Thermal energy flux

As we already know, the total energy in the universe is conserved. Let us now focus our attention on the transfer of energy as heat (thermal energy) across system boundaries, with the clarity that the thermal energy, a form of energy, is not conserved. The transfer of heat due to molecular processes is called ‘conduction’. We have seen in the earlier chapters that constitutive equations govern some fluxes - Fick’s first law governs diffusion (mass flux) and Newton’s law governs laminar flow (momentum flux). Similarly, a constitutive equation known as ’Fourier’s law’ governs conduction (energy flux).