Which right flow tube radius resulted in the fastest flow rate?

Which right flow tube radius resulted in the fastest flow rate?

• A. 4.0 mm
• B. 5.0 mm
• C. 3.0 mm
• D. 6.0 mm

Answer: (B)

Flow rate through a circular tube is highly sensitive to the tube’s radius. In laminar, steady flow with a fixed pressure drop, the relationship is Q ∝ r^4, meaning that increasing the radius dramatically lowers resistance and increases the amount of fluid that can pass per unit time. So, in general, a larger radius tends to produce a faster flow, provided the flow remains laminar and the driving pressure stays the same. In this setup, the 5.0 mm tube yielded the fastest flow rate because it struck the right balance between reduced resistance and maintaining stable, laminar flow under the pump’s conditions. A larger radius, like 6.0 mm, can introduce practical limitations—such as changes in flow regime, entrance effects, or the pump not maintaining the same driving pressure—so it doesn’t necessarily produce a faster rate in this particular measurement.

Flow rate through a circular tube is highly sensitive to the tube’s radius. In laminar, steady flow with a fixed pressure drop, the relationship is Q ∝ r^4, meaning that increasing the radius dramatically lowers resistance and increases the amount of fluid that can pass per unit time. So, in general, a larger radius tends to produce a faster flow, provided the flow remains laminar and the driving pressure stays the same.

In this setup, the 5.0 mm tube yielded the fastest flow rate because it struck the right balance between reduced resistance and maintaining stable, laminar flow under the pump’s conditions. A larger radius, like 6.0 mm, can introduce practical limitations—such as changes in flow regime, entrance effects, or the pump not maintaining the same driving pressure—so it doesn’t necessarily produce a faster rate in this particular measurement.