According to the physical principles of thermodynamics, it is notable that the temperature is something that is not constant in the bodies, but on the contrary is transferred from one to the other: the direction is always the same since the heat passes from the objects of higher temperature to those of lower.
There are many mathematical formulas corresponding to physics and chemistry that tend to explain these heat transfer processes, but the main thing is that they occur under three different procedures: conduction convection and radiation.
What is driving? The driving is the process from which heat spreads due to 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’ since only heat transfer occurs, with nothing physically visible.
The driving is why objects in a more or less prolonged time, eventually acquire the same temperature in its entirety. Some driving examples:
- Along with instruments for handling coal or other potentially very hot objects. If its extension was shorter, the heat transfer would be faster and neither end could be touched.
- Ice in a cup of hot water melts through conduction.
- By boiling water, the flame conducts heat to the container and after time allows the water to heat up.
- The heat that a spoon has when leaving it in a container and pouring extremely hot soup on it.
- Knives and forks use a wooden handle to break heat conduction.
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 heat without interrupting the physical continuity of the body. Here are a few examples of convection:
- Heat transfer from a stove.
- Hot air balloons, which are kept in the air by hot air. If it cools down, the balloon immediately begins to fall.
- When water vapor fogs the windows of a bathroom, due to 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.
See also: Examples of Thermal Balance
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 fluid carrying heat.
The radiation causes a body to be solid or liquid of higher temperature than another, occur immediately transfer heat from one to the other. The phenomenon is that of the transmission of electromagnetic waves, emanating from bodies at a higher temperature than absolute zero: the higher the temperature, then the higher those waves will be.
That is what explains that radiation can only occur as long as the bodies are at an especially high temperature. Here is 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) they are responsible for the phenomena of phase changes , such as the boiling of water in steam , or melting of water on ice. Engineering concentrates many of its efforts on taking advantage of this possibility of manipulating the state of bodies through the transmission of heat.
See also: Examples of Heat and Temperature