1. For 1 casing with 99 membranes: QR = 1 m3/h/membrane/m/s x 99 membranes x 3.5 m/s = 346.5 m3/h. Using this flow and, to reduce the pressure drop, a circulation speed in the loop of 1.5-2 m/s is taken, then the diameter of the recirculation loop should be 12”.