COURSE DESCRIPTION This course provides an introduction to the most powerful engineering principles you will ever learn - Thermodynamics: the science of transferring energy from one place or form to another place or form. We will introduce the tools you need to analyze energy systems from solar panels, to engines, to insulated coffee mugs. More specifically, we will cover the topics of mass and energy conservation principles; first law analysis of control mass and control volume systems; properties and behavior of pure substances; and applications to thermodynamic systems operating at steady state conditions. COURSE FORMAT The class consists of lecture videos, which average 8 to 12 minutes in length. The videos include integrated In-Video Quiz questions. There are also quizzes at the end of each section, which include problems to practice your analytical skills that are not part of video lectures. There are no exams. GRADING POLICY Each question is worth 1 point. A correct answer is worth +1 point. An incorrect answer is worth 0 points. There is no partial credit. You can attempt each quiz up to three times every 8 hours, with an unlimited number of total attempts. The number of questions that need to be answered correctly to pass are displayed at the beginning of each quiz. Following the Mastery Learning model, students must pass all 8 practice quizzes with a score of 80% or higher in order to complete the course. ESTIMATED WORKLOAD If you follow the suggested deadlines, lectures and quizzes will each take approximately ~3 hours per week each, for a total of ~6 hours per week. TARGET AUDIENCE Basic undergraduate engineering or science student. FREQUENTLY ASKED QUESTIONS - What are the prerequisites for taking this course? An introductory background (high school or first year college level) in chemistry, physics, and calculus will help you be successful in this class. -What will this class prepare me for in the academic world? Thermodynamics is a prerequisite for many follow-on courses, like heat transfer, internal combustion engines, propulsion, and gas dynamics, to name a few. -What will this class prepare me for in the real world? Energy is one of the top challenges we face as a global society. Energy demands are deeply tied to the other major challenges of clean water, health, food resources, and poverty. Understanding how energy systems work is key to understanding how to meet all these needs around the world. Because energy demands are only increasing, this course also provides the foundation for many rewarding professional careers.
02.06 - 2D Phase Diagrams
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En provenance du cours de University of Michigan
Introduction to Thermodynamics: Transferring Energy from Here to There
490 notes
University of Michigan
490 notes
À partir de la leçon
Week 2
In this module, we will get started with the fundamental definitions for energy transfer, including the definitions of work transfer and heat transfer. We will also show (by example) how state diagrams are valuable for explaining energy transfer processes. Then, we have all the tools we need to define the 1st Law of Thermodynamics also called the Conservation of Energy. Your second assignment will emphasize these principles and skills.
Rencontrer les enseignants
Margaret Wooldridge, Ph.D.Arthur F. Thurnau Professor
Mechanical Engineering, Aerospace Engineering
Okay, welcome back. So when we left we had gone through an
introduction to all the different state phases on our state diagram for the
pressure volume diagram. So I'm going to orient you again here.
So we had the solids on the leftmost. We have liquids and then as we move
through the saturation dome, or the vapor dome, we come out the other side and we
have vapors or gasses. Between the liquids and the vapors, we
have the vapor dome where both phases are present.
Between the solid and a liquid, we have the solid-liquid region where both phases
are present. So Last time I said I labelled two
isotherms, those are lines of constant temperature, as T B and T A, and our
question to you was which temperature is higher if we were to label this arrow as
being the direction. In this direction, what is happening to
the temperature? Is the temperature increasing or is the
temperature decreasing? So, the, you could use anything that
works for you, in terms of understanding these state diagrams, is fine.
But one thought process you might have gone through would be to say okay, well
I'm going to sit at a fixed volume here. And as I moo, specific volume, or, or
inverse density if you prefer. But, as I said at a specific volume and
as I increase the pressure, what's going to happen to the fluid, what's
going to happen to the temperature of the fluid.
So, again, at a fixed specific volume, as you increase the pressure, you're going
to have to (no period) Increase the temperature of a fluid.
So the correct answer is that TB is greater than TA, that's not true, and
that this is the direction of increasuing temperature.
Again, so whatever thought process you went through or thought exercise or
thought experiment you went through, that's great, that's the best way for you
to understand. And if some of you came up with the
correct correct response, that's fine. So, however you do it is fine.
So, what I wanted to do, one last, make this just a little bit more complicated
this figure is I want to add this the triple line which I did not have on their
before and the triple line here is where you have all 3 phases present hence the
name. Triple line not triple line.
all three phases present. And what's kind of a neat thing to just
understand is that the drawing that I showed for you, where there's the solid
liquid region actually bumps to the left here, is for a fluid where it contracts
unfreezing. And this interface would actually move to
the dotted line if we had a fluid that expands on freezing.
[NOISE] Now in energy systems we typically need to have fluids that move,
so solids don't work so well for us. But their really fun for lot's of other
systems that we might consider, so. I'll say that in thermodynamics, our
working fluids, the fluids that actually do the work in terms of power generation,
are typically liquids and vapors. So we typically don't operation in this
region, most of our fluids are up here on the upper-right hand quadrant of the PD
diagram. So this is kind of getting into detail
that's fun, but not really neseccary for a lot of what we do.
Okay, but I did want to introduce, so that was the PV diagram that again we've
looked at that for awhile. Let's add another diagram to our list of
tools. and it's, we use this one, mostly just to
remind ourselves of all those definitions that we talked about before.
So what am I talking about? The pressure temperature diagram.
Again, this is the most tactile diagram, the most tactile variables in terms of
our understanding. It's very intuitive for us to understand
processes and state conditions on P-T, pressure-temperature, diagrams.
And so, what I just wanted to do was remind you; I'm going to sketch here
again a Two dimensional rendering here of the pressure-temperature diagram.
And here's my critical point, and here's the vapor region, and here's the solid
region, and here's the liquid region. So, now we have the three phases as
identified on our P-T diagram: solid, liquid, vapor.
So, this is just again a reminder of, well, if I take a liquid and I transition
from a liquid to a vapor, that that process is referred to as vaporization.
or if you prefer it's evaporation. Mm-kay.
And if I move from a vapor or a gas, remember I use those interchangeably, to
a liquid, then I have a process that's referred to as condensation.
[SOUND] If I go from a solid to a vapor, that process is sublimation.
[SOUND] And the one that everybody's familiar with or most everybody's
familiar with, is when you take dry ice, which is carbon dioxide.
And if you, usually people use that for shipping things that need to be kept cold
for a long period of time. And if you ever pulled out a bar of dry
ice you could see the vapor coming off it, and that's a very common sublimation
example. and of course if you take a solid and
change it into a liquid you're melting it.
You're not melfing it, you're melting it. and that gives you again some orientation
in terms of. The a PT diagram in terms of common phase
changes so those are all things that I would expect you to be familiar with so
if I told you what do you have a vapor that's undergoing a condensation process
you'd know that explicitly its going to take you through the vapor dome so start
you outside the vapor dome and put you back into the liquid region okay well not
back into but put you into the liquid region.
Okay so now we have these great diagrams for our for our use and again there
really meant to give us a, a pictorial understanding of the states.
So we can see that if I know pressure and volume I should be able to uniquely
define temperature if I know. temperature and pressure I should be able
to uniquely define specific [UNKNOWN]. So, we can move between these different
variables, these different thermodynamic properties with ease.
Okay. Having said that, now I want you to
assay, okay let's go back to that P V diagram.
because we did a bunch of examples where we used P V diagrams, but there weren't
any saturation domes or vapor domes on them.
And we didn't look at isotherms and isobars, and things like that.
But they were there, they're implicit. Okay?
So, take our example that we considered earlier about how we had the two step
process where we were compressing and then expanding air.
Okay, what we're going to find is that well, for us to condense air into a
liquid takes a lot. You can do it, and I'm sure many of you
are familiar with liquid Nitrogen, liquid Oxygen and liquid air.
Okay, you have to really compress the heck out of it, and you have to drop the
temperatures quite a bit. So, they're typically cryogenic systems.
So that means, in that system that we considered before, here is our little
example. We said we were going to, remember, we,
do the polytropic compression process from one to two, and then we did an
expansion, constant pressure expansion process from two to three.
That vapor dome is on that figure, it's just way down here.
Note, not to scale. Okay?
And, again I'll try and use my different colors here to emphasize this, there were
lines of constant temperature on there as well, or we didn't draw them on there I
should say, but they would look something like this.
Okay. So they would have curvature that would
be different curvature than the, so these are my isotherms.
[SOUND] And they would have different curvature than the polytropic process.
Okay. So just need to remember that these state
diagrams are valid for every substance. Every substance can be defined, every
simple substance, every pure substance can be defined in terms of the state
diagram. So we talked about isotherms and isobars
already, I'm just going to flip. so I just wanted to emphasize again, two
more things and I promise we'll get off the subject of these phase diagrams
because they tend to be pretty dry. Oh, no pun intended.
so let's go back to the pv diagram that we had talked about before.
And again, typically we only consider phase change between liquids and gasses
because we need to be able to have our fluids moving and we don't move solids so
well, although we can. and so we typically cheat and we just put
the saturation region as a simple dome. Okay, so this is my saturation region.
And again, I'll label it as liquid. And here's my vapor.
Okay. And then we know my lines of, constant
temperature. In the dome, the lines of constant
temperature have to be straight lines because again we know that the pressure
and temperature are dependent within the saturation region.
So this is the saturation dome. Vapor dome, all sorts of names.
Saturation regions, vapor dome, etc., etc.
So I told you before that if we have a saturated liquid or a a saturated vapor
that uniquely defines the state, assuming we know one other independent intensive
variable. So if I know temperature and I tell you
it's a saturated vapor. Then let's say its this temperature TA or
T1 we'll call it here, that defines if its a saturated vapor at T1 that uniquely
defines the point shown on this graph okay so now I want to introduce that term
quality. Quality in thermodynamics has a very
specific meaning, and it is in fact a thermodynamic property.
In addition too, I hope you do high quality work.
So, quality is only defined within the saturation region.
So quality is defined as the mass of vapor relative to the mass of liquid plus
mass of vapor present in the system. And it's given, I, I misspoke earlier,
there is an x in thermodynamics and that x is the quality.
So the x defines, is the variable notation that we use to define quality.
You can see that it should be dimensionless, because we have mass
divided by mass, so it's actually dimensionless like this.
And you can see that it's a fraction, where if you have a fully saturated
vapor, where all of your mixture, and by mixture I mean phase mixture.
Is in the vapor phase, then your quality is equal to one.
And if all of your mixture is in the liquid phase, then that's a quality of
zero. So x=1 is saturated vapor.
Then X equal to zero is a saturated liquid and so these lines these isotherms
which are also isobars within the saturation region are defining this line
up to the critical critical point. That defines the line where the quality
is equal to 0. That's the saturated the saturated liquid
line. And then this line here on this side is
the saturated vapor line. Where x is equal to 1.
saturated liquid, okay. So, if I were to go at some arbitrary
location between these two endpoints, and say, okay, well that's a quality of 30%
or 0.3 You would again, if you have the quality and the pressure or the quality
and the temperature, you fully define the state.
Okay, so again we want to emphasize, quality is only defined within that dome.
[NOISE] [SOUND] Okay. so again that's, we'll keep coming back
to these examples of these phase diagrams and how to put states on, and how to put
our processes on them. But again, I want you to be thinking in
terms of the phase diagrams, the units, the sign convention are all cumulative.
They're all built. And work together to help you understand
the system and for you to be able to conduct your analysis accurately, with
good intuitive understanding. I did want to close with one question for
you. And that's a question of if you were to
what I want you to do is to sketch what constant pressure condensation looks like
on this PV diagram, assuming you start with an unsaturated vapor and end with a
condensed liquid. Okay, so lots of words so I wanted to
write that down so you can understand, and they're all meant to cue to to very
specific places. So, what you - again, draw on a PV
diagram condensation from, and I'll, again I'm going to use this as a teaching
moment. This region here to the right of the
saturation line. This is referred to as the superheated
region. [SOUND] And that has a very specific
meaning in that it's superheated to a temperature higher than the saturation
temperature. Okay.
So, that's vapor is at a temperature greater than T saturation.
Okay, and if you have a subcooled liquid. So this again.
So this area is a superheated region. And a superheated vapor is, a superheated
vapor, oops now I said it twice. Vapor.
A superheated vapor is, is a vapor at a temperature greater than T Sat.
A subcooled, so in this region we're going to define subcooled liquids, So,
that's the super-heated vapor region, this is the sub-cooled liquid region, and
a sub-cooled liquid Is at a temperature cooler than the saturated liquid
temperature. So is at a temperature, is at a temp
lower than the saturation temperature. Of that pressure or that condition.
So in other words you have to be for a sub-cooled liquid, you're essentially to
the left of the saturated liquid line. For super heated vapor you're to the
right of the saturated vapor line. Okay?
That's it. One, alright that looks like a one.
Alright, so again let's get back to our question.
Draw on a PV diagram, so first of all, always practice good habits.
So draw your PV diagram, label the axis, put the dome on there and write, and put
on there your isotherms. Okay, few examples.
Typically I like three isotherms. Okay.
So, draw your PV diagram, put the dome on your diagram, put the 3 isothermes on
your diagram, understand which temperature is higher then the other, so,
again, these are lines of increasing temperature here and on that diagram I
you to draw a condensation from a superheated vapor to a sub-cooled liquid,
okay? So your superheated vapor is state 1,
your sub-cooled liquid is state 2. Sketch that on your P-V diagram, and
we'll talk about that next time. Thank you.
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