# A Guide to Thermodynamics

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## Basics

Thermodynamics is a physical science describing how systems change when they interact with each other or their surroundings. These interactions occur through transfer of energy and can be studied either at the macroscopic scale, through changes in temperature, pressure and volume, or at the micro-scale, by analyzing the collective motion of their particles using statistical methods.

The field was firstly developed due to the need of increased steam engine efficiency in the early 19th century. The famous French physicist Nicolas Léonard Sadi Carnot (1824), often described as the “Father of thermodynamics,” was the first to study heat engines through a scientific scope and laid the foundations for the second law of thermodynamics through his well-known Carnot cycle.

Other fields of physics and chemistry also use thermodynamic principles, including chemical and mechanical engineering, aerospace engineering, biomedical engineering, materials science, and even economics. Visit these links to get to know the fundamentals of thermodynamics:

## Variables and Thermodynamic Processes

After having checked the basics, we are introduced to a series of thermodynamic processes that involve the change of all system’s state variables (temperature, volume, pressure) except one. For example, an isothermal process (Boyle’s law) occurs when the temperature is kept constant, the isobaric process (Charle’s law) occurs at constant pressure, and the isochoric process (Gay-Lussac’s law) when the volume is stable. There are other processes as well, such as the adiabatic, the isentropic, the isenthalpic, etc. All these take place with the exchange of heat and work between a given thermodynamic system and its enviroment.

Discover more about processes and terms such as energy, heat, entropy and enthalpy in the following articles:

## The Four Principles or Laws

The field involves a set of four laws whose main role is to define the physical quantities of temperature, heat, energy, and entropy, and to describe how the transfer of energy as heat and work takes place in thermodynamic systems.

These four laws summarize all the important thermodynamic principles and can be expressed in various forms. They are known as the zeroth, first, second, and third law of thermodynamics and are considered to be fundamental physical laws, applicable in other natural sciences as well.

For more details visit the articles related to each law correspondingly and learn more about entropy, the physical quantity introduced by the third law:

## Cycles and Engines

Thermodynamic cycles are nothing more but a succession of thermodynamic processes that transfer heat and work between a given system and its environment. The combination of any of the above processes form a cycle that works in accordance to the four laws mentioned earlier. Their importance lies in the fact that they are actually the basis for the function of heat engines. The most simple and well-known are the Carnot cycle, the Ericsson cycle, the Otto, and the Diesel cycle:

## Applications

Apart from being important theoretical tools, the principles of thermodynamics have been used by scientists for a wide range of applications since the early 19th century. Many technological wonders and everyday appliances are based on these principles: internal combustion engines and jet engines, (cars, motorcycles, trucks, ships, aeroplanes), air and gas compressors, blowers, fans, heat exchangers, evaporators, condensers, air-conditioning systems, radiators, coolers, heaters, thermometers, refrigerators and the list goes on and on.

Some of these applications are described here in more detail:

## Final Considerations

As mentioned earlier, apart from the theory for studying a system’s interactions with its environment, the field also provided the principles for the operation of the first steam or heat engines. But, thermodynamics has much more to offer. A wide range of phenomena occurring in nature, within biological systems, ecosystems, and the universe itself could find some interesting explanations here.

Thermodynamics is a very promising field that is still evolving; it should continue to provide us with new perspectives for science, nature, and even our own lives.

## References

• Introduction to Thermodynamics, Canteach.Candu.Org
• Author’s experience and expertise