Frictional Pressure Loss in Rough and Smooth Pipe

4 Frictional Pressure Loss in Rough and Smooth Pipe 

We now have to thank Stanton and Pannell, and also Moody, for their studies of flow using numerous fluids in pipes of various diameters and surface roughness and for the evolution of a very useful chart (see Fig. 40.6). This chart enables us to calculate the frictional pressure loss in a variety of circular cross-section pipes. The chart plots Reynolds number (Re), in terms of two more dimensionless groups a friction factor ( ), which represents the resistance to flow per unit area of pipe surface with respect to fluid density and velocity and a roughness factor e/ID, which represents the length or height of surface projections relative to pipe diameter. 

Fioure 40.6 Friction factor c ) vs. Reynolds number. (Reproduced by kind permission of J. F. Richardson. ) 

Please bear in mind that two other friction factors are also in common use. These are the Fanning friction factor,/, which equals 2( ), and the Moody friction factor,/, which equals 8( ). 

Looking at the friction factor chart (Fig. 40.6), we see how the experimental data further confirms Reynold s earlier work and helps us even today with our own field work. Once we have determined the friction factor ( ) for the pipe flow we are studying, all that remains is to evaluate the frictional pressure loss, AP/from 

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