Generalize Darcy-Weisbach for laminar flow

[mdbartos]

See:

pipedream/pipedream_solver/nsuperlink.py

Line 1857 in d381c66

f = 0.25 / (np.log10(n_ik / (3.7 * 4 * R_ik) + 5.74 / (Re**0.9)))**2