What are the types of heat transfer?

Heat transfer in nature allows the universe to exist in the form to which we are all accustomed. It is difficult to say how the world would look, the process of heat transfer would disappear even for a moment. Let's take a closer look at what kinds of heat transfer exist and what is meant by this term.

According to the generally accepted definition, heat transfer is a physical process in which thermal energy is distributed in one way or another between several bodies with different degrees of heating. The process stops when the temperature is equalized, or, in other words, when thermodynamic equilibrium is reached.

Let's enumerate what are the basic types of heat transfer: convection, heat conductivity, radiation. All other possible varieties are a combination of two or more basic methods. This point must always be taken into account.

Convection is familiar to everyone from childhood. The very Latin word "convectio" means a transfer. Consequently, when convection takes place, the heat transfer takes place by the flows of the substance itself. It is characteristic for gases and liquids, although sometimes occurs in some bulk materials. Let's imagine a hot summer day: above the surface of the heated earth is noticeably a light haze - this distortion is explained by the ascending air currents. With the nightfall, when the heating effect of the sun's rays ceases, the process of equalizing the temperatures of the surface of the earth and air begins: the soil communicates thermal energy to the lower layers of the atmosphere (this is a mixed mechanism of heat transfer), which rise up, replaced by colder air masses. Here's another example: put the reboiler in a container of water and turn it on. With close observation, moving streams of water are noticeable. Hot masses are displaced from the source of heat, and in their place comes the colder ones.

What could be better than an interesting conversation over a cup of hot tea on a cold winter evening? At the same time, it is enough to distract for a moment and take hold of the peeping edge of a metal spoon to quickly pull back your hand, avoiding a burn. The reason is simple - some types of heat transfer very quickly heated metal spoons to the water temperature in the cup. We are talking about heat conduction. Situations in which you can meet with this type of heat transfer, a huge amount. Let's give a definition: thermal conductivity is the transfer of heat energy from a more heated part of the body to a colder one by means of the particles making up the body (electrons, atoms, molecules). A special case is the transfer of heat between different objects in contact. Different materials have different thermal conductivity. So, if you heat one end of a wooden bar, then the second one will be cold. But if you do such an experiment with a metal rod, the result will be the opposite. This difference is due to the difference in the internal structure of materials.

Considering the types of heat transfer, we can not fail to mention the transfer of heat by radiation. The heat source generates electromagnetic waves with a wavelength of up to 1000 μm (the infrared part of the spectrum). The intensity of the radiant flux and the temperature of the heated body are in direct correlation. To understand how radiation transfers heat, it is enough to conduct a small experiment - to light a fire and place a transparent glass between oneself and by fire. Despite the barrier, the heat will still be transmitted. Or look at the cat, which in winter lies on the windowsill under the sun, basking. It's simple - in these examples, the thermal energy is transmitted by radiation. One of the features of this method of heat transfer is independence from intermediate media. If, during convection, the transfer takes place by the substance itself (gas), and in case of thermal conductivity - by particles, the radiation does not need "intermediaries". Thus, the Sun transfers its heat through the vacuum precisely through radiation.