In the previous videos, we've examined the first law of thermodynamics- the law of conservation of energy and the second law of thermodynamics- the law that entropy increase. They were defined in the context of science textbooks. these two laws are two enormous laws of nature that show which direction energy flows and that energy can change into various forms during the process of energy flow. They form a big scientific paradigm that has yet to see any exceptions Then here's the question up to now we have seen these two laws be researched and born through heat engines but how can these laws in reality activate the engines using steam? How can steam be converted into work in the engines and why does energy that becomes converted always need the concept of efficiency? In this episode, we will observe the kinetic theory of gas which is the basics of what activates steam. The 4 basic processes of thermodynamics and the following principle of motion of the Carnot heat engine together with science cookie. If we want to talk about the 4 basic processes of thermodynamics, we need to change the first principle of thermodynamics that Joule discovered into an expression and observe what meaning each term holds In order to explain the first principle of thermodynamics in detail, we need a bit of technical math like the Maxwell equation, but we will ignore all that and express this in the simplest theoretical way We can express it like this as explained before, it is important to set a boundary when talking about thermodynamics let's assume that we are using this box as a boundary We put inside this box the quantity of heat, in other words energy worth delta-Q. As a side note, delta here means how much Q has changed since the Q that was first in the box, thus how much energy has been put in. Then two big changes happen inside one is the shaking energy of the gas that is filled inside and the kinetic energy is increased. Such an energy is called 'internal energy' in that it is the energy of the molecules that make up gas but in our eyes, nothing has changed so internal energy is also dormant energy thus potential energy. Because of this we express this as "U" Since we need to look into the amount that has changed because of the external heat we add delta to this and also call it delta-U another change is the the change of the size of the box from the increase of volume of the gas inside the box due to heat what the change of the box means is that the gas pushed the box with pressure and looking closely, this is the same as applying pressure to an object and moving it thus gas has done work on the box The physical quantity of work is W this has come from the w of work through this, we have observed two changes the boundary that has become heated may face changes in internal energy and can work or two changes can happen at once expression wise,
delta-Q = delta=U + delta W this is the expression that shows the first law of thermodynamics the first law of thermodynamics expressed as an equation can be shown like this. unit that is inserted into a certain sum changes the internal energy that makes up the sum, or makes the internal energy work thus heat energy is converted into work or another form of energy. for your information, work is usually expressed as W=Fs because work is the physical quantity of how much the energy added to the object moves the object. But specially, when gas works the work (W) can be expressed as the pressure of gas (P) multiplied by the changed volume (V) why is this so? it's because pressure is expressed by the force per unit and volume area multiplied by height multiplying these two physical quantities, you can understand why this happens right? Now we can assume several situations through this equation we will see how the first theory of thermodynamics works one by one by observing 4 very special cases. Shall we observe them one by one? First shall we observe the 'isothermal process' that shows the situation in which gas inside the boundary we have chosen is heated but there is no change in temperature, thus, what happens when heat is provided inside the boundary where the temperature is constant In order to satisfy these conditions, we need a very big heat source that is in contact with the boundary and thus keeping the temperature inside the boundary constant For instance We can think it is the same case as a plastic bottle in the wide sea or as a piston which is placed on the extremely huge Ondol. We'll take the latter case. Provide thermal energy into the piston little by little. Let's suppose that this heat is being provided so slowly that the temperature of gases can continuously remain the same. What will happen to the gases whose temperature is kept constant? Right. According to the first law of thermodynamics, delta-Q=delat-U+delta-W, In the piston gauge that has got heat,
internal energy should be changed or something should happen. What did I say internal energy means? Right. It means Kinetic and vibrational energy that tiny gases have. In other words, it is potential energy. However, Ludwig Boltzmann said that molecule's vibration and movement
is namely the temperature, didn't he? What it means is that internal energy is the one
that is only related to "temperature". The condition that the temperature is held constant means
that the internal energy is constant as well. That's why another should be changed. Right. There should be some work. So, supply of energy in the isothermal process will emerge
as the work that the gases have done right away. Thermal energy will emerge as the increase in volume.
In other words, as the gases' work. This shows how the sothermal process is being made. This time, let's say that the size of the borders can't be changed. By either providing the heat or removing the heat, the size is kept constant. What will happen in this situation? This case would be the gases that are put in the very hard airtight container. According to delta-Q=delta-U+delta-W, if the heat is provided in the situation that the size is not changed, the internal energy, I mean the temperature of the gases will increase naturally. I keep saying that the inter energy is for representing the temperature, don;t I? On the contrary, what if removing the heat? Of course, the gases will become cold. What does it mean that the gases become cold? Right. It means that the internal energy is decreasing. The next process that we'll look over is the same state
as the piston which used to be our toys when we were young. That is, it is the constant-pressure process
that is made in the place where this "pressure" remains the same. Because what we should do is only to create the condition
that the pressure is kept constant. In the air pressure that keeps 1Atmosphere all the time, the stopper is filled with flexible substances like a rubber balloon. Also, this is the process that is made
in the same state as the softly moving piston. To explain it more easily, let's study this with a piston. The heat that is applied into the piston will increase not only the temperature of the gas, but also the size of it
until the internal pressure has equalized with the external one. In other words, by the thermal energy's supply, the internal energy will increase and there will be some work at the same time. The process that clearly shows what the first law of thermodynamics wants to say is this constant-pressure process In the piston gauge that has got heat,
internal energy should be changed or there should be some work. The last process that I want to introduce is the very unique process, but we can often see it easily or it is effectively utilized in an ergonomical way. This process that is called "adiabatic process"
is different from the previous three processes. This process means that it is processed so fast
that the heat can't be moved or it occurs in the space that completely closes the heat. This process typically occurs in a rapidly expanding cylinder that is used for liquefaction or in air mass over the high mountains. For explanation, I'll make a model. To explain the ideal adiabatic process, it should be processed very slowly. Because of insulation, I mean because the heat is closed, there is no heat coming from outside. It means that delta-Q=0. Through the rest of sections, we can make a formula like delta-U=delta-W. What on earth does it mean? Right. If the value for delta-Wis the positive number,
in other words if this gases are expanded and work in this frame the external energy, the temperature of the gases will decrease. On the contrary, if the value for delta-Wis the negative number, in other words, if the gases in the frame are compressed and given some work, the internal energy, the temperature of the gases will increase. Because of this process, the clouds are formed
on the mountainside on the top of the mountains. The higher the altitude is, the lower the pressure covering the air, and the gases coming up along the slope is expanded in an instant. Because of the adiabatic expansion that occurs at the moment, the temperature of the gases instantly decreases. And the vapor that is instantly congealed becomes clouds. On the contrary, if the air mass that has almost no moisture comes down along the slope, it is contracted by the surrounding pressure unlike the previous case. Because of the adiabatic compression that occurs at the moment, the temperature of the gases increase, but because there is no water, the wind blows warm and dry. That's why there is Föehn, which is Korean seasonal wind. So far, we've looked over several special cases of the first law of thermodynamics. Then, how do these processes actually make a steam engine? That is, how do they become the engine that changes heat into electric power? For the answer, let's look over what happens in the Carnot heat engine... We can find out. The Carnot engine was invented by Sadi Carnot, a French technologist and natural philosopher, It's the name of the ideal engine that was created to maximize the efficiency of heat using caloric, and it's still used as a measure of the most ideal efficiency. Here's how the engine works. First of all, we know through the second law of thermodynamics that when high and low heat sources meet, the heat moves naturally, thanks to the nature's ability to move in the direction of equal temperature, an equal state. In the middle of this heat shift, the Carnot engine is slightly raised. And the gases in this engine are slowly supplied with heat, acting as the mediator of the heat shift. Now, the model that I'm showing you is literally an ideal engine, so let's say that the heat that it's getting is causing the gas in the engine to expand, at any rate, at a constant temperature. But it wouldn't matter if it was just a fine expansion, but the volume of gas in the piston quickly grows because of the movement of the piston! This process, which was so rapidly expanding that there was no time for heat to enter from the outside, is going to be insulation. The volume is expanding, and naturally the internal energy, the temperature, is going to drop. But this time, according to the second law of thermodynamics, the heat in the cylinder that is in contact with a low heat source will slowly escape. It's an ideal engine, so if the temperature stays the same and the heat escapes, the gas should reduce the volume, right? But the volume was already shrinking because of engine motion. The volume is shrinking. But gee, because the piston is already shrinking, and this time it's squeezing the gas. Again, in this process of insulation compression, the gas is returned to its original temperature, which we call the Carnot cycle. In this process, the efficiency calculations of the most ideal heat engine, in which heat flows from hot to cold heat sources and this flow turns into work through a piston, are used to analyze the efficiency of the actual engines. Carnot engine is, literally, without any theoretical loss and is interpreted as working on an ideal gas basis, so it must be ideal engine itself. Efficiency can also be calculated by simply comparing the temperature. If, as Sir Calvin pointed out, all of the heat energy could be turned into work, the efficiency of this engine could be 100 percent. Permanent engine with no heat loss. It has already been established through entropy law that no permanent engine can exist, such as a miracle of sudden water rising, against the second law of thermodynamics. The fact that the heat engine works, in itself, makes it impossible for permanent engine. So many people are still trying to realize the idea of infinite power without giving up, but unfortunately, unless our universe changes, it's an unworkable idea. So, in this way, we looked at how the first and second laws of thermodynamics are revealed in our nature, and how engineers applied this scientific knowledge to engineering with Science Cookies. In fact, there are two more laws of thermodynamics. If you look at the serial number of this series, you can see that it actually starts with zero and ends with three, right? That's right. Thermodynamics has four laws, including zero and three. That's the zero law of thermodynamics, the law in which every material exchanges its heat until it's at the same temperature, thermal equilibrium, after a long time and the third law of thermodynamics, the law that matter essentially never, never can reach zero degrees. These two laws have actually been completed since the second law of thermodynamics was enacted, and the nature of the very tiny world slowly came to light. What did they look at, and this new law came up in the air? The world came into being because of the birth of 'quantum mechanics' which is the law that explains temperature, pressure, and volume, and the nature of the smaller world, and the study that tries to explain the interaction of all the materials in the world. And so it is a kind of study
that looked at how we consist of and how we interact. And they eventually come up with a strange combination of the nature of the world that thermal statistics add up to, and of the objects that make up the very small world that we meet at the end, called 'quantum statistics'. Aren't you curious about the story of the world? It was Science Cookies. Thank you. Thank you to all the viewers and subscribers who love and watch Science Cookies. If this video was informative and fun, please press 'Like', subscribe and set alarm. This video was also produced through the support of many subscribers and viewers who came to my channel after the notification alert
and specially supported by these people who supported this channel through channel membership subscription. I would also like to thank KOFAC for its support for the production of this series. Science Cookies grows through your subscription and watching. If you want to hear behind stories about science or interesting science stories, please join the Science Cookies Channel by clicking the 'Like' and subscription buttons. Thank you for watching this episode. I'll keep seeing you. Like always, science like cookies. I will continue to love you. It was fun. I watched it a few times. - This book?
- No, Science Cookies channel! My kids are watching it, too. Oh, really? I told my kids to look up something, and they were looking for it through YouTube. - So I said, "What is it?" And they were watching your channel.
- Oh, really? It's an honor. They asked me something, and I said "Hey, don't ask your dad,
look for it through YouTube, You guys." And they were watching it later. - Oh, really?
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- Yes!
