What should middle school students do and what should they not do in class?

Middle school students should listen carefully to the class, take notes carefully, actively think about the questions raised by the teacher, should not sleep, should not talk to classmates, should not make small movements below, etc.

Discharge cooling is another type of convection cooling. Unlike regenerative cooling, the coolant used for exhaust cooling absorbs heat to the thrust chamber and is discharged out of the combustion chamber instead of entering the combustion chamber to participate in combustion. Direct drain coolant reduces the thrust chamber specific impulse, so the coolant flow for drain cooling needs to be minimized while only using drain cooling at the outlet section of the nozzle that is relatively less heated.

There is also radiative cooling, in which the heat flow is transferred from the combustion products to the thrust chamber, and then the heat is radiated by the thrust chamber wall to the surrounding space. Radiative cooling is characterized by simplicity and small structural mass. It is mainly used in the extension section of large nozzles and the thrust chamber of small thrust engines using high-temperature resistant materials.

When cooling in the thrust chamber of the tissue, a relatively low temperature liquid or gas protective layer is established on the surface of the thrust chamber wall to reduce the heat flow to the thrust chamber wall, reduce the wall temperature, and achieve cooling. Internal cooling is mainly divided into three methods: internal cooling (shield cooling), membrane cooling and diaphoretic cooling of head tissues. After the internal cooling measures are adopted in the thrust chamber, the mixing ratio near the wall of the combustion chamber is different from the optimal mixing ratio in the central area (in most cases, the near-wall layer rich in fuel is used) due to the need to reduce the temperature of the protective layer, resulting in the uneven distribution of the mixing ratio along the cross-section of the combustion chamber, so that the combustion efficiency is reduced to a certain extent.

Membrane cooling is similar to shield cooling in that it cools the thrust chamber wall by establishing a uniform and stable coolant film or air film protective layer near the inner wall surface, except that the coolant used to establish the protective layer is not injected by the injector, but is supplied through a special cooling belt. The cooling band is generally arranged in a cross-section of the combustion chamber or the convergence section of the nozzle. There can be several cooling bands along the length of the combustion chamber.

In order to improve the stability of the membrane, the coolant often flows through the gaps or small holes in the cooling belts, and when sweating is used, the thrust chamber wall or part of the inner wall is made of porous material with a pore diameter of tens of microns. Porous materials are usually sintered with metal powders or pressed with metal mesh. In this case, the number of pores per unit area is increased by making the micropores in the material as evenly distributed as possible.

The liquid coolant penetrates into the inner wall, creating a protective film that reduces the density of the heat transferred to the wall. When the flow rate of liquid coolant used for sweat cooling is above a certain threshold, a liquid film is formed near the wall of the thrust chamber. When the coolant flow rate is below the critical flow, the inner wall temperature will be higher than the coolant boiling point at the current pressure, and some or all of the coolant will evaporate, forming an air film.

In addition to the above thermal protection, there are other thermal protection methods such as: ablation cooling, thermal insulation cooling, hot melt cooling and composite protection of chamber walls. 3. Thermal protection scheme of high enthalpy gas generator Based on the above methods and the actual situation, the thermal protection method of high enthalpy gas generator is obtained.

The combustion chamber of a high-enthalpy gas generator differs from that of a liquid rocket engine, eliminating the front thrust chamber part, making its structure simpler and more effective. Then, the thermal protection involved is the thermal protection part of the combustion chamber wall. As the fuel enters the combustion chamber, it quickly decomposes and releases large quantities.

Many people often like to make some noise in class, because many people have never thought very seriously about their learning and life in class, and they don't know what they can do in class and what they can't do in class. So there will be a situation of making trouble in class.

1. Don't be distracted.

The last thing you can do in class is to be distracted. Because the purpose of class is to learn knowledge, but if you are distracted from class and do other things, it will lead to not paying attention to the class, so that you will miss the key points of knowledge taught by the teacher, and it will be more difficult to understand and learn later. Therefore, it is recommended that everyone should be serious in class.

In addition, I would like to remind everyone that you should not ignore the teacher's lecture rhythm in order to take notes in class, otherwise it is also easy to miss something.

2. Disturb others.

In addition to being distracted, disturbing others during class is also a very undesirable thing. Many people want to find someone to chat with or find someone to make trouble when they are bored in class, which not only treats them badly, but also drags others into the water and affects others to take classes seriously.

Therefore, it is best for everyone to be in good spirits when you are in class, and not to be willful to others. After all, the other party may be very eager to attend the lecture.

3. Don't sleep.

Many people will sleep during class, which is not suitable for this practice. If you sleep underneath, it will make the teacher feel disrespected, and at the same time, the teacher's confidence will be hindered, which may affect the teacher's mood and teaching quality. Therefore, I hope that everyone will rest on their stomachs when they get out of class.

You can't talk back to the teacher in class, you can't make small movements in class, you can't make noise in class, you can't take notes in class, you can't interrupt the teacher's lecture ideas in class, you can't play with mobile phones in class, you can't listen to *** in class, you can't write homework in other subjects in class, you can't eat or drink in class, you can't make noise and make loud noises in class, you can't read extracurricular books in class, you can't sleep and nap in class, you can't pass notes in class, you can't play games with others in class, you can't disturb others in class, You can't be in Cao Ying's heart in Han ,!! in class

1.You are not allowed to talk in class.

2. There will be no small actions in class.

3. Do not drink water during class.

4. You can't talk to each other in class.

5. Do not eat in class.

6, the curse is small