【作者】 蒋文明；

【导师】 刘中良；

【作者基本信息】 北京工业大学 ， 热能工程， 2010， 博士

【摘要】 超音速分离管天然气除湿净化技术较常规天然气处理技术有一系列的优点,如设备结构简单,占地面积小,重量轻,没有运动部件,无需消耗任何外部动力等。但是,为了保证超音速分离管具有良好的分离效果,必须了解来自井口的天然气在超音速分离管的关键部件——Laval喷管内部的超音速流动与凝结特性,揭示其影响因素,探索有效提高分离效率的技术途径。本文的研究目标在于揭示天然气在喷管内的凝结流动机理,采用理论与实验相结合的方法,综合应用非平衡热力学、气体动力学、传热传质学、两相流体动力学以及计算流体力学等相关理论对Laval喷管内的可压缩凝结性气体的流动过程进行较为系统全面的研究。首先,根据喷管内水蒸气凝结过程,建立了喷管内水蒸气自发凝结模型,并与前人结果进行了对比,表明所建立的数学模型能够正确反映喷管内水蒸气超音速流动凝结参数的分布特征。利用所建立的数学模型研究了摩擦阻力、喷管膨胀率对水蒸气自发凝结过程的影响,结果表明,这两个参数对水蒸气的自发凝结过程都有明显而直接的影响。在此基础上,建立了非均相凝结流动过程的数学模型,研究了外界核心对水蒸气超音速流动的影响,证明:外界核心的存在对蒸汽的凝结有明显促进作用。建立了喷管内双组份可凝结气体混合物超音速流动的数学模型,研究了氮气-水蒸气、甲烷-水蒸气、甲烷-壬烷在喷管内的超音速流动与凝结过程。结果发现,氮气-水蒸气在其它进口参数相同的条件下,入口压力、温度、过饱和度对极限过冷度、成核率、液滴数、液滴的平均半径和液相质量分数均有明显的影响;甲烷-水蒸气在喷管喉部之后(x=10.0 mm)过冷度很快上升到40K左右,达到Wilson点,蒸汽突然开始凝结,成核率从0急剧上升到1024量级,水滴数目急剧增加,同时释放出大量的凝结潜热加热周围气体,引起“凝结冲波”现象;甲烷-壬烷的过冷度沿喷管沿程不断增大到72K左右才发生凝结成核现象。由于液滴数量较少和壬烷潜热较小的原因,在压力和温度曲线上没有出现像甲烷-水蒸气发生自发凝结时那样明显的“凝结冲波”现象。再后,建立了喷管内三组分可凝结气体混合物超音速流动的物理模型和数学模型,并对甲烷-水蒸气-壬烷在喷管内的超音速凝结过程进行了模拟研究。研究发现,水蒸气的存在,在一定意义上促进了壬烷蒸汽的凝结。通过对甲烷-水蒸气-壬烷在喷管内超音速流现象的理论分析研究,初步了解了井口天然气的相关凝结特性,为实现对井口天然气液滴成核与液滴生长的控制、提高超音速分离管的分离效率提供理论依据。最后,搭建了用于压缩空气凝结特性测试的实验系统,并对湿空气的超音速流动及其凝结特性进行了实验研究并与理论模拟结果进行了比较。研究表明,非均相凝结模型与实验结果吻合较好;把湿空气在喷管内发生的凝结过程视为非均相凝结是比较合理的,也验证了所建立的非均相凝结模型。更多还原

【Abstract】 Natural gas supersonic dehydration and purification technology is of a series of advantages over conventional natural gas treatment methods, such as very simple equipment structure, small in size, light in weight, no moving parts and needing no extra energy but the excess pressure of wells. However, in order to ensure the designed separation performance, it is of vital importance to understand the flow and condensation characteristics of natural gases in Laval nozzle which is the key part of the supersonic dehydration and purification system. The present work is aimed at understanding the flow and condensation characteristics of natural gases flowing through Laval nozzles. The main work is summarized as follows.A spontaneous condensation mathematical model for supersonic flow with condensation of water vapor in Laval nozzles is developed. The numerical results of the model are compared with and the good agreement is obtained with the experimental data from literatures. The model was then extended to study the influences of friction drag and expansion rate on spontaneous condensation parameters of condensable water vapor flow through Laval nozzles. The results show that both the friction drag and the expansion rate have obvious and important influences on the flow and condensation characteristics. A numerical simulation was also performed for the water vapor supersonic flow in Laval nozzles with the existence of exoteric nuclei. It was found that the exoteric nuclei may significantly promote the water vapor condensation process.A spontaneous condensation physical mathematical model for supersonic condensing flow of two-component gas mixtures (one non-condensable inert gas and condensable vapor) in Laval nozzles is established to study the supersonic flow and spontaneous condensation process of nitrogen-water, methane-water and methane-nonane mixtures. The obvious influences of inlet pressure, temperature and supersaturation were found from the simulation results of the nitrogen-water vapor flow process on extreme supercooling, nucleation rate, droplet number, droplet size and liquid phase fraction. For the methane-water vapor flow, the supercooling increases to 40K right after the throat of the nozzle (x=10.0mm), and the vapor begin to condense companying with a condensation shock and a heating effect to the flow from latent heat release, the nucleation rate quickly increases to 1024kg-1s-1. Nonane in the methane-nonane vapor mixture begins to condense as the supercooling increases to 72K. No obvious condensation shock can be observed of the methane-nonane vapor mixture flow, which may be well attributed to the fact that the latent heat and the quantity of the nonane condensed are much smaller than water vapor.A mechanism and mathematical model is developed for the supersonic flow and spontaneous condensation process of three-component mixtures (one non-condensable insert gas plus two different condensable gases). And then the model is used to simulate the supersonic flow and condensation characteristics of methane-water vapor-nonane mixtures. It is found that the existence of water vapor is enhanced the condensation process of nonane vapor to some extent. The mechanism model and the simulation results are helpful for understanding the flow and condensation characteristics of natural gas, controlling the nucleation rate and/or droplet growth rate, and improving the separation efficiency of supersonic separators.An experimental rig for testing the flow and condensation characteristics of wet air is set up, a series of experimental results are obtained. The simulation results from the previous physical and theoretical model are compared against the experimental results. It is found that the heterogeneous model can predict the experimental data of both pressure and droplet sizes.更多还原