Question

What happens when the velocity of liquid exceeds the critical velocity?

Answer 1

Hint: We need to know that the velocity with which the liquid flow changes from streamlined to turbulent flow is known as the critical velocity of the fluid. We need to discuss in detail the flow of liquid as its velocity exceeds the critical velocity.


Complete step by step solution:
Whenever we look at liquid we think about its speed as in how fast or slow it is flowing. There are two types of liquid flow namely streamline flow and turbulent flow. Streamflow is described by a single’s atom path in a fluid.
Streamline flow is known as laminar flow. A streamlined flow is steady, smooth and predictable. The physical properties like velocity, pressure etc. at each point remain constant. The flow consists of the lamina which has thin layers parallel to each other. In a streamlined flow, these layers of water are flowing on top of each other at different speeds.
Now when the velocity of the fluid increases gradually, the streamline flow continues to be straight and parallel to the pipe wall but once the velocity exceeds the critical point which can be called the breaking point, the flow becomes turbulent. The critical velocity can be calculated using the following problem
\[{v_c} = \dfrac{{k\eta }}{{r\rho }}\]
Where $k$ is Reynold’s number.
$\eta $ is the coefficient of viscosity of a liquid
$r$ is the radius of the flow
$\rho $ is the density of the liquid

Note: Note that turbulent flow is the opposite of the streamline flow. It is an irregular motion caused by high velocities or abrupt changes in velocities. Fluid is not passing in parallel fashion like in streamline flow and there is mixing in lateral layers of the flow.