary. So then the equations

that govern this type of actuators are
different than the ones we

will introduce.

So also for hot gas generators, we

want a ball.

Also this type of family, we want...

We won't analyze it. Okay, clear?

For this, there are no courses.

For this, you have some dedicated
courses.

Okay? In aerospace, not in mechanical
engineering.

Okay, so we will deal with process
control, drives, and mobile

applications. That's the families.

actuators we will introduce in this
course.

Good.

So, hydraulic systems have been in use

since long time.

Okay, that's the historical perspective
I like.

The first application were water mills,
water wheels.

There is a track record of waterways
back to 4 ,000 B .C.

The waterways were horizontal, so they
were rotating

in the horizontal plane. The axis was
vertical, and they were used for

ground stones.

So there was a flow here that moved
these rudders and the wheel rotated and

moved rhinestone on top.

Okay?

The solution wasn't very efficient. Can
you imagine why?

Why is this solution not that efficient?

The water isn't completely released.

here, okay, so it's dragged along the
whole rotation.

Okay, so the innovation was brought in

14 after Christ, AD, by

Vitruvius, a Roman engineer.

He rotated the wheel from horizontal to
vertical, okay, and then due to gravity,

the water is completely raised.

Of course, there is an additional
component here, which is coupled gears

rotate the motion from the horizontal
axis to a vertical one. That's the

complexity. But much more efficient.

It was used for sawmills in the later
years.

Sawmills, palms, forge bellows, tip
numbers, tip numbers, and so on. Okay?

today, if you go up in the mountains, in
the Alps, you will see saw

industries that take the power, of
course now they are off, but they are

museums, with mechanisms like this.

The water wheel was

the first mechanical system used to
replace the work by humans

and animals.

So the use of machines for helping
machines, complicated machines, not

utensili, was started 4 ,000 years
before Christ. So 6 ,000 years

from now.

Good.

Okay, current day hydraulic systems had
their beginning before the end of the

19th century when the invention of what
steam engine and the development

of The factory system spurred the need
to develop a method for transmitting

power from one point to the other.

Before that, they used long shafts or
belts, okay?

But long shafts, long belts are
deformable, okay? So then you may have

heard about torsional vibrations.

You may have heard about other problems
with long, long shafts.

Instead, if you have a fluid, you put it
in pressure. A liquid, you put it in

pressure.

Besides the, say, leakages you may have
along the pipe, besides the

internal resistances you have in the
fluid, what you have at the beginning,

at the entrance of the pipe, you have at
the end.

Okay? So it's... And actually, no
vibrations.

if you are in stationary conditions to
occur okay so this was believed

hydraulic power was used to transfer
mechanical energy

from one point to another point quite
far away one from the other okay so

initially there was chemical energy
converted

into mechanical energy

then into pressure energy, then back
into mechanical energy in some other

Quite a big amount of conversions, each
one with an efficiency.

Okay?

During the first industrial revolution,
the development of food power was

greatly emphasized, and several
countries started developing

large hydraulic circuits.

for using high pressure water pipes and
steam engine driven

pumps. Of course, the fluid inside the
pipes didn't reach 300 bars,

much lower than today, else everything
would have

exploded. And the use was to bring power
from

one place to another.

Then they started developing hydraulic
accumulators, okay? So the steam engine

shouldn't be on all the time, okay? The
fluid power was accumulated somewhere

and released later on. Control valves,
you may need, from one pipe,

you may need to power two machines,
okay, at a given position, but each

comes with a different required force or
required speed.

then control valves, and actuators, and
they were

developed, say, by trial and error,
okay? Back those days, no equations

were applied, okay?

Then, suddenly, something happened,
which was the discovery

of electric machines, okay?

machines, the transfer of energy was
through pressure,

okay, was, say, substituted by the
transfer of energy through

electricity. Much simpler, okay? The
cables did

heat up due to Joule's effect, but if
the current wasn't that high, then they

didn't burn while pipes had the problem
of leakages had the problem of problem

of explosion okay and actually the use
of electricity

gave say a sudden or it seemed

hydraulic power was over okay so the

hydraulic industry nearly died okay

Luckily, of course I'm joking, something
happened beginning of, or mid

of last century, and the lucky thing,
I'm joking again, was World

War II, okay?

The war required to have, in small

spaces in fact, huge forces for talks.

Okay, so then the fluid power was
restarted, not to

bring around energy, but for the purpose
of

generating high effort.

And the main applications were in
warship gun, turrets, aircraft control,

and land roving vehicles.

Okay?

Today... the fluid power systems,
hydraulic systems, are again in

this niche here.

So whenever you need high force torque
in small spaces, then you use hydraulic

actuators. Okay?

Else, it's better to use electric
motors.

Clear? If you have to bring power
around, use electricity, not fluids in

pressure. Okay?

So this tremendous torque or force to
inertia ratio.

Inertia, mass.

And torque force.

So for a given mass, the amount of
torque force is much higher than the one

could obtain with electric motors.

And that, as I said, is the market today
of these devices.

Okay.

Until today, so until the beginning of
the Second World War, everything was

done by trial and error.

The United States felt that this trial
and error

didn't lead to fast improvements.

So the government decided to pay, to
fund MIT

for... defining a mathematical framework
for hydraulic actuators.

The output of those researches ended up
in this fluid power control

by Blackburn and others, and the book
was published in 1960.

That's the first book about a general
framework.

for modeling and predicting the behavior
of hydraulic actuators.

Okay? Clear?

Now, today we don't use that book
anymore.

After the Second World War, the modeling
of hydraulic actuators was

taken over by companies that sponsored
and paid for this textbook here,

Hydraulic Control Systems, by Merrill.
That's the Bible I told you.

So the book dates back 1967, and still
today, that's the reference book for

hydraulic actuators, okay?

There you find all the formulas you need
for designing, optimizing actuators,

okay? Of course, today we go further by
applying numerical simulations like CFD,

multiphysics, and so on, but the
reference is still this book here.

Okay.

That's the perspective for hydraulics.
Now pneumatics.

Okay.

There's a hydraulic system we are all
aware of and

we all have.

Which is this hydraulic system.

Very efficient.

Very long lasting.

Blood system, okay?

Think of our blood system. It should
last from 80 to 100 years,

not always. Someone dies earlier.

It has an extension of approximately 100
,000 kilometers.

So if you measure all veins and whatever
you have in the body, you end up with

100.

thousand kilometers. Quite a long
system.

Okay? And should be maintenance free.

Okay.

Now the first pneumatic use was the
blowing on

tinder to fan a flame.

Okay? To start a fire and then to cook.

That was the first use of a pneumatic
system.

which are our lungs, okay?

First system ever.

So we can process 100 liters per minute,
and of course you fall, okay,

so six cubic meters of air per hour, and

the octane pressure may be up to 0 .08
bars, not that high, okay?

In healthy conditions, the reliability
of the human compressor is unsurpassed,

and it costs nothing to service, if you
have slaves.

Now, of course, slaves are not that
common today, and

some years ago they found out that even
if you put ten people blowing on the

fire, then probably you won't heat the
fire up.

to a temperature necessary for melting
metals.

Okay, so in order to increase the
temperature of fire to be

able to melt metals, such as gold,
copper, tin, lead, five thousand years

they started bringing the old ones up in
the mountains where you have high wind.

And still today you may find these ovens
if you walk up in the mountains, even

in our house.

And later Egyptians and Sumerians
developed

this blast pipe.

This focalizes the air in a given point.
This increases

locally the temperature.

And again you have somebody blowing
there.

Not that good. Even today, this process
is used by

goldsmiths over the world.

So they blow with a pipe in the fire to
increase temperature.

Now, the evolution of this was the hand
-powered bellow.

Okay. Some of you may have seen one
still existing today.

More efficient was the foot -powered
bellow. Was it more efficient?

We have more force in the legs than in
the arms, usually.

Unless you are an orangutan.

Okay? Good.

This, again, was developed in ancient
Egypt.

Okay? And you see here these two guys
walking all the time and blowing air in

the fire to increase temperature.

Okay?

That's the birth of compressed air as we
know it today.

Then in Greek times, Sisyphus developed
an organ

that was working based on compressed
air.

You pump the air through these actuators
within this system here, this

accumulator. and due to compressed air,
the water was pushed

down, clear to all, okay?

Once you open this valve here, or this
valve, and this valve here, okay, the

pressure of water pushed the air to the
right, uh,

uh, tone.

No, I don't know what the cane is
called. Okay?

And so the player

the playing of the organ was independent
of the slaves pumping air

into the reservoir.

Okay? This was invented 250 years

before Christ.

Okay? So quite a long time ago.

And the Sibos eventually enjoyed
compressed air alone up to the

development of a catapult based on the
same principle.

So you compress there and then you
release this suddenly and the object was

pushed away as catapults work.

This wasn't that much used those times.

If you see, go in a museum and look at
how catapults work, they

work not on compressed air but on
elastic energy.

sudden release of elastic energy, okay?
But still he invented this type of

catapult.

Heron, first century before Christ,
developed a machine

that was sort of magic, okay?

If there was fire on the altar here,
then the fire heated

up This is a body without water.

Oh, the air, okay? The air pushed down
the water. The water was pressed

into this secure, into this container,
okay?

And due to the increased weight of the
container, this mechanism did open the

doors of the temple, okay?

Once you, say,

turned, or turned off, um, extinguished
the fire, okay, the elasticity of

these other two ropes did close the, uh,
the, um,

the doors of the temple.

Clear? And that was magic. So the
believers there did see the doors open

if the fire was on.

and did see the doors closing when the
fire was off, okay? No one working

except slaves down here that should
bring the water back to the reservoir

one closure, okay?

Magic.

Okay, then nothing done on pneumatics
until 1667

by Denis Patin in France.

He used compressed air to transport
objects through pipes.

Okay? Not to transport energy, but what
he saw was that if you put, say, a piece

of paper in a pipe and then blow,
increase the pressure on one side, then

brings the paper to the other end of the
pipe.

Okay? And this was the starting of
pneumatic conveyance.

Okay? 200 years later, almost, okay?

Latimer Clark and Rammel developed, and
the engineer, this was a physical

experiment, not that interesting at all.
They developed a pneumatic conveyor

system in London, okay, for the post,
local post, okay?

So then you had a pipe in your home, and
they regulated the, say, connections,

and the letter ended up in your home.

rather than having a postman coming to
your home. Of course, few people around

London could have this facility. The
others didn't

even know how to read.

This nomadic post was,

say, seen as a revolution those times.

So it was introduced in several cities,
not only London, but also Berlin, New

York, and Paris.

And the post system of Paris is still
existing, and it

extended up to 137 kilometers throughout
the city.

And, yeah, in 1937, now it's there as a

historical remnant.

No one is using it anymore.

We don't even write mails anymore,
right?

Messages, emails, and other stuff.

Okay, besides the post, which is of
relative interest, in 1810,

the trains started being powered by
compressed

air. Okay, how did they work?

Look at the picture, how did they work?

They had a steam, they had a boiler.

Somebody was pushing carbon into an
oven. The fire

did, say, make the, did

start the production of steam. The steam
was used to set the wheels

in motion.

We call this type of steam trains
cafetiere because they

were famous for their white steam coming
out.

And of course somebody was pushing all
the time carbon into the oven.

And they had to recharge water.

If you have seen any western film, you
see they stop and then they recharge

water.

So now it's historic and no one is using
this type of propulsion anymore.

In 1869 Westinghouse introduced the
chromatic brake.

So if there's a leakage, if the pipe
breaks, then the pressure drops, the

wagon is red.

So the pressure within the pipes is
there to keep the brakes open.

When the pressure is released through a
spring, the brakes close and the wagon

is stopped.

This system here is still used today in
all freight trains.

If you go to the side of the freight
train, you will see these black pipes

going around from one wagon to the
other, okay?

So very fail -safe. It was the first
fail -safe system developed.

Okay? If they break, so something
happens to the transmission, to the

between one wagon and the other, then
you break.

Okay?

Okay, this I said.

Okay, the first use for some, say,

operation.

human driven operation was the the

hammer drill pneumatic hammer drill for
the

say opening of a tunnel in Mount Cenis
in US

so they had a steam generator on one
side, long pipes

and then the drilling system within the
mountain okay now if you this same

system of course scaled down and not
with a steam engine but with an electric

motor increasing the pressure is today
used in any uh by any

mechanical guy for say mounting your
tires okay

and many other operations are done
pneumatically okay

The pipes were seven kilometers long.

Of course, the use of compressed

air had the advantage of lowering the
risk and

speeding up the drilling.

Before that, you know how they did build
tunnels?

By hand, okay?

like this, with the icone, okay, this
was automatic, and compressed air, in

fact, if you have a leakage, it is just
air, so it's not dangerous

for the people, or less dangerous, okay,
so, quite well used today,

it's not like this, they use
electricity.

Okay.

Now some definitions which we will use
throughout the course.

We introduce two flow rates.

One is mass flow rate, the other one is
volume flow rate. Different symbols.

Mass flow rate is m dot.

The symbol. The volume flow rate is qv.

Mass flow rate does not depend is the
given in mass per time,

does not depend on the reference
conditions, whereas volume flow rate

Okay? So, while the mass is fixed, the
volume occupied by a given mass is

different depending on temperature,
pressure, and so on. Okay? So, this is

we use the two.

Okay? This QB, of course, is a function
of Tb.

M whatsoever.

Okay? While M dot, in fact, is not a
function of P, V, M, whatever.

T. Okay. Then we introduce pressure.

The definition is as simple as the one
you see there. Force over cross -section

area. Okay?

Perpendicular to the surface.

Okay?

Of course, there are many different
pressures you should be aware of.

absolute pressure is the pressure
measured with reference to absolute

This is complete vacuum, okay?

It is equal to the sum of the
atmospheric pressure and the gauge

Atmospheric pressure is the one, the
absolute pressure of the atmosphere

measured at the place under
consideration.

Gauge pressure, or relative pressure, is
the Pressure measured with reference to

the atmospheric pressure.

Gauch, relative, effective pressure.

Okay?

Relative, we use in general, it's not
that used.

But, we also have different, other
different pressures.

Static pressure is the pressure exerted
by a fluid standing still.

Dynamic pressure is the increase in...
pressure if the fluid is in motion.

And you know, it's equal to one half
times rho times v squared, where rho is

density of the fluid, w is the speed of
the fluid.

That's the kinetic contribution to the
pressure.

Okay? This is called dynamic pressure.
Total pressure is the sum of the two.

Okay? Of course, the dynamic pressure

You don't see any, say, dissipation
here. So it's the pressure we would

if all the kinetic energy is converted
into pressure energy.

In reality, there's a transformation
going on, thus some energy is lost.

Still, we consider it as isoentropic,
okay? So fully reversible,

no dissipation in the conversion, okay?

That's theoretical.

That's not the real pressure you may
obtain.

So total pressure is, say, simple to use
in formulas. It's

not the maximum pressure you will be
able to obtain.

Okay? In SI units, the pressure should
be measured in pascals.

Okay? B, capital A, small.

Pascals with P capital due to the fact
that it comes from the family name of a

guy, Blaise Pascal, okay? So please
remember this, P always capital.

The 1 Pascal, which is 1 Newton over 1
square meter, as you may

imagine, is a very small pressure.

Thus, typically, to shrink down the
numbers, okay, We use

kilopascals or better megapascals. So 10
to the 6th

pascals. Okay? Clear?

Okay. All the unit is bar, which is 10
to the 5th pascals.

Okay? And it's widely used in compressed
air. Shouldn't be used, but in practice

you always see.

say, values given in bars.

Okay?

So then pascals is used to denote the
absolute pressure, the above, and

bars is used for gauge pressure.

Okay?

Now, there are reference, remember,
volume flow rate depends on the

boundary conditions, so we have to
define standard reference conditions.

For those, there are different
standards.

The most used one is this ISO

8778 that defines the standard reference

atmosphere, which is characterized by
100 kilopascals,

293 ,15

kelvins, which is equal to 20 degrees
centigrade, okay?

Relative humidity doesn't matter, but
it's given to 65 %

the gas constant, okay?

288 joules per kilos per kelvin, and the
density 1 ,185

kilos per cubic meters, okay?

This is given by the standard. So, if
you're asked for the

standard reference atmosphere, you
should go to the standards and take

values. Okay? No discussion.

Then there are two other standards, the
ISO 2787 and the ISO

63582. They use the same value as the

ISO 8778 for the atmospheric

standard atmospheric pressure okay there
is another standard ISO

2533 which defines a different standard
atmospheric

atmosphere okay it's called standardized
earth atmosphere okay you

see it's a little bit different for what
concerns the pressure it used to be 10

to the

100 kilopascals, okay? So 10 to the 5
pascals. Now it's a little bit higher.

It's 101 kilopascals, comma 3 to 5,
okay?

The temperature is, it used to be 293
,15

kelvins. It's 288, okay? So it's not 20
degrees

centigrade, it's 15 degrees centigrade.

and the density comes as a consequence.

Okay? So please, if you are asked for
the standard reference

atmosphere, use this value. If you are
asked for the standardized Earth

atmosphere, use these other values.

Okay? No discussion.

It's defined in the standards.

Okay? And this is a conversion table.

I always get confused, that's why I put
this table here, because worldwide

they use completely different values.

Okay? In English -speaking countries,
they don't use

pascals, they don't use bar, they use
psi.

Okay? Pound per square inch.

Okay? Then you have to go look on
Google, which is the conversion.

Okay? Now you have everything in here.

Less common is this technical
atmosphere.

Never bumped into it, but I found the
table with that. So I use this on,

say, physics books.

You may find this Torricelli measure of
the

atmosphere. Okay?

Clear? Now, you have, that's the end of
the lesson. You have learned, say,

how to do, how many topics you will have
to study during the course. You have

learned how to, how the exam will be.

Some historical background, some
definitions.

Okay? From the next lesson, will be on
Wednesday.

And then we will start using introducing
equations.

Okay?

Questions for today?

Great. Then see you on Wednesday.