The thermal energy , also known as heat energy or heat is that which manifests itself as heat . It is, however, a product of the movement or vibration of atoms, so it is a manifestation of the internal energy of the system, which is nothing more than the accumulated kinetic energy of the particles.
This type of energy is measured, like the others, in joules ( J ), according to the international system, although it is also usual to talk about calories: 4.18 joules, the amount of caloric energy needed to raise a gram of one degree of a degree Water.
The amount of thermal energy in a system, as will be assumed, has directly to do with the temperature exhibited by it. Thus, the more thermal energy (heat) we introduce to a container with water , for example, the higher its temperature will rise, until reaching the necessary for a phase change: the water evaporates and passes from liquid to gaseous.
Transmission of heat energy
Thermal or caloric energy can be transmitted from one medium to another or from one body to another in three specific ways:
- Transmission of heat by radiation. In this first case the thermal energy is displaced by electromagnetic waves, as is the case with the sun’s energy. It is also what happens when we turn on the heating: the air is radiated from heat and the temperature rises.
- Heat transmission by conduction. This case occurs when a hot body comes into direct physical contact with a cooler body, resulting in heat being transmitted and temperatures being equated. This does not happen if the initial temperature is the same.
- Transmission of heat by convection . This is the name given to the displacement of hot particles in a colder environment, such as wind: the air that moves contains particles at a higher temperature that make us perceive the whole as hot air.
Examples of heat energy
- Boil the water . As we said earlier, by introducing heat from a flame into a container of water, we can raise the temperature by multiplying the thermal energy of the system (its internal energy) to force the water to a phase change ( evaporation ). The same happens with ice: if we extract it from the freezer, the heat from the environment will radiate towards the solid until it becomes liquid water again.
- Fireplaces . A chimney is only a place where a constant organic matter combustion is maintained so that the heat energy produced by the fire radiates to the joint rooms and keeps the house warm.
- The heaters. Useful to maintain water at an ideal temperature, electric heaters operate based on a set of metallic resistances that transform electrical energy into heat energy, increasing the temperature of the water to the proper point.
- The sun . The largest source of heat energy available to us is the sun, whose constant combustion processes radiate enormous amounts of heat and light to the universe that surrounds it. Cold-blooded animals take advantage of this energy source, for example, by exposing themselves to sunlight to warm their body.
- The atomic bomb . The atomic bombs and their pacific version, the nuclear power plants, do nothing but produce atomic reactions in chain (controlled in the case of power plants and without control in the case of pumps) to generate large amounts of heat energy from the alteration of the fundamental energies of the atom .
- The homemade thermos . A thermos filled with hot coffee, for example, is ideal for observing the caloric energy that radiates (if we put our hands close) and the energy that is conserved (if we drink a cup). This happens because the thermo material prevents or reduces the heat radiation considerably and preserves the temperature of the liquid.
- The cooking ovens . The ovens work from the concentration of thermal energy to increase the temperature and exercise changes in food (cooking). This energy comes from the transformation of electrical energy (by resistances) or from the continuous combustion of natural gas.
- The human body . The chemical reactions that take place inside our body, including our own breathing, generate a quantity of thermal energy that keeps our body temperature around 37 ° C. That energy is perceptible and transmissible, in fact the coats work preventing the escape of that heat through the surface of the skin.
- The combustion of organic matter . Burning wood, coal or other flammable organic substances is a method of obtaining thermal energy usual in the history of mankind. In fact, today that heat is used to boil water which in turn mobilizes the turbines that generate electricity.
- The rubbing of the surfaces . The kinetic energy and friction can often become caloric energy, as happens when we repeatedly rub our bare hands and feel how friction raises the temperature. This movement increases the thermal energy and can then be transmitted by contact, if we apply freshly rubbed hands on another part of the body, as in the massages.
- A running engine . The internal combustion engines generate thermal energy in abundance, since the controlled explosion in its interior and the electric flow of many of its parts, as well as the constant movement of the pistons, transform into heat all the energy they handle. This thermal energy can be perceived by placing your hands on the hood when the car has been in operation.
- An incandescent light bulb . The passage of electricity in the filament of an incandescent bulb produces light (yellow), but also produces heat: that’s why it costs to change a bulb that was on for a long time, its surface has accumulated thermal energy that radiates the passage of electrons.
- The melting of metals . In metallurgy, the metallic solids that are worked are exposed to very high temperatures in large smelting furnaces. This is to increase its thermal energy to the point of forcing, as in the water example, a phase change. Thus, the metal becomes liquid and can be mixed or molded. During the time it takes to cool and solidify again, the metal will radiate the surplus of thermal energy to the environment.
- The environmental water vapor . In places with high environmental humidity, in which the air is loaded with water particles, the heat is perceived much more than in the drier places, giving rise to the elevated thermal sensation. This is because the water in suspension is heated and by convection of the thermal energy we perceive the environment at a higher temperature than it is.
- The thermal waters . Under the earth’s crust there is water in deposits subjected to high pressures and high temperatures, which when springing to the surface becomes thermal waters. These liquids have such thermal energy that they can melt frozen layers when they reach the surface, causing large jets of steam (geysers).