Name: pipe flow regimes and reynolds number
Uploaded: 2026-01-28T11:54:30.000Z
Duration: 1 min 22 s
Channel: JoVE

Pipe flow describes fluid movement through enclosed, fully-filled conduits, typically cylindrical pipes like water pipes or hydraulic hoses, engineered to withstand higher pressure gradients without deforming.
Rectangular conduits, such as air conditioning and heating ducts, typically handle lower pressures.
In pipe flow, movement is pressure-driven, whereas open-channel flow relies solely on gravity.
Osborne Reynolds pioneered fluid flow classification in pipes using his dye injection experiment.
By injecting dye into water flowing through pipes, Reynolds identified three distinct regimes: laminar, transitional, and turbulent.
At low flow rates, the dye forms a smooth streakline; with increasing flow, it begins to fluctuate and eventually disperses randomly.
The Reynolds number, a key dimensionless parameter, represents the ratio of inertial to viscous forces in pipe flow.
The Reynolds number depends on fluid velocity, density, viscosity, and the pipe diameter. For smooth, circular pipes, flows are typically laminar below 2100, turbulent above 4000, and transitional in between.

general characteristics of pipe flow i

General Characteristics of Pipe Flow I

Pipe flow refers to the movement of fluids within fully enclosed conduits, typically cylindrical in shape, such as water pipes or hydraulic hoses. These conduits are designed to withstand high-pressure gradients that drive fluid movement, contrasting with open-channel flows, where gravity is the primary driving force. Rectangular conduits, like air conditioning and heating ducts, generally operate at lower pressures and are less suited for high-pressure applications.
The classification of fluid flow in pipes was pioneered by Osborne Reynolds through his foundational dye injection experiments. Reynolds identified three flow regimes &#8212; laminar, transitional, and turbulent &#8212; based on fluid velocity. At low velocities, the dye maintained a smooth streakline, indicating laminar flow, where fluid particles follow orderly, parallel paths. As velocity increased, the dye began to oscillate, marking the transitional regime, and at higher velocities, it dispersed unpredictably in the turbulent regime, where random, chaotic motion dominates.
These observations led to the development of the Reynolds number, a dimensionless quantity that indicates the balance of inertial and viscous forces in the flow. The Reynolds number is calculated based on fluid velocity, density, viscosity, and pipe diameter and serves as an indicator of flow type: laminar for values below 2100, turbulent for values above 4000, and transitional in the range between. In laminar flow, velocity remains steady over time, while turbulent flow exhibits unsteady, fluctuating velocities with random components perpendicular to the pipe axis. By calculating the Reynolds number, engineers can predict flow behavior in pipe systems, aiding in the design and optimization of pipelines, hydraulic systems, and fluid transport networks across various industries.

Pipe flow describes fluid movement through enclosed, fully-filled conduits, typically cylindrical pipes like water pipes or hydraulic hoses, engineered to ...

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JoVE Core

Civil Engineering

Unit 1

Flow in Pipes

KEY TERMS AND CONCEPTS

pipe flow regimes and reynolds number

Pipe flow is the movement of fluids through fully enclosed conduits such as water pipes and hydraulic hoses. These pipes are built to handle high-pressure gradients that drive the fluid forward. That is different from open-channel flow, where gravity is the main driving force. Rectangular conduits, such as air conditioning and heating ducts, usually work at lower pressures and are less suited for high-pressure use.

Osborne Reynolds first classified pipe flow with dye injection experiments. He showed that flow changes with fluid velocity. At low velocity, the dye stayed as a smooth streakline. This pattern shows laminar flow, where fluid particles move in orderly, parallel paths.

As velocity increased, the dye began to oscillate. That marked the transitional regime, which lies between laminar and turbulent flow. At even higher velocity, the dye spread in an unpredictable way. This is turbulent flow, where random and chaotic motion dominates.

These experiments led to the Reynolds number, a dimensionless quantity that helps predict flow behavior. It is based on fluid velocity, density, viscosity, and pipe diameter. A Reynolds number below 2100 indicates laminar flow, while values above 4000 indicate turbulent flow. The range between these values is transitional.

Flow type also changes how velocity behaves over time. In laminar flow, velocity stays steady. In turbulent flow, velocity is unsteady and fluctuates. Turbulent flow also includes random motion perpendicular to the pipe axis. Engineers use the Reynolds number to help design and optimize pipelines, hydraulic systems, and other fluid transport networks.

Pipe Flow Regimes and Reynolds Number

Pipe flow is the movement of fluids through fully enclosed conduits such as water pipes and hydraulic hoses. These pipes are built to handle high-pressure gradients that drive the fluid forward. That is different from open-channel flow, where gravity is the main driving force. Rectangular conduits, such as air conditioning and heating ducts, usually work at lower pressures and are less suited for high-pressure use. Osborne Reynolds first classified pipe flow with dye injection experiments. He...

general characteristics of pipe flow ii

Pipe Entrance Length and Pressure Changes

Pipe flow changes as fluid moves from the pipe entrance to a fully developed state. At the entrance, the velocity profile is still adjusting. Viscous effects create a boundary layer along the wall, and that layer grows until it fills the whole pipe cross-section. When the boundary layer merges across the pipe, the flow becomes fully developed. At that point, the velocity profile stays steady along the pipe length. The distance needed to reach this state is called the entrance length. It...

laminar flow

Pipe Flow Patterns and Pressure Loss

Pipe flow patterns can be smooth, changing, or chaotic, and laminar flow is the smoothest form. In laminar flow, fluid particles move in parallel paths with very little mixing between layers. This happens when viscous forces are stronger than inertial forces. The flow regime in a pipe is often described with the Reynolds number, a dimensionless value that depends on fluid density, flow speed, pipe diameter, and dynamic viscosity. A Reynolds number below about 2100 usually means laminar flow.

laminar flow: problem solving

Pipe Size for Laminar Air Flow

Laminar flow in a pipe means the fluid moves in smooth, parallel layers with very little mixing or turbulence. In fluid mechanics, keeping flow laminar is important when engineers want precise control of flow behavior. The Reynolds number is the key value used to check this. It is a dimensionless number that depends on the fluid’s speed, density, viscosity, and the pipe’s diameter. A Reynolds number of 2100 or lower shows laminar flow. Higher values lead to turbulence. For air flowing through...

turbulent flow

Turbulent Flow in Pipes and Mixing

Turbulent flow is a fluid pattern with irregular changes in speed and pressure. It looks chaotic when compared with laminar flow, which moves in smooth, parallel layers with little mixing. In turbulent flow, the motion is highly irregular and three-dimensional. This behavior starts when the fluid speed becomes high enough to create instabilities in the velocity profile. Small disturbances, called turbulent spots, can appear at a critical speed. As the Reynolds number, a ratio of inertial...

turbulent flow: problem solving

Carbonation Flow and Reynolds Number

Carbonation uses carbon dioxide gas to dissolve gas into a liquid, as in carbonated drinks. Efficient carbonation depends on temperature, pressure, and flow conditions. By controlling these factors, more CO2 can dissolve in the liquid. Temperature plays a major role in CO2 solubility. Here, both the CO2 gas and the liquid are cooled to 20°C. Lower temperatures increase solubility, so a larger volume of gas can dissolve. Pressure also helps drive carbonation. At 20°C, the CO2 gas is...

major losses in pipes

Pipe Pressure Drop from Wall Friction

Pipe pressure drop from wall friction is a major loss in fluid flow. As a fluid moves through a pipe, friction along the pipe walls removes energy. That energy loss shows up as a drop in pressure. The size of the drop depends on the flow conditions and on the physical properties of both the fluid and the pipe. Flow in a pipe is often described as laminar or turbulent using the Reynolds number. This dimensionless number compares inertial forces with viscous forces in the fluid. In laminar flow,...

minor losses in pipes

Pipe Fittings and Valve Head Loss

Pipe fittings and valves can cause head loss in a pipe system. These losses happen when flow is disturbed by bends, expansions, entries, exits, and other components. The fluid loses energy because the flow becomes less steady and more turbulent. Valves are a major source of minor loss because they block or guide the fluid path. A closed valve or a partly closed valve adds resistance and creates turbulence. The amount of energy loss depends on the valve shape, its position, and the way the flow...

single pipe systems

Pipe Flow Problems by What You Know

Pipe flow problems are grouped by the information that is known and the result that needs to be found. In fluid mechanics, these are often called Type I, Type II, and Type III problems. Each type uses fluid properties, pipe details, and operating conditions to answer a different engineering question. In a Type I problem, the fluid density and viscosity are known. The pipe diameter, length, and surface roughness are also known. The flow rate or average velocity is given, and the goal is to find...

multiple pipe systems

Pipe Flow Paths in Series and Parallel

Multiple pipe systems move fluids through connected pipe paths in engineering networks. They help control flow distribution, pressure, and head loss. These systems are grouped into series, parallel, loop, and network configurations, and each one behaves differently. In a series configuration, fluid passes through one pipe segment after another. The flow rate stays the same through every segment. Head loss builds up across the path, so the total loss from entry point A to exit point B is the...

pipe flowrate measurement

Comparing Orifice, Nozzle and Venturi Meters

Orifice, nozzle, and Venturi meters are used to measure fluid flowrate in pipes by narrowing the flow area. The smaller opening makes the fluid move faster and lowers the pressure. The pressure difference, together with Bernoulli’s principle and real-world corrections, is used to calculate flowrate. The orifice meter is the simplest and least expensive option. It uses a flat plate with a hole in the center to create a measurable pressure drop. It is often used in water treatment, oil and gas...

pipe flowrate measurement: problem solving

pipe-flowrate-measurement-problem-solving

Spray Tank Pipe Flow Rate Calculation

Spray tank pipe flow rate calculation uses fluid mechanics to find how fast pesticide moves through a pressurized system. The tank is pressurized to 150 kPa and holds the liquid at a height of 0.80 meters. The liquid then travels through a 1.9 meter pipe with a diameter of 0.015 meters and an angle of 0.698 radians before reaching a 0.007 meter nozzle that sprays the pesticide. Accurate flow rate matters because the pesticide must be applied evenly across the plants. The first step is to find...

design example: designing a residential plumbing system

design-example-designing-a-residential-plumbing-system

Residential Plumbing Flow and Pressure Design

Residential plumbing flow and pressure design starts with water demand, flow rate, and pressure needs. These systems are sized by looking at how many people live in the home and what fixtures they use. The goal is to provide reliable water delivery while keeping the system efficient. A key part of the design is the Reynolds number. This dimensionless value helps classify flow in a pipe as laminar, which is smooth, or turbulent, which is more mixed and irregular. It depends on factors such as...

key terms and concepts

Explore laminar, transitional, and turbulent pipe flow, plus Reynolds number, with clear examples from dye experiments and fluid movement in pipes.

Pipe Flow Regimes and Reynolds Number | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

Pipe Flow Regimes and Reynolds Number

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