Types of fluid flow in pipe
Steady and Unsteady Flow
Steady flow
A steady flow can be defined as one in which the conditions like velocity, pressure and cross section although may differ from point to point does not change with time. Note that there may be slight variations in velocity and pressure but if the average values are constant then it is considered to be a steady flow. For eg. Water flowing from a pipe that has constant diameter and velocity.
Unsteady flow
An unsteady flow can be described as conditions that change with time. For eg. Water flowing from a pipe that has constant diameter and connected to a pump which also pumps water at a constant rate and then is switched off.
Uniform and Non-Uniform Flow
Uniform flow
A uniform flow can be defined when the flow velocity has the same magnitude and direction at every point in the fluid.
Non-uniform flow
A non-uniform flow can be defined when the velocity is not the same at all point during the flow.
Compressible and incompressible flow
Compressible flow
Compressible flow is when the density of the flow becomes variable.
Incompressible flow
Incompressible flow is the flow of liquid when the density remains constant in any fluid parcel. Incompressible flow is also known as isochoric flow. For eg. The stream of water gushing at high speed from a garden hose pipe. When the hose is pointed down, water flows narrow but when held up vertically, it spreads like a fountain.
Rotational and irrotational flow
Fluid elements in rotational flow rotate and fluid elements having irrotational flow do not rotate.
In rotational fluid, the fluid particles spin about their axis while flowing along a streamline. In irrotational fluid, the fluid particles do not rotate on their own axis while flowing along a streamline.
One, two and three dimensional flow
A flow is said to be one, two and three-dimensional if the flow velocity varies in one, two or three primary dimensions.
One-dimensional flow is when the flow parameter is expressed as functions of time and one space coordinate only.
For instance velocity, is a function of time and only one space coordinate exists, say x.
u=f(x), v=0 and w=0
The x, y, and z velocity components are u, v and w, respectively.
Two-dimensional flow is when flow characteristics are the function of time and two rectangular space co-ordinates.
u= f1(x,y,), v= f2(x,y,) and w= 0.
Three-dimensional fluid flow is a form of fluid flow in which velocity is a function of time and three mutually perpendicular directions.
u= f1(x,y,z), v= f2(x,y,z) and w= f3(x,y,z).
Laminar and Turbulent Flow
Depending on the velocity, pipe size, and fluid viscosity, a liquid flowing through a closed channel like a pipe or between two flat plates is either in a laminar or turbulent flow.
Laminar flow
Air moves predictably and in parallel layers in a laminar flow from the supply airflow in the ceiling. Without passing through clean air again, the air is driven downward and, in the direction of the ceiling, returns. Any undesired particles are moved straight out of the room, preventing contamination.
Turbulent flow
A typical room with a return grille and supply diffuser in the ceiling is in a turbulent flow. As a result of pressure and temperature variations, the air travels in this situation unpredictably. Air molecules constantly collide, contaminating the air as particles are carried about the space and eventually expelled through the return grille.
When operated at various flow rates, laminar and turbulent flows can coexist in the same tube network.
Laminar stream flow
When water is arranged in parallel layers and flows organized, this is called laminar streamflow. Water molecules travel along the stream while remaining in their layer. Because these streams typically have few rocks or other physical obstacles, this arrangement is frequently feasible. Water moves straight and in a line along the stream channel so the stream flow in an orderly. The water often has modest velocity and travels silently because of the straight direction of the flow. A small, meandering canal is an example of a stream with laminar streamflow. The water would appear to move slowly and gently, and there would be no rocks.
Turbulent stream flow
Water that does not flow in parallel layers or in an organized way is said to have turbulent streamflow. There are rocks and other physical obstacles in the water of streams with turbulent streamflow. Water molecules are a mix between the parallel layers as they run into these barriers. The water flow is uneven and random; it does not follow a straight path. High stream velocity is a common characteristic of turbulent streamflow, which results in more erratic and dramatic water movement. Due to the water striking obstacles and being thrown around with greater power, these streams are frequently loud.
Significance of Reynolds Number
The relationship between inertia and viscous forces is known as the Reynolds number (NRe). It is a dimensionless number that details several flow types, including turbulent, transitional, and laminar flow.
Laminar Flow
When the viscous force exceeds the flow at a low Reynolds number, the flow is referred to as laminar flow.
The pressure head loss in a pipe for laminar flow is smaller and inversely related to velocity.
Turbulent Flow
The inertia force is greater with a higher Reynolds number; the flow is referred to as turbulent flow.
The pressure head loss in a pipe for a turbulent flow is high and proportionate to Vn.
Laminar and turbulent are two alternative regimes within which the fluid flow can be determined. A critical issue influenced by both fluid and flow properties is the transition between the regimes. There are two types of crucial Reynolds numbers: internal and exterior. While the Reynolds number for the laminar-turbulent transition can be adequately described for internal flow, external flow definitions are more challenging to come up with.
Characteristics
Laminar Flow
Smooth streamlines and intensely regulated motion are traits of laminar flow. The velocity profile is unchanged throughout the flow direction. Each fluid particle flows at a constant axial speed along a streamline.
A straight pipe with the laminar flow having several fluid cylinders moving relative to one another, with the outer cylinder attached to the pipe wall and the others moving toward the center of the pipe at increasing speeds.
The complete region of a simple circular tube experiences a constant laminar flow of an incompressible fluid with all characteristics.
Laminar flow is unusual in practical water systems, although simple theoretical analysis is still workable.
Turbulent Flow
The irregular movement of the fluid’s particles defines the flow. Fluid particles travel chaotically. Due to this, the deterministic treatment of turbulent flow is replaced with statistical treatment.
Higher velocities, lower viscosities, and higher typical linear dimensions are all conducive to turbulent flow.
A balanced velocity distribution can be seen over the pipe segment in a turbulent flow. This causes the entire fluid to flow at a single value and drop quickly, very close to the walls. The property is known as “diffusivity”; it gives a flow more significant mixing and faster rates of mass, momentum, and energy movement.
When viscous shear stress transforms external kinetic energy from a turbulent flow into internal energy, the process is known as dissipative.
How to avoid turbulent flow?
- Avoid mounting the flow meter directly behind a valve or other restriction.
- At the instrument’s inlet, use a pipe ten times longer than it is wide. At the instrument’s exit, use a pipe length that is four times as long as the pipe diameter. Use a pipe length of at least 12 mm (12″) for gas flow rates of more than 100 l/min.
- Before the flow reaches the sensor, it is filtered by a turbulence filter, creating a laminar flow. Nowadays, some people utilize flow meters like the Bronkhorst low delta P.
- It is best to avoid using elbow couplings near flow meters.
Applications
Laminar Flow
Taps- The water flow appears steady when a fixture is only slightly opened, and water is allowed to pour out quickly due to the laminar flow created when a fluid moves at a low velocity because the layers do not mix.
Aircraft- Because it permits an even flow of air particles over the aircraft’s surface, the laminar flow of air is a vital component for ensuring a smooth flight.
Rivers- Laminar flow is commonly found in stagnant rivers. Water moves slowly and smoothly in still rivers and other bodies of water. Because there are no waves or swirls in the water body, the various water layers do not interfere and move in a straight line parallel to one another.
Turbulent Flow
Taps- The water usually pours out quickly when a tap or faucet is fully opened. Because the fluid is moving at such a high velocity, its nearby layers are mixing, and the flow is becoming chaotic. It is implied that turbulent flow exists of the flow chaotic nature.
Aircraft- You must have traveled in an Aircraft that experienced turbulence. Due to the air’s turbulent flow, air molecules are thrown around and mixed. Physical, thermal, or mechanical elements can impact turbulence in an airplane.
Air from Fan or AC- Through the moving blades of a fan, the air is moved throughout the room. It indicates an irregular airflow within the space. The atmosphere is combined with dust particles. In light of this, turbulent flow is shown by the air flowing from a fan or an air conditioner.
Advantages
Laminar Flow
- Laminar flow is a movement where fluid moves in layers without interruption
- Using CFD software, laminar flow makes it simple to examine the fluid flow
Known about: Pipe volume calculator: Uses, advantages and needs
Turbulent Flow
- The quantity of air resistance and noise increases in a turbulent flow
- Additionally, thermal mixing and heat conduction are accelerated by turbulent flow
Difference Between Laminar And Turbulent Flow
Conclusion
It concluded turbulent and laminar flow that is one of the most crucial components. The difference between the turbulent and laminar laws must be measured, and it was concluded that the flow could be defined and measured by the Reynolds number.
FAQs
What makes laminar flow preferable to turbulent flow?
While turbulent flows are unstable and unpredictable, laminar flows are streamlined and uniform.
Does the turbulent or laminar flow improve heat transmission?
The increase in heat transfer rate is greater under turbulent flow circumstances than it is under laminar flow conditions.
What distinguishes laminar flow from turbulent flow?
Laminar flows happen when the Reynolds number is low, while turbulent flows happen when the Reynolds is high.
Laminar or turbulent flow moves more quickly?
When compared to laminar flow, turbulent flow is faster. Turbulence occurs at a higher Reynolds number.
What is the turbulent Reynolds number?
Reynolds numbers exceeding 2,000 is turbulent.
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