| Summary: | 博士 === 國立臺灣大學 === 機械工程學研究所 === 87 === This study investigates the characteristics of ejector that is the key-component of steam-jet refrigeration system. In addition, design method for enhancement of ejector performance is provided by using a noval application of petal nozzle.
The behavior and characteristics of a petal nozzle are investigated experimentally by testing it under various operating conditions, i.e. generator temperature, evaporator temperature and condenser temperature. In addition, the effects of AR (area ratio of constant area section of ejector to nozzle throat) and mixing length on ejector performance are studied by testing ejectors with various values of AR and mixing length of ejector. For comparison, a conventional conical nozzle with the same Mach number as that of petal nozzle is also used. Experimental results demonstrate that the compression ratio and the entrainment ratio can be enhanced if using the petal nozzle in an ejector with a larger AR value. Moreover, for the ejector with a petal nozzle, an optimum AR value exists under which a maximum compression ratio can be found. The results also show that decreasing the mixing length can increasing the performance of ejector.
An one-dimensional ejector theory is used to examine the effects on ejector performance of three isentropic efficiencies: nozzle efficiency ηn, mixing efficiency ηm, and diffuser efficiency ηd. Theoretical analysis demonstrates that mixing efficiency profoundly affects ejector performance, but that the other two efficiencies have slightly influenced ejector performance. This finding suggests that efficient mixing can promote ejector performance. This study also attempts to improve mixing efficiency using a petal nozzle. The results prove that using a petal nozzle can improve ejector performance.
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