Abstract:

Wet steam condensation flows presents a high degree of non-equilibrium characteristics. At present, the condensation parameters are obtained by using semi-empirical formula, while heat transfer temperature difference and coupling problems are seldom considered. A simple condensation nucleation model and droplet growth model for non-equilibrium phase change of wet steam is established in this study. In order to calculate the wet steam parameters and condensation shock wave distribution of non-equilibrium condensation flows, the second-order TVD scheme is adopted. The influence of thermodynamic properties of inlet wet steam on the non-equilibrium condensation flow is examined, the influence of inlet pressure on the condensation characteristic is discussed, and various patterns of inlet subcooled temperature on nucleation rate, droplet number, condensation shock are summarized. It is found that as inlet pressure increases, the condensing location moves upstream. At a lower import subcooled temperature, the condensing position moves downstream. At higher Mach number, nucleation occurs. As the import subcooled temperature increase, the wetness of non-equilibrium condensation phase transition will be higher. After the onset of condensation shock, steam expands continuously along the nozzle and the flow pattern is similar to isentropic flow.

Key words: wet steam, transonic, two-phase flow, condensation, thermodynamics, shock wave

摘要：

水蒸气凝结两相流动呈现高度的非平衡特性。目前,凝结参数都是利用半经验公式得出,很少考虑两相间传热温差以及耦合问题。在湿蒸汽两相流输运方程的基础上,建立了一种准确简单的凝结成核和水滴生长模型,采用具有较好激波捕获效果的高精度二阶TVD格式进行离散,计算了湿蒸汽非平衡凝结流动参数及凝结冲波分布。着重研究了湿蒸汽非平衡凝结流动的热力学特性,讨论了进口压力对凝结特性的影响,归纳了进口过冷度对成核率、水滴数、凝结冲波形态的变化规律。研究表明:进口压力增加,凝结位置逐渐向上游移动;进口过冷度降低,凝结位置向下游移动,达到较高的Mach数后,才会出现凝结成核;进口过冷度越高,非平衡凝结相变产生的湿度越高。凝结冲波出现后,湿蒸汽沿喷管继续高速流动,其流动规律与等熵流动相似。

关键词: 湿蒸汽, 跨声速, 两相流, 凝结, 热力学, 激波