Numerical Simulation And Characteristic Analysis Of Direct Contact Condensation In Steam Ejector

In the event of a power loss accident in nuclear power plant,the decay heat in the core should be extracted in time to prevent the core meltdown accident.Since the start-up of traditional power equipment is uncertain,researchers are exploring the applicability of using steam ejector as passive safety devices for nuclear power plants.There is a severe direct contact condensation phenomenon inside the steam ejector,and its performance is affected by various factors.Based on previous experiments and related parameters,this paper conducted numerical simulation and validation of the direct contact condensation phenomenon in a steam ejector by using computational fluid software Fluent,and analyzed the effects of different steam mass flow rate,outlet pressure,and mixing throat diameter on the internal flow field and operating performance of the ejector.Based on the above work,air was mixed as non-condensable gas in the working steam,the effect of non-condensable gas on the performance of steam ejector was studied.The main contents and conclusions of this paper are as follows:Firstly,a numerical model was constructed to simulate the direct contact condensation phenomenon in the steam ejector,and the validity of the numerical model was verified by comparing with previous experimental data.The multiphase flow Euler model,the Lee model and the standard k-epsilon model were used to simulate the direct contact condensation phenomenon in the steam ejector.The simulation results of axial pressure calculated by using the same geometrical structure as the literature were in good agreemet with the experimental results,and the maximum deviation between them was5.7%,which verified the validity of the numerical model.Secondly,the effects of steam inlet mass flow rate,outlet pressure,and mixing throat diameter on the performance of the steam ejector were analyzed and summarized.With the increase of steam inlet mass flow rate,steam pressure in the mixing section is reduced,steam ejection ability to supercooled water is enhanced,and the working efficiency of steam ejector is improved.When the outlet pressure is increased,its influence spreads to the mixing section and diffuser section.As the pressure in the mixing section increases,the steam ejection ability to supercooled water decreases,the working efficiency of steam ejector decreases,and the condensation shock wave in the mixing section is inhibited.When the diameter of the throat of the mixing section is increased,the ejection ability of steam to supercooled water is enhanced,and the working efficiency of the steam ejector is improved.Finally,the influence of non-condensable gas on the performance of the steam ejector was analyzed and summarized.As the air mass fraction increases,the obstruction effect of air on the heat and mass transfer process between steam and supercooled water increases,the penetration length of steam plumes increases,the pressure in the mixing section increases,the ejection ability of steam to supercooled water decreases,the working efficiency of steam ejector decreases,and the condensation shock wave in the mixing section are suppressed.When the air mass fraction is 4%,increasing the steam inlet pressure reduces the pressure in the mixing section,enhances the steam ejection ability to supercooled water,improves the working efficiency.The work of this paper further clarified the influence law of different operating conditions,structural parameters and air mass fraction on the performance of steam ejector,which can provide a theoretical basis for the structural design and optimization of steam ejector,and has important significance for improving the performance of steam ejector and improving its efficiency.