Q1: At low Reynolds number

ANS:C - viscous forces control and inertial forces are unimportant.

At low Reynolds numbers, viscous forces control the flow, and inertial forces are unimportant. Here’s an explanation:

• Reynolds Number (Re): The Reynolds number is a dimensionless quantity that characterizes the relative importance of inertial forces to viscous forces in fluid flow. It is defined as: Re=ρVLμRe = \frac{\rho V L}{\mu}Re=μρVL​ where:
  • ρ\rhoρ is the density of the fluid,
  • VVV is the characteristic velocity of the flow,
  • LLL is a characteristic length (such as the diameter of a pipe),
  • μ\muμ is the dynamic viscosity of the fluid.
• Low Reynolds Number: When the Reynolds number is low (typically Re<2000Re < 2000Re<2000), viscous forces dominate over inertial forces. This means that the viscosity of the fluid significantly affects the behavior of the flow, and the flow tends to be laminar with smooth and orderly fluid motion.
• Behavior at Low Reynolds Number: At low Reynolds numbers, the flow is characterized by layers of fluid moving smoothly and without significant mixing between layers. In this regime, viscous forces are responsible for resisting flow and controlling the movement of fluid particles.