From the paragraph provided, extract the mechanisms of heat transfer.

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.

The mechanisms of heat transfer include thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes, although engineers also consider mass transfer in the form of advection a form of heat transfer.