FLOW THROUGH PIPES 

INTRODUCTION 

A sort of flow that occurs inside a closed conduit at a certain pressure is called flow-through pipes or fluid flow. Open channel flow is another form of flow. In various pipes and pipeline systems, these fluid flows are used to convey chemicals, petroleum products, gas products, sewage flows, home water supply, etc.

Because all real fluids have a certain degree of viscosity, the flow of all real fluids is known as viscous flow. The physical characteristics of the pipe and the external forces affecting the piping system by displacement and loads are similar to the properties of viscosity, which are characterized by the shear stresses or the frictional forces between the fluid layers and fluid to a solid surface. The pipe system is impacted in numerous ways by the flow of the fluid and the flow characteristics. 

HOW DO FLUIDS GO THROUGH PIPES ?

There is always some energy causing the fluid to flow, no matter where it is. The moving fluid has three main forms of energy: flow energy (pressure head), kinetic energy, and potential energy. There are essentially two reasons why fluids go via pipes.

In this case, where gravity energy changes into kinetic energy, the pipes are tilted to make the flow go downhill.

The second method is to produce a pressure differential using various types of pumps. by exerting pressure on the pipe that is greater at one end than the other. Fluids are accelerated into the discharge line by means of impellers, which are connected to the motor. This affects the system's internal flow rate. The pipe system it is attached to determines the pressure and flow rate that the pump will deliver. 

LOSSES OF ENERGY (HEAD) IN PIPES

When liquid is flowing through pipes, the liquid experience some resistance due to which some of the energy of liquid is lost.

Two types of losses

     1)    Major losses.

     2)     Minor Losses.

Major Losses	Minor Losses
Major losses due to friction and It’s calculated by - a)   Darcy-Weisbach equation b)   Chezy’s Formula	·       Head loss due to sudden enlargement ·       Head loss due to sudden contraction ·       Head loss at inlet/entrance of pipe ·       Head loss at outlet or exit of pipe ·       Head loss due an obstruction in pipes ·       Head loss due to bend ·       Head loss due to pipe fitting

  

        Major Losses

       Major Loss is defined as significant damage or destruction to the EG Facility or any portion of it caused by fire or other calamity, or the taking, requisitioning, or sale of    the use, occupancy, or title to the EG Facility or any significant portion of it as a result of any actual or threatened eminent domain proceeding or other action by any person or entity with the authority to evict.

   Darcy’s-Weisbach Equation :-

 According to the Darcy’s- Welsbach equations, the loss of head due to friction – 

Where, ' f ' function of Reynolds number or Darcy’s co-efficient of friction. Value of f is derived as under :-  

Reynolds number (R_e)

It’s a dimension less quantity therefore it does not have any unit.

Where,

  V = mean velocity of fluid flowing though pipes

d = dimeter of pipe

v = Kinematic viscosity of fluid

L = Length of pipe

p = Density of pipes

µ = Dynamic viscosity 

·       The value of Reynolds number decides, whether the flow is laminar and turbulent

·       In case of circular pipes, if R_e is < 2000, the flow is said to be laminar.

·       If R_e > 4000, then the flow is said to be turbulent flow.

·      If value of R_e is lies between 2000 to 4000 the flow changes from laminar to turbulent.

Modified Darcy-Weisbech Equation :-

 ·         If 'h,' is the loss of head due to friction and 'L' is the length of pipe, then, the ratio (hf/L)  called as loss of head per unit length of pipe and is denoted by i. 

 ·         This loss of head due to friction is calculated by using Chezy's formula, which gives average velocity of fluid as, 

Where,

                   ...... ( for Circular pipe)

c = Chezzy’s constant

l = Loss of head per unit length of time = (hf/L)

Fluid Mechanics and Machinery.

Factors Affecting on Fluid Friction Factor

 Factors affecting the value of friction factor are:

(a) Reynolds number (R_e) of pipe flow.

(b) Relative roughness of pipe. 

            (c) Temperature of fluid.

            (d) Density of fluid.

            (e) Density of fluid. 

 MINOR LOSSES :- 

             (1) Loss of head due to sudden enlargement:

Fig -1 

Consider a fluid flowing through a pipe, which has sudden enlargement as show

             in  Consider two sections 1-1 and 2 - 2 before and after enlargement.

     Let,

       P₁ =  Pressure Intensity at section 1-1

  V₁= Velocity of flow at section 1-1

     A₁ = Flow area of pipe at section 1-1

Let, P₂ V₂ and A₂ be the corresponding values at section 2-2.

The loss of head due to sudden enlargement is expressed as,

        

 

  (2) Loss of Head due to sudden contraction :

Fig -2

  Consider a fluid flowing in a pipe, which has a sudden contraction in area, Consider two  sections 1-1 and 2-2 before and after contraction respectively. As the fluid flows   from larger pipe to smaller pipe, the area of flow goes on decreasing and

  After section C-C, sudden enlargement of flow area takes place. Therefore, it can be  easily observed that, loss of head due to sudden contraction is actually due to sudden enlargement from vena-contracta section C-C to smaller pipe Section.   

  If the value of C_c is not given then, the loss of head due too sudden contraction is taken  as,

 (3) Loss of head at the entrance/inlet of pipe:

  Fig -3

•   This is the loss of energy head, which occurs at the inlet of pipe.
•   This loss is similar to the loss of head due to sudden contraction in flow area.
•   When a water tank or reservoir is connected to a circular pipe, the water enters the pipe  and leads to loss of head at entrance or inlet of pipe.

  This type of head loss depends upon the form or structure of entrance. For a sharp edge entrance, this loss is slightly more than a rounded or bell mouthed entrance. 

    (4) Loss of head at the exit/outlet of pipe: 

Fig - 4

  ·   This is the loss of head (or energy), which occurs at the outlet of pipe.

   ·   When the outlet of pipe carrying fluid is connected to a tank or reservoir, the loss of head occurs due to loss of velocity of fluid in the tank or reservoir.

   ·  Similarly, when the outlet of pipe is free to atmosphere, the velocity of fluid gets dissipated in the form of a free jet. It leads to loss of head at outlet of pipe. 

    (5) Loss of head due to bend in pipe :

Fig -5

   While passing through a bend in pipe, direction of flow changes suddenly. Therefore, the fluid flow gets separated from the inside boundary (surface) of pipe. The flow separation leads to change in velocity of flow and eddies are formed. This decreases the energy of flowing fluid, causing head loss.

   (6) Loss of head due to an obstruction in a pipe :

fig- 6

   Whenever there is an obstruction in a pipe, the loss of head (energy) takes place due to reduction in cross-sectional area of pipe at the place, where obstruction is present.  

   There is a sudden enlargement in the area of flow beyond the obstruction.

  It can be easily understood that, loss of head due to an obstruction in pipe is actually due to sudden enlargement in area of flow after obstruction, i.e. downstream-side. 

   (7) Loss of head due to various pipe fitting :

        Loss of head occurs due to various pipe fittings such as valves, couplings etc.

   Power Transimitted Through Pipes :

   Power is transmitted through the pipes by water or any other fluid flowing through them.  

   The amount of power transmitted depends upon,

   (a) Weight of fluid flowing through pipe.

   (b) Net head available at the end of pipe.

   We have, Weight of water flowing per second = w × Q.

    If the head available at inlet of pipe = H and Head lost due to friction = h_f   

   Then, net head available at outlet of pipe = h = H - h_f [Neglecting minor losses].

     Pipes in Series or Compound Pipe

     When two or more pipes of different length and dimeters are connected to each other to   form a pipe line the arrangement is called a Pipes in series or Compound Pipes.  

     

    Pipes in Parallel

    Sometimes, when quantity of fluid flowing per second (discharge) from one reservoir  to  another reservoir is to be increased, then, an additional pipeline is laid down along  with the existing one. Such an arrangement is called as "Pipes in parallel".

   Contributors :-

   1. Avdhut Adane

   2. Hariom Aher

   3. Archana Aldar

   4. Antara Vispute

   5. Sohan Bachhav

       

                

 

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