Thermodynamics: Core Of Industry

Although everybody has an intuitive feeling of what energy is, it is difficult to provide a precise definition of it. Thermodynamics is the branch that deals with the relationships between heat and other forms of energy. In particular, it describes how thermal energy is converted to other forms of energy and how it affects matter. The name thermodynamics originates from the Greek words therme (heat) and dynamis (power), which is most descriptive of the early efforts to convert heat into power. Today the same name is broadly described to include all aspects of energy and energy transformations, including power generation, refrigeration, and relationships among the properties of matter.

The fundamental principles of thermodynamics are originally expressed in four laws.

The first and second laws of thermodynamics developed in the 1850s, originally out of the works of William Rankine, Rudolph Clausius, and Lord Kelvin. And the third one was explained by chemist Walther Nernst during the years 1906-1912. One of the most fundamental laws of nature is the conservation of energy principle. It simply states that during an interaction, energy can change from one form to another but the total amount of energy remains constant. That is, energy cannot be created or destroyed. A rock falling off a cliff, for example, picks up speed as a result of its potential energy being converted to kinetic energy (Fig. 1). The conservation of energy principle also forms the backbone of the diet industry: A person who has a greater energy input (food) than energy output (exercise) will gain weight, on the contrary, a person who has a smaller energy input than output will lose weight. The change in the energy content of a body or any other system is equal to the difference between the energy input and the energy output.

Figure 1

The first law of thermodynamics is simply an expression of the conservation of energy principle which states that the total increase in the energy of a system is equal to the increase in thermal energy plus the work done on the system. This states that heat is a form of energy and is therefore subject to the principle of conservation. The second law of thermodynamics asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing the quality of energy. This, basically, means that heat energy cannot be transferred from a body at a lower temperature to a body at a higher temperature without the addition of energy. To concretize, a block of ice placed on a hot stove surely melts. Such a process is called irreversible because no slight change will cause the melted water to turn back into ice, and heat energy will never be transferred from ice to stove. To fully understand the third law of thermodynamics, an important term should be comprehended. This essential term is called entropy. Entropy helps to explain why physical processes go one way and not the other, so the second law can also be stated as that the total entropy of a system either increases or remains constant in any spontaneous process; it never decreases. Entropy is often described as a measurement of disorder or randomness that is unavailable for doing useful work. It is an extensive property of a thermodynamic system, which means its value changes depending on the amount of matter that is present. In a more scientific manner, it is the measure of a system’s thermal energy per unit temperature. It is usually denoted by the letter S and has units of joules per kelvin (J⋅K−1). Entropy can be positive or negative; a highly ordered system has low entropy. An ice example can be again provided to exemplify the situation. A block of ice will increase in entropy as it melts as it's easy to visualize the increase in the disorder of the system. Ice consists of water molecules bonded to each other in a crystal lattice. As ice melts, molecules gain more energy, spread further apart, and lose their structure to form a liquid. So, the ice loses its orderliness and possesses more randomness, hence, its entropy increases.

Coming back to the third law, it states that the entropy of a perfect crystal of a pure substance approaches zero as the temperature approaches zero. This is because as there is no heat energy at absolute zero, there can be no waste energy. Also, this can be interpreted by the definition of entropy, the measure of disorder, as a perfect crystal is by definition perfectly ordered. There is also the zeroth law of thermodynamics which states that if two bodies are in thermal equilibrium with some third body, then they are also in equilibrium with each other. This establishes temperature as a fundamental and measurable property of matter. In addition to the laws of thermodynamics, its engineering applications in the industrial world are also essential points.

All activities in nature involve some interaction between energy and matter; It is, therefore, difficult to imagine a field that has nothing to do with thermodynamics. Therefore, occupying a decent understanding of the basic principles of thermodynamics has long been an important part of engineering education. Thermodynamics is common in many engineering systems, industries, and other areas of life, and one does not need to go very far to see some application areas of it. An ordinary house is, to some extent, exhibits applications of thermodynamics. Many ordinary household tools and appliances are designed, in whole or in part, by using the principles of thermodynamics. Some examples include the electric or gas range, the heating, and air-conditioning systems, the refrigerator, the humidifier, the pressure cooker, the water heater, the shower, the iron, and even the computer and the TV.

Real Life Applications of Thermodynamics

On a larger scale, thermodynamics plays a major part in the design and analysis of automotive engines, rockets, jet engines, and conventional or nuclear power plants, solar collectors, and the design of vehicles from ordinary cars to airplanes. Even our energy-efficient homes are designed on the basis of minimizing heat loss in winter and heat gain in summer. To substantially comprehend these applications and actualize them in the best way possible requires engineering at its pinnacle. So, thermodynamics is actually a branch of engineering that has the potential to enlighten the concepts behind all scientific systems that industry actively uses.

-Güney Baver Gürbüz

References:

“Applications of Thermodynamics Laws. Carnot, Stirling, Ericsson, Diesel Cycles.” Bright Hub Engineering, 10 June 2009, www.brighthubengineering.com/thermodynamics/38344-thermodynamics-integral-part-of-our-life/#:~:text=All%20the%20refrigerators%2C%20deep%20freezers,run%20on%20various%20thermodynamic%20cycles.                                                                              
                                                                                                                                                                Lucas, Jim. “What Is Thermodynamics?” LiveScience, Purch, 8 May 2015, www.livescience.com/50776-thermodynamics.html.                                                                                                                                                                                                                                                                                                                                   
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                                                                                   “What Is Entropy?” RSC Education, 1 July 2009, edu.rsc.org/feature/what-is-entropy/2020274.article.