- #1
kosig
- 10
- 0
Hello. I have been asked to calculate the pressure drop across our fuel system. It is a large system with many fittings and bends. My numbers don't seem to make sense to me Please help...
Before I begin, I use equation dp=(K*density*MeanVelocity^2)/(2*g) to calculate pressure drop.
To calculate mean Velocity I am using V=(2.951e-5*W)/(d^2*rho)
where W is flow in lb/hr d=inner diameter (in) and rho=density (lb/in^3)
As far as I can tell this gives mean velocity in ft/s which I convert to in/hr. And I use g in terms of in/hr^2 which gives me final units of lb/in^2.
First: I was told to compare the drop as mass flow (lb/hr) changes from 0-5000 lb/hr. Also the applicable temperatures are -60-300 F. For ease here I will just pick a temp and a flow. These are what the system contains and the K values I assigned each feature-
4 gradual diameter contractions .23
2 gradual expansions .17
5 sharp 90 deg bends 1.1
4 gradual 90 bends .12
1 gradual 180 bend 2.17
10 "T" which I make the 90 bend 1.1
Total K=20.41
Total length=204.88 inches
I then try to use dp=(K*density*MeanVelocity^2)/(2*g)
where K= fL/d+loss from fittings
I got that the pressure drops 6e12 psi...What am I doing wrong?
Before I begin, I use equation dp=(K*density*MeanVelocity^2)/(2*g) to calculate pressure drop.
To calculate mean Velocity I am using V=(2.951e-5*W)/(d^2*rho)
where W is flow in lb/hr d=inner diameter (in) and rho=density (lb/in^3)
As far as I can tell this gives mean velocity in ft/s which I convert to in/hr. And I use g in terms of in/hr^2 which gives me final units of lb/in^2.
First: I was told to compare the drop as mass flow (lb/hr) changes from 0-5000 lb/hr. Also the applicable temperatures are -60-300 F. For ease here I will just pick a temp and a flow. These are what the system contains and the K values I assigned each feature-
4 gradual diameter contractions .23
2 gradual expansions .17
5 sharp 90 deg bends 1.1
4 gradual 90 bends .12
1 gradual 180 bend 2.17
10 "T" which I make the 90 bend 1.1
Total K=20.41
Total length=204.88 inches
I then try to use dp=(K*density*MeanVelocity^2)/(2*g)
where K= fL/d+loss from fittings
I got that the pressure drops 6e12 psi...What am I doing wrong?