The space is very cold, why is the space station worried about overheating in the warehouse and increasing heat dissipation?

2020-01-24 | Quantum Science original |

Universe space is very cold, the interstellar dust temperature can reach -260 ° C, and the temperature of the cosmic microwave background radiation is -270.15 ° C, which is only 2.7K higher than absolute zero. And absolute zero is the lowest temperature at which material atoms and molecules stop thermal movement.This is just a theoretical concept. The temperature of the universe is so low, but if our human body is exposed to space, it will not die because of the cold, nor will it freeze instantly, and even you will not feel cold, but will die.Low-pressure environment; of course, the International Space Station will not worry about the space being too cold, but will heat up the astronaut's space capsule. Instead, it will need to add extra equipment and increase the heat dissipation area to cool the space station. Why?

First understand the simple concept: what is heat? What is temperature?

All substances are composed of molecules and atoms. And atoms and molecules always move randomly including translation, rotation, vibration in different ways. The movement of atoms and molecules generates heat or thermal energy. Therefore all substances haveThere is thermal energy. The more violently the atoms or molecules move randomly, the higher the heat or thermal energy. Of course, the higher the temperature we use to measure thermal energy.

The picture above is a water molecule animation for dynamic simulation. The green line represents the hydrogen bond between oxygen and hydrogen. The hydrogen bond is much weaker than the covalent bond. However, when a large number of hydrogen bonds work together, they will produceStrong thermal effect. So what is the temperature?

Temperature is a measure of the average kinetic energy of the movement of material molecules. It is a collective expression of the thermal movement of a large number of molecules and contains statistical significance. For individual molecules, temperature is not significant. Because some atoms and molecules move faster than others.Temperature is the average of the energy of all atoms and molecules in a given system. Temperature has nothing to do with how much matter is in the system. It is only the average of system energy. In simple terms, temperature is the physical quantity that people use to cool and heat stars.

So how is the heat lost? That is, how is the heat transferred?

The thermal energy can be transferred from one place to another in three ways: solid conduction, convection of a fluid liquid or gas, and thermal radiation. But of these three methods: conduction is the most effective way to transfer heat. IfThere is a temperature difference in the system, and the heat is always transferred from higher to lower temperatures.

Heat conduction

When two objects are in contact with each other at different temperatures, heat conduction occurs. Thermal energy flows from the hotter object to the colder object until they are at the same temperature. Conduction is a single occurrence of heat through the collision of material moleculesDirectional movement, where the two objects are in contact, the faster moving molecules in the hotter object collide with the slower moving molecules in the colder object.

When they collide, the faster molecules transfer part of the energy kinetic energy to the slower molecules. The slower molecules get more thermal energy kinetic energy and occur with other molecules in the cooler objectsCollision. This process continues until the thermal energy from the hotter object has completely spread to the colder object.

Some substances transfer heat more easily than others. Solids are better than liquids, and liquids are better than gases. Metals are good conductors of heat, and air is a bad conductor of heat. When you touch hotter or colder than your skinThings, such as when you wash your hands in warm or cold water, or we are in contact with hot or cold air, this is the typical conductive heat transfer. This is the fastest and most effective way to lose heat. Needless to say, exposureIn the cold air, you can immediately understand what heat loss is.

Convection :

Convection is usually the most effective heat transfer method in liquids and gases. Convection occurs when the hotter area of ​​a liquid or gas rises to a colder area. When this happens, the temperature is lowerThe liquid or gas will replace the higher temperature area. This cycle leads to a continuous convection mode, the heat is transferred to the colder area. When we boil water in the pot, we will see hot convection. RisingAir bubbles are the warmer part of water rising to the colder part. We have also heard the phrase "hot air rises, cold air falls" is a description of atmospheric convection. Heat is transferred through the circulation of air.

Heat radiation :

Both conduction and convection require matter to transfer heat. Radiation is the least efficient method of heat transfer. It does not depend on any contact between the heat source and the heated object. For example, we can feel even if we are not in contact with the sun.The heat to it. Heat can be transmitted in a vacuum by thermal radiation. Thermal radiation commonly referred to as infrared radiation is an electromagnetic radiation or light. Radiation is a form of energy transmission and consists of electromagnetic waves traveling at the speed of light.No mass exchange or media is required.

When a high-energy electron of an atom drops to a lower energy level, the object emits radiation. The lost energy is emitted in the form of light or electromagnetic radiation. The absorbed energy of the atom can also be an electron "jump" to a higher energy levelAll objects absorb and emit radiation. When the absorption of energy balances the emission of energy, the temperature of the object remains constant. If the absorption of energy is greater than the emission of energy, the temperature of the object rises. If the absorption of energy is less than that of the energyLaunch, then the temperature of the object will drop.

Mastering the above knowledge, we can solve the problem perfectly.

Why is the International Space Station afraid of overheating, and it is necessary to specifically increase the heat dissipation area to cool down?

Why does the human body freeze when exposed to space? I believe you already have the answer, but I will repeat it.

One of the most common misconceptions about outer space is that anything that enters outer space is immediately frozen. But in fact, because the space is vacuum, there is no medium to conduct heat to take away the heat, and the thermal energy can only beIt is slowly lost through electromagnetic radiation light, and this electromagnetic radiation is still in the infrared band. It is conceivable how slow this process is, so that it would take trillions of years for stars like white dwarfs to die.To cool down, in fact they may be the last hot spots in the universe. Here is another example :

If we reach into the pre-heated oven, the temperature of the air is the same as that of the metal shelf, but only the shelf burns the skin, because it is a dense crystal that can conduct heat very effectively, and the air isComposed of a gas with much lower mass and density, air is a poor heat conductor in comparison. Also in winter we dare to approach the stove to heat it by heat radiation, but you definitely do n’t dare touch the stove with your hands. TheseThe examples show that heat conduction is much more efficient than heat radiation.

Also, at the same temperature, metal objects are much colder than air. You can touch the metal objects around you to try it out, because metal can take away the heat of the body faster.

The vacuum basically does not cause heat transfer, so the heat loss is very slow. And there are many equipment on the International Space Station, each of which will generate heat, and the large amount of heat accumulation will cause personnel to be unable to bear it.Huge space radiator for ammonia to increase radiation area.

What about the human body? When we are instantly exposed to space, we only lose heat from the body through thermal radiation, so we may not feel cold, and we will die because of low-pressure lung rupture.

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