 Consider the steady state one-dimensional convection diffusion equation,

where formula_11 is the density, formula_12 is the velocity vector, formula_13 is the property being transported, formula_14 is the coefficient of diffusion and formula_15 is the source term responsible for generation of the property formula_13.Making the flux balance of this property about a control volume we get,

Here formula_19 is the normal to the surface of control volume.Ignoring the source term, the equation further reduces to