enertec-sm

In nature heat is transmitted from a warmer body to a colder one, always looking for balance. Heat can propagate in three different ways, which sometimes can coexist: conduction, convection and radiation.

Conduction occurs when the bodies are directly in touch and the speed of transmitting heat depends on the thermal conductivity of the material itself. Practically it is the propagation of heat from a warmer part to a colder one of the same body, or in other words the transmission of molecular impacts without transport of matter. This happens for instance when heat passes through a wall the surfaces of which have got different temperatures.

Convection occurs with transport of matter, that is with motion of molecules; this transmission is therefore only possible in fluids - liquids or gases - . If we place a pan full of water to heat on a flame, it is not the molecules transmitting its to their neighbours, but it is the hot molecules themselves which move upwards creating convective currents. This phenomenon can be explained very easily: the water on the bottom heats up, so it becomes less dense and goes up to the surface thanks to Archimedes' thrust, leaving its place to the more dense cold water which is getting down at the sides. Even in gases, and therefore in the air, the propagation of heat occurs by convection: it's enough to watch any object placed behind a hot radiator to see it trembling, which reveals the existence of the convective motions of hot air. Therefore there is transport of matter in convection.

Radiation is the transmission of heat in the form of rays - the word itself explains it -, similar to light rays, but called calorific rays or infrared rays. The sun heat cannot reach the earth either by convection or by conduction as our planet is isolated in vacuum and the molecules which should carry the sun heat are missing. The sun heat reaches the earth in the same way as the light does, in the shape of electromagnetic waves, that is through rays propagating also into vacuum. A characteristic of these calorific rays is that they go across the air without any heating effect on it, and only when they meet a solid body they transform their energy into heat. As we learn from the sun in nature, radiating heat is the most natural condition of heating, assuring full biocompatibility, without moving dusts and bacteria and without deionising the air.