P(E, W) = p • A (kp = (kp/m²) • m²)
Note: The above formulae are simplified and intended only for purposes of rough estimation.
10.2 Gas-law calculations
10.2.1 Calculating the pressure drop in a gas pipe
dp = FL + Ztot
dp = pressure drop (N/m²)
FL = friction losses in the gas pipe (N/m²)
Ztot = sum total of friction losses from valves, fittings, etc. (N/m²)
dp = cp l/D • D/2 v2
+ (cfl D/2 • v2 + . . . + cfn • D/2 • v2)
(approximation formula)
cp = coefficient of pipe friction (-)
l = length of pipe section (m)
D = pipe diameter(m)
g = density of biogas (1.2 kg/m³)
v = velocity of gas in the pipe (m/s)
cf = friction coefficients of valve, fittings, etc.
Q=v•A
Q = gas flow (m³/s)
v = velocity of gas in the pipe (m/s)
A = p r2 = cross-sectional area of pipe
The coefficient of pipe friction (cp = non. dimensional) is a function of:
- the pipe material and internal surface roughness
- pipe diameter
- flow parameter (Reynolds number)
For pipe diameters in the 1/2" . . . 1" range, the coefficients of friction read:
PVC tubes approx. 0.03
steel pipes approx. 0.04
Some individual friction-loss factors (cf; nondimensional)
elbow
constriction
branch
0.5
0.02-0.1
0.8-2.0
valve 3.0
water trap 3 - 5
10.2.2 Calculating gas parameters
Temperature-dependent change of volume and density
D = DN • P • TN / (PN • T)
V = VN • PN • T / (P • TN)
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