Dear Yahia Albasha, You might ...

Dear Yahia Albasha, You might calculate flux / permeate of each Vessel but not each element. As a Vessel contains different configuration elements say up to 7 or so on. So all the elements are connected to each other to give you resultant permeate. You can put sampling point or flow meter at each vessel to understand how much feed you give in and how much you are getting as permeate and how many elements are there in the vessel (so you could have total area of membranes per vessel). This is how it works. By the way why are you willing to know what each element is giving you the flux as normally the membranes manufacturer while selecting the membranes for your specific needs, they give you what could be the estimated flux / permeate from their system. In case if you are not getting the desired, then you can investigate the reasons which could be many and most of the time these are learned by experience while you are running a plant specially at the initial stages to stabilize the system. In other words, sometimes theoretical things becomes difficult while you go practical.