Theoretical And Experimental Study On The Non-isobaric And Non-constant Area Mixing Model Ejector

The ejector,as a device for boosting pressure,recovering low-pressure fluid,vacuuming,harvesting mechanical energy,etc.,is widely used in industry,agriculture,food processing,aerospace and other fields.It has great advantages of simple structure,low cost,reliable performance and no moving parts.Ejector can be driven by low-grade thermal energy(such as solar energy,waste heat,waste heat,etc).Against the attempt to peak and neutralize the carbon emission,improving energy efficiency and utilization of new energies have become important methods to address the energy crisis,as well as a hot topic.Related researches on the application of ejectors have also moved to a new stage.Overviewing the existing research results and applications of ejector,it is clear that the main factor that limits the application is its relatively low efficiency,especially when used in the refrigeration system.The performance of ejector refrigeration system is lower than those of other heat-driven refrigeration systems.As a key component of the system,the efficiency of the ejector directly affects the performance of the system.To improve the performance of ejector,the mechanism of energy conversion in the ejector is studied,along with the analyses of flow process and irreversible losses of internal fluid.It is found that the irreversible loss of the mixing chamber seriously affects the efficiency.The mixing process in the mixing chamber is extremely complicated.For two fluids with different flow velocities,mass flow rates,temperatures,densities and other parameters,the complex momentum exchange and energy transfer are carried out,involving intensive fluid acceleration,vortex,impact,choking in the mixing chamber,and caused various irreversible losses in the chamber.Based on the existing physical model,a novel non-isobaric and non-constant area mixing model was proposed.To minimize the entropy increase in mixing process,the calculus of variations was used to obtain the axial pressure distribution of the mixing process and optimize the wall profile,which significantly benefits the stability of mixing process and reduce irreversible loss caused by the discrepancies of velocity,pressure and chemical potential(due to density difference)of two fluids.Therefore,an increase of mixing efficiency is identified.As for mixing process,velocity discrepancy of two fluids is an important factor leading to irreversible losses.In this paper,the influence of the inlet pressure of mixing chamber on the performance of ejector is studied.The suction chamber with convergent structure is used to improve the flow velocity before mixing.On this basis,the geometrical dimensions of working nozzle and suction chamber are designed to reduce the velocity discrepancy of two fluids in the mixing process,to improve the mixing process efficiency.A new method of ejector modeling was proposed.The ejector with convergent suction chamber and novel wall profile of mixing chamber was designed and manufactured.The ejector test rig was designed and built.The performance of the new ejector was studied by numerical simulation and experimental investigation.Compared with the conventional ejector,the experiment results showed that the entrainment ratio and work recovery efficiency were enhanced by 16.1% and 10.5%,respectively.The experimental results coincided well with the simulation model and illustrated great advantages of the proposed novel ejector.