الفهرس 
INTRODUCTION AND LITERATURE REVIEWOnly 14 pages are availabe for public view
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Abstract
A great challenge all over the world is to find new resources for fresh potable water with low production cost. Water desalination technique is considered one of those main resources. Not only sea water but also brackish-water desalination, using reverse osmosis “RO” process is considered to be an energy intensive process, due to the high pressure of the membrane inlet stream (20-70 bar) depending upon the conductivity of feed water. The pressure, developed by the high pressure pump in the RO process, feeding the membrane is damped and lost in the concentrate stream through the throttling valve used to build up and control the inlet pressure to membranes in the conventional RO systems (with no energy recovery devices). Consequently, energy recovery has been a main parameter for the reduction of energy consumption in RO processes, causing a reduction of the permeate water production running cost. Many types of energy recovery devices are designed and developed to be used in high-capacity reverse osmosis plants. On the other hand, most of energy recovery devices are not commonly used in low-capacity desalination plants, (smaller than 50 m3/day), to reduce the capital cost of RO plants.Isobaric energy recovery systems are considered high efficient devices,they mainly consist of high-pressure pump, booster pump and energy recovery device as pressure exchangers. The booster pump in the RO systems is used to compensate the lost pressure through the membranes and the energy recovery device, to discharge the feed flow with pressure value equals to that obtained by the high-pressure pump (membrane inletpressure).iii In the present work, a new isobaric energy recovery system is designed, manufactured and tested experimentally, to overcome the three disadvantages of isobaric energy recovery device (ERD), Mix between feed flow and concentrate flow through ERD, booster pump in high pressure stream, feed pump lost energy through the throttle valve. In addition, the proposed energy recovery device consist of double acting hydraulic cylinder (DAC) which can be applied in reverse osmosis plants with low and moderate capacities at different conductivities (brackish and sea water) with high efficiency and low capital cost. The DAC simply controlled by hydraulic directional control valve (DCV), limit switches, and four check valves.An experimental study is conducted for a brackish and seawater reverse osmosis system of average capacity (40 m3/day), the RO unit is designed and installed especially for this research to operate using ERD(PX-30S and DAC) respectively. Different parameters (pressure, flow rate and specific energy consumption) are recorded at different conductivities of feed water (28, 37, 45 & 53 mS/cm). The experimental measurements are compared; the comparison shows promising results for the total specific energy consumption values for RO unit using (DAC). The main point is that the pressure DROP through DAC and RO membranes are compensated by the existing feed pump of the RO system, with no need for any extra high-pressure booster pump to be used in the high-pressure stream. Moreover there is no Mix occurring between feed and concentrate flow through the DAC.