Fully developed flow, Reynolds number
Fully developed flow, Reynolds number
(OP)
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
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





RE: Fully developed flow, Reynolds number
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
RE: Fully developed flow, Reynolds number
http://www.engineeringtoolbox.com/entrance-length-...
http://www.leb.eei.uni-erlangen.de/winterakademie/...
RE: Fully developed flow, Reynolds number
RE: Fully developed flow, Reynolds number
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
RE: Fully developed flow, Reynolds number
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
RE: Fully developed flow, Reynolds number
RE: Fully developed flow, Reynolds number
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.