Next: Conservation of Momentum Up: Presenting the Hydrodynamic Equations Previous: Momentum Transport

Conservation of Mass

Considering mass, it is obvious that the rate of mass accumulation within any
finite volume equals the mass flux across the boundaries of the volume. In
absence of external sources and drains of matter the model must read2.6:

where is the mass density and
u is the velocity. Since we consider a
compressible medium, the compression term is generally non-zero, as opposed to the incompressible
case.

The mass may be found by integrating the density across the volume of
interest, i.e. sum the density in the parcels that make up the volume.

Peter Søndergaard & Jan Vittrup Hansen