Finding pipe diameter from pressure drop formula with given flow rate

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
1 reply · 2K views
mrose94
Messages
1
Reaction score
0
Homework Statement
A compressor delivers 300 s–1 of free air into a pipe at a pressure of
6 bar gauge. Using the pressure drop formula: Pressure drop = 800lQ^2/Rd^5.31. Calculate the minimum diameter of pipe if the pressure drop in a system is
to be limited to 0.3 bar when is delivered through a pipe of equivalent
length 160 m .
Relevant Equations
pressure drop = 800lQ^2/Rd^5.31
Hello.

My attempt at the solution is as follows:

l = 160m
Q= 300 ls-1
R= p2/p1= 6+1.01/1.01 = 6.94 (2dp)
d = Unknown
Pressure drop = 0.3 Bar

0.3 = 800*160*300^2/6.94*d^5.31

0.3 = 1.152x10^10/6.94*d^5.31

0.3 ( 6.94*d^5.31) = 1.152x10^10

6.94*d^5.31 = 1.152x10^10/0.3

d^5.31 = (1.152x10^10/0.3)/6.94

d= 5.31 root (1.152x10^10/0.3)/6.94

d= 394984.81 mm (I think mm is correct?)

d= 394.98 M

I'm struggling to see how this answer can be correct as an internal diameter of a pipe being so large seems ridiculous to me. Any help as to where I've gone wrong would be appreciated. Thank you!
 
Physics news on Phys.org
In the pressure drop formula what are the units of the various parameters supposed to be?