Question

The critical Reynolds number for the transition from laminar to turbulent flow in a pipe is approximately

• A. 500
• B. 2000
• C. 2300
• D. 4300

Hint:

Reynolds Number for Pipe Flow. Laminar: Re<~2300. Turbulent: Re>~4000. Transition: ~2300<Re<~4000. The critical Reynolds number marking the typical end of stable laminar flow is often taken as ~2300.

Answer 1

The Correct Option is C

The Reynolds number (Re) is a dimensionless quantity used to predict flow patterns.
For flow inside a circular pipe, it is defined as \(Re = \frac{\rho v D}{\mu}\), where \(\rho\) is density, \(v\) is average velocity, \(D\) is pipe diameter, and \(\mu\) is dynamic viscosity.
The flow regime transitions from laminar to turbulent over a range of Reynolds numbers.
- Flow is generally considered laminar for \(Re \lesssim 2000-2300\).
- Flow is generally considered fully turbulent for \(Re \gtrsim 4000\).
- The region between these values (\(\approx 2300\) to \(4000\)) is the transition region, where the flow can be intermittently laminar or turbulent.
The *critical* Reynolds number usually refers to the approximate lower bound at which turbulence typically starts to appear in pipe flow under normal conditions.
While the exact value can vary slightly depending on entrance conditions and pipe roughness, a value of approximately 2300 is commonly cited as the critical Reynolds number for transition in pipe flow.
Some sources use 2000 or 2100, but 2300 is a widely accepted standard value.