Is Water or Air More Viscous at High Reynolds Numbers?

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SUMMARY

At moderate to high Reynolds numbers, the viscosity of fluids behaves differently based on their physical properties. Incompressible flow conditions indicate that air, which has a lower density and viscosity compared to water, will exhibit dominant inertial forces, leading to reduced effective viscosity. As Reynolds number (Re) approaches infinity, the viscous forces diminish, confirming that water, despite its higher viscosity, is less significant in this context. Therefore, under the specified conditions, air is less viscous than water.

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Homework Statement


Which fluid is more viscous at moderate to high Reynolds number if used in this situation? Air or Water? The flow is incompressible and has velocity V and size L.

Homework Equations



Re = inerial forces/viscous forces = rho*V*L / mu

as Re approaches infinity, viscosity approaches zero

The Attempt at a Solution



I know that if Re is high, inertial forces dominate. Therefore, viscous forces are small.

inertial forces / Re = viscous force => wouldn't water always be more viscous assuming the same Re, V, and L is used for both air and water?

I think there is more to this problem that I am missing. Thanks for any help.
 
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UFeng said:

Homework Statement


Which fluid is more viscous at moderate to high Reynolds number if used in this situation? Air or Water? The flow is incompressible and has velocity V and size L.

Homework Equations



Re = inerial forces/viscous forces = rho*V*L / mu

as Re approaches infinity, viscosity approaches zero

The Attempt at a Solution



I know that if Re is high, inertial forces dominate. Therefore, viscous forces are small.

inertial forces / Re = viscous force => wouldn't water always be more viscous assuming the same Re, V, and L is used for both air and water?

I think there is more to this problem that I am missing. Thanks for any help.

Sounds good to me. Plus the problem states that the flow is incompressible which intuitively would rule out air.

CS
 

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