High-pressure water as the driving fluid in an ejector refrigeration system

Results are presented from an experimental investigation into the use of high-pressure water as the driving fluid in an ejector refrigeration system, the purpose of which was to chill water. The investigation originated from the concept of boosting the refrigeration capacity available for local-area use in underground mines, by utilising directly the high static pressures available from pipelines carrying large quantities of water down deep mine shafts. Previous studies of liquid–gas ejectors (jet pumps) were limited to driving water pressures up to 1950 kPa. The present work considers driving pressures between 4000 and 15,000 kPa, for which no design or performance information could be found in the literature. An experimental facility was used to investigate vacuum boiling under batch (static) operating conditions. The dimensions of the ejector components (nozzle and mixing tube diameters and mixing tube length) could be varied in order to achieve the best performance. No previously-reported ejector system has achieved a reduction in the process liquid temperature in the evaporator (which is saturated at the evaporator pressure) to a level below the temperature of the driving fluid. In contrast, the present work demonstrated that such a cooling effect could occur under batch conditions with driving water pressures above 5000 kPa. Using the measured evaporator transient temperature response it was possible to estimate the performance of a continuously-operating water cooling system.