Fluid mechanics Reynolds number equation query

In summary, the conversation is about calculating the density of a fluid with a critical velocity of 2m/s at Re=2000 in a pipe of bore 90mm with a dynamic viscosity of 0.09cP. The formula used is (Re*mu)/(Um*D) and the result obtained is 1 kg/m^3, which is comparable to the density of air.
  • #1
smegal
7
0
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

[tex]\rho[/tex]=?
Um (V) =2m/s
D=0.09m
[tex]\mu[/tex]=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



[tex]\rho[/tex]= (Re*[tex]\mu[/tex])/(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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  • #2
1 what? Units please :biggrin:

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

That is a very low density.
 
  • #4
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)
 

1. What is the Reynolds number equation and what does it represent?

The Reynolds number equation is a dimensionless number that represents the ratio of inertial forces to viscous forces in a fluid flow. It is calculated by multiplying the fluid's density, velocity, and characteristic length, and dividing by the fluid's viscosity. This equation is used to determine the type of flow (laminar or turbulent) in a fluid, and to predict the behavior and resistance of the fluid to flow.

2. How is the Reynolds number used in fluid mechanics?

The Reynolds number is used in fluid mechanics to characterize the flow of a fluid. It helps determine if the flow is laminar or turbulent, which affects the behavior and resistance of the fluid. It is also used to predict the transition from laminar to turbulent flow, and to determine the drag force on an object in a fluid flow.

3. What are the applications of the Reynolds number equation?

The Reynolds number equation has many applications in fluid mechanics. It is used in the design and analysis of pipes, pumps, turbines, and other fluid systems. It is also used in aerodynamics to study the flow of air around objects, such as airplanes and cars. Additionally, it has applications in the biomedical field, such as in understanding blood flow in arteries and veins.

4. Can the Reynolds number be used for all types of fluids?

No, the Reynolds number is only applicable to Newtonian fluids, which have a constant viscosity regardless of shear rate. Non-Newtonian fluids, such as blood, mud, and polymer solutions, have variable viscosity and therefore cannot be accurately characterized by the Reynolds number.

5. How does the Reynolds number affect the behavior of a fluid?

The Reynolds number is directly related to the type of flow in a fluid. A low Reynolds number indicates a laminar flow, where the fluid moves in smooth, well-ordered layers. A high Reynolds number indicates a turbulent flow, where the fluid moves in a chaotic, random manner. The behavior of a fluid, such as drag force and pressure drop, is greatly influenced by the type of flow, which is determined by the Reynolds number.

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