# Reynolds Number problem

1. Sep 11, 2008

### cheertcc101

The question gives this ..

The Reynolds number, Re, is a dimensionless group which characterizes the intensity of a flow. For large Re, a flow is turbulent; for small Re , it is laminar. For pipe flow, Re=u(density)D/mu, where D is pipe diameter and mu is dynamic viscosity.

If D and mu are fixed, what is the effect of increasing mass flow rate on Re?
and
If mass flow rate and mu are fixed, what is the effect of increasing D on Re?

Any help is appreciated,

Thanks!!

2. Sep 11, 2008

### FredGarvin

First of all, while Re is used to characterize the type of flow, it is a ratio of forces in a flowing fluid. It is a ratio of the inertial forces to the viscous forces.

Start by looking at what defines the mass flow rate...$$\dot{m}=\rho*A*V$$

You'll also need to look at the fact that area is $$A=\frac{1}{4}\pi*D^2$$