Thermodynamic methods of flow analysis taking into account the irreversibility of processes

It is shown that the change in the total energy of flows of a continuous medium in time includes not only the change in internal energy due to "internal" and "external" heat exchange (taking into account dissipation), but also the dual effect of both the dissipative part of the power of viscous friction forces and the non-dissipative part of the mechanical power spent on the deformation of the volumes of the medium under the action of pressure. In addition, the change in the kinetic energy of the fluid in time occurs due not only to mass forces, but also due to both the second non-dissipative part of the mechanical power of the forces of unbalanced hydrodynamic pressure on the movement of the elements of the medium, and the non-dissipative part of the power of viscous friction forces, which is responsible for the formation of a particular distribution of kinetic energy between elementary volumes of the fluid, i.e. the formation of velocity profiles in the flows. As an example, the dissipation of mechanical energy in laminar fluid flows is evaluated, and an example of solving the problem using the variational approach of thermodynamics of irreversible processes is also given.