Question

The Reynolds number of a flow is the ratio of:
A. Gravity force to viscous force
B. Gravity force to pressure force
C. Inertial force to viscous force
D. Viscous force to pressure forces

Answer 1

The Reynolds number is a convenient parameter for determining whether there will be a laminar or turbulent flow state. Because of specific fluid velocities the ratio is subject to relative internal movement.

Complete step-by-step solution:
To answer this question, first, we need to know about Reynolds number. The Reynolds number is measured at less than 2300, and the fluid flow is called laminar. When the Reynolds number exceeds 4000 the flow of the fluid is known as turbulent. While many engineering projects cope with either turbulent or laminar flow, between the two phases there is an intermediate phase which exists. Transitional flow is defined as the flows that exist between the 2300 and 4000 Reynolds numbers.

Now lets us find the solution from the given options-
Gravity force to viscous force is not the ratio of Reynolds number because Reynolds number calculates the flow of a fluid that determines as laminar or turbulent.
Gravity force to pressure force is not the Reynolds number ratio, since the Reynolds number determines the flow of a fluid deciding as laminar or turbulent.

Reynolds Number is a calculation that determines the flow of a fluid by the ratio of the inertial forces to the viscous forces. Here is the Reynolds Number Equation:
$RE = \dfrac{{pVD}}{\mu }$

P refers to the density of the fluid, V is the velocity of the fluid, D is the pipe's diameter that contains the fluid that flows, and μ is the coefficient of viscosity.
The equation of Reynolds number is $RE = \dfrac{{pVD}}{\mu }$ so, viscous force to pressure forces is not the ratio of Reynolds number.

Thus, the right answer is option C i.e., Inertial force to viscous force.

Note: The number of Reynolds is the ratio of inertial forces to viscous forces within a fluid that is confined to relative internal motion based on different fluid velocities, known as a boundary layer in the case of a boundary surface such as a pipe’s interior.