# Fluid mechanics Reynolds number equation query

1. May 9, 2009

### smegal

Calculate the density of a fluid if a ctitical velocity of 2m/s at Re=2000 in a pipe of bore 90mm at a dynamic viscosity oc 0.09cP

I have calcualted the variables to SI units and found

$$\rho$$=?
Um (V) =2m/s
D=0.09m
$$\mu$$=0.09X10^-3

I am rearranging this formula
http://www.rpgroup.caltech.edu/%7Enatsirt/aph162/webpages/F2WP2/reynoldsNumberFormula.png [Broken][/URL]

3. The attempt at a solution

$$\rho$$= (Re*$$\mu$$)/(Um*D)

I keep getting 1 as the answer for the density. Have I converted something to SI units incorrectly?

Thanks.

Last edited by a moderator: May 4, 2017
2. May 9, 2009

### diazona

Also, why do you suspect 1 is wrong?

3. May 9, 2009

### smegal

kg/m^3

That is a very low density.

4. May 9, 2009

### Redbelly98

Staff Emeritus
That's comparable to air, which is 1.2 kg/m^3 under normal conditions (20 C, 1 atm)