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After completing his secondary schooling, David Enskog entered Uppsala University. He continued to study there for his doctorate after taking his first degree. In 1917 he was awarded his Ph.D. and then he spent several years teaching in secondary schools and colleges.
In 1930 Enskog was appointed professor of mathematics and mechanics at the Royal Institute of Technology in Stockholm.
Enskog worked on the Maxwell Boltzmann equations. These had first been formulated by Maxwell in 1867 to describe the flow of molecules, momentum and energy of a gas. This was reformulated by Boltzmann in 1872 in terms of a velocity distribution function. Enskog began to work on this equation for his master's degree at Uppsala and made a remarkable prediction.
If a mixture of two gases is subjected to a temperature difference, the gas with the larger molecules concentrates at the lower temperature. A simple theory does not predict this behaviour. However Enskog predicted it in a paper written in 1911. In 1917 Chapman independently predicted it, but their theory was questioned until Chapman persuaded a chemist F W Dootson to conduct experiments; the theory was verified.
Hilbert published a new approach to the Maxwell Boltzmann equations in 1912. Enskog used Hilbert's methods to work out a series expansion of the velocity distribution function and wrote this up for his doctoral dissertation at Uppsala in 1917.
How to extend the Maxwell Boltzmann equation to include collisions of more than two bodies was not clear. However Enskog made an important advance in 1921, although it described the rather artificial situation treating molecules as hard spheres.
Chapman, who was still working on the Maxwell Boltzmann equations, saw the importance of Enskog's methods and developed them further. The book S Chapman and T G Cowling, The Mathematical Theory of Nonuniform Gases is the classic text on the modern kinetic theory of gases based on the approach by Enskog and Chapman. Although the advent of quantum theory was to lessen the impact of this theory, it was later seen to be still important in the new context.
Chapman recommended Enskog for the chair at the Royal Institute of Technology. However Chapman wrote later:
His transfer to a university chair seemed rather to bring him new duties than increased leisure, and this, with renewed illhealth, reduced his productivity in later years.
References (3 books/articles)