Question

A dimensionless number which represents the ratio of inertia to viscous force is:

• A. Reynold’s number
• B. Froud’s number
• C. Prandtl number
• D. Stanton number

Hint:

To remember: Reynolds = Ratio of Inertia over Viscosity. Think of it as the struggle between the fluid's speed and its "stickiness."

Answer 1

The Correct Option is A

Concept: Dimensionless numbers are used in fluid mechanics to characterize the behavior of fluid flow.

• Reynold's Number ($Re$): Relates inertia and viscosity.

• Prandtl Number ($Pr$): Relates momentum diffusivity to thermal diffusivity.

• Froude Number ($Fr$): Relates inertia to gravitational force.

Step 1: Defining the Reynolds Number formula.
$Re = \frac{\rho \cdot v \cdot D}{\mu}$ Where $\rho$ is density, $v$ is velocity, $D$ is diameter, and $\mu$ is dynamic viscosity.

Step 2: Interpreting the forces.
The numerator ($\rho \cdot v \cdot D$) represents the inertial forces (the tendency of the fluid to keep moving). The denominator ($\mu$) represents the viscous forces (the internal friction of the fluid).

Step 3: Significance.
This ratio determines whether a flow is laminar (viscous forces dominate) or turbulent (inertia dominates). Final Answer: (A)