Who discoved thermodynamics?

Answer 1

That question is as broad as asking "Who discovered physics?" There were many individuals who contributed key elements of theory, experimental data, practical applications, and mathematics to the field of study we call "thermodynamics".

It might be argued that thermodynamics as a science started with the work of Otto von Guericke building vacuum pumps and Robert Boyle & Robert Hooke who built on his work to develop some of the first equations of state, noting that for a gas at fixed temperature, changes in pressure and volume are inversely proportional (which is essential the basis of the Ideal Gas Law). Concepts of heat capacity and latent heat of phase change were developed by Joseph Black and James Watt - whose work made steam engines practical.

Nicolas Léonard Sadi Carnot collected and built on the work of these and other previous scientists and engineers to produce the first real treatise on thermodynamics (Réflexions sur la puissance motrice du feu et sur les machines propres à développer cette puissance - which, in English would be Reflections on the Motive Power of Fire and on Machines Fitted to Develop that Power) and thus is often referred to as the "father of thermodyamics" - but he could hardly be considered as the sole person to "discover" thermodynamics.

A list of the most significant would also include Lord Kelvin (William Thompson), Émile Clapeyron, Rudolph Clausius, James Maxwell, Ludwig Boltzman, Max Planck, Johannes Diderik van der Waals, Hermann von Helmholtz, J. Willard Gibbs, Gilbert Lewis & Merle Randall. This is hardly a complete list, but if you look at the contributions of each of these individuals you can see how credit for "discovering" thermodynamic must be broadly shared.

Answer 2

Benjamin Thomson (also known as Count Rumford)in 1798