physics

Pipe flow

Pipe flow is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Pipe flow rather than just read about it. In short: In fluid mechanics, pipe flow is a type of fluid flow within a closed conduit, such as a pipe, duct or tube. It is also called as Internal flow.

Key takeaways

Pipe flow belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Pipe flow to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Pipe flow from memory before moving on to harder problems.

Reference excerpt

In fluid mechanics, pipe flow is a type of fluid flow within a closed conduit, such as a pipe, duct or tube. It is also called as Internal flow. The other type of flow within a conduit is open channel flow. These two types of flow are similar in many ways, but differ in one important aspect. Pipe flow does not have a free surface which is found in open-channel flow. Pipe flow, being confined within closed conduit, does not exert direct atmospheric pressure, but does exert hydraulic pressure on the conduit. Not all flow within a closed conduit is considered pipe flow. Storm sewers are closed conduits but usually maintain a free surface and therefore are considered open-channel flow. The exception to this is when a storm sewer operates at full capacity, and then can become pipe flow. Energy in pipe flow is expressed as head and is defined by the Bernoulli equation. In order to conceptualize head along the course of flow within a pipe, diagrams often contain a hydraulic grade line (HGL). The viscous shear forces in the fluid causes pipe flow to experience frictional losses as defined by the Darcy-Weisbach formula.

Laminar-turbulence transition The behavior of pipe flow is governed mainly by the effects of viscosity and gravity relative to the inertial forces of the flow. Depending on the effect of viscosity relative to inertia, as represented by the Reynolds number, the flow can be either laminar or turbulent. For circular pipes of different surface roughness, at a Reynolds number below the critical value of approximately 2000 pipe flow will ultimately be laminar, whereas above the critical value turbulent flow can persist, as shown in Moody chart. For non-circular pipes, such as rectangular ducts, the critical Reynolds number is shifted, but still ∼ O ( 10 3 ) {\displaystyle \sim {\mathcal {O}}(10^{3})} depending on the aspect ratio. Earlier transition to turbulence, happening at Reynolds number one order of magnitude smaller, i.e. ∼ O ( 10 2 ) {\displaystyle \sim {\mathcal {O}}(10^{2})} , can happen in channels with special geometrical shapes, such as the Tesla valve. Flow through pipes can roughly be divided into two:

Laminar flow - see Hagen-Poiseuille flow Turbulent flow - see Moody diagram

See also Mathematical equations and concepts Bernoulli equation Darcy–Weisbach equation Torricelli's law Fields of study Hydraulics Fluid Mechanics Types of fluid flow Open channel flow Plug flow Fluid properties Viscosity Fluid phenomena Head

References

Further reading Chow, V. T. (1959/2008). Open-Channel Hydraulics. Caldwell, New Jersey: Blackburn Press. ISBN 9780070859067.

Worked examples

Example 1 — a first encounter with Pipe flow

Start with the simplest possible case. Write down what Pipe flow claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Pipe flow before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Pipe flow ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Pipe flow

In research: Pipe flow appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Pipe flow in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Pipe flow is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fluid dynamics, Fluid mechanics, Piping, so understanding it makes those chapters shorter.
In everyday life: Look for Pipe flow outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Pipe flow in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Pipe flow means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Pipe flow out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Pipe flow in simple terms?

In fluid mechanics, pipe flow is a type of fluid flow within a closed conduit, such as a pipe, duct or tube. It is also called as Internal flow.

Why does Pipe flow matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Pipe flow?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Pipe flow.