Heat transfer in nature allows the universe to exist in the form that we are all used to. It is difficult to say how the world would look if the heat transfer process disappeared even for a moment. Let's take a closer look at what types 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 their temperatures are equalized, or, in other words, when thermodynamic equilibrium is reached.
We list what are the basic types of heat transfer: convection, thermal conductivity, radiation. All other possible varieties are a combination of two or more basic methods. This point must always be considered.
Convection is familiar to everyone since childhood. The Latin word "convectio" itself means transference. Consequently, during convection, heat transfer takes place by the flows of the substance itself. It is characteristic of gases and liquids, although it sometimes occurs in some bulk materials. Imagine a hot summer day: a light haze is noticeably above the surface of the heated earth - this distortion is explained by ascending air currents. With the onset of night, when the heating effect of the sun's rays ceases, the process of equalizing the surface temperatures of the earth and air begins: the soil transfers thermal energy to the lower layers of the atmosphere (this is a mixed mechanism of heat transfer), which rise up, being replaced by colder air masses. Here is another example: we put the boiler in a container of water and plug it into the network. With careful observation, moving streams of water are noticeable. Hot masses are displaced from the heat source, and colder ones come in their place.
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 be distracted for a moment and grasp the peeling edge of a metal spoon to quickly pull your hand away, avoiding a burn. The reason is simple - some types of heat transfer very quickly heated the metal of the spoon to the temperature of the water in the cup. It's about heat conduction. There are a huge number of situations in which you can meet this type of heat transfer. Let us define: thermal conductivity is the transfer of thermal energy from a hotter part of a body to a colder one through the particles that make 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 block, the second will be cold. But if you do such an experiment with a metal rod, then the result will be the opposite. This difference is due to the difference in the internal structure of the materials.
Considering the types of heat transfer, one cannot but mention the transfer of heat by radiation. The heat source generates electromagnetic waves with a wavelength of up to 1000 microns (infrared part of the spectrum). The intensity of the radiant flux and the temperature of the heated body are directly dependent. To understand how radiation transfers heat, it is enough to conduct a small experiment - to light a fire and place transparent glass between itself and the fire. Despite the barrier, 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, 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 during heat conduction by particles, then the radiation does not need “intermediaries”. So, the Sun transfers its heat through a vacuum precisely through radiation.