When does colder mean hotter

Professor Nikolai Brilliantov from our Department of Mathematics has developed a theory to explain ‘heating by cooling’, where the temperature of a granular gas increases while the total energy drops down - a peculiar phenomenon which can be observed both on Earth and in space.

Granular gases are one of the few examples where this scientific mystery can be observed. These systems are widely spread in nature in the form of aerosols and smoke on the Earth, or in the form of interstellar dust, planetary rings and proto-planetary discs in space.

The stunning ‘heating by cooling’ effect corresponds, in physical terms, to a negative heat capacity. Aggregating granular gases is the second object in the world, after gravitating systems, which manifests this astonishing property.

Professor Brilliantov has elaborated a novel mathematical tool to explain this - generalised Smoluchowski equations. While classical Smoluchowski equations, which have been known for more than a century, deal with evolution of agglomerates concentration only, the new equations describe the evolution of the agglomerates temperature as well.

The direct microscopic modelling of the system, by extensive computer simulations, has confirmed the existence of this surprising regime and other predictions of the theory.

“Understanding different regimes of the evolution of aggregating granular gases is important to comprehend numerous natural phenomena where these systems are involved,” adds Professor Brilliantov.

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