Are you drinking fully developed flow or still developing flow? So, when you drink something like a macchiato, are you drinking fully developed flow or just developing flow? What's the left foot? Left foot or right foot? It's fully developed flow, right? Why is that? As shown here, usually, in the case of a straw, when the diameter is about ten times, it is said to be enough. So, when you drink bubble tea with a thick straw, even if it's about 5mm, it's about 5cm, right? Even if it's 10cm, oh, even if it's 1cm, there are not many straws that reach 1cm, but about 10cm is enough because usually, straws are about 15 to 20cm long, so it becomes fully developed flow. You can roughly understand, right? Also, when you drink lemon juice with a straw, I think lemon juice is about...

I think it will come out at a level of around 50 to 60. So, if you say 25, well, most of you, when you drink it, it's fully developed. So, the entrance length is not actually that long. Now, the reason why the entrance length is important is why it's important is that if you don't know the entrance length, we can't use the speed profile inside. When we talk about some average speed or the Bernoulli equation, the streamline flow, in the case of streamline flow, the velocity profile is already out there. So, if we know the middle speed, that's the maximum speed, and based on that, we can integrate and find out the flow rate and do things like that. So, it's important for the flow to be fully developed. And when you measure the flow rate, you need to measure it in the fully developed zone. That's the key point. Okay, so in general, passing through a tube, passing through a pipe.

Let's look into heat transfer. Now, the interesting part here is for you to know a bit about the personal aspect. As I mentioned, there is no need for you to solve calculation problems. What you need to understand now is the concept. In your textbooks, if you look at Chapter 8-4, there you go, 8-4. How many pages? So, on page 497, I went there just now. Where did I go? - 4 is on page 498. You guys go to page 48, and in this part, the key point is when we have a tube and a fluid passes through the tube. When a fluid passes through a tube, and the tube is hot, and the passing fluid is cold, basically, the fluid avoids the tube. This mechanism is very interesting, involving heat exchangers and much more.

Because of writing, boilers, and bathhouses, when you take a shower, hot water comes out like this, right? The pipe is exposed outside, and so on. Electric cars are the same. When charging the battery, you will end up moving mass anyway. Now, the important concept here is that even students who solved problems while bluffing may not have deeply thought about it. What we need to generally approach the problem is how much heat the fluid receives when it passes through the fluid wall pipe. So, there are two approaches to how much heat the fluid receives when passing through the pipe. So, now, the important concept is what? When we solve problems generally, what we need is how much heat the fluid receives when passing through the fluid wall pipe. So, there are two approaches to how much heat the fluid receives when passing through the pipe. So, now, the important concept is what?

If we talk about two approaches to overcoming this, the method of conduction and the method of convection are ultimately essential. So, in the end, when we model all heat transfer, energy transfer by heat, it is essential to have a temperature difference. So, a temperature difference is needed, and that temperature difference induces heat transfer in the area, and we need a proportionality coefficient for that, which we call h. So, when we convert it to per unit area, it becomes h times delta. Now, what is important here is, based on Newton's cooling law, ultimately, if there is a temperature difference and a heat transfer coefficient, we can determine it. This is naturally how we think about energy transfer from a transfer perspective. So, if there is a temperature difference, there is certainly transfer. Therefore, the crucial point here is what kind of temperature difference we are talking about.

Basically, there is a surface temperature on the heat transfer tube of this tube, and then there is the temperature of the fluid. The problem is, even if you think about it a little, that's the problem. As the cold fluid gradually passes through, the temperature of the fluid increases. So, if the length of the tube is infinitely long, what happens to the surface temperature of the tube and the temperature of the fluid? Ultimately, they will become the same. In other words, if the surface temperature of the tube is 80 degrees and cold water enters, even if the water is around 20 degrees, as it flows, the temperature of the cold water will rise to 20, 30, 40 degrees. But if the surface temperature of the tube is 80 degrees, no matter how long it flows, the temperature of the cold water cannot reach 90 degrees. In the end, it will become 80 degrees. So, now the problem we need to solve is, we know the surface temperature, but where is the delta and where is the delta located?

So, what is TM here? It is the Temperature Measurement. So, now, it's about the temperature of the fluid, the difference with the average temperature of the fluid. So, how are we going to calculate this average temperature of the fluid? This is the key point. Another interesting thing is that two concepts come up. Two concepts. Another concept is about heating the tube. We define this in two cases. So, we have a tube and a pipe. When the fluid passes through the pipe for heat transfer, we define the condition of this pipe in two ways. Heat transfer is something you might already know, but how should we define it in two forms? We define the state of the pipe in two states. The counter flow is the heat exchanger, and the heat exchanger has counter flow and parallel flow. We will do that next week. Heat exchanger.

It's not that they are ignoring it, but this is shocking. No, it's not that these friends don't remember. It's about ignoring the thickness of this pipe, which is related to heat conduction. Apart from that, there is this - when heat transfer occurs in this pipe, we define the state of the pipe's heat transfer into two states. It's not about the scale. When I give a hint in English, there are values ​​corresponding to the human boundary condition and the Dirichlet boundary condition. Look at that, you may not know it well. So, solving this problem is not as important as understanding the concept. It's actually a bit sad because I don't even remember solving this problem, but I did solve it at some point. Now, in heat transfer, they are asking about a concept that is really important, and saying that they don't know. It's a pity even for those who have taken the class. What are the two conditions? In fact, the state of the pipe is.

There are various conditions that can be used when we apply heat. But now, in order to interpret and understand the system, we divide it into two categories and unfold the approach to understanding. How should we understand it? The real problem is that we can't remember. Counter flow thickness skill, that's it. Surface temperature, heat generation, something was close, should we wait a little longer? If we wait a little longer, it seems like it will come out. It won't come out. Ah, dividing into two states, approaching the understanding and interpretation in different ways. The first method is when the amount of heat transferred from the surface to the fluid is the same. In reality, heat transfer is not constant on the surface because the fluid makes contact, which makes the surface easier, right? Next, providing continuous heat to the surface is more difficult than expected. However, it is possible. By connecting electric heat wires, what can we do?

If we continue to supply 500, it will continue anyway, but the fact is constant surface temperature. As I mentioned earlier, when we apply heat to the pipe, we want to understand the fluid flowing in the middle. So during your classes, we actually derive this with a derived formula, plug in the formula values, and calculate things like the final temperature of the fluid passing through the pipe. In practice, it is more important to know why we derived those formulas and how we approached them. Because as I mentioned, artificial intelligence will do all those calculation methods. Also, because Chaeji PT4 came out this time, it seems great roughly.

Even if you compare, if you put the problem in there, it will solve everything. So, if you ask them how much is the pipe surface temperature and how the fluid flow is, and in this situation, how much heat transfer rate will come out, they will tell you. But no matter how much I look at artificial intelligence and so on, it seems like they won't be able to tell. What I mean is, for example, if you put a battery pack on the floor of an electric car, how much will the temperature rise in the summer? So, in driving situations, how to design heat transfer, I think artificial intelligence won't be able to tell you. So, after you design it, how much the pipe costs, how it passes, and how much heat is generated, and how much value comes out, and how to optimize it, I think they need to learn the data.

It seems like it might be difficult to explain how to optimize the energy in this system in a creative way. So, in terms of this system, how can we optimize energy in the system in a creative way? I feel like I can't explain it properly. Look, when you join a company, even Hyundai now, they may be a bit late in terms of content and time. So, when you join Hyundai later, you can also work at Hyundai Heavy Industries, and Hyundai Heavy Industries may not build ships in the way they are building them now. Also, Hyundai may not build cars the way they are building them now. What's interesting is that when you go to Hyundai, they may not make electric cars. They may not make rechargeable electric cars using batteries. I read an article today that there is a supercar using hydrogen fuel cells.

They said it came out, so now we can create a system using hydrogen fuel cells, or we could do something like develop other fusion power, or since the price of oil is going down, we could also make gasoline cars again. So, the future of mobility, as I always mentioned, we cannot know what form it will take until we pass through. We cannot know before we pass through. However, no matter what form mobility takes, the flow of energy and movement still need to exist, right? So, even if artificial intelligence can be a great supplementary tool like a dictionary, it doesn't seem possible to ask AI to create mobility in advance because ultimately, artificial intelligence is based on learning nodes and existing data on the internet to generate.

You know, in terms of creativity, when you look at the solutions they come up with, if you just look at it quietly, they gather the pieces on the internet and create the best answers, the most probable ones, as if they were answering like a human. I understand that. But it seems like they can't create cases that are not there. But what's interesting about this is, as I mentioned, these days, the problems we solve, these kinds of things, ultimately, even though it seems like the latest technology, people like Newton, and then Faraday, and others, have already predicted everything. We just apply that to applications like this. That's right. It's like what we are doing now is just applying those concepts that have already been established, like the laws of nature, like Newton's laws, to semiconductors, to cars, to ships.

It's ultimately a matter of whether to apply it, allowing the UAV to carry semiconductor cars, but the law of Bae Ru Nung is that now, even though artificial intelligence can solve such problems, it seems that it cannot create the law of Barry. When I see what I'm doing now, in that sense, even if I do research and read papers, I think, Wow, those people were really geniuses. I jokingly say this often, but it seems like there are Protoss people. They don't seem human, especially Newton or, in particular, people like Riemann or Riemann. They really seem like mentally ill. Mentally ill. So, we ordinary people cannot understand this high-level way of thinking. I don't even want to be friends with that person because the way they solve problems is too extreme. If they solved it like this, especially if they solved it by Laplace transform, the differentiation, it's completely different. It's really a joke.

No, that's not it. So when you see something like that, it seems amazing. But the way I research, or actually the way we study, is not like artificial intelligence, just acquiring existing knowledge. So, we apply it. But really, we change our way of life, how we design products, and even bring in concepts like Leonardo da Vinci, not Leonardo DiCaprio, but da Vinci's principles. When you go deep into that, there's the flow. Yes, the person who first made the concept of the Shanghai formula, especially Maxwell's boundary concept, when you see things like this, you wonder how they could have thought of it without computers. We think about these things. Similarly, our problem is actually fluid passing through a pipe. But with the pipe and the system through which the fluid passes, it's about mobility in the past.

Regardless of the form in which mobility comes out now, it will definitely be necessary, right? So, now we need to understand those characteristics. In the future, when a company says, Oh, let's not make electric cars this time, let's make a photosynthesis car, it could happen, right? Hyundai is making electric cars now, but in the future, they could make barley cars. Even if they make barley cars instead of electric cars, those who can talk about how much heat should be transferred to barley in the pipes based on the knowledge of heat transfer they learned will become the people who lead technological innovation in the company. Honestly, nowadays, artificial intelligence has even come out. The CPU we purchased for our lab this time has 96 cores. So, if we process them in parallel, each artificial intelligence will be stupid.

However, if we bundle that into nodes now and throw away about ten columns, oh, if one person can search the internet and provide an answer at the same time, the performance is achieved. But now, the direction in which this should proceed, we as humans need to take the lead, especially those of you who have been mainly focused on work until now. For example, you have probably put a lot of emphasis on how to improve existing products. If Hyundai had the Grandeur and then made the Genesis with better durability, etc., but from now on, your main task at work will not be so much about maintaining and improving existing products. Instead, it seems there will be much less of that. Rather than that, it will be about completely new innovative ways that are different from the existing methods.

Creating and now you guys are making cars, making helicopters, making fighter jets, and doing this kind of thing is more likely to change dramatically. In the past, when a car was made, the company would inherit the car made by senior employees, and continue to make cars more like cars, polishing the same thing, oiling it, making it better. That was human life. But now, that cycle has changed. Now, seniors are not making the cars anymore. Oh, that's not necessary now. Through new mechanisms, you are more likely to develop completely new products. Because if you guys keep repeating and improving through the company like in the past, AI will do that job now. So.

The number of people doing such work is decreasing, and instead, new mechanisms are being proposed based on functions for you to understand. These new mechanisms perform the same role as before, but with different operating methods, costing less and involving many fewer steps. You should be able to propose such things. However, in the past, without artificial intelligence, reducing steps in this way would have a high risk of failure because you need to test it. By testing it this way and that way, various undesirable situations arose during the tests. Only the ones that overcame these challenges in testing were able to enter the market. Now, with artificial intelligence, everything is done on a computer digitally, based on learning. So, since computers can handle such tests for you, the key is how much more innovative mechanisms you can propose.

Where does such innovative mechanism come from? Like a hermit under a waterfall at Gyeryongsan, enduring the splashes, holding such a posture firmly. Isn't it amazing? Knowledge and new technologies are developed in that way. The cars and airplanes you use, someone, like Leonardo da Vinci, Newton, or Bernoulli, smart individuals, entered a cave somewhere, trained for about 30 months, suddenly had an insight, and started saying, From today, it's going to be a car. No, that's not how it happened. Before that, there were people who had been continuously developing similar technological concepts. After learning from them, adding their own thoughts little by little, passing it on to future generations, it has been tested by people, evolved over time, and one day, modern civilization, which you possess, was achieved.

There are various things that make up these, right? Just like that, the repetitive tests in the field of testing concepts are all done by artificial intelligence, and that stage has become very short. Think about it in the past. When automatic machines and cars came out, it took a very long time for them to speak. Because speaking had already been verified. But things like steam cars and gasoline cars made by Daimler, are they as durable as horses, as fast as horses, or as convenient to use? Verifying things like this took a very long time. But now it's not like that. The transition from gasoline cars to electric cars will be much shorter, and probably the transition from electric cars to the next generation of mobility, of course, we don't know what it will be, but the transition will be much shorter. It will really be much shorter. And even in this shortening, it's very new.

Many concepts will come up, and now it's your role to create those new concepts. The probability is high that you will do that. So, where do these new concepts come from? As I mentioned, these new concepts emerge based on the concepts passed down to you from your seniors. Okay, it was a long explanation. So, what is the key point in the end? Regardless of what future mobility or energy systems come out, it is important for you to understand how fluid energy passing through pipes will be transmitted. However, it's not just about calculating numbers like in heat transfer. It's also about how those who have solved problems by solving these calculations will perceive it. In my opinion, this is something that needs to be taken seriously.

I think you've tried it, so let's think about that. So, what is the simplest way for us? When there is a pipe, water flows through the pipe, right? So, the simplest way to heat the water passing through the pipe is to burn a fire outside the pipe. In fact, that's how a boiler works. When the tube passes through the boiler, the fire is lit outside. In this way, heat is applied. So, what is this situation close to? In fact, it's close to constant surface heat flux. By burning a fire outside, you heat it. Then, what do you use later? You wind the wire and heat it with electricity. So, you heat it with electricity. When heating with electricity, if you maintain the power and voltage constant, the voltage and power are kept constant.

Of course, it should be calculated in watts, considering efficiency. But if we also calculate the efficiency, in fact, it's easier to maintain a constant flux case. However, in reality, it is very difficult to maintain a constant surface temperature. Because as soon as contact is made, heat transfer occurs, causing the temperature to change. Assuming that the surface temperature remains constant makes it very difficult to solve the problem. Nevertheless, even if we look at it very finely, the heat transfer in the system is not constant. Why? Because it changes depending on the fluid temperature. Therefore, despite this, when we consider these two systems together, when fluid temperature is transferred in the pipe and heat transfer occurs, understanding how heat transfer will occur is divided into two categories for a reason. Why?

We found it very helpful to understand things in two major categories like this, and it has been very helpful for us in many cases where we needed to use something. So, how does this now connect to a concept? Do any of you happen to know the concept of linear combination, which is a very important concept, especially in creating new concepts in future mobility that did not exist before? Linear combination, does anyone know about it? I have mentioned this a few times in my class, but if you don't know, linear combination, linear combination, does anyone know about it? I just explained the concept of linear combination very simply with base vectors creating a space. That's right, Yoon-soo. Should I just write it as it is?

The basis vector was expanded like this, but what does this mean now? It would be great if you could understand this concept well. Let's approach it like this. So, we don't know what the future of mobility will be, but now, when it comes to what kind of energy system will be most used in future mobility, we can ask you in a brainstorming format. Right? We can ask you in advance what the energy source for future mobility will be and how it will operate. Let's discuss it like this. For example, what are the possible scenarios? And we might also have some doubts ourselves. Have we really covered all possible cases we can talk about? Have we truly covered everything we have mentioned? This is a bit like that.

I'm worried. What should I think about? First of all, what is a linear combination? As mentioned here, the basic vector space, which means when two vectors that are not included in each other meet, they create a new space. What does this mean? Explaining like this may not be understandable, but what's best is to give an example. For instance, when you want to represent a 2-dimensional plane, it's best to use two vectors, let's say, vector x and vector y. So, when you combine vector x and vector y, you can create a 2-dimensional space based on the XY axis. Now, if you want to create a 3-dimensional space, you combine vectors x, y, and z, then you can mark the 3-dimensional space. The interesting thing is, let's say X vector and Y vector are 1 0 and 0 1, then these two are independent.

That's right, because one constant multiple cannot represent the other. Multiplying by 10 or 100 won't represent 01 because the directions are completely different. Now, 10 represents only one direction and 01 represents a different direction. By combining these two constant multiples, any point in a 2D space can be represented, which is what Yunsoo mentioned as the basis vector space. Similarly, using 3D vectors xyz, the easiest way to represent them in vector form is by using three vectors like 100, 010, 001. By doing this, we can represent 327 as 3x + 2y + 7b, right? So, by using 3D vectors, we can represent all points in our 3D space.

You can represent points. Let's use an analogy. Now, I will show you two cases here. Let's call this one constant surface flux as 10. Then, let's call the constant surface 01. So, these two states, one is a state where the flux on the surface is constant, and the other is a state where the surface temperature is constant. Let's consider these two as base vectors. Let's think of these two as basic vectors that can represent all cases of heat transfer to the fluid in this pipe. So, when we transfer heat in the pipe, as I mentioned earlier, even if we maintained the temperature at 100 degrees, the moment the water starts flowing, the surface temperature will drop. Therefore, to increase the temperature again, we need to increase the flux.

We need to increase the heat flux, right? So, now that we have increased the heat flux and maintained the expressions, the state of the fluid and the pipe wall in the pipe is within a certain space. In the context of constant flux, two states are generated within a space. Do you understand the concept? So, now similarly, when you want to understand a three-dimensional space, you don't need to see everything in the three-dimensional space. With just 10010001, you can represent everything in an unexplored three-dimensional space. Similarly, after understanding each case, by linearly combining these two, you can understand all cases of heat transfer from the surface of the pipe, how the temperature is on the surface, and how heat is transferred from the surface to the fluid.

Just think about it. So, in the case of constant surface heat flux, it's better to write it like this. As I mentioned before, when the heat flux given at the surface is the same. Let's copy this. Similarly, when the surface temperatures are the same on both sides, when the fluid enters the pipe, there will be a temperature, and then the exit temperature of the fluid coming out through the pipe will be our concern. And also, we will need the average temperature of the fluid. So, let's talk about how these things are defined and how we will look at this system. As I mentioned earlier, it's important how heat is transferred from the pipe to the fluid, the mechanism or method.

Understanding this is important, right? But now, there is another very interesting part here. There is a very interesting way in how we are going to understand this. What is it? It's called the heat transfer coefficient. What does this mean? Suddenly, an unfamiliar font. What kind of font is this? This is what I just highlighted. Oh, can this color be changed as well? Oh, it can be changed. What is the difference between these two? The ultimate heat transfer coefficient, Q. It represents the amount of heat the fluid receives as it passes through the pipe. Now, this has been expressed in two forms. The one above represents the heat transfer coefficient with the pipe and the temperature difference of the fluid. That's right. It just shows the convection heat transfer equation. Newton's cooling law. But the one below.

What is the formula below? m - ptti n, what is it? What kind of formula is that? That can be used as a final exam question, right? It's not about flow rate, it's not about flow rate. What does MCP tti mean? I will ask questions like this as exam questions. Then, this could be the answer, right? So, if you write in black, it's wrong, if you write in orange, it's wrong, but if you write in yellow below, it's correct. You can also create questions like that. What about it? It's not about flow rate, it's about m- flow rate, right? Mass flow rate. So, you multiply by specific heat and tti, it's about what kind of heat transfer, based on what kind of heat transfer, it's about heat transfer based on the pipe, not pressure difference. It's not pressure difference inside the fluid. What is it? It's too broad. What is inside the fluid? Internal heat capacity of the fluid, right? Heat capacity. But it's capacity, what is it? Unit volume, molecular heat energy reserve, right?

This is the correct answer, the enthalpy of the married, so now we look at heat transfer in two ways. What is orange? It's how much heat transfer the fluid received from the pipe, that's what we're interested in. So, how much heat did the fluid receive from the pipe? So, interpreting this, there is a temperature difference between the fluid and the pipe, and there is a heat transfer coefficient, so when you multiply them, you get the amount of heat received. That's the orange method. Now, what is the yellow method? It's the mass flow rate of the fluid passing through the pipe. So, the interesting thing is that the yellow method doesn't care about heat transfer at all. Whether it's convection, conduction, or anything, it doesn't care about heat transfer itself. But what does it focus on? The mass, the mass of the fluid passing through the pipe, what happens to the fluid in the pipe.

I don't know what's going to happen, the temperature before entering, the temperature after entering, and then multiplying the specific heat due to the temperature difference, as the student at this school mentioned, the thermal energy inside the fluid, so, whatever heat is received through conduction, anyway, it passed through the pipe. I don't know what happens inside the pipe, before entering the pipe, after entering the pipe, comparing the energy difference between these two, it turns out that it is the amount of heat transfer due to the temperature difference. There are two ways to solve it. So, the orange highlighted Q above represents the heat transfer representing the thermal energy transfer due to heat transfer, and what the Q below represents is, I don't know what happened in the heated pipe. It's about the thermal energy capacity of the system before and after the heat is released, subtracting the thermal energy capacity of the system after passing through the pipe, the thermal energy of the fluid after passing through the pipe.

How do we calculate how much it has changed? So, of course, before the fluid passes through the pipe, after passing through, right, the heat changes, right? So, before going into the bank, you went in and came out, right? So, combining the money taken out using the ATM machine at the bank, it should be the same, right? Do you understand what it is, everyone? So now, actually going to the bank and taking out money from the cash dispenser is a transfer of heat, right? Now, what is the equation below? Transferring heat, not spending time at the bank, right? How much was there before going in? Now, after going to the bank, touching the ATM, and then how much is there? That's it. If you look at that, the difference is what you received, right? So, by connecting these two, we solve the pipe equation a lot. So, you need to know a bit about that part. So, now, simply, how do we solve that? If we solve that, what can we do?

Earlier, as I mentioned, now we can know the temperature of the fluid at the outlet if it's not the average temperature. We can know the temperature of the fluid at the outlet. So, as I mentioned earlier, it becomes one of the two bases. When the heat transferred from the surface to the stunt phase case is constant, now the fluid flows like this, and when it hits in the x direction here, under the heater, it provides a constant amount of energy, like 500W or 700W, as I said before. Then, as I mentioned earlier, it is completed in this way. It is completed in this way. Even though it may seem difficult, what is QAS? It's what comes before HTM. So, what it means is, it's the amount of heat transfer by convection heat transfer. As I mentioned before, it's like, what's conduction, I don't know, but how much energy was there before the fluid entered and how much was there after it came out.

We put the dog down to walk. If we put it down, what can we do now? We mostly know the incoming fluid temperature. But now what I'm really curious about is, when we heat it to, let's say, 500 degrees Celsius and feed coal, how much heat should we apply to the pipe to find out the temperature of the fluid coming out through the pipe? I'm really curious about that. For example, let's think like this. It's not about future mobility, but think about a nuclear power plant. Do you know how a nuclear power plant emits electricity? A student named Heo Jaewon asked me if it's about the specific heat transfer and the difference in heat capacity. Is it the same in the end? He said that the amount of heat transferred is equal to the difference in heat energy. Well, since I know a lot about this.

When talking about nuclear fission, before I explain, many friends don't know much. When asked how electricity is generated at a nuclear power plant, some friends say that the electrons from nuclear fission are absorbed by advanced devices, not blocked by radiation, but undergo a change of state. Since boiling water is a change of state, it's simple. If nuclear fission occurs rapidly, it becomes a nuclear bomb and explodes. However, if nuclear fission is slowly controlled by rods, it doesn't explode but generates very hot heat. In nuclear fission power generation, the very hot heat generated is used to boil water. As Yoon Soo mentioned, boiling water at high temperatures.

High-pressure steam is generated, right? So, what do we do with this high-temperature, high-pressure steam? We rotate a turbine. So, now we rotate the turbine. Ah, after rotating the turbine, there will be some steam left, right? However, since the turbine has been rotated once, the temperature and pressure may have decreased a bit. But it's still hot, and some of it may have turned into water, but some will still remain as steam. So, a steam trap is used. Some high-efficiency power plants rotate a small secondary turbine with the steam that comes out after rotating the turbine once. There are cases like that. However, usually, they don't do that. So, what should we do with the hot steam that comes out after rotating the turbine? In your opinion, we shouldn't just discard the hot water, right? That's right.

I wish I could turn the wings back. Back in the day, my dear colleagues, I was curious about that. Now, as it is said, cool it down, and after cooling it down, reheat it. I don't quite understand that. So, when I talk about humidity, it doesn't seem right. Colleagues, the reason is not clear, and cooling towers work hard to cool down the humidity. After I talk about humidity, I have a reason to reheat it. So, we shouldn't just release the steam because the steam is contaminated with radiation. Therefore, the steam should not be released outside. Don't just throw it away, boil the water again, and turn it back. So, after turning the turbine once, why not just put the steam that comes out directly into the boiler and boil it again instead of creating steam again, which would require more energy? So, I thought a lot about not doing that and just heating the steam that comes out to high temperature and pressure.

As many of you have mentioned, after turning the turbine once and releasing the high-temperature steam, of course, the temperature and pressure would be better than before turning it, but it is still hot and the steam is intentionally sent back, stop it, cool it down, and then send it back to the boiler. It's not a boiler, it's back to the nuclear reactor where nuclear fission occurs, and it's boiled again. Why do we need to do this? If we're going to boil it anyway, wouldn't it be better to put in the hot one right away? It's not about the temperature. Here, you need knowledge of heat transfer. That's why when people come to the company without learning heat transfer, they talk like this. In the past, there was a time when a graduate student was selected from a university, and that school didn't know about heat transfer, so they didn't know anything. That's why they asked, Why don't you know?

They say they didn't hear about the choice, not about replacing the coolant. There is a reason why we need a coolant. It's not about replacing the coolant. So, you guys don't know well. Oh, there is no friend who really knows about this. So, you did well to take the future mobility class. Oh, I have to talk about this in my class too. So, the day before the class, I'm busy solving problems, explaining formulas, solving problems, and giving a few examples. But now that we are talking about future mobility in detail, it's nice. Vapor is similar to cooling in phase change. But let's think about it this way. Naturally, when we think about it, the steam that comes out after turning the turbine is very hot. It's completely hot, so it's not that easy to turn the turbine again.

It's still piping hot, right? But instead of ordering that, you can just put it directly into the boiler. The noodles use less energy than ordering them, so it would be much more beneficial. Why bother ordering it then? By the way, let me tell you, we cool it down. How do we cool it down? We mix cold water with it. If we mix the cooling water, contamination occurs. So, we can't mix them. What we do is, we build a heat exchanger. The reason why most nuclear power plants are built to the ground is to turn the steam turbine. After turning the turbine, we exchange heat with seawater. Without contaminating the water itself, we have hot pipes flowing in the middle, and on the outside, we create a double pipe system. The seawater flows on the outside, thickening it, so that the radiation does not exchange and only the heat energy is exchanged. That's how it's done.

Now, we cool it down with seawater. So, when we cool it down with seawater, what happens is, we turn the turbine. So, through nuclear power generation, it becomes cooling water. How hot do you think it is? It's not like heavy water or tritiated water, it's just normal seawater, right? How hot do you think it is? The steam has low density, so it's efficient. However, if you want to go deeper into this, you should be able to explain one more step. Usually, what we do is, we take the steam and instead of boiling it again in the boiler, we cool it down completely by using seawater, turning it completely into liquid form. But now, what's the problem with this? The problem is, this is where the issue arises, even the seawater gets hot.

It's like drawing seawater at 20 degrees, so the temperature won't be as high as hundreds of degrees like steam, but it rises up to about 60 to 70 degrees. So, in fact, it's just an exchange of heat with the seawater, so there is no radiation contamination. Therefore, it needs to be returned to the sea. If it's just returned near the power plant, there would be quite a lot of water, right? The water near the power plant is very hot, so environmental changes will occur. People like haenyeo who dive for seafood could get hurt because it's hot. That's why the water should not be discharged near the coast. It should be discharged far away. Do you understand? Now, about this topic, when it comes to the pipes, the question is, how far away from the sea should it be discharged?

The key point is where you need to discharge. It seems like the time is up as if we were wrapping up earlier, so I'll pause the lecture here, and I will resume right away when we come back to the next lecture.

열역학12 1

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