Why the Fluid Friction Factor should be Abandoned, and the Moody Chart Transformed

ABSTRACT

The “fluid friction factor” (f) should be abandoned because it is a mathematically undesirable parameter that complicates the solution of fluid flow problems.

f is the dimensionless group π²gPD⁵/8LW². This group is mathematically undesirable because it includes ΔP, W, and D. Therefore if f is used in the solution of a problem, the problem must be solved with ΔP, W, and D in the same term, even though fluid flow problems are generally much easier to solve if ΔP, W, and D are in separate terms. (Just as it is generally much easier to solve equations if x and y are in separate terms).

The mathematical complication introduced by f is illustrated by the Moody chart (Fig. 1). Because the chart is based on f, it must be read iteratively (or by trial-and-error) to determine W or D. But if the Moody chart is transformed in order to eliminate f, the transformed chart (Fig. 2) is read directly to determine ΔP, W, or D.

The fluid flow methodology described herein altogether abandons f, and allows fluid flow problems to be solved in the simplest possible manner.