【作者】 李鹏；

【导师】 杨勇；

【作者基本信息】 大连理工大学 ， 热能工程， 2016， 硕士

【摘要】 喷射式真空泵结构简单,无运动部件,安装简单,维修保养费用低,不消耗电能,这些特点使得喷射式抽真空系统广泛应用于化工、石油、冶金、制冷、食品工业等工程行业。本文从喷射式抽真空系统中核心装置喷射器的结构设计计算,及其特性曲线的计算方法着手,整理出喷射器结构设计与性能计算程序,以及蒸汽喷射器抽真空系统抽吸时间计算方法。接着,对喷射式抽真空系统工作性能做出评价,并对喷射式抽真空系统进行了(火用)析。本文模拟出喷射式抽真空系统把一个密闭室的压力从P0抽吸至P,工作蒸汽参数、出口流体参数对抽吸时间的影响规律。在密闭室压力达到某一值之前,工作蒸汽压力与出口流体压力的变化对抽气时间几乎没有影响,而在该压力值之后,抽真空系统性能明显降低,密闭室压力下降非常缓慢。选用工作蒸汽压力0.78MPa,出口流体压力保持在0.095MPa,可以使本文模拟尺寸的喷射式抽真空系统获得最好的抽吸效果。对于固定结构的单级喷射器抽真空系统,系统极限真空度随着动力蒸汽压力升高而提高,而随着出口流体压力升高而降低；对于单级喷射器抽真空系统,随着动力蒸汽压力升高抽真空系统单位抽气量越大,系统抽吸能力越强,同时,得出系统稳定运行时出口流体压力越大单位蒸汽耗量越多,系统节能效果越差。系统稳定运行时抽吸流体压力越大单位蒸汽耗量越少,系统节能效果越好。在研究工作蒸汽压力、抽吸流体压力对抽真空系统中喷射器(火用)损的影响时,发现混合室(火用)损是喷射器(火用)损的主要来源。随着工作流体压力从0.28MPa增加到1.08MPa,混合室(火用)损占喷射器(火用)损比重由52.3%上升到74.7%,而随着抽吸气体压力从0.02MPa变化到0.07MPa,混合室(火用)损占喷射器(火用)损比重由73.7%下降到57.5%。随着喷射器混合室直径增大混合室(火用)损增加,在不同的真空段混合室直径的变化对混合室炯损影响有较大的差别。根据唯象等熵理想喷射器模型计算出了相应工况下的理想喷射系数,定量说明了本文设计喷射器满足喷射器效率η大于实际喷射系数与理想喷射系数之比u/u’。更多还原

【Abstract】 Jet vacuum pump is applied broadly in petrochemical,metallurgy,refrigeration and food industry due to its simplicity and reliability as well as it has no motive part and no costs of mechanical work and electronic energy.The purpose of this article is to conclude the calculation program of ejector’s structure and performance based on the structure design and characteristic curves of ejector which is core unit of jet vacuum pump system.Otherwise,it evaluates the performance and analysis exergy ofjet vacuum system.This paper simulated pressure from PO to P in a closed chamber and the influence of working steam parameters and outlet fluid parameters to extraction time. The results indicated that working steam parameters and outlet fluid parameters has no effect on extraction time before pressure reaches certain value,however,the performance of vacuum system is reduced significantly after this value,and the pressure drop very slow in a closed chamber.It can be seen that the jet vacuum system has the best performance when working steam pressure was 0.78MPa and outlet fluid pressure was 0.095MPa.For the fixed structure of single-stage ejector vacuum system,it concluded that the limiting vacuum increased when the motive steam pressure rise while decreased with outlet fluid pressure.With the increasing of motive steam pressure,the unit swept volume was greater,and the extraction ability of vacuum system increased. At the same time,it is concluded that the greater of outlet pressure,the greater of unit steam consumption,and the energy efficient is poorer.However,the system energy efficient is better with the increasing of suction fluid pressure when the system at stable operation.According to the research,exergy loss in mixing chamber is the main exergy loss compared with working steam pressure and suction steam pressure.The exergy loss of mixing chamber increased from 52.3% to 74.7% with working steam pressure increasing from 0.28MPa to 1.08MPa.However,the exergy loss of mixing chamber decreased from 73.7% to 57.5% with suction steam pressure increasing from 0.02MPa to 0.07MPa.When diameter of mixing chamber increased,both the exergy loss of mixing chamber and the exergy loss of ejector increased.lt has big difference on exergy loss of mixing chamber because the change of diameter of vacuum mixing chamber.According to victoria isentropic ideal ejector model, we can calculate the ideal entrainment ratio under corresponding operating conditions, quantitatively described that the designed ejector of this paper meet ejector efficiency η is greater than the ratio of actual entrainmentratio and ideal entrainmentratio.更多还原