Supersonic nozzle performance prediction considering the homogeneous-heterogeneous coupling spontaneous non-equilibrium condensation

Abstract

Supersonic nozzles are widely applied in steam turbines and other industrial fields. Condensation occurs due to rapid expansion of steam flowing through a sonic nozzle. The process is affected by the presence of steam impurities. The primary purpose of this study is to investigate the impact of different heterogeneous particles (solid particles, tiny droplets and NaCl particles) at different concentrations on the non-equilibrium condensing flow, and to classify and calculate condensation losses and total static isentropic efficiency resulting from the non-equilibrium condensation phenomenon. First, the proposed non-equilibrium condensation model is estimated numerically using the Barschdorff nozzle, and the model accuracy is validated by comparing the results with existing experimental data. Second, the effect of different particle concentrations on several condensing flows is studied using the Barschdorff nozzle. The results show that homogeneous condensation will get weaker with an increase in the particle concentration in the vapour condensing flow with solid particles and NaCl particles. Moreover, homogeneous condensation will be slightly enhanced first and then weakened with an increase in the particle concentration in the vapour condensing flow with tiny droplets. The steam condensing flow with different heterogeneous particles at the same particle concentration and the process of pure steam condensation are analysed. The results show that impurity particles in steam have a significant impeding effect on the process of homogeneous condensation. The losses are classified in the Barschdorff nozzle, and the magnitude of the losses and the flow total static isentropic efficiency are estimated. As the particle concentration increases from 1014[1/kg] to 1015[1/kg], the total static isentropic efficiency of solid particles and tiny droplets increases by 12.8 % and 9.6 %, respectively, while the total static isentropic efficiency of NaCl particles decreases by 27.2 %. This indicates that an appropriate increase in the particle concentration can effectively reduce condensation losses and improve total static isentropic efficiency. The paper describes the effect of heterogeneous particles on the steam condensing flow, providing a reference for future research on heterogeneous condensation processes.