Fluid Flow

What is Fluid Flow?

Fluid Flow is a part of fluid mechanics and deals with fluid dynamics. Fluids such as gases and liquids in motion is called as fluid flow. Motion of a fluid subjected to unbalanced forces. This motion continues as long as unbalanced forces are applied.

For example, if you are pouring a water from a mug, the velocity of water is very high over the lip, moderately high approaching the lip, and very low at the bottom of the mug. The unbalanced force is gravity, and the flow continues as long as water is available and the mug is tilted.

fluid flow

Types of Fluid Flow

Fluid flow has all kinds of aspects — steady or unsteady, compressible or incompressible, viscous or nonviscous, and rotational or irrotational, to name a few. Some of these characteristics reflect properties of the liquid itself, and others focus on how the fluid is moving.

Steady or Unsteady Flow: Fluid flow can be steady or unsteady, depending on the fluid’s velocity:

  • Steady: In steady fluid flow, the velocity of the fluid is constant at any point.
  • Unsteady: When the flow is unsteady, the fluid’s velocity can differ between any two points.

Viscous or Nonviscous Flow: Liquid flow can be viscous or nonviscous.

Viscosity is a measure of the thickness of a fluid, and very gloppy fluids such as motor oil or shampoo are called viscous fluids.

Fluid Flow Rate

The volume of fluid replaced in a given interval of time is called the fluid flow rate.
\(Mass\;flow\;rate = \rho \: A\; V\)
ρ = density
V = Velocity
A = area

\(Flow \; rate = Area \times Velocity\)

Fluid Flow Through a Pipe

The general capacity of the pipes varies on its size. The table given below shows the capacity of the flow of fluid based on its size.

Pipe size (in inch) Maximum Flow (in gal/min) Velocity (in ft/s) Head Loss in (ft / 100 ft)
2 45 4.3 3.9
2.5 75 5.0 4.1
3 130 5.6 3.9
4 260 6.6 4.0
6 800 8.9 4.0
8 1600 10.3 3.8
10 3000 12.2 4.0
12 4700 13.4 4.0
14 6000 14.2 4.0
16 8000 14.5 3.5
18 10000 14.3 3.0
20 12000 13.8 2.4
24 18000 14.4 2.1

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What are the main causes of water pollution in the Ganga river?