In the previous lecture, we considered the conservation of total mass over a CV, by applying the general Reynolds Transport theorem. Now, we obtain the differential form of the equation, also known as the continuity equation. Consider CV of
(Fig. 13a)
CV is bound by six CSs.
fluid- density
Consider CS marked 1: Rate of mass-in:
(It is equivalent to to of the Reynold’s transport theorem)
CS marked 2: Rate of mass-out:
fluid- density 
of the Reynold’s transport theorem)
