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.
02.04 - Heat Transfer
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En provenance du cours de University of Michigan
Introduction to Thermodynamics: Transferring Energy from Here to There
671 note
University of Michigan
671 note
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. So, hopefully you looked at that
expression. You went
The problem with that expression is in the notation that's used to represent the
heat transfer. Heat transfer is not a system property.
So we can't say what's the heat transfer at state two, and what's the heat
transfer at state one? Instead, we need to say what's the net
heat transfer as the system underwent the process from one to two, from state one
to state two. So that's why we use this type of
notation. Okay.
The Q1 to 2, and we never ever do I want to see you write anything that has a Q
with just a single subscript associated with it, because the implication is that
you're defining the heat transfer at a state, and that would be incorrect.
Okay, so there are three types of heat transfer.
Conduction, convection, and radiation. And like I said in the previous segment,
heat transfer is a discipline in an of itself.
We could spend 16 weeks discussing the details of each of these modes of heat
transfer. So what I really just want to introduce
you to today, is that the heat transfer due to conduction.
Is proportional to a temperature difference.
So if my system is at some temperature other than the system environment, so
let's call that the ambient, I'm going to have heat transferred due to conduction.
Okay? The same thing is true- For convextion
heat transfer. Okay, so convexion and conduction are
proportional to the first order of the temperature difference.
So hopefully you can see where we're headed here, in that I said first order.
Radiation. Is actually proportional to the
temperature difference, the difference of the temperatures raised to the fourth
power. So that would be 4 for the system, T,
ambient. Okay.
So. what should be hopefully quite obvious to
you is that as the temperature in the system, or alternatively as the
temperature in the ambient increases, radiator becomes more and more important,
okay? More so than convection and conduction
because it's got that fourth order power on the temperature difference.
So again in this class what we need to know is just really that if there's a
temperature difference then I need to consider whether or not heat transfer is
important. So a lot of times we'll take our system
and we'll say oh we're going to treat that turban as being adiabatic.
Or we'll treat that compressor or pump as being adiabatic.
Well, if you've ever stood next to a pump or a turban or a compressor when its
operating. You'd know full and well it's not
adiabatic, and that there's a lot of heat being rejected by those systems, and by
rejected I mean that there's heat out of the system, so if you stood next to your
pump, just if you even have a compressor that you would use to fill the tire, fill
the air in the tires of your car or you bicycle or your basketball.
You know that that process, you have a lot of heat that's rejected by the
compressor. Okay, so it's good for us to understand
what those drivers are for the heat transfer, and whether or not we need to
include them, okay. But a lot of times we will simplify this
system by calling it adiabatic, okay. And we recall from the last segment
adiabatic means heat transfer zero So, in reality, what we're typically saying is
that we're going to treat the system as having negligible heat transfer relative
to the other energy transfers in the systems.
Okay. So, hopefully that gives you at least
whets your appetite for you to go seek out courses on heat transfer.
It's a great area and again, very sophisticated.
The physics of the different areas of conduction and convection and radiation
are very different. So it ends up being a very fun course to
take. and it's not a pyramid scheme.
So you essentially have to rebuild your learning as you move to each different
discipline of conduction, convection and radiation.
Okay. So The conservation of energy, let's get
back to our guiding principles for thermodynamics.
It says that, in it's most general description, all the energy transfer in
minus all the energy transfer out is balanced by the change in the system.
So, in other words, the net heat transfer in, which we defined as positive.
Minus the network transfer out, which we defined as positive, it equal to the
change in the system energy for some time interval.
So it matters how much time has been considered.
We can also write the conservation of energy on a rate basis.
So we would take all of the expressions that are in our This is our generic form
of the conservation of energy. And we can say, oh we're going to do that
on a rate basis. And that would change the expression like
that. Okay, where again over dot means rate
basis [SOUND]. So, hopefully at this point you've
learned that thermodynamics is a very sensitive area in terms of the notation.
It's case sensitive, it's notation sensitive, the units are important, all
of that matters. So be very careful as you take notes or
as you do and as you do your analysis that your notation is very consistent and
thoughtful. Because again that notation is really
meant to help you. Okay.
Both of these conservation of energy expressions are for a closed system.
And I will, will elaborate that. It's going to take us a while to get
there before we have the tools to talk about open systems.
But this gives us at least enough information to start talking about the
next steps. In terms of that energy expression there,
the energy of the state, that energy expression.
Okay, we have ideas on how we would quantify the heat transfer and the work
transfer, what about the energy of the system?
And again, we already know how to evaluate expressions for kinetic and
potential energy, we need to be able to evaluate the internal energy.
We need to know how to describe the state of the system at equilibrium, which is
described by the system properties, so if I know the properties of the system, I
can define the state of the system. Okay, I snuck in there a little
qualifier, at equilibrium, I don't want to go into too much detail here, but
thermodynamics only considers equilibrium conditions.
We don't consider a non-equilibrated systems so that's important for you to
understand is whether or not the system could be considered in an equilibrated
state. That's a steady state where things are
unchanging, right? So that's where we talk about chemically
equilibrium the system is not undergoing spontaneous chemical reaction.
It's under static equilibrium, so it's not being subject to some force that's
causing the system state to change. So, those are the things you want to be
thinking about in terms of how you define your system.
Can it be considered equilibrium states? Okay, moving on, we need to be able to
describe the system, we need to be able to evaluate the system properties.
In order to determine the state of the system.
So a long time ago through a really interesting history, you can look at the
development of this, it was determined that you need two independent intensive
thermodynamic properties to completely describe the state of a simple
compressible substance. Phew, lots of information there.
In reality, I kind of cheated. You actually need two independent
thermodynamic properties. They don't have to be intensive as long
as you know the mass of the system. So, they could be two independent
thermodynamic properties and the mass, and that would completely describe the
state. But for our class, we're going to say,
nope, I need two intensive thermodynamic properties.
That means I need the specific internal energy, the temperature, the pressure,
the specific volume, the density. What I can't use are total quantities.
Well, I shouldn't say I can't, you can, but again, you need to know the mass.
So, again, we're going to simplify our lives and say we need intensive
thermodynamic properties. to describe the state of a simple
compressible substance. Ooh, so there's again some, some, seems
like that's pretty lot of theory might be behind those words, and there is a lot of
theory. A simple compressible substance is
essentially virtually any of the substances that we're going to consider
here. Be like air.
It's capable of undergoing expansion and compression work, like we've been talking
about. So that's what that means.
If we were to have complex substances, then our theory would not necessarily
apply. Mixtures would be a classic example of
something that we would need additional thermodynamic information for us to fully
describe the state. Okay.
so with that, I want you to be thinking back into the state of materials and I
want you to answer, again, simple question for you, softball.
What are the three phases of matter? And we'll follow up on that when we get
back.
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