ASHRAE FUNDAMENTALS IP CH 22-2013 Pipe Sizing.pdf
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1、22.1CHAPTER 22 PIPE SIZINGPressure Drop Equations . 22.1WATER PIPING 22.5Flow Rate Limitations. 22.5Hydronic System Piping 22.6Service Water Piping 22.8STEAM PIPING. 22.15Low-Pressure Steam Piping . 22.16High-Pressure Steam Piping . 22.16Steam Condensate Systems 22.16GAS PIPING 22.20FUEL OIL PIPING
2、22.21HIS CHAPTER includes tables and charts to size piping forTvarious fluid flow systems. Further details on specific pipingsystems can be found in appropriate chapters of the ASHRAEHandbook.Two related but distinct concerns emerge when designing a fluidflow system: sizing the pipe and determining
3、the flow/pressure rela-tionship. The two are often confused because they can use the sameequations and design tools. Nevertheless, they should be determinedseparately.The emphasis in this chapter is on the problem of sizing the pipe,and to this end design charts and tables for specific fluids are pr
4、e-sented in addition to the equations that describe the flow of fluids inpipes. Once a system has been sized, it should be analyzed withmore detailed methods of calculation to determine the pump headrequired to achieve the desired flow. Computerized methods arewell suited to handling the details of
5、calculating losses around anextensive system.PRESSURE DROP EQUATIONSDarcy-Weisbach EquationPressure drop caused by fluid friction in fully developed flows ofall “well-behaved” (Newtonian) fluids is described by the Darcy-Weisbach equation:p = f (1)wherep = pressure drop, lbf/ft2f = friction factor,
6、dimensionless (from Moody chart, Figure 13 in Chapter 3)L = length of pipe, ftD = internal diameter of pipe, ft = fluid density at mean temperature, lbm/ft3V = average velocity, fpsgc= units conversion factor, 32.2 ftlbm/lbfs2This equation is often presented in head or specific energyform ash = (2)w
7、hereh = head loss, ftg = acceleration of gravity, ft/s2In this form, the fluids density does not appear explicitly (al-though it is in the Reynolds number, which influences f ).The friction factor f is a function of pipe roughness , inside diam-eter D, and parameter Re, the Reynolds number:Re = DV/
8、(3)whereRe = Reynolds number, dimensionless = absolute roughness of pipe wall, ft = dynamic viscosity of fluid, lbm/ftsThe friction factor is frequently presented on a Moody chart (Fig-ure 13 in Chapter 3) giving f as a function of Re with /D as a param-eter.A useful fit of smooth and rough pipe dat
9、a for the usual turbulentflow regime is the Colebrook equation:= 1.74 2log (4)Another form of Equation (4) appears in Chapter 21, but the twoare equivalent. Equation (4) is useful in showing behavior at limit-ing cases: as /D approaches 0 (smooth limit), the 18.7/Re termdominates; at high /D and Re
10、(fully rough limit), the 2/D termdominates.Equation (4) is implicit in f; that is, f appears on both sides, so avalue for f is usually obtained iteratively.Hazen-Williams EquationA less widely used alternative to the Darcy-Weisbach formulationfor calculating pressure drop is the Hazen-Williams equat
11、ion, whichis expressed asp = 3.022L (5)orh = 3.022L (6)where C = roughness factor.Typical values of C are 150 for plastic pipe and copper tubing,140 for new steel pipe, down to 100 and below for badly corroded orvery rough pipe.Valve and Fitting LossesValves and fittings cause pressure losses greate
12、r than thosecaused by the pipe alone. One formulation expresses losses asp = K or h = K (7)The preparation of this chapter is assigned to TC 6.1, Hydronic and SteamEquipment and Systems.LD-gc-V22- p-gcg-f LD-V22g- =1f-2D-18.7Re f -+fVC-1.8521D-1.167ggc-VC-1.8521D-1.167gc-V22- V22g- 22.2 2013 ASHRAE
13、HandbookFundamentalswhere K = geometry- and size-dependent loss coefficient (Tables1 to 4).Example 1. Determine the pressure drop for 60F water flowing at 4 fpsthrough a nominal 1 in., 90 threaded elbow.Solution: From Table 1, the K for a 1 in., 90 threaded elbow is 1.5.p = 1.5 62.4/32.2 42/2 = 23.3
14、 lb/ft2or 0.16 psiThe loss coefficient for valves appears in another form as Cv, adimensional coefficient expressing the flow through a valve at aspecified pressure drop.Q = Cv(8)whereQ = volumetric flow, gpmCv= valve coefficient, gpm at p = 1 psip = pressure drop, psiSee the section on Control Valv
15、e Sizing in Chapter 47 of the 2012ASHRAE HandbookHVAC Systems and Equipment for moreinformation on valve coefficients.Example 2. Determine the volumetric flow through a valve with Cv= 10for an allowable pressure drop of 5 psi.Solution: Q = 10 = 22.4 gpmAlternative formulations express fitting losses
16、 in terms of equiv-alent lengths of straight pipe (Table 8 and Figure 7). Pressure lossdata for fittings are also presented in Idelchik (1986). p5Table 1 K Factors: Threaded Pipe FittingsNominal PipeDia., in.90StandardElbow90 Long-RadiusElbow45ElbowReturn BendTee-LineTee-BranchGlobe ValveGate ValveA
17、ngle ValveSwing Check ValveBell Mouth InletSquare InletProjected Inlet3/8 2.5 0.38 2.5 0.90 2.7 20 0.40 8.0 0.05 0.5 1.01/2 2.1 0.37 2.1 0.90 2.4 14 0.33 5.5 0.05 0.5 1.03/4 1.7 0.92 0.35 1.7 0.90 2.1 10 0.28 6.1 3.7 0.05 0.5 1.01 1.5 0.78 0.34 1.5 0.90 1.8 9 0.24 4.6 3.0 0.05 0.5 1.01 1/4 1.3 0.65
18、0.33 1.3 0.90 1.7 8.5 0.22 3.6 2.7 0.05 0.5 1.01 1/2 1.2 0.54 0.32 1.2 0.90 1.6 8 0.19 2.9 2.5 0.05 0.5 1.02 1.0 0.42 0.31 1.0 0.90 1.4 7 0.17 2.1 2.3 0.05 0.5 1.02 1/2 0.85 0.35 0.30 0.85 0.90 1.3 6.5 0.16 1.6 2.2 0.05 0.5 1.03 0.80 0.31 0.29 0.80 0.90 1.2 6 0.14 1.3 2.1 0.05 0.5 1.04 0.70 0.24 0.2
19、8 0.70 0.90 1.1 5.7 0.12 1.0 2.0 0.05 0.5 1.0Source: Engineering Data Book (Hydraulic Institute 1990).Table 2 K Factors: Flanged Welded Pipe FittingsNominal PipeDia., in.90StandardElbow90 Long-RadiusElbow45 Long-RadiusElbowReturn BendStandardReturn Bend Long-RadiusTee-LineTee-BranchGlobeValveGateVal
20、veAngleValveSwing Check Valve1 0.43 0.41 0.22 0.43 0.43 0.26 1.0 13 4.8 2.01 1/4 0.41 0.37 0.22 0.41 0.38 0.25 0.95 12 3.7 2.01 1/2 0.40 0.35 0.21 0.40 0.35 0.23 0.90 10 3.0 2.02 0.38 0.30 0.20 0.38 0.30 0.20 0.84 9 0.34 2.5 2.02 1/2 0.35 0.28 0.19 0.35 0.27 0.18 0.79 8 0.27 2.3 2.03 0.34 0.25 0.18
21、0.34 0.25 0.17 0.76 7 0.22 2.2 2.04 0.31 0.22 0.18 0.31 0.22 0.15 0.70 6.5 0.16 2.1 2.06 0.29 0.18 0.17 0.29 0.18 0.12 0.62 6 0.10 2.1 2.08 0.27 0.16 0.17 0.27 0.15 0.10 0.58 5.7 0.08 2.1 2.010 0.25 0.14 0.16 0.25 0.14 0.09 0.53 5.7 0.06 2.1 2.012 0.24 0.13 0.16 0.24 0.13 0.08 0.50 5.7 0.05 2.1 2.0S
22、ource: Engineering Data Book (Hydraulic Institute 1990).Table 3 Approximate Range of Variation for K Factors90 Elbow Regular threaded 20% above 2 in. Tee Threaded, line or branch 25%40% below 2 in. Flanged, line or branch 35%Long-radius threaded 25% Globe valve Threaded 25%Regular flanged 35% Flange
23、d 25%Long-radius flanged 30% Gate valve Threaded 25%45 Elbow Regular threaded 10% Flanged 50%Long-radius flanged 10% Angle valve Threaded 20%Return bend(180)Regular threadedRegular flangedLong-radius flanged25%35%30%Flanged 50%Check valve Threaded 50%Flanged +200%80%Source: Engineering Data Book (Hy
24、draulic Institute 1990).Pipe Sizing 22.3Table 4 Summary of K Values for Ells, Reducers, and ExpansionsPastaASHRAE Researchb,c4 fps 8 fps 12 fps2 in. S.R.eell (R/D = 1) thread 0.60 to 1.0 (1.0)d0.60 0.68 0.7364 in. S.R. ell (R/D = 1) weld 0.30 to 0.34 0.37 0.34 0.331 in. L.R. ell (R/D = 1.5) weld to
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