Pipe flow regime – transitional (neither laminar nor turbulent) The flow in a pipe is neither laminar nor fully turbulent when the Reynolds number is:

Introduction:
The transitional regime bridges laminar and turbulent behavior. Disturbances may intermittently grow or decay, making friction factor and velocity profile uncertain.

Given Data / Assumptions:

• Internal flow in a circular pipe.
• Reynolds number based on diameter and bulk velocity.
• Thresholds consistent with the option ranges provided.

Concept / Approach:
Common classification: laminar for Re < 2000; transitional for an intermediate window; turbulent beyond the upper threshold. Here, the question uses 2000–2800 as the transition band.

Step-by-Step Solution:
1) Identify laminar threshold: Re < 2000.2) Identify turbulent threshold: Re > 2800 (per options).3) Therefore, 2000 ≤ Re ≤ 2800 → transitional → neither purely laminar nor fully turbulent.

Verification / Alternative check:
Laboratory pipe flows show intermittency, puffs, and slugs in this band; friction factor correlations become unreliable.

Why Other Options Are Wrong:

• Less than 2000: laminar.
• More than 2800: turbulent.
• None of these: incorrect, since the transitional band is explicitly given.

Common Pitfalls:
Using a single universal cutoff (e.g., 4000) without checking the convention used in a given problem.

Final Answer:
between 2000 and 2800