Some Comments about the Friction Factor Method and Turbulent Flow

6 SOME COMMENTS ABOUT THE FRICTION FACTOR METHOD AND TURBULENT FLOW 

The three precejding examples show how we use the friction factor plot (Fig. 6.10). However, the calculations are not reliable to better than 10 percent, because the exact values of the roughnesses are seldom known to 

The plot is made up for sections of pipe which contain no valves, elbows, sudden contractions, sudden expansions, etc. These are probably present in all the actual situations described in Examples 6.3, 6.4, and 6.5. In Secs. 6.8 and 6.9 we discuss how to account for them. 

The data on which the plot is based are all taken well downstream of the entrance to the pipe. We discuss the entrance region briefly in Chap. 11. 

The friction factor plot is a generalization of experimental data. One should not attach too much theoretical significance to it. So far no one has been able to calculate friction factors for turbulent flow without starting with experimental data. 

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