Viking ESFR Technical Data Manual page 10

Page 10
March 7, 2008
ESFR PRE-PRIMED SINGLE
INTERLOCK PREACTION
TECHNICAL DATA
COLD STORAGE SYSTEM
The Viking Corporation, 210 N Industrial Park Road, Hastings MI 49058
Telephone: 269-945-9501 Technical Services 877-384-5464 Fax: 269-945-4495 Email: techsvcs@vikingcorp.com
Darcy-Weisbach Method for Calculating Friction in Piping:
Most hydraulic calculation software used in the sprinkler industry today has the option for conducting
the piping friction loss calculations with the Darcy-Weisbach method. The reason for conducting the
additional 6 sprinkler head calculation is to verify that the available water supply pressure is adequate
for the initial discharge of propylene glycol solution. The example calculations provided in Figures 6-
8 illustrate the difference in results that can occur when calculating for the more viscous propylene
glycol solution versus the standard Hazen-Williams calculation for water illustrated in Figures 3-4.
For those not familiar with the Darcy-Weisbach method below is the basic procedure that is used to
conduct the calculation. This is intended only to provide the designer with an understanding of the
concepts of the method. It is not practical that the calculation be done by hand as this would be much
too time consuming and subject to potential errors.
2
The Darcy-Weisbach Formula as found in most text is written as: h= (f) (l) (v) / (d) (2) (g)
h=friction loss (ft of head)
f=friction factor (from Moody Diagram-Figure 10)
l=length of pipe (ft)
v=velocity (ft/sec)
d=diameter of pipe (ft)
g=gravitational constant (32.2 ft/sec 2 )
This formula can be rearranged and simplified to:
2 5
When the calculated Reynolds Number (Re) is >2000 =0.000216 fLρQ /d =Friction Loss (psi)
When the calculated Reynolds Number (Re) is <2000 =0.000273 μLQ/d
4 =Friction Loss (psi)
Where:
Re=50.6Qρ/dμ
Q=flow (gpm)
ρ=density (lbs/ft
3 )
d=internal pipe diameter (in)
D=internal pipe diameter (ft)
L=pipe length (ft)
μ=dynamic viscosity (cps)
ε= .00033 for steel pipe
f=friction factor, If Re > 2000, use Moody Diagram (Figure 10). If Re < 2000, f = 64/Re.
Procedure:
1. Calculate Reynolds Number (Re) = 50.6Qρ/dμ
2. Calculate relative roughness of pipe = ε/D
ε= .00033 (ft)
D=internal pipe diameter (ft)
3. Use Moody Diagram (Figure 10) to find "f" if Re > 2000. If Re < 2000, f = 64/Re.
4. Use fiction loss in hydraulic calculation.