Continuity equation describes the phenomenon of fluid flow through a pipe converse mass.

Let us consider the conservation of mass in closed system. So, we get the following equation-

A_{1}V_{1}_{1}t = A_{2}V_{2}_{2}t

Or,

A_{1}V_{1}_{1} = A_{2}V_{2}_{2}

Where,

A_{1} ,A_{2} = Cross-sectional area at inlet and outlet of the given pipe

V_{1} ,V_{2} = Velocities at inlet and outlet of pipe

_{1} ,_{2} = Densities of liquid at inlet and outlet of pipe

Consider Fig. 4.4 shows flow of an incompressible fluid,

In case of incompressible fluid, we know that densities are same at inlet and outlet-

Hence,

_{1} =_{2}

From the above equation,

**A _{1}V_{1}**

**=**

**A**

_{2}V_{2}