Study Of The Performance, Configuration And Particular Flow Phenomena Of An Ejector

As a fluid machine, ejector is widely applied in industries, such as being used as a heal pump to enhance pressure or take advantage of waste heat or as a compressor in an ejectoi refrigeration/cooling system. Limited by experimental equipments and computer capability, not enough work has been done to obtain the ejector inside flow profile of the complex flowing and mixing process. Until now the design and evaluation of an ejector usually base on 1-D analysis. There is limitation on inspecting insight flow field and mastering the effects of operating condition parameters and geometric parameters of an ejector on its entrainment ratio and critical compression ratio So it is difficult to improve the COP of an ejector.In this paper, three-dimensional Navier-Stokes equations are solved with Chen-Kim k-εturbulent model to simulate the insight complex flow field of a steam ejector. Through observing flow field and analyzing the simulation results, many relations between ejector COP and operating parameters or ejector structures are mastered. The main work and results of this paper are given as follows:1 Selecting a turbulence model which is suitable for ejector numerical simulation. Four popular turbulence models and 1-D Sokolov analytical method were used in simulating the flow process in a steam ejector which was used in an experiment. The numerical simulation results show that the results gained with Chen-Kim k-ε model are moreidentified with that of experimental results. Considering that the calculation time with Chen-Kim k-ε model is the shortest, Chen-Kim k-ε turbulence model was selected toanalyse the compressible characters of the supersonic working flow in the ejector and the effect of the structure on its performance.2 Improving the mathematical model for steam ejector simulation by introducing steam property relations. Since overheat steam, saturated steam and condensed water coexist in a steam ejector, it is not reasonable to regard steam as an ideal gas during numerical analysis. So in this paper, real gas related expressions of steam properties was adding into the PHOENICS software. This improvement adequately considers the compressible characteristics of the supersonic steam in the ejector, so it makes the simulation results be more identified with real conditions and makes it possible to investigate phase transition phenomenon which cannot be avoided in a steam ejector but hard to master through measurement.3 Summing up the relationships between the ejector performance and its operating condition parameters systematically. From the computational results, how the motive fluid pressure, the suction fluid pressure and the discharging fluid pressure influence the ejector entrainment ratio and critical discharging pressure was concluded. Two parameters, namely expansion ratio and critical compression ratio, are introduced to conclude the relationships between this three pressures, such as the related expression of expansion ratio and critical compression ratio for a given ejector and the related expression of themaximum expansion ratio and Mach number at the nozzle outlet. These two relative expressions can be used to design a suitable ejector for certain working parameters or analyse a given ejector parameter characteristics in order to correctly apply and operate it.4 Analyzing the effect of ejector structures on entrainment ratio and critical compression ratio. Taking advantages of the flexibility, easy repetition, and low cost of numerical simulation, the effect on the maximum entrainment ratio and critical compression ratio of each component configuration of the ejector, viz. the nozzle, the absorber, the mixing-chamber, and the diffuser, is analysed respectively. Optimal shape and dimension of each component is concluded. A novel nozzle, a nozzle with an adjustable needle, is used in the ejector as a method of adjusting ejector performance. These results can be used as guidelines for ejector designing to enhance the ejector COP.5 Comprehending the reason of shocks emerging, their positions, and their e...