Happy New Year 2015

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Free and Forced Vortex flow with Examples

Vortex flow is defined as the flow of a fluid along a curved path or the flow of a rotating mass of fluid is known as Vortex flow. The following are the two types of Vortex flow:

1. Free Vortex Flow and
2. Forced Vortex Flow 

Free Vortex Flow

When no external torque is required to rotate the fluid mass that type of flow is called free vortex flow.

Examples:

• Flow of liquid through a hole provided at the bottom of the container
• Flow through kitchen sink
• Draining the bath tub
• Flow of liquid around a circular bend in pipe
• A whirlpool in a river
• The flow fields due to a tornado.

Forced Vortex Flow

Forced vortex flow is defined as that type of vortex flow in which some external torque is required to rotate the fluid mass.

Examples:

• Flow of water through the runner of a turbine
• Flow of liquid through the passage of impeller of centrifugal pumps
• Rotation of water in a washing machine

Pitot Tube

Pitot Tube is a device used for measuring the velocity of flow at any point in a pipe or a channel. The Pitot tube was invented by the French Engineer Henri Pitot.

The principle of Pitot tube is based on the Bernoulli's equation, where each term can be interpreted as a form of pressure. If the velocity of flow at a point becomes zero, the pressure there is increased due to the conversion of kinetic energy into pressure energy.

The pitot tube is robust and simple to use. In its simplest form, it consists of a glass tube bent at right angles.

What is an Orifice?

An orifice is a small opening provided on the side or bottom of a tank, through which a fluid is flowing. The opening can be of any shape or cross-section, like rectangular, triangular or circular. The orifices may discharge fluid into the atmosphere or from one tank to another.

Orifices are classified based on the shape or the cross-sectional area as:

• Rectangular orifice
• Circular orifice
• Triangular orifice and
• Square orifice

Orifices are classified based on the size of the orifice and the head of fluid above the orifice as:

• Small orifice and
  
• Large orifice

Depending on the shape of the upstream edge of the orifices, they are classified as:

• Sharp-edged orifice and
• Bell-mouthed orifice

They are also classified based on the nature of the discharge as:

• Partially submerged or drowned orifice
• Fully submerged or drowned orifice
  
• Free discharging orifices
  

Displacement thickness

Displacement thickness is a measure of boundary layer thickness. Displacement thickness is defined as the distance by which the boundary layer should be displaced to compensate for the reduction in flow rate on account of boundary layer formation. The concept of displacement thickness finds its application in the design of ducts and wind tunnels.