Darcy Friction Factor (VBA)

darcy.bas

Function f(e, D, Re)
    ' Returns: Darcy friction factor
    ' Parameters:
    '   e: absolute roughness
    '   D: duct diameter
    '   Re: Reynold's number
    A = -2 * Log10(e / D / 3.7 + 12 / Re)
    B = -2 * Log10(e / D / 3.7 + 2.51 * A / Re)
    C = -2 * Log10(e / D / 3.7 + 2.51 * B / Re)
    f = (A - (B - A) ^ 2 / (C - 2 * B + A)) ^ -2
End Function

Private Function Log10(x)
    Log10 = Log(x) / Log(10)
End Function