| Summary: | 碩士 === 國立雲林科技大學 === 機械工程技術研究所 === 85 ===
Cavitating Venturi (CV) has been widely accepted as a flow control device in many different industries. However, the design and the operation of a cavitating venturi used in space is quite different in many ways from that used in the industry, such as low mass flowrate, small size, low pressure difference between inlet and outlet, and low inlet subcooling. In 1990, cavitating Venturi's performance tests had been carried out at U.S. NASA Johnson Space Center using liquid ammonia as the operation fluid. It is found that under low inlet subcooling, a phenomenon called over flow will occur. Although data was obtained and analyzed, no useful correlation was achieved. Therefore, the objective of this study is to conduct a performance test on Cavitating Venturi (CV) under low inlet subcooling. Water is uses as the operation fluid. Data acquisition and analysis are carried out under normal choked flow, over flow and recovery conditions. The effects of different factors, such as CV's size and donfiguration, fluid properties, flow condition and inlet subcooling, on CV's performance are evaluated.
Based on the test results, the loss coefficient of the cavitating venturi with throat diameter of 1.16mm and 0.91mm is 0.19 and 0.22 correspondingly. For a cavitating venturi under fixed operation temperature, it is noticed that under the higher inlet pressure, the throat superheat becomes more obvious as it resumed choked flow. However, if we fix the inlet pressure and varied the operation temperature, a lower superheat is obtained at the recovery under higher inlet temperature. In addition, when the operation temperature and inlet pressure are fixed, the CV with bigger throat diameter has smaller rechoked pressure ratio because of the lower loss coefficient. Also, according to the analysis, the trend of the superheat can be reasonably predicted using the pool boiling theory. Hopefully, with more test data in the future, a correlation concerning cavitating venturi's behavior on throat superheat can be established, which will be very useful for predictig the flow recovery accurately.
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