K value for a double shutoff quick disconnect.
K value for a double shutoff quick disconnect.
(OP)
I am doing a relatively simple flow analysis on a piping network and I ran into a problem. The piping network was some quick disconnects that are giving me large minor losses. For instance, the manufacturers catalog data shows that at 8gpm the qd has a 5psi(guage) pressure drop. From manometry deltaZ=(deltaP/specific weight) right? Using this simple equation should give the equivalent height(or depth if you prefer) of the fluid corresponding to this pressure change. Also the minor loss of some component could be found by Hm=(K*V^2)/(2*g), where Hm is the head loss. Solving for K gives (2*Hm*g)/V^2. I am after the K value(I am summing all minor losses) but when I substitute in say 8gpm and the 5psi drop, I end up with K being around 45 which seems absurd. I think I am doing this wrong but am not sure. Any ideas/criticism please let me know. Thanks
Pipe ID=0.82 in, g=32.174 ft/s^2, V=Q/A=4.86ft/s,specific weight=43.73 lb/ft^3, rho=1.359 slug/ft^3, Re=360 which is <2300 so laminar, if I forgot anything else just ask me.
Pipe ID=0.82 in, g=32.174 ft/s^2, V=Q/A=4.86ft/s,specific weight=43.73 lb/ft^3, rho=1.359 slug/ft^3, Re=360 which is <2300 so laminar, if I forgot anything else just ask me.





RE: K value for a double shutoff quick disconnect.
I assume your viscosity is 5.99E+01 cp. Then given the conditions you describe, I estimate the equivalent length of a 5 psi drop is about 17.3 feet of 0.82 pipe or a K value of about 6.4.
Also, are you using psi when you should be using psf?
RE: K value for a double shutoff quick disconnect.
RE: K value for a double shutoff quick disconnect.
K can be gotten from the relation L/D = K/ft, where ft is the fully turbulent flow friction factor, L is the equiv L and D is the pipe dia(in L units.)
RE: K value for a double shutoff quick disconnect.
V=15.9 m/s
ρ=700 kg/m3
velocity head H=ρV2/2=88000 Pa = 0.88 bar = 13 psi
K=5/13=0.4
prex
http://www.xcalcs.com
Online tools for structural design
RE: K value for a double shutoff quick disconnect.
The short answer is that you are spot on with your calcs. It is a long time since I tried to work in pounds force per square foot and slugs per cubic foot! Thank goodness for the SI system. I agree with prex that the old units were awful (NB prex, 4.86 ft/s is 1.48 m/s and not 15.9 m/s).
The reason for your seemingly high K value is the low Reynolds number. Compilations of K values should always include the warning that they apply to turbulent flow only. In turbulent flow the K value of a fitting is more-or-less independent of the Reynolds number, but the K value of a given fitting increases as the Reynolds number decreases below 2300. Hooper introduced the 2-K method and later Darby extended it to the 3-K method in an effort to take changing diameter and Reynolds number into account. These concepts are discussed at http://www.cheresources.com/eqlength.shtml
RE: K value for a double shutoff quick disconnect.
RE: K value for a double shutoff quick disconnect.
Such an astute observation deserves more than one star. Good link. Do you have a copy of the Hooper paper that you can make available?
RE: K value for a double shutoff quick disconnect.
RE: K value for a double shutoff quick disconnect.
I think there would be copyright issues preventing me distributing copies of this article. If you cannot get to a university library yourself I would think that you could request a copy of the article via your local library. The reference was in the link I gave previously