Question

In smooth pipes, Laminar flow is encountered at what value of Reynolds number?

(a) More than 2100

(b) 2100-4000

(c) More than 4000

(d) Less than 2100

The question was posed to me in an online quiz.

This intriguing question originated from Fluids in Motion in section Fluid Flow and Mixing of Bioprocess Engineering

Answer 1

Correct option is (d) Less than 2100

For explanation: One of the most significant outcomes of Reynolds’ experiments is that there is a critical Reynolds number which marks the upper boundary for laminar flow in pipes. In smooth pipes, laminar flow is encountered at Reynolds numbers less than 2100. Under normal conditions, flow is turbulent at Re above about 4000. Between 2100 and 4000 is the transition region where flow may be either laminar or turbulent depending on conditions at the entrance of the pipe and other variables.