- What is heat transfer?
- Driving
- Convection
- Radiation
- Insulators and radiation barriers
- Units of measurement of heat transfer
We explain what heat transfer is and how it occurs by conduction, convection and radiation. In addition, insulators and measures.
Heat is always transferred from higher to lower temperature systems.What is heat transfer?
It is called heat transfer, heat transfer, or heat transfer. heat to thephysical phenomenon which consists of the transfer of heat energy from one medium to another.
This occurs when twosystems that are at differenttemperatures are put in contact, allowing the flow of energy from the point of highest temperature to the lowest, until reaching athermal equilibrium, in which the temperatures are equalized.
The heat transfer process is unstoppable (it cannot be stopped) although it can be slowed down (it can be slowed down), using bars and insulators. But as long as there is a difference in heat in the universe, the heat will tend to transfer through the available media. Depending on them, said transfer may occur in three modes: conduction, convection and radiation.
Driving
Heat conduction is often used for cooking food.Conduction is called the transfer of heat through the direct contact of the particles of one material with those of another, without transferring matter between the bodies. Occurs in all aggregation states: solid, liquid or gaseous, although in the latter two convection is usually preferred.
The amount of heat that is transferred through conduction is determined by Fourier's Law, according to which the rate of heat transfer through a body is proportional to the temperature gradient that exists in it.
A simple example is seen in an electric stove: the burner is heated by the effect of electrical resistances and that heat is transferred by conduction to the pan that we deposit on it and, in turn, the pan will do the same with the food what are we going to cook.
It also happens when, by accident, we touch the hot pan with our hand: the heat will transfer to our skin on contact, causing a burn.
Convection
Convection is similar to conduction, except that it occurs in cases where a fluid receives heat and moves to transmit it within a space where it is contained. Convection is the transport of heat by means of movement of a fluid, be it gaseous or liquid.
This transfer occurs in the terms set forth by Newton's Law of Cooling, which states that a body loses its heat at a rate proportional to the difference in temperature between the body and its surroundings.
A clear example of this occurs when we heat water in a container. The heat transferred by conduction from the container to the liquid will heat the portions that are in direct contact with it, which will rise and force other cold portions of the liquid to take their place, thus heating the container evenly. Water.
Radiation
The last type of heat transfer is also the only one that can occur in the absence of contact and, therefore, also of a physical medium, that is, in a vacuum.
This is because its origin is in the thermal movement of the particles loaded with thematter, which triggers the emission of electromagnetic particles, that is, of thermal radiation, its intensity being dependent on its temperature and the length waveform of the radiation considered.
Generally, bodies in this situation emit ultraviolet radiation, but from certain temperatures they can emit radiation in the visible spectrum, that is, light. The amount of heat radiated in this way can be determined by the Stefan-Boltzmann Law.
Every day we observe the best example of thermal radiation: the Sun. Despite being 149.6 million kilometers from our planet, the temperature of the Sun is so high that it radiates enormous amounts of light and heat into space.
Both things reach the land surface and they keep it warm and illuminated, with wavelengths ranging from ultraviolet to infrared, obviously going through the entire visible spectrum.
Insulators and radiation barriers
As we have said, the heat transfer cannot be prevented, but it can be slowed down, through the use of certain and certain materials. This is because all materials transfer heat in one way or another, but not at the same rate or with the same ease.
Those that transmit it quickly and efficiently are called thermal conductors. On the contrary, those that do it slowly and laboriously, are called thermal insulators (conduction and convection) or barriers (radiation).
A clear example of insulating materials are those that make up a thermos, which allow keeping a hot or cold liquid for a longer amount of time, by slowing down its heat exchange with the environment.
Units of measurement of heat transfer
According to him International System of Measurements, the conductivity of a body is expressed in joules (J), as for the job and the Energy. However, there are other commonly used units to measure heat transfer:
- Kilocalories (Kcal). A calorie is defined as the amount of heat required to raise in a degree Celsius the temperature of a gram of water. It is a measure often used in nutrition to measure the chemical energy contained in food. One kilocalorie equals 1000 calories.
- BTU (from English British Thermal Unit or British thermal unit). It is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit, which is equivalent to 252 calories. This measure is commonly used in English-speaking countries, mainly the United Kingdom and the United States.