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Sunday, 2 September 2018

FRICTIONAL LOSS IN PIPE FLOW

We were discussing the concept of laminar and turbulent flow and also the basics of Reynolds experiment, in the subject of fluid mechanics, in our recent posts. 

Now we will go ahead to find out the basics of frictional loss in pipes, in the subject of fluid mechanics, with the help of this post. 

Frictional loss in pipes

As we are quite aware that when liquid flows through a pipe, velocity of the liquid layer adjacent to the pipe wall will be zero. Velocity of liquid will be increasing from the pipe wall and therefore there will be produced velocity gradient and shear stress in the liquid due to viscosity of liquid. 

This viscous action will cause the loss of energy which will b termed as frictional loss or loss of head due to friction. 

Head loss in pipe flow system due to viscous effect i.e. due to friction will be termed as major head loss and will be indicated by h L-Major

Frictional head losses are losses due to shear stress on the pipe walls. Frictional head losses i.e. major head losses in pipe flow problem will be calculated with the help of Darcy-Weisbach formula as mentioned below. 

Darcy-Weisbach formula will be used to calculate the major loss in pipe flow, it does not matter that pipe is horizontal, vertical or on inclined plane. 

Friction factor as mentioned above will be determined on the basis of type of flow i.e. Laminar flow, Transition flow and turbulent flow. We can refer below equations in order to determine the friction factor. 

On the basis of Reynolds experiment, William Froude had concluded the following laws as mentioned here. 
  1. Frictional resistance for turbulent flow will be proportional to the Vn, where value of n will be in the range of 1.5 to 2. 
  2. Frictional resistance for turbulent flow will be proportional to the density of the fluid. 
  3. Frictional resistance for turbulent flow will be proportional to the surface area in contact. 
  4. Frictional resistance for turbulent flow will not be dependent over value of pressure. 
  5. Frictional resistance for turbulent flow will be dependent over the nature of the surface in contact. 

Further we will go ahead to derive the expression of loss of head due to friction in pipes, in the subject of fluid mechanics, with the help of our next post. 

Do you have any suggestions? Please write in comment box. 

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google 

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