Pipe relative roughness

Scope, 52 Basis, 52 Compressible Flow Vapors and Gases, 54 Factors of Safety for Design Basis, 56 Pipe, Fittings, and Valves, 56 Pipe, 56 Usual Industry Pipe Sizes and Classes Practice, 59 Total Line Pressure Drop, 64 Background Information, 64 Reynolds Number, R,. (Sometimes used Nr ), 67 Friction Factor, f, 68 Pipe—Relative Roughness, 68 Pressure Drop in Fittings, Valves, Connections Incompressible Fluid, 71 Common Denominator for Use of K Factors in a System of Varying Sizes of Internal Dimensions, 72 Validity of K Values,... 

Miscellaneous losses Total length of inlet piping Relative roughness, e/d... 

Figure 6 was created in this manner for a series of decade values of He. It may be used in place of the Moody chart for standard pipeline design problems. Because of the manner in which the empirical correlation for B was determined, no correction for pipe relative roughness is needed when one is dealing with commercial grade-steel line pipe. 

Figure 4.1 Moody diagram Fanning friction factor, f, vs. Reynolds number for the range of commercial pipe relative roughnesses.

Z>) For completely turbulent flow, we assume that viscous forces are negligible compared with the pressure and inertia forces, so that the only important force ratio should be the pressure coefficient. The length/ diameter ratio should be important as well as the pipe roughness. If we assume that for a constant pipe relative roughness the pressure coefficient is a constant times the length/diameter ratio, we can solve for the pressure drop per unit length ... 

Moody plot, chart, diagram A dimensionless representation of friction factor with Reynolds number tor a fluid flowing in a pipe. Presented on log-log scales, the diagram includes laminar, transition, and turbulent flow regimes. It also includes the effects of pipe relative roughness as a dimensionless ratio of absolute roughness with internal pipe diameter. The plot was developed in 1942 by American engineer and professor of hydraulics at Princeton, Louis Ferry Moody (1880-1953). 

Calculate the pressure drop of water through a 50-m long smooth horizontal pipe. The inlet pressure is 100 kPa, the average fluid velocity is 1 m/s. The pipe diameter is 10 cm and the pipe relative roughness is zero. Fluid density is 1 kg/L and viscosity is 1 cP. 

For laminar flow (Re < 2000), generally found only in circuits handling heavy oils or other viscous fluids, / = 16/Re. For turbulent flow, the friction factor is dependent on the relative roughness of the pipe and on the Reynolds number. An approximation of the Fanning friction factor for turbulent flow in smooth pipes, reasonably good up to Re = 150,000, is given by / = (0.079)/(4i e ). 

For smooth pipe, the friction factor is a function only of the Reynolds number. In rough pipe, the relative roughness /D also affects the friction factor. Figure 6-9 plots/as a function of Re and /D. Values of for various materials are given in Table 6-1. The Fanning friction factor should not be confused with the Darcy friction fac tor used by Moody Trans. ASME, 66, 671 [1944]), which is four times greater. Using the momentum equation, the stress at the wall of the pipe may be expressed in terms of the friction factor ... 

There are two approaches to fluid-generated noise control—source or path treatment. Path treatment means absorbing or blocking the transmission of noise after it has been created. The pipe itself is a barrier. The sound pressure level inside a standard schedule pipe is roughly 40-60 dB higher than on the outside. Thicker walled pipe reduces levels some at more, and adding acoustical insulation on the outside of the pipe reduces ambient levels up to 10 dB per inch of thickness. Since noise propagates relatively unimpeded inside the... 

Figure 3. Relative roughness of pipe materials and friction factors for complete turbulence. ...

The friction factor depends on the Reynolds number and duct wall relative roughness e/D, where e is the average height ol the roughness in rhe duct wall. The friction factor is shown in Fig. 9.46. For a Urge Reynolds number, the friction factor / is considered constant for rough pipe surfaces. The friction pressure loss is Ap c. ... 

Figure 2-11. Relative roughness factors for new clean pipe. Reprinted by permission from Pipe Friction Manual, 1954, The Hydraulic Institute. Also see Engineering Data Book, 1st Ed., 1979, The Hydraulic Institute. Data from L. F. Moody, see note Figure 2-3.

The relative roughness is expressed as E D, where E = the surface roughness and D = the internal pipe diameter. Typical values of E D are 0.0015 for drawn tubing, 0.046 for commercial steel and 0.12 for asphalted cast iron. 

Relative roughness, pipe, 132 Friction losses, 181 also see Chapter 2 Friction, head loss, 68 Compressible fluids, 101 Factor, 68 Vacuum lines, 131 Gas constants, R, 378 Gravity settlers, 228 Head, 180-200 Calculations, 183, 184, 185 Discharge, 180, 187 Friction, 183 Liquid, 183... 

Now the friction factor R/pu2 is a function of the Reynolds number Re and the relative roughness e/d of the pipe surface which will normally be constant along a given pipe. The Reynolds number is given by ... 

Values for the absolute surface roughness of commonly used pipes are given in Table 5.2. The parameter to use with Figure 5.7 is the relative roughness, given by ... 

Figure 5.7. Pipe friction versus Reynolds number and relative roughness...

Absolute roughness commercial steel pipe, table 5.2 = 0.46 mm Relative roughness, e/d = 0.046/40 = 0.001 Friction factor from Figure 5.7, / = 0.0027... 

Equation (7-25) is implicit for Dec, because the friction factor (/) depends upon Dec through the Reynolds number and the relative roughness of the pipe. It can be solved by iteration in a straightforward manner, however, by the procedure used for the unknown diameter problem in Chapter 6. That is, first assume a value for/ (say, 0.005), calculate Z>ec from Eq. (7-25), and use this diameter to compute the Reynolds number and relative roughness then use these values to find / (from the Moody diagram or Churchill equation). If this value is not the same as the originally assumed value, used it in place of the assumed value and repeat the process until the values of / agree. 

For turbulent flow of a Newtonian fluid, / decreases gradually with Re, which must be the case in view of the fact that the pressure drop varies with flow rate to a power slightly lower than 2.0. It is also found with turbulent flow that the value of / depends on the relative roughness of the pipe wall. The relative roughness is equal to eld, where e is the absolute roughness and d, the internal diameter of the pipe. Values of absolute roughness for various kinds of pipes and ducts are given in Table 2.1. 

Turbulent flow of Newtonian fluids is described in terms of the Fanning friction factor, which is correlated against the Reynolds number with the relative roughness of the pipe wall as a parameter. The same approach is adopted for non-Newtonian flow but the generalized Reynolds number is used. 

Using the relative roughness factor and friction factor to be 0.0006 and 0.004 again. The frictional loss in the pipe is... 

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