Types of heat transfer thermal conductivity convection thermal radiation. Types of heat transfer: heat transfer coefficient. Thermal conductivity coefficients of various substances

This results in a temperature balance between the left and right sides, because in physics there are no two energetically very different states next to each other. So, if the screw is warm on the left here, that also means that the particles in the screw are faster. And these fast particles now hit slower particles, which then speed up, then hit others, and so on. and so the heat is transferred from the left slowly to the right. Now there are substances that are better heat conductors than others. Of course, if you keep a plastic spoon in boiling water, it will heat up less quickly than a silver spoon, for example.

In general, we can say: good conductors of heat are also usually good electrical conductors, such as copper. So, first of all, for thermal conductivity. Incidentally, liquids and gases can also conduct heat. But then mixing and diffusion within the substance plays an important role. The point how heat is transferred: namely, heat flow or is called convection. Heat flow can occur in water. Here we give an example of a sea current. Sea current can be caused by temperature differences in the water at different locations.

For example, if you are warmer on the left side, you will get current where the water gets colder. Warm ocean currents can then release heat into the environment and thus greatly influence the climate. It is the transfer of internal energy from one body to another. Let's look at another example heat flow: hair dryer. The hair dryer inflates the air in its inner part and then blows it outward towards our head. And there, for example, the internal energy of the air can be transferred to our hair.

So this was an example of how heat can be transferred through airflow. Now for the last example of heat flow: heating. Water flows in the heating pipe. Water is heated in the basement. Because the hot water has a lower density than the cold one, it now flows upwards where it can release the stored heat to the environment. Specify how to transfer heat: thermal radiation. The typical heat sink is the sun. She sends her warm rays to the earth. And what exactly are these rays?

The sun's rays are also only electromagnetic waves, so they have the same properties as light, for example. They are not in the visible range, but rather mostly in the infrared range. Well, it's longer than light. And the peculiarity of thermal radiation, in contrast to heat conduction or heat flow, is that the transfer can also take place in a vacuum, that is, regardless of the need for heat transfer. Another example of thermal radiation is a fire. Although heat is transferred through conduction and heat flow, we are primarily able to heat up in a fire through radiant heat.

Well it was for three different ways heat transfer. So, we summarize again: heat, that is, the energy form. Like sea current, or thermal radiation, for example, the sun. Okay, so heat is an energy form that can be transferred. But what is temperature in contrast? And temperature describes, in contrast to heat, the average kinetic energy of particles. In other words, by measuring the temperature difference across a body, you can see how much heat has been transferred to another body. This is the difference between temperature and temperature.

First, there is metal inside the flask, which is gradually heated by thermal conduction. This metal transfers its heat into the air. There may be heat flow. And the whole lamp emits a lot of heat, unfortunately, although it should produce more light. You always have adverse side effects. So I hope you enjoyed the video. Until then, see you next time! One of the main problems we face when trying to understand the world is that it is very difficult to isolate a particular phenomenon from the rest.

In real life, we find that multiple events occur, each with different causes and effects at the same time. And this is the main problem of the social sciences: the variables in the game are infinite, and it is generally not feasible or unethical to conduct an experiment to test a hypothesis.

Fortunately, in other areas of science, things are much simpler, for example, physics, which studies bodies and their interactions, and it is often easy to conduct an experiment that isolates one phenomenon from another. But in any case, we find that a person who does not study this subject usually sees something difficult and impenetrable in it. On the other hand, many people with a scientific mind tend to analyze more things than necessary and see the world more or less as follows.

Many times schools don't teach basic tools to their students so they understand something as simple as heat transfer. It may seem silly, but keeping these things in mind helps us in many aspects of life: thinking about how to effectively protect us depending on the weather, even for or to keep a cold beer. Whether we like it or not, science is everywhere. Rather, we need a certain base of scientific knowledge in order to interact more effectively with the Universe.

Heat, for physics, is the transfer of energy from a body with a higher temperature to which there is less. Contrary to what many believe, heat is not temperature, but energy transfer. So the same phrase "heat transfer" would be redundant, but it is used in the same way. When we say that water is hot, we are saying that it has a lot of thermal energy. This would mean that their molecules vibrate strongly, so if we touch them, they will transfer these vibrations into their hands, and depending on how strong they are, they can harm us.

Touching a hot body is not the only way to transfer heat energy, there are three ways. It will be conduction, there is also radiation and convection, but in most cases all three situations occur at the same time, and some more than others. That's why these three chocolate bunnies were sacrificed to show each of them in the most isolated way.

In the first case, we see the killer placing a hot iron on a chocolate bunny. The melting point of chocolate is around 36º, and iron is certainly over 100º, so molecules of the same tend to transfer some of their temperature to the chocolate, melting it little by little while it cools slowly. Conduction occurs when two substances are in contact, and heat transfer occurs from more high temperature to the bottom until the system is in thermal equilibrium. This phenomenon occurs mainly between solids and to a lesser extent in liquids.

In gases, thermal conductivity is minimal because the molecules are widely separated from each other. In the second case, a dose of infrared radiation is applied to the rabbit. It happens that radiation is not only what they have atomic bombs, but they're just very small, massless particles that behave like waves of different frequencies. Depending on the frequency they have, they are radio waves, infrared, light, ultraviolet rays, x-rays. Each of them with different properties and characteristics has the ability to interact with what we call light.

X-rays can pass through flesh, but not much denser things like bones or metals. Infrared radiation interacts with almost all substances, and when it reaches from the lamp to the surface of the chocolate, its temperature increases. All bodies emit infrared radiation, the higher their temperature, the more they emit. This is one of the reasons bodies tend to "cool down" or thermally equilibrate. environment. Even if it does not come into contact with anything, the body loses energy in the form of infrared radiation.

Finally, the third rabbit suffers from a hair dryer fit. A jet of hot air hits your face. We said that gases do not have good thermal conductivity, because the molecules interact equally weakly with each other. But if we create a big movement, we will make a lot of particles in contact with the rabbit. This way the air will lose temperature and the chocolate will rise, balancing. In thermodynamics, convection is the transfer of heat through the movement of a fluid, in other areas of physics, as in fluid mechanics, it is called convection. simple movement liquids, without interest whether the transfer is heat.

In real life, we can use these concepts to understand how a thermos maintains the temperature of the liquid it stores. All those who have ever broken one will know that they are made from a double layer of mirror glass. Mirroring serves to keep heat from being lost by radiation, since infrared rays are reflected on mirrored surfaces and do not leave the container. The space between the two layers of glass lies in the fact that heat is not transferred by conduction: those of best quality have a "vacuum" or air at very low pressure.

We said that the conductivity of gases is minimal, since their molecules interact very little. Well, the fewer molecules, the less interaction there will be. If a perfect vacuum were achieved, the transmission through the wiring would be zero. The thermos also keeps temperatures lower than environmental ones. The same goes for conduction, and the mirror will serve so that the infrared radiation coming from our body is not absorbed by it.

Heat is the transfer of energy. In gastronomy, it is used to change food chemically and physically and thus make it easier to digest, chew, change taste and make them safer. This transfer of energy always tends to equalize the temperature of the elements in the system, so the hot part is cooled and the cold part is heated, resulting in equalization of its temperatures.

The transfer of energy can be carried out by three different mechanisms. The conductivity of heat is given by the transfer of kinetic energy between molecules. Its speed and efficiency are directly dependent on thermal conductivity, which is different in each substance. In the kitchen, this moment is of key importance when choosing the material with which the pots and pans are made, and the grill or grate that we will use. Materials that conduct heat better will be able to transfer heat earlier and better into food.

Among common materials, copper and aluminum pots are the fastest heat, while iron and steel take longer to change temperature but retain more heat. This heat transfer mechanism is one that is tested when the pot is cooked in a pot of water or fired in the oven. In both cases, water and air, respectively, circulate within the system, homogenizing the temperature.