喷嘴出口状态对水蒸汽喷射器流动行为及其性能的影响

Numerical Investigation of the Nozzle Exit State and Its Effect on the Performance of the Steam Ejector

水蒸气喷射器作为一种结构简单、运行稳定的真空获得设备,其内部流动过程十分复杂。目前关于蒸汽喷射器的研究已较为完善,然而对于蒸汽喷射器的膨胀状态的研究很少涉及。为了进一步完善蒸汽喷射器的膨胀状态的分类,并且对在不同膨胀状态下蒸汽喷射器的内部流动行为及其对蒸汽喷射器性能的影响进行研究。文章以数值模拟技术为主要研究方法,研究了蒸汽喷射器喷嘴不同出口状态的流场结构及其对水蒸气喷射器性能的影响。结果表明:喷嘴的运行状态可分为欠膨胀状态、完全膨胀状态、过膨胀状态以及非拉瓦尔喷嘴状态,并且引射压力的变化对扩压器壁面剪切应力的影响远远大于喷嘴。在兼顾水蒸气喷射器的抽气能力、效率、排气能力以及获得真空度能力的同时,蒸汽喷射器在完全膨胀区域与过膨胀区域运行时可以获得较高的引射系数和压缩比,并且在过膨胀区域内具有最优的工况条件。此外,完全膨胀区域仅为一个点值。

As a simple and stable vacuum acquisition device,the internal flow process of the steam ejector is very complicated.At present,the research on the steam ejector has been relatively perfect,but the research on the expansion state of the steam ejector is rarely involved.To further improve the classification of the expansion state,the internal flow behavior of the steam ejector under different expansion states and its influence on the performance of the steam ejector are studied.In this paper,the CFD method is used as the main research method to study the flow field structure of different nozzle exit states and its influence on the performance of the steam ejector.The results show that the nozzle exit state can be divided into under-expanded state,full-expanded state,over-expanded state and non-Laval nozzle state,and the change of the secondary fluid pressure has a greater influence on the wall shear stress of the ejector than that of the nozzle.While taking into account the pumping capacity,efficiency,exhaust capacity and vacuum capacity of the steam ejector,the steam ejector can obtain a higher entrainment ratio and compression ratio in the full-expanded zone and over-expanded zone,and there is an optimal working condition in the over-expanded zone.In addition,the full-expanded zone is only a point value.