甲烷和壬烷蒸汽在超音速喷管中的凝结过程

Study on Condensation Process of Methane and Nonane Mixture in Supersonic Nozzle

为了解甲烷和壬烷蒸汽在超音速喷管中的凝结特性规律,建立了甲烷和壬烷蒸汽的超音速凝结流动数值模型,对甲烷和壬烷蒸汽的超音速凝结流动进行了数值计算。研究发现:当x=100.0 mm时,壬烷蒸汽的过冷度达到72K左右,同时壬烷蒸汽的过饱和度上升到21 904才发生自发凝结现象,比甲烷—水蒸气混合物发生自发凝结的位置延迟很多,分析其主要原因是由于壬烷蒸汽分子比水分子大,凝结需要更大的自由能障,必须达到较高过冷度或过饱和度时才能实现凝结;而且在甲烷—壬烷蒸汽的压力和温度曲线上找不到"凝结冲波"现象,主要原因是壬烷蒸汽发生凝结生成的壬烷凝结液滴数量较少,增长速度较慢,同时壬烷蒸汽的凝结潜热较小,导致单位时间内放出的凝结潜热较少,无法实现对周围气体的充分加热,致使甲烷—壬烷蒸汽混合物无"凝结冲波"现象。

In order to find out the condensation characteristics and rules of methane and nonane mixture in supersonic nozzle,a mathematical model is established to investigate and calculate condensation flow conditions of the mixture in supersonic nozzle and the results show that nonane vapor begins to condense spontaneously only if its degree of supercooling reaches about 72K and its degree of supersaturation reaches about 21904 at x=100.0mm,its spontaneous condensation is later than that of methane and water vapor mixture because nonane molecule is much bigger than water molecule and more free energy barrier are needed for higher degree of supercooling.There is no 'Condensation Shock Wave' found in pressure and temperature distribution curves due to little latent heat released by nonane condensation per unit time.