Flow Through Pipes

Authors: Shreyash Gurav, Parth Gurjar, Sumedh Habde, Adarsh Halake, Harsh Rikame

What is fluid ?

Fluid is defined as the substance which can continuously deform under an applied external flow. Fluids are liquid or gas and are taken into consideration as per the given condition. Fluids occupy the space, contain the finite mass and are tangible.

Fluid flow inside the pipe

Fluid flow is the motion of fluid caused due to various unbalanced forces. The flow of the real fluids is viscous flow. Viscous properties of the fluids are mainly characterized  by frictional forces or the shear stresses in between fluid to solid surface and fluid layers. Flow through pipe has household as well as industrial applications. Applications of fluid flow in the pipes are to transport petroleum and gas products, household water supply and to transport the chemicals. 

Type of fluid flow as well as the flow parameters (displacement and loads caused by the external forces) affect the piping system.

How does the fluid flow in the pipes

There should be some energy that will cause the fluid to flow. Flow energy, Kinetic energy and Potential energy are the energies that can make a fluid flow. Mainly there are two causes that make the fluid flow.

1. By tilting the pipe downhill so that the fluid flows due to the gravitational action. In this case gravitational energy gets transformed into kinetic energy. 

2. By creating the pressure difference using different types of pumps.This method can be used by applying the higher pressure at one end and lower at the other, as a result the flow of fluid will be from higher to lower pressure. Pumps are used in this system which uses the impellers, then they are connected to motor to accelerate the given fluids into the discharge line, and this makes the flow rate inside the system. 

Source - tec-science

Flow Rate

Flow rate is the volume of fluid that passes through the cross section of pipe in the given time. Flow Rate depends upon the area of pipe through which the liquid is passing, velocity of fluid, and the type of liquid.

Formula,

Flow Rate (Q) = Av

Where, Q=Flow Rate (in m3 /s)

             A=Area of the pipe (in m2)

             v=Velocity of the fluid (in m/s)

Types of flow

 

The types of flow in a pipe can be subdivided as laminar and turbulent flow.

1. Laminar Flow - The flow in which the layers slowly move in the pipe without mixing with each other. Fluid flows in laminar flow when the velocity of the fluid is low or the fluid is very much viscous.

Laminar flow can be divided into three types.

1. Unidirectional laminar flow

2. Pulsatile laminar flow

3. Oscillatory laminar flow 

      

          Examples of laminar flow :

           Oil flow through a tube

           Blood flow through the capillaries

           Smoke rising from the incense stick (rising up to small height in a straight line).

2. Turbulent Flow - In the turbulent flow the velocity of the fluid exceeds the threshold value for the fluid in the given pipe. The fluid starts fluctuating with time. In this case the velocity at the center of the pipe equals the average flow velocity.

Turbulent flow occurs when the velocity of the fluid is high and turbulent flow mostly occurs in the wide and big pipes. Both the magnitude and the direction is continuously changed in this type of flow.

Source - The constructor.org

The flow type is determined by Reynolds number, Re=VD/v

Where, D = Diameter of the pipe

             V = Mean velocity of flow of fluid in the pipe.

             v = Kinematic viscosity of the given fluid.

Reynolds Number	Condition of the flow
Re<2100	Laminar Flow
2100<Re<4000	Transitional Flow
Re>4000	Turbulent Flow.

Impact on Flow through pipes due to Fluid Properties

Temperature is the aspect that changes the viscosity and density of the given fluid. Also, when the flow is turbulent flow, the internal roughness of the pipe changes thus the length and diameter gets slightly affected. If the position of supply and discharge containers is changed relative to the pump position, then the fluid properties in the system get deviated and thus it impacts the flow through the pipes.

Head Loss

In the pipes and systems the losses are expressed in terms of equivalent fluid columns and this is known as the head loss.

Impact of properties in flow through pipes -

1. Density - If the density of fluid is high then the mass will be high which makes the system dense and compact.

2. Viscosity - If the viscosity of fluid is high then we will have to set the performance of pumps to equal to additional shear resistance.

3. Pressure - As pressure of fluid increases its velocity decreases, but we have to keep the sum of pressure, kinetic energy and potential energy constant.

Losses in the flow through pipe 

The losses can be classified into two types:

1. Major loss - This loss is due to pipe wall friction. Major losses are calculated by using the Darcy Weisbach equation and Chezy's formula.

2. Minor loss - This loss is due to eddy formations in the fluid (caused by sudden increase and decrease in the velocity of fluid).

Connections in Pipes

1. Pipes in Series

Pipes are said to be in series if the pipes of different diameters are connected to each other through the ends.

                       Here the total loss in the energy will be equal to the sum of losses in each pipe.

Discharge passing through each pipe is equal, 

Q=A1V1=A2V2=A3V3

The sum of total head loss in the system is equal to the difference in liquid surface levels.

Source - tutorhelpdesk.com

2. Pipes in Parallel

The pipes are said to be in parallel if the pipe gets divided into two or more sub parts and again these pipes join together downstream to form a single pipe. Here the rate of fluid flow is equal to the sum of the rate of flow (branch pipes).

The total pressure loss across all branches of pipes is equal, Q=Q1+Q2

Source - Examhill

Boundary Layers 

Laminar boundary layer flow 

This is a very smooth flow and creates less skin friction drag than the turbulent flow. But laminar boundary layer flow is less stable.

Turbulent boundary layer flow 

Some distance before the leading edge, the laminar flow breaks down and the turbulent flow starts.

Source - Ninova.itu.edu

Conclusion

Fluids are the substance that can flow. The fluids flow through the pipe in two ways, by giving the slope or by the pressure difference. Depending on the diameter of pipe, velocity and kinematic viscosity the flow can be divided into three parts which are laminar, transitional and turbulent flow. The Reynolds number is used to find the type of flow. Flow can also be differentiated in two more types depending on the connections in the pipe. Thus, the flow through pipes is carried out. And this application is widely used in households as well as in the industrial sector to transport the chemicals, gas products and many more.