Which fluid is more viscous

  • Thread starter UFeng
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  • #1
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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.
 

Answers and Replies

  • #2
stewartcs
Science Advisor
2,177
3

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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