Solution-diffusion reverse osmosis (same equations as the 3D version):
pi = i C R T (van t Hoff), T = 298 K
pi_avg = (pi_feed + pi_conc)/2, conc = feed/(1 - r)
NDP = dP - pi_avg ; Jw = A_m NDP
Cp = B Cf 1.2 / (Jw + B) , R = 1 - Cp/Cf
SEC = dP Qf / (3.6e6 eta Qp), eta = 0.75
min SEC = pi_feed ln(1/(1-r)) / r
Below the osmotic pressure there is no flow; higher pressure raises flux but also energy per cubic metre.