超声速喷管内CO2气体凝结特性研究

Study on condensation properties of CO2 gas in supersonic nozzle

关键词:  超声速  CO₂气体  喷管  凝结  酸性组分  天然气 

Key words:  supersonic  CO₂ gas  Laval nozzle  condensation  sour components  natural gas

摘要:

基于欧拉——欧拉双流体模型,建立气相及液相流动控制方程组,结合凝结成核与液滴生长理论,对喷管内CO₂气体的凝结特性进行了数值模拟研究。结果 表明,采用的数学模型和数值计算方法可较准确地反映喷管内气体的凝结流动过程。CO₂气体凝结潜热较小,凝结冲波现象不明显；气体进入喷管特别是在经过喉部之后,在马赫数增大的同时,压力和温度降低,过冷度增加,最大可至30 K左右,并于凝结发生后快速下降至约5 K；CO₂气体成核过程在时间和空间上表现出急剧性。凝结起始位置距喉部约2.21 mm,成核率由0激增至2.04×10²¹ m-3·s-1,液滴数目达到10¹⁵的数量级；凝结核心形成后,气体分子在一定的过冷度下在液滴表面团聚、液化,液滴半径和湿度迅速增加。成核过程结束后,已有凝结核心仍能不断生长,至喷管出口处液滴半径增至1.46×10-7 m,湿度可达0.093 5。 

Abstract:

Based on Euler-Euler two-fluid model, the gas and liquid flow control equations were established. Combined with the theory of condensation nucleation and droplet growth, the condensation properties of CO₂ in a Laval nozzle were simulated. The results showed that both the mathematical models and numerical calculation methods used could reflect the process of gas condensation in the Laval nozzle accurately. The condensation wave of CO₂ was not obvious due to its small latent heat of condensation. As the gas flow into the nozzle, the Mach number increased while pressure and temperature decreased, the undercooling increased up to 30 K, and then declined quickly to about 5 K after the occurrence of condensation. The process of nucleation showed a sharp both in time and space. Wilson point is about 2.21 mm from the throat, the nucleation rate increased sharply from 0 to 2.04×10²¹ m-3·s-1, while the number of droplets reached the order of 10¹⁵ instantly. After the formation of condensation core, gas molecules under certain degree of undercooling accumulated and liquefied on the droplets surface, causing droplet radius as well as humidity to increase rapidly. After the process of nucleation, the existing coagulation cores kept growing with the droplet radius increasing to 1.46×10-7 m and the humidity up to 0.093 5 at the exit of the Laval nozzle.