A Study On The Flow And Phase Change Characteristics In Steam Ejector

Steam ejector is very practical and has broad application prospects.There is specific complexity in the flow of steam ejector.In order to enhance the injection performance,the flow in steam ejector should be deeply analyzed.In this study,theoretical analysis,numerical simulation and experimental tests were used to investigate the flow and the phase change mechanism in steam ejector.The main contents are as follows.The one-phase numerical model is established.The flow and the influence of the operating parameter on the injection performance of steam ejector are investigated.The results show that there is a critical value for the back pressure and an optimum value for the primary pressure and the injection performance enhances with the entrained pressure.And the mixing chamber has an optimum range for the length and an optimum value for the convergence angle.An experimental system that used to investigate visual steam ejector is designed and set up.Visual and high-speed video technology is employed in visual experiment of the flow in mixing chamber of steam ejector.The flow in mixing chamber of steam ejector is researched by the experiments,which has great effects on the injection performance.The results show that there is obvious liquid water in the mixing chamber.There is a wet steam flow with lots of mist-state droplets near the axis of mixing chamber and many droplets and liquid film or water flows exist on the internal face of mixing chamber.The influence of the entrained pressure on the flow of mixing chamber is analyzed by the visual experiments and the theory of constant-pressure mixing steam ejector.The visual experimental results show that the higher the entrained pressure,the closer the beginning of the water film or water flows to the outlet of nozzle.The closer to the outlet of nozzle indicates the faster increasing of the flowing velocity nearing the mixing chamber wall.The theory of constant-pressure mixing steam ejector shows that the location of constant-pressure mixing is constant and the expanding degree and the flowing velocity increase as the entrained pressure increases.The experimental results and the theoretical analysis are partly mutual verified.The wet steam model being suitable for the transonic two-ohase flow is established.The wet steam model contains nucleation and droplet growth and introduces mass fraction and the number density in the droplets functions.It is the Eulerian-Eulerian two-phase flowing model.The two-phase flow in the steam ejector is simulated by employing the wet steam model.The results show that the entrainment ratio of the steam ejector is a slightly higher than the ideal gas model,and the influence of the operating conditions and the geometrical parameters of the mixing chamber on the injection performance is similar with the ideal gas model.The distribution of the pressure,velocity and temperature in the mixing chamber of steam ejector is analyzed by the ideal gas and wet steam model.And then,the reason why the entrainment ratio of the steam ejector in the wet steam model is a slightly higher than the ideal gas model is illuminated.The results show that there is condensation in the wet steam model.The latent heat has heating effect on steam and the decreasing of temperature that is reason by the expanding of gas is counteracted.Thus the changing of the temperature in the wet steam is far less than the ideal gas.In the wet steam,the flow is steadier and the part of high pressure near the inlet of entrained steam is less than the ideal gas,and the reducing of velocity is also less than the ideal gas.Thus the entrainment performance of the primary steam in the wet steam is stronger than the ideal gas.While the slightly higher pressure at the outlet of nozzle in the wet steam model goes against the promotion of the entrainment ratio.