Fluid mechanics Reynolds number equation query

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Homework Help Overview

The discussion revolves around calculating the density of a fluid using the Reynolds number equation in the context of fluid mechanics. The original poster presents a scenario involving critical velocity, pipe dimensions, and dynamic viscosity.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to rearrange the Reynolds number formula to solve for fluid density but questions the validity of their result. Other participants inquire about unit conversions and express skepticism regarding the calculated density value.

Discussion Status

The discussion is ongoing, with participants questioning the assumptions made about unit conversions and the plausibility of the resulting density. There is no consensus yet, but the inquiry into the low density value has prompted further exploration.

Contextual Notes

The original poster has converted variables to SI units and is working within the constraints of a specific problem setup, including given values for velocity, diameter, and viscosity. The discussion highlights potential issues with these conversions.

smegal
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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 [/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.
 
Last edited by a moderator:
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1 what? Units please :biggrin:

Also, why do you suspect 1 is wrong?
 
kg/m^3

That is a very low density.
 
smegal said:
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)
 

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