  Filtration of real gases described by Peng-Robinson equations of state in
3-dimensional space is studied. Thermodynamic states are considered as either
Legendrian submanifolds in contact space, or Lagrangian submanifolds in
symplectic space. The correspondence between singularities of their projection
on the plane of intensives and phase transitions is shown, and coexistence
curves in various coordinates are constructed. A method of finding explicit
solutions of the Dirichlet boundary problem is provided and the case of a
number of sources is discussed in details. The domains corresponding to
different phases are shown.
