Fully developed flow, Reynolds number

[KRISHNACHAITANYAKC9]

Hi,
For my experiment I was asked to determine the length of the tube for a fully developed flow to occur, with the following flow parameters.
Flow rate : 1, 5, 15 lit/min
Fluid: Water
Tube Id: 1 inch.
My question How do I find out the length of the tube required to have a fully developed flow at its end. A valve is connected to the end, so the flow should be fully developed at the end when it hits the valve. The length of the tube is unknown. How would one use reynolds number to calculate this?

Thanks & Regards

 

[zdas04]

What are you trying to prove with your experiment? Before you get too far you should know that pipe sizes below 1.5 inch are very much dominated by surface tension and adhesion. You never get fully developed flow in a 1-inch, it is always unstable.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[BigInch]

Google knows,

http://www.engineeringtoolbox.com/entrance-length-flow-d_615.html

http://www.leb.eei.uni-erlangen.de/winterakademie/2006/result/content/course01/pdf/0110.pdf

 

[dbill74]

Sounds like a homework problem. If so, talk to your professor.

 

[cvg]

first, define the issue

theoretically, fully developed (hydraulic) means the velocity profile across the pipe is not changing. The boundary layer is fully developed. so regardless of pipe diameter, you have fully developed flow which will occur in a certain length of pipe without any change in velocity, direction, elevation, cross section, flow rate, temperature, roughness or anything else that would tend to perturb the flow.

If you are running an experiment, than you wont need reynolds number to calculate anything. you will need to measure the velocity profile at different locations to see if it is stabilized

 

[zdas04]

cvg,
I think you are oversimplifying a bit. What you say is true when the boundary layer on one side of the pipe does not interact with the boundary layer on the other side of the pipe. In 1-inch and smaller, that is frequently not the case.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

 

[cvg]

again, that is why the first line of my response is important. If you are "conducting an experiment", than define the issue. the term "fully developed" in the context of his experiment needs to be defined. You might be right, maybe the velocity profile is small tubes is never "fully developed", assuming water at normal temperatures and pressures

 

[georgeverghese]

Think this experiment is to determine when turbulent flow in this 1inch pipe begins.

We have laminar flow for all cases when Nre <2000 ( approx)

We have fully turbulent flow when Nre >3000 (approx)

The experiment is to find out when exactly turbulent flow is reached.

We can get a hint on what parameters influence this by looking at the graphs for heat transfer coeff Nnu vs Nre. Heat transfer behavior in tubes and pipes parallels that for fluid flow

In the Nusselt number (Nnu) profile, we can see a transition region whose extent is influenced by the L/D ratio. This L/D ratio influence must have a parallel in fluid flow, when transition flow changes to turbulent.

So I would suspect the profile for the friction factor would show a similar discontinuity ( when plotted against Nre) as Nre moves from 2000 to 3000 or so.