An evaporator comprising: a partitioned vessel for including a first effect and a second effect ; a first enclosure , wherein the first enclosure is a polymeric heat exchanger membrane having a thickness in the range of 0.03 to 0.05 mm and the first enclosure is disposed in the first effect and the first enclosure has a first receiver configured to receive vapors; a second enclosure , wherein the second enclosure is a polymeric heat exchanger membrane having a thickness in the range of 0.03 to 0.05 mm and the second enclosure is disposed in the second effect , wherein the second enclosure has a second receiver and the second receiver is configured to receive vapors from the first effect , wherein each of the first enclosure and the second enclosure is a sealed enclosure; a barometric coupler as a concentrate transfer mechanism, said barometric coupler couples the first effect and second effect , wherein, the barometric coupler is arranged to maintain a lower differential pressure in the range of 10 to 25 millibar absolute pressure across the first effect and the second effect , and wherein the first effect is configured to receive a feed and the second effect is configured to receive a concentrated feed from the first effect ; and the first enclosure has a first outer surface and the second enclosure has a second outer surface and the first effect is provided with a first recirculation pump (RP) configured to circulate the feed on the first outer surface and the second effect is provided with a second recirculation pump configured to circulate the concentrated feed on the second outer surface . a partitioned vessel for including a first effect and a second effect ; a first enclosure , wherein the first enclosure is a polymeric heat exchanger membrane having a thickness in the range of 0.03 to 0.05 mm and the first enclosure is disposed in the first effect and the first enclosure has a first receiver configured to receive vapors; a second enclosure , wherein the second enclosure is a polymeric heat exchanger membrane having a thickness in the range of 0.03 to 0.05 mm and the second enclosure is disposed in the second effect , wherein the second enclosure has a second receiver and the second receiver is configured to receive vapors from the first effect , wherein each of the first enclosure and the second enclosure is a sealed enclosure; a barometric coupler as a concentrate transfer mechanism, said barometric coupler couples the first effect and second effect , wherein, the barometric coupler is arranged to maintain a lower differential pressure in the range of 10 to 25 millibar absolute pressure across the first effect and the second effect , and wherein the first effect is configured to receive a feed and the second effect is configured to receive a concentrated feed from the first effect ; and the first enclosure has a first outer surface and the second enclosure has a second outer surface and the first effect is provided with a first recirculation pump (RP) configured to circulate the feed on the first outer surface and the second effect is provided with a second recirculation pump configured to circulate the concentrated feed on the second outer surface . <EOS>