Question

State the formula for critical velocity in terms of Reynold's number for a flow of a fluid.

Hint:

Reynold's number determines flow type; critical \( Re \) varies by system, typically around 2000 for pipes.

Answer 1

The critical velocity \( v_c \) for fluid flow in a tube, where the flow transitions from laminar to turbulent, is related to Reynold's number \( Re \). The formula is: \[ v_c = \frac{Re \eta}{\rho d}, \] where \( \eta \) is the coefficient of viscosity, \( \rho \) is the fluid density, and \( d \) is the diameter of the tube.
Answer: \( v_c = \frac{Re \eta}{\rho d} \).