According to the physical principles of thermodynamics, it is notable that temperature is something that is not constant in bodies but instead is transferred from one to another: the direction is always the same since heat passes from the objects of higher temperature to those of minor.
There are many mathematical formulas corresponding to physics and chemistry tending to explain these processes of heat transfer, but the central thing is that they occur under three different procedures: conduction, convection, and radiation.
What is conduction? Conduction is the process from which the heat propagates due to the thermal agitation of the molecules, without there being a real displacement of them. It is a very simple process to understand and at the same time ‘ invisible’ because only heat transfer occurs, with nothing visible physical.
Conduction is why objects in a more or less long time, eventually acquire the same temperature in its entirety. Some driving examples:
- Along the instruments to manipulate coal or other potentially very hot objects. If its extension were shorter, heat transfer would be faster and neither end could be touched.
- The ice in a rate of hot water melts by means of driving.
- By boiling water, the flame conducts the heat to the container and after a while allows the water to warm up.
- The heat that a spoon has when leaving it in a container and pouring an extremely hot soup over it.
- The knives and forks use a wooden handle to break with the conduction of heat.
Examples of Convection
What is convection? The convection is the heat transfer based on the actual motion of the molecules of a substance: here involves a fluid which can be gas or liquid.
The transmission convective heat may occur only in fluids where natural movement (the fluid extracts heat from the hot zone and changes densities) or forced circulation (through a fan the fluid moves), the particles can move transporting the heat without interrupting the physical continuity of the body. Here a series of convection examples:
- The heat transfer of a stove.
- Hot air balloons, which are held in the air by hot air. If it cools, the balloon immediately begins to fall.
- When the water vapor fogs the glass of a bath, by the hot temperature of the water when bathing.
- The hand or hair dryer, which transmits heat by forced convection.
- The heat transfer generated by the human body when a person is barefoot.
What is radiation? The radiation is the heat emitted by a body due to its temperature, in a process that lacks contact between bodies or intermediate fluids transported heat.
The radiation causes a body to be solid or liquid of higher temperature than another, occur immediately transfer heat to each other. The phenomenon is that of the transmission of electromagnetic waves, emitted by bodies at a higher temperature than absolute zero: the higher the temperature, the greater these waves will be.
That is what explains that radiation can only occur while the bodies are at a particularly high temperature. Next, a group of examples where radiation occurs:
- The transmission of electromagnetic waves through the microwave oven.
- The heat emitted by a radiator.
- Solar ultraviolet radiation, precisely the process that determines the Earth’s temperature.
- The light emitted by an incandescent lamp.
- The emission of gamma rays by a nucleus.
The processes of heat transmission increase and decrease the temperatures of the affected bodies, but also sometimes (as exemplified by ice) are responsible for the phenomena of phase changes, such as the boiling of water in steam, or the fusion of water in ice. Engineering concentrates many of its efforts to take advantage of this possibility of manipulating the state of bodies through the transmission of heat.