Fluid in motion
Introduction : In our daily life we come across a large number of activity which involve motion of a fluid like water flowing in a river, Crude oil flowing through a pipe, A flood in a river, etc. This activity involves liquid which is in motion. In this topic we are going to study the fluid which are in motion.
Hydrodynamics: The branch of mechanics which deals with the study of fluid in motion is called as hydrodynamics.
Terms related to hydrodynamics
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| Flow tube |
Flowline : The path traced by the molecule in a moving fluid is called as flowline.
Streamline : The curve whose tangent gives the direction of velocity of the flow at that point is called as streamline.
Flowtube : The imaginary boundary that bounds all the flowline is called as flowtube.
There are two types of flow :
1) Laminar or Streamline flow : The flow in which, velocity of each particle of fluid is same at a given point throughout the path is called as Laminar flow.
1) Turbulent flow: The flow in which, velocity of particle of fluid is not same throughout the path and changes continuously with time is called as Turbulent flow.
Critical Velocity and Reynolds number : When liquid is flowing slowly in a liquid, it is a streamline flow , the velocity may gradually change due to some physical factor. The minimum velocity beyond which the streamline flow becomes turbulent is called as critical velocity.
The expression for critical velocity is given by,
where,
Vc = Critical velocity
Rn = Reynolds number
ղ = Coefficient of viscosity
ρ = density of a fluid
d = diameter of a pipe
The flow of a fluid is also determine by a number called as Reynolds number which is given by,
Condition :
1) If the Reynolds number is less then 1000, the flow is laminar or streamline.
2) If the Reynolds number is greater then 2000, the flow is turbulent.
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