Thermodynamics is the study of the conversion of energy between two forms, heat and work. However, its beginnings date back long before these three concepts were established: for a long time, it was only a matter of focusing on the nature of heat. In other words, what exactly does “hot” mean? Can it be measured?
The first reflections on the nature of matter and fire date back to ancient Greece and already gave rise to atomic theory. But these were mainly philosophical constructions, based more on an organized spiritual view of the world than on actual observations.
It was not until the 17th century that serious research on this subject began. The concept of temperature, which is easier to grasp than heat, was initially the focus of attention. Designing a thermometer indeed raises many engineering and physics problems: how to link this idea of “temperature” to an observable phenomenon directly, in a predictable and reproducible way?
During these years and until 1850, thermodynamics remained at the macroscopic scale – there was no mention of atoms or molecules yet. It generated a lot of interest because it directly addressed phenomena of friction and heat transfer, which only occur in one direction, and which a Newtonian mechanistic view of the universe cannot explain.
The great development of thermal machines, at the beginning of the 19th century, caught science off guard. Early engines pumped water out of mines, but thermodynamics –which did not even bear its name at the time– could not explain how. It would take about thirty years before theory caught up with practice and a coherent vision of thermodynamics was established, allowing, for example, to predict an engine’s efficiency.
In 1865, German physicist Rudolf Clausius concluded nearly a century of trial and error by making explicit the foundational principles of what would come to be known as “thermodynamics”: what we now know as the two laws. In doing so, he generalized his observations on a gas balloon to the entire universe. On their side, the Scottish James Clerk Maxwell and the Austrian Ludwig Boltzmann reconciled thermodynamics with particle physics by working at the microscopic level. As the 20th century progressed, the concept of uncertainty became accepted and thermodynamics became a matter of probabilities and quantifying disorder; it even laid the physical foundations of information theory.
In the meantime, the industrial revolution had taken place. Moving away from water pumps, the heat engine transitioned to powering locomotives, then ships, automobiles, electrical generators, and aircraft. Our way of life, in which human physical strength is no longer of any importance, shows how dependent we have become on the power and precision that this engine provides. In essence, it is the reason why our environment differs so much from that of our ancestors, and from what our descendants will experience. Thermodynamics helps us understand the bewildering operation of this machine, which is both ordinary and frightening.
During this series of ten chapters on Engineering Thermodynamics, we will progress from the elementary behavior of fluids up to the theory of engines – with the objective of providing students with a good understanding of the operation of heat engines and a solid foundation to later study engine design and fluid mechanics.