Machinery's Handbook, 31st Edition
2782
Hazen-Williams Equation Table 23. Hazen-Williams Coefficient, Selected Values Pipe Type C h Pipe Type
C h
Corrugated Metal ABS Plastic
60 130
Copper
130–140 130–140
Drawn metal Ductile iron pipe Fiberglass Galvanized iron Ductile iron, cement lined
Aluminum
130–150 130–140
140 120 150 120 130
Brass
Cast iron
100 130
new unlined 10 years old 20 years old 40 years old
107–113 89–100 64–83
Glass Lead Plastic
130–140 130–150
asphalt coated bituminous lined cement lined sea-coated
100 140 140 120 140 120
Polyethylene PVC, CPVC Steel new unlined
140 150
140–150
Concrete
100–140
lined, steel forms lined, wooden forms
Energy Loss for Gas Flow: Bernoulli’s equation can be applied to examine pressure loss for gas flow through pipes. Gas flowing through pipes can be considered incompressible and treated like a liquid if the pressure ratio is small enough. Pressure ratio is calculated using the following equation. Engineering judgment should be used when applying this equation. In different industries, different values are used to make the decision how to treat gas flow. PR % 100 p 1 p 2 – p 1 --------- = where p is pressure at the point of interest and PR% is the pressure ratio. Pressure drop for gas flow in pipes can be calculated most easily if certain assumptions are made. One can assume flow is isothermal, the gas is perfect, the pipe is straight and horizontal, the friction factor is constant, and flow is steady. This simplifies the pressure drop equation to the following form: p i 2 p o 2 – Z m RT m · = where p i and p o are the inlet and outlet pressures, Z m is the mean compressibility factor, R is the gas constant, T is temperature, A is pipe cross sectional area, f is the friction factor, L is pipe length, D is inner diameter, and m · is mass flow rate. Alternative methods of calculation include the Weymouth and Panhandle formula, and the Renouard equation for natural gas flow. A -- 2 f L D -- Energy Loss in Pipe and Tube Bends.— The energy lost by fluid in a pipe bend is caused by both friction and momentum changes as the direction of flow changes. This loss de - pends on the bend angle, the curvature ratio (bend mean radius divided by pipe diameter, R / D ), the roughness of the pipe, and the angle of bend. To compute the energy lost by liq uids in bends, use the following equations and Table 24. h l K b = K b f where the head loss, h l , is expressed in units of length; V is the average velocity in the pipe; and K b is the bend loss coefficient; f is the friction factor given in the Moody diagram, (Fig. 1); and L e / D is given in Table 24. K b increases with relative roughness (or screwed connec tions) and bend angle, but decreases with the curvature ratio. V 2 2 g --- L e D = ---
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