Which statement about Reynolds number is true?

Which statement about Reynolds number is true?

• A. It increases with flow speed
• B. It decreases with vessel diameter
• C. It is independent of blood density
• D. It decreases with viscosity

Answer: (A)

Reynolds number shows how strong inertial (motion-related) forces are compared with viscous (friction) forces in a flowing fluid. The standard relationship is Re = (rho × v × D) / mu, where rho is density, v is flow speed, D is a characteristic diameter, and mu is dynamic viscosity. Because velocity v sits in the numerator, increasing flow speed raises Reynolds number. This makes the statement that Reynolds number increases with flow speed the true, most direct takeaway. In broader terms, Reynolds number also grows with larger diameter and higher density, and it decreases with higher viscosity, but the clearest way speed affects it—and the one most commonly tested—is the direct, proportional relationship to flow speed.

Reynolds number shows how strong inertial (motion-related) forces are compared with viscous (friction) forces in a flowing fluid. The standard relationship is Re = (rho × v × D) / mu, where rho is density, v is flow speed, D is a characteristic diameter, and mu is dynamic viscosity. Because velocity v sits in the numerator, increasing flow speed raises Reynolds number. This makes the statement that Reynolds number increases with flow speed the true, most direct takeaway. In broader terms, Reynolds number also grows with larger diameter and higher density, and it decreases with higher viscosity, but the clearest way speed affects it—and the one most commonly tested—is the direct, proportional relationship to flow speed.