# Fluid mechanics Reynolds number equation query

1.I have been asked to:

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]

## 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.

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## Answers and Replies

diazona
Homework Helper
1 what? Units please

Also, why do you suspect 1 is wrong?

kg/m^3

That is a very low density.

Redbelly98
Staff Emeritus
Homework Helper
kg/m^3

That is a very low density.

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