Thermodynamics, what it is and its applications
Thermodynamics is a science based on the study of energy. Thermodynamic processes occur daily in everyday life, in homes, in industry, with the transformation of energy, such as in air conditioning equipment, refrigerators, cars, boilers, among others. Hence the importance of the study of Thermodynamics, based on four basic laws that establish the relationships between the quality and quantity of energy, and the thermodynamic properties.
To understand the laws of Thermodynamics, in an easy way, one has to start from some basic concepts that are exposed below, such as energy, heat, temperature, among others.
We invite you to see the article The Power of Watt's Law (Applications - Exercises)
Thermodynamics
A Little History:
Thermodynamics studies the exchanges and transformations of energy in processes. Already in the 1600s Galileo began to carry out studies in this area, with the invention of the glass thermometer, and the relationship of the density of a fluid and its temperature.
With the industrial revolution, studies are carried out to know the relationships between heat, work and the energy of fuels, as well as to improve the performance of steam engines, emerging thermodynamics as a study science, starting in 1697 with the Thomas Savery's steam engine. The first and second laws of thermodynamics were established in 1850. Many scientists such as Joule, Kelvin, Clausius, Boltzmann, Carnot, Clapeyron, Gibbs, Maxwell, among others, contributed to the development of this science, "Thermodynamics."
What is thermodynamics?
Thermodynamics is a science that studies energy transformations. Since initially it was studied how to transform heat into power, in steam engines, the Greek words "thermos" and "dynamis" were used to name this new science, forming the word "thermodynamics". See figure 1.
Thermodynamic Applications
The area of application of thermodynamics is very wide. The transformation of energy occurs in multiple processes from the human body, with the digestion of food, to numerous industrial processes for the production of products. In homes there are also devices where thermodynamics is applied to irons, water heaters, air conditioners, among others. The principles of thermodynamics are also applied in a wide variety of other fields, such as in power plants, automobiles, and rockets. See figure 2.
Basics of Thermodynamics
Energy (E)
Property of any material or non-material body or system that can be transformed by modifying its situation or state. It is also defined as the potential or the ability to move matter. In figure 3 you can see some energy sources.
Forms of energy
Energy comes in many forms, such as wind, electrical, mechanical, nuclear energy, among others. In the study of thermodynamics, kinetic energy, potential energy and internal energy of bodies are used. The kinetic energy (Ec) is related to the speed, the potential energy (Ep) with the height and the internal energy (U) with the movement of the internal molecules. See figure 4.
Heat (Q):
Transfer of thermal energy between two bodies that are at different temperatures. Heat is measured in Joule, BTU, pound-feet, or in calories.
Temperature (T):
It is a measure of the kinetic energy of the atoms or molecules that make up any material object. It measures the degree of agitation of the internal molecules of an object, of its thermal energy. The greater the movement of the molecules, the higher the temperature. It is measured in degrees Celsius, degrees Kelvin, degrees Rankine, or degrees Fahrenheit. In figure 5 the equivalence between some temperature scales is presented.
Thermodynamic Principles
The study of energy transformations in thermodynamics is based on four laws. The first and second laws are related to the quality and quantity of energy; while the third and fourth laws are related to thermodynamic properties (temperature and entropy). See figures 6 and 7.
First Law of Thermodynamics:
The first law establishes the principle of conservation of energy. Energy can be transferred from one body to another, or changed to another form of energy, but it is always conserved, so the total amount of energy always remains constant.
A skating ramp is a good example of the Law of Conservation of energy, where it is found that energy is not created or destroyed, but is transformed into another type of energy. For a skater like the one in figure 8, when only the gravitational force influences, we have to:
- Position 1: When the skater is at the top of the ramp, he has internal energy and potential energy due to the height he is at, but his kinetic energy is zero since he is not in motion (speed = 0 m / s).
- Position 2: As the skater begins to slide down the ramp, the height decreases, decreasing the internal energy and the potential energy, but increasing his kinetic energy, as his speed increases. The energy is transformed into kinetic energy. When the skater reaches the lowest point of the ramp (position 2), his potential energy is zero (height = 0m), while he acquires the highest speed in his journey down the ramp.
- Position 3: As the ramp goes up, the skater loses speed, decreasing his kinetic energy, but the internal energy increases, and the potential energy, as he gains height.
Second law of thermodynamics:
The second law is related to the "quality" of energy, in the optimization of the conversion and / or transmission of energy. This law establishes that in real processes the quality of energy tends to decrease. The definition of the thermodynamic property "entropy" is introduced. In the statements of the second law, it is established when a process can occur and when it cannot, even if the first law continues to be fulfilled. See figure 9.
Zero Law:
The zero law states that if two systems in equilibrium with a third they are in equilibrium with each other. For example, for Figure 10, if A is in thermal equilibrium with C, and C is in thermal equilibrium with B, then A is in thermal equilibrium with B.
Other concepts of the Termodynamics
System
Part of the universe that is of interest or study. For the cup of coffee in Figure 11, the "system" is the content of the cup (coffee) where the transfer of thermal energy can be studied. See figure 12. [4]
Environment
It is the rest of the universe external to the system under study. In Figure 12, the coffee cup is considered the "border" that contains the coffee (system) and what is outside the cup (border) is the "environment" of the system.
Thermodynamic Equilibrium
State in which the properties of the system are well defined and do not vary over time. When a system presents thermal equilibrium, mechanical equilibrium and chemical equilibrium, it is in "thermodynamic equilibrium". In equilibrium, a system cannot modify its state unless an external agent acts on it. See figure 13.
Walls
Entity that allows or prevents interactions between systems. If the wall allows the passage of substance, it is said to be a permeable wall. An adiabatic wall is one that does not allow heat transfer between two systems. When the wall allows the transfer of thermal energy, it is called the diathermic wall. See figure 14.
Conclusions
Energy is the ability to move matter. This can be transformed by modifying its situation or state.
Thermodynamics is a science that studies the exchanges and transformations of energy in processes. The study of energy transformations in thermodynamics is based on four laws. The first and second laws are related to the quality and quantity of energy; while the third and fourth laws are related to thermodynamic properties (temperature and entropy).
Temperature is a measure of the degree of agitation of the molecules that make up a body, while heat is the transfer of thermal energy between two bodies that are at different temperatures.
Thermodynamic equilibrium exists when the system is simultaneously in thermal equilibrium, mechanical equilibrium and chemical equilibrium.
Thank-you note: For the development of this article we have had the honor of having the advice of the Ing. Marisol Pino, Specialist in Industrial Instrumentation and Control.