Molecular Hydrodynamic: A Physical Approaches

The old and better known problem of gas flow between two vessels ruled by vacuum valve is discussed. An analysis based on combination of hydrodynamic and molecular physics approaches. The new notion of hydrodynamic degree of freedom is introduced to explain the results of experiments with water vapor flow. These experiments have been showing the unusual behavior of adjacent vapor samples. The construction of explanation used the concept of weak discontinuity for gas discharge that was consequence of valve operation. Euler’s equation was discussed from molecular point of view.