Rearranging equations to find Internal roughness of a pipe.
For my one of my lab sessions we ran water through some pipe and recorded the time taken to fill the 40L basin, as well as knowing the head loss.
I have to find the internal roughness(ks) of the pipes using the following equations:
I know the: Reynolds number (66273.93)
Diameter (0.018m)
Friction factor (0.00214949)
I'm currently having trouble rearranging the equations and simply putting in the numbers as I currently come up with negative numbers for internal roughness.
I've linked how I've rearranged the equations to find x, so it's possible to see where I may have gone wrong.
Posted Oct 30, 2015, 12:36 AM UTC
210
what did the not-rearranged equations look like?
Also, where did you get friction factor from? I think it might be too low which is why you are getting negative values
I got the friction factor from using the Darcy-Weisback equation.
The original equations look like:
Barr
Colebrook-White
Moody
Prandt/Karman
I also got a negative value when I calculated it earlier.
Can you give me all the values (with units) that you used to calculate friction factor from the Darcy-Weisback eqn
I used:
Head flow (hf) as 0.207m
Velocity as 4.1m/s
Diameter as 0.018m
Length as 2m
Hm... no idea then. The only thing left I could think of is if there was an error in one of those values. Where did you get velocity or hf from?
I'm guessing the prof gave you diameter and length of pipe so the error can't be there.
The reason why I am thinking friction factor might be low is cause look at this moody chart below: You can't even get a pipe roughness from the chart cause the friction factor ranges start at .01
https://upload.wikimedia.org/wikipedia/commons/thumb/8/80/Moody_diagram.jpg/1024px-Moody_diagram.jpg