マルチノズル亜音速空気エゼクタの性能 : ノズルスペーシングおよびディフューザ平行部の影響 Performance of Subsonic Air Ejector with Multiple Nozzles : Effects of Dimensions of Nozzle Spacing and Parallel Part of Diffuser

シングルノズルエゼクタに関する研究は,今日までに多数発表されてきたが,マルチノズルを有する亜音速空気エゼクタに関する研究はほとんどなされておらず,その設計資料も見あたらない.本研究では,マルチノズル亜音速空気エゼクタのノズルスペーシングと,ディフューザの平行部の寸法がエゼクタの性能に及ぼす影響について実験し,シングルノズルエゼクタの場合と比較・検討した.その結果,マルチノズルを採用することによって,シングルノズルエゼクタに比べて次のことが可能となることが明らかとなった.1)ディフューザの平行部の短縮2)騒音の低減

Many theoretical and/or experimental studies on the performance of the supersonic ejector with single nozzle have been published. However, few studies have been reported on the supersonic ejector with multiple nozzles and the subsonic ejector with multiple nozzles. This report offers some new data for the design of the subsonic ejector with multiple nozzles. The effects of the dimensions of the parallel part of the diffuser and the nozzle spacing on the performance of the multiple nozzle subsonic air ejector were investigated experimentally. Parallel parts having lengths of 1, 2, 3, 4, 5, 6, 7 and 9 times the diameter of the parallel part of the diffuser were tested. The nozzle spacing was varied from of -1/2 to 1 times the diameter of the parallel part of the diffuser. The ejector was run under the following conditions. The driving air pressure was kept constant at 400mmHg or 200mmHg. The entrained air flowing into the low pressure tank from the atmosphere was driven by the ejector. The temperature of both the driving and the entrained air was kept equal to the room temperature. The mixed air was exhausted to the atmosphere through the exhaust pipe. The performance of each test ejector was measured and the results were compared. The performance of the ejector was described by the ratio of entrained air flow to driving air flow, ratio of driving air pressure to entrained air pressure at the ejector entrance, compression ratio of the entrained air, and the adiabatic efficiency. The results can be summarized as follows; 1) The optimum length of the parallel part of the diffuser of the multiple nozzle ejector can be reduced to about 1/√<N> times that of the single nozzle ejector, where N is the number of nozzles. The nozzle spacing of the multiple nozzle ejector should be made slightly larger than that of the single nozzle ejector. 2) The use of multiple nozzles contributes to a reduction of ejector noise during operation. 3) The maximum efficiency of a single nozzle ejector with the optimum dimensions (η_<max>&ap;25%) is about 1% greater than that for a multiple nozzle ejector with the optimum dimensions. In the range beyond k at which efficiency is maximum, the multiple nozzle ejector demonstrates slightly better performance than the single nozzle ejector.