The thermal energy, also known as caloric energy or calorific, is one that manifests itself in the form of heat. It is, however, a product of the movement or vibration of the 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. For instance: the chimneys, the Sun, the hot springs.
This type of energy is measured, like the others, in joules (J), according to the international system, although it is also usual to speak of calories: 4.18 joules, the amount of caloric energy necessary to raise a gram of water by one degree centigrade.
The amount of thermal energy in a system, as will be supposed, it 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 more its temperature will rise, until it reaches that necessary for a phase change: the water evaporates and goes from liquid to gaseous.
Thermal energy transmission
Thermal or heat energy can be transmitted from one medium to another or from one body to another in three specific ways:
- Radiation heat transmission. In this first case, the thermal energy moves through electromagnetic waves, just as it happens with the energy of the Sun. It is also what happens when we turn on the heating: the air is radiated with heat and the temperature rises.
- Heat transmission by conduction. This case occurs when a hot body comes into direct physical contact with a colder one, causing heat to be transmitted and temperatures equalize. This does not happen if the initial temperature is the same.
- Heat transmission by convection. This is the name given to the movement of hot particles in a colder environment, such as the wind: the moving air contains particles at a higher temperature that make us perceive the whole as hot air.
Examples of thermal energy
- Boil the water. As we said before, by introducing heat from a flame to 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 remove it from the freezer, the heat from the environment will radiate towards the solid until it becomes liquid water again.
- Chimneys. A fireplace is nothing more than a place in which a constant burning of organic matter is maintained so that the heat energy produced by the fire radiates to the joint rooms and keeps the house warm.
- Heaters. Useful to keep the 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.
- Sun. The largest source of thermal energy available to us is the sun, whose constant combustion processes radiate enormous amounts of heat and light to the surrounding universe. Cold-blooded animals take advantage of this energy source, for example, exposing themselves to sunlight to warm their bodies.
- The atomic bomb. Atomic bombs and their peaceful version, nuclear power plants, do nothing but produce atomic chain reactions (controlled in the case of power plants and uncontrolled in the case of bombs) to generate large amounts of heat energy from the alteration of the fundamental energies of the atom.
- Homemade thermos. A thermos full of hot coffee, for example, is ideal for observing the caloric energy that radiates (if we bring our hand closer to it) and that which is conserved (if we have a cup). This occurs because the material of the thermos prevents or considerably reduces heat radiation and preserves the temperature of the liquid.
- Baking ovens. The ovens work from the concentration of thermal energy to increase the temperature and exert changes in the food (cook it). This energy comes from the transformation of electrical energy (by resistors) or from the continuous combustion of natural gas.
- The human body. The chemical reactions that take place within our body, including our own breathing, generate an amount of thermal energy that maintains our body temperature around 37 ° C. That energy is perceptible and transmittable, in fact the coats work by 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 common 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 surfaces. Kinetic energy and friction can often be converted to heat energy, such as when we repeatedly rub our bare hands and feel the friction raise 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 massages.
- A running engine. Internal combustion engines generate abundant thermal energy, since the controlled explosion inside them and the electrical flow of many of their parts, as well as the constant movement of the pistons, transform all the energy they handle into heat. This heat energy can be felt by putting your hands on the hood when the car has been running.
- An incandescent light bulb. The passage of electricity in the filament of an incandescent bulb produces light (yellow), but it also produces heat: that is why it is difficult to change a bulb that has been on for a long time, its surface has accumulated the thermal energy that radiates from the passage of electrons.
- Casting of metals. In metallurgy, the metal solids that are worked are exposed to extremely high temperatures in large smelting furnaces. This is to increase its thermal energy to the point of forcing, as in the example of water, 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 excess heat energy into the environment.
- Environmental water vapor. In places with high humidity, where the air is loaded with water particles, the heat is perceived much more than in drier places, giving rise to a high thermal sensation. This is due to the fact that the water in suspension is heated and by convection of the thermal energy makes us perceive the environment at a higher temperature than it is.
- Hot springs. Under the earth’s crust there is water in reservoirs subjected to high pressures and high temperatures, which when sprouting towards the surface becomes thermal waters. These liquids have such thermal energy that they can melt icy layers upon reaching the surface, causing large jets of steam (geysers).