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A pressure exchanger transfers pressure energy from a high pressure fluid stream to a low pressure fluid stream. Many industrial processes operate at elevated pressures and have high pressure waste streams. One way of providing a high pressure fluid to such a process is to transfer the waste pressure to a low pressure stream using a pressure exchanger. One particularly efficient type of pressure exchanger is a rotary pressure exchanger. This device uses a cylindrical rotor with longitudinal ducts parallel to its rotational axis. The rotor spins inside a sleeve between two end covers. Pressure energy is transferred directly from the high pressure stream to the low pressure stream in the ducts of the rotor. Some fluid that remains in the ducts serves as a barrier that inhibits mixing between the streams. This rotational action is similar to that of an old fashioned machine gun firing high pressure bullets and it is continuously refilled with new fluid cartridges. The ducts of the rotor charge and discharge as the pressure transfer process repeats itself. The performance of a pressure exchanger is measured by the efficiency of the energy transfer process and by the degree of mixing between the streams. The energy of the streams is the product of their flow rates and pressures. Efficiency is a function of the pressure differentials and the volumetric losses (leakage) through the device computed with the following equation: : where Q is flow, P is pressure, L is leakage flow, HDP is high pressure differential, LDP is low pressure differential, the subscript B refers to the low pressure feed to the device and the subscript G refers to the high pressure feed to the device. Mixing is a function of the concentrations of the species in the inlet streams and the ratio of flow rates to the device. ==Reverse Osmosis with Pressure Exchangers== One application in which pressure exchangers are widely used is reverse osmosis (RO). In an RO system, pressure exchangers are used as energy recovery devices (ERDs). As illustrated, high-pressure concentrate from the membranes () is directed () to the ERD (). The ERD uses this high-pressure concentrate stream to pressurize the low-pressure seawater stream (stream () becomes stream ()), which it then merges (with the aid of a circulation pump ()) into the highest-pressure seawater stream created by the high-pressure pump (). This combined stream feeds the membranes (). The concentrate leaves the ERD at low pressure (), expelled by the incoming feedwater flow (). Pressure exchangers save energy in these systems by reducing the load on the high pressure pump. In a seawater RO system operating at a 40% membrane water recovery rate, the ERD supplies 60% of the membrane feed flow. Energy is consumed by the circulation pump, however, because this pump merely circulates and does not pressurize water, its energy consumption is almost negligible: less than 3% of the energy consumed by the high pressure pump. Therefore, nearly 60% of the membrane feed flow is pressurized with almost no energy input. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pressure exchanger」の詳細全文を読む スポンサード リンク
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