Modeling And Investigation Of A Steam-water Ejector

With the rapid improvement of the economy and industry,people's living standards are improved greatly,but the energy wastage and environmental pollution become more and more serious.Energy-saving and environmental protection has become a major issue around the world,so more attention has been paid to the low-grade energy and renewable energy.Injector is a remarkable role in raising energy efficiency and utilizing lower level heat sources in the heat pump,refrigeration cycle,as well as the seawater desalination system.The air-liquid two-phase injector is a kind of jet pump powered by high pressure steam.High-pressure steam becomes supersonic flow through the jet,then it would mix with low pressure water.Two flows transfer heat directly and they achieve the balance of speed and pressure,and shock wave occurs in the mixing chamber,resulting in the increases of temperature and pressure.The injector has the characteristics of simple structure,no moving parts and low running cost.But the ejector coefficient of injector is low,besides there is no uniform design standards.Therefore,adequate research concerning the principle and the internal flow field of injector is the key to promote the ejector device using.Many scholars established injector one-dimensional model.In this paper,on the basis of the results of other researchers,we established a one-dimensional model that the velocity of nozzle throat components a characteristic quantity combining thermodynamics and hydromechanics.The published experimental data was also used to verify this model,and the study showed that the maximum error between the calculated results and the experimental results was 9.5%.Then we analyzed the performance parameters of injector using the new model,the conclusion is as follows:the compression ratio increased in conjunction with the escalation of inlet steam pressure,but decreased along with the expansion of the inlet water pressure.The compression ratio increases much more rapidly under a lower inlet water pressure and a higher inlet steam pressure.The pressure of the injector increases under the increase of the area of throat.The compression ratio increases with the isentropic efficiency of throat.The entrainment ratio decreased sharply with the increase of the area ratio of throat.The exergy destruction mainly occurs in the nozzle,and followed by the mixing chamber.The numerical simulation of the injector is carried out under different pressure of ejector nozzle.The results proved that the current model can more adequately predict the injector parameters.The pressure declines slowly at the beginning of the flowing process.Next,shock wave occurs behind the throat while the pressure drops rapidly,and the exergy destruction increases.The pressure declines slowly after a short distance.The length of the shock wave increases with the increase of inlet pressure.