Hello, we're going to dive a little deeper into the second law of energy
conversion today. we are covering the energy conversion
section where we're dealing with energy converting from one form to another.
And the laws of nature that we have to abide by in order to make that
conversion. And the, whereas the first law talks
about energy in has got to equal energy out.
We can't create or destroy total energy. This one has to do with the value of
energy if you recall, that when I just summarized it very quickly.
That is like even though you have a pound of gold and a pound of lead, they have
different values. Well, if you have one kilojoule of work,
and one kilojoule of thermal energy, they have the same energy but they have
different values in most cases. value from a thermonamic value, and
interestingly enough, the thermonamic value ties with economic value.
work and electricity will cost, if you're trying to buy it, will cost you a lot
more than natural gas, for instance, to produce heat.
So when we say value, it's not just thermodynamic but also economic value,
Many things have what we call a quality that we arbitrarily assign to them of
one, which is the highest quality. Work, electricity, kinetic energy and
radiation all have a quality value of 1 and then we downgrade anything that has
quality value less than these to some lower number than one.
and work of course we, we produce it with a power plant.
Electricity we produce it with a generator, kinetic energy, wind turbine.
I hadn't talked about this one. wind turbine of course, takes the kinetic
energy out of the air. Or extract some of it, not all of it.
And extracts the kinetic energy from the wind and uses that kinetic energy to
rotate a shaft to turn a generator to produce electricity, which a wind farm
does. Radiation we produce, use that radiation
energy from the sun to produce electricity with a solar cell.
and then we have thermal energy. That one, thermal energy is the oddball
here as unfortunately are just a fact that most of our energy comes from fossil
fuels which we burn the fossil fuels to produce thermal energy or heat.
In order to get the energy out of. So most of the energy conversion
processes that it, somewhere along the line involves thermal energy that we've
extracted or heat or we've extracted from burning fossil fuels, and that value
vary, of that energy, that thermal energy or heat, varies with the temperature Of
the object that, has that heat or thermal energy.
And, of course, combustion is what produces the high temperature that has,
that has the high thermal energy. now, unless this is a rather complicated
slide, but let me, let me just walk through it with you here and number one,
the thing we want to notice is the vertical scale of high up has higher
quality and low down. On the bottom, has 0 qualities.
So we go from 0 quality energy to high quality energy of 1.
And, you know, if you've got 3000 degrees fahrenheit, you're somewhere right here.
The lower the temperature, the lower the quality is.
So Quality and temperature go together. Here's temperature on the shown scale on
this side and the quality value on that side, but high temperature increases the
quality of the thermal energry. and work and electricity of course are up
here, they're up there with a quality of one.
That's the work and electricity which is the most valuable in things we have to
pay the most for when we want them. The the lower temperature examples of the
lower temperature thermal energy. That we want and use, is cooking.
Cooking doesn't have to be at five, 3000 degrees Fahrenheit obviously.
We burn everything. But cooking is not so high temperature.
Hot water for our showers is only around 30, 40 degrees Centigrade.
And 100, 110 degrees Fahrenheit. space heating is very low, relatively
speaking. So you're talking about a house that's
maintained at 22 degrees Centigrade or 72 degrees Fahrenheit.
And, when the outside temperature is, maybe, 0 degrees centigrade or 32 degrees
Fahrenheit, so that that is low quality energy, which is good if that's what we
need because it's cheaper and easier to get.
The lower the quality is of the energy or the thermal energy in this case The
cheaper it is, and the easier it is to get and convert and produce.
and at ambient temperature, we have zero quality.
Now, here's 1 thing we have to understand.
There's a lot of energy in the ambient. Air.
The molecules in the air are bouncing around and that will with thermal energy
at ambient temperature. So there's a lot of energy there.
A lot of energy. But it has no value, has no value.
I'll give you a quick story I, a, [UNKNOWN], sheet rock we call it here in
the U.S. Sheet rock manufacturers came to me one
time and wanted to help him, or take a project to deal wall boards that makes up
the inside wall of houses. And put something in the wall boards that
would. Take the energy out of the ambient air,
and produce electricity to drive the house.
And he was convinced this was the grate idea.
As a matter of fact when I told him I couldn't do that and it violated all the
laws of nature. He actually went to the president of the
university and he had to be the vice president of marketing and tried to force
me to, to take it. But you can't, can't violate the laws of
nature. so there's a lot of energy in the ambient
temperature air. But it has no value.
Has zero value. Zero quality over here at ambient
temperature. They go together, even though there's a
lot of thermal energy there, there's not anything you can do with it, nothing you
can do with it. So, you can study this in a little bit
and again, high temperature, high quality up here, low temperature Zero quality and
decreasing value. you have .1, .2, .3, .5.
You go on up the scale and energy value as you move on up to a higher and higher
temperature. combustion flames have pretty high
temperature and have pretty high quality of the thermal energy in that flame.
Let me. Okay, so here's, here's what the second
law of thermodynamics tells you, you cannot do.
There's a big X here, tells you, you cannot do it.
I cannot, no one can. Cannot take low, quality in here.
Again, this is high quality. It's vertical in the highest part of the
scale and, and low quality is the bottom part of the scale of the graph.
I put heat in at a low temperature. You could even say, well I'm going to put
it in an ambient temperature. And I'm going to convert it 100% on a one
on one basis to electricity of work. Does not violate the first law of
thermodynamics. I put in one unit of energy here and I
get out one unit of energy there. So I have not created or destroyed
energy. But the second law of thermodynamics will
not let you do that. Why won't it let you do that? Why does
gravity pull down? I don't know. We just observe the laws of nature and
don't try to figure out why the universe was made the way it was.
but this is, the, one of the reasons the 2nd law is so misunderstood, is it's one
of the very few laws, as a matter of fact as far as I know, the only one.
And that is totally stated as a negative statement.
You notice that the first law is energy in has got to equal energy out, because
you cannot or destroy it, total energy. But this one merely says what we cannot
do. Well, when we stop and think about it,
there are an infinite number of ways to make a negative statement.
I'll give you one of the, the most obscure ways that you hear connected to
the 2nd law alot. And that is, the [INAUDIBLE] of the
universe cannot decrease. Well, that, that's a true statement, but,
it doesn't give me many, much intuity of understanding what the 2nd law says you
can or cannot do. But you hear many, many, many different
statements of the law, all of them negative.
And onto the equivalent you can prove any accurately stated negative statement of
the second law from any other. Any negative statement of the second law
could accurately state it can be proven from any other.
And so that's one reason that intuitively it's a little bit harder to graph.
And it's certainly is not intuitive that you can't do this, let me give you a very
fundamental example. If I have a hot cup of coffee, if I have
a cup of coffee and it's at room temperature, I bring it into the
classroom and I set it down, and it's cooled down to where it's ambient
temperature, 70 degrees farheinheit or 21 degrees centigrate, and and I say I want
a hot cup of coffee. Well, there's nothing that says that some
process won't Cool the ambient air down a little bit and put that thermal energy
into the cup and make the cup hot, hot coffee.
That would be increase in the quality of the thermal energy in the coffee, but it
won't, can't happen. You've never observed that to happen,
it'll always cool down. We can go from high quality energy to low
quality energy very easily and as a matter of fact, the universe moves in
that direction. but we cannot go from low quality energy
and up to high quality energy with no other net effect.
With no other net effect. And notice, there's nothing else going on
here. 1 unit of energy, low-quality thermal
energy coming in, and I have high quality electricity at work, 1 unit coming out.
Nothing else going on, it cannot happen. That's 1 statement of the 2nd Law of
Thermodynamics. What can we do? Well, let me get rid of
this, my writing here. What can we do? Well this is what a auto
engine, an auto engine, a diesel A deisel engine or a, or a electric power plant,
does, this power system represents any, any one of those.
And what does it do? Well we put in combustion energy into the plant, we
drive it with, and drive the engine with gasoline that comes from oil or we drive
the deisel with deisel fuel or drive a power plant with natural gas or coal.
And we put it in, we put 3 BTU's in. Notice it's not 0 quality though, it's
not 0 quality, it has some quality because it's, it's at a relatively high
temperature. We can produce high quality energy, but
to do it we've got to degrade Other energy, some of it.
We cannot do it. We cannot have 3 BTUs going in, and 3
BTUs coming out as electricity. We can have 1 BTU of en-, of electricity
coming out, and 2 BTUs coming out at ambient temperature that we are rejecting
to the river, with a quality of zero. So if you're going to upgrade.
From part of the energy, I've got to downgrade the rest of it.
I cannot upgrade all of it. So I can only upgrade it if I use the
downgrading of, of, of some section, some segment of the energy to drive the
upgrade. And that's what an auto engine, a diesel
power, diesel engine or power plant does. And this is maybe a little difficult to
grasp, but is 1 thing, by the way I've had people and read articles where
engineers are really stupid because we're throwing away 2/3's of our energy to the
river. We need to be using.
Well, that would be great if you could do it, but the second law of thermodynamics
will not allow you to convert all of this combustion energy into electricity.
You have got to throw a lot of it away at zero quality, or a low quality close to
zero. If you're throwing it away to the
atmosphere of the river. It is a 0 quality.
So there's, a, people say we're throwing away all this thermal energy at ambient
temperature, and we need to recover it and do something with it.
It has no value just like the ambient am, molecules in the air have lots of energy
as they bounce around, but they have no value.
We can't do anything with them. That's just the laws of nature.
Okay. that's a very quick overview of the
second law of energy conversion. Which is highly misunderstood, or not
understood at all by a lot of, lot of people and a lot of our Population.
Which is not surprising. when we look at it, we see that it's not
very straightforward. To understand, particularly from an
intuitive concept. Why you have to do it the way we have,
nature says we have to do it is not clear at all.
But why does gravity pull down when i jump out of a building, I fall down
rather than going up. That's just how the laws of nature are.
Okay, thank you.