Roughness piping material

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 ... 

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

Thus, if we were to use the same pipe material (commercial steel) for the model as in the field, we would also have to use the same diameter (48 in.). This is obviously not practical, but a smaller diameter for the model would obviously require a much smoother material in the lab (because Dm -C Df requires em drawn tubing such as copper or stainless steel, all of which have equivalent roughness values of the order of 0.00006 in. (see Table 6-1). 

The opposite conclusion would presumably apply to dilatant fluids and for these the pressure drop in a rough pipe may perhaps exceed that for a Newtonian fluid. A similar situation might also arise for Bingham-plastic and pseudoplastic materials which exhibit elastic recovery to a high degree. 

FIGURE 3B Roughness factors for selected types of pipe materials. [Adapted from Moody, L. F. (1944). Trans. ASME 66, 671-684.]... 

The friction factor, f, depends on the Reynolds number and the relative roughness, e/D. Table 8.4 contains roughness factors, s, for several pipe materials. Surface roughness is very irregular and non-uniform. Thus, e for any pipe material is an average value. Figure 8.16 is a plot of the friction factor as a function of Reynolds number with the relative roughness as a parameter. 

A detailed review of other explicit equations is given by Gregory and Fogarasi [7]. Different piping materials are often used in the chemical process industries, and at a high Reynolds number, the friction factor is affected by the roughness of the surface. This is measured as the ratio e/D of projections on the surface to the diameter of the pipe. Glass and plastic pipe essentially have e = 0. Values of e are shown in Table 3-3. 

The actual size of the roughness elements on any surface will vary with the material, age and usage, deposits, dirt, scale, rust, etc. Typical values for various materials are given in Table 5.3. The most common pipe material—clean, new, commercial steel—has an effective roughness of about 0.0018 in. (0.045 mm). Other surfaces, such as concrete, may vary as much as several orders of magnitude, depending upon the nature of the surface finish. 

There are insnfficient data in the literatnre to provide a reliable estimate of the effect of roughness on friction loss for non-Newtonian flnids in tnrbnlent flow. However, the influence of roughness is normally neglected, since the laminar bonndary layer thickness for such fluids is typically much larger than for Newtonian fluids (i.e., the flow conditions most often fall in the hydraulically smooth range for common pipe materials). An expression by Darby et al. (1992) for / for the power law flnid, which applies to both laminar and turbulent flow, is... 

Petrol flows through a horizontal pipe with DN25 (internal diameter dj = 27.2 mm, cross sectional areapR = 5.81 x 10 " m ) and a length of 100 m. At a distance of 1 = 10 m downstream a leak with a cross sectional area of Fl = 7.85 X 10 m opens. Upstream of the leak there is a shut-off valve with a friction coefficient = 0.8. The built-in devices downstream from the leak are represented by the friction coefficient Ca = 3. The roughness of the pipe material is k = 0.4 mm and the coefficient of discharge p = 0.62. The pressure upstream is Pi = 2 bar (it is assumed to be constant despite flow and losses from the leak). The atmospheric pressure is pa = 1 bar. 

Table 20.3. Absolute surface roughness of selected pipe materials...

For real pipes, we need an additional parameter to describe the flow - the tube roughness. Roughness is an inherent property of the pipe material glass tubes are smoother... 

Roughness of the pipe wall is an important design parameter for pressure drop calculation. The roughness depends on the type of pipe being used. Most commonly used pipe materials have roughnesses as given in Table 2.3. 

An ASME 2 1 elliptical heads can ensure an increase in pressure resistance of die vessel. Fermenter jackets (e.g., half-pipe, diameter, or true type) should be constructed to sustain die vessel s rated pressure and, thus, enhance its strength. The construction material is type 316L stainless steel, which features an internal mechanical-polish finish of 2B-mill or 25-Roughness Average (Ra) depending on the nature of the fermentation. 

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