三组分混合物超音速凝结机理

Condensation mechanism of the ternary mixture in supersonic flows

为了解天然气混合物中水蒸气、重烃在喷管内的凝结机理,明确其液滴成核与液滴生长的基本规律,研究了甲烷-水蒸气-壬烷三组分混合物在喷管内的超音速凝结过程。首先在已有双组分混合物超音速凝结数学模型的基础上,结合国外最新研究成果,建立了三组分混合物在喷管内的超音速凝结过程物理模型;然后根据双组分混合物的超音速凝结模拟结果,建立了三组分混合物在喷管内的超音速凝结过程数学模型并进行了模拟计算。结果表明,在甲烷-水蒸气-壬烷混合物中,水蒸气较早出现自发凝结现象(x=4.0 mm),并且形成的水滴充当了壬烷蒸气发生凝结的外界核心,降低了壬烷蒸气发生凝结的自由能障,促使壬烷蒸气在过冷度38.3 K和过饱和度37.4下就发生凝结现象,即水蒸气的存在在一定意义上促进了壬烷蒸气的凝结。

The supersonic condensation process of a ternary mixture, including methane, water vapor and nonane, in a nozzle was studied in order to understand the condensation mechanism, nucleation and droplet growth rules of water vapor and heavy hydrocar- bons from natural gas mixture. Firstly, based on the existing mathematic model of the two-component mixture supersonic condensa- tion and combined with the latest research results at home and abroad, a physical model for the condensation process of the ternary mixture in supersonic flows was built. Secondly, a mathematic model of the ternary mixture supersonic condensation was built and applied in analog computation according to simulation results of the two component mixture supersonic condensation. The result showed that in the ternary mixture, water vapor begins to condensate spontaneously prior to nonane vapor （x = 4.0 mm）, forming droplets to serve as allochthonous nuclei for nonane vapor condensation and lowering the free energy barrier of nonane vapor. Conse quently, nonane vapor begins to condensate at a lower subcooling （38.3 K） and supersaturation （37.4）. In other words, the occur- rence of water vapor in a sense accelerates the condensation process of nonane vapor.