Flow Through Pipe

Flow Through Pipes

 

Introduction of fluid

Fluids are any substances that can flow. Fluids are defined as either liquids, gases, or mixtures of the two. They are tangible, take up space, and have a finite mass. They are materials that are composed of various molecules or particles. When the substance's particle's relative position with respect to time changes, they are said to be flowing. The fluids' new qualities include:

·       There are no shapes in it.

·       It takes up the shape of the pipe or vessel through which it is flowing.

·       It can swell beneath its weight.

·       It does have a mass of its own.

The study of force and its effects is known as mechanics. Surface force and body force are the forces that are exerted on the fluid (Gravitational force)

 

Fluid flow inside pipeline

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

Since all real fluids have some 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 shear stresses or frictional forces between the fluid layers and fluid to a solid surface. The pipe system is impacted in numerous ways by the fluid's flow and flow characteristics.

 

Theory behind the pipe flow

Fig 1: Flow through pipe[1]

Imagine a pipe with laminar fluid flow. The water molecules will slow down and come to a complete stop close to the pipe walls as a result of surface contact between the water and the wall. Due to friction, this layer of water molecules will also force the adjacent layer to flow of water to slow down. Water drops in the pipe's core must maintain a constant velocity to make up for this velocity and maintain a consistent volumetric flow rate. As a result, the velocity boundary layer begins to form along the pipe's boundary walls and progresses in the flow direction until it reaches the pipe's centre. The hydrodynamic entrance length is the distance from the pipe inlet to the location where the boundary layer combines. The completely developed region is the area that extends past the hydrodynamic entrance length.

 

How does Fluid flow in Pipes?

 

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

1. Tilting the pipes to create a downward flow in the case where gravitational energy is converted to kinetic energy.

 

2. The second method involves applying more pressure to one end of the pipe than the other end in order to generate a pressure difference between the two ends using different kinds of pumps. 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 piping system that the pump is linked to does not control the pressure or flow rate that the pump will deliver.

 

Losses in Flow through Pipes

Energy will be lost each time a fluid flows inside a pipe. The losses that occur while fluid moves through pipes can be divided into:

1) Major losses

2) Minor losses

Major Losses: This is due to the pipe wall friction.

They are frictional resistance forces that depend on the fluid density, surface type, fluid properties, and solid wall in contact while being pressure-independent and proportionate to volume. The following formulas, the Darcy Weisbach equation and the Chezys formula, can be used to compute major losses:

Minor losses: Eddy formations in the fluid, brought by abrupt increases in (contraction) and decreases (enlargement) of fluid velocity result in energy losses due to barriers, pipe bends, and pipe fittings. These losses are proportional to the square of the flow rate. Most of the time they are calculated using loss coefficient symbolized as (k).  

Types of flows

Laminar or turbulent flow are two different forms of flow that can pass through a pipe. The Reynolds number (Re), a non-dimensional number, is used to categories different types of flow-through pipes.

Re =ρVD /µ

Where, ρ is the density of the fluid, V is the average velocity of flow, D is the hydraulic diameter and µ is the coefficient of dynamic viscosity.

Laminar flow

Laminar flow is the gradual, layer-by-layer motion of a fluid in a pipe with little or no mixing. Usually happens when the fluid is extremely viscous and the velocity is low. The center of the pipes will have the highest flow, while the pipe walls will experience the lowest flow. (Refer fig no 2)

Turbulent flow

When the flow velocity in a pipe surpasses a certain threshold value, or when the velocity is high. With time, the fluid's flow turns turbulent and fluctuates in an erratic manner. The average flow velocity and the velocity at the pipe's centre are roughly equal.  

Fig. 2: Laminar vs Turbulent Flow [4]

Reynolds Number	Condition of flow
Re < 2000	Laminar
2000 < Re < 4000	Transitional
Re > 4000	Turbulent

Fig 4: Reynolds schematics sketches of pipe flow transition. (a) Laminar viscous flow at extremely small velocity (b) Transitional flow as the velocity increase and (c) Turbulent flow at high velocity

Impact of Fluid Properties on Flow through Pipes

           The piping system through which the fluid is flowing is significantly impacted by the fluid's characteristics.

          When the fluid density is higher, the mass will also be higher, making the system compact and dense. This is known as density (mass/unit volume).

           We must modify the performance of the pumps to compensate for the increased shear resistance as the fluid viscosity rises. Typically, there will be a slight decrease in intake, a larger decrease in head or pressure, and an abrupt spike in power draw.

          The fluid's pressure and velocity are inversely proportional to keep the algebraic total of the potential, kinetic energy, and pressure constant, hence Bernoulli's principle states that as pressure rises, velocity falls.

The fluid qualities like density, velocity, and viscosity that affect the fluid flow in the piping system are influenced by some system factors.

• The fluid's viscosity and density will vary as a result of the temperature change.

• The inner diameter and length. The internal roughness of the pipes in a turbulent flow.

• How supply and discharge containers are positioned in relation to the pump.

• Adding rises and falls to the existing pipe layout.

• The quantity and variety of bends in the system.

• The system's total number of valves and other pipe fittings.

• The pipework's conditions at the entrance and exit.

The specific gravity (relative density) [density of fluid/density of standard fluid] is another crucial characteristic of the fluid.

The outlet pressure varies according to the change in density when the fluid's specific gravity is changed. (Lighter fluids exert less pressure.) Surface tension will have a growing hold-up, causing the pressure drop to become unaffected.

Conclusion

A thorough analysis of flow through pipes has been conducted, and different frictional losses have been researched. That includes the description of flow through pipes in this page, as well as the effects of fluid characteristics on flow through pipes.

 

References:- https://whatispiping.com/fluid-flow-flow-through-pipes/

https://skill-lync.com/blogs/simulating-flow-through-a-pipe-using-openfoam

http://www.tezu.ernet.in/dmech/people/smkmech_files/smk/ME202/lec1.pdf

https://theconstructor.org/fluid-mechanics

Guided By:- Prof. Dr. Nitin Borse.

By:-Om Panchal, Parth Gupta, Rohit Patil, Vishal Patil, Mayuri Pawar.