Which fluid is more viscous

[UFeng]

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.

 

[stewartcs]

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

 

[kerimek]

Your understanding is correct. In general, water would be more viscous than air at moderate to high Reynolds number. This is because water has a higher viscosity compared to air, meaning that it has a higher resistance to flow and will experience more viscous forces at the same Reynolds number. However, there are other factors that can affect the viscosity of a fluid, such as temperature and pressure. In some cases, air may have a higher viscosity than water due to these factors. Therefore, it is important to consider all relevant variables when determining which fluid is more viscous in a particular situation.