Original subtitles

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.